Developing a Compensator using Cerrobend Materials

ABSTRACT
In external beam radiotherapy (EBRT), dose optimization is achieved by conforming the dose distribution to the shape of the intended target whilst minimizing radiation to normal tissues in close proximity to the target. This is achieved by modulating the intensities of the radiation across the radiation portals forming the irradiation geometry used for the treatment. Compensators may be used to achieve the above effect and can be used to approximate the fluence map by appropriate linear attenuation coefficient of individual beamlets making up the original open beam fluence. This may be done with a treatment planning system (TPS) with inverse planning capabilities or with a bolus placed on the surface of the patient at the beam entrance point. This work describe the procedures for designing, constructing and dosimetric considerations of cerrobend compensator for high energy photon beams, using the bolus option on the surface of the phantom planned with Prowess Panther TPS. Also correction factors that account with effects of field size, treatment depth and changes in thickness ratio because of using bolus were introduced. The cerrobend compensator was adjusted to account for beam divergence and reduction in dose contributed by scattered radiation. The correction factors were applied to the thickness ratio for determination of appropriate thickness of cerrobend that mimic bolus. The measurements were done in Theratron Equinox 100 cobalt-60 teletherapy unit using Cerrobend slabs constructed to account for divergence of the beam for the maximum field size considered in this research (30×30 cm2). The narrow and broad beam linear attenuation coefficient for cerrobend were determined using simple attenuation model, varying the field size from 4×4 cm2 to 30×30 cm2 field sizes in air, and also varying the thickness of cerrobend from 0.5cm to 4.6cm. The value found was 0.4574cm-1 and also the field size dependence of linear attenuation coefficient were investigated. The scatter produced by cerrobend was accessed and evaluated. The scatter-to-primary ratio dose contribution was found to be negligible for small field size as reported by Dimitriadis (2002), and can cause error in the final dose calculation up to 13.3% for 30×30 cm2 and 4.09 cm thickness of cerrobend. The cerrobend compensator was successful designed and constructed. The dosimetric accuracy for constructed cerrobend compensator was found to be deviating with that predicted with Prowess Panther Treatment Planning System with percentage error ranging from 0.365 to 25%, which is associated with limitations in producing precise thickness of cerrobend with the same accuracy of that generated by the equation 3.04 and limitations in generating flat surface topography and also the presence of air bubble in the cerrobend compensator which was not investigated in thiswork.
CHAPTER I

INTRODUCTION

BACKGROUND

Cancer is a significant health care problem. On average about half of all cancer patients are treated with radiation therapy worldwide (IAEA, 2004).
Radiotherapy, also referred to as radiation therapy, radiation oncology or therapeutic radiology is one of the three modalities used to treat malignant disease (cancer) the other two being chemotherapy and surgery (Suntharalingamn et al, 2005). Radiotherapy uses ionizing radiation to eradicate cancerous cells with the least possible damage to normal tissues.
The first therapeutic use of ionizing radiation was demonstrated in 1897 by Wilhelm Alexander Freud, a German surgeon before Vienna Medical Society when he demonstrated the disappearance of a hairy mole following treatment with x-ray (Hall, 2000). The first recorded experiment in radiobiology was also performed by Becquerel when he advertently left a radium container in his vest pocket and subsequently described the skin erythema two weeks later (Hall, 2000).

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The modalities of radiotherapy are divided into two types, tele-therapy and brachytherapy. Brachytherapy is a method of treatment in which sealed sources are used to deliver radiation at short distances by interstitial, intracavitary or surface application (Khan, 2010). Tele-therapy is a treatment modality in which the source of radiation is at a distance from the patient, also called external beam radiation therapy, it uses photons ranging from kilo voltage to megavoltage photons, and electron beams from linear accelerators or Co-60 tele therapy units. In External Beam Radiation Therapy (EBRT), the methodology of treatment depends on different factors, which may include the shape and size of the tumour to be treated within the patient, sparing of normal tissues within the vicinity of the target from excessive irradiation, financial constraints and the quest of optimization of radiation dose to the target. There are different treatment techniques ranging from 2-D conventional radiotherapy to more advanced Intensity Modulated Radiotherapy (IMRT). IMRT is a treatment planning and delivery technique that can greatly improve the process of conformal radiotherapy which refers to the process of blocking a beam with irregular shaped beam portal so that the dose delivered corresponds more closely to tumour whilst reducing the dose to normal tissue. In developing countries, most of the centrees are restricted to a Co-60 tele therapy unit with basic treatment planning and simulation capabilities.
Patients present irregular surface topographies and tissue heterogeneities. According to Chang (2004), a compensator is a traditional tool for modern application and is an alternative IMRT delivery technique.
In IMRT, the compensator is used not in the sense of compensating for missing tissue or tissue heterogeneity but as beam intensifier like dynamic wedges and multileaf collimators (MLC). The goal is to achieve dose uniformity throughout the whole target volume and, more importantly to spare critical structures according to the dose and dose volume constraint prescribed by the clinicians for specific patients (Jiango et al, 1998). Therefore, compensators are designed to produce an optimized primary fluency profile at the patient’s surface. This is achieved by modulating the intensities of the radiation across the radiation portals forming the irradiation geometry used for the treatment.
There are various methods by which compensators can be made. According to Williams and Thwaites (2000), the three main types are grid-blocking system, contour system and a system using machined compensator. The first compensators made by Ellis et al. (1958) were constructed by stacking aluminum pillars. Another method reported by Lam et al. (1983) describes the construction of compensators from thin sheets of lead. Today compensators are more commonly made from molds filled with molten alloy or wax. Using molds is advantageous since it results in compensators with smoother surfaces and thus greater accuracy.
To make a compensator for an IMRT practice, it is required to calculate the effective attenuation coefficient () of its materials, which is affected by various factors as field size, depth, off- axis distance, compensator thickness (Haghparast et al, 2013). A number of elements have been used to form compensators which include tungsten-epoxy mixture (Xu et al, 2002), Lucite (Khan et al, 1970), gypsum (Weeks et al, 1988), tin-wax (Van et al, 1995), tin (Chang et al, 2000), cerrobend (Waltz BJ et al, 1973), steel (Van et al, 1995), aluminum (Ellis et al, 1959), brass (Ellis et al, 1959; Tess, 2014), lead (Leung et al, 1974; Cunnighan et al, 1976; Andrew et al, 1982; Spicka et al, 1988), coper (Tess, 2014). In this study, a cerrobend compensator will be constructed using a simple attenuation model to determine its effective attenuation coefficient. Film and an ionization chamber will be used for dosimetric measurements and for verification of measured dose distribution and compared with those calculated with the PROWESS Panther TPS software at Korle-Bu Teaching Hospital.

PROBLEM STATEMENT

In external beam radiotherapy (EBRT), dose optimization is achieved by conforming the dose distribution to the shape of the intended target whilst minimizing radiation to normal tissues in close proximity to the target. Most dosimetric measurements are done on flat surface and homogenous medium, however patient’s surface is highly irregular and internal tissues are heterogeneous. The main aim of radiation therapy is to deliver uniform dose distribution within +7 % and –5 % (ICRU report 50, 1993) of the dose prescription without exceeding the tolerance dose of the critical structure around tumor volume. To achieve this goal, the above irregularities should be corrected. Thus different studies suggested and implemented bolus which is a tissue equivalent material placed at the surface of the patient to compensate the missing tissue. However, this technique doesn’t spare the skin beneath the bolus. This is because, the buildup region is in the bolus and Dmax (depth of maximum dose) will be at skin surface. To solve such complications compensators have been introduced by different people on different approaches to correct both surface irregularity and tissue heterogeneity which is now done by using MLC based IMRT.
Advanced technological innovations in anatomic and functional imaging modalities (CT, MRI, PET, and US) have led to improved visualization and the delineation of tumour. Radiation treatment planning and delivered techniques have also seen a marked improvement. Intensity modulated radiotherapy (IMRT) provides a high degree of dose conformity to the planning target volume (PTV) and the conformal avoidance of organs at risk. Therefore radiation field is not only geometrically shaped to conform to the outline of the planning target volume at the beams eye view, but is also intensity modulated.
The National Centre for Radiotherapy and Nuclear Medicine of Korle-Bu Teaching Hospital (KBTH) presently uses paraffin wax for construction of a compensator and cerrobend for shielding blocks, but there is a need to implement physical compensator based IMRT using materials which are available in the Centre and is inexpensive. This research will focus on design and construction and dosimetric considerations of cerrobend compensators to modulate the intensities of the radiation across the radiation portals forming the irradiation geometry used for the treatment.

OBJECTIVES

GENERAL OBJECTIVE

The general objective of this work is designing and constructing a compensator using cerrobend materials.

SPECIFIC OBJECTIVES

To clarify the effect of scattered photons generated within the compensator on head scatter factor.
To evaluate dosimetric accuracy and dose coverage.
To compare and evaluate measured and predicted data.
To evaluate the variation of dose distribution by the compensator.

SCOPE AND LIMITATION

The scope of this thesis is in the area of the IMRT by means of physical compensators specifically using cerrobend which are manually fabricated. In most centres which are practicing IMRT, the construction of the compensator to provide the needed modulation is done by generating a fluency map of the radiation portal needed. This is done with a treatment planning system (TPS) with inverse planning capabilities or with a bolus placed on the surface of the patient at the beam entrance point. The bolus option will be used in this research as currently there is no TPS in the country that can do inverse planning. In this case, the cerrobend compensator will be used to replicate dosimetric effects of the bolus placed on the surface of the patient. According to Jiang et al (1998), the calculation of compensator thickness profile (an optimized primary fluency profile) is straightforward typically using the exponentially attenuation model. With reference to this, the shape of the compensator will be adjusted to account for beam divergence and reduction in dose contributed by scattered radiation. Thus the dosimetric considerations is part of the scope of this research. The measurement will be made from a Co-60 tele therapy machine at Korle Bu Teaching Hospital (KBTH).

RELEVANCE OF THE PROJECT WORK

In radiation oncology, a patient should get the best treatment option as much as possible in order to improve quality of patient care. So the expected results such as correction factors to account for reduction in scatter for using the cerrobend compensator to mimic bolus would have immense contribution to scientific and technical knowledge. From this work, it will be possible to implement IMRT delivering technique at National Centre for Radiotherapy and Nuclear medicine of Korle-Bu Teaching Hospital. The clinical implementation of IMRT technique requires at least two systems (Khan, 2010), which are: treatment planning computer system that can calculate non-uniform fluence maps for multiple beams directed from different directions to maximize dose to target while minimizing dose to critical normal structures. This may be done with a treatment planning system (TPS) with inverse planning capabilities or with a bolus placed on the surface of the patient at the beam entrance point. The second one, is a system delivering a non-uniform fluence as planned, so each of these systems must be appropriately tested and commissioned before the actual clinical use. The bolus option will be used in this research as currently there is no TPS in the country that can do inverse planning. The cerrobend compensator will be used to replicate dosimetric effects of the bolus placed on the surface of the patient. Similar research was done using different materials by Teclehaimanot (2014) in which the results were not in the clinically acceptable levels, so with this work we are expecting to reach such clinical levels with deviation less than 5%.
Intensity modulated radiotherapy (IMRT) is widely used in clinical applications in developed countries, for the treatment of malignant and non-malignant diseases. This technique uses multiple radiation beams of non-uniform intensities. The beams are modulated to the required intensity maps for delivering highly conformal doses of radiation to the treatment targets, while sparing the adjacent normal tissue structures. This treatment technique has superior dosimetric advantages over 2-dimensional (2D) and conventional 3-dimensional conformal radiotherapy (3DCRT) treatments. It can potentially benefit the patient in three ways. Firstly, by improving conformity with target dose, it can reduce the probability of in-field recurrence. Secondly, by reducing irradiation of normal tissue, it can minimize the degree of morbidity associated with treatment. Finally, by facilitating escalation of dose, it can improve local control (Cheung, 2006).
Compensator based IMRT has a lot of advantages over MLC, many literature reported by Taherkhani (2010), report that the penumbra regions created by MLCs are larger than those generated by cerrobend blocks. Compensators provide more consistent dose, impose no limitations on the dose delivery rate, reduce skin surface doses, and because of the high density of the cerrobend allows improved skin sparing with low production rate of secondary electrons (Gray, 1979; Hine, 1951) reported by Shery (1987). It gives continuous intensity modulation, high spatial resolution, gives room to treat large field size, easy quality assurance (QA), shorter treatment time delivery with some drawbacks which are lack of automation (Chang, 2004), but there are some disadvantages like the therapist having to go to the treatment room to change the compensator in multiple fields and production cost, being labor intensive and time consuming. But now these drawbacks have been fixed in many developed countries by introducing a milling machine which is incorporated with the Treatment Planning System (TPS), and an automated compensator-IMRT technique (Javedan et al. 2008).
Other main advantage of using cerrobend in this research are: its low melting point of 1580F (700C) which makes it easy to be recycled. It is readily available, inexpensive, high density (9.8g/cm3) and is used as shielding blocks in EBRT where doses are reduced by 95% or 99% of their initial value.
As a material for compensation with high energy photons, cerrobend provides several advantages over tissue equivalent material (Shery, 1987). In the past, Cerrobend had not been considered as an excellent compensator material despite its high density. Recently Chang et al (2004) found that there are cerrobend filling techniques that produce smooth and accurate compensators with consistent density. Solidified Cerrobend in the compensator mold becomes one of the top choices of compensator material. And it can be easily shaped to the intended form with uniform density using the technique described by (Chang, 2004).
Chang et al (2004) showed that compensator-IMRT technique has several benefits for delivering continuous intensity modulation and have shown that the finer resolution compensator-IMRT technique can also produce dosimetry that is closer to the ideal IMRT treatment (without any delivery limitation) compared with the segmental MLC IMRT technique. From this work the patients treated at the National Centre of Radiotherapy and Nuclear Medicine will benefit from all the advantages of IMRT techniques mentioned above. Consequently patients will also get a better and inexpensive treatment option.
 

Use of Sustainable Materials in Construction

Introduction

Belum Eco Resort or better known as the Belum Rainforest Resort is one of the hundred islands located in the Tasik Belum, Perak. It is located very near to the famous Royal Belum National Park. Belum Rainforest is an island free from air and noise pollution. It is also the largest manmade lake in Perak and it is15, 200 hectares big. Belum-Temenggor Forest Reserve ( BTFR) is among the last remaining virgin forest in Malaysia where biodiversity is practically unharmed. The Belum Rainforest Resort is one of Malaysia’s premier ecotourism holiday destinations until today. Set in the midst of a tropical paradise, Pulau Banding, the Belum Rainforest Resort, is everything nature-lovers and holiday-goers expect in a getaway destination. This island is a place with complete relaxation and serenity. It is surrounded by stunning views and surroundings. This adventurous island is definitely worth a visit for those who wants to get close to the nature.
Belum Eco Resort’s (BER) design revolves around green eco concept. Until today, BER continues to proudly practice ‘Responsible Tourism’. The development of the resort was completely manmade and hand-built, without using any technology.

SUSTAINABLE MATERIAL

Sustainable materials are materials that can be used throughout our everyday lives and it is used in the present without compromising its availability for use by latter generations. It also means that sustainable materials are materials that can be produced in required volumes without depleting non-renewable resources and also without disrupting the equilibrium of the environment. A sustainable material used in a building usually benefits the humans and also the general environment. It is this sustainability that is keeping the environment ecosystem balanced and it is actually accommodating the earth. It is not easy to fully describe what a sustainable material is and the best way of explaining it is to look at it as the materials that are being used to achieve environmental benefits unlike any other conventional materials. Sustainable materials do share some general characteristics which are the natural abundance, the help to extract some amount of energy used and also the help of recycling.
3. THE SUSTAINABLE MATERIALS USED IN THE TWO BUILDINGS
Both the Villa and the modern house are built using reinforced concrete as their building structure. Reinforced concrete, in its many forms, is an important building material that can provide many sustainable advantages by virtue of its economic construction, thermal mass, durability, fire resistance, acoustic performance, adaptability and recyclability. Concrete is one of the sustainable building materials that is always being used in most buildings and when both the energy consumed during its manufacture and its inherent properties in-use are taken into account. Whereas, reinforced concrete, it is a composite material comprising concrete and steel. Concrete provides high compressive strength while steel on the other hand provides its tensile strength in the form of embedded reinforcing bars and mesh. Reinforced concrete is chosen to be used in both the Villa and the modern house because concrete is a friend of the environment in all stages of its life span, from raw material production to demolition, making it a natural choice for sustainable home construction. Besides that, reinforced concrete construction has also been developed for low-energy construction and thus it is very suitable to be used in both the Villa and the modern house.

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Other than that, the similar sustainable materials used the in the villa and the modern house is steel. This is because steel is an excellent reusable material. Steel can also be recycled from time to time without any deprivation in the properties or even the quality of the steel performance. Steel construction in the industry nowadays has always been outstanding in the low waste credentials during all life cycle stages of the building. It is the fact where steel construction generates very little waste. Any waste generated during construction of steel is being recycled. This is therefore, not even any waste from steel products on the construction site can be found. Steel is chosen to be used as staircases in both the Villa and the modern house in the Belum Rainforest Resort because steel has one of the uppermost strength to weight ratio of any other construction material. Other than that, steel also provides a clean, effective and fast construction technique, which will not affect the building activities on the environment of the Belum Rainforest Resort. The entire steel used as the staircases there in the Villa and the modern house are 100% recyclable.
Lastly, the similar sustainable material used in the villa and the modern house in Belum Rainforest Resort is glass. Glass produces very little environmental influence to the resort that will make it a good sustainable material of choice to be used in both the Villa and the modern house. In addition to that, glass is made out of many unpolluted materials that are not contaminated and its developing process is highly energy efficient that will only require low level of water. The making of glass and the construction of glass actually generates very little waste. Glass is used as windows, skylights and openings in the Villa and modern house. Glass is an ideal sustainable material to be used because even if the windows or the skylights in the Villa and the modern house in the Belum Rainforest Resort is broken, the broken pieces of the glass are recyclable. Thus, this will contributes to even lower environmental impact. Glass is also very essential in the Villa and the modern house because glass allows maximum sunlight to penetrate into the buildings and also allow maximum views outside the buildings. These transparency characteristic of glass very special among the sustainable building materials and it definitely provide many advantages to both the Villa and the modern house.
4. ADVANTAGES OF USING SUSTAINABLE MATERIAL
In a sustainable building, professional workers like the architects, the engineers and the contractors are required to work together on the sustainable materials used and also the material constructions. Sustainable design and its construction method used actually helps to reduce on emissions of polluted gasses released into the earth’s ozone layer. It also helps to decrease the water and energy costs. The advantages of using sustainable materials in the Villa and the modern house can be commonly be categorized in the subsequent methods which are the environmental advantages, economic advantages and social advantages.
The main reason of using sustainable materials in the Villa and the modern house is to preserve our mother nature and avoid the reduction of the earth’s natural resources.
The environmental benefits when sustainable changes are made throughout each stage of the project’s progress in the Belum Rainforest Resort allow us to protect the ecology of the famous Royal Belum National Park and to reduce emissions of polluted gases. It also helps to enhance the air and water value, preserve water, decrease waste streams, conserve and restore natural resource, helps to control and reduce waste and lastly, to control the temperature. Not only does a sustainable material help to improve the quality of the environment in the Royal Belum Rainforest Resort but it also has many commercial advantages as well. From the usage of sustainable materials, decreasing energy intake, and improving water efficiency will allow us to reduce the operating charges, helps to optimize the life cycle of the Building, increase property value in Belum and improve the number of visitors coming to the famous Royal Belum Rainforest Resort. Eventhough the environmental and economic advantages of the sustainable materials and sustainable buildings are acknowledged, the social advantages of the sustainable materials and the sustainable buildings are often not being taken into account. By refining the interior ecological value in the Villa and the modern house, and at the same time, we can also improve the visitors comfort and health. Besides that, we are able to create an aesthetically pleasing environment in the Royal Belum Rainforest Resort. It also helps to minimize the strain on local infrastructure, helps to increase the awareness of the workers working in the resort and to increase the workers’ productivity.
5. SUSTAINABLE MATERIAL LIFE TIME IN THE BUILDING
Basically, a sustainable building’s life time environmental effect embraces all working and exemplified components. Working impacts are those materials that consume energy when it is in use whereas the exemplified impacts are always because of the production and construction of the building materials. The durability of reinforced concrete structures in the Villa and the modern house in Belum Rainforest is mostly reliant on the worth of the concrete, least amount of contraction or cracking in the concrete, little to literally nothing amount of oxidization of the reinforced steel in the reinforced concrete, remedial of concrete, and excellence organization of reinforced concrete structure. If the concrete structure is properly designed and constructed it is going to be very long lasting and only little maintenance is required. The durability of the reinforced concrete in the Villa and the modern house is influenced by the exposure conditions or the area of exposure, the type of cement used and the quality of concrete used.
Steel is used as the staircase in the Villa and also the modern house. One of the very good explanations for selecting steel staircases is their unbelievable strength and great durability. Steel staircases are very solid and are able of supporting huge quantities of mass. This is actually does not only benefits the people who use the stairs but it also means that we can actually create more rare stair plans. Steel itself is already very strong material and there is no need to even worry about the expanding or contracting of the steel in the weather disorders in Malaysia. Plus, steel staircases will not rot, warp or even succumb to termites.The steel staircases in the Villa and also the modern house are also being preserved so that it won’t corrode or oxidize even if they are in contact with water or air.
Yet another reason steel staircase chosen to be built in the Villa and the modern house is because it is very reasonable. Steel staircases, when it is properly bring about, will last for more than ten years and only very little maintenance or even no maintenance at all is needed. No replacement of structural component or painting is even needed at all because they last so long and they are very durable.
The durability of glass can be witnessed in our everyday lives especially in most cities with ancient churches.Glass in the Villa is used at the windows, skylights and openings. Whereas, Glass in the modern house is used as windows. Glass has extremely high durability and it will not break at all unless it is smashed by extreme masses. If not, the glass will continue to stay the same for an extended period of time. Actually, a normal glass can already resist masses applied at fast rates and it is better than the same weight being pressured over a slower period. The only thing is that glass actually agonizes from the pressure oxidization.
5.1 BUILDING CONCEPT USED IN THESE TWO BUILDINGS
Green building or sustainable building concept basically concentrates mainly on two points which is to improve the efficiency of the buildings which consume energy, water and materials and also to decrease the building footprint on the environment and also the impact to the human’s health. All these can be taken through a better site selection, the design of the building, construction method of the sustainable materials used in the Villa and the modern house, procedure taken, maintenance when the work is done, and removal throughout the complete life cycle. The concept of green building includes and incorporates a variation of approaches during the design, construction and operation of building projects. The consumption of green building materials and products represents one important strategy in the design of a building. By using green building materials or sustainable materials, it brings a lot of advantages to everyone. By using sustainable materials in the Villa and also the modern house in Belum, it helps to reduce the maintenance cost or the additional charges over the lifespan of the building because sustainable materials does not really need maintenance. Sustainable materials help to conserve energy in the Villa and also the modern house. Besides that, it will also help to improve occupant’s health and productivity. Sustainable construction materials are always being used by many developers and its used in all the buildings in Belum Rainforest because it brings a lot of benefit and it has numerous features like nothing or little harmfulness, great recyclability, nothing or little off gassing of polluted air discharges. Sustainable materials have very high durability, it can be reused and recycled, and it is sustainably harvested material.
6. THE SUSTAINABLE MATERIALS EFFECT ON THE POETIC QUALITY IN THE BUILDINGS
Both the Villa and the modern house are built using reinforced concrete as their building structure. However, both of these buildings have very different poetic quality. The usage of reinforced concrete in the Villa makes the building look huge and spacious and thus, it creates a very dramatic and welcoming feeling. In contrary to the former, the modern house itself has very limited area and the usage of reinforced concrete in the building makes the modern house looks clean and the fact that the house is actually very small is being concealed by the cleanliness and the simplicity of the reinforced concrete structure. The usage of steel in the Villa in Belum Rainforest is used at the staircase and also the windows framing. Steel staircase in the Villa creates a very open and light feeling as you are walking up and down the stairs. This is because the staircase itself is very light and and because of the gaps between the railings and the holes on the treads and risers, it gives the user a very open feeling and also it creates a floating feeling. The steel stairs in the modern house helps to soften the building because from far, the modern house basically looks like a square concrete box and with the stairs, the modern house looks balanced with volume and geometry.
Glass is used in the Villa in Belum Rainforest as the openings, skylights and windows. The glass in the Villa creates a very open area as if you’re standing or living outdoor next to the nature but you’re actually indoor in an enclosed space. The poetic quality of the glass in the Villa is that it creates an outdoor feeling even though you’re actually indoor. Glass in the modern house is used as a frame. It frames the trees outside the modern house and it creates and extra space outside the modern house to give a feeling as if the modern house is actually bigger than it is. It’s basically helps to volumize the indoor and outdoor space of the modern house.
7. Conclusion
The sustainable materials used in the Villa and also the modern house in Belum has successfully made the building a green building and has successfully Increase the efficiency of the buildings which are using energy, water and materials. It has also successfully reduced the building effects of people’s health and also the atmosphere. The Villa is to hold any event and to accommodate friends and a few families while the modern is to only accommodate a couple or two friends. It is fascinating how these two buildings that were built using the same building materials but have different poetic qualities in their building. The sustainable materials used in the two buildings have successfully created different poetic quality with the use of the same materials. I feel that it is time for the government and the developers to be aware of the importance of using sustainable materials in a building to save the environment and also the earth.
 

Creep Behaviour of Materials

Chen Yi Ling 

The objectives of the experiment are:

To measure the creep deformation in lead and polypropylene at room temperature
To determine the effect of stress on the creep deformation of lead and polypropylene
To appreciate the difference in creep behaviour between these two classes of materials
To be aware of creep as a design consideration

Theory

2.1. Introduction
Deformation under a certain applied load over a period of time at a particular temperature is defined as creep, and it limits the load carrying capacity among structual materials.
When subjected to a stress greater or equal to its yield stress, the material deforms plastically. Alternately, when the stress is less than its yield stress, the material will deform elastically.
However, when the material has to withstand stress at high temperature, permanent deformation will occur even if the stress is below the yield stress obtained from a tensile test. Under a constant stress, the strain vary as a function of time as shown in Figure 2.1.1. [1]

The different stages of creep are:
Primary Creep/Transient Creep

Strain rate decreases with time and deformation becomes difficult as strain increases. (i.e. Strain Hardening)

Secondary Creep/Steady Creep

Strain rate is constant
The occurrence is due to the balance between strain hardening and strain softening (Structure Recovery)

Tertiary Creep/Approaching Rupture

Strain rate increases with time and the material is fractured.
Increase in creep rate is due to the increasing number of damages such as cavities, cracks and necking.
The damaging phenomena reduce the cross-sectional area, which increase the applied stress when placed under constant load.

Viscoelastic materials such as polymers and metals are susceptible to creep. When subjected to a sudden force, the response of a polymeric material can be detected using the Kelvin-Voigt model (Figure 2.1.2)

Viscoelastic materials experience an increase in strain with time when subjected to a constant stress, this is termed as viscoelastic creep. At t0 (Figure 2.1.3), viscoelastic material is able to maintain for a significant long period of time when loaded with a constant stress. The material eventually fails when it responds to the stress with an increasing strain. In contrast, when the stress is maintained for a shorter period of time, the material experience an initial strain until t1 in which the stress is relieved. The strain then immediately decrease gradually to a residual strain. [3]

In this experiment, we will study the creep behaviour of a low-melting point metal (Lead, Pb) and a polymer (Polypropylene, PP) at room temperature.
2.2. Creep in Metals
Creep can be observed in all metals if its operating temperature exceeds 0.3 to 0.5Tm [5] (Tm = Absolute Melting Temperature) (Figure 2.2.1)

Creep strain (ε) depends on several variables, the most important variables are stress (σ) and temperature (T). Using stress and temperature, the creep rate () can be defined as:
——————– (Equation 2.2.1)
Where,
A = Constant
n = Stress Exponent
E = Activation energy for creep
R = Universal gas constant
Creep rate () increase as stress and temperature increase, hence Equation 2.2.1 can be redefined as:
——————– (Equation 2.2.2)
Whereby n is the slope of vs lnA at constant temperature.
2.3. Creep in Polymers

The creep in polymers is almost similar to the creep in metal as it is depends on stress and temperature, with a few exceptions. Comparing Figure 2.2.1 and Figure 2.3.1, the two graphs look similar except that Figure 2.3.1 has a recovery phase, which is termed as the reversal of creep.
Possessing viscoelastic properties, the behavior of the material can be predicted using the Kelvin-Voigt model (Figure 2.1.2) as mentioned earlier, and hence, it will be used in this experiment.
Equation 2.3.1 shows the relationship between the creep strain (ε) and time under constant stress:
——————– (Equation 2.3.1)
Where and are the constant of the spring and dashpot respectively (Figure 2.1.2)
On the other hand, Equation 2.3.2 shows the creep strain in relation to time:
——————– (Equation 2.3.2)
Where is a constant.
The data obtained can be plotted into an isochronous graph by taking the constant time section through the creep curves for a specific temperature. And the results obtained formed the isochronous graph.

Experimental Procedures

3.1 Equipment for Creep Testing

The load was applied steadily to the specimen using the lever principle shown in Figure 3.1.1. Steel pins were used to kept the specimen in place on one side of the lever and the weight hanger on the other.
The weight hanger consist of 2 pinning position; the topmost hole was used when the hanger and loads were in rest position while the lower hole was used when the hanger was loaded.
The following table shows the mass for the parts of the equipment which should be taken into consideration during the calculation of tensile force on the specimen

Parts

Mass (kg)

Lever Arm

0.4

Weight Hanger

0.16

Pins

0.04 each

If m was the mass of the load on the weight hanger, then the tensile force acting on the specimen can be defined by taking moment about pivot as shown in Figure 3.1.2.

[(F+0.04) x 42] – [0.40 x 147] – [(0.16 + 0.04 +m) x 336] = 0
————— (Equation 3.1.1)
Where, g is the acceleration due to gravity = 9.807m/s2
The extension of the specimen was measured using a dial gauge (DG). The DG was placed into a tube tightened using a nylon pinch screw to hold the DG in its place. It should be noted that the nylon pinch screw should only be tighten sufficiently to prevent the DG from moving when the loads were placed.
The top of the DG was attached to the set up using a grooved plate which was bolted to the lever arm. This arrangement was to ensure the groove in this plate was two times the distance from the pivot to the centre of the specimen. Hence, the extension of the specimen detected by the DG was twice the actual extension of the specimen. And to counter for inaccuracy when zeroing the DG, an additional 3mm was taken into account before the start of the experiment.
Thus, the actual extension of the specimen can be calculated by:
————— (Equation 3.1.2)
3.2 Experiment Methods
For the measurement of creep in lead, the load applied would be 0.9, 1.0 and 1.1kg. For the measurement of creep in polypropylene, the load applied would be 0.7, 0.8 and 0.9kg.
Before conducting the experiment, the width, length, thickness and gauge length of the specimen was measured thrice using an electronic vernier caliper; the readings used for the calculation would be the average reading (highlighted in orange).

Lead

Load (kg)

Width (mm)

Length (mm)

Thickness (mm)

Gauge Length (mm)

0.9

4.92

89.64

1.75

20.09

4.91

89.43

1.74

19.52

4.88

89.53

1.74

19.99

4.903

89.533

1.743

18.867

1.0

4.91

89.46

1.73

20.83

4.93

89.46

1.76

20.78

4.84

89.49

1.74

20.66

4.893

89.47

1.743

20.757

1.1

4.82

89.19

1.72

22.21

4.81

89.04

1.76

22.70

4.83

89.24

1.71

22.75

4.82

89.157

1.73

22.553

 
 
 
 
 

Polypropylene

Load (kg)

Width (mm)

Length (mm)

Thickness (mm)

Gauge Length (mm)

0.6

4.78

89.04

0.88

21.28

0.7

4.77

89.30

0.93

19.13

0.8

4.91

89.02

0.90

21.50

 
 
 
 
 

3.2.1 Experiment 1: Creep of Lead

The lever arm was held in place using 2 pins; 1 of it to be inserted into the bearing block and the other onto the topmost hole of the weight hanger.
Attached the specimen onto the set up using 2 pins.
Place the Dial Gauge into the hole/tube but do not tighten the nylon screw yet.
Attach the groove plate at the top of the Dial Gauge and lever arm and secure it using a thumb nut.
Release the pin holding the weight hanger to take up any free movement.
Make sure the specimen was placed vertically.
Carefully adjust the Dial Gauge until the inner dial reads 3mm and the outer ring reads 0, then tighten the nylon screw.
Load the required weight onto the hanger.
Raise the loaded weight hanger to the lower hole (loading position) and insert the pin.
Gently release the load and start stop watch.
Record reading every 15 seconds for 30 minutes or till the specimen ruptures.

In order to determine the secondary creep rate for each applied stress, 3 extension-time creep curves were required. The creep rate can be calculated using the following equation:
————— (Equation 3.2.1.1)
Where

In this experiment, ln vs ln plot was required. Hence, the stress () on the specimen is given by:
————— (Equation 3.2.1.2)
Where, F is the load applied to the specimen (N)
3.2.2 Experiment 2: Creep of Polypropylene
The test of creep of polypropylene is similar to that of lead, with a couple of exceptions. Before placing the specimen onto the set up, 2 ‘U’ brackets should be fitted over the 2 ends of the specimen. For polypropylene, elastic recovery was possible hence the specimen was not required to be tested until failure. Note that 15 minutes, 12 minutes and 7 minutes were the extension time required for 0.6kg, 0.7kg and 0.8kg respectively

Place the required load onto the weight hanger.
Record the extension for every 15 seconds for specific duration.
After the extension period, remove the weights on the weight hanger and continue to record the reading (elastic recovery phase) every 15 seconds for 10 minutes or when the needle on the Dial Gauge stop moving for 1 minute.
Repeat for other loads.
Plot extension vs time curve to show the creep and recovery curve.

In this experiment, strain vs stress plot was required. Hence, the strain rate () on the specimen is given by:
————— (Equation 3.2.2.1)
Where

Results

Results for Lead

The increment of extension () was selected based on the results reflected on Figure 4.1.1.
The creep rate (έ) of Lead was determine using Equation 3.2.1.1.

Load (kg)

[l2 – l1]

Creep Rate, (s-1)

0.9

19.87

1.0

20.76

1.1

22.55

The stress () applied onto the lead specimen was calculated using Equation 3.2.1.2.

Load, kg

Applied Load, F (N)

Area, A (mm2)

Stress, (MPa)

0.9

99.639

8.526

11.686

1.0

107.484

8.525

12.608

1.1

115.330

8.339

13.830

By adding ln to the values of and έ,

Load, kg

ln

lnέ

0.9

2.458

-10.119

1.0

2.534

-8.798

1.1

2.627

-8.310

Using the data from Table 4.1.1, we can plot a linear graph.

Based on Figure 4.1.2, the stress exponent (n) from the straight line was 10.503.

Results for Polypropylene

A sudden drop was observed for 0.7kg, this was due to human error as results was not recorded promptly on specific time.
Using Equation 3.2.1.2 & 3.2.2.1, the stress and strain rate is shown below:

Load

Width (mm)

Thickness (mm)

Area, A (mm2)

Applied Load, F (N)

Stress, (MPa)

0.6

4.78

0.88

4.206

76.102

18.094

0.7

4.77

0.93

4.436

83.948

18.924

0.8

4.91

0.90

4.419

91.794

20.773

Load, kg

Extension (mm)

Strain Rate,

45s

240s

405s

45s

240s

405s

0.6

21.28

1.04

1.32

1.44

0.049

0.062

0.068

0.7

19.13

1.19

1.47

1.59

0.062

0.077

0.083

0.8

21.50

1.49

2.42

3.17

0.069

0.113

0.147

 
 
 
 
 
 
 
 

Load, kg

Stress, (MPa)

Strain Rate,

45s

240s

405s

0.6

18.094

0.049

0.062

0.068

0.7

18.924

0.062

0.077

0.083

0.8

20.773

0.069

0.113

0.147

 
 
 
 
 

Based on Figure 4.2.1, when stress is constant, the strain increases as time increases, which tallies with the theory.
5. Discussion

Usefulness of the Plot of lnσ vs lnέ

By plotting lnσ against lnέ, we can determine the gradient (n) or the stress exponent of the specimen, which correspond to the controlling mechanism of creep under testing conditions.

Stress Exponent for Lead

The stress exponent indicates the influence of deformation rate on the mechanical strength of the specimen.[7]
At low stresses, n equals to 1, which indicates pure diffusion creep. At high stresses, n > 1, indicating other creeping mechanism besides pure diffusion.

Factors affecting the stress exponent value

The stress exponent for lead in this experiment was found out to be 10.503. And the factors which affects the value is the type of creeping mechanism behind the specimen.
Some creeping mechanisms include Coble creep (Grain boundary diffusion) and Dislocation creep/climb (Power law creep).[8]

Creep of Metals in Design Consideration

The following are some methods to minimize creeping in metals:

Employ materials with high Tm
Reduce the effect of grain boundaries by using a single crystal with large grains or adding solid solutions to eliminate vacancies[9]

Creep is an important consideration for when a component have to support a load at temperatures where Tabs/TM > 0.4.[10]
For high temperature, creep is an important consideration in these three areas:

Displacement-limited applications such as turbine rotors in jet engines
Rupture-limited applications such as high pressure steam pipes
Stress Relaxation limited applications such as tightened bolts and suspended cables [11]

Viscoelastic Behaviour

Materials which exhibits both viscous and elastic property during deformation is known as viscoelasticity.[12] In this experiment, both lead and polypropylene exhibits viscoelasticity to different extend. For lead, the time taken in which the specimen rupture decreases as the stress increases. However, its viscoelasticity is not high hence, its recovery phase is not as significant as polypropylene. Furthermore, the structure of lead is more crystalline than polypropylene, which means it is more brittle and more prone to rupture.
For polypropylene, the extension increases as the stress increases. The extension and recovery rate of each load are as follow:

Load (kg)

Extension (%)

Recovery (%)

0.6

44.9

22.1

0.7

38.9

Not applicable due to experimental error

0.8

63.0

15.5

Recovery rate is possible on polypropylene specimen because it has higher elasticity due to its amorphous structure. The amorphous structure untangles and lengthens out until it becomes crystalline.

Conclusion

In conclusion, the results obtained from the experiment is true to theory. Unfortunately, during the creep test for lead, some results are missing due to some human error resulting in an incomplete graph as depicted in Figure 4.2.1.
For the creep in lead, load 1.0kg and 1.1kg rupture before 30 minutes. This shows that the heavier the load, the faster the creep rate. At even high temperature, t
 

Fabrication and Investigation of the Properties of 2D Hybrid Materials

Fabrication and Investigation of the Properties of 2D Hybrid Materials

Abstract: 2D nanomaterials have the potential to redefine and enhance our lives from invention of wearable electronics to the production of pollutant free water. This literature review explores the properties of these 2D materials and its future prospective, focusing on the fabrication of hybrid materials from graphene and MoS2 and its uses in electrochemical devices. The structure of the hybrid material heterostructures and its advantage of being able to possess the combined properties of its constituent 2D materials is also a topic of discussion in this review. Furthermore, the review describes the current production methods of these 2D materials and introduces the revolutionary method used in UCL labs and it’s benefits in terms of scalability. Apart from that, this review examines the methods used to analyse the 2D materials. This includes the use of TEM, XRD and Raman spectroscopy. The review also gives a summary of the aim and outline for the 4th year MSci research project which will be undertaken by the author over the course of the next 6 months.

Table of Contents

1.Introduction

2.Relevant 2D Nanomaterials

2.1Graphene

2.2Molybdenum Disulphide (MoS2)

3.Hybrid Materials and Heterostructures

4.Applications

5. Production Method of 2D materials

6. Limitations of current batteries

7. Project Aim

8. Outline

9. References

Since the discovery of Graphene, the rise of the revolution of 2D materials in the 21st century has sparked a large interest amongst the academic community. This has led to many fundamental investigations due to its potential applications in fields such as nanoelectronics, flexible devices, sustainable energy and catalyst [1]. 2d materials are materials with thickness of a few nanometres or less, comparable to thickness of a single layer of atom. There is a strong bonding inside the plane between the atoms and weak van der Waals bonding between the planes. The figure below shows some examples of the structures of these materials.

Figure 1: From left to right, graphene, hBN and MoS2. The figure illustrates the top and side view of these materials and the distance between its layers. Taken from ref[2].

2D materials are normally categorized as 2D allotropes of elements, or compounds that has 2 or more covalently bonded elements [2]. The electrons in these types of materials are only free to move in 2 dimensions and their restricted motions are governed by quantum mechanics.

These materials normally have enhanced properties compared to their 3D counterparts such as mechanically strength, flexibility, optically transparent and a good conductor of heat and electricity as they have very high surface area ratio. This enables them to be imbedded in other materials to form functional composites and constructed into nanoscale devices.

Thanks to their minimum defects, some 2D materials exhibit large mobilities in charge carriers as scattering is minimized [3]. Moreover, some 2D semiconducting materials such as MoS2 which are transition metal-dichalcogenides (TMDs) have interesting electronic band structures as they are thinned to monolayers which allows the absorption of photons between the infrared to the ultraviolet region [4] [5]. A larger number of electronic transitions options are now allowed, and this opens the door for high performance optoelectronic devices and fields related to optics and photonics [6].

Figure 2: Illustrates electron mobility at room temperature against the bandgap for various materials. Experimental data for GNRs, graphene and BLG were taken from ref [8]. III–V materials, from left to right InSb, InAs, In0.53Ga0.47As, InP, GaAs, In0.52Al0.48As, Al0.3Ga0.7As, Ga0.51In0.49P. Data for these materials were compiled from ref [7]. Data for silicene and germanene were taken from ref [9] [10] [11]. Data for MoS2 taken from ref [9] [12] [13] [14] [15] [16] [17] [18]. Data for WS2, MoSe2 and WSe2 were taken from ref [19] [20] [21] [22].

Despite the potential applications, it still is a challenge to integrate 2D functional layers with 3D systems which is one of the topics of this research.

2.1Graphene

Graphene is one of the most studied material since its isolation by Andre Geim and Konstantin Novoselov in 2004 at the University of Manchester [23]. Graphene is an allotrope of carbon, in fact it is the basic structural element of other allotropes of carbon such as graphite, diamond and fullerenes. It has only a single layer of carbon atoms arranged in a hexagonal lattice and has a zero-bandgap due to the small overlap between its valence and conduction bands. See figure 1. Graphene is well researched for its properties such as its ultrahigh carrier mobility, exceptional electric and thermal conductivity, larger surface to volume ratio, excellent optical transparency, quantum hall effect and high Young’s modules [24]. Other than that, graphene is known to be very strong. It has an incredible tensile strength of 130.5 GPa which is 200 times higher than steel but at the same time it is very flexible [25]. Coupled with its ability to conduct heat and electricity very efficiently, this makes graphene very desirable to be used in electronic components.

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2.2Molybdenum Disulphide (MoS2)

The bulk of MoS2 is composed of its monolayers stacked on each other and held together by weak van der Waals force and as before there is a difference in property between the bulk and the monolayer of MoS2. In particular, the bulk MoS2 has an indirect electronic band gap of 1.2 eV [26] [27] while the monolayer has a direct band gap of 1.8 eV [28]. Unlike graphene, this layer dependence of band structure property of MoS2 makes its optoelectronic properties much more interesting and useful [29]. Other than that, MoS2 also possess high mechanical strength, electrical conductivity and emits light which opens up to more applications such as photodetectors. See figure 1 for structure of MoS2.

Hybrid materials are materials consisting of 2 or more constituents at the microscopic level, with new properties created from the formation of new electron orbitals between these materials [30]. The new properties may be a combination of the individual properties of its constituent materials. Traditionally, the constituents are made up of an organic and inorganic material and the hybrid materials can be classified based on the interactions between its constituents. Class I hybrid materials exhibit weak interactions between the organic and inorganic constituents such as hydrogen bonding, van der Waals interaction and weak electrostatic force. Class II hybrid materials exhibit strong interactions between its constituents such as covalent bonding [31].

Heterostructures are simply hybrid materials arranged in such a way that the 2D monolayers are stacked in a vertical stack with van der Waals forces holding them together. [32] When stacking these layers together, the synergic effect becomes dominant where charge distribution might be affected between neighbouring and distant layers. This leads to numerous exciting physics phenomena and yields a range of possible applications. For examples, high electron mobility graphene transistors and LED are produced by encapsulating graphene with hexagonal boron nitride (hBN) [33].

Figure 3: Schematic of a traditional heterostructure LED taken from ref [33]. The encapsulating hBN layers act as tunnelling barriers while the grapheme layers act as electrodes to which a bias voltage (Vbias) is applied. The electrodes will then inject electron and holes into the central layer of monolayer MoS2 which has a direct bandgap. The electrons and holes will combine here to emit photons.

The following are the possible applications of 2D materials in the various areas:

i)                    Energy: Batteries Storage and Consumption, Super Capacitors, Solar Cells

ii)                  Electronics: Integrated circuits, wearable electronics, optoelectronics

iii)                Automotive: Thermal Management, Fuel Cells

iv)                Medical: Drug Delivery, bio-sensing, anti-bacterial coating

My project focuses more on fabrication of hybrid materials to be used in electrochemical devices for energy storage based on the UCL production novel routes for 2D material. This will be discussed in the next section.

Mechanical exfoliation was performed for isolating graphene flakes for the first time, by using adhesive tapes to separate them from the bulk and transfer them onto a silicon wafer. To successfully exfoliate, a peeling force needs to be applied to a single or a few atom-thick sheets by attaching them to a scotch tape. The material can then be cleaved from the tape using a substrate. [34]

Chemical vapour deposition (CVD) is the method where the desired deposit is produced by exposing the wafer(substrate) to volatile precursors which then will react and decompose on the substrate’s surface [35].

Although monolayers produced by the mechanical exfoliation and CVD methods are of high quality, yet these methods lack scalability and are costly which proves them to be unsuitable for many applications [36].

My project attempts to use new method of the liquid exfoliation process developed by the UCL team instead, to overcome these issues on scalability. It is important for 2D nanomaterials to achieve liquid-phase delamination from their bulky counterparts as this makes the production of these materials scalable and easily manipulated for applications [37] [38] [39] [40] [41] [42]. The current methods involve applying significant energy in the form of shear force [40], ultrasonication [39] [40] [41] and chemical reaction [43] to break apart the layers of the 2D materials which are held together by the strong van der Waals force thanks to the maximized surface area of these layers. The same can also be achieved by introducing charges onto the layers and via electrochemical intercalation [44] [45] [46] [47]. These methods only produce metastable dispersions which can be stabilized by the addition of functional groups, but this deteriorates the property of the material.

Figure 4: Visualization from ref [36] on how the current liquid phase exfoliation techniques are performed.

The above methods focus on retarding reaggregation as opposed to dissolution driven by thermodynamics as seen in particles such as NaCl (table salt) which dissolve in solvents and are much more stable [48]. The team at UCL has succeeded in doing this by forming layered 2D material salts which dissolve spontaneously without any chemical reaction in a polar solvent to form an ionic solution [48].

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The process begins with the intercalation of the negatively charged layered material with alkali-metal cations. This produces a salt in which there is a transfer of charge between the conduction band of the layered material and the valence electrons of the intercalants. [49] [50] [51]. The layered material salt is then carefully dissolved in a aprotic polar solvent such as tetrahydrofuran, THF or N,N-dimethylformamide, DMF [48]. This solution is only stable in an inert environment. It precipitates fast when exposed to air. One of the biggest advantages of this process is that the morphology of the initial material is maintained, and the salt solution doesn’t reaggregate. The charge on the negatively charged nanosheet solutes are also reversible which facilitates electroplating of the 2D materials. Upon drying this will initiate novel self-assembly of the 2D material on the electroplated surface [48]. This method has high scalability and cost friendly as well.

A few techniques will be used during the course of this project to analyze the final 2D material. Raman Spectroscopy is used to find low-frequency phonons in the material which helps to identify the particles present in the material. It relies on inelastic scattering where a monochromatic light from a laser interacts with the phonons in the system which results in the energy shift of the emitted photons. This shift in energy gives us information of the extent of intercalation [44]. Next, x-ray diffraction helps to determine the molecular structure of the material and gives information of the effect intercalation has on the lattice spacing from Bragg’s Law. Another method that will be used is the transmission electron microscopy (TEM), where an image is formed from the interaction of the beam of electron transmitted through the material. The image produced can then be magnified to observe the structure of the 2D material.

Nanomaterials in liquids makes it easier to print, assemble and embed these 2D materials into coating and composites which is ideal in applications for energy generation and storage [36] [48].

An ideal energy storage unit should have high energy and high-power density. As such lithium ion batteries, one of the commonly used rechargeable batteries, comes quite close to this requirement but it isn’t suitable for large scale application such as in electric cars [52].

A typical lithium ion battery consists of a graphite electrode as the anode (negative) and a transition-metal oxide as the cathode (positive). These 2 electrodes are isolated by a porous polyethylene or a polypropylene thin film separator which are filled with lithium ion conducting organic electrolyte [53].

Figure 5: Schematic of a Li ion battery from ref [53].  The battery is charging when the cathode is oxidized to produce Li+ ions and electrons. The ions travel through the electrolyte while the electrons travel through the external circuit to reach the anode. The opposite happens during discharge.

Although Lithium batteries has a high energy density, it has a relatively low self-discharge compared to nickel-based batteries. Lithium ion batteries require an additional protection circuit to maintain the voltage and current within safety limits. Furthermore, the battery is prone to aging, so most batteries are only expected to function for 3 years. The rechargeable capability falters as they age. Not to mention, they are quite expensive to manufacture as compared to nickel-based batteries.

The aim of my project is to fabricate a hybrid material using graphene and MoS2 by utilizing the new liquid exfoliation method used by the UCL team as discussed in section 5. It is predicted that this hybrid material will have a new combined property of both graphene and MoS2. Thus, it is also the aim of the project to study the properties of this hybrid material and to explore options to use sodium ions (Na+), instead of potassium (K+) and lithium (Li+) ions during intercalation to produce the layered material salt.  This is because, sodium is much more abundant resource as opposed to potassium and lithium. In the event of the success of this project with sodium ions, people from around the globe would be given equal opportunity to benefit by employing this new liquid exfoliation method and to develop it further to the point we are able to produce scalable 2D materials to be used in our daily life applications such as in energy storage and generation.

The total duration of my project is 25 weeks commencing on the 1st of October 2018 and ending on the last day of term 2 which is the 22th March of 2019. No work will be done during reading week in both terms which are on week 6 and week 20. No work will also be done in the labs during winter break which is from week 12 till week 14.

Week 1 to 3: Read research materials, familiarize with the concept of the project and work on the literature review.

Week 4 to 5: Submit literature review on the 22nd of October 2018. Attend safety and equipment training. Practice X-ray diffraction technique on graphene and MoS2. Receive feedback for literature review.

Week 7 to 9: Start making the layered material salt with potassium and lithium ions based on the new liquid exfoliation technique developed by the UCL team. Learn Raman Spectroscopy technique and use it to analyze the layered material.

Week 10 to 11: Explore mixing graphene and MoS2 layered salt together to create a hybrid 2D material.

Week 12 to 14: Work on progress report during winter break.

Week 15 to 25: Submit progress report and receiver feedback for it. Attend progress interview with supervisors. Continue working with data collected in term 1. Analyze the hybrid material fabricated from graphene and MoS2. Attempt intercalation with sodium ions and analyze the property of this material. If time permits, experiments for battery storage and generation will be carried out with this hybrid material.

Week 20 to 25: Work on final report alongside with the project which is due on the 22nd of March 2019.

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Classes of Electroactive Polymer Materials

There are different classes of electroactive polymer materials. There are electronic EAP, ionic EAP, carbon nanotube actuators and conductive polymer actuators.

Recent research work has allowed us to enhance the E-M performance using electroactive polymers. These electroactive polymers have better electro-magnetic performance than crystals and ceramics. This has led to the creation of many devices including actuators, sensors, and transducers. Electric EAPs are further classified into ferroelectric polymers, dielectric EAP, and electro-viscoelastic elastomers. Among the ferroelectric polymer actuators, the most common copolymer is the poly (vinylidene fluoride) or PVDF. These polymers, most commonly used as sheets, have metallic electrodes that increase the stiffness and decrease the piezoelectric response [1]. Key advantages of using a ferroelectric material are that they can be operated in air, vacuum or water and within a wide range of temperatures. Dielectric EAPs are materials in which actuation is caused by electrostatic forces. Dielectric elastomers have a polymer film between two electrodes. As seen in figure 5, when an electric field is induced between the electrodes, the shape of the elastomer changes, which aids in the use of these as actuators. When a dielectric material is subjected to an electric field, positive and negative charges appear on its surfaces. This generates a coulombic force, which in turn generates a stress, which results in a strain response. The most popular type of electric EAP in today’s world, however, is the electro-viscoelastic elastomer. These materials are composite of silicone elastomers and a polar phase. As an electric field is applied to a viscoelastic elastomer, the shear modulus changes. Electric EAPs can operate for long periods of time, with rapid response times. They can also handle high strains if a voltage is applied, however, they require high voltages upwards of 150Mv per m, and have low glass transition temperature, which limits how low the temperature can be [2].

Figure 5: Schematic of the charges and how the shape of the elastomer changes upon an applied current.

Ionic EAPs or Ionic polymer-metal composites are composed of ionic gel polymer planted with metal electrodes. These devices are being researched for their possible use in the field of artificial muscle-like actuators. When you apply a voltage, the cations on the side with the dragging water move, and this results in a pressure gradient for the ionic gel polymer [3]. They are soft materials, that can be molded into almost any shape and can be activated in water.  These actuators are used for their low voltage needs, and relatively large responses. As of now there are no working electrically driven gel muscles, however, in light of recent studies and the data collected, it is not far from reality. Few studies have considered using inorganic fibers/ plates in order to reinforce the gels. This results in a significant increase in the modulus. Despite all the positive attributes associated with the ionic EAPs, they are not widely used because of the slow response compared to the other EAPs. It is also important to note that it is hard to produce a consistent material with ionic EAPs. However, their full potential of composites is yet to be fully explored.

One of the most common EAPs found today are made out of conducting polymers. Conducting polymers belong to family of compounds that are made of monomer units with chemical bonds that under certain conditions such as doping, ensure that there is conductivity in the polymer. As shown in figure 6, when these polymers are grown in the presence of small anions the volume change is a result of stress gradient that is created by the interface during the oxidation or reduction processes [4]. Actuators are made from four main types of conducting polymers. Polypyrrole (PPy), Polyaniline (PANi), Poly(3,4-ethylenedioxythiophene) (PEDOT), and carbon nano tubes are the main types of electroactive polymers that are used as actuators.  Shown in figure 7,on the next page, are the chemical structures of the three most commonly used polymers for conducting actuators.

Figure 6: Bending movement of conductive polymer films

According to a study conducted by the journal of physics, PPy or polypyrrole, was the most studied conducting polymer for actuators.  The main reason for this is due to it electrodeposition properties. Electrodeposition is a process, also known as electroplating, which is most commonly used to increase corrosion protection and abrasion resistance, as well as to deposit a layer of another material that can help with different properties [5]. In most actuators PPy is used as the additional layer on top of metal electrodes. With voltages ranging from 1-3 V, strain rates ranging from 2 to 30 percent, and high stresses reaching up to 30 MPa, it is the perfect candidate for the use in an actuator. They are also used due to the low power that is needed to output a large amount of steady force[6]. Though PPy exhibits great properties needed for actuators, the formulation of the polymer is rather difficult due to the insolubility in aqueous or organic solutions.

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Polyaniline, or PANi is the second most studied polymer next to PPy. The main reason for the interest in this polymer is because it is prepared chemically by oxidative polymerization in aqueous acid solutions. This results in easy fabrication of films, and fibers that can be used on the actuators. Due to the acidic nature of the polymer, however, the PANi polymer is avoided despite its ease in production. It was also found that the most stable region for the operation was in the pH4 regime. It is however being research that PANi can be used as microtubes as building blocks for polymer actuators.

One of the most important polymers that is currently being researched however is the PEDOT also known as poly(3,4-ethylenedioxythiophene). This is one of the most widely used polymers in this field due to a variety of applications, such as transparency, high capacitance and conduction, and because of its high stability. Though the polymer contains many properties that are essential for actuators, the toughness of the PEDOT films is much lower than that of PANi films and the PPy films.  Despite the lack of strength, PEDOT is still one of the most commonly used polymers in the actuator field, due to its high stability in electrochemical reactions.

Figure 7: Chemical structures of commonly used electroactive polymers including, PPy, PANi, and PEDOT [7]

Another less common material that is now being researched for actuators is CNT or carbon nanotubes. These materials have excellent electrical and mechanical properties that are derived from their structure. These tubes consist of hollow cylinders of covalently bonded carbon, which is almost one atomic layer thick. They are made using a process called chemical vapor deposition. Chemical vapor deposition is a method used to produce high quality materials typically. This technique helps produce thin films that can then be used for various tasks. This process is used to deposit hydrocarbons over metal catalysts. These tubes are then taken through a filtering process that results in mats of single walled nanotube ropes that are intertwined with each other. This is when certain fluorinated membranes such as polyvinylidene fluoride, are used to prevent strong adhesion between the membrane and the nanotubes themselves. After these mats are created, they are referred to as “Bucky paper”, due to the paper like structure. Single walled carbon nanotubes were shown to generate higher stresses than natural muscle. These materials were shown to have high stiffness, strength and yield strains. Macroscopic natural actuators are made with billions of CNTs. With CNTs, it is also possible to produce large actuator strains with low voltage which makes it a much more desirable material. Direct conversion of electrical energy to mechanical energy through a response is important for actuators [7]. The performance of these tubes depends on their ability to remove charges.

For many years, EAPs were given little attention due to the small amount of viable materials. With the emergence of new materials, and better technologies, they are starting to be researched again. With the wide variety of the different types of polymer actuators, the applications are endless. Since EAP materials can be transformed into various shapes, it makes them very versatile. They can be used in a variety of fields including artificial muscles, tactile displays, and microfluids. One of the most practical, and common application for EAPs is artificial muscles. Over the past few years, many scientists and researchers have discovered the similarities between the electroactive polymers and human muscles. EAPs are highly damage tolerant, resilient, and can be manipulated to produce large actuation strains. These devices can produce forces up to 25 MPa and have actuation strains of over 300 percent [9]. Both these attributes combined with the ability to perform these tasks in less a second, make it a perfect candidate for artificial muscles. Also, the high fracture toughness makes it relatively resilient and aids in the longevity of the product. Electroactive polymers are also recently being researched for refreshable braille displays. Braille is a tactile writing system that is used by visually impaired people [12]. This concept utilizes the basic concept of an EAP actuator. A row of EAP actuators is placed on one side, and a row of electrodes is placed on the other side. A braille dot is placed on all the actuators, and a voltage is applied. The voltage lowers or raises the actuators which results in a braille system that is fast and refreshable.

The EAPs are also used for microfluidics. Microfluidic devices control and manipulate fluids that are restricted into a small capillary.  Microfluidics has a variety of application including drug delivery systems. Microfluidic devices use EAPs because of their low fabrication costs, and robustness. In the past few years there are many researches being conducted on siloxanes and its ability to function as a smart material. They are considered ‘smart’ because the shape of a siloxane can be changed very rapidly in the presence of an electric field. When this electric field is converted into mechanical energy, it can be used to move fluids using channeled networks [10]. Electroactive polymers are also promising for the file of drug delivery systems. They are especially useful in “on-off” conditions where the drug release mechanism might need to be controlled while the pharmaceutical ingredients are being released in the body. Common polymers that are used for this include polyaniline, polypyrrole, polythiophene and even polyethylene. These polymers are blended into corresponding hydrogels, with the pharmaceutical compound, which allows you to have a patient-controlled drug delivery system [11].

The cost of electroactive polymers depends on the intended use. For majority of the electroactive polymers that are used, they can be bought from various retailers and are fairly easy to access. A table of common electroactive polymers, along with their corresponding prices is shown. The prices of the polymers can range between 30 dollars per 10 grams to upwards of 290 dollars per 10 grams, depending on the application [8]. The processing of these polymers is relatively hard and cannot be done with conventional techniques such as extrusion and molding. In some cases, formation of gels is done using irradiation of pre-existing shapes. Another way to do so is using polymerization of monomer solutions[13]. The characterization of the different devices and materials is done according to their properties. While certain polymers such as PPu and PANi are characterized using techniques such as chronopotentiometry, other devices such as nanotubes are characterized using neutron diffraction, and x-ray photoelectron spectroscopy [14].  Using electroactive polymers for actuators is also more environmentally friendly than using other materials. The ease of production, alongside with the low production time makes electroactive polymers a much more viable option. 

Table 1: Common electroactive polymers and their corresponding prices

Overall there is a wide variety of applications for electroactive polymers including actuators, artificial muscles, tactile displays, as well as microfluid devices. They are relatively cheap and have short production times. There properties, alongside with its production methods make it a viable candidate for a huge array of applications.

References

[1] Anion Exchange Membranes. (n.d.). Retrieved from https://www.fuelcellstore.com/fuel-cell-components/membranes/anion-exchange-membrane?sort=p.price&order=ASC

[2] Bar-Cohen, Y. (2004). Electroactive polymer (EAP) actuators as artificial muscles: Reality, potential, and challenges. Bellingham, WA: SPIE Press.

[3] Carpi, F., & Smela, E. (2009). Biomedical applications of electroactive polymer actuators. Oxford: Wiley-Blackwell.

[4] Cohen, B., Dr. (2010, May). Electroactive Polymers as actuators. Retrieved February 3, 2019, from https://www.sciencedirect.com/topics/chemistry/electroactive-polymers

[5] Electroactive Polymers as Actuators. (2017, June 23). Retrieved from https://www.sciencedirect.com/science/article/pii/B9780081021354000084

[6] Madden, J. D. (1970, January 01). Polypyrrole Actuators: Properties and Initial Applications. Retrieved from https://link.springer.com/chapter/10.1007/978-1-84628-372-7_5

[7] Polsiak, J., Dr, & Lediaev, L., Dr. (n.d.). Actuators based on PVDF sheets with flexible PEDOT polymer electrodes. Retrieved February 17, 2019, from https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1612402

[8] Polypyrrole | Sigma-Aldrich. (n.d.). Retrieved from https://www.sigmaaldrich.com/catalog/search?term=polypyrrole&interface=All&N=0&mode=match partialmax&lang=en®ion=US&focus=product

[9] Price, A. K., Anderson, K. M., & Culbertson, C. T. (2009, July 21). Demonstration of an integrated electroactive polymer actuator on a microfluidic electrophoresis device. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/19568678

[10] Refreshable Braille Displays. (n.d.). Retrieved from http://www.afb.org/prodBrowseCatResults.aspx?CatID=43

[11] Thummala, P., Huang, L., Zhang, Z., & Andersen, M. A. (2012). Analysis of Dielectric Electro Active Polymer actuator and its high voltage driving circuits. 2012 IEEE International Power Modulator and High Voltage Conference (IPMHVC). doi:10.1109/ipmhvc.2012.6518779

[12] Université du Luxembourg. (n.d.). Electrodeposition. Retrieved February 20, 2019, from https://wwwfr.uni.lu/recherche/fstc/physics_and_materials_science_research_unit/research_areas/photovoltaics/research/electrodeposition

[13] Wang, W., Dr. (n.d.). Electroactive polymers. Lecture. Retrieved February 2, 2019, from https://depts.washington.edu/mictech/optics/sensors/week7.pdf

[14] Kaneto, K. (2016). Research Trends of Soft Actuators based on Electroactive Polymers and Conducting Polymers. Journal of Physics: Conference Series,704, 012004. doi:10.1088/1742-6596/704/1/012004

[15] Boeva, Z. A., & Sergeyev, V. (2014). Polyaniline: Synthesis, properties, and application. Journal of Polymer Science,56(1), 144-153. doi:10.1107/s0108768107031758/bs5044sup1.cif

Applications of Engineering Materials in Aerospace

In this project I will discuss in details the applications of engineering materials in Engineering and its many application in the Aerospace and Formula 1. Materials are key in engineering because the correct materials are needed to meet the needed of the environment that they are meant for use in. In aerospace the materials that are generally used are thing such as: titanium, aluminium, carbon fibre. For example titanium and titanium alloys are used in aerospace engine combustion chamber which can be in the region of 2000C in some instances.
Application of materials in Formula 1
Formula 1 is a motor racing category in which the cars can reach extremely high straight line speed and cornering speeds. For them to be able to reach to be able to reach such high speeds and operate in such conditions, the cars much be built from extremely light and strong materials such as carbon fibre and titanium. Carbon-fiber-reinforced polymer is used extensively in high-end automobile racing .The high cost of carbon fiber is mitigated by the material’s unsurpassed strength-to-weight ratio, and low weight is essential for high-performance automobile racing. Race-car manufacturers have also developed methods to give carbon fiber pieces strength in a certain direction, making it strong in a load-bearing direction, but weak in directions where little or no load would be placed on the member.

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Materials such as titanium are also used a lot throughout a formula one engine because of the fact that it is extremely strong and light which allows it the engine to operate at extreme engine speeds such as 20000RPM for a sustained period of time without resulting in engine failure. A material called Inconel is used in the construction of the cars exhaust pipe because of its ability to hold its shape and continue to work as in intended at high temperatures in the region of 900-1000 C . Quite often in formula the rule makers often dictate what materials are permissible in the construction in various parts of the car and what materials are forbidden. This often due to trying to stop the teams from using very expensive materials in the development of the cars, which would send spending sky high. Materials such as beryllium alloys where banned in the use of the construction of the engine as a cost cutting measure. When with the FIA, the regulators of the sport, top teams with big budgets quite easily end up spending in the region of £250 million a year on the development of the car.
The chassis of the car also knows as the monocoque because of how it’s constructed as one piece. The chassis of the car is also sometime referred to as the “survival cell” because it has been designed to cocoon the driver in the event of crash and protect them from injury. The chassis also has to be very light as well so that it is possible to reach highest possible acceleration which gives the teams a possible advantage over their rivals. Another reason for a strong chassis in grand prix racing is that the chassis is also used as mounting point for the engine and the gearbox. The reason this is done again to save as much weight as possible whilst maximizing the structural integrity of the car. The material that can do all then things is carbon fiber which was first used in formula 1 when a British engineer called John Barnard built the McLaren MP4-1 chassis from carbon fiber. The material should just how strong it when McLaren driver John Watson had a heavy crash at the Italian grand prix at the Monza circuit , and managed to get out without any major injuries. The car did go to win 6 grand Prix because it was significantly ahead of its rivals in terms of the materials used in its construction which gave it huge advantage over the rest of the field considering that this versatile and super strong was introduced in 1983.
Limitations and recyclability of the materials used in Formula 1 and that
The limitations of many of the materials is that that most of it is very expensive because of the nature of the materials which puts allot of strain on the smaller teams with smaller budgets especially since 60% of the car is constructed from carbon fibre. Carbon fibre is a recyclable material but the problem with it is that the more it is recycled the more of its structural integrity it losses, like plastic, and therefore the quality of it goes down significantly which means that it can only be used for things such as road paving fillers.
The metal parts of the car such as the cars such as the car’s engine and internal parts of the gearbox, such as the gear ratio, gear forks and the main shaft, can all be very easily recycled without the loss of the strength or quality of the material. Materials such as titanium and steel alloyed which are used for internal parts of the gearbox and also the engines major castings ( cylinder heads , crankshaft, engine block , camshafts) can be melted down and made back into gear ratio or many other things such as aerospace quality components which are found in aircraft fuselage or deep within the engines.
Material applications in the Aerospace Industry
Material research, development and application are absolutely vital in the aerospace industry because through the development of materials that planes are flying higher, faster and safer than ever before. Through the use of ultra light and ultra strong materials such as GLARE (Glass Laminate Aluminum Reinforced Epoxy). GLARE is a “Glass Laminate Aluminum Reinforced Epoxy” FML, composed of several very thin layers of metal (usually aluminum) interspersed with layers of glass-fiber “pre-peg“, bonded together with a matrix such as epoxy. The uni-directional pre-preg layers may be aligned in different directions to suit the predicted stress conditions.
Although GLARE is a composite material, [1] its material properties and fabrication are very similar to bulk aluminum metal sheets. It has far less in common with composite structures when it comes to design, manufacture, inspection or maintenance. GLARE parts are constructed and repaired using mostly conventional metal material techniques.
With the application of such materials in aerospace, it has allowed engineers to create bigger planes which are also very economical at the same time. the use of fatigue resistant materials such as GLARE and carbon fibre also reduce maintenance of aircraft because they don’t need to be checked for cracks as often as planes which are made from aluminium and aluminium alloys. Which are plane from aluminium are more prone to what is known as “metal fatigue”. Metal fatigue happens as a result of continuous loading from the years of pressurisation cycles that a plane goes when it increases and decreases in altitude.
Many aerospace companies such Rolls Royce have an in-house material science research department which spend millions of pounds in research with the hope that it will lead to better quality materials which will be able to function correctly in extreme environments such within the core of a high bypass turbo fan engine, where the temperatures can be in excess of 2000C. The materials are used for this are usually titanium alloys because of its ability to stay in its original shape. If you look closely at the picture of the turbine blade bellow , it can be observed that many small holes have been very precisely drilled in and this is to aid the cooling of the blade and stop in from melting and ultimately causing an entire engine failure. Another reason why such ultra light materials are used is because, the engineers want to minimize the mass of the components as much as possible because this reduces the inertia of the part and this will result in better response time from the engine ,when the pilots engine increase power to the engine. Lighter components also reduce the fuel consumption of and the engine which is especially important considering the fuel prices as they continue to rise. This is something that airlines will pay extra close attention to because they are always looking to minimize their cost to increase their profits, this is especially important at the moment give the current state of the global economy.
Materials in aerospace are also select for their ability to be able to absorb tremendous amounts of energy from unlikely event of an engine failure or an uncontrolled explosion of some sort. Aerospace engine manufacture such as Rolls Royce and General Electric also take the extra step of detonating a fan blade to see whether the engines fan case absorb and contain the impact and to stop parts of the engine escaping and causing further impact to the aircraft. Manufacturers often spend as much as $30 million on this test, at there on expense to prove to potential passengers and airline customers that the engine is truly safe and air worthy.

 

CAD/CAM Materials in Dentistry

Abstract-

In this literature review, the topic CAD and CAM materials was the main focus of the review. Throughout the review, a total of four aspects were discussed in relation to the topic. Those aspects include processing, structures, properties and performance. In the performance aspect, different types of scanners, which include the optical scanners, mechanical scanners and IOS scanners. Advantages were also provided for the IOS scanner and design softwares where it was discussed is to how they function and operate. The structures aspects touches on the new hybrid structure which was introduced. The properties aspect mainly touches on the hardness as the mechanical properties and translucency as the optical properties. The performance aspect discusses the CEREC system and see the different components of the system and explain how it operates and functions.  

Introduction-

The CAD/CAM process in dentistry describes an unintended restoration which was designed by a computer (Computer Aided Design) and was milled by a computer assisted machine (Computer Aided Machined). The very first system was introduced/launched and developed by Duret and colleagues in 1971, but it was not commonly used because of it’s lack of precision of it’s digitizing, computing power and materials. After 10 years, Mormann and Brandestini invented the CEREC System in Zurich, Switzerland (Rekow 1991). The abbreviation form the system was Ceramic Reconstruction. The system was responsible for the exponential increase in demand of CAD/CAM technology through the industry and the world (Liu 2008).

In the last 20 years of the technology’s existence, new and exciting developments have led to the success of dental CAD and CAM technology. Different methods have been gathered to collect 3D data of the tooth using optical cameras, mechanical cameras and design softwares (Giordano 2006).

Methodology

Keywords Used in Search

Author

Name of Source

Platform

Date Found

Year Published

Cad,cam materials dentistry

F Beuer

Digital dentistry: an overview of recent developments for CAD/CAM generated restorations

Google Scholar

4/9/19

2008

Structure of cad and cam systems in dentistry

T Miyazaki, Y Hotta

CAD/CAM systems available for the fabrication of crown and bridge restorations

Google Scholar

4/9/19

13th May 2011

Properties of cad and cam materials in dentistry

Alhenaki, Aasem Mutlaq

Comparison of mechanical and optical properties between three different CAD/CAM materials

Proquest

7/9/19

2015

Properties of Cad and cam materials in dentistry

Adriana Postiglione Buhrer Samra

CAD/CAM in dentistry – a critical review

Proquest

7/9/19

2016

advantages of optical scanners in dentistry

F, Mangano

Intraoral scanners in dentistry: a review of the current literature

Proquest

7/9/19

2017

Cerec system

Constantiniuc

MANAGEMENT OF PROSTHETIC RESTORATIONS WITH THE CEREC SYSTEM

Proquest

8/9/19

July-September 2014

Structure of cad and cam systems in dentistry

ED Rekow

Dental CAD/CAM Systems

Google Scholar

8/9/19

1991

Structure of cad and cam systems in dentistry

WM Palin

Trends in Indirect Dentistry: 8. CAD/CAM Technology

Google Scholar

8/9/19

June 7th 2017

Cad, cam materials in dentistry

Russel Giordano

Materials for chairside CAD/CAM–produced restorations

Google Scholar

8/9/19

1st September 2006

Cad, cam materials in dentistry

PR Liu

Panorama of dental CAD/CAM restorative systems.

Google Scholar

8/9/19

2008

Body-

Processing- As in many other industries, production stages are increasingly becoming automated in dental technology. Dental restorations which are formed with computer assistance have become even more common in the last couple of years. Many different components, such as scanners and design softwares which have been introduced in the field and they all have a significant purpose to making the dentist’s job easier. The more common scanners which are used are called optical scanners, intraoral 3D scanners and mechanical scanners. (Beuer 2008).

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There are various types of optical sensors available, which may be used intra and extra-orally. The optical sensor works with an active triangulation process, this is where a sensors captures the patterns of the light and shade which is projected. The receptor of the sensor interprets the changes in depth in the terms of it’s distances, generating a tridimensional image. However, as digitalization of the data is obtained by the reflection of light captured by a PSD sensor (Fig 1), diffusion may interfere in the precision of the digitalized images. This may be minimized, for example, with the help of sprays that must be applied on the surfaces to be copied, especially in the oral cavity (Samra 2016). The need for performing this procedure must be considered in the choice of the data acquisition process.

Intraoral scanners (IOS) are devices for capturing optical impressions in dentistry. They are also similar to other three -dimensional scanners, a light source is projected on to the object that is due to be scanned, in this scenario, it includes prepared teeth and implant scan bodies on the implant, which is used for transferring the 3D implant position (Mangano 2017). The images of the tissues are captured by imaging sensor which are then processed by the software, which then generate point cloud. These clouds are triangulated by the same software which results in a 3D surface model. The surface model of the tissues are the result of the optical impressions (Mangano 2017). The scanner itself offers many advantages, such as time efficiency, elimination of plaster casts and increased and better communication with the technicians.  

In several studies which have been conducted in the past, have shown that optical impressions are time-efficient, as they are reducing the working times when they are compared to other conventional impressions. Even though the recent introduction of IOS, with the latest technology that is introduced can complete a full arch scan in less than 3 minutes (Mangano 2017).  With normal conventional impressions which can take a full 3-5minutes. This does not seem like a massive difference, but when added throughout the year it is massive.

For the clinician, optical impression allows the removal of a unavoidable step (the convential impression is constructed on the detection of physical impressions and the casting of gypsum models. The exclusion of conventional impression materials results into immediate savings for the clinician which come along with the reduction of consumables costs.

With IOS, the clinician and the dental technician can judge the quality of the impression. After a scan is finished, the dentist can directly email the results to the laboratory and the technician himself can check the results to see if they are accurate. If the technician is not satisfied, he immediately sends an email to the clinician make another one. This happens without any loss of time and without having to call the patient for a different appointment. This also builds and strengthens communication between the clinician and the technician.

In mechanical scanners, the master cast is read mechanically line-by-line by the means of a ruby ball and the three-dimensional structure is then measured. An example of a mechanical scanner in the industry is the Procera Scanner from Nobel Biocare (Samra 2016). This specific type of scanner is established by it’s ability to scan at a high accuracy, this is where the diameter of the ruby ball is set to the smallest grinder which is present in the milling system.

Figure 1- White light projector pattern during the scanning process by an optical scanner

(Beuer 2008)

Design Softwares are mainly provided by the manufacturers for the production and to design various dental restorations. With this type of software being available to dentists, crown and fixed partial dentures frameworks (FDP) can be made (fig 2); some systems also offer the function to design full anatomical crowns, partial crowns, inlays, inlay retained FDPs. The software of CAD/CAM systems presently available on the market is being constantly improved.

Figure 2: Screenshot of CAD-construction of 14 single crown copings

Structures- A new hybrid structure of CAD/CAM porcelain crowns adhered to the CAD/CAM zirconia framework (PAZ) has been proposed (Fig 3). In this system, zirconia frameworks are digitized and porcelain crowns are also fabricated by the CAD/CAM process. Milled porcelain crowns are adhered to zirconia frameworks using adhesive resin cements and the final restoration is completed. Manipulation of the structure is reproducible and reliable without conventional manual porcelain work. Adhesive treatments reinforce the durability of porcelain. Even if porcelain chips, repairing it is easy using the preserved data. (Fig 4 shows a clinical case of the PAZ bridge.)

Fig 3

 

Figure 4

 

 

Properties-

Mechanical properties mainly include it’s hardness. Hardness of a material is defined as the resistance to permanent deformation. The testing for hardness is completed by applying a secure load to an indenter, which then forms a symmetrical shaped indentation on the surface of the material, which is finally then measured by a microscope (Palin 2017). The values of hardness are then calculated using the dimensions of the indentation and the load applied. Overall, there are multiple methods for the testing of hardness of a material (Alhenak 2015). The Vickers hardness is test is more commonly used in the dental. It consists of a 136-degree diamond pyramid-shaped indenter under a standardized force, to produce a square indentation, which are also then are measured under the use of a microscope. Hardness is a vital property when restorative materials are compared. The hardness of the restoration may indicate the level of abrasiveness of a material against the natural dentition. Now, moving on to the next importance property, which are optical properties.

Optical properties which include translucency. Translucency has been characterised as the one of the primary optical characteristics to achieve a good match to a natural tooth structure. (Alhenak 2015). Translucency occurs when light partially spreads or reflects while passing through an object. More the light that passes through the tooth structure, the translucency of the material increases. The translucency of a natural tooth is evident when a noticeable amount of light passes through its incisal and/or proximal aspect due to the presence of a high proportion of enamel compared to the underlying dentin. Now to discuss how the performance of the CEREC system and see the different components of the system and explain how it operates and functions.

Performance-

The CEREC systems starts with an optical impression of the preparation and antagonist teeth. The Optical impression of is captured by an IOS camera, which then sends the image of the prepared teeth right into the software of the system (Constantiniuc 2014). The finished product is the equivalent of the actual clinical situation, which then appears on the screen in a 3D view, which then offers the opportunity to picture the appearance of the dental preparation.

The system is able to detect limits of the preparation, but there is an second option where it is possible for the practitioner to manually keep track off all the limits. The system is also able to plan the occlusion using an algorithm which is based on a biomechanical principle which is similar to natural dentition eruption (Constantiniuc 2014).

 

 

 

 

 

Components of the CEREC System-    All images/info was found and used here are from (Constantiniuc 2014).

The CEREC system is a modular system which is consisted of two units which is connected Hertzian waves; the first image used is for acquisition (Fig 5) and the second (Fig 6) for the production of dental restoration.

Figure 5

Image Acquisition and Design Component

Figure 6- Milling System

                                         

The milling device is equipped with two diamond burrs, which have conical and cylindrical shape. The cylindral diamond burr performs under a jet of water, which results in a speedy and concise modeling  of the ceramic block. (Fig 7) The burr allows reproduction of the fine details of occlusal morphology.

Figure 7

Figure 8

Using supportable and biocompatible materials, which is associated with correct dental preparation, with the use of the CEREC systems provides prosthetic repair with superior durability. Primarily, fine- structured feldspathic ceramics were exclusively used, this is due to the material’s mechanical properties which reduces crack propagation. The fedspathic porcelain is then joint together with different manufactured crystals which are processed through the CEREC system. (Fig 8)

Besides fedspathic porcelains, there are a wide range of options to the type of materials available for CAD and CAM materials for dental; zirconium oxide, aluminium, lithium disilicate, synthetic materials, precious and nonprecious alloys. The choice for which material is used, followed by certain requirements that also include the advantages of these materials:

Properties which are similar to those of enamel

Possibility to individualize the hue of the block and to glaze the restoration

Increased strength, far superior or equal to the pressed ceramic

STAGES

To sum the information discussed, the procedure involved for the CEREC system includes two main stages. The first stage mainly consists in the preparation of the surfaces of the tooth, which is then followed by the optical impression of the dental preparation and the antagonist teeth. Finally, also at this stage, the last form of the prosthetic restoration is designed. The second stage consists of milling and refinement of the restoration which is obtained in the first stage. If the working session is split in two stages, the duration of the clinical phase is reduced. In the final and last stage, adhesive fixation is completed by the practitioner, where the final product (tooth) is inserted with the other 14 crowns (Fig 9).

Figure 9.

Conclusion-

To conclude, a total of four aspects were discussed, processing, structure, properties and performance.  The processing aspect discussed the different types of scanners, which include the optical scanners, mechanical scanners and IOS scanners. The structures aspects touches on the new hybrid structure which was introduced. The properties aspect mainly touches on the hardness as the mechanical properties and translucency as the optical properties. The performance aspect discusses the CEREC system and see the different components of the system

References

Palin, W.M. and Burke, F.J.T., 2005. Trends in indirect dentistry: 8. CAD/CAM technology. Dental update, 32(10), pp.566-572.

Giordano, R., 2006. Materials for chairside CAD/CAM–produced restorations. The Journal of the American Dental Association, 137, pp.14S-21S.

Liu, P.R. and Essig, M.E., 2008. Panorama of dental CAD/CAM restorative systems. Compendium of continuing education in dentistry (Jamesburg, NJ: 1995), 29(8), pp.482-484.

Rekow, E.D., 1991. Dental CAD/CAM systems. JADA, 122(12), pp.43-48.

Beuer, F., Schweiger, J. and Edelhoff, D., 2008. Digital dentistry: an overview of recent developments for CAD/CAM generated restorations. British dental journal, 204(9), p.505.

Miyazaki, T. and Hotta, Y., 2011. CAD/CAM systems available for the fabrication of crown and bridge restorations. Australian dental journal, 56, pp.97-106.

Constantiniuc, M 2014, ‘MANAGEMENT OF PROSTHETIC RESTORATIONS WITH THE CEREC SYSTEM’, Prosthetic Dentistry, vol. 4, no. 3, p. 8.

Mangano, F., Gandolfi, A., Luongo, G. and Logozzo, S. (2017). Intraoral scanners in dentistry: a review of the current literature. BMC Oral Health, 17(1).

Buhrer Samra, A.P., Morais, E., Mazur, R.F., Vieira, S.R. and Rached, R.N. (2016). CAD/CAM in dentistry – a critical review. Revista Odonto Ciência, 31(3), p.140.

Alhenaki, A.M. (2015). COMPARISON OF MECHANICAL AND OPTICAL PROPERTIES BETWEEN THREE DIFFERENT CAD/CAM MATERIALS. NOVA SOUTHEASTERN UNIVERSITY, [online] 1(1), p.101.Available http://search.proquest.com.libraryproxy.griffith.edu.au/docview/1701975564?accountid=14543.

 

The Use of CES to Compare Engineering Materials

In engineering, the selection of materials is one of the most critical stages in the design phase. Engineers, designers, and contractors must make, not only the best choices possible, but also the correct choice when presented with a task. This is to ensure the material selected performs the job it is tasked with doing. The only way to make these choices is by understanding the constraints of the design and the requirements at hand. Without these fundamental properties, a situation may arise where something goes wrong due to a small difference in a materials property which could affect service life, structural integrity and more importantly the safety of the user(s). Due to all these factors, ensuring that the right material is selected is of utmost importance in any field.
This report will outline the steps that had to be taken to find the top 6 ranked materials by using Cambridge Engineering Selector (CES) to use in the manufacture of a flywheel for efficient energy storage which stores as much energy per unit weight by analysis of material indices.

2.1 Translating the problem
In the modern era, companies of design and manufacture can depend on vast databases and software programmes that assist them in their selection of materials. CES is an important selection programme that allows engineers to first compare but then also choose the material relevant to their task. The benefit of using this database is that by entering certain constraint parameters, the software can screen thousands of materials in just several seconds.
The constraints for this task were used to form certain relationships or dimensionless variables in the form of material indices. A material index is a combination of material properties that characterise the performance of a material with a specific purpose [1].
For this material selection, the goal was to use CES to screen and then identify the top six materials to be used in a flywheel for efficient energy storage systems. The material must be able to store as much energy per unit mass as possible without failure. The breakdown for the task can be seen in Table 1 below:

Function

Flywheel

 
Objective

Store as much energy per unit mass
Um
 without failure

 
 
Constraints

Fixed Radius R
Adequate toughness for crack tolerance
Centrifugal Stress is not greater than failure stress causing a burst
Cost

Table 1 – Design requirements for flywheel task.
 
2.2 Material Index Analysis
The material index for the flywheel was calculated by manipulating the equations in the steps that are shown below. [2]
R is the fixed radius of the disk; t is the thickness and ω is the angular velocity during rotation.
U=12Jω2=12π2ρR4tω2#1
Where J=(π2)ρR4t is the moment of inertia of the flywheel disk and ρ is the density of the material used. After some simplification, this equation leads to:
U=π4ρR4tω2#2
The mass of the disk is given as:
m=πR2tρ#3
Therefore, to find the maximum energy per unit mass, equation 2 is divided by 3 to give us:
Um=π4ρR4tω2πR2tρ
∴Um=14R2ω2#5
The maximum centrifugal stress is given as:
σmax=12ρR2ω2#6
As mentioned above in Table 1, the centrifugal stress must not be greater than the failure stress and that the flywheel must hold as much energy per unit mass. From these given parameters, manipulation of ratios can be carried out to find the final Um which will in turn give the material index required.
Umσmax=14R2ω212ρR2ω2=12ρ#7
Um=12σmaxρ#8
Following these manipulations, the material index required is given as:
M1=σmaxρ KJKg#9
This shows that the materials with the highest ratio of ultimate tensile strength over density will be best suited to be picked for the manufacture of the flywheel in this project.
Finally, a second material index must be used. When looking at the table with constraints, cost per kilogram and toughness must form a simple ratio. This gives:
M2=GC#10
Where G is the toughness of the materials and C is the cost.
2.3 Material Screening using CES
Following the establishment of the two material indices, the next phase is to commence the material screening on the CES database. A graph of ultimate tensile strength versus density (M1) was plotted on a logarithmic scale and the stored materials were shown. Figure 1 below shows the results obtained.

Figure 1 – Stage 1 Plot (Tensile Strength vs Density)
Once all the materials from the database were supplied on the chart, filtering for materials could continue. A line of gradient 1 was plotted on the graph which allows the user to be able to change the position gradually. This enables materials below to be eliminated until the point occurs that only materials remain. Figure 2 below shows the updated chart.

Figure 2 – Stage 1 plot with line of gradient 1 showing passed materials highlighted in Black.
Once the first stage was completed, M2 was then plot on a second graph. Once again it was plot on a logarithmic scale. Following the plot of the chart, a box was added in the region where the appropriate toughness and cost regions would occur. Straight lines (horizontal/vertical) were not used due to the fact they would represent limits. In the case of this project, toughness and cost are secondary constraints and were left arbitrary.

Figure 3 – Stage 2 plot with limit box (Toughness vs Cost/kg)
Finally, by using the intersection button on CS, the screening was completed. By using this function, it allows the user to identify which materials passed both stages from the given parameters. Figure 4 shows the combination of both stages and the final materials are named in Table 2

Figure 4 – Completed screening (materials that passed both stages)

Table 2 – Final materials in alphabetical order
2.4 Ranking of Materials
Now that the top six materials are found, further consideration can take place to form a final judgement on which material is to be ranked top. To assist in the final decision, current knowledge on material science will be used as well as considering published studies regarding similar work. Using the CES database, the materials characteristics will also be recorded and compared with one another. For this case, tensile strength, density, and toughness were compared and these influenced the final ranking. Toughness had to be considered due to the original constraint in Table 1 of the flywheel requiring a crack tolerance.

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For each material property, a range of values were given on the CES software. To avoid any major discrepancies, the minimum value was taken into consideration. The reason for this is that not all the sample materials may be able to reach their maximum value therefore, the minimum values will be less likely to cause errors. Shown below in Table 3 is the final ranking of materials.

Table 3 – Final material ranking
The overall first place material was the “Carbon Fiber, high strength (5-micron, f)” also known as Carbon Fiber Reinforced Polymer (CFRP). The reasoning for this decision is that although the silica has a higher Material Index, meaning that in theory it will store more energy per unit mass, the CFRP has a higher toughness value. This is key because the CFRP disk will be able to endure more fatigue due to cracking and still be able to perform.
Also, CFRP’s have been tried and tested in this role. It has been shown that they can store approximately 200kJ/kg whereas a traditional material such us lead can only store around 1kJ/kg making it ideal for modern use. Finally, the material has a low density which allows it to be lightweight, yet it still have a high tensile strength meaning the structural integrity of the flywheel will not be an issue. When looking at toughness, although it is lower than the Silica, the ratio of toughness compared to the other parameters is very similar to that of the second ranked material.
Although the Carbon Fiber is almost double the cost of the silica, the safety of the user should be the main priority. The reason for this high cost is the time-consuming manufacturing of the material in that lattice sheets must be woven from a single carbon strands and a resin is used to keep it in its final shape due to it being synthetically produced.
Finally, materials ranked 3-6 are not suitable for this type of application. This is because they are fabric materials used in the applications of electrical wiring insulation. Due to this, they would not be suitable in producing a solid disk that rotates and at the high rotation speeds they could rip themselves apart causing damage to the product they are used in.

3.1 Ashby Charts
The charts from CES shown in Figure 2 and 3 depict how different material families perform under the given characteristics. The different material envelopes highlighted in the figures show a range of materials that include low density, light foams in the bottom left to high density, heavy Tungsten materials in the top right. By using the software, it allows the scanning of materials on both extremes of the material spectrum to be analysed and included. By adjusting the straight linear plot on the graph, the optimum material could be found with relative ease and the remaining materials could be eliminated in this screening process due to the gradient of the given line. This shows that the main reason for materials being eliminated is due to the order of the material index that was calculated. For example, if the tensile strength were greater, this would cause a steeper gradient to occur and would produces a greater number of materials to be included.
3.2 Other Considered Factors
The main characteristics used for this task was the density of the material and the tensile strength. Although these did not have numerical values applied to them, sensible estimates had to be considered. As an example, if the material used was to dense (e.g. tungsten) then the weight of the flywheel would be to great and the energy stored would not be adequate to rotate it.
Other factors that were considered for this project, for ranking and as a material index, were the cost of materials and the toughness. The cost of the material had to be economical for the application otherwise the device could have been manufactured at a loss. The cost must be justified when choosing a more expensive material such as the Carbon Fiber. As mentioned earlier, the CFRP has been used safely in this application meaning the safety factor and prior use justifies the cost. As for the toughness, it was the same situation as the cost in that no fixed value was set although a sensible value had to be decided on.
Finally, the radius of the flywheel was left arbitrary. If a selected value were decided upon, it would again mean that certain materials would be omitted or made available. This is because geometric parameters of any structure play a major part in performance and changing the size or shape could cause the material to act differently when the final product is produced.
3.3 Advantages & Disadvantages of Using CES
A great advantage of using CES is the ease of use. An inexperienced individual can easily navigate around the software and prior knowledge is not key for use. Training on it is easy and due to the vast number of people using it, resources are readily available either on the software itself or online to the general public due to it being used as a current analysis tool in industry. Another key advantage is the large number of properties that can be analysed. Numerous combinations can be plotted on the charts to find relevant relationships for different material indices to achieve a vast number of depictions to choose materials for a given specification.
The main disadvantage of the software however is the generalisation of the materials. Although thousands of materials are stored on the database, the variations of each material are basic. Only modern materials such as the Carbon Fiber composite have variations stored whereas more well-known and older materials contain a limited amount. Another disadvantage due to these variations are the range of values of properties that are given for materials. For some materials, the range of values are large, this could cause issues. A material may not reach a stated value on the software due to being a variation and this could cause issues for manufactures.
3.4 Individual Feedback
Overall, I believe that CES is a key part of any design process. After seeing the ease of use for the software, it has allowed an engineering student to select and compare materials for a given task with reliability and maximum efficiency. I feel that this software will be used more regularly in the future as it will allow me to solve any future material selection processes that may occur.

[1] City, University of London “Lecture 2 – Selection of Materials”
[2] Michael F. Ashby “Materials Selection in Mechanical Design” 5th Edition (2017)
 

Composite Materials in Leaf Springs: A Review

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Testing Heat Sink Materials

Heat Sinks?

Abstract…………………………………………………………….

Introduction………………………………………………………….

Research…………………………………………………………..

Biblical Application…………………………………………………..

Experimental Section……………………………………………………

Materials and Methods

Results

Discussion

Conclusion

Bibliography

 LEDs (Light Emitting Diode) are used in almost every machine whether it be a tractor, assembly line or a elevator. They are in these machines because they are energy efficient using less than ninety percent less energy than other light sources and are environment friendly. Four different types of heat sinks will be tested with red LEDs, one of the four will have no heat sink attached to it and will be timed by how long it stays on before it burns out. The LEDs were tested five times on each heat sink. Of the four heat sinks tested: no heat sink, mineral water, aluminum, and copper: no heat sink stayed on the longest.

What heat sink will prevent a diode from frying the longest? This experiment will test what type of heat sink will prevent the diode from frying the longest. Some of the heat sinks that will be used are copper, aluminum and mineral oil.

Research

To understand how circuit boards are made, their first needs to be a understanding of soldering. Soldering is when solder is melted into a liquid to bind electrical components to a Perf Board. Solder is usually made of tin and lead. The most common solder is made up of sixty percent tin and forty percent lead. When you solder the tip of the soldering iron gets hot, so be careful not to touch it. Each time something is bound with the soldering iron, the tip of the soldering iron must be cleaned. The reason behind this is because the tip of the soldering iron oxidizes and can get the metal dirty causing the metal to not bind properly. The solder in this experiment will be used to bind the Perf Board with the diode. The specific diode that will be used in the experiment is a LED.

LEDs are a semiconductor device that emits incoherent monochromatic light. A LED contains a chip of semiconducting impregnated with impurities make a PN junction. The color of the LEDs depends on the amount of bandgap energy in the materials forming the PN junction. The materials used in the PN junction give of this bandgap energy that corresponds to near-infrared, visible or near-ultraviolet light. During the experiment the LED will have a heat sink around it to prevent it from frying faster than it does without one.

The heat sinks that will be used for the experiment will be passive heat sinks. Passive heat sinks have no moving parts, for example a fan. The most common material for a heat sink is aluminum because, it is light weight and has good thermal conductivity. There are many different types of passive heat sinks. A few of them are bonded heat sinks, skived heat sink and a stamped heat sink.

Biblical Application

Genesis 31:40 says, “This was my situation: The heat consumed me in the daytime and the cold at night, and sleep fled from my eyes.” This verse can be applied to the experiment since diodes give off a lot of heat which make them fry faster but, with heat sinks the diodes fry slower. They fry slower because, the heat sink moves the heat away from the diode so it gets cold. When the verse says, “the heat consumed me”, it represents a diode without a heat sink. The diode with a heat sink is when the cold consumes him at night, since the heat sink is making the diode cold.

Experimental Section

Materials and Methods

The following materials were used in this project:

Mineral oil

Aluminum heat sink

Copper heat sink

4 Wired alligator clips

19.5V Power supply

Perf Board

Insulated copper wire

Soldering Iron

Solder

2 Rotary Potentiometer, 1kohm, 2 W, ± 10%, 93 Series, 1 Turns, Linear

30-50 LED, Red, Through Hole, T-1 (3mm), 20 mA, 1.85V, 640 nm (Bought 50)

Rocker Switch, Non Illuminated, DPST, On-Off, Black, Panel, 10 A

Stopwatch(Recorded the experiment and wrote down the times after I was done)

Grinder(Used to take off most of the LED casing without exposing it to air)

Small plastic container

The steps used to conduct the testing of this project are:

Make the LED Burn Out Circuit.

Attach a LED to the positive and negative ends of the circuit(The long wire on the LED is negative and the short end is positive)

Test the circuit with one LED (If it the circuit doesn’t work make sure the positive and negative wires aren’t touching each other

Attach another LED to the circuit

Turn on the circuit and record how long the LED was on till it burned out

Repeat Steps 4-5 four more times then proceed to Step 7

Grind fifteen LEDs plastic casing until there is just a little plastic around the casing

Pour mineral oil in a small plastic cup

Attach a grinded LED to the circuit and put it in the mineral oil

Turn on the circuit and record how long the LED was on till it burned out

Repeat Steps 8-9 four more times then proceed to Step 11

Make an aluminum casing for the LED, make sure that there is a hole to see the light from the grinded LED and a place to easily put in and remove the LED

Put a grinded LED in the aluminum casing and attach it to the circuit

Turn on the circuit and record how long the LED was on till it burned out

Repeat Steps 13-14 four more times then proceed to Step 16

Make a copper casing for the LED, make sure that there is a hole to see the light from the grinded LED and a place to easily put in and remove the LED

Put a grinded LED in the copper casing and attach it to the circuit

Turn on the circuit and record how long the LED was on till it burned out

Repeat Steps 17-18 four more times

Results

The graph shows how long the LEDs lasted.

 

Discussion

 This experiment did not work. A few of the reasons it didn’t work is because of some of the heat sinks were not designed as they should have and the power had to be increased by a power supply instead of AA batteries because the LED was not burning out. Some of the reasons the experiment did not work as it should have was due to procrastination.

Conclusion

Based on the results, the hypothesis was incorrect. There were certain things that should have been thought of before the experiment that was not

Akhtar, Farozan. “Why Are LED Lights Becoming Popular?” 99acres Article, 17 June 2016, www.99acres.com/articles/why-are-led-lights-becoming-popular.html.

 “6 Heat Sink Types: Which One Is Best for Your Project?” Gabrian, 13 Dec. 2017, www.gabrian.com/6-heat-sink-types/.

Jeff. “Announcing the ‘Soldering Is Easy’ Complete Comic Book!” MightyOhm, 18 Feb. 2018, mightyohm.com/blog/2011/04/soldering-is-easy-comic-book/.

Light-Emitting Diodes (LEDs).” Emred, 18 July 2007, web.archive.org/web/20180319221605/http:/www.emred.fi:80/htmls_en/leds_en.html.