Browsing by Author "Jarvis, Alan Lawrence Leigh."

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The application of electrical resistance tomography within a vacuum sugar pan in order to better understand its boiling dynamics.
(2010) Sanderson, Daniel.; Jarvis, Alan Lawrence Leigh.
This dissertation is concerned with the application of tomography within the sugar industry; in particular non-accessible locations found in a sugar mill. In this study, the focus of research is that of a vacuum pan, and if better understood through tomographical techniques could significantly improve mill efficiency and throughput. The tomography system comprises unique mechanical interfaces, data acquisition modules and software algorithms in order to generate images which reflect the dynamics in the tomographical sensor zone. The distribution of gas (low conductivity) and liquid (high conductivity) within a tube is of main interest in order to understand the boiling dynamics and ultimately pan design. This is attained by determining the internal cross-sectional spatial distribution of conductivity of a number of tubes within the pan simultaneously. Thermal properties of the contents of the sugar pan (a syrup-like substance known as massecuite) at different boiling stages can be estimated based on the tomographical data. Data acquisition is achieved via an in-house designed electronic state machine. A neighbourhood back-projection reconstruction technique was developed in MATLAB in order to generate tomographical images. Results from the system have identified different boiling dynamics which improve the understanding and design of vacuum sugar pans.
Baseline demand responsiveness framework for the conventional grid through appliance scheduling by evolutionary metaheuristics.
(2020) Doho, Goncalves Justino.; Matthews, Alan Peter.; Jarvis, Alan Lawrence Leigh.
A major problem of many energy environments nowadays, is an obsolete and highly inefficient electricity supply system, the Conventional Grid (CG), characterized by a high peak to average ratio, out of an uncontrollable demand, worsened by a native lack of communications infrastructures and resources for performing a proper automated demand side management, which has resulted in blackouts, harsh user discomfort, high electricity cost, huge economic losses and a high carbon footprint. Designed to tackle this problem is the emerging Smart Grid (SG). Most research works are devoted to providing automation and efficiency to the SG (or the intermediate SG-like) environments. There is a scarcity of research devoted to providing automated demand responsiveness to the information layer deprived CG environments, although as evident, an Automated Demand Response (ADR) is badly required, since there is still a long way until we get to the SG, all the more when developing world is concerned. Such context, set our focus towards the CG. So, this research work, developed a framework for providing a "blind" baseline Demand Responsiveness (bbDR) for CG environments, wherein, a pseudo real time electricity pricing function, built from a country load profile, is used as a guiding function for the autonomous scheduling of controllable appliances, which seeks to improve electricity consumption patterns, while also preserving user satisfaction by complying to their preferences. For performance evaluation, the optimized energy consumption patterns (peak load, peak to average ratio, load and cost profiles and mean energy rate) of the controlled use of appliances, are compared to those ones produced by their uncontrolled use. The controlled usage schedules are produced by an evolutionary metaheuristics, whilst the uncontrolled usage is stochastically generated from appliances’ rate-of-use probabilities sourced from the literature. The results proved that, such framework is capable of, without DR communications, delivering meaningful, ADR-like, performances to a communications deprived CG environment. As part of the work for simulating the above bbDR framework, we developed and demonstrated a Real Parameter Blackbox Optimization Approach to Appliance Scheduling (RPBBOAS) model, which describes the household, and provides the logical interface with the optimization algorithms. This real parameter model, vis-a-vis its discrete parameter counterpart, tackles combinatorial explosion by, in a novel way, reducing the problem dimension that is traded with the external blackbox optimization algorithms, in such a way that boosts performance and widens the window of applicable algorithms. While developing the above RPBBOAS model, readily available state-of-the-art metaheuristics showed a lackluster performance, which propelled us to design a novel hybrid evolutionary metaheuristics (Hy- PERGDx) that was eventually used in the bbDR simulations. It showed a better all-around performance and robustness vs the state-of-the-art, when benchmarked on a wide range of non-linear problems. Overall, such deliveries, demonstrated the potential of the proposed bbDR framework for improving demand patterns and quality of service figures, in a communication free way, which with an appropriate follow-up development, makes it suitable for application in severely affected, communications deprived (or communications limited), energy networks such as South Africa or worse energy ecosystems.
The design and construction of a cryostat for thermal battery investigations.
(2011) Swann, Brett Matthew.; Jarvis, Alan Lawrence Leigh.
A test cryostat was constructed to investigate the potential of a locally made thermal battery. A thermal battery is proposed to be a useful component in the construction of future superconducting fault current limiter (SFCL) systems. The heat generated from a SFCL under quench conditions can be conducted into a solid nitrogen thermal battery. This is an alternative to using a liquid cryogen which on evaporation would form a highly nonconductive vapour layer around the SFCL and could be potentially explosive. The relevant heat transfer mechanisms for cryostat design were analyzed to ensure that the cryostat was capable of solidifying nitrogen and thus be used as a thermal battery. The experimental stage was ultimately capable of reaching a temperature of 40 K. Using a resistor to mimic the normal state of a superconductor, the performance of the thermal battery was determined by subjecting it to transient thermal events. The effect of solid nitrogen crystal size was investigated by performing pulse tests on solid nitrogen formed at different rates. It was found that slowly formed solid nitrogen performed better and stabilised the resistor’s temperature more quickly. The phenomenon of ‘dry-out’ was also investigated for different formation rates by subjecting the solid nitrogen to multiple heating pulses. It was found to become very significant after the first pulse when using quickly formed solid nitrogen, but did not manifest in slowly formed solid nitrogen.
The development and application of a real-time electrical resistance tomography system.
(2012) Adigun, Peter Ayotola.; Jarvis, Alan Lawrence Leigh.
This dissertation focuses on the application of tomography in the sugar milling process, specifically within the vacuum pan. The research aims to improve the efficiency and throughput of a sugar mill by producing real-time images of the boiling dynamic in the pan and hence can be used as a diagnostic tool. The real-time tomography system is a combination of ruggedized data collecting hardware, a switching circuit and software algorithms. The system described in this dissertation uses 16 electrodes and estimates images based on the distinct differences in conductivities to be found in the vacuum pan, i.e. a conductive syrup-like fluid (massecuite) and bubbles. There is a direct correlation between the bubbles produced during the boiling process and heat transfer in the pan. From this correlation one can determine how well the pan is operating. The system has been developed in order to monitor specific parts of a pan for optimal boiling. A binary reconstructed image identifies either massecuite or water vapour. Each image is reconstructed using a modified neighbourhood data collection method and a back projection algorithm. The data collection and image reconstruction take place simultaneously, making it possible to generate images in real-time. Each image frame is reconstructed at approximately 1.1 frames per second. Most of the system was developed in LabVIEW, with some added external drive electronics, and functions seamlessly. The tomography system is LAN enabled hence measurements are initiated through a remote PC on the same network and the reconstructed images are streamed to the user. The laboratory results demonstrate that it is possible to generate tomographic images from bubbles vs massecuite, tap water and deionized water in real-time.
A DSP-enhanced AC susceptometer for characterisation of high temperature superconductors.
(2014) Babet, Sergio Stephane.; Jarvis, Alan Lawrence Leigh.
DSP-based susceptometer was designed and implemented to study granular HTS Y1Ba2Cu3O7-x (YBCO) superconducting specimens. The AC susceptometer is made up of a primary coil driven by an AC signal and two sensing coils: a balancing coil and a pickup coil which senses the magnetic response of a superconducting specimen. A particular feature of the AC susceptometer was a digital lock-in amplifier which was designed and implemented in DASYLab instead of using a conventional lock-in amplifier. The lock-in amplifier was necessary to separate the real and imaginary parts of AC susceptibility response of the superconducting sample placed into one of the sensing coils. Granular YBCO material is known for having a low critical current density, , due to a weak link effect. Grain boundaries, which are responsible for the weak link effect, comprise of regions of high stress fields. In one experiment to test the apparatus, YBCO specimens were doped with hydrogen with the aim of relieving stresses to improve the intergranular critical current. The AC susceptometer was successfully used to characterise the intergranular critical current of YBCO samples. The relative intergranular critical current was successfully estimated using a critical state model, based on Bean model. The migration of H2 molecules into the YBCO‟s lattice was not successful in relieving the stresses at the grain boundaries, and resulted in the deterioration of intergranular critical current.
An experimental investigation into the joining of bulk high temperature superconductors.
(2005) Pillay, Marlini.; Jarvis, Alan Lawrence Leigh.
Current melt texturing processes can only produce high-quality High Temperature Superconducting (HTSC) domains of a few centimetres in size. Increasing the size of the domain by a joining technique is investigated. The parent HTSC melt textured domains of YBa2CU307-li (Y 123), were used in this research to investigate the joining technique. The solder powders used to form the seam were HTSC YbBa2Cu307-li (YbI23), which has a peritectic temperature of approximately 925 cC, Yb2BatCu\07_o (Yb211), Silver Oxide (Ag20) and Y123. A total of 8 different superconducting 'solders' were manufactured using these powders. Microstructural analyses using a scanning electron microscope (SEM) and an optical microscope were conducted on each sample. It was found that mechanisms occurring during the growth of the seam affect the performance of the join. During the growth, three interfaces are formed. The interface between the parent and the growth front produced an excellent join whereas most of the microstructural defects were present at the intersection of the two growth fronts also known as the impingement boundary. The effect of the addition of Yb211 and silver particles to the join were investigated. It was found that although Yb211 particles improve the flux pinning and viscosity of the solder and the silver improves the intergranular critical current density (Jc) [1], they also reduce the effective cross-sectional area of the joined sample. Thus, the amount of non-superconducting particles added needs to be optimised. Transport measurements were taken to evaluate the current carrying capacity of each sample. It was found that Sample 2-A (Yb123 + 5%Ag20) has the highest Jc of approximately 142 A/cm 2 at 80 K while Sample 3-A (Y123 + 5%Ag20) has the poorest Jc of about 37 A/cm2 at 80 K. Resistivity vs. Temperature graphs show that all joined samples were superconducting implying that the joining process was successful in establishing a superconducting join. Magnetic field maps of the parent and joined samples were captured using a Hall Probe. It was found that the joined sample could trap almost 95 % of the field that could be trapped by the parent. From these results, it was concluded that joining HTSC bulk pieces is possible using an external 'soldering' agent.
Experiments in thin film deposition : plasma-based fabrication of carbon nanotubes and magnesium diboride thin films.
(2004) Coetsee, Dirk.; Jarvis, Alan Lawrence Leigh.; Doyle, Terence Brian.
A simple, low-cost plasma reactor was developed for the purpose of carrying out thin film deposition experiments. The reactor is based largely on the Atmospheric Pressure Nonequilibrium Plasma (APNEP) design with a simple modification. It was used in an attempt to fabricate magnesium diboride thin films via a novel, but unsuccessful CVD process where plasma etching provides a precursor boron flux. Carbon nanotubes were successfully synthesised with the apparatus using a plasma-based variation of the floating catalyst or vapour phase growth method. The affect of various parameters and chemicals on the quality of nanotube production was assessed.
Frequency response analysis of a current limiting reactor.
(2022) Kuppan, Levashen.; Swanson, Andrew Graham.; Jarvis, Alan Lawrence Leigh.
With the demand for electricity continuously increasing, power systems are required to increase capacity to meet such demands which can entail integrating renewable energy resources to the grid. This increase in capacity would mean a likewise increase in fault levels in the network which can result in costly damage to components such as circuit breakers, transformers and cables. Air-core reactors are commonly employed to prevent such damages from occurring, however, the increase in fault levels must also be accounted for in the design of reactors as they are also subject to transients. This dissertation documents the development of models to accurately represent an Air-core reactor in order to gain a better understanding of the design considerations required. Two models are developed for two desktop reactors using different methods as a form of cross-validation. The first model is developed in MATLAB r2020a and utilises an analytical approach through an equivalent circuit method (ECM). Equations are used to compute the inductive, capacitive and resistive components which are then used to guide the development of the FEM models. The second model is developed using COMSOL Multiphysics software which is based on the Finite Element Method (FEM) approach. A 2D-axisymmetrical model is constructed and simulated using COMSOL’s Magnetic and Electric field physics in the frequency domain from which a frequency response is obtained as well as values for the inductive, resistive and capacitive components. Final validation of the FEM models is done through comparisons to measured results of the two desktop reactors. FEM simulated RLC components showed fairly good agreement to the measured values, particularly the inductance having a difference of 3.4 μH and a capacitance difference of 1 pF for Reactor 1. The FEM simulated frequency response of 1.5 MHz differed by 0.4 MHz when compared to the measured frequency response for Reactor 2 of 1.9 MHz. A sensitivity analysis is conducted for the FEM model in order to obtain an understanding of the design considerations required for the air-core reactor. Simulations are performed on the FEM model with changes to geometry, permittivity of the insulation medium and resistivity of the copper coil. The effects of these changes on the RLC parameters and resonance frequencies are documented. The FEM model is then scaled to a full-scaled reactor which showed good agreement between the expected inductance of 2.24 mH and the simulated inductance of 2.28 MH. The resultant resonant frequency was observed to occur at 380 kHz. The aim of this is to develop an understanding of parameters and equations that should be considered in the design process of reactors which will then be employed in the development of a superconducting fault current limiter (SFCL).
Hybrid media streaming architecture, focussing on quantification of scalability of media streaming architectures, including streaming protocal evaluation.
(2013) Frederick, Wayne.; Jarvis, Alan Lawrence Leigh.
An analysis of media streaming architectures is performed in this dissertation drawing focus to the advantages and disadvantages of the various architectures. Detailed examination is given to scalability of decentralized Peer-to-Peer (P2P) systems in comparison to centralized client-server systems in an aim to quantify the difference in scalability between the architectures. Research has indicated that decentralized architectures are found to have better scalability. Taking into consideration the various factors and protocols encountered in many researched multimedia streaming architectures, a decentralized P2P Video on Demand (VoD) media streaming system using Set-Top Boxes (STBs) is proposed. Both centralized and decentralized architectures are simulated in Network Simulator 2 (NS2), with the inclusion of an enhanced Evalvid (Video Evaluation) toolset which allows utilization of Peak Signal to Noise Ratio (PSNR) to determine received video quality. An evaluation methodology, referred to as the Quality and Scalability Quantification System (QSQS), is developed and successfully tested using PSNR to determine differences in quality and scalability between the architectures. Results indicate that the decentralized architecture has on average 15 % higher delivered video quality and 34 % higher scalability than the centralized architecture under similar operating conditions. Under very high network loads, drawbacks to decentralized architectures are observed and examined, with a centralized nature emerging amongst peer nodes causing a resultant loss in network robustness. In response to this, a protocol that introduces serving peers is implemented in the decentralized architecture. Evaluation of the serving peer protocol found an increase of almost 30 % in delivered video quality to all peers when compared to the standard architecture. Performance of the evaluation methodology in evaluating the serving peer protocol enhances possibilities of using this method as a Quality of Experience (QoE) indicator in addition to existing Quality of Service (QoS) evaluation methods.
Investigation into the effect of rotationally shifted arcing horna on a sub-transmission 132kV system.
(2016) Smith, Brett.; Swanson, Andrew Graham.; Jarvis, Alan Lawrence Leigh.
Insulators perform a vital role in a high voltage transmission system as they are expected to withstand normal operating voltages as well as external overvoltages such as those caused by lightning strikes. These arcing horns are primarily fitted to protect the insulator against arc damage in the event of a flashover occurring. In addition to this, they perform a role in the insulation level of the sub-transmission system by providing coordinated protection from backflashover events that are caused by direct strikes to transmission towers. Currently, the eThekwini Municipality maintains the need of placing arcing horns on their 132kV insulators within a certain span length of a nearby substation. The arcing horns are subject to rotational shifts in the event of adverse weather conditions and this leads to unscheduled maintenance and replacement of the insulator arcing horn arrangement. This upkeep is both costly and time consuming and is a process which may not be necessary. The rotational shift leads to a longer flashover distance and higher breakdown strength and implies that the system will be better protected against flashover and backflashover. However the integrity of the insulation co-ordination of the system is compromised in the process. This work investigates the effect of the rotation of the arcing horns on both the protection of the insulator as well as the sub-transmission system by means of an insulation co-ordination study implemented in ATP/EMTP. The study was used to determine the probability of a lightning strike causing back flashover. The model in ATP/EMTP was dependent on a leader progression model and an experiment, conducted on 22kV and 88kV insulators, to validate the breakdown mechanism was undertaken. It was noted that different break- down mechanisms exist for varying spark gap distances which could influence the trend of the results; a correlation between the model and the experiment was derived. The rotation of arcing horns on the insulators do not require immediate maintenance or replacement of the unit. The leader progression model yielded results in conjunction with the experiment which indicate the lowest possible breakdown voltages for each rotated arrangement. While allowing the arcing horns to rotate result in greater system protection by increasing the basic insulation level of the sub-transmission system and thereby decreases the occurrence of backflashover and the associated earth fault. The degree through which they rotate should be monitored as they could potentially pose an issue to the insulation co-ordination of the system.
Investigation into the synthesis and carbon doping of MgB₂for possible bulk superconducting fault current limiters application.
(2012) Archer, Jonathan Celvin.; Jarvis, Alan Lawrence Leigh.
Magnesium Diboride (MgB₂) bulk superconductor has been manufactured for use in superconducting fault current limiters (SFCLs) via in situ reaction. SFCLs have proven to be a viable means for limiting surge currents on power lines by dissipating fault energy as the superconductor quenches. As the current limiting behaviour is determined by the normal resistance (Rn), research has been conducted to evaluate an effective means to increase Rn for bulk superconducting MgB₂. Other researchers have previously looked into the improvement and optimisation of the critical current, Jc, by carbon doping and other flux pinning techniques. Carbon doping has been confirmed as a means to increase Rn, and was implemented by chemical vapour deposition (CVD) at 600 ºC in a tubular furnace apparatus. Intragranular doping was achieved by CVD on the boron precursor powder. In situ manufacturing of MgB₂ bulk was performed using the reactive liquid magnesium infiltration technique. Carbon doping provided an adequate increase in Rn, for a small decrease in the critical temperature, Tc.
Investigation of different graphite precursors for graphene oxide supercapacitors.
(2021) Perumal, Solan.; Jarvis, Alan Lawrence Leigh.
The impact of non-renewable energy sources has had adverse effects on the environment resulting in climate change. Many countries have undertaken a call for renewable energy sources as a cleaner and more sustainable alternative. With the change towards renewable energy sources, storing this energy has become a challenge due to its intermittent nature. An energy storage device that could help solve the above problem is a supercapacitor due to its high power density, long cycle life, and high rate capability, which are desirable characteristics for energy storage devices. Supercapacitors downfall is their low energy density. Improvement in the electrode material of the supercapacitor may help address the low energy density issue. A promising candidate is graphene oxide (GO). GO has shown notable potential as electrode material in past research due to the pseudocapacitance effect. The primary precursor for the synthesis of GO is graphite. Varying graphite precursors may yield GO with different properties. In this research, graphite precursors with different characteristics were investigated to determine the effect they have on GO supercapacitor energy storage capabilities. Eight graphite precursors were used to synthesise GO. The samples were characterised using High-Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM), Elemental Analysis, Fourier Transform Infrared (FTIR) Spectroscopy and Raman Spectroscopy. GO supercapacitors were fabricated using GO as an active electrode material, stainless steel plates as current collectors, and phosphoric acid (H3PO4) hydrogel polymer as electrolyte and separator. The electrochemical testing conducted on GO electrode material were Cyclic Voltammetry (CV) at different scan rates to determine specific capacitance and energy density. It was found that increasing flake size of natural graphite precursors produced GO with higher specific capacitance with an implicit limiting point. With the lack of peaks between the voltage limits of the CV curves for GO produced from natural graphite precursors, this indicated that the pseudocapacitance effect from oxygen functional groups is insignificant to the overall specific capacitance for these samples. These results led to further research into other possible factors that can be playing a role in GO’s high specific capacitance. It was observed that GO produced from the smallest flake size (0.045 mm) synthetic graphite precursor had the highest specific capacitance compared to GO produced from natural graphite precursor of all flake sizes investigated in this research. Firstly, the synthetic GO sample produced from smallest flake size had higher crystallinity compared to natural GO samples which were estimated using Raman spectroscopy. Secondly, high oxygen content shown in elemental analysis and peaks observed between voltage limits of CV curves provided a high pseudocapacitance effect that is significant to the overall capacitance. Thirdly, low amount of defects determined from low ID/IG (Intensity of D band/Intensity of G band) ratio in Raman spectrum may enable the ions from the electrolyte to move through the GO structure efficiently. It is the combination of these characteristics that attribute to GO produced from smallest flake size (0.045 mm) synthetic graphite precursor that improved energy storage capabilities and be an excellent electrode material to use in supercapacitors.
An investigation of the influence of silver doping on the intergranular 'weak-link' properties of the superconducting system Y1Ba2Cu307-x.
(2006) Jarvis, Alan Lawrence Leigh.; Broadhurst, Anthony D.; Doyle, Terence Brian.
High-temperature superconducting materials have found considerable technological application and still have a largely unrealised potential. The key to unlocking this potential depends on a better understanding of their properties; in particular, the maximum 'critical current density' which these materials, in the form of wires, tapes, thin-films and bulk monolithic forms, are able to support for high-current applications. The 'critical current density' in a polycrystalline high-temperature oxide superconductor system is determined by a percolation process of the super current through a three dimensional grain-boundary network. Grain-boundaries in these systems behave as Josephson junction 'weak-links' and they severely limit the critical current density in the presence of even moderate self or applied magnetic fields. In the present work, isothermal quasi-static magnetisation measurements on the polycrystalline YIBa2Cu307-x system are presented and analysed. An effective granular penetration depth in conjunction with a critical state model, which includes an approximate treatment for the percolation process, is used to obtain many of the salient physical parameters of the grain-boundary Josephson junctions and of the three-dimensional grain boundary junction network. Determination of the temperature and magnetic field dependence of several of these parameters, in particular a magnetic field-independent critical current which depends on the micro structure of the grain-boundary junction network, allows for testing and verification of models of the weak-link and network behaviour. This treatment has been carried out specifically on various silver doped polycrystalline Y1Ba2Cu30 7-x specimens in order to determine and quantify the effects of silver doping. An improvement in the critical current density with silver doping is explained in terms of silver scavenging and ridding grain-boundaries of impurities, and a proximity effect where trace amounts of silver residing in the grain-boundaries decreases the normal resistance of the grain-boundary Josephson junction. The insight gained from silver doping experimentation led to a macroscopic investigation into the joining of large single-domain YIBa2Cu307-x specimens for large-scale applications.
An investigation of various hydrocarbon sources in the production of carbon nanoparticles via a plasma enhanced chemical vapour deposition technique.
(2010) Singh, Shivan Royith.; Jarvis, Alan Lawrence Leigh.
A simple, low cost microwave plasma enhanced chemical vapour deposition (PECVD) technique for the production of carbon nanostructures has been developed in the School‟s Materials Science Laboratory. The technique utilises a conventional microwave oven as an energy source, various hydrocarbons as a carbon source, a metallic aerial as a catalyst and hydrogen to support the process. The input hydrocarbon and the hydrogen flow rate are independently varied to investigate their effect on the resultant nanostructures. This technique allows for the production of carbon nanotubes (CNTs), onion-like nanostructures structures (ONSs) and amorphous carbon, which has been verified via transmission and scanning electron microscopy. A change in input parameters results in the controllable yield of CNTs versus ONSs. The formation of amorphous carbon is reduced by controlling the hydrogen flow rate. In further experiments, the thermal conductivity of the ONSs is investigated using the "Lee‟s Disk" method. It was observed that bulk ONS specimens exhibit a thermal conductivity above that of amorphous carbon powder. Insufficient quantities of CNTs were grown using this method to facilitate a comparable thermal conductivity investigation.
Production of graphene for the frabrication of graphene fibres.
(2016) Ojageer, Sarisha.; Jarvis, Alan Lawrence Leigh.; Swanson, Andrew Graham.
Graphene consists of a single atomic layer of carbon atoms arranged in a hexagonal lattice and exhibits two-dimensional properties. This material is of particular interest as it is a highly efficient conductor of heat and electricity and possesses an exceptionally high strength-to-weight ratio. The uses of graphene extend to a variety of industries, including the fields of life sciences; electronics; and chemistry. The properties of graphene are largely determined by the method of fabrication thereof. These methods include chemical vapour deposition as well as mechanical and chemical exfoliation. In this study, research has been conducted to investigate these various fabrication routes so as to determine a reliable method of producing graphene of a high quality for the production and study of graphene fibres. Specifically, graphene produced via the chemical oxidation of graphite was investigated due to its cost-effectiveness, viability and scalable nature. This process resulted in the production of an intermediate product, graphene oxide, which was then reduced to form graphene. Thermal and chemical reduction methods of graphene were also investigated. The produced graphene exhibits high correlation with graphene reported in the literature. The quality of the synthesised material was analysed using various diagnostic tools, including Scanning and Transmission Electron Microscopy, Energy-Dispersive X-Ray Spectroscopy and X-Ray Diffraction. The graphene was used for the fabrication of graphene fibres with the addition of the polymer materials, polyvinyl alcohol and polystyrene. A microscopic fibre fabrication route was explored and the outcome of this research was the production of graphene nanofibres which may be used in various applications, including strengthening fillers in composite materials.
Synthesis and characterisation of magnetic graphene-nanoparticle composites for water purification.
(2021) Malinga, Nduduzo Nkanyiso.; Jarvis, Alan Lawrence Leigh.
The synthesis of reduced graphene oxide is investigated in this work, with a focus on water purification. The work stems from the interest gained from the discovery of graphene and its high surface area. The study focused on the synthesis of reduced graphene oxide. This afforded the synthesis of reduced graphene oxide nanoparticles composites and doped reduced graphene oxide. The composites were produced with magnetic nickel, cobalt and cobalt ferrite nanoparticles. The doped reduced graphene oxide was synthesized using nitrogen and boron as dopants. The prepared samples were rGO, N-rGO, B-rGO, Co-rGO, Ni-rGO and FeCo-rGO. All the samples were characterized using Transmission Electron Microscopy (TEM), Fourier Transform Infra-red (FTIR) spectroscopy, Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Raman Spectroscopy and X-ray Diffraction (XRD). All the samples were found to have magnetic properties. The composites have superparamagnetic properties and FeCo-rGO had the highest magnetization at 12.54 emu.g-1. The conductivity results showed that the doped samples and composites had better conductivity than rGO with the Ni-rGO having the highest conductivity of 62695.82 S.m-1. All samples had conductivity which were similar to semiconductors. The prepared samples have high surface area and a large number adsorption sites and thus were used in applications of water purification in the removal of Cr(VI) ions from solution. The Co-rGO was found to have the ability to adsorb the Cr(VI) in form of CrO42- while other samples catalysed reduction of Cr(VI) to Cr(III). Thus Co-rGO was used in the removal of Cr(VI) ions from solution. The adsorption of Cr(VI) ions occurs through electrostatic interaction between CrO42- and Co-rGO. The optimum conditions for the removal of chromium ions were experimentally determined. The conditions, were a dosage of 300 mg.L-1, a pH of 8, contact time 90 minutes and temperature was 298 K. The removal efficiency was affected by the concentration of chromium ions and there was 90 % removal efficiency for the concentration of 20 mg.L-1
Synthesis and functionality of boron-, nitrogen- and oxygen-doped shaped carbon-based nanomaterials and titania nanocomposites in electrochemical capacitors.
(2017) Mombeshora, Edwin Tonderai.; Nyamori, Vincent Onserio.; Ndungu, Patrick Gathura.; Jarvis, Alan Lawrence Leigh.
Abstract available in PDF file.
Using inclined plane test to compare tracking on silicon rubber under HVAC and HVDC.
(2018) Mafasigodo, Khumbulani.; Swanson, Andrew Graham.; Jarvis, Alan Lawrence Leigh.
This dissertation presents research work conducted on high-temperature vulcanised (HTV) silicon rubber electrical tracking and erosion performances under HVDC and HVAC. The aim was to evaluate the performance under outdoor environmental conditions. Failure of polymer insulators is an area that has not been researched thoroughly in the past decade. The aging mechanism of insulators is of paramount importance in manufacturing and design. Outdoor conditions like humidity, moisture, pollution affect the durability of most insulators. Silicon rubber is widely used in power distribution and transmission insulation networks. It is also being used in power devices such as metal oxide surge arresters as the electrical insulation. Its advantages are that it is lightweight, low cost, easily processed, has good dielectric and hydrophobicity properties and has better pollution performance in outdoor insulation systems. The first part of this research looks at the procedure for testing following the normative recommendations as per IEC 60587: 2007 standard. Constant tracking voltage method was implemented in the inclined plane test for electrical tracking and erosion. A voltage of 4.5 kV was applied for all +DC, -DC and AC testing. The failure criteria as per IEC-60587 were followed. The most monitored criteria were that the leakage current magnitude should be below 60 mA. An increase in leakage current magnitude and duration of discharges were observed under +DC test conditions. The tracking time was recorded to be less under –DC than in +DC. The average current under +DC increases with the voltage application duration, however under AC the current does not increase. Under –DC voltage the current flow was observed to be less intermittent. Sample surface degradation mechanism was seen to be different in +DC, -DC and AC. A data logger monitored the leakage current measurements. An average leakage current of 9.40 mA was found under +DC. An average leakage current under –DC was measured to be 8.92 mA. Under AC voltage an average current of 11.90 mA was recorded. The second part of the study looked at the quantitative analysis techniques of silicon rubber. Silicon rubber test samples were carried out using scanning electron microscope (SEM) with Energy Dispersive Spectroscope (EDS), Fourier transform infrared microscope (FTIR) and transmission electron microscope (TEM). These physiochemical tests results were comparable for both DC and AC, it was concluded that the insulator deterioration was due to surface tracking and dry-band arcing discharges which resulted in the erosion of the test samples. The work reveals that +DC is more aggressive for the test samples tested. It was concluded that under +DC conditions tracking is more severe as compared to –DC and AC.