Defects in single crystal diamond grown by chemical vapour deposition (SC-CVD) have been studied using electron paramagnetic resonance (EPR) and optical techniques. Annealing studies in the temperature range of 900 - 1600°C have been performed and the changes in EPR and Fourier transform infrared (FTIR) spectra for nitrogen doped SC-CVD have been documented. It has been possible to model the annealing behaviour of several hydrogen related defects and the associated kinetics and annealing parameters have been determined. Previously unreported optical absorption lines have been detected in the as-grown and annealed nitrogen doped samples. FTIR spectroscopy has been performed in conjunction with an applied uniaxial-stress to investigate hydrogen related absorption features in diamond. Several absorption lines have shown to shift and split under the application of uniaxial-stress and the symmetry and stress-splitting parameters for these defects have been determined. Models for the defects responsible are proposed. The mid-infrared absorption line at 3123 cm-1 is suggested to originate from a C-H stretch mode at the paramagnetic negative nitrogen-vacancy-hydrogen complex. For a 3123 cm-1 absorption line with a Lorentz linewidth of 3.8(2) cm-1, 1 cm-1 of absorption at 3123 cm-1 corresponds to 25(10) ppm of NVH- centres. A previously unreported paramagnetic defect has been detected and is given the label WAR1. It has an S = 1 ground state and a pseudo-C3v symmetry; the g and D spin Hamiltonian parameters have been determined and suggest that the defect is vacancy related.

Radioactive radon gas, after being released from rocks, soils and building structures, can pose a significant health threat to the building occupants. This is of particular concern in tight HVAC (Heating, Ventilating and Air-Conditioning) serviced buildings where there is re-circulating air with limited fresh air intake. A thorough survey was initiated at the Hong Kong University of Science and Technology (HKUST) in 1996 and results indicate a radon average concentration of 107 Bq/m3, which is approximately 50% of the World Health Organisation's (WHO) recommended standard (200 Bq/m3). About 10% of the measurements were in excess of this WHO limit, while 46% of the samples also showed average peak radon concentrations (264 Bq/m3) in excess of this WHO limit. To overcome these elevated indoor radon concentrations, their characteristics at HKUST was studied. Radon level was found to increase linearly as a function of the length of the HVAC shut off period, and decrease exponentially upon system resumption. Radon level predictive models were developed after a series of room chamber experiments with modification factors defined to account for the indoor sinks in an effort to enhance the accuracy and applicability of the models. Following a campus-wide energy audit, two energy efficient radon management approaches were derived from the predictive models and were subsequently integrated into the existing HKUST operations. The first was defined as an Active Radon Control Approach (ARCA), where HVAC operation schedules were modified to yield an energy saving potential of around HK$2.7 Million a year. ARCA is optimised to reduce the radon dose to the HKUST occupants following the radiation protection principle of "As Low as Reasonably Achievable (ALARA)", and with considerations of economical and operational constraints. The other was a Passive Radon Control Approach (PRCA) using Polyurethane-based (P-u) paint to cover building material surfaces to reduce the radon emission.

The sponsoring company for this Engineering Doctorate is a manufacturer of passive fire protection materials with about 80 employees. Its primary products are specialist coatings that provide protection from the heat of a fire. Since it is essentially a chemical blending company its core technical skills have been in the chemical formulation of these products. The company employed the Research Engineer (R. E.) to help find new applications for its materials and widen its product range. It identified that domestic Liquid Petroleum Gas cylinders are potentially dangerous because they may explode when exposed to the heat of a fire. It determined to develop an enclosure to protect them from fire for 30 minutes using its fire resistant coatings. This project was conceived as a simple diversification, transferring existing company technology to a new market area. However, LPG cylinders are very sensitive to fire and require highly effective insulation from heat to make them safe. To meet the company specification, the R. E. developed a new composite fire insulation eight times as effective as the original solution, by combining one of the company's products with other materials. The effectiveness of the insulation and the enclosure design were proven by completely engulfing it in flame from a burning pool of aviation fuel. A series of these tests showed that the R. E.'s design reliably keeps LPG cylinders cool and safe for more than 30 minutes. This experimental work was assessed by the Loss Prevention Council who have based a new fire test standard on it. During the development process it became apparent that the capabilities required to manufacture an engineered product are quite different from those needed for the creation of new coatings and materials. This new product required a revolutionary advance in the company's approach to design, test methods and production technology. The R. E. has developed a new method of fire testing to provide heat flow data for use in computer models. This is now used to reduce the number of prototypes needed for testing and so compress development time. In order to manufacture the new product the R. E. has had to develop new ways of processing the company's materials. These new moulding techniques have delivered substantial improvements in finish and reduction in material wastage. The capability of the company to produce complex shapes from materials that are difficult to process has been greatly enhanced. Although the Gas Safe product itself has not yet achieved commercial success, the Engineering Doctorate programme has made a positive contribution to the company. In the last two years a number of interesting new projects have been undertaken that would have been impossible without the new engineering approach and production techniques. These are now beginning to show a return and several new products based on this work are under development.

Reported in this thesis are the results of a combined theoretical and experimental study into improvements to the solid adsorption refrigeration or heat pumping cycle using the ammonia-activated charcoal pair. The three areas which have been examined are the cycle thermodynamics, the porosity characteristics of ammonia-charcoal pairs and the heat transfer through an ammonia granular charcoal packed bed. It was found through the use of advanced thermodynamic cycles utilizing multiple beds that the coefficient of performance of a refrigerator could be increased by sv 250% and the coefficient of amplification of a heat pump could be increased by co 110%. The coefficients of performance and amplification may also be increased to a lesser degree by judicious choice of the charcoal porosity characteristics. A survey of charcoal porosity characteristics revealed that the useful energy per cycle could be doubled by the correct choice of charcoal. The thermal conductivity of an ammonia granular charcoal bed was measured using a novel piece of apparatus. From the results it was decided for all practical purposes that the bed conductivity may be considered constant and equal to 0.165 W/m K. The power output of the cycle was found from modelling the dynamic desorption of a reactor using a one-dimensional finite difference model set in radial coordinates. The cycle simulations revealed that ideally the reactor should be constructed from solid charcoal shapes manufactured in such a way as to incorporate paths of enhanced conductance and be integral with the containing vessel wall.

Silicon carbide (SiC), with its wide bandgap, high thermal conductivity and natural oxide is a substrate that has given rise to a new generation of power devices than can operate at high temperature, high power and high frequency, though the material is not without its problems. SiC "heterojunction devices" are layers of germanium (Ge) or silicon (Si) that are deposited via molecular beam epitaxy (MBE) or wafer bonded onto the SiC surface. These narrow bandgap thin films can provide a high mobility channel region overcoming SiC's crippling channel mobility, which is most often made worse by a high density of interface states. Concentrating predominantly on Ge/SiC heterojunctions, this thesis characterises the physical and electrical nature of these structures, investigating the rectifying properties of the heterojunction interface and the ability of these layers to support a depletion region. A physical analysis of the layers revealed that the Ge formed in an unexpectedly uniform fashion, given the large lattice mismatch involved. At a deposition temperature of 500oC the Ge initially clumped into wide, shallow islands before merging, forming at best a 300 nm polycrystalline layer with a surface roughness of only 6 nm. This was in contrast to MBE deposited Si/SiC layers that formed tall islands that at 1 μm thick, still had not merged. After being formed into Ge/SiC heterojunction diodes they were electrically characterised. The layers displayed near ideal (η = 1:05) turn-on characteristics, low turn-on voltage (approximately 0.3 V less than Ni/SiC SBDs), reasonable on-resistance (12 m­Ωcm2) and minimal leakage current. The devices were shown to suffer severe Fermi level pinning that defined the way the materials' bands aligned. This occurred as a result of an inhomogeneous interface that also caused fluctuations in the size of the Schottky barrier height across the interface. New characterisation techniques relating to these phenomena were applied to a heterojunction for the first time. MBE formed Ge/SiC layers and wafer bonded Si/SiC layers were formed into MOS capacitors through the deposition of the high-K dielectric hafnium oxide (HfO2). The increased conduction band offset between oxide and narrow bandgap semiconductor suppressed leakage problems often seen in HfO2/SiC structures. Capacitance-voltage results showed that they could both support a depletion region, though the best results came from the MBE Ge/SiC diodes. Current-voltage results showed that the more uniform Si/SiC devices could block 3.5 MV/cm.

The wide-scale usage of VOCs in industrial processes requires monitoring the concentrations of these vapours to keep a safe operating environment. Most combustible hydrocarbons can be ignited as a gas-air mixture in the range of 0.5% to 15% by volume. This has led to the development of several portable air quality monitoring instruments. However, the high costs and lack of durability of these instruments has remained an issue to be addressed. This PhD thesis reports on the development and characterization of a novel low cost smart gas sensor technology adaptable for use in a portable instrument. The smart gas sensor devices have been developed to target four different VOCs in air. The smart gas sensor device combines a smart ASIC (SRL 194 designed at SRL, Warwick University) fabricated in standard 0.7 μm CMOS technology and two alkyl-dithiol based self-assembled gold nanoparticle chemoresistive sensors (fabricated at Sony Deutschland GmbH) in a ratiometric array to offer a robust system which can address the common mode variations found in polymer based gas sensor systems. The ratiometric ASIC sensor array architecture allows for the reduction of the baseline value’s dependence on environmental variations and the elimination of baseline drift due to long term application of DC voltage. Three ratiometric array arrangements - mono-type uni-variate with only one chemosensor per device, mono-type bi-variate with two chemosensors of the same film material per device and duo-type with a polar and a non-polar chemosensor per device and their variations were characterized in an automated FIA test station against exposure to methanol, ethanol, propan-1-ol, and toluene at 30°C and 0-5% rh. It was determined that the devices’ response output to VOC analytes was entirely dependent on the variation of the resistance ratio of the chemoresistive sensors in the ratiometric sensor array. The effects of variations of the temperature and rh on the smart sensor output were calibrated. The mono-type devices gave a high magnitude response to the vapours whereas the duo-type arrangement offered a high degree of discrimination between the test analytes with little post-processing steps. Three different alkyl-dithiol chemoresistive sensor films on gold electrodes were successfully used as the VOC vapour sensitive elements in each arrangement. The effects of using a silicone sealant gel as a partitioning layer were characterized and it was observed that at vapour concentrations less than 3000 ppm the silicone encapsulated chemosensor devices reported a larger response to the VOC analytes as compared to those without the silicone. The test devices reported promising response repeatability and reproducibility with excellent return to baseline properties, a negligible hysteresis and an error margin of under 10%. Ideal operating temperature was determined to be 40°C at which rh variations were found to be minimal. The test devices were found to be robust with little variation in the quality of the device output over the course of 18 months. The novel research demonstrated that it is possible to get high level of diversification between analytes from a low cost and robust gas sensor system for monitoring VOCs. The work carried out here has opened the opportunity to develop highly integrated programmable hand-held gas sensor and e-nose systems for environmental monitoring use in health and safety applications.

On an international basis, coal is used extensively for power generation and this is likely to remain the case well into this century. Although many standard tests are currently used to assess and select coals for combustion purposes, these have proven to be unable to predict coal burnout behaviour. For a power station based on coal combustion, a clear knowledge and understanding of the coals offered in the market is essential to achieve optimum conversions and to meet environmental constraints. There is, therefore, a need to develop suitable and efficient methods and techniques to characterise coals so that the combustion plant performance can be predicted more effectively. In the present work, a series of experiments were conducted to characterise chars obtained from a Drop Tube Furnace (DTF) and a 1 MW combustion rig from which the effect of particle size distribution on coal reactions during devolatilisation and combustion of pulverised coal have been studied. The effect of temperature on coal pyrolysis in the DTF was also assessed. The coals used in this study were mainly from South America whose coals are widely traded internationally, and were characterised by standard tests and a novel automated image analysis technique called the Reactivity Assessment Program (RAP). The morphology of the chars were examined manually and using an automated image analysis technique and thermogravimetric analysis. The aim of this study was to provide a better understanding of the RAP and the automatic image analysis of chars, particularly related to South American coals. The results indicated that temperature significantly influences the coal behaviour during devolatilisation, and hence, the reactivity and morphology of the char generated. The structure and morphology of the char were found to play a significant role in burnout of the residual char, with a significant effect of coal type and particle size. Multiple linear regressions of char properties, such as intrinsic reactivity, morphology, and burnout, against particle size and maceral content of the feed coal were performed. The results showed that there was only a good correlation of high temperature volatiles with macerals. Subsequently when rank was included in the regressions, the correlation remarkably improved in all cases. However, when a novel approach which involved the correlations of char properties with bands of the grey scale histogram (RAP profile) of the coals was performed, much better correlations were achieved. The initial improvement is related, evidently, to the inclusion of the variation of vitrinite structure with rank. The grey scale histogram of coal takes this stage further by including the variation in reflectance for all the macerals. Therefore, the results indicate that the RAP analysis provides a simple and objective technique to predict the combustion behaviour of coals.

There is huge need to develop an alternative to hydrocarbons fuel, which does not produce CO2 or contribute to global warming - 'the hydrogen economy' is such an alternative, however the storage of hydrogen is the key technical barrier that must be overcome. The potential of graphitic nanofibres (GNFs) to be used as materials to allow the solid-state storage of hydrogen has thus been investigated. This has been conducted with a view to further developing the understanding of the mechanism(s) of hydrogen storage in GNFs and modifying the material structure to maximise the amount of hydrogen that can be reversibly stored in the material. GNFs were synthesised using chemical vapour deposition (CVD) with careful control of temperature and gas mixture to create predominately herringbone GNFs from both Iron and Nickel catalysts. Within this, it was found that once GNF growth has been initiated under certain conditions, alteration of those conditions does not alter the fundamental structure of the GNF synthesised, but can increase the carbon yield, although reorientation of the surfaces was observed. The GNFs synthesised were subsequently chemically (acid washed and CO2 oxidised) and thermally treated to remove the residual CVD catalyst and alter their surface structures in an attempt to allow dihydrogen molecules to penetrate and adsorb onto the internal graphene layers. However, it was found that after initial growth, the surface layers of the GNFs became re-orientated parallel to the fibre axis - representing a large energy barrier to adsorption onto the surfaces of the internal graphene layers. By careful use and control of conditions, this re-orientated layer can be removed to yield GNFs with cleaned surfaces. Once GNFs with cleaned edges had been synthesised, these were modified to remove oxygen species from their surfaces. To further develop the understanding of the potential hydrogen uptake mechanisms, Pd particles were introduced to the GNF surfaces to act as catalyst gateways. By carefully controlling the variables of the incipient wetness process, a variety of morphologies and structures were synthesised. This allowed the precise determination of the hydrogen uptake mechanism occurring in samples by Kubas binding, Dissociation or Spill-over mechanisms. All of the GNFs created have had their hydrogen uptake capacities precisely determined using a Sieverts apparatus designed and constructed by the author. None of the samples were found to adsorb any significant levels of hydrogen (>0.1 wt%), regardless of the treatments applied to them – this result has been discussed in light of the existing claims for high hydrogen uptake in GNFs made within the literature. The conclusion of this thesis is that no hydrogen uptake capacity could be observed in the GNFs synthesised during the project, however, the development of the uptake mechanisms and GNF structures has led to suggested modifications that may yield GNFs suitable for storing large quantities of hydrogen (i.e. in excess of US-DOE targets).

Nearly half the worlds population is dependent on wood as their primary energy source. Therefore with deforestation becoming increasingly prevalent in many regions of the developing world, there is an urgent need to improve combustion efficiency of stoves or to find alternative fuels. Densification of loose biomass residues into briquettes is a means of upgrading the feedstock material. Briquettes are easier to store, more convenient to use and burn at a more steady and controlled rate than loose biomass. This investigation focuses on understanding some of their combustion characteristics and the relationship to the briquette design and manufacture process. The social context of the work is presented through an informal case study considering the potential of briquetting in Ghana. The initial experimental work focuses on developing a process to manufacture newspaper briquettes of consistent quality at low-pressures using a wet technique, and a method to burn them in a controlled way is suggested. These techniques were used to carry out a study on rectangular slab-shaped briquettes, looking at the effect of process variables (density, moisture content and size) on briquette burn-rate. An analytical expression for the normalised burn-rate (NBR) of a briquette in free-air, in terms of these of these variables, was found by numerical fitting. The effect of shape on combustion was also experimentally investigated using cylindrical briquettes with a central hole (holey briquettes) burning in free-air and an analytical expression was derived for their burn rate. The NBR behaviour of sawdust briquettes, rapeseed oil residue briquettes as well as slabs of pine wood was then studied. Rapeseed oil residue has a very different calorific value from that of newspaper, and a method was suggested for predicting the difference in rate as a function of difference in calorific value. In the second phase of the work, a numerical model of pyrolysis was developed. The model assumed that heat transfer through the fuel limited the rate of pyrolysis. The thermal parameters (thermal conductivity, heat capacity and thermal diffusivity) were estimated using a heat probe method, and the kinetic parameters found by numerical optimization. The model was shown to predict, for newspaper briquettes, the experimentally observed size dependent behaviour of the normalised burn rate, and the trend observed for the effect of changes in density. The model was applied to predict the effect of changes in a briquettes thermal parameters on burn rate, and an analytical expression found by numerical fitting. This provides a means of estimating relative changes in burn rate due to changes in fuel properties, and forms the basis for a pyrolysis sub-model for use in stove optimisation. Such a model has the advantage of being able to vary key, easily quantifiable and easily controlled solid biomass briquette properties relative to the behaviour and properties of a well understood fuel such as wood. In the final part of the study, some of the limitations of the numerical model are explored by completing a sensitivity study investigating the relative effect of some of the key assumptions made.

Uncontrolled segregation in particulate mixtures has long been considered as an annoying, and costly, feature encountered in many materials handling operations and although the onset is not clear, many believe it to be driven by the differences in particulate physical properties. An increasing number of usefully scaled laboratory and computer simulation investigations are being carried, particularly by the physics community, to help our understanding of this phenomenon. Physicists at the University of Nottingham have identified that through careful control of frequency and acceleration during vertical vibration, different types of particles can be positioned and/or segregated in a small rectangular cell. An extension of this work resulted in the design of a new small scale batch separator capable of recovering at least one separated particle layer in a different chamber. This work has explored the scale up of the small particle separator to operate in a semi-continuous mode. Since complete experimental know how of particle segregation phenomena is still deficient an empirical design strategy was used. This scaled up particle separator was driven by a pneumatically powered vertical vibration bench in which dry, non-cohesive particulate mixtures of varying densities and sizes (<1000µm) were vertically vibrated under different conditions to assess their separation behaviours. Experiments with regular (e.g. glass and bronze) and irregular shaped particle mixtures (e.g. comminuted glass and bronze) showed that lower magnitudes of vertical vibration frequency (30±10%), dimensionless acceleration (3±10%), particle bed heights (20 and 40mm in majority of the investigated cases) and partition gap sizes (5 and 10mm) were important for separation. Finally, the technique was employed to separate various industrially relevant particle mixtures (shredded printed circuit boards, iridium and aluminium oxide and shredded personal computer wires). Two-dimensional Discrete Element Modelling (DEM) with interstitial fluid interactions simulated with a maximum of 1000 virtual glass and bronze particles showed some important aspects of particle segregation such as; layered particle separation, high density particles ending on top and bottom of the particle bed, convection currents, particle bed tilting and partitioned particle separation. The application of Positron Emission Particle Tracking (PEPT) to glass, bronze, ilmenite and sand particles showed distinct trajectory maps in three dimension (X,Y and Z) with varying particle speeds in the vertically vibrated particle mixtures. The low density particles were mostly observed to move in the middle while the high density particles patrolled in the outer periphery of the separation cell. These distinct particle motions suggested that convection currents played an important role in controlling segregation. Furthermore, the application of a smoke blanket visualization technique showed the existence of air convection currents on top of the vertically vibrating particle mixtures. The experiments on the scaled up semi-continuous particle separator confirmed what was identified previously in that good particle separation could be achieved through careful control of the frequency and acceleration during vertical vibration. This information lays the foundations for a new breed of low cost, dry separator for fine particulate mixtures. Key Words: Vertical vibration, particle separator, fine particle mixtures, dry separation, PEPT, DEM, smoke visualizations.