While oxy-fuel combustion research is developing and large scale projects are proceeding, little information is available on oxy-biomass combustion and cocombustion with coal. To address this knowledge gap, this research conducted has involved comprehensive laboratory based fundamental investigation of biomass firing and co-firing under oxy-fuel conditions and compared it to conventional air firing conditions. First, TGA was employed to understand the fundamental behaviour of biomass devolatilisation, char combustion and nitrogen partitioning between volatiles and residual char. The results revealed that C02 did not have effect on the devolatilisation of sawdust at temperatures below 1100 grad. C due to higher mass transfer resistance of primary volatiles in C02 than in N2 at low temperatures. Secondly,. by optimising the devolatilisation procedure in a combustion system that simulates closely to an industrial scale such as drop tube furnace (DTF), the devolatilisation/char combustion characteristics of sawdust was investigated. The effect of CO2 on volatile yields, nitrogen partitioning and char burnout were all significant in relation to N2• While coal combustion additives are being used to enhance coal burnout, this study observed improved coal char burnout when biomass char was co-fired with coal char, again a faster burnout was observed in oxy-firing condition compared to air firing. This was due to the catalytic effect of biomass inherent alkali and alkaline earth metals. Similarly, improved volatile yields were observed during codevolatilisation. These fundamental results have provided insight into oxybiomass' firing and co-firing and the data can be used in appropriate CFD modelling to aid the design of oxy-biomass co-firing burners.

Conversion of carbon dioxide into useful products has become highly desirable in recent years in order to both mitigate carbon dioxide emissions to the atmosphere and develop non-fossil energy sources. A variety of methods exist for the electro-reduction of carbon dioxide in solution to useful products, such as carbon monoxide and hydrocarbons. However, none of these processes are able to directly convert carbon dioxide to carbon. In this thesis, the conversion of carbon dioxide into solid carbon via molten carbonate electrolysis has been investigated. Both the past literature and the present work have shown that carbon nanopowder can be produced via this process, so it is highly likely that the electro-deposited carbon obtained is a valuable product. Although this process has been known since the 1960s, there are still many areas where our knowledge of the process is lacking. Hence, this thesis is focussed primarily on the reactions occurring in the molten carbonate electrolyte, the properties of the electro-deposited carbon and the re-oxidation of the electro-deposited carbon. Using cyclic voltammetry carried out at platinum working electrodes, it was found that carbon was electro-deposited at the cathodic limit in the Li2CO3-Na2CO3 and Li2CO3-K2CO3 electrolytes at temperatures of ca. 600 °C and ca. 700 °C, probably by the following reaction: CO32- + 4e- → C + 3O2- One novel finding of this research is that carbon electro-deposition competed with other cathodic reactions at the cathodic limit, which included alkali metal formation, carbon monoxide formation and alkali metal carbide formation. However, the carbon electro-deposition reaction dominated over the other cathodic reactions once the metal working electrode surface had become covered with a layer of electro-deposited carbon. This was probably because a lower overpotential is required to deposit carbon onto carbon, as opposed to carbon onto metal. Moreover, the other cathodic reactions may have been catalysed by the bare metal working electrode surface before it became covered with carbon. Electrochemical re-oxidation of electro-deposited carbon was found to occur via a process consisting of at least two stages, which was deduced using cyclic voltammetry in conjunction with the re-oxidation of electro-deposited carbon via galvanostatic chronopotentiometry. These stages may have corresponded to the oxidation of portions of the carbon with different morphologies. Carbon was electro-deposited onto mild steel working electrodes via chronoamperometry in the Li2CO3-Na2CO3, Li2CO3-K2CO3 and Li2CO3-Na2CO3-K2CO3 electrolytes. The highest apparent electro-deposition rate obtained was 0.183 g/cm2.h at an applied potential of -2.98 V vs. Ag/AgCl, using the Li2CO3-K2CO3 electrolyte at 708 °C. The average current efficiencies obtained for carbon electro-deposition were: 74.4 % for Li2CO3-Na2CO3, 79.0 % for Li2CO3-K2CO3 and 51.2 % for Li2CO3-Na2CO3-K2CO3. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy revealed that the washed carbon deposits mostly consisted of fine quasi-spherical carbon particles, some as small as 60 nm in diameter. All of the electro-deposited carbon appeared to be amorphous.

On the long list of solid-state hydrogen storage materials, magnesium hydride stands out for its relatively high hydrogen storage capacity of 7.7 wt%, combined with the low cost and abundance of magnesium. For practical applications however, issues such as the slow kinetics and the high stability of magnesium hydride must be resolved in order to reduce the potential operating temperatures of a magnesium-based solid-state hydrogen storage system. Catalysis has been widely used to improve the hydrogen storage kinetics and thin film techniques have been used to explore novel structures and combinations of materials in order to improve both the kinetics and thermodynamics of hydrogen storage in magnesium. The original contribution to knowledge of this work lies in the study and understanding of the evolution of a range of novel thin film multilayer coatings and the effect of the structure, structural evolution and materials on the hydrogen storage properties of these materials, each consisting of 150 layers of magnesium, < 20 nm thick, separated by < 3 nm thick layers of a nickel-rich, iron-based transition metal mix, chromium and vanadium. The samples, as well as a non-catalysed control sample, were produced by means of magnetron-assisted physical vapour deposition and delaminated from the substrate for volumetric, gravimetric and calorimetric hydrogen cycling measurements. The coatings were analysed both before and after hydrogen cycling to understand the structural evolution of the coatings from highly structured thin film multilayers to flaky thin film particles containing finely distributed nano-crystalline catalyst particles. The formation of the intermetallic Mg2Ni in one of the samples was found to be beneficial for the hydrogenation kinetics, whilst the dehydrogenation kinetics were found to be affected mostly by the nano-crystalline transition metal phases that formed in the catalysed samples during hydrogen cycling. This resulted in hydrogenation and dehydrogenation of magnesium hydride in less than 4 and 13 minutes at 250°C with activation energies as low as 60.6 ± 2.5 kJ mol-1.

It was proposed that a phase separated system might be utilised to deliver a concentrated polysaccharide mucosal protective coating in gastro oesophageal reflux disease (GORD). In this context the phase behaviour of xanthan gum in combination with sodium alginate and other polymers was studied. Above a threshold concentration of alginate, aqueous mixtures of xanthan exhibited phase separation, resulting in loss of normal viscoelastic properties and the formation of a low viscosity system. The shape of the phase diagram showed behaviour typical of a segregative system, with the continuous phase composed exclusively of alginate and the disperse phase being rich in xanthan gum. Increasing alginate molecular weight reduced the threshold concentration for separation, as predicted by the Flory-Huggins theory, but changes in alginate mannuronate:guluronate ratio had no effect. Increasing ionic strength elevated the threshold concentration. Xanthan separation was elicited by other aqueous anionic polyelectrolytes, but not neutral water soluble polymers. Scleroglucan, another rigid-rod polysaccharide, was investigated as an alternative to xanthan but did not show similar separation behaviour, suggesting that the charge on the xanthan molecule is a necessary prerequisite. Reversal of phase separation by dilution across the phase boundary provided increases in viscosity. A 1% xanthan:2% alginate mixture doubled in viscosity whereas if diluted with simulated gastric fluid a seven-fold increase was seen, as a result of conversion to an alginic acid gel. This offers a mechanism for producing the desired viscosity barrier. Low viscosity polyelectrolytes, with concentrations close to the phase boundary yielded the greatest viscosity increases. In the phase separated system, the disperse phase exhibited an unusual strand-like morphology whose birefringence suggests a liquid crystalline structure. The variable size of the strands was explained in terms of kinetics of xanthan molecular aggregation in media of different viscosity.

Hydrogen is an ideal energy carrier as it only produces water as a by-product. However, technical and social issues first need to be overcome in order to achieve such economy. In particular, this work focuses on solid state hydrogen storage as it is a key technological challenge. Herein, potential candidates currently investigated are porous materials that physisorb molecular hydrogen with fast kinetics and good reversibility in order to meet mobile transportation requirements. The goal is to be able to optimize the sorption properties of a compound by tuning critical parameters such as its pore size and/or its specific surface area. Carbon nanofibres were investigated as potentially cost-efficient materials. Engineering routes such as the integration of hetero-species by nitrogen doping and exfoliation / intercalation were performed on various carbon nanostructures affecting the surface topology of the engineered compounds compared to the as-prepared materials although the excess uptakes at 77 K and 20 bar remained low ca. 0.6 wt. %. Metal-organic frameworks are a promising class of porous materials and are currently strong competitors as hydrogen storage media thanks to their flexibility in structure design. A series of Cu (II) - frameworks have been found to have exceptional sorption properties at 77 K and 20 bar up to 7 wt. %. The successful combination of neutron techniques at NIST-CNR and ISIS-RAL enabled a clear insight of the adsorption site distribution of two Cu (11) - frameworks using para-H2 and D2 as probing gases. A common feature for the MOFs investigated was that dihydrogen preferentially coordinated to the exposed metal centres ca. 2.4 Å, followed by sorption at two discrete sites located within triangular windows connecting the MOF cavities. It revealed the co-existence of preferential site-specific with non-site specific adsorption within the pore structure which is different from the common concept of dihydrogen interacting with a homogeneous surface. It was also possible to follow the dynamics of hydrogen molecules at different coverage of the surface through the rotational transitions of the para-H2 molecule.

There is around 9.5 kJ/L of energy contained in UK wastewater which is wasted through traditional aeration treatment. Microbial fuel cell (MFC) technology provides a new approach to carry the promise of both treating wastewater without aeration and producing renewable energy in the form of electricity and H2. This work has contributed to making this a reality. In this work, MFC designs were developed and constructed to test their energy performances. The power densities ranged from 13.3 mW/m2 to 30 mW/m2. The coulombic efficiency based on the contained substrates is in the range of 1 % to 7 0/0. The Chemical Oxygen Demand (COD) removal conversion per pass of MFCs arrived at 3.0 0/0. The H2 recovery rate was about 14 % with H2 yield of 11.6 mg/g COD. Comparative study suggested that continuous flow, no membrane and single chamber design can be used effectively in MFC for further application. The high temperature CO2 oxidation treatment of carbon anode materials resulted in an improvement of power by a factor of 2 when applied to MFC. Scanning Electron Microscopy (SEM) study and the textural property measurements based on Brunauer Emmett Teller (BET) theory suggested that treatments help bacteria to grow on the material surface resulting in power improvement. Graphite as cathode decreased the MFC power density by around 50 % compared to that of MFC with Pt contained cathode, but the cost is 1/1000 that of the Pt makes it a very attractive alternative. A typical industry case study for implementation of MFC were carried out that considerable energy cost savings and water disposal savings can offset the installation within 1-2 year. It shows that the MFC technology has a promising future for the sustainable development of the world with further research.

Hydrogen as an energy vector offers great potential for mobile energy generation through fuel cell technology, however this depends on safe, mobile and high density storage of hydrogen. The destabilised multi-component complex hydride system LiBH4 : MgH2 was investigated in order to characterise the destabilisation reactions which enable reduction of operating temperatures for this high capacity system (ca. 9.8 wt.%). In-situ neutron diffraction showed that regardless of stoichiometry similar reaction paths were followed forming LiH and MgB¬2¬ when decomposed under H¬2 and Mg-Li alloys (Mg0.816Li0.184 and Mg0.70Li0.30) when under dynamic vacuum. Hydrogen isotherms of the 0.3LiBH4 : MgH¬2¬ showed a dual plateau behaviour with the lower plateau due to the destabilised LiBH4 reaction. Thermodynamic data calculated from the isotherm results showed a significant reduction in the T(1bar) for LiBH4 to 322 C (cf. 459 C for LiBH4(l)). Cycling behaviour of 0.3LiBH4 : MgH2 system decomposed under both reaction environments showed very fast kinetics on deuteriding at 400C and 100 bar D2, reaching 90 % conversion within 20 minutes. In contrast 2LiBH4 : MgH2 samples had kinetics an order of magnitude slower and after 4 hours conversions <50 %. These results demonstrate the strong influence of stoichiometry in the cycling kinetics compared to decomposition conditions. Investigation of catalysts found dispersion of metal hydrides through long ball-milling times, or dispersion through reaction with metal halide additions provided the greatest degree of kinetic advantage, with pre-milled NbH providing the best kinetic improvement without reducing capacity due to Li-halide formation. Finally, additions of LiAlH4 to the system formed an Al dispersion through the sample during decomposition, which acted both as a catalyst and destabilising agent on the MgH2 component, forming Mg-Al-Li alloys. Decomposition under H2 also showed a destabilisation effect for the LiBH4 component.

Kerosene is a common fuel for domestic heating systems. Dating petroleum spill contamination is of considerable International Interest. An accurate determination of the age of spills is needed to inform the process of assigning legal and financial responsibility. The pollution of sons and groundwater by kerosene spills is of major concern to householders and their insurers as well as regulators. Released kerosene may persist in the soil as a source of hazardous hydrocarbons for a long time, but not as long as diesel, because of the low solubility and the moderate to low volatility of kerosene constituents. Generally, hydrocarbons in kerosene biodegrade significantly under aerobic conditions provided that sufficient amounts of essential nutrients are present. Extractable petroleum hydrocarbon (EPH) analyses by Jones Environmental laboratories Ltd of soil polluted following kerosene spills were used to develop an empirical model which considered biotic and abiotic factors found at spill sites to determine the time since the kerosene spill.

This study combines cure kinetics modelling and thermal and ultrasonic cure monitoring to characterize the cure state of a complex commercial modified epoxy thermosetting system of industrial importance containing two epoxies, diethylene triamine hardener, external catalyst, aliphatic reactive diluent, and mica. Both catalyst and reactive diluent in the formulation of two epoxy resin mixture keep this complex system odd from others and to some extent a new one to report cure kinetics to the best of our knowledge. The cure was monitored using differential scanning calorimetry (DSC) and broadband ultrasonic techniques over a group of isothermal cure temperatures within corresponding acceptable time scales. The sensitivities of both techniques to the chemical, physical, and mechanical changes associated with each part of the cure was discussed comprehensively and critically together with an inspection of the similarities between them coupled with qualitative and quantitative correlations. An in depth details analysis of the chemical cure kinetics of the investigated system was presented utilizing the model free iso-conversional method coupled with the light of physics of advanced kinetics research. The modelling of the calorimetric cure kinetics of the epoxy system under study was developed utilizing the empirical approach of fitting of the experimental data to various kinetic models. The best fit model which best possibly describe the non-typical autocatalytic cure behaviour of the resin system and predicts the reaction course was evaluated and analyzed in details. Utilization of the maximum attained conversion at a specific curing temperature enables this model to most closely simulate the curing reaction under both chemical controlled and diffusion controlled conditions with almost a reasonable degree of satisfaction over the entire range of conversion and temperature studied without the a priori need of a glass transition temperature model. The non-conventional autocatalytic effect and prediction of the trimolecular catalysis mechanism of the curing reaction was found to be manifested in temperature dependence of reaction orders, which was elucidated and justified. In comparison to other epoxy resins without reactive diluents, the analysis of our data shows that most possibly, the reactive diluent increased the maximum value of calorimetric conversion and reaction rate, reduced the viscosity, while the values of activation energy and process parameters remained within the typical values of epoxy formulations and the crosslink density was unaffected. The performance of each particular model tested was discussed along with their comparisons. Implementing diffusion factor in conventional models some useful information associated with the diffusion controlled kinetics related to our data were explored. The cure kinetics was also analyzed from both kinetic and thermodynamic viewpoint in the context of Horie model. This approach we employed, is, to some extent uncommon, can contribute towards a new way of characterization and the critical understanding of the cure reaction from the microkinetic standpoint providing information of the effect of reactive diluent on kinetics, regarding reaction pathways, kinetic homogeneity I inhomogeneity associated with reaction phase and the properties of the end product which are important to monitor and ultimately control the cure to attain desired properties in the end material. A TTT diagram of the cure process of this system was also constructed. The ultrasonic compression wave velocity was demonstrated to be the most interesting and potential parameter for monitoring and characterizing the cure process at all stages which provided with the information of degree of mechanical property development and can detect gelation and vitrification that occur during cure. Therefore, ultrasonic velocity measurement could be exploited for non-destructive on-line process control in an industrial environment. It was demonstrated that ultrasonic compression wave velocity can be used as a predictor of calorimetric conversion measurements and thus can be used to track chemical reaction online which is of potential importance for cure monitoring. Though system specific, the methodology we utilized, at least in part, constitutes a novel way of quantifying the degree of cure of a commercial epoxy thermoset network from ultrasonic longitudinal velocity measurements which is interesting and promising. It was found that the DSC is much more sensitive to changes occurring at the early stages of the cure but is relatively insensitive to the changes occurring at the latter stage. Ultrasonic compression wave velocity shows a better sensitivity at the end of the cure. It was also demonstrated that ultrasonic compression wave attenuation, real and imaginary parts of compression modulus, ultrasonic loss tangent and associated central relaxation time, also provided information of the material state and the cure process as well. The end of cure ultrasonic data, in general, provide a convenient assessment of final product quality.

Cold gas dynamic spraying, CGDS, is a relatively new technique used to deposit materials onto the surface of a substrate. It differs to the majority of other thermal spray techniques as the substrate and particles are not exposed to high temperatures during the spraying process. This makes CGDS particularly advantageous for spraying materials such as titanium which react at high temperature. The aim of this project was to investigate the potential use of titanium coatings by CGDS as a surface treatment for medical prostheses. Titanium powder was deposited onto Ti6A14V substrate using helium gas at room temperature. Titanium coatings were also produced by a competing spray technique, shrouded arc spraying, to allow for a comparison of the two techniques to be made. Mechanical properties of the titanium coatings were measured and the influence of subsequent heat treating on the mechanical properties was also investigated. The coatings were characterised by investigating properties such as their bond strength, residual stress and stiffness, as well as the influence of the cold spray titanium coating on the fatigue life of a sprayed substrate. Scanning electron microscopy and optical microscopy techniques were also used to characterise the deposits. To further develop and optimise the CGDS process aluminium and copper coatings were also deposited and their mechanical properties compared to that of the titanium deposits. Additionally particle image velocimetry, PIV, was used to improve general understanding of the cold spray process and the effect that spray parameters have on the particle impact velocity. In the case of fatigue endurance limit and despite a compressive residual stress state measured in the titanium CGDS coatings, a 15% reduction in fatigue endurance limit was observed following the application of a CGDS titanium coating to the as received substrate, but no significant reduction was observed on its application to the grit blasted substrate. By four point bend testing it was observed that the ratio of the modulus of the titanium deposit to that of the corresponding bulk material (the modulus ratio) was 0.17, significantly below unity. For copper and aluminium, also deposited by cold spray, a modulus ratio of 0.41 and 0.16 was observed. The volume fraction and aspect ratio of porosity in each deposit was measured by SEM. However, an Eshelby equivalent homogeneous inclusion model supplied with these data was not able to predict the low modulus ratios observed. Instead, imperfect inter-particle bonding within the deposit (akin to through-thickness cracks) is the source of the low modulus ratios, with the tenacious oxide on the titanium and aluminium powder particles being more effective at preventing oxide disruption and formation of metallurgical bonds between particles upon impact, hence the lower modulus ratio for these material types. A method was developed to visually show the imperfect inter-particle bonding expected to be found within the CGDS deposits. Although porosity levels are low within cold spray deposits, individual particles are found to not be well bonded to each other which results in low coating moduli. By increasing the primary gas pressure in the cold spray process an increase in the degree of inter-particle bond formation occurred. Heat treating of the titanium coating at 1150 °C was found to improve the bond strength of the coating but drastically reduced the fatigue endurance limit. The same heat treatment temperature was found to increase the modulus ratio of the coating to 0.36 and this is attributed to a greater level of inter-particle bonding within the titanium coating occurring by diffusion bonding. However a reduction in the fatigue endurance limit was observed. This is most likely due to phase changes of the Ti6A14V substrate, the stress relaxation nature of heat treating and oxygen embrittlement occurring, despite an argon furnace used. Diagnostic tools such as particle velocity measurements are also used to gain a further general understanding of the CGDS process. Particle velocity measurements were made for titanium and copper powders using helium and nitrogen gas and a range of spray parameters. Particles of less than 9 pm in diameter were found to have the slowest particle velocities for both the copper and titanium powders. For the titanium powder up to a 200 m s-1 variation was found between the smallest and largest sized particles. This knowledge may be used in the future to optimise the size distribution of a powder feedstock prior to being used for cold spray deposition. Overall the titanium powder produced the highest particle velocities compared to the copper powder due to its lower density and therefore being easier to accelerate by the gas flow. A particle model was used to predict particle velocities. Generally the model predicted higher particle velocities then the maximum measured particle velocities and this is due to the model not taking into consideration of particles interacting with one another, the external walls of the nozzle, or the external atmosphere. These factors would all lead to particle deceleration. In comparison to titanium coatings produced by the shrouded arc process, the titanium CGDS coatings performed admirably. The shrouded arc coatings had a considerably lower fatigue endurance limit, due to tensile residual stresses within the coating, forming as particles cool on impact. However, the shrouded arc coatings showed a higher modulus ratio of approximately 1/3, which is comparable to coatings produced by other thermal spray methods.