Deposition of TiC coatings is usually carried out by chemical vapour deposition. Recently deposition by sputtering and activated reactive evaporation has been reported. The ion plating technique (conventional and reactive), so far, does not seem to be successful. However, the present investigation using a third variation, chemical ion plating, produced adherent, uniform, dense, microcrystalline Tic coatings on steel substrates, characteristics expected when ion plating is used. Deposition took place on the cathode in an argon assisted glow discharge using gaseous reactants (TiC14, C2H2 and H2). The parameters investigated were: the pressure, voltage and current of the discharge, the reactants ratio and indirectly the temperature of the substrate. It was found that the factor governing the deposition was the discharge current, heating the substrate to temperatures where the reaction is thermodynamically feasible. The coatings were characterized by X-ray diffraction techniques. Their microstructure, thickness, uniformity and surface topography were studied by optical and scanning electron microscopy. The X- ray diffraction pattern showed only TiC with mean lattice parameter of 4.347 +/- 0.009 A which is higher than the corresponding value in the literature (4.328 A) probably due to the stresses accumulated during deposition and the presence of Cl impurities. Electron probe micro- analysis showed that the coatings consist of Ti, Cl (4%) and C in greater than stoichiometric proportions, as was confirmed also by chemical analysis. Oxygen was not detectable. The C was not detected as a second phase because it was non-crystalline and because the coating was very fine grained (below 1000 A). The properties of the coatings changed with composition. Vickers microhardness values reached 2700 - 3000 kgmm-2, the values accepted for Tic, at high concentrations of C. The good adhesion between coatings and substrate, observed on qualitative basis, was assessed by the frequently used scratching test and was best at high C content. However, at high C contents partial spalling occurred which was avoided at low C contents or when carburized steel substrates were used. Deposition rate increased as the C content increased. Finally the friction coefficient of coatings against a stainless steel counter-face decreased at high C contents (from 0.28 to 0.18).

Corrugated diaphragms are used for pressure measurement and control in a variety of applications. Their designs have become more critical in recent years because of the trend towards miniaturisation and the necessity to increase their stiffness to minimise vibration effects which demands the use of higher working stresses. This is particularly true of precision equipment used in aircraft applications. Finite element computer models were constructed and the predicted deflections compared with the measured ones to assess the accuracy of their predicted stresses. A pressure cycling rig has been designed and built enabling a series of fatigue tests to be done on diaphragms. The results were compared with the fatigue properties of the material in tension and bending, enabling a fatigue criterion, based on the tensile strain on the maximum shear plane, to be postulated. The effects of cyclic loading on diaphragms' pressure/deflection curves was also investigated. The results of the theoretical investigations and the fatigue teats have been combined to produce design criteria and graphs for the guidance of designers.

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Rutile, TiO2, has drawn significant attention due to its unique properties. In this project, the structural and electrical properties of undoped and Cr/Al/Ga/Zn-doped rutile have been investigated. Undoped rutile is increasingly oxygen-deficient on heating in air above ~700 °C. The weight loss is generally too small for accurate measurement, but the electrical properties of quenched samples provide a sensitive qualitative indicator of oxygen content since their conductivity can vary by many orders of magnitude. The lattice parameters of quenched samples show an unusual dependence on quench temperature and, by implication, on oxygen stoichiometry. Lattice parameters increase with a small oxygen loss, δ; chemical expansion of the lattice occurs and is attributed to increase in average Ti-O bond lengths. At higher δ, lattice parameters start to decrease, giving a chemical contraction effect attributed to partial collapse of columns of edge-sharing TiO6 octahedra in the rutile structure and elimination of oxygen vacancies by crystallographic shear, CS, plane formation. Oxygen-deficient rutile samples quenched from above 700 °C are n-type, whereas samples annealed and measured at 450-500 °C are p-type and believed to be slightly oxygen-rich. Holes are located on oxide ions at or near the sample surface and arise from redox electron transfer between under-bonded surface oxide ions and adsorbed O2 molecules. Samples annealed between 550 and 600 °C show cross-over between n- and p-type behavior. Cr-doped rutile, Ti1-xCrxO2-x/2-δ, samples show a volume expansion at low Cr content, which is associated with the larger size of Cr3+ and the increase in average M-O bond length. At relatively higher Cr content, samples show an unusual volume contraction effect, which is also believed to be attributed to the formation of shear planes. The electrical properties of Cr-doped rutile are very dependent on composition x. Impedance results show that at low dopant concentration (0.001 ≤ x ≤ 0.01), samples are two-phase mixtures. The phase identified by R2C2 is more resistive than R1C1 and has larger activation energy. R2C2 represents a phase with very small Cr3+ dopant concentration, i.e. x = 0.001 ± 0.0005, and R1C1 represents a phase with relatively higher dopant content, i.e. x = 0.008 ± 0.002. In addition, since Cr content of both phases are different, R2C2 may have random point defects, such as oxygen vacancies. With relatively higher dopant content, oxygen vacancies collapse to form shear planes, i.e. defects present in the phase R1C1 may be random shear planes. At low x, Cr-doped rutile samples show mixed conduction, with p-type electronic conduction and oxide ion conduction. The location of holes is thought to be related with O2- ions as well. At higher x, a p-n transition is observed; samples are semiconducting and have small activation energy (~0.2 eV). Such semiconductivity is attributed to intrinsic hopping of charge carriers associated with Cr-Cr or Cr-Ti. Since orbital overlap may occur, charge carriers could hop between Cr3+ and Ti4+ and thus, Cr4+ and Ti3+ are generated and samples become semiconducting. Moreover, if oxygen vacancies collapse to form shear planes, the distance between Cr-Cr or Cr-Ti in face-sharing octahedra in the shear planes are smaller, and hopping of charge carriers becomes easier and the conductivity increases. Moreover, polaron hopping is an alternative description of the amount of semiconductivity. Electrical properties of Al-doped TiO2 are dependent on cooling condition. Samples show a p-n transition with increasing quench temperature. The p-type conductivity is driven by surface absorption of oxygen and associated with O- at the sample surface. Ga-doped TiO2 shows an n-p transition with increasing dopant concentration, whereas such electronic conduction is quite weak. Maybe with Ga3+ doping in TiO2, ionic compensation is the main compensation mechanism. With Zn2+ doping, it is clear that the homogeneity of rutile ceramics improves in some degree. However, Zn-doped samples still show evidence of a constriction resistance or a dipole orientation-related impedance. Zn-doped rutile samples show n-type conduction.

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Considering the high overall costs of radioactive waste disposal and the growing requirements for improved quality of the final waste form, the benefits offered by thermal processing become very significant. Key drivers for the application of thermal treatment processes include the reduced volume, improved passive safety, and superior long term stability of the vitrified wasteform products. Currently, a fundamental lack of scientific knowledge and understanding significantly hinders the uptake of thermal treatment processes for the immobilisation and disposal of plutonium contaminated material waste. The project will contribute to accelerating the acquisition of knowledge and experience required to support the Nuclear Decommissioning Authority (NDA) in deploying thermal technologies as a national asset for intermediate level waste (ILW) treatment. Plutonium contaminated materials (PCM) waste is a sub category of ILW. The current treatment method for PCM is supercompaction and cement encapsulation, however, there are significant concerns regarding the reliability of the treatment method to consistently deliver a waste form suitable for long term performance. This project follows on from previous work which provided proof of concept studies for thermally treating PCM waste. This work uses a soda lime silica (SLS) glass cullet as the glass forming additive to aid vitrification, providing substantial benefits in terms of costs saving compared to previous work. The thermal treatment experiments showed no violent reactions between the waste simulant and the glass additives. The Ce (acting as a Pu surrogate) was effectively partitioned within the slag fractions of the waste form, with crystalline regions present in certain formulations. The Ce was found as trivalent species providing confidence that the slag component of the wasteforms developed here could incorporate Pu at the concentrations expected from treatment of PCM wastes. The materials produced here are broadly comparable, in terms of durability, to other simulant UK ILW glass products considered potentially suitable for geological disposal. The project also investigates the potential to use the glass forming oxides found within the ILW itself to aid vitrification. Using suitable ternary phase diagrams, it is possible to use the waste and any additional additives to create a formulation to ensure a glass is successfully formed at a reasonable operating temperature whilst always maintaining compatibility with currently available technology platforms. This method was utilised to vitrify representative pond scabbling waste. The simulant waste contained high levels of SiO2 which, in combination with glass forming oxides, were successfully vitrified. Characterisation studies were performed to understand the relationship between Na2O and B2O3 and the effect this had on the microstructure of the resultant structure of the glass. Glass dissolution experiments were also performed to test the performance of the glass in conditions expected within a geological disposal facility (GDF). The thesis also includes the results of samples acquired from a three month student placement working with Kurion's geomelt facility at the Workington site (UK). Contained within this PhD are experiments which aim to provide significant information into the mechanism that drive glass alteration. However this data has only been applicable to short-term alteration. The research presented in Chapter 7 aims to understand the long term mechanism of the vitrified PCM waste by using 250 year old slag samples as a glass alteration analogue. The results presented provide evidence for the long term durability of the vitrified PCM waste samples.

CoCrMo alloys have been widely used in hip replacements. On the one hand, they have exhibited excellent long-term survival rates, but recently high failure rates have been observed, associated with adverse local tissue reactions. It is still a puzzle why CoCrMo alloys sometimes work very well, while at the other times the wear rate is unacceptably high. There have been several reports that the formation of a surface carbonaceous layer appears to reduce the wear rate. Equally, the formation of surface deformations and nanocrystalline layer has been observed, but it remains unclear whether this is a beneficial or detrimental phenomenon. The application of CoCrMo in hip joints results in mechanical aspects in term of wear and electrochemical aspects in term of corrosion in what is called tribocorrosion. Therefore, the current work was designed to carefully cover some factors that have not been well investigated in the literature using different approaches for data analysis. The study was divided into two major parts; tribological study and tribocorrosion study. In the tribological study, a direct correlation was found between the surface deformation and the presence of a carbonaceous layer with the wear behaviour. The lowest specific wear rate was associated with the formation of a carbonaceous layer. A wear transition was observed at higher load, related to the loss of the carbonaceous layer and the formation of a thick subsurface nanocrystalline layer. The formation of the carbonaceous layer appeared to be associated with the removal of the surface protective oxide film. Additionally, it was shown that the superior mechanical properties of a thick nanocrystalline sub-surface layer could not protect the surface from a high wear rate. Although the formation of a thick nanocrystalline subsurface layer resulted in the highest surface mechanical properties, it also coincided with the highest wear rate. In the tribocorrosion part of the study, the mechanical and electrochemical contributions in tribocorrosion were separated using synergistic and mechanistic approaches. The influence of load, load-potential dual effect and sliding speed-potential dual effect were all studied. The results showed a significant effect of re-passivating the worn surfaces on the wear behaviour of the material. At low loads and slow sliding speed, the worn surfaces were able to re-passivate at OCP which in turn had a significant effect on the microstructure of these surfaces and consequently on the mechanical properties and the tribocorrosion behaviour. Furthermore, the results of load-potential and sliding speed-potential showed a correlation between the mechanical contribution of tribocorrosion and the hardness of the worn surfaces that is the harder worn surfaces wear less mechanically at OCP. Such this correlation was not found at anodic potentials. The results also showed that the surface carbonaceous layer did not form on the surfaces that were covered by an oxide layer and a high cathodic potential was needed to almost entirely remove the oxide film. This is in good agreement with the results of the tribological study of the work which pointed out a certain minimum load is necessary to totally remove the oxide layer and helped in the formation of a carbonaceous layer on the worn surfaces. A correlation between the COF and the thermodynamic stability of the surface was observed. Throughout the whole study, whenever the system was able to establish new thermodynamic stability (at low load and slow sliding at OCP and at all tested anodic potentials), COF significantly decreased. The study defined two surface status, passivating worn surfaces (the surface tries to re-passivate) with high COF, and passivated surfaces (already passivated) with low COF.