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Air plasma sprayed thermal barrier coating (APS TBC) systems are usually applied to engine components to reduce the temperature of the substrate and increase the efficiency of engines. However, failure of these coatings leads to oxidation and corrosion of the substrate. Therefore, a thorough understanding of the coating failure is necessary to predict the lifetime of coated components. This project has carried out stress analysis and prediction of subsequent failure of APS TBC systems associated with sintering of the TBC, oxidation of the bond coat (BC), substrate geometry, undulations at the coating interfaces and coating fracture toughness. Stress analysis is crucial for predicting TBC failure as stresses in the vicinity of the coating interfaces cause cracks and subsequent coating delamination. The Finite element (FE) method was used for stress analysis of TBC systems at high temperature stage and at cooling stage after operation. Initially, FE model of an axisymmetric unit cell representing the slice of a coated cylinder was used. Different radii for cylinders were used to investigate the significance of substrate curvature on coating stresses. The effect of asperities at the coating interface on residual stresses was observed using 3D models. The models were built based on the actual geometries of asperities, which were extracted from 3D SEM images of the coating interfaces. An Arrhenius approach was utilised to implement changes in mechanical and physical properties of TBC due to sintering. BC oxidation and related changes in its composition were also implemented. The accuracy of assumptions for FE models was validated by comparing the evaluated stresses against experimental results by project partners. Finally, the effects of stresses and fracture toughness of the coatings and coating interfaces on failure of the TBC system were studied, using cohesive surface modelling and extended finite element modelling (XFEM) methods.

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.

The present work studies the effect of changes in the formulation of coil coatings on their mechanical properties. The paint systems investigated were generally based on polyester binders that were heat-cured with hexa(methoxymethyl)melamine (HMMM). The chemical structure of the polyester, as well as the concentrations of the materials present in the formulations, was systematically changed and the mechanical properties of free-films of the paints were studied at a variety of different temperatures. Changes in the polyester back-bone resulted in significant changes in the glass transition temperature, Tg, of the paints. For example, the substitution of phthalic acid in the polyester, with iso-phthalic acid, resulted in a decrease in Tg from 36 to 8 °C. At the same time, the respective effect on the mechanical properties was modest. On the other hand, changes in cross-link density resulted in dramatic changes in the mechanical properties of the paints. For example, the maximum strain at failure decreased from 180% to 30% when the concentration of the HMMM cross-linker in the paint was increased from about 5 wt% to about 30 wt%. The effects of temperature and loading rate on the mechanical properties of the free-films of the paints were also investigated. Multi-frequency dynamic mechanical analysis (DMA) was used to obtain the correspondence between time and temperature, at low strains, in a quantitative way. This correspondence was extended to large strains, when tensile data under a range of different temperatures and loading rates were considered. Modelling studies were also performed, where a hybrid visco-elastic/hyper-elastic model was used to predict the tensile behaviour of the paints, with good agreement between the predictions and the measured data. Finally, steel panels coated with a selection of the paint systems were tested in bending, using a T-bend test at 0T. An important finding was the increase in the amount of damage in the coating with time after bending, even though the panels were not deformed further. It was generally found that panels coated with paints which showed large values of strain to failure and toughness when tested as free-films, and also with little tendency for elastic recovery, suffered the least amount of damage when tested in bending.

Low emissivity (Low-E) coatings are applied to large area architectural glazing to reduce heat losses from buildings. They combine high visible transparency with high reflectance in the far-infrared region. To achieve this combination of properties, Low-E coatings generally consist of dielectric-silver-dielectric multi-layer systems or stacks, where the thin (~10 nm) silver layer reflects long wavelength IR back into the building and the dielectric layers both protect the silver and act as anti-reflectance layers. The dielectric layers are commonly TiO2, SnO2 or ZnO, and all the layers are usually deposited by magnetron sputtering. The market for Low-E coatings has grown considerably in recent years due to environmental legislation and increased energy costs. To further expand the market, the next generation of Low-E coatings are increasingly being deposited onto toughenable glass, which is post-deposition annealed at temperatures of up to 650oC. However, under these conditions, silver atoms are highly mobile and can rapidly diffuse through the other constituent layers of the coating stack, which can have a detrimental impact on the performance of the coating. Diffusion in polycrystalline films occurs much faster than in bulk samples and by different mechanisms. This is caused by the physical properties of thin films, which may contain a high density of defects such as dislocations, vacancies and grain boundaries that can act as pathways for diffusion processes. The aim of this project therefore is to carry out a detailed study of diffusion processes in dielectric-silver coating systems deposited under industrially relevant conditions (i.e. using commercially available magnetron designs and power deliver modes). TiO2 coatings have been deposited onto float glass substrates by reactive pulsed magnetron sputtering and characterised using Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction. The coatings have been annealed at temperatures in the range of 100oC to 800oC and re-analysed to determine the effect of annealing on the film structures. An interesting transition from a weakly crystalline rutile-like structure with very small grain sizes to a strongly crystalline anatase structure or mixed-phase structure with much larger grains was observed as annealing temperature was increased. Selected coatings were over coated with silver and annealed for a second time. These coatings were analysed by X-ray photoelectron spectroscopy and secondary ion mass spectrometry to determine the diffusion profiles of silver through the titania layer and the reverse diffusion of sodium from the glass substrates. Little difference in the diffusion rate of silver was observed with annealing temperature, but sodium was observed to diffuse significantly faster through samples annealed at higher temperature range. Similar studies have been performed for Al-doped ZnO, Zn2SnO4 and Si3N4 coatings. These films have been post-deposition annealed at 650oC then over coated with silver and re-annealed at 250oC. Diffusion profiles for both Ag and Na atoms were measured using secondary ion mass spectrometry. Finally dielectric/Ag/dielectric layers were deposited to investigate the behaviour of silver and sodium after annealing at 250oC. The basic models of diffusion mechanisms in thin films have been developed using Fick’s second diffusion law. Analytical modelling was used to fit the experimental data into a concentration dependent curve that represents the solution to Fick’s second law. Moreover selected dielectric/Ag/dielectric stacks were subjected to temperature dependency of silver diffusion studies using Arrhenius diffusion principle. Samples were post-deposition annealed at the temperature range of 200-650oC for 5 minutes to investigate silver diffusion at different heat treatment conditions and diffusivity values were used to find activation energies and frequency factors from Arrhenius plot. Overall findings from the diffusion studies are that from dielectric materials investigated in this work Al-doped ZnO coatings have the best barrier properties for silver atoms diffusion and show relatively low values for sodium diffusion, when not annealed at relatively high temperatures. Zinc stannate, on the other hand, was found to be the material through which atoms investigated here diffuse fairly easily. Both silver and sodium atoms were found to have the highest diffusion rates through zinc stannate films relative to the other coatings investigated in this work.

The work described in this thesis formed part of a larger collaborative project between Manchester Metropolitan University, the University of Liverpool, and our industry partner Teer Coatings Ltd., which was entitled "Dual source pulsed plasmas for the production of ultra-high performance coatings." Closed field unbalanced magnetron sputtering (CFUBMS) has become a mainstay of sputter deposition techniques. However improvements and new approaches are always being sought. This project has focused on the application of one variation, pulsed substrate bias (PSB) deposition, to the reactive sputter deposition of chromium nitride. CrxN is of great interest to industry, as it offers similar wear and corrosion resistance to the better known TiN, but with greater thermal stability. Pulsed substrate biasing is a relatively recent technology. It potentially allows scope for improvement of coating structure, and hence tribology, through greater ion bombardment of the coating during deposition. The initial aims of this project were: To characterise the pulsed CFUBMS system during reactive deposition of CrxN; to gain an understanding of the plasma behaviour and processes during deposition; to understand the influence of the pulsed plasma over coating microstructures, and relate relevant changes in these microstructures to changes in coating tribology. With the resultant data the project then turned to identifying the strengths and weaknesses of PSB deposition, and finding means to enhance coating performance using the technique. Plasma studies were largely undertaken at the University of Liverpool, using optical spectrometry, CCD camera imaging, and Langmuir probe measurements. Based on these finding 5 coatings were deposited at MMU, and subjected to structural and tribological tests such as scratch adhesion testing, nanoindentation, thrust washer wear testing, surface profilometry, and optical microscopy. Selected coatings were deposited onto cutting tools (twist drills) and tested to failure in a simulated industrial environment. Coating microstructure was investigated at MMU by SEM and EDS. Selected coatings were investigated by XRD at the University of Sofia, and by TEM at Oxford University. The pulsed CFUBMS system is shown to be adequately stable to reactively sputter CrxN. PSB deposition is shown to increase ion bombardment at the substrate. Enhanced ion bombardment is in turn related to the growth of a denser coating, with a more ordered crystallographic structure with greater surface hardness. However the PSB approach is also shown to increase compressive stress within the coating, and potentially damage effective adhesion. As a consequence we have sought to combine the DC bias and PSB methods, as well as changes in coating stoichiometry, in a series of layered coatings. The best performing of these layered coating architectures is significantly harder wearing than standard CrN coatings, and approaches the wear resistance of CrTiAlN coatings in drill tests. Pulsed substrate bias deposition is a potentially powerful addition to the portfolio of sputter coating techniques. Here it has been successfully applied to enhance the microstructure, tribology, and wear resistance of CrxN coatings.

Poly(vinyl alcohol) (PVA) is a polymer used in numerous applications, principally those in which its high water solubility is a desirable asset. However there are also areas where PVA is limited by its inherent solubility (for example some specific environments in the biomedical field). This work has sought to overcome such limits by manipulating the surface of PVA in order to propose various means by which the surface solvent resistance might be increased while maintaining the bulk properties of the polymer. Both chemical and physical modifications have been tried and in each case progress has been made towards insolubilizing a single surface of the polymer when in film form. Grafting various species onto the surface of PVA was successfully performed. It is believed that such species bonded to the PVA via attachment to the hydroxyl groups (though this has not been proven conclusively). The data contained herein has led to the conclusion that the primary factor in reducing solubility this way is the removal of the hydroxyl groups, and not the attachment of specifically highly hydrophobic molecules. Introducing permanent cross-links into the surface region has been attempted via various routes. The data recorded shows promise however the system is far from optimised. The biggest challenge remaining is to optimise the depth of material cross-linked. Some steps have been made towards understanding and controlling this parameter though there is much scope for further investigation. The methods used have built on those used for bulk cross-linking and as such are new for the case of surface specific treatment. An interesting phenomenon in some semi-crystalline polymers reported in recent years is that of surface specific crystallization. This effect has been successfully induced and observed in PVA to produce what is believed to be a highly crystalline surface layer, and crystalline regions of PVA are generally accepted to be more water resistant than amorphous ones. In summary, in this work several surface-specific treatments for PVA have been trialled, providing options for post-film forming modification to reduce the surface water sensitivity whilst retaining the bulk properties of the polymer.

In this thesis we report on a system of colloidal plates and spheres developed to model the key particles found in paint and other industrial formulations. From theories of mixtures of particles of different shapes and sizes one would expect entropic phase sep- aration to occur at sufficiently high volume fractions, due to the gains in free volume. An aqueous system consisting of synthetic nano-gibbsite Al(OHh plates and alumina coated silica nano-spheres were sterically stabilized with a commercial stabiliser in wa- ter to create near-hard particle interactions. The stabilizer was chosen, by using in the first instance an NMR spin-spin relaxation technique. This gave a pseudo-adsorption isotherm. This technique was complemented with electrophoresis and elemental anal- ysis. The addition of the stabilizer to the suspension of plates modified the kinetics of the isotropic-nematic phase formation, with larger domains forming than in a surfac- tant free system. Colloidal plate-sphere mixtures were investigated using small-angle neutron scattering (SANS), optical microscopy (polarising and differential interference contrast). In SANS,' for dilute suspensions using contrast matching, the addition of colloidal plates to colloidal spheres showed an increase in density fluctuations of the spheres, which agreed well with theoretical predictions. The birefringence of the sys- tems was also observed in order to study the isotropic-nematic (I-N) transition. On adding spheres, the I-N transition occurs at a lower platelet concentration. The impact of the plate __ ~(Ls

Static and dynamic nanoindentation of polystyrene and poly(methyl methacrylate) coatings on glass substrate was studied during this project. An analytical determination of the reduced modulus profile of the coating/substrate system was developed, and the delamination behaviour of the coatings was investigated. Reduced moduli profiles showed an unexpected drop which was attributed to delamination and which has not previously been reported. The reduced modulus profiles of the coating/substrate systems were extracted and sigmoidal equations were fitted to them. It was found that the best fitting equation was a sigmoid with 2 adjustable parameters that control the slope of the sigmoid and its offset point. The variety of equations proposed in the literature was found to give less good fits. Those two parameters were found to be proportional to the coating thickness. Thus based on these results for a given coating thickness the reduced modulus profile of further PS & PMMA coatings of any thickness can be predicted without any testing, and the thickness of PS & PMMA coatings can be determined with just a few nanoindents. A novel way to determine when delamination of coatings occurred was found by plotting the variation of the final depth of indent against the contact depth. The delamination load, the depth at which it occurs and the radius of delamination can all be deduced. Delamination was found to reduce the measured coating/substrate modulus under static nanoindentation, this drop in modulus also indicated the indentation depth and load at which the delamination of coatings occurs. This drop in modulus was not present in dynamic nanoindentation. Nanoindentation tests were made with both Berkovich tip and a cube corner tip; it was found that the reduced modulus profile and delamination behaviour of the coating/substrate system was independent of the tip geometry. A comparison of the static and dynamic nanoindentation of PS and PMMA coatings showed that the reduced modulus profiles had very similar shapes in both methods used. A stress analysis was used to calculate the critical indent depth (her), maximum indentation depth at which the properties of the substrate goes unnoticed, for PS. It was shown that a glass substrate has a smaller critical indent depth than a PS one.

The structure of two-component coatings codeposited by magnetron sputter ion plating was studied. This apparently simple topic has never been studied systematically and has led to a number of unexpected and very interesting results. The systems that were studied included materials with 100% solid-solubility, (titanium and zirconium) totally insoluble materials (chromium and copper) and materials that can form intermetallic compounds (titanium and aluminium). Variables studied included method of deposition, composition of the coating and energy of ion bombardment during deposition. Two approaches were used for the deposition process. These were multilayer deposition from vertically opposed magnetrons and codeposition from coplanar magnetrons, both using closed field magnetic arrays. Both methods are fundamentally the same. It is the orientation and manipulation of the substrates during the deposition process which leads to either a multilayer coating structure or a codeposited homogeneous coating. The flexibility of the coating technique was demonstrated and a greater understanding was gained of both the structure and properties of alloy coatings and how these are influenced by the deposition parameters in a magnetron sputtering system. The coating structures were studied using SEM and XRD and their properties by different mechanical tests. Prior studies in this field have shown that such coatings can have unexpected properties. For example, energetic ion bombardment is known to cause the production of 'non equilibrium' phases and can extend the normal solubility range. Thus HCP Ti-Al coatings can be deposited which would be expected to have good tribological properties. Properties such as this have been studied and exploited for suitable applications. Further studies showed how parameters such as ion current density are dependant on target current and have a large influence on coating structures and properties. This is all of importance to materials scientists, surface engineers and manufacturers of coating equipment.

Thermal spraying is widely used to produce application-based superior surfaces on relatively cheap bulk materials, thus saving materials and cost. The concept is based on the assumption that the coating offers the same superior properties as the bulk material of the same composition. However, the use of thermal spray coatings for corrosion protection requires an awareness regarding microstructural modification during coating deposition and due to which, a performance gap may exist between coating and the bulk material.

Thermal barrier coatings (TBCs) are usually applied on high temperature gas turbine components. They reduce the need for additional cooling of the exposed surfaces and improve the durability of the underlying materials. However, the lack of reliable lifting methods limits their applicability in the design of turbine components and so they are usually employed as additional protection for components that already meet the design requirements. In order to develop failure models and equations of practical interest, the mechanical behaviour and degradation of properties of coatings at elevated temperature needs to be understood. Several phenomena such as the growth of an oxide layer, degradation of bond coats, creep and thermal expansion mismatch between the different layers that compose the TBC contribute in the development of stresses at high temperature. The effect of thermal cycling has been covered in previous research, giving rise to models that explained how accumulated cyclic inelastic strains occurred in the bond coat and oxide layer due to the thermal expansion mismatch. This favoured the wrinkling of the oxide layer and the concentration of stresses, which could eventually cause crack nucleation, growth and failure of the coating. The research contained in this thesis focuses mainly on the development of stress concentrations during high temperature exposure. A coupled micro-structural-mechanical constitutive model was implemented in order to take into account the processes the coatings undergo at high temperature. High tensile stresses, perpendicular to the oxide-top coat interface, which may induce crack nucleation within the oxide layer at high temperature, were obtained.

The overall aim of this research project was to expand the understanding of the deposition of titanium and the nickel-based superalloy Inconel 718 by spray deposition methods. The spray processes employed were cold spraying and high velocity oxy-fuel (HVOF) thermal spraying. The first part of the work was undertaken to expand the understanding of the deposition of titanium by cold spraying; the HVOF process is unsuitable for Ti because of the metal's high reactivity. The deposits were produced from commercially pure titanium using cold spray equipment designed in the University. Using helium gas, the effects of different powder particle size ranges, types of substrate, substrate preparation methods, and spray parameter conditions on deposit formation were investigated. Using a simple one-dimensional model of compressible gas flow and particle acceleration, particle velocity distributions were calculated to aid interpretation of experimental data. Results show that titanium can be successfully cold sprayed onto substrates of Ti6AI4V and mild steel, with the critical velocity for deposition of this powder type of approximately 690 m s-1. The level of porosity was generally in the range of 13-23% and the adhesive bond strength was dependent on surface preparation but independent of gas pressure with values ranging from 22 MPa to 10 MPa for ground and grit blasted substrates respectively. This compares with a value of around 80 MPa which is typical for well adhered HVOF sprayed coatings. The second part of the study was concerned with comparing the deposition of Inconel 718 by cold spraying and HVOF thermal spraying; the latter employed a JP5000 liquid fuel gun. A Tecnar DPV-2000 instrument was used to systematically investigate the effect of changes in spray parameters (spraying stand-off distance, oxygen/fuel ratio, total mass flow rate, combustion pressure), on particle velocity and temperature during HVOF spraying. It was found that generally the particle velocity was more strongly affected by the stand-off distance and combustion pressure of the spraying gun whereas the particle temperature was mostly influenced by the particle size and combustion pressure. The microstructures of coatings sprayed under 4 different well controlled conditions were investigated and changes in the morphology of splats and partially melted particles in the coating were related to the particle temperature and velocity at impact. The HVOF had high bond strength and low oxygen level of typically 0.45 wt% (corresponding to an oxide content of less than 1.6 wt.%). By contrast, in the cold sprayed coatings, the bonding was considerably low (-14 MPa), independently from the process conditions. It was found that the process parameter that mainly affected the properties of the cold sprayed deposits was the gas pressure. More specifically, the microhardness of the coatings increased with the pressure whereas the relative porosity decreased.

Mono-functional self assembled monolayer of alkanecarboxylic (Nonanoic and Nonadeconic) and alkanephosphonic (Octylphosphonic and Octadecylphosphonic) acids and of bi-functional Aminobutylphosphonic acid were prepared on mild steel surfaces. The self assembled monolayers (SAMs) were characterized by means of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Contact angle measurement, while the anti-corrosion performance has been studied using electrochemical impedance spectroscopy (EIS).

Yttria-stabilized-zirconia (YSZ) coatings have been fabricated on metallic (Fecralloy) substrates using a colloidal processing technique, namely electrophoretic deposition (EPD). The deposition of YSZ particles has been examined as a function of EPD conditions and suspension properties.

This thesis documents some significant progress in improving the understanding of how complex multilayer surfaces respond under mixed rolling-sliding contact. By utilising advanced finite element simulation techniques a unique method for modelling multilayer contact was developed. Capable of simulating mixed rollingsliding contact in surfaces with up to eight layers; this method was applied to model the response of three complex coated systems commercially available from Oerlikon Balzers Coatings Ltd.

Following the introduction of legislation restricting the manufacture and use of coatings containing volatile organic solvents, alternative waterborne coatings are increasingly being adopted for adhesive, protective, and decorative applications. Better understanding is therefore sought of the behaviour of waterborne coatings during drying and film formation, and of their physical characteristics after film formation is complete. This thesis describes one-dimensional Magnetic Resonance Imaging studies of the distribution of water and solid particles through the depth of aqueous latex layers during drying which investigate how particle distribution and concentration are influenced by the competing forces of diffusion and evaporation. The manner in which the balance of these forces affects the formation of a crust or dry layer at the latex-air interface is also investigated. In the case of acrylic latexes, the same technique has been used to show that, when re-wet by the application of further latex during drying, drying layers absorb a quantity of water proportional to the water volume fraction at the time of re-wetting. A study is also reported in which Nuclear Magnetic Resonance diffusometry and, for the first time, two-dimensional Nuclear Magnetic Resonance relaxation and diffusion correlation and exchange measurements are used to investigate waterborne coatings. These methods allow both the pore size and the total pore volume of some emulsion paint products to be estimated.

In this research, the electrical conductivity and thermal properties of polyethersulphone (PES) insulating polymer were improved, at its optimum micromechanical properties, by filling with electrically and thermally conductive graphite, for use in coatings for electrostatic dissipation applications. The graphite employed was a micro-/nano-graphite with aspect ratios in the range 100-600. Two types of the graphite, untreated and treated, were used for PES composites and LiCI-doped PES composite fabrication via a solution method. The treated graphite was surface functionalised by concentrated nitric acid treatment. FT-IR indicated the effectiveness of concentrated nitric acid treatment in introducing additional -COOH groups on the surfaces of the graphite. XRD, SEM and TEM revealed the dispersion of the graphite throughout the PES matrix in both an immiscIble and disordered manner, and the existence of aggregates of graphite. Nanoindentation testing showed insignificant decreases in the nanohardness and elastic modulus of the PES/treated graphite composites when the treated graphite content was not more than 5 wt%; whereas, increasing the content of the treated graphite increased the nanoscratch resistance of the composites. Due to the high aspect ratio of the graphite, the electrical conductivities of the PES/untreated and PES/treated graphite composites were enhanced at low loadings. An initial conducting pathway was formed at lower than 3 wt% of the filler. The enhancement by 2 orders of magnitude of the electrical conductivity of a PES/treated graphite composite could be accomplished by doping with 0.06 wt% of LiC!. MDSC showed improvements in the thermal conductivity of the PES matrix by 165 and 91% with the addition of 5 wt% of the untreated and treated graphite, respectively. DSC curves illustrated higher glass transition temperatures of the PES/graphite composites and doped PES/graphite composites, compared to the pure PES. Decreases in relaxation enthalpy WIth time, due to physical ageing of PES, were smaller when the PES was filled with the graphite or LiCI-doped graphite. The decrease in relaxation enthalpy of the materials was accompanied by increases in glass transition temperature and characteristIc length. Physical ageing also led to a decrease in the electrical conductivities of the PES/graphite composites and doped PES/graphite composites.

In this thesis we consider mathematical models for the industrial process of curtain coating, particularly as related to the paper industry.

This thesis is concerned with flows relating to the continuous coating of multiple layers on moving webs using the slide bead process. The lowermost layer is generally known as a carrier layer when the viscosity and flow rate are both small compared with the corresponding properties of the other layers. This study is predominantly experimental in nature and broad in scope as addressing issues relating to an industrial slide coating process used for the manufacture of photographic products and inkjet media. Novel specialist pieces of equipment have been designed and built for visualizing such flows as part of this work. The studies have been carried out using a pilot coating machine and ancillary flow control facilities currently owned by HARMAN technology Limited. The new techniques enable fresh insight into the interaction between the carrier layer and the surface properties of the substrate, including roughness, surface free energy, electric charge and porosity - an area of investigation that has hitherto been largely ignored. The behaviour of the bead when coating embossed webs showing a "stippled" finish is of particular interest when compared with apparently equally rough substrates of equivalent surface energy. Increasing slide angle is shown to be advantageous to expanding the coating window for difficult substrates. The results show that the widely perceived criteria for a carrier layer needs to be redefined when coating rough surfaces of low surface energy using this process. Charge assisted coating is shown likely to be superior to conventional slide bead coating for minimising waste due to streaks. The studies include the visualisation of flows at the slot exit and on the slide. The methods allow the profile of the interface as well as the free surface to be monitored and give new insight into two major unreported effects limiting the use of a thin low viscosity carrier layer. The scope also extends to the study of waves induced in the surface of wet multi-layer coatings when subjected to the impact of air from an impingement dryer - an area of considerable interest to the coating technologist yet largely ignored by the equipment supplier.

This thesis reports on the microstructure of Al-Sn based powders and the development of Al-Sn based coatings for automotive shell bearing applications deposited using the high velocity oxy-liquid fuel (HVOLF) thermal spray technique. The microstructure of the coating and its associated physical and chemical properties, such as microhardness and corrosion resistance, are investigated as a function of the HVOLF thermal spraying parameters. In particular, a detailed microstructural understanding of the thermal sprayed coatings is developed to explain the coating properties. Two alloy systems, Al-12wt. %Sn-1 wt. %Cu and Al-20wt. %Sn-3wt. %Si have been investigated in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis. The high resolution transmission electron microscope (HRTEM), electron energy loss spectroscopy (EELS) and energy filtered TEM have also been used to examine nanoscale precipitates as supplementary methods. The statistical image analysis of fine scale particulate dispersions has also been used to study the second phase evolution with annealing. The microstructure of the large gas atomised powder particles used in the HVOLF thermal spray process comprise dendritic Al and interdendritic Sn, whilst the small powder particles exhibit fine scale Sn particles distributed within an Al matrix. The as-sprayed coatings comprise a mixture of melted and partially melted splats due to the full and partial melting of the deposited powder. Nanoscale Sn particles distributed in the Al matrix are present in fully melted regions, whilst micron / sub-micron Sn particle distributions and Sn-particle free Al regions delineate partially melted regions. Cu remains in solid solution within the Al matrix of the Al-12wt. %Sn-1 wt. %Cu as-sprayed coatings, whilst Si formed nanoscale particles in the Al-20wt.%Sn-3wt.%Si as-sprayed coatings. The critical cooling rate to form the metastable liquid phase separationh within Al-12wt%Sn alloys is put forward according to calculation. If the cooling rate is lower than the critical cooling rate, dendritic Al and interdendritic Sn are formed, thereby explaining the structure of large gas atomised powder particles. If the cooling rate is higher than the critical cooling rate, a liquid phase separation reaction occurs to form fine scale Sn dispersion. The calculated critical Al-12wt.%Sn powder diameter for liquid phase separation is close to the experimentally observed Al-12wt. %Sn-l wt. %Cu powder diameter. The discrepancy between experiment result and theoretical calculation is attributed to the additional element Cu promoting the liquid phase separation. The nano and sub-micron scale Sn distribution in small gas atomised powder particles and the as-sprayed coatings is attributed to the cooling rate being higher than the critical cooling rate. The dendritic structure of the large Al-Sn-Cu gas atomised powder is due to the cooling rate being lower than the critical value. Heat treatments are applied to the as-sprayed coatings to alter the mechanical and chemical properties, such as, microhardness and corrosion resistance, of the bearing material coatings. Annealing causes the nanoscale and sub-micron Sn particles to coarsen within both Al-12wt.%Sn-1 wt.%Cu and Al-20wt.%Sn-wt.3%Si coatings according to the analysis of SEM and TEM images. The Sn particles coarsen greatly within the Al-12wt.%Sn-1wt.%Cu coatings annealed at 300°C for 5 hours, as compared with coatings annealed for 1 hour. The Ɵ’-phase (CuAl2) also precipitates in the Al-12wt.%Sn- 1 wt.%Cu coatings after annealing at 300°C. Annealing also causes fine scale Si particles to coarsen greatly in the Si containing alloy. The microhardness decreases in the annealed coatings for both alloys and is attributed to a coarsening of Sn particles and the release of residual strain within the as-sprayed coatings. As compared with the as-sprayed coatings and the coatings annealed at 300°C for 1 hour, the corrosion rate in 0.1M NaCI solution of Al-12wt.%Sn-1wt.%Cu coatings annealed at 450°C for 1 hour is very greatly reduced. However, an annealing temperature of ~450°C is not appropriate for these coatings because of the introduction of interlayer cracks and a coating / substrate reaction which might degrade the mechanical properties of the bearing.

The preparation, type and stability of emulsions stabilised solely by solid silica particles has been investigated in detail using a combination of conductivity, stability, light diffraction, optical microscopy and contact angle measurements. The wettability of the particles in situ at the oil-water interface plays a major role in such systems. The stability of aqueous colloidal dispersions in the presence of various electrolytes and over a range of pH is shown to be important in determining the stability of toluene-in-water emulsions formed from them. Partial flocculation of the silica dispersions enhances the emulsion stability whereas strong flocculation results in unstable emulsions. Inversion of emulsion type occurs via two mechanisms. Catastrophic inversion of water-in-oil emulsions stabilised by hydrophobic silica particles occurs upon increasing the volume fraction of water in the system. Transitional inversion of emulsions at fixed volume fraction of water has been achieved by varying the mass fraction of hydrophilic (or hydrophobic) particles in systems containing particle mixtures. Neither inversion mechanism exhibits hysteresis, in contrast to surfactant-stabilised systems. The energy of attachment of a particle to the oil-water interface is shown to be dependent on the contact angle and the interfacial tension. The contact angle was varied by changing the hydrophobicity of the silica particles. Particles of intermediate hydrophobicity were most effective at stabilising emulsions which is thought to be due to the contact angle at the oil-water interface being close to 90°. The interfacial tension was affected by changing the nature of the oil phase or by'replacing water with various polar liquids. Undecanol-water emulsions stabilised by silica particles of intermediate hydrophobicity break down via gel formation followed by coalescence. The wettability of the silica surface was varied in situ by varying the pH of the aqueous phase. Increasing the pH causes dissociation of silanol groups, which increases the affinity of the particles for the aqueous phase. The type and stability of emulsions and the contact angle of an aqueous drop under toluene on hydrophobically modified glass slides were measured as a function of pH. The results are modelled using simple theory. The wettability of hydrophobic pigment surfaces is dependent on the type and concentration of added surfactant. The findings are discussed in terms of surfactant adsorption at the relevant interfaces.

The work in this thesis is primarily aimed at supporting the NBe (Nuclear, Biological and Chemical) aspect of Crusader 21, the military clothing programme for the early 21st Century. This aims to produce a multi-purpose, systems-orientated combat ensemble for the UK Armed Services. Conventional "wet" techniques for chemically modifying fabrics have certain disadvantages, however employing plasma technology may provide a route for many novel "multi-functional effects" fabrics such as repellency against toxic chemical agents. In order to produce repellent coatings the surface must have a low surface energy. To obtain this, inert chemical groups need to be attached to the solid substrate. In addition to chemistry, surface roughness plays an important role in repellency. Liquid repellent surfaces have been produced by the pulsed plasma polymerisation of I H, 1 H,2H,2H -heptadecafluorodecyl acrylate. These films have chemical functionalities indicative of polymerisation occurring through the acrylate double bond, as shown by Infrared Spectroscopy analysis. Structural retention was optimised using experimental design techniques and resulted in a critical surface tension of wetting as low as 4.3 mN m-I (c.f. Teflon 18.5 mN m-I). Plasma deposition of a functionalised surface followed by reaction with a fluorinated alcohol proved less affective. Enhanced deposition rates for 1 H, 1 H,2H-perfluorododec-I-ene, over the saturated analogue, have indicated that polymerisation can occur during the off-time of the pulsed plasma period, via free radical polymerisation pathways. X-ray Photoelectron Spectroscopy (XPS) has indicated greater structural group retention for monomers containing double bonds. In order to obtain super liquid repellency the effect of surface roughness was investigated, where both commercially available rough surfaces and plasma roughened substrates were utilised. Once optimised, the rough surfaces were coated with 1 H, 1 H,2H,2H-heptadecafluorodecyl acrylate and produced super repellent films.

For many decades gas turbine engineers have investigated methods to improve engine efficiency further. These methods include advances in the composition and processing of materials, intricate cooling techniques, and the use of protective coatings. Thermal barrier coatings (TBCs) are the most promising development in superalloy coatings research in recent years with the potential to reduce metal surface temperature, or increase turbine entry temperature, by 70-200°C. In order for TBCs to be exploited to their full potential, they need to be applied to the most demanding of stationary and rotating components, such as first stage blades and vanes. Comprehensive reviews of coating processes indicate that this can only be achieved on rotating components by depositing a strain-tolerant layer applied by the electron beam-physical vapour deposition (EB-PVD) coating process. A computer program has been developed in Visual c++ based on the Knudsen cosine law and aimed at calculating the coating thickness distribution around any component, but typically turbine blades. This should permit the controlled deposition to tailor the TBC performance and durability. Various evaporation characteristics have been accommodated by developing a generalised point source evaporation model that involves real and virtual sources. Substrates with complex geometry can be modelled by generating an STL file from a CAD package with the geometric information of the component, which may include shadow-masks. Visualisation of the coated thickness distributions around components was achieved using OpenGL library functions within the computer model. This study then proceeded to verify the computer model by first measuring the coating thickness for experimental trial runs and then comparing the calculated coating thickness to that measured using a laboratory coater. Predicted thickness distributions are in good agreement even for the simplified evaporation model, but can be improved further by increasing the complexity of the source model.

Prosthetic cardiac valve surgery is a well-established technique, but the search continues for engineering materials with sup..e rior mechanical characteristics in order to extend the service life of the implant. The introduction of pyrolytic carbon was seen as a breakthrough in the development of wear resistant, non-thrombogenic materials for such applications. However, thrombo-embolic phenomena and the need for anticoagulation treatment following valve insertion remain the main problems associated with artificial materials in this application. The work carried out in this research has studied the haemocompatibility of a commercially available, wear resistant TiffiN/TiCfDLC multilayer structure, and a second TiN coating deposited by RF reactive sputtering of a titanium target in a ArIN2 environment, as candidate materials for a heart valve prosthesis. The structure of the RF deposited tiN coating was assessed as a function of deposition conditions, and was seen to develop a particular preferred crystallographic orientation. The nature of this texture was influenced by the condition of the underlying substrate. The effect of substrate condition on the biocompatibility of the tiN coating was studied by assessment of fibroblast attachment and spreading, and by haemolytic analysis of released haemoglobin. The results showed that the initial attachment and orientation of fibroblast cells was influenced by the substrate condition, but no influence on the degree of spreading and haemolytic nature was observed. Characterisation of the TiN coating and the components of the multilayer structure was carried out by Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), stylus profilometry and contact angle measurement. Haemocompatibility was studied by the interaction of the surfaces with plasma proteins, blood platelets and red blood ceUs. Cytotoxicity was studied using the MTT test. The degree of platelet activation on the surfaces correlated with their surface energy. The greatest degree of platelet spreading was observed on the more hydrophilic coatings. The lack of platelet activation seen on the DLC coating is attributed to its smooth surface and hydrophobic nature, resulting in higher levels of adsorption of anticoagulation proteins. The RF sputtered TiN coating caused significant levels of haemolysis and fibroblast cell death. None of the components of the multilayer structure caused such effects, although thrombus formation was observed to a degree on the Ti, TiN and TiC components of this structure. The toxic nature of the RF deposited TiN coating was not attributed to surface chemistry or roughness, but rather to a combination of the hydrophilic nature and the defect state of the surface.

This thesis describes investigations into a number of coating processes using experimental, analytical and computational techniques. The first problem, considered experimentally, is that of reverse roll coating with a liquid reservoir positioned directly above horizontally aligned rollers. Measurements of the film thickness as a function of the height of fluid in the reservoir and speed ratio are presented. When the wetting line is located downstream of the nip, either a decrease in the height of the associated hydrostatic head or an increase in the speed ratio causes a reduction in the thickness of the outgoing film. However, when the wetting line is located upstream of the nip the opposite is found to be true. The bead-break instability in forward meniscus coating is considered both experimentally and analytically. Agreement between predictions from a simple mathematical model of the stable bead and experimentally determined meniscus positions is seen to be excellent. A perturbation hypothesis is used to predict the onset of the bead-break instability, at which the upstream meniscus accelerates rapidly towards the downstream one, so the two collide and the bead collapses. The results from the model compare well with experiments. An outline of a method for using the bead-break instability as a design criterion is also presented. Typically in a slot, blade or knife coater the downstream meniscus is assumed to pin at a corner of the coating device. In chapter 5, a series of experiments and a corresponding computational study, are presented which illustrate that the meniscus can advance up the face of such coating devices (in this case a roll-flat plate system). Reducing the corner angle is seen to reduce the size of the climb region and the associated recirculation at this point at the downstream meniscus. It is also shown that the meniscus can detach from the corner and retreat into the gap, which can in turn give rise to the ribbing instability. An offset gravure coating arrangement is considered in chapter 6. The coating arrangement is split into two areas of study - the offset gravure nip and the kiss coating bead. An experimental investigation of the offset nip with the two rolls vertically aligned and running at the same speed in forward mode reveals two ways in which the metered film thickness can be influenced. Either increasing the nip force by pressing the two rolls together or decreasing the roll speeds causes a reduction in the metered film thickness. At higher speeds the metered film thickness is observed to asymptote to a limiting value, the value of which depends on the gravure pattern. The reverse mode kiss coating bead operating at speed ratios greater than one is also investigated. Experiments reveal that under these conditions, all the fluid is transferred from the roll surface to the web and the two make contact due to the generation of a sub-ambient pressure field within the bead. Two models based on lubrication theory are derived, one assuming an infinitely tensioned web and a second that incorporates the effect of web flexibility. The latter is found to give much better agreement with the experimental data. Finally a perturbation hypothesis is applied to these to models in order to predict the onset of the ribbing instability, both of which are found to give reasonable agreement with the experimental data. Finally, the results of a systematic experimental investigation of reverse mode direct gravure coating is reported, where the web runs directly over a gravure roll surface. This wide ranging parametric study illustrates the effect of the operating parameters on the final film thickness. Key findings are that speed ratio, fluid properties and cell shape and size can significantly influence the final film thickness. For a fixed roll speed it is observed that as the web speed is increased the gravure bead becomes unstable. This results in streaking on the web, and gives an upper limit to the speed ratio.

Alkyd emulsions are currently being developed for coating applications. These paints combine the technical advantages of alkyd polymers, which give coatings of a high gloss finish, with the environmental and health benefits of solvent-free systems. Nonetheless, the drying and film formation of these systems involve several steps, none of which is well understood yet. These include creaming or sedimentation, evaporation of the continuous water phase, coalescence of the alkyd droplets, a possible phase-inversion, and the oxidative cross-linking of the alkyd polymer to form a hard coating. In this thesis. Magnetic Resonance Microscopy is used to investigate the film formation of alkyd emulsion coatings. As the process is complex, studies on a different range of emulsions and related systems are performed to gain further insight into the different steps involved. A combination of Liquid State Microscopy, diffusometry and broad line imaging (Stray Field Magnetic Resonance Imaging) is employed, and it is shown that this combination provides results extremely rich in information. First, a study of the cream layer and the creaming dynamics of model bulk oil-in-water emulsions containing different concentrations of thickener is presented. The experimental data are compared to the predictions of a numerical model, and evidence is gained that the presence of the thickener induces flocculation according to a depletion mechanism. Then, the water evaporation from alkyd emulsion droplets is investigated and the water concentration across the droplet is modelled according to an original model based on lateral diffusion of water. There is no evidence from spectroscopy and diffusometry for phase-inversion during the drying of alkyd emulsion coatings. Finally the cross-linking of alkyds containing driers is found to be non-uniform across the film thickness.

A detailed study has been made of the atmospheric pressure chemical vapour deposition (CVD) of tungsten carbide coatings onto powder metallurgy (PM) BT42 grade high speed steel (HSS) indexable cutting tool inserts. The pyrolysis of tungsten hexacarbonyl (W(CO)6) deposition route was utilised in conjunction with a laboratory-scale hot-wall CVD reactor. After numerous coating runs, deposition conditions were established under which rudimentary tungsten carbide coatings could be deposited at 350°C. The characteristics of these coatings were determined using an established characterisation procedure. This involved the following techniques: X-ray diffraction, ball cratering, Auger electron spectroscopy (AES), optical microscopy, fractography/scanning electron microscopy (SEM), profilometry, scratch adhesion testing and micro-indentation hardness testing.