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Cathodic disbandment is a major mode of failure of organic coatings during cathodic protection. In this thesis factors influencing the rate of cathodic disbandment and the failure mode of cathodic disbandment of two polymer systems have been investigated. The polymer systems chosen were a chlorinated rubber and a polyamine cured epoxy on mild steel substrates. The interfacial chemistry of disbandment has been studied by X-ray photoelectron spectroscopy (XPS). The application of acoustic emission to monitor the progress of cathodic disbandment was also studied. The disbandment process of the chlorinated rubber and the epoxy polyamine coatings during cathodic polarisation in alkali metal chloride solutions has been shown to be electrochemical in nature. The disbandment of the coatings is primarily caused by attack of the coating/substrate interfacial bonds by the hydroxyl ions generated on the substrate surface under the disbanded coating. The disbondment rate of both coatings tested is controlled by the following factors: coating thickness, applied cathodic potential, electrolyte, electrolyte concentration of the test solution, surface treatment of the substrate, and the nature of the coating. The surface treatment of the substrate has a substantial effect on the disbandment rate; it not only changes the actual area of the interface where cathodic disbandment occurs but also changes the resistance to cathodic disbandment. The initiation of the cathodic disbandment is found to be mainly controlled by a process involving water permeation through the coating. However, the initiation is also influenced by other factors controlling the disbandment rate, such as surface treatment of the substrate, the electrolyte in the test solution.

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No description available.

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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.

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.

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

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. Cr. N 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 Cr. N; 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 Cr-N. 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 Cr. N coatings.

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<plre"'te size ratio was also studied and found to have a noticeable effect , on the phase behaviour of the mixtures. SANS results showed a larger increase in the density fluctuations of the spheres at higher size ratios, and these fluctuations are a precursor to phase separation. Increases in the size ratio led to phase separations of the mixtures occurring at lower colloid volume fractions. This is due to an increase in the effective attraction between both particle types when mixed together. The main conclusion of the thesis is that mixtures of colloidal spheres and plates tend to phase separate, even at low concentrations of the particles. The phase separation is driven by . entropy. This is in contrast with observations in the coating industry where such mix- tures supposedly remain intimately mixed. Presumably these systems are at sufficiently high concentrations to be dynamically arrested.