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.

The structure of two-component coatings codeposited by magnetron sputter ion plating was studied. This apparently simple topic has never been studied tematically and has led to a number of unexpected and very interesting results.

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.

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.

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.

Certain technologically advanced coating systems for defence use require organic binders with elevated infrared (IR) transparency. This thesis comprises the first phase of a study to try and produce materials which meet these requirements. A materials evaluation programme was completed using preordained selection criteria. An in-depth study was made of one family of the shortlisted candidate materials: linear poly(methoxy-cyanurate)s. These thermally stable polymers were prepared by phase transfer polymerisation of dichlorotriazines with aromatic bisphenois. The samples were analysed by differential scanning calorimetry, thermogravimetric analysis, elemental analysis and nuclear magnetic resonance spectroscopy. The transparency of the materials was determined using a hemispherical directional reflectometer. At thicknesses of 50 mum, the spectral emissivity of the linear poly(methoxy-cyanurate)s was of the order of 0.25 between 3 and 5 mum and 0.65 between 8 and 12 mum. The linear poly(methoxy-cyanurate)s typically underwent major decomposition at temperatures greater than 300 °C in nitrogen and air. These new materials are more transparent and thermally stable than the poly(urethane) binders currently used in many defence coatings. However, spectral data and model compound studies suggest that poly(methoxy-cyanurate)s isomerise at temperatures above 200 °C. This is contrary to the hypotheses of other workers in the field. Computer simulation methods, evaluated in the course of the study, were used as an aid to assignment of IR spectra and to investigate strategies for improving upon the IR transparency of the poly(methoxy-cyanurate)s between 8 and 12 mum. Novel linear poly(methoxy-thiocyanurate)s and terpoly(methoxy-cyanurate-thiocyanurate)s were prepared to try and improve upon the thermochemical stability and spectral transparency of the simple cyanurate polymers. These materials were characterised using the methods listed above. All steps which were taken to try and improve the spectral transparency of the polymers between 8 and 12 mum failed due to problems with overlapping bands. In light of the project findings, certain material selection criteria have been modified. Suggestions for future research based on these new guidelines are made at the end of the thesis.

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.

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 gives an account of an extensive experimental investigation of the operation of a twin roll coater. Two distinct modes of operation are identified: Classical (fullyflooded inlet) and Meniscus (ultra-starved inlet). The former has been the subject of investigation for a number of years; the latter is less well known and would appear to have escaped the attention of the Coating Community at large prior to the research work reported here being carried out. A detailed description of how the key features of an industrial roll coater can be reproduced using a piece of simple but well designed experimental apparatus, which encapsulates all the necessary elements for an in-depth study of the flow, is presented. Various methods are used to visualise the flow. These include dye injection and novel computerised particle tracking techniques, coupled with state-of-the-art image processing and High Speed Video photography. Experiments reveal that the flow associated with the Classical mode of operation is essentially one-dimensional throughout the nip; Meniscus coating flow, on the other hand, is uniquely two-dimensional, containing large vortical structures. Also the pressure distributions are found to be quite distinct. A fully-flooded nip results in a pressure profile which exhibits a characteristic maximum and minimum, while an ultra-starved nip produces one which is linear and entirely sub-ambient. The transformation of the flow from one mode of operation to the other is then considered, a key feature of which is the behaviour of the upstream free surface which movesin to a minimum point and then out again as the flux is reduced, giving a non-singular result, that is, there are two non-dimensional values of the flux for each free surface position. Finally, the subject of instability in roll coating is addressed, for both the Classical and Meniscus regimes. A number of new instabilities were observed using High Speed Video photography and tentative explanations for their occurrence are given.