Browsing by Author "Seraffon, Maud"

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    Assessment of Coating Performance on Waterwalls and Superheaters in a Pulverised Fuel-Fired Power Station
    (Springer, 2017-01-11) Simms, Nigel J.; Seraffon, Maud; Pidcock, Andrew; Davis, Colin
    Protective coatings offer one route to increase the lives of heat exchangers in pulverised fuel power plants. A range of candidate coatings have been exposed on the waterwall and superheaters of a 500 MWe UK power station unit for periods of up to ~4 years (24,880 operating hours), during which time this unit was fired on a mixture of UK and world-traded coals. Both nickel- and iron-based candidate coatings were included, applied using high velocity oxy-fuel or arc-wire process; a selection of these also had a surface sealant applied to investigate its effectiveness. Dimensional metrology was used to evaluate coating performances, with SEM/EDX examinations used to investigate the various degradation mechanisms found. Both the waterwall and superheater environments generated their characteristic corrosion damage morphologies which depended on the radial positions around the tube. Coating performances were found to depend on the initial coating quality rather than composition, and were not improved by the use of a sealant.
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    Low temperature ITO thin film deposition for solar cells
    (Cranfield University, 2008-09) Seraffon, Maud; Impey, Susan A.; Lawson, K. J.; Rao, Jeff
    The electrical and optical properties as well as the microstructure of indium tin oxide thin films deposited on glass and flexible substrates is demonstrated in this project report. This project is a part of an MSc in Advanced Materials at Cranfield University. The understanding and improvement of indium tin oxide coatings deposited by magnetron sputtering on both glass and polymer substrates has been an area of extensive research in the last decade. This technology appears to be very interesting in terms of money saving and efficiency in the solar cell domains where the coatings are used in thin film solar cells. Research into the thin film solar cells mechanism, the sputtering process and ITO coatings is reported, along with detailed consideration of the best results obtained in the past in terms of ITO films’ electrical and optical properties. ITO thin films were deposited on glass and different sputtering parameters were changed in order to investigate their influence on the coatings properties: film thickness, chamber pressure, rotation, oxygen amount and sputtering power. A decision was made to establish the best sputtering parameters. These parameters were set to deposit ITO on polyethylene terephthalate (flexible substrate). The samples were also annealed at 150°C and 370°C. An ITO thin film with a resistivity of 1x10-4 Ωcm and a 90% transmissivity was obtained. An Energy Dispersive Spectrometry analysis was finally made on samples showing a substoichiometric composition of the ITO films.
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    Performances of air plasma sprayed thermal barrier coatings for industrial gas turbines
    (Cranfield University, 2012) Seraffon, Maud; Nicholls, J. R.; Simms, Nigel J.
    Future industrial gas turbines will be required to operate at higher temperatures to increase operating efficiencies and will be subjected to more frequent thermal cycles. The temperatures that the substrates of components exposed in the harshest environments experience can be reduced using air-cooling systems coupled with ceramic thermal barrier coatings (TBCs); however, few studies have been carried out at the substrate temperatures encountered in industrial gas turbines (e.g. 900 – 1000 °C). Better understanding of their behaviour during service and, their various potential failure mechanisms, would allow more accurate prediction of TBC lifetimes and improve coatings. The aim of this research, as a part of the Supergen Plant Life Extension (PLE) project, was (a) to investigate the influence of industrial gas turbine blade geometry on TBC system lifetimes, and (b) to extend knowledge on the effect of bond coat composition on the oxide growth at temperatures below 1000 °C. The main results of this thesis, obtained using mass change and characterisation techniques, increase the understanding of the significant interactions between the different coating layers, samples’ geometry, interdiffusion and failure mechanisms involved during oxidation. Curvature was found to affect the quality of manufacture and thus promoted premature failure at the convex features of modified aerofoil-shaped samples. In parallel new bond coat compositions, suitable for industrial gas turbines were suggested from the wide range investigated in oxidation exposures. The selective growth of protective Cr2O3 or Al2O3 oxides or other mixed oxides was observed and mapped in ternary diagrams. Furthermore two novel techniques were successfully used during this project. Pulsed flash thermography proved to be efficient in identifying areas of sub-surface TBC delamination non-destructively. Magnetron co-sputtering using 2 and 3 targets was found to be a flexible method to deposit thick coatings with a wide range of compositions.