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Properties of suspension plasma sprayed zirconia coatings using different plasma torches

Abstract : In this PhD thesis several scientific issues regarding Suspension Plasma Sprayed (SPS) zirconia coatings were studied. The coatings were analyzed mainly in terms of the application as insulating top-coat of Thermal Barrier Coatings (TBC’s). These multilayer coatings are applied onto the metallic parts of e.g. gas turbines to protect them against high temperature loads caused by the hot exhaust gases. But the initial assessment of the possibility of the use of Suspension Plasma Spraying to produce electrolyte layer in Solid Oxide Fuel Cells was done also. SOFC’s seem to be the most promising fuel cell types currently. (See Chapter 1-2 with the literature review) The first important research goal was to analyze the possibility of producing coatings being various in terms of the microstructure. The main aim was to obtain coatings characterized by very porous and irregular structure (called columnar-like) but also very dense and homogeneous coatings with typical two-zones microstructure. For this purpose two zirconia powders were used: (i) fully yttria-stabilized zirconia and (ii) ytrria-ceria-stabilized zirconia. The powders had different chemical composition, particle size and morphology. These powders were used for a suspension formulation. The other variable in the spray process was suspension concentration. The suspension with a solid content in range of 2.5 and 30 wt. % were prepared and sprayed. All suspensions were home-produced. A very important concept of this work was the use of four various, commercially-available, plasma torches, namely: (i) SG-100, (ii) TriplexPro-200, (iii) Axial III and (iv) WSP-H 500. The torches were different interms of design, electric power, plasma stabilization mode and the suspension injection angle. Due to the big differences between plasma torches and SPS set-ups the spray process parameters were chosen in each case individually. The last variable in theexperiment design was the topography and roughness of substrate in order to evaluate its influence on the coatings growth-up mechanisms. The substrates were prepared prior to spraying by: (i) grit-blasting, (ii) laser-treatment and by (iii) grinding. The wideii spray experiment allowed complex analysis of SPS coatings microstructure, coatings growth-up mechanisms and the development of SPS process itself. [...]
Keywords : SPS
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Pawel Sokolowski. Properties of suspension plasma sprayed zirconia coatings using different plasma torches. Materials. Université de Limoges, 2016. English. ⟨NNT : 2016LIMO0133⟩. ⟨tel-01953309⟩

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