A certain level of porosity is always presented in thermal spray ceramic coatings. LPPS or some specific APS processes can allow to reduce it but it is difficult to obtain coatings with a low thickness (less than 100 m) which are fully gas-tight because of cracks or interconnected pores. This gas-tight property is for example very suitable for the ceramic electrolyte of solid oxide fuel cells (SOFC). Some ZrO 2 -Y 2 O 3 coatings were obtained by the VLPPS process, a LPPS system operating at a pressure of about 100 Pa. The specific structure of these coatings is a mixture of condensed vapors and splats. The results are very satisfying because ZrO 2 -Y 2 O 3 coatings with a thickness of about 70 micrometers are tight under a hydrogen pressure of 2x105 Pa. This paper presents some ZrO 2 -Y 2 O 3 coatings obtained by different processes (APS, LPPS and VLPPS) and their properties.

In this paper a comparative study on the microstructure and photocatalytic performances of titanium dioxide coatings elaborated by various thermal spraying methods (plasma spraying in atmospheric conditions, suspension plasma spraying and high-velocity oxy-fuel spraying) was proposed. Agglomerated spray-dried anatase TiO 2 powder was used as feedstock material for spraying. Morphology and microstructural characteristics of the coatings were mainly studied by scanning electron microscopy and X-ray diffraction. The photocatalytic behavior of the TiO 2 -based surfaces was evaluated from the conversion rate of gaseous nitrogen oxides (NOx). It was found that the crystalline structure strongly depended on the technique of thermal spraying deposition. Moreover, a high amount of anatase was suitable for the photocatalytic degradation of the pollutants. Suspension plasma spraying permitted to retain the original anatase phase and to obtain very reactive TiO 2 surfaces for the nitrogen oxides removal.

Very low pressure plasma spraying (LPPS) is the objective of numerous studies for the past years. However, numerical simulations and experiments revealed some difficulties such as the presence of successive expansions and constrictions of the plasma jet that has an influence on the deposition efficiency and on the coating structure. Optimization of the plasma gun is thus required and the use of bell-contoured De Laval nozzle extensions seems particularly promising. In this paper, new developments concerning the use of an in-house bell-contoured nozzle extension are presented and both numerical calculations and experiments were performed.