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.

The suspension plasma spraying using a liquid as material feedstock is a promising technique to elaborate thin and nanostructured coatings. This work deals with the study of suspensions in order to obtain specific microstructural coatings. The slurries were prepared starting from nanosized titania powders. Distilled water and alcohol were used as solvents and appropriate dispersing agents were employed to stabilize the suspensions. An external injection system that ensures the atomisation and radial injection of the suspension into Ar-H 2 plasma under atmospheric conditions was designed. The coatings were characterized by scanning electron microscopy and differences in the microstructure of the deposits were observed. Efforts were made to understand the relationship between liquid feedstock properties, injection/plasma parameters and coatings microstructural characteristics.

TiO 2 and TiO 2 -Al composites coatings were prepared by plasma spraying using a reconstituted nanosized feedstock via a spray drying method. Effects of various spray conditions on the microstructure, porosity, microhardness and wear resistance related to the mechanical performance of coatings were evaluated. The coatings sprayed at relatively low plasma power were composed of two distinct microstructures of well defined lamellar structure, similar to microstructure of conventional plasma sprayed coatings typically observed from fully melted particles, and embedded nano or sub-micron particles originated from partial/non-molten particles of feedstock materials. The fraction of partial/non-molten particles in coating layers was increased by Al additive. Such a characteristic of blended microstructure of coatings was clearly confirmed from a bimodal distribution of microhardness described by Weibull plots. The optimized addition of Al into TiO 2 improved mechanical properties such as microhardness and wear resistance.

Titanium dioxide (TiO 2 ) is an attractive material for numerous technological applications such as photocatalytic applications. The photocatalysts allow the environmental purification of air and water by the decomposition of toxic organic compounds and removal of harmful gases. This work was focused on the production and evaluation of the environmental properties of titanium dioxide coatings obtained by the plasma spray technique. To carry out the step of validation of the TiO 2 coatings for their environmental functionalities, a control test of the photocatalytic effectiveness was performed with respect to nitrogen oxides. A custom-designed test chamber has been developed. The photocatalytic properties of different coatings were studied as a function of various parameters (porosity, anatase/rutile ratio, nature of the substrate).