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.

Al 2 O 3 -TiO 2 materials are very attractive materials for the manufacturing of wear resistant ceramics coatings. Moreover, nanostructured coatings show superior properties (higher hardness and enhanced fracture toughness) as compared to their counterparts containing microscale grains. The aim of this study is to produce nanostructured Al 2 O 3 -TiO 2 coatings through the plasma spraying technique that can lead to metastable transformations. The starting powders containing 13wt% and 44wt% of titania, have been mechanically activated by high energy ball milling with a planetary mill, (Model P4 by Fritsch, Germany) using steel vials and balls in such conditions to obtained the high pressure TiO 2 II phase. The milled powders were then plasma sprayed with an Ar:H 2 gas mixture, by varying the plasma parameters (gas flow rates, nozzle diameter, aggregates size). The effect of the milling and the spraying conditions on the crystalline phases and the microhardness of the coatings are evaluated.

This paper deals with the elaboration of titanium dioxide coatings designed for photocatalytic applications, obtained by suspension plasma spraying (SPS), an alternative of the atmospheric plasma spraying (APS) in which the material feedstock is a suspension of the powder to be sprayed. Two different TiO 2 powders were dispersed in distilled water and ethanol and injected in Ar-H 2 or Ar-H 2 -He plasma under atmospheric conditions. SEM and XRD analysis were performed to study the microstructure and surface features of the titania coatings. Photocatalytic efficiency of the elaborated samples was evaluated from the conversion rate of different air pollutants: NOx and SO 2 . The present results showed that the suspension plasma spraying allows to produce reactive surfaces for the removal of air pollutants that in the same working conditions, present a higher photocatalytic activity compared to that of the initial raw powders.

In this paper, the modified method of plasma spraying using liquid suspension feedstock was used to elaborate thin titanium dioxide coatings. TiO 2 Degussa P25 powder were dispersed by continuous stirring in distilled water and alcoholic solutions and injected in an Ar-H 2 or Ar-H 2 -He plasma plume under atmospheric conditions. Scanning electron microscopy and X-ray diffraction were performed to study the microstructure and crystalline phases of titanium dioxide coatings. The anatase content in the elaborated TiO 2 deposits strongly depended on the type of the suspension solvent. The photocatalytic activity of the titanium dioxide coatings was evaluated from the conversion rate of nitrogen oxides and compared with that of the initial powder. The obtained results allowed to affirm that the method of the liquid plasma spraying proved to be a promising technique to elaborate photocatalytic TiO 2 coatings for the removal of nitrogen oxides pollutants.

Titanium dioxide (TiO 2 ) has emerged as an excellent photocatalyst material for environmental purification about two decades ago. In order to avoid the use of TiO 2 powder, which requires later separation from the treated liquid, few researchers reported on ways of fixing TiO 2 . In these cases, many difficulties must be overcome such as maintaining the photoactive anatase phase as well as the mechanical stability and avoiding the mass transfer limitations. Thermal spraying seems to be an appropriate process to provide ceramic coatings exhibiting such characteristics. The present work assesses the influence of several spray parameters on the morphology of deposits, dominated by two void systems – interlamellar pores and interlamellar cracks – and on their crystalline structures. TiO 2 was atmospherically plasma sprayed by systematically varying the process conditions including torch power, plasma gas mixture Ar/H 2 and Ar/He, and cooling device. An analytical procedure based on XRD patterns was established for the determination of the relative amounts of anatase and rutile in the coatings. An Ar/He mixture as compared to an Ar/H 2 one seems to enhance the formation of anatase from 38vol% to 44vol%. In both cases, a reduction of the plasma power increases the amount of anatase. Several methods of porosity determination were performed: image analysis, Archimedean porosimetry and calculation from phases, mass and thickness. Generally, the results indicate a total porosity varying between 15 and 25% depending on the spraying conditions.