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The removal of hexavalent chromium Cr(VI) from aqueous solutions is successfully achieved over the new hetero-system La 2 NiO 4 /TiO 2 at pH~4 under solar light. La 2 NiO 4 was found to be a direct band gap semiconductor with an optical transition of 1.30 eV. The photo-electrochemical characterization of the sensitizer La 2 NiO 4 is undertaken to predict the electrons injection in TiO 2 which acts as electrons Bridge to adsorbed HCrO 4 −. This compound presents a p-type semiconductor with a flat band potential of 0.18 V SCE - more cathodic than that of TiO 2 . The photoactivity is strongly enhanced in the presence of oxalic acid as hole scavenger. The saturation is due to Cr3+ oxidation by photoholes and the competitive water reduction. The reutilization shows a negligible deactivation effect and the hetero-system could be promising for increasing the quality of water.

Plasma spraying is mainly employed for surface treatment providing coating for protection of materials against wear, erosion and corrosion. Improving coating quality requires a better understanding of the behavior of the arc created inside the direct current arc plasma torches. The present work is devoted to the determination of plasma torch parameters using an analytical calculation on the cathode spot parameters. A model of a heat transfer in the cathode spot on an electrode in the arc discharge is developed and analytical expressions for the spot radius and temperature as functions of basic characteristics of the discharge and the electrode material are obtained. The dependence of the spot radius on the time, the cathode drop voltage and current is investigated. The sequence of calculation of voltage-current characteristics of DC arc plasma torch is proposed. It is shown that the Steenbeck model of arc discharge in cylindrical channel makes it possible to carry out this calculation.