Plasma spray deposition of Al-Al2O3 coatings doped with metal oxides: catalytic applications

Al-Al2O3 (70% γ-phase) coatings 30–50 μm thick well-adhered to the steel sheets and with a highly developed surface area (100–120 m2 g−1) were formed employing plasma-spray technology at atmospheric pressure in air. The plasma-gun with two sequential powder feeders was developed offering the ability to control particle trajectories through the plasma flame, and thus their thermal history. The Al powder is mainly melted and oxidized. Al(OH)3 powder passes through the plasma torch with partial dissociation and is incorporated in the matrix of growing film with subsequent decomposition during thermal annealing at 560°C for 90 min. The good adhesion results are explained by the surface pre-treatment effects taking place on the periphery of the plasma torch moving along the surface of steel sheets. The plasma sprayed Al-Al2O3 coatings doped with CuO and Cr2O3 oxides showed characteristic catalytic combustion behaviors.