Preparation of composite powder based on nano-TiO2 and Cr2O3 using a spray dryer, for atmospheric plasma spraying, designed for HPAL systems

In this study, composite coatings based on TiO₂ and TiO₂–Cr₂O₃ nanopowders were fabricated by air plasma spraying for High-Pressure Acid Leaching (HPAL) systems. Nanopowders were agglomerated in aqueous medium using polyvinyl alcohol and spray-dried into spherical granules. Coatings were deposited onto 12Kh18N10T stainless steel substrates. X-ray diffraction (XRD) analysis revealed rutile TiO₂ and Cr₂O₃ as the main crystalline phases, with minor Ti₂O₃. For TiO₂-only coatings, the XRD pattern showed predominantly rutile (R-TiO₂) and a small amount of anatase (A-TiO₂); brookite was absent. Rutile formation is attributed to high plasma spraying temperatures that promote anatase-to-rutile transformation. The coatings had dense microstructures with low porosity due to optimized powder preparation and spraying. Microhardness of TiO₂–Cr₂O₃ coatings reached 1015 HV, 40% higher than pure TiO₂ (723 HV). Tribological tests under a 3 N load and 500 m sliding distance showed a reduced friction coefficient from 0.98 to 0.65. The wear rate of TiO₂–Cr₂O₃ coatings was 4.2 × 10⁻⁵ mm³/N·m, indicating enhanced wear resistance. These findings demonstrate that Cr₂O₃ addition and optimized powder processing yield harder, denser, and more durable coatings, suitable for harsh service conditions.