Phase Transformations of Electrochemically Prepared Precursors of the TiO2–ZrO2–Y2O3 and TiO2–Al2O3–ZrO2–Y2O3 Oxide Systems

This paper reports on the preparation of precursors of mixed oxide systems by an electrochemical process based on anodic dissolution of titanium in an electrolyte containing Cl^–, NO^3–, Al³⁺, Zr⁴⁺, and Y³⁺ ions in the presence of OH^– ions electrogenerated on a cathode, interaction of electrode reaction products, their hydrolysis, and coprecipitation of hydrolyzed species. Synthesis was carried out in a coaxial diaphragmless electrochemical reactor having electrodes differing considerably in area and resulted in the formation of primary particles of precursors to oxide phases through hydrolysis, polycondensation, and crystallization. The proposed approach allows complex titania-based systems to be prepared in the form of anatase and brookite phases stable in the temperature range 80–550°C, and the addition of Al³⁺ ions leads to the formation of the boehmite phase, which undergoes no changes up to 550°C. Heat treatment of the precipitates at 1100°C raised the degree of crystallinity of the samples, and all of the synthesized oxide systems were found to contain the rutile phase (TiO₂) and the mixed oxide TiZrO₂. The formation of Ti₂Y₂O₇ makes it possible to stabilize the cubic zirconia phase formed during the electrolysis process, which ensures high mechanical strength, corrosion resistance, and sinterability of ceramic particles based on alumina- and yttria-modified titania and zirconia.