Microwave combustion synthesis of Co-Ni aluminate spinel for electrophoretic deposition

Aluminate spinels represent a versatile class of functional materials with potential in catalytic, electronic, and protective coating applications, yet the research on room-temperature, rapid and tunable techniques to form such ceramic coatings remains limited. In this study, Co0.4Ni0.6Al2O4 powders were synthesized using a microwave-assisted combustion method, so as to examine the influence of different fuel-to-oxidizer (F/O) ratios on combustion behavior, phase formation, and product yield. The results demonstrate that an excess of the fuel leads to localized overheating, carbonaceous residues, and secondary phases, whereas an insufficient amount of fuel results in weak combustion and incomplete crystallization. Among the tested formulations, an F/O ratio of 0.5 produced a highly crystalline spinel phase with no detectable impurities and provided the highest yield, confirming its suitability for efficient spinel formation. The optimized powder was subsequently evaluated for its applicability in electrophoretic deposition (EPD) using an ethanol suspension. Spinel coatings were successfully deposited on SUS 304 stainless steel substrates after different intervals of time. After calcination, ceramic layers were obtained, demonstrating the feasibility of integrating microwave-combusted Co–Ni aluminate spinels into the EPD process. The data revealed that the deposition yield increased steadily with time, while the deposition rate declined, consistent with the characteristic EPD kinetics. This work provides a deeper understanding of the synthesis–deposition pathway and offers foundational insights for the future optimization of Co–Ni aluminate-based ceramic coatings.