Resumo:
In this work, ferritic stainless steel 444 was coated with ceramic films of MnCo2O4 and MnFe2O4 for application as interconnects in Solid Oxide Fuel Cells (SOFCs) through indirect brazing. The synthesis of the spinel-structured oxides MnCo2O4 and MnFe2O4 was evaluated via microwave hydrothermal technique, using low values of time and temperature. The synthesis parameters aimed to produce ceramics with the lowest resistivity. Only the cobaltite samples synthesized at 100 and 130°C for 5 minutes achieved a single phase; other synthesis parameters resulted in phases originating from intermediate reactions. After sintering, samples synthesized at 130°C for 5 minutes showed the lowest conductivity values: 669.7 Ω⁻¹cm⁻¹ and 6513.7 Ω⁻¹cm⁻¹ at 200°C for ferrite and cobaltite, respectively. The chosen ceramics were impregnated with titanium metal via wet impregnation to improve the interaction between the ceramic and the brazing alloy, enhance electrical resistance, and achieve a closer thermal expansion coefficient to that of the base metal to be coated. The wet impregnation process using TiH2 as the metal source proved feasible for both ceramics, resulting in ceramic particles “decorated” with titanium particles, as confirmed by the reduction in their band gap energy. The use of a brazing alloy with a melting temperature of 700°C limited the sintering temperature of the films, preventing the achievement of film densification values and the establishment of metal/ceramic bonding points, both with and without impregnation. The use of metal impregnation techniques proved possible in this work and is a promising method for applications not only in metal/ceramic joining but also in areas such as photocatalysis, electrocatalysis, and sensor fabrication.
