Preparation and sintering behaviour of spinel-type Co xNiMn 2− xO 4 (0.2 ≤ x ≤ 1.2) by the ethylene glycol–metal nitrate polymerized complex process

Abstract

Spinel-type powders of composition Co x NiMn 2− x O 4 (0.2 ≤ x ≤ 1.2) were prepared by auto-combustion of ethylene glycol–metal nitrate polymerized gel precursors. A pure spinel-type phase, with no intermediate compounds, was attained from the burning of the polymerized gel precursor and subsequent calcining at 600–700 °C. The formation, the structural evolution of the spinel-type phase, and calcined powder characteristics have been studied by using different techniques, having found that the properties were strongly dependent of the chemical composition. Sintering of the Co x NiMn 2− x O 4 powders have been studied by both the constant rate of heating (CRH) and the conventional ramp-and-holding methods. Density increased with the increasing of the Co content, and theoretically dense bodies (≥99.9% of the theoretical density) with submicronic average grain sizes were obtained at a temperature as low as 1050 °C for 6 h in the case of the Co 1.2NiMn 0.8O 4 composition. Above that temperature, a slow bloating phenomena as consequence of the evolution of oxygen gas with the corresponding decreasing in density, and the beginning of an exaggerated grain growth in the sintered samples was present. Microstructure of the sintered samples has also been studied.