| In this research, the effect of precursor (metal vs oxide) and heating rate on the MnCo2O4 spinel formation was studied. The research objective was to synthesize porous and well-bonded MnCo 2O4 cubic spinel for cathode-side contact layers in intermediate temperature solid oxide fuel cells and to develop a mechanistic explanation for the high sinterability observed at reduced temperatures for the cobalt metal containing precursor mixtures.;A variety of metallic and oxide precursors with different particle sizes were examined for their effect on phase and microstructural evolution with X-ray diffraction, thermogravimetric analysis -- differential scanning calorimetry, optical microscopy and scanning electron microscopy. It was found that for manganese metal precursors a small particle size was critical to single-phase synthesis, whereas manganese oxide precursors were universally synthesized to MnCo2O4. Contact layer bonding depended upon the cobalt precursor used; contact material synthesized from cobalt oxide precursors demonstrated negligible sintering and interparticle bonding, whereas cobalt metal precursors were shown to densify and bond the contact layer. The critical importance of cobalt metal precursors for the synthesis of well-bonded contact layers was demonstrated by testing of interfacial bond strength and area-specific resistance. The heating rate, on the other hand, was found to have no effect on the sintering behavior and the contact layer properties.;Single-phase formation was achieved via cobalt volumetric expansion and oxide intergrowth during oxidation, followed by diffusion of cobalt and manganese cations above 800°C. It is proposed that other spinel compositions may also be synthesized by the use of metal precursors which experience volume expansion and oxide intergrowth during oxidation. |
