COPRECIPITATION SYNTHESIS OF DOPED LANTHANUM CHROMITE

Two coprecipitation methods were used to synthesize powder precursors of doped lanthanum chromite (La, Ca)(Cr, Co)O3. The effects of synthesis method and calcination temperature on the composition, sintered density, and microstructure of pressed compacts of (La, Ca)(Cr, Co)O3 were studied by differential thermal analysis/thermogravimetric analysis, x-ray diffraction, scanning electron microscopy, and density measurement. The cation ratios in the precipitated solids were, with few exceptions, within experimental error of the desired compositions for all four components. Powders obtained by both techniques could be sintered to densities exceeding 93% at 1400-degrees-C. The highest densities were obtained with calcining temperatures from 450 to 700-degrees-C. The sintered microstructures exhibited uniform grain sizes averaging 3-5 mum. The Cr(VI) compounds, CaCrO4 and La2CrO6, were observed in all of the calcined powders. The possible role of these phases on chromite densification is discussed.