SYNTHESIS AND CHARACTERIZATION OF Y2O3-ZRO2 AND Y2O3-CEO2-ZRO2 PRECURSOR POWDERS

Thixotropic gels of the precursor powders of the titled compounds have been prepared by the addition of oxalic acid to the mixed solutions o f metal salts at room temperature (approximate to 27 degrees C). The c lear sols of yttrium-zirconyl oxalate (YZO) and yttrium-cerium-zircony l oxalate (YCZO) gelled within a few hours and were oven-dried at 40 d egrees C. The various stages of gelation behaviour of the sols are exp lained on the basis of DLVO theory. By repeptizing the dried gel powde rs with water, concentrated sols were prepared. The gelation time as a function of chloride ion concentration is discussed for both sols. Th e nature of the temperature dependence of the dried gel powders was st udied by means of thermogravimetric analysis and differential thermal analysis. Powder X-ray diffraction was used to study the crystallizati on behaviour of the dried amorphous gel powders. It is found that thes e powders crystallize in tetragonal phase when calcined at 850 degrees C for 1 h. Estimation of surface area and infra-red characterization have also been carried out for the prepared powders. (C) 1996 Elsevier Science Limited