Preparation of spherical, monosized Y 2O 3 precursor particles

Abstract

Spherical, monosized yttria precursor particles were obtained by homogeneous precipitation in aqueous solutions by reaction with the thermal decomposition products of urea. Increasing [Y 3+ above 0.05 M resulted in a deviation from spherical morphology and caused agglomeration of particles. Over the concentration range studied, excess urea did not affect particle morphology, but increased the yield. Increasing aging time appeared to increase particle size as well as to improve yield, as long as the urea was not depleted. The approximate chemical composition of the precipitate was YOHCO 3. The YOHCO 3 particles formed were amorphous to X-rays, and underwent a two-stage thermal decomposition, first forming Y 2O 2CO 3 near 180°C, and then cubic Y 2O 3 above 610°C. Generation of CO 3 2− appeared to be crucial to the formation of the solid phase. Heating the aqueous yttrium solution with trichloroacetic acid (CCl 3COOH) instead of urea as the precipitating agent produced a solid phase, while heating the same solution with formamide (HCONH 2) substituted for urea formed no precipitate.