Hydrothermal technique is a useful method to prepare ceramics powders with controlled size and morphology. We need high temperatures to prepare rare earth oxides under hydrothermal conditions, because many compounds such as hydrates, hydroxides, and oxyhydroxides are stable at low temperatures. However, these low temperature stable compounds were transformed to oxides by calcination at high temperatures. At the transformation, the oxides retain the original morphology of low temperature stable compounds. Thus we can prepare rare earth oxides with various morphologies.. It was find that bundle of nano wires of Y(OH)3 were formed by hydrothermal treatment of Y2O3 in 6.7 x 10-2 M acetic acid at 200 ℃. In this study, this technique was applied to the other rare earth oxides. Hydroxides of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho were successfully prepared. The morphology of the hydroxides change in concord with the atomic number of the rare earth elements. Hydroxides of Er, Tm, Yb, and Lu were not formed but needle crystals of acetates with a chemical formula of Re3O(OH)6(CH3COO)・2H2O (Re= Er, Tm, Yb, Lu) were crystallized. Concentration and pH of acetic acid had effects on crystallized phases. When the concentration of acetic acid was increased, layered compounds of 251-LRH (Ln2(OH)5(CH3COO)・nH2O) were crystallized. All these compounds were easily converted to oxides by calcination in air.
Prof. Kazumichi Yanagisawa received his B.Eng. (Shinshu University) and Ph. D. (Tokyo Institute of Technology) degree in 1976 and 1986, respectively. He was a Postdoctoral Fellow in Pennsylvania State Univ. till the end of 1990. Since April 1981, he joined Kochi University and was promoted to Professor with tenure in April 1999. He was the recipient of the Ceramics Society of Japan Awards for academic achievements in ceramic science and technology (2005), Science Award of Japanese Association of Inorganic Phosphorus Chemistry (2005), Science Award of the Society of Inorganic Materials, Japan (2004). He is has published over 300 peer-reviewed journal papers in the field of hydrothermal synthesis.