含硫酸ジルコニア微結晶の生成プロセスと結晶成長

抄録

Zirconium sulfate solutions were hydrothermally treated at temperatures from 200° to 250°C for various periods of time. Crystalline phases, morphology and amount of solid products were investigated to study, especially, the formation process of zirconium oxide sulfate (ZOS), being submicron thin hexagonal crystals with a chemical composition of Zr₃O₅SO₄⋅nH₂O. Crystalline phases of the solid products varied with H₂SO₄ concentration of the solution; at 240°C for 3 days, m-ZrO₂ and t-ZrO₂, ZOS and/or a pseudo-ZOS phase (PZOS) and ZrOSO₄⋅H₂O at H₂SO₄ concentrations below 0.2mol/l, in the range of 0.2-2.0mol/l and above 2.5mol/l respectively, PZOS formed generally at lower temperature or at the early stage of the hydrothermal process, and its amount decreased with increasing H₂SO₄ concentration. Since the PZOS phase was metastable at higher temperature or higher H₂SO₄ concentration, it gradually changed to ZOS with a prolonged hydrothermal treatment time. The ZOS crystals were considered to be formed by a neucleation and crystal growth process. The crystal size of the ZOS increased with increasing H₂SO₄ concentration but was almost independent of Zr concentration. Effect of seeding and repeated treating on the crystal growth of ZOS was confirmed in a solution containing 1.6mol/l H₂SO₄ at 250°C.