Crystallisation of titanium, zirconium and hafnium oxides and some titanate and zirconate compounds under hydrothermal conditions

Abstract

Crystallization of titanium, zirconium and hafnium oxides in KF, NaF, NH 4F solutions was studied at 450–700°C and 800–3000 atm. Under otherwise identical conditions the quantity of carrying substance decreases from TiO 2 to ZrO 2 and HfO 2, and increases in NaF<KF<NH 4F solutions. The substance is transferred from the hot to the cold zone of the autoclave in KF, NaF solutions, and is transferred in a reverse direction in a NH 4F solution. The spontaneous crystallization of rutile and its growth on seed crystal was studied. The growth rate of the faces {110} and {100} was 0.2–0.3 mm/day at 550–600°C and Δ T= 20–35°C. The growth of ZrO 2 and HfO 2 was realized in a horizontally placed vessel under analogous conditions (550–600 °C, Δ T = 15–30°C). Crystallization of some titanates and zirconates of lead was brought about in a KF solution. PbTi 3O 7 · K 2O· 0.5 PbO · 7 TiO 2, PbTiO 3 and PbZrO 3 were obtained at 450–700 °C and 800–3000 atm. Vigorous crystallization of PbTiO 3 and PbZrO 3 takes place above 550 °C. Recrystallization of mixed Pb(Ti 0.5 Zr 0.5)O 3 crystals resulted in Pb(Ti,Zr)O 3 with TiO 2 concentration up to 25%.