Experimental Studies on Crystal Growth of Anatase under Hydrothermal Conditions

How metal mineral grows in hydrothermal fluids from a metal ion or metallic compound to the macrocrystals is one of the most fundamental problems in mineralogy and metallogeny. In this study, a series of non-isothermal and non-isochronic hydrolysis experiments of potassium titanium fluoride (K₂TiF₆) solution were investigated at temperatures from 200 to 400℃ and pressure of 100 MPa. The results show that anatases, with varied morphology, were synthetized in the hydrothermal conditions. With increasing reactive time and temperature, the anatase can grow up from dozens of nanometers to 10 micrometers or more. Remarkably, the anatases that were synthetized within 10 h or at higher temperatures exceeds those over 10 h or at lower temperatures in the rate of growth, which suggests the supersaturation level of Ti and temperature dependence on the crystal morphology, grain size and the rate of growth of the anatase. Generally speaking, classical nucleation and growth, oriented attachment, and Ostwald ripening are involved in the growth of the hydrothermal anatase, in which the supersaturation level of metal in hydrothermal fluids and dissolution-precipitation process are decisive to control the rate of anatase growth. Finally, we consider anatase as a typomorphic mineral that its morphology could be used to decipher the formation temperature, generation relationship of minerals, and even the evolution of F-bearing hydrothermal fluids.