HYDROTHERMAL GROWTH OF POTASSIUM TITANYL ARSENATE (KTA) IN LARGE AUTOCLAVES

Solubility and phase relations were investigated for selected K/As ratios in KH2AsO4-KOH solutions at 600-degrees-C and 2040 atm. All initial data were obtained with 5 mm diameter X 50 mm long platinum capsules in Tem-Pres type autoclaves. The most favorable results were repeated in Morey type autoclaves of 2.2 cm diameter. The P-V-T data were generated and extrapolated for use in gold liners and Rene 41 autoclaves with a pressure balancing method. Transfer to the 3.8 cm diameter X 46 cm long autoclaves with gold liners was achieved. Both nutrient and larger seed crystals were grown from a K2WO4-Li2WO4 flux. The internal and external degrees of fill were adjusted to obtain a balance of pressure at 1700 atm and 590-degrees-C. Initial growth runs were made for 1-2 weeks under a gradient of 30-degrees-C with a 4 molar KH2AsO4 mineralizer. Natural facet seeds were employed first while later runs utilized (011) cut and polished seeds.