METHOD OF α-CRISTOBALITE Russian patent published in 2000 - IPC

FIELD: chemical industry, more particularly manufacture of ingot molds. SUBSTANCE: method comprises autoclave hydrothermal treatment of amorphous silica prepared by reacting hexafluorosilicic acid with gaseous ammonia. Process for preparing α-cristobalite is carried out in the presence of crystallization activator, e.g. silicic acid sol in amount of 0.02-0.06% in terms of α, based on weight of amorphous silica. Method makes it possible to prepare product with yield of 99.8%, to reduce power consumption due to lower process temperature, to simplify equipment used and to utilize hexafluorosilicic acid which is waste product resulting from extraction phosphoric acid production. EFFECT: more efficient preparation method. 1 ex, 2 tbl