Stability of Inorganic Fluorine-Bearing Compounds: II, Complex Fluorides

The thermal stabilities of some alkali and alkaline-earth fluosilicates and cuspidine when heated in atmospheres of dry and moist air were investigated. IN the decomposition of K₂SiF₆ the compound K₃SiF₇ was noted. The alkali and alkaline-earth fluosilicates lose SiF₄ whereas cuspidine does not. In moist air atmospheres, α-cristobalite is found among the residual products from the fluosilicates of sodium and potassium. K₂TiF₆ hydrolyzes, first at low temperatures to an intermediate series of compounds and then at higher temperatures to fluorine-free potassium titanates. Both K₂ZrF₆ and Na₅Zr₂FI₃ hydrolyze to ZrO₂ and the alkali fluoride by way of an intermediate heptafluoride (M₃ZrF₇).