SOLID STATE FORMATION OF BARIUM, STRONTIUM AND LEAD FELDSPARS IN CLAY- SULFATE MIXTURES

Abstract

Mixtures of kao;in-type clays and sulfates with theoretical compositions of the barium, strontium, and lead feldspars were x rayed continuously during heating to 1400 deg C at a rate of 5 deg C per minute. Formation of the feldspars in the solid state is characterized by the appearance of a metastable phase with a structure similar to hexagonal celsian and hexagonal anorthite. The barium hexagonal phase is very persistent. Prolonged heating is necessary to convert it completely to the feldspar, the conversion proceeding more rapidly with increasing temperature. The strontium and lead hexagonal phases are, however, very unstable, having been detected only during continuous x-ray investigation. They also change to the feldspars, the change occurring more rapidly with increasing temperature. The presence of small amounts of impurities has a marked effect on the formation temperatures and reaction rates. Titania tends to lower formation temperatures of the reaction products and to enhance the x-ray diffraction maxima. Potash tends to inhibit formation of the hexagonal phases and to promote formation of the feldspars in the barium and strontium compositions but has little effect on the lead phases. (auth)