Showing papers in "American Ceramic Society Bulletin in 1965"

The clay mineral concept

Abstract: IT IS NOW GENERALLY AGREED THAT SOILS, CLAYS, AND SHALES ARE COMPOSED OF EXTREMELY SMALL PARTICLES OF A FEW MINERALS KNOWN AS THE CLAY MINERALS. CLAY MINERALS ARE GENERALLY CRYSTALLINE - SOME CLAYS CONTAIN MATERIAL AMORPHOUS TO DIFFRACTION TECHNIQUES, BUT SUCH MATERIAL IS BELIEVED TO BE RELATIVELY RARE. STRUCTURE AND COMPOSITION OF THE CLAY MINERALS DETERMINE THEIR PROPERTIES WHICH IN TURN LARGELY DETERMINE BULK PROPERTIES OF THE CLAY ITSELF. CLAY MINERAL COMPOSITION OF ARGILLACEOUS MATERIAL IS OFTEN COMPLEX BECAUSE OF THE MIXING OF MINERALS INDISCRETE PARTICLES AND/ OR AS MIXED-LAYER ASSEMBLAGES. STRUCTURE AND COMPOSITION ARE BRIEFLY REVIEWED FROM THE POINT OF VIEW OF THE INFLUENCE OF THE ATOMIC ARRANGEMENT AND DEGREE OF STRUCTURAL ORDER ON PHYSICAL PROPERTIES. CERTAIN CHARACTERISTICS OF THE CLAY MINERALS, SUCH AS ION EXCHANGE, WATER ABSORPTION, AND REACTION WITH ORGANIC COMPOUNDS, ARE OF A SPECIAL INTEREST IN A CONSIDERATION OF THE CERAMIC PROPERTIES OF CLAY. /AUTHOR/

Dehydration of gypsum

Abstract: Studies of the dehydration of gypsum in dry air atmospheres have shown that the hemihydrate of calcium sulfate is not a stable phase in the temperature range 90-140 deg C. The final product of dehydration was always anhydrous. Discontinuities in the weight loss versus time curves for powdered gypsum at a point corresponding to the loss of about 75 percent of the original sample water is evidence that dehydration involves consecutive reactions and not simply the transformation of gypsum to the anhydrous salt. These rate studies also indicated that the activation energy for dehydration of gypsum is considerably less than that associated with the dehydration of the hemihydrate. The polyscrystalline phase that formed when monocrystals of gypsum were dehydrated had hexagonal symmetry and showed preferred orientation relative to the monoclinic parent crystal. the c sub O axis of the dehydration product was aligned approximately perpendicular to the direction in the original single crystal. /Author/