INFLUENCE OF TIME AND TEMPERATURE ON REACTIONS AND TRANSFORMATIONS OFCLINOCHLORE AS A CERAMIC CLAY MINERAL

Clay minerals of the chlorite family are important constituents of cla ys used for the production of bricks, tiles, and clay pipes. The therm al behaviour of the magnesian chlorite clinochlore (Mg10Al2) (Si6Al2) O-20 (OH)(16)) has been determined and is expressed as a time-temperat ure-transformation diagram. The thermal decomposition of clinochlore i s dominated by the initial presence of two layer types: a talc like la yer alternating with a brucite like layer. Water loss first involves d ehydration of the brucite layer with a theoretical 9.75% loss at simil ar to 590 degrees C, followed by gradual dehydration, complete by 870 degrees C, of the talc layer involving a further 3.25% loss. The forma tion of forsterite, enstatite, and spinel at higher temperatures is a consequence of control on nucleation by the layered structure of the c lay mineral. This accounts for failure to produce cordierite as predic ted by the equilibrium phase diagrams for the system MgO-Al2O3-SiO2. ( C) 1997 The Institute of Materials.