INFLUENCE OF GRINDING CONTAMINATION ON HIGH-TEMPERATURE PHASES OF PYROPHYLLITE

Phases formed at high temperatures from ground pyrophyllite in porcela in and agate mortars have been studied by X-ray diffraction. Cordierit e (2MgO.2Al2O3.5SiO2) as one crystalline phase appears in ground sampl es in a hard porcelain mortar after being treated above 1300-degrees-C , due to the reaction of enstatite (MgO.SiO2), derived from the balls used, with mullite (mainly 3Al2O3.2SiO2) and cristobalite (SiO2) origi nating from the decomposed pyrophyllite sample during heating. After m illing experiments using agate mortar and balls, the formation of cris tobalite at lower temperatures, in ground as opposed to unground mater ials in hard porcelain, is attributed to contamination resulting from the mill and balls used