Thermal Behavior, Chemical, Mineralogical and Optical Characterization of Clays (Kaolin) for Industrial Use as Refractory Material

The kaolin is an important component of a wide variety of industrial products, therefore kaolin samples of region mines Huayacocotla, Veracruz and Alumbres, Hidalgo were collected, these were treated to reduce the size particle employment an agate mortar and part of each one were analyzed using analytical techniques such as: absorption and emission atomic spectroscopy (AEAS), optical microscopy of polarization (OMP); X-rays diffraction (XRD); scanning electron microscopy (SEM); refractory test under ASTM standard C-24-79 using a pyrometric cone mold designed on ASTM standard C-24 and thermal test at different temperatures up to 1600 °C with heating and cooling rate of 2.5 °C·min-1; thermogravimetric analysis (TGA) was carried out in a thermogravimetric analyzer with sample placed in alumina crucibles of high purity and the temperature was increased from room temperature up to 1000 °C with a heating rate of 10 oC·min-1. Dates from elemental analysis were converted to percentage in oxides form of major elements. The analysis by OMP showed kaolin alteration degree in the region due to minerals such: plagioclase, feldspar and quartz, hydrothermal alteration of epithermal type represented by oxidation, sulfides (pyrite, galena) and association with chlorite. X-ray diffraction allowed determining to cristobalite (SiO2) as majority phase in Huayacocotla and quartz (SiO2) in Alumbres. Minority phases were observed in both areas such: dickite (Al2O3·Si2O5·(OH)4), alunyte (KAl3(OH)6(SO4)2) and kaolinite (Al2O3·2SiO2·2H2O). Microanalysis with MEB showed kaolinite morphology, but structural formulas were not possible to determine due to impurities of Na, K, and Mg; those elements are present in clay complex group like: illite-alunite-dickite. Kaolin softening point was determined in 1300-1600 °C range, and it makes it feasible as refractory material of low and high temperature. Thermogravimetric analysis showed two decomposition areas, the first between 300-600 °C, which corresponds to crystallization water, and SO and SO2 gases and the second from 700-1000 °C where an exothermic signal appears due to premullite phase formation.