Nano-Scale Cordierite Glass-Ceramic from Natural Raw Materials with Different Fluoride Additions

Stable cordierite glass-ceramics were prepared from natural kaolin, silica sand and magnesite as raw materials. Furthermore the effect of fluorine additions was tested by addingAlF(3) or MgF(2)tothe glass composition. Stable cordierite was crystallized in all glass-ceramic samples during thermal treatment at temperatures in the range from 900to 1200 degrees C. In the microstructure cordierite, crystals of sizes 15to 50 nm in parent sample and 500 nm to 1 mu m in the sample prepared using AlF3 as raw material were observed, while in the sample prepared from MgF(2)as raw materials, the crystal sizes were > 1 mu m. The coefficients of thermal expansion of the present cordierite glass-ceramic (CTE) were found to be, 1.14 x 10(-6) K-1 (100-300 degrees C) for the parent glass and 4.93 x 10(-6) K-1(100-500 degrees C) for the glass-ceramic containing high AlF(3)sample.Also, the microhardness values were between 5. 20 and 6.34 GPa for glass-ceramic samples. The densities of cordierite glass-ceramics increased from 2.07 g/cc in the parent sample to 2.54 g/cc and 2.58 g/cc in AlF3 and MgF2 containing samples, respectively. The resultant material can resist the temperature up to 1200 degrees C.