Thermal shock of quartz lascas

As a pre-treatment to grinding, quartz lascas (crushed pieces) were thermally shocked into room-temperature water by quenching from temperatures between 50 and 800 °C. Comminuted particles exhibited two distinctive geometries, granular forT_q(quench) <T_c (573 °C) and needle-like whenT_q>T_c. The needle-like shapes become thinner and longer with increasing temperature aboveT_c. The differences in shape are believed to result from the differences in the crack generation patterns which are governed by the thermoelastic properties in the -phase and -phase of the quartz during the thermal shock process. Crack densities induced by the thermal shock were measured as a function ofT_q. For the temperature range of 200 °C<T_q<T_c andT_c<T_q<800 °C, the resulting crack densities were determined to be governed by the rate of crack nucleation, which is characterized by an Arrhenius-type equation. The activation energies associated with the crack nucleation rates for the two regions were determined to be 14 and 39 kJ mol^–1, respectively.