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-degrees-C. Comminuted particles exhibited two distinctive geometries, granular for T(q)(quench) T(c). The needle-like shapes become thinner and longer with increasing temperature above T(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 alpha-phase and beta-phase of the quartz during the thermal shock process. Crack densities induced by the thermal shock were measured as a function of T(q). For the temperature range of approximately 200-degrees-C < T(q) < T(c) and T(c) < T(q) < approximately 800-degrees-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 1 4 and 39 kJ mol-1, respectively.28195223522