Deformation of experimentally shock-loaded quartz powders: X-ray line broadening studies

Quartz powders (mean grain size: 22 μm) were pressed into sample discs of different green densities (ρ₀=1.65; 1.85 and 2.05 g/cm³) and subjected to shock pressure between 1.5 and 17.0 GPa. Peak shock pressures were determined by the impedance method using the Hugoniot curves of steel and quartz powders. Fourier techniques were used to analyse the line broadening of 5 X-ray reflections in each case. The Fourier coefficients were subjected to a Rothman-Cohen correction before further processing. The coherent domain size decreases abruptly from several thousand Ångström in the unshocked state to about 800 Å at 1.5 GPa, and reaches a constant mean value of about 200 to 300 Å at dynamic pressures of about 4 GPa. At very high dynamic pressures (?15 GPa) there is further fragmentation to very small domain size. There is no systematic correlation between sample density and coherent domain size produced by the shock event. A more or less linear dependency exists between microstrain and pressure for each starting density of the quartz powder. The observation that microstrain decreases with increasing starting density could be explained by the fact that increasingly larger portions of the input energy are consumed to create fresh surfaces by comminution. Consequently, less energy will be available for strain strengthening. The stored energies in the shocked quartz powders are of the same order as the surface energy. Shock-treated quartz should therefore be suitable for accelerating any activated process such as sintering.