Specific surface area studies of shock-modified inorganic powders

Modification of inorganic powders with high-pressure shock-wave loading is of interest for shock-activated sintering, material synthesis, shock-enhanced catalytic activity, dynamic compaction, and shock-enhanced solid-state reactivity. The specific surface area of shock-modified powders is a direct quantitative measure of powder morphology changes, yet few studies have been carried out on powders subjected to controlled shock-loading conditions. In the present work aluminium oxide, zinc oxide, aluminium nitride, titanium carbide and titanium diboride powder compacts were subjected to controlled shock-loading to peak pressures of from 4 to 27 GPa at various starting densities, and characterized with specific surface area measurements by the BET (gas adsorption) method. Low-temperature cyclical thermal pretreatment and outgassing pretreatment of the shock powders at 250° C were employed; the former improves the reliability of the BET measurements, and makes the surfaces of the shock-modified powders more chemically active than those of the starting powders. Each powder shows a somewhat different response to shock-loading, ranging from a decrease in specific surface by a factor of six for zinc oxide to a 200% increase for titanium diboride. Shock-induced changes in specific surface show four characteristic behaviours as shock pressure is increased. Well-understood and controllable shock-loading conditions are found to be essential to shock-modification studies. An update on earlier measurements on rutile, zirconia and silicon nitride is also reported.