Effect of spherically converging stress waves on the phase composition,structure, and physicochemical transformations of the mixture of aluminum and quartz powders

The phase composition and structure of a mixture of aluminum and quartz powders taken in a ratio of 1:1 have been studied after loading by spherical converging shock waves. A number of concentric layers (zones) have been observed in a meridian section of the sample after shock-wave loading. The pressures in the converging shock wave and in the diverging shock wave reflected from the center of the sample have been estimated as a function of the radial position of Lagrangian particles on the basis of the calculation of pressure profiles P(R, t). The data on the phase composition of different zones are considered in respect to the pressures induced by the converging and diverging shock waves at their boundaries. It has been established that pressures below ～45 GPa cause only additional compacting of the material and deformation of aluminum and quartz. In this case, the quartz grain size substantially decreases up to the transition into the X-ray amorphous state. The attainment of a pressure of ～45 GPa initiates the solid-state reaction of SiO₂ decomposition, which leads to the precipitation of pure silicon and the evolution of oxygen. The beginning of the silicon precipitation and the chemical reaction of Al₂O₃ formation are separated over the pressure scale. The critical pressure, which is necessary for the solid-state chemical reaction of the Al₂O₃ formation is about 50 GPa.