Effects of shock-wave loading in oxides

Abstract

This paper reports results of experimental study of the influence of shock waves on the structure, ion valence, and phase composition of oxides, including the minerals tenorite (CuO) and hausmannite (Mn3O4) and perovskite-structured manganite LaMnO3. Shock-wave loading (SWL) was modeled by explosion experiments in spherical and cylindrical (in the case of tenorite) configurations. The results of strong quasi-static shear deformations of oxides under pressure are also given for comparison. The main focus was the investigation of shock wave-induced changes in oxides at the level of chemical bonds, disturbances of ionic composition and stoichiometry, relation of these processes to the formation of micro(nano)structures in the minerals, and stages and microscopic mechanisms of the development of new dense phases. It was shown that SWL-affected oxides can be successfully investigated by various methods of X-ray spectroscopy (photoelectron, absorption, and emission) and nuclear techniques (Rutherford back scattering, nuclear reaction analysis, and positron annihilation spectroscopy). Crystal structure and phase composition were explored by X-ray and neutron diffraction methods. Microscopic structures were investigated by optical, scanning electron, and scanning tunneling microscopy. It was shown that the effects of SWL are initially manifested in oxides as a stoichiometry violation, an increase in the number of low-valence cations, and formation of a micro(nano)structure. Plastic deformations developed during SWL are especially important for these processes. The decomposition of oxides during the solid-phase stage of shock metamorphism under the influence of high pressures, temperatures, and severe plastic deformations produces oxides with a low degree of oxidation and free oxygen, which can migrate over considerable distances to form new compounds. The ultradeep penetration of particles of the surrounding matrix into the target mineral during SWL can also serve as a mechanism of shock metamorphism at the solid-phase stage of transformation.