Role of water impurity in impact fracture of quartz in the vicinity of the phase transition at 573°C

Synthetic quartz single crystals are subjected to fracture by a falling load in the temperature range from 20 to 650°C (i.e., including the region of the α → β phase transition). The intensity of integrated acoustic emission (AE) generated during the impact is recorded in the frequency range from 80 kHz to 1 MHz. In the temperature range 20–300°C and at temperatures above the phase transition temperature (573°C), the energy distributions in temporal AE series are correctly described by the exponential function typical of random events, but at 400 and 500°C, the energy distributions follow the power law typical of correlated accumulation of microcracks in heterogeneous materials. The temperature effect is explained by the presence of submicrometer inclusions of a vapor—water mixture in the material, which exist as a rule in natural and synthetic quartz single crystals. Upon heating of the material to a certain critical temperature, the internal pressure in the bubbles of liquid attains a value for which the shock wave causes cracking around a large number of uniformly distributed inclusions. As a result, a correlated improper process of accumulation of microscopic defects, which is obviously observed only in heterogeneous materials, evolves in the bulk of deformed quartz heated to 400–500°C.