Observation and interpretation of drastic weakening of polycrystalline quartz in hydrous- and alkali-containing environments

The incorporation of OH related point defects and its weakening effect on plastic deformation of quartz materials are of great importance in many engineering and geological processes. In this study, we report the drastic weakening of polycrystalline quartz in a hydrous environment and an environment also containing an alkali (NaOH) and propose an approach of point defect chemistry to understand the origin and underlying mechanisms of this effect. Based on creep results from controlled water-containing environments, the rate controlling processes on creep of a polycrystalline quartz material are investigated. Results show that the defects incorporated into quartz crystals in a hydrous environment are mainly oxygen interstitials , hydrogen interstitials or , and substitutional hydrogen for silicon . Although all the dominant creep deformation originated from dislocation glide and climb, the rate controlling process is the diffusion of with jogs and kinks, coupled with the diffusion of , at higher temperatures, but changes to the diffusion of with charged kinks and jogs at lower temperatures. The incorporation of the OH related defects into quartz crystals is to promote these rate controlling processes under the synergistic effects of oxygen and hydrogen activities, and the diffusivity and/or solubility of the defects from an alkali-containing environment accelerates these processes and cause further weakening. These results will provide a new strategy for understanding the hydrolytic and alkaline weakening and evaluating the performance of engineering components and evolution of geological events associated with different chemical environments.