Formation of talc fault gouge analog using high-energy ball mill

Fault gouge, located in highly deformed fault cores, shows substantial particle size reduction and loss of crystallinity, which could affect the physicochemical properties and thus control the slip behavior and earthquake stability of a fault. To systematically investigate the effect of deformed fault gouge on fault slip behavior in laboratory-scale experiments, a fault gouge analog with variable particle size and crystallinity is required. However, the systematic study for formation of a fault gouge analog (i.e., controlling the particle size and crystallinity) was not performed well. In this study, we investigated the effect of the rotation speed of a high-energy ball mill on particle size reduction rate and degree of amorphization. As the rotation speed increased from 500 to 2000 rpm, the comminution rate linearly increased, and reached a reduced particle size limit. The degree of amorphization and its rate also increased with increasing rotation speed. Upon grinding, the X-ray diffraction (XRD) peaks markedly decreased and reached critical amorphization points within 120 min, except for the case of grinding with a rotation speed of 500 rpm. Talc ground with a rotation speed of 500 rpm did not reach steady-state in mechanical amorphization after 360 min of grinding, thus necessitating prolonged grinding for further amorphization. A comparison of talc powders having similar specific surface areas, but ground at different rotation speeds, shows that grinding with a higher rotation speed for a shorter duration preserves the crystalline structure relatively well compared with grinding at a lower rotation speed for a longer duration. These results indicate that optimizing the grinding rotation speed facilitates the formation of talc fault gouge analogs with systematically varying particle size and crystallinity. The specific surface area of talc increased from 6.1 to 365 m2/g, and the degree of crystallinity decreased from approximately 75% to 11%. Our results indicate that an artificial talc fault gouge can be prepared by varying the particle size and crystallinity using a high-energy ball mill.