First-principles investigation of brucite and gibbsite: An application to their macroscopic frictional characteristics

Abstract:

Because layered structure minerals are often observed in natural faults and have lower friction coefficients than the other common rocks and rock-forming minerals, it has been suggested that their frictional characteristics are related to fault strength. Despite their importance for understanding fault dynamics, what controls their frictional characteristics has not been clarified yet. As the friction coefficients of these minerals depend on the mineral species, the atomic-scale crystal structure can be a clue for understanding the mechanism. The weak interlayer friction of them has been thought to contribute to their low friction coefficients; therefore, the variation of potential energy during the interlayer deformation (potential energy surface, PES) was calculated in this study by using first-principles calculations based on density functional theory to derive interlayer friction theoretically. Brucite and gibbsite were investigated because they have similar layered structure minerals but different macroscopic friction coefficients suggested by previous experimental studies. According to the adhesion theory of friction, we found that the atomic-scale frictional parameters obtained by using the PES could explain the macroscopic friction coefficients when taking the experimental indentation strengths into account. Thus, the interlayer friction plays a primary role in the frictional properties of layered structure minerals.