Crystallographic controls on the frictional behavior of dry and water‐saturated sheet structure minerals

Abstract

[1] We compare the frictional strengths of 17 sheet structure mineral powders, measured under dry and water-saturated conditions, to identify the factors that cause many of them to be relatively weak. The dry coefficient of friction m ranges upward from 0.2 for graphite, leveling off at 0.8 for margarite, clintonite, gibbsite, kaolinite, and lizardite. The values of m (dry) correlate directly with calculated (001) interlayer bond strengths of the minerals. This correlation occurs because shear becomes localized along boundary and Riedel shears and the platy minerals in them rotate into alignment with the shear planes. For those gouges with m (dry) < 0.8, shear occurs by breaking the interlayer bonds to form new cleavage surfaces. Where m (dry) = 0.8, consistent with Byerlee's law, the interlayer bonds are sufficiently strong that other frictional processes dominate. The transition in dry friction mechanisms corresponds to calculated surface energies of 2-3 J/m 2 . Adding water causes m to decrease for every mineral tested except graphite. If the minerals are separated into groups with similar crystal structures, m (wet) increases with increasing interlayer bond strength within each group. This relationship also holds for the swelling clay montmorillonite, whose water-saturated strength is consistent with the strengths of nonswelling clays of similar crystal structure. Water in the saturated gouges forms thin, structured films between the plate surfaces. The polar water molecules are bonded to the plate surfaces in proportion to the mineral's surface energy, and m (wet) reflects the stresses required to shear through the water films.

Frictional properties of the shallow Nankai Trough accretionary sediments dependent on the content of clay minerals

“…Clay-poor gouge samples likely experienced substantial grain-size reduction and compaction, resulting in slip hardening (e.g., Morrow and Byerlee 1989). In contrast, in clay-rich gouge samples, initial compaction hardening was likely followed by weakening due to preferred alignment of clay minerals along shear planes (e.g., Moore and Lockner 2004). Except for siltstone sample C2652 and tuff sample C9087, whose (a − b) and Δμ ss /ΔlnV sliding values are smaller than those of the other samples, there is a tendency for the (a − b) value to decrease while the Δμ ss / ΔlnV sliding value increases with increasing clay mineral content (Figure 8).…”

Effects of humidity and interlayer cations on the frictional strength of montmorillonite

“…Moore and Lockner (2004) suggested that the (001) bonding strength is a primary factor controlling frictional coefficient of the sheet silicates; however, recent experiments by Behnsen and Faulkner (2012) found the friction coefficient of various clay minerals were deviated significantly from the value predicted from the electrostatic separation energy. Sakuma and Suehara (2015) calculated interlayer bonding energy using the first-principles based density functional theory without using the empirical approximation of charge distributions in minerals, and they showed that there is no clear correlation with the frictional strength for layered minerals.…”

Expansion characteristics of organo montmorillonites during the intercalation, aging, drying and rehydration processes: Effect of surfactant/CEC ratio

“…Several previous reports indicated that X-ray diffraction (XRD) is still the most widely used method for characterizing the structure of OMt in water, and the results showed that water molecules can always cause evident swelling of OMt [33][34][35][36]. According to the XRD characterization results, Zhu et al [18] recently proposed a set of structural models for wet OMt.…”