Surface and interfacial free energies of quartz

Abstract

Water and electrolytes cause significant changes in brittle fracture strength and subcritical fracture propagation velocities in quartz and quartz rocks. The changes may be caused, in part, by changes in surface free energy. Experimental fracture surface energies of quartz range from about 400 mJ m−2 to about 11.5 J m−2. Thermodynamic surface free energies are likely to be lower than fracture surface energies owing to dissipative energy losses and failure to achieve equilibrium surface structure. Thermodynamic surface free energies are sensitive to environmental composition. Reaction of water vapor with pristine fracture surfaces reduces surface energy by hydroxylation, but the extent of reduction is not known. Adsorption of water vapor on the hydroxylated surface and immersion in liquid water reduce surface energy by 75–230 and 72 mJ m−2 respectively. In an electrolyte, the surface free energy is maximum at the point of zero charge, where adsorption of ionic solutes is least. Adsorption of hydrogen ion, hydroxide ion, and electrolytes reduce surface energy as concentration increases, by tens of mJ m−2. All of these surface energy changes are qualitatively consistent with changes in fracture behavior caused by the same variables.