Occurrence and Mechanism of Rebinder Effects in CaF2

Abstract

A study has been made of the influence of adsorbed species on the room-temperature mobility of near-surface dislocations introduced into freshly cleaved {111} CaF2 surfaces by a diamond indenter. It was found that, in general, adsorbed surface-active ions or molecules decrease dislocation mobility, i.e., increase microhardness. Studies of the relaxation behavior of near-surface dislocations in CaF2 exposed to solutions of DMF in DMSO revealed that these environments also can influence dislocation mobility in the absence of stresses imposed by a loaded indenter. Moreover, for any particular DMSO-DMF environment, a correlation exists between the extent of dislocation motion induced by a loaded indenter and the amount of relaxation which occurs after the indenter is removed. From these and other observations it is concluded that indenter-lubrication effects do not play a fundamental role in the occurrence of Rebinder phenomena in CaF2. The results of this work are consistent, however, with the view that Rebinder effects in ionic solids are associated with chemisorption-induced changes in the state of ionization of near-surface point defects and dislocations. Such changes introduce variations in their mutual interactions which are then manifested as environmentally induced changes in the mobility of near-surface dislocations, and hence in microhardness.

Influence of CO2on the long-term chemomechanical behavior of an oolitic limestone

“…Indeed, generally speaking, the "Rehbinder effect" [Rehbinder and Lichtman, 1957], due to the reduction of the surface energy of different kinds of walls (e.g., pores, flaw, microfissure) by the adsorbed water, promotes the propagation of these walls if the deviatoric stress is high enough. In addition, Westwood and Goldheim [1968] suggested that the adsorbance of a polar fluid onto the crystal surface modifies the interactive behavior of point and line (dislocations) defects which largely determine the mobility of dislocations during the plastic deformation of ionic crystals, such as calcite. Hence, even though our experimental conditions (T = 70°C; Pc = 15-20 MPa) do not favor intracrystalline plastic deformation in calcite [Rutter, 1983;De Bresser et al, 2002;Zhang and Spiers, 2005b], the contribution of intracrystalline viscoplasticity to the creep of our wet (Pi = 10 MPa) limestone sample ( Figure 12) may not be negligible.…”

Estimation of the damage of a porous limestone from continuous (P- and S-) wave velocity measurements under uniaxial loading and different hydrous conditions

“…Rehbinder & Lichtman (1957) attributed the weakening of single crystals by the action of water to a reduction of interfacial tension and suggested that this reduces the work hardening component due to the pile-up of dislocations at the crystal-fluid interface, and increases the probability of emergence of dislocations onto the crystal surface. Westwood & Goldheim (1968) have suggested that the adsorbance of a polar fluid onto the crystal surface modify the interactive behaviour of point and line (dislocations) defects which largely determine the mobility of dislocations during the plastic deformation of ionic crystals, such as calcite. They also suggested that this is not a surface effect, like the alteration of the surface energy of the crystal, but one which penetrates up to 10 μm into the crystal.…”

Growth of color centres and hardening of CaF2 by heavy dose of γ-irradiation

“…: After the completion of microhardness measurements the specimens were etched with a 0.7 n solution of HNO, to reveal dislocation etch pits and the distribution of dislocations around the indentation. The characteristic features of such dislocation patterns or rosettes in CaF, have been described earlier by Westwood and Goldheim [15]. The length of the arms of such rosette patterns on the { 111} planes of CaF, is proportional to the mobility of edge dislocations.…”