Surface Energy of {100} Potassium Chloride

A modified Obreimov-Gilman cleavage technique utilizing the apparent variation of cleavage surface energy with crack length and specimen dimensions has been used to determine the true surface energy γ0 of the {100} planes of potassium chloride at room temperature. γ0 {100} KCl was found to be 110±5 ergs/cm2, in good agreement with Born and Stern's theoretical estimate of γ0 (108 ergs/cm2) but not with more recent estimates of this quantity (160–185 ergs/cm2). Possible causes for this discrepancy are discussed. Other experiments revealed that the presence of a solvent environment at the crack tip increased the cleavage fracture energy only some two or three times. This suggests that the Gurney-Pulliam phenomenon of precipitation at a crack tip is not primarily responsible for the increased strength and ductility of ionic crystals tested in solvent environments (Joffe's effect).