Effect of the Anticaking Agent FeCN on the Creeping Properties of Alkali Halide Crystals

Fe(CN)64- (abbreviated as FeCN) is a well-known anticaking agent for NaCl that has a nearly perfect geometrical fit to the (001) surface. In this work, the investigation of the action of FeCN on nucleation and creeping is extended to a wide range of alkali halides of both the NaCl and CsCl structures. It was found that FeCN is a powerful nucleation inhibitor and enhances the creeping of alkali halides when FeCN geometrically fits well in the octahedral surface site of hosts with the NaCl crystal structure. The tested alkali halides that do not fall in this group or that have the CsCl structure show some reduction in creeping upon the addition of FeCN, while NaF and LiCl did not show a difference. For this category of crystals, there is a poor fit of the FeCN ion in the crystal surface. This study shows that a strong adsorption strength of FeCN enhances creeping, whereas a weak interaction reduces the creeping of alkali halide crystals.