Crystal forms of anhydrous calcium stearate derivable from calcium stearate monohydrate

Abstract

Anhydrous calcium stearate can be obtained at room temperature in any one of three forms, or mixtures thereof, by dehydration of calcium stearate monohydrate. Calcium stearate VIA is believed to be the stable modification. Calcium stearate VIH is an anhydrous crystalline powder having the same X-ray diffraction pattern as calcium stearate monohydrate. Calcium stearate VIN is relatively amorphous with respect to interchain spacings although it exhibits a crystalline long spacing. Samples of calcium stearate hydrate which yield calcium stearate VIH upon dehydration lack a second order thermal transition at 48°C characteristic of calcium stearate hydrate samples which yield calcium stearate VIA upon dehydration. Evidence is presented supporting the interpretation that transformation of the hydrate type structure to the anhydrous type is inhibited by impurities in the calcium stearate, particularly adsorbed calcium salts and foreign fatty acid anions.