X-Ray Diffraction Investigation of Sodium Stearate from Room Temperature to the Melting Point

Sodium stearate of the gamma-polymorphic form was photographed by Cu Kα x-rays in a powder camera at seven temperatures between room temperature and 301°C. The long spacing is constant up to 132°C, the transition temperature between the subwaxy and waxy phases, whereupon it continues to decrease markedly in length up to the melting point. The two most intense short spacings increase in length up to about the transition between the stable waxy crystalline phase to superwaxy phase at 167°C. Both lines then appear to coalesce to form a single line up to above the final melting point, from liquid crystal to liquid, at 288°C. The space lattice was assumed to be monoclinic over the whole temperature range studied, with hexagonal close packing of the chains themselves above 167°C, possibly as a result of molecular rotation of the chains about their axes.