PHASE-TRANSFORMATIONS IN SULFATHIAZOLE DURING MECHANICAL ACTIVATION

The effect of mechanical treatment in a planetary ball mill on the tra nsformations of polymorphs of sulfathiazole were studied by means of X -ray diffraction analysis, infrared spectroscopy and differential scan ning calorimetry. It has been shown that mechanical treatment initiate s transitions of sulfathiazole polymorphs III reversible I. In an init ial period of mechanical treatment a part of the sulfathiazole was con verted into a noncrystalline solid. Preliminary mechanical treatment o f form III resulted in the reduction of III --> I phase transition tem perature by 20-30-degrees-C in the samples without form I and by 40-50 -degrees-C in the samples where the part of the substance were transfo rmed into form I during mechanical treatment. Single crystal thermomic roscopy studies showed that III --> I phase transition proceeds via nu cleation and a rapid advance of an interface through the crystal. It s eems that deformation of crystals during mechanical treatment and form ation of noncrystalline solid with high extent of disordering make pro bable the initiation of phase transition of sulfathiazole during mecha nical treatment.