PHASE-TRANSFORMATIONS IN SULFATHIAZOLE DURING MECHANICAL ACTIVATION

The effect of mechanical treatment in a planetary ball mill on the transformations of polymorphs of sulfathiazole were studied by means of X-ray diffraction analysis, infrared spectroscopy and differential scanning calorimetry. It has been shown that mechanical treatment initiates transitions of sulfathiazole polymorphs III reversible I. In an initial period of mechanical treatment a part of the sulfathiazole was converted into a noncrystalline solid. Preliminary mechanical treatment of form III resulted in the reduction of III --> I phase transition temperature 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 transformed into form I during mechanical treatment. Single crystal thermomicroscopy studies showed that III --> I phase transition proceeds via nucleation and a rapid advance of an interface through the crystal. It seems that deformation of crystals during mechanical treatment and formation of noncrystalline solid with high extent of disordering make probable the initiation of phase transition of sulfathiazole during mechanical treatment.