Sulfadiazine N-methylpyrrolidone solvate (SD-NMP) was prepared by solution crystallization method. The molar ratio of sulfadiazine (SD) to N-methylpyrrolidone (NMP) in the solvate was 1:2 from the calculation of thermal gravimetric data. The desolvation bebavior of SD-NMP solvate was investigated by thermal gravimetric analysis

hot stage microscopy

scanning electron microscopy

powder X-ray diffraction and Fourier transform infrared spectroscopy. According to the same crystal habit and crystal form between the desolvation product of SD-NMP solvate and sulfadiazine crystal

it can be known that the formation and desolvation of SD-NMP solvate was a reversible transformation process. The desolvation kinetics of SD-NMP solvate under temperature of 70℃

75℃

80℃ and 85℃ was studied by use of the model fitting method according to the different reaction models. The results showed that the most appropriate model was the geometrical contraction one

and the desolvation of SD-NMP solvate was attributed to phase boundary reaction and the rate-limiting step was the inward advance of the phase boundary from the surface to the center of the crystals. The above research results were consistent with the WET3 theory.