The crystallization process of noncrystalline indomethacin (IMC) obtained by the grinding and by the fusion method was analyzed by a kinetic method. The noncrystalline samples of IMC were the α form ground for 10 h at 4°C (GNCγ), the γ form ground for 10h at 4°C (GNCγ) and the fused solid (NC). Ten kinetic models were employed, and crystallinity was determined by X-ray diffractometry. Data obtained were used to determine the thermodynamic parameters and crystallization mechanism.
Under isothermal conditions GNCγ crystallized in both the α and γ forms simultaneously. The GNCγ and NC crystallized in the γ form, and the results of the Hancock-Sharp method suggested that both crystallizations occurred by a two-dimensional phase boundary reaction; the activation energies (E) were estimated to be 24.1 and 27.2 kcal/mol. The crystallization rate of GNCγ was about 60 times faster than that of NC, and therefore NC was a very stable noncrystalline solid. These results suggest that there are several kinds of noncrystalline solids.