Generation and extinction of crystal nuclei in an extremely non-equilibrium glassy state of salol

Strange generation and subsequent extinction of crystal nuclei were observed in the glassy state of salol (phenyl salicylate) during the course of ageing at very low constant-temperatures. The presence/absence of crystal nuclei within the glass were judged, by using a differential scanning calorimeter (DSC), from whether the crystal growth and fusion phenomena were observed in the following heating process or not. The liquid sample was cooled rapidly at 200 K min⁻¹ from 333 K above the fusion temperature down to a desired ageing temperature (T_a) below the glass transition temperature (T_g = 220 K), aged there for different periods (t_a), and then heated up to 213 K at 200 K min⁻¹. The DSC measurement was carried out at 10 K min⁻¹ from 213 to 333 K. The ageing periods were taken in a range between 30 s and 316 min. At T_a = 213 K, crystal nucleation was found to proceed for ageing longer than 100 min. No crystal nucleation was found at T_a in between 123 and 193 K. At T_a below 113 K, crystal nuclei were found immediately after the rapid cooling, then extinguished, and again generated; some nuclei formed initially, survived for longer ageing at 103 K. The generation and extinction phenomena of crystal nuclei are discussed as a general event occurring in glasses located in an extremely non-equilibrium state.