Kinetics of the β → α Transformation of Tin: Role of α-Tin Nucleation

The influence of α-Sn nucleation on the kinetics of the β → α phase transformation are investigated, using in situ synchrotron powder X-ray diffraction (PXRD) with variable temperature control. In the entire thermal history of the α → β → α transformations, the population of α-Sn at the onset of the β → α transformation was varied by controlling the α → β transformation under isothermal conditions. The degree of α-Sn nucleation is found to have a correlation with the transformation kinetics of β → α. The growth component n is determined by both temperature and transformation time (fraction). By introducing an impingement factor, the transformation curves yielded a good fit to the modified Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. At the commencement of the reaction, insufficient nucleation was found in samples subject to long anneals, and additional nucleation was required, at the kinetically optimal temperature of -45 °C.