XRD study of the kinetics of β ↔ α transformations in tin

Abstract

The transformation kinetics of βSn (white tin) to and from αSn (grey tin) are studied by synchrotron X-ray diffraction of seeded powder samples of 99.99% Sn. An analysis of thermal expansion behaviour revealed that the volume change of transformation increases as the temperature decreases. The βSn → αSn transformation was well described by Johnson–Mehl–Avrami kinetics with an Avrami exponent of 3, which was confirmed to be due to three-dimesional growth from pre-existing nuclei by a microstructural study. The αSn → βSn transformation exhibited a decreasing Avrami exponent from ∼4 to ∼1 during the transformation. Time–Temperature–Transformation curves are plotted from the isothermal transformation data and are compared with past work.

Keywords:

• phase transformations
• X-ray diffraction
• crystal structure
• tin pest
• Pb-free soldering
• time–temperature–transformation

Acknowledgements

This research had been conducted under an international cooperative research programme between the University of Queensland (UQ), Australia and Nihon Superior Company, Japan, and partially supported by an ARC-Linkage programme (project ID: LP100200250). PXRD experiments were performed at the Australian Synchrotron Powder Diffraction Beamline (project ID: AS112/PD3712, AS122/PD/4903). The authors acknowledge the facilities, and the scientific and technical assistance, of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis (UQ), and Dr Y.Q. Wu and Mr D. Mu (UQ) for their contributions on PXRD experiments.