Abstract
The kinetics of the phase transformation of thallium and its dilute alloys were investigated using X-ray diffraction and calorimetry. Pure thallium exhibits a β(bcc)→α(hcp) phase transformation on cooling at 508 K. With alloying additions, the crystal structure for each phase does not change, although the size of the unit cell increases. The enthalpy and the temperature of phase transformation for each alloy have been determined. From these data, the chemical free energy change associated with the phase transformation of each alloy was calculated using an equation separated into volume dependent and volume independent contributions. The latter is interpreted on the basis of a change in the electronic chemical potential associated with the electrons occupying different energy states in the Brillouin zones of the two structural modifications. The valence electrons make an outstanding contribution to the chemical free energy change required for the phase change.
MST/1420
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