Quenching and annealing experiments with electrical resistivity measurements were applied to magnesium to investigate the formation of thermal vacancies. Two specimens made from materials differing in impurity contents were examined. One of the specimens quenched in a methanol bath at -80C from elevated temperatures ranging from 160 to 500C revealed a significant decrease in electrical resistance after annealing for 10 min in the bath. Based upon the annealing behaviors at low temperatures (-100 to -60C) after quenching from 200C, this decrease was thought to be due to the presence of hydrogen in solution. The other specimen, presumably containing smaller amounts of hydrogen, was quenched in iced water from elevated temperatures (200 to 560C) which yielded results characterized by two thermal activation processes. These processes had the activation energies 54.1kJ/mol (0.56eV) and 89.8kJ/mol (0.93eV) for the lower and higher quenching temperature ranges, respectively. The former was ascribed to the formation energy of a vacancy interacting with hydrogen and the latter to the intrinsic formation energy of a vacancy. The difference between these energies, 35.7kJ/mol (0.37eV), was the binding energy between a vacancy and a hydrogen atom.

Effects of Hydrogen on the Vacancy Formation in Magnesium. M.Yamada, M.Hida, T.Senuma: Materials Transactions, 2008, 49[9], 2006-11