Removal of inorganic impurities from molten Mo through electron beam melting

초록

Efficient production of high-purity Mo requires a detailed understanding of the relationship between volatile refining efficiency and ingot growth rate, which has not been extensively studied in previous research. This study investigates the thermodynamic mechanisms and impurity-removal behavior during the electron beam melting of Mo. Using electron beam irradiation, impurity levels were reduced, achieving an enhancement in purity from the 99.7 % to the 99.97 %. The relationship between electron-beam output power and Mo dissolution was examined, alongside impurity volatilization trends during the melting process. A heat equation incorporating radiative heat was applied to determine the correlation between the temperature and beam energy used for Mo irradiation. The vapor pressures of Mo and its impurities were analyzed using the Antoine function model to elucidate thermodynamic volatilization characteristics. Impurity behavior, including tendencies to volatilize or condense, was confirmed through activity coefficients (Redlich-Kister polynomial model), while the binding energies of atoms were estimated using density functional theory calculations. Phase diagram analysis enabled the derivation of separation factors between Mo and its impurities. These findings demonstrate the feasibility of designing impurity-specific strategies to achieve high-purity Mo by thermodynamically selecting impurity- removable elements.

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