Distribution Model Of Lowly Volatile Impurity In Rare Earth Metal Purified By Vacuum Distillation

Distribution model of lowly volatile impurity in distillate was established based on the mass conservation of the solute at evaporating surface, and this model and the modified model were verified by two vacuum distillation purification experiments using terbium (Tb) metal respectively. The research results indicated that, the mass transfer control steps of the lowly volatile impurities of Al, Ti and Ni are the hybrid mass-transfer process or the evaporation mass-transfer process; the concentrations of Al, Ti and Ni impurities in distillate present exponentially increasing tendency as the distillation continues; the experimental results of Al impurity agree well with the results calculated by Calphad but are larger than the results calculated by Miedema, which the average standard deviations are +/- 0.048 and +/- 0.478 respectively; the experimental results of Ti impurity are lower than the results calculated by Miedema, while the experimental results of Ni impurity are greater than the results calculated by Miedema, which the average standard deviations of Ti and Ni impurities are +/- 0.392 and +/- 0.683 respectively; the second experimental results of Ti and Ni impurities are consistent with the calculated results of modified model, which the average standard deviations are +/- 0.096 and +/- 0.105 respectively.