金属ランタンによるレア・アース酸化物 (Sm₂O₃, Eu₂O₃, Tm₂O₃およびYb₂O₃) の還元反応機構

抄録

Reduction reaction and mechanism of samarium, europium, thulium and ytterbium oxides with metallic lanthanum have been investigated under the conditions of high temperature and vacuum atmosphere. Samples were used in the compact state prepared by pressing both rare earth oxide and metallic lanthanum powders.
Reduction reaction of each rare earth oxide with metallic lanthanum parabolically proceeded with prolonged time. Reduction curve for each oxide could be arranged by using both logarithms of reactivity degree and time. The slope of a straight line obtained was about 0.5 for the reduction of each rare earth oxide. Apparant activation energies of the reduction reaction calculated from Arrhenius plots were 96 kJ/mol for samarium oxide, 236 kJ/mol for europium oxide, 154 kJ/mol for thulium oxide and 243 kJ/mol for ytterbium oxide, respectively.
An electrochemical reduction model based on Wagner’s theory being used for high temperature oxidation of metal was applied for the reduction mechanism of each rare earth oxide with metallic lanthanum. From this model, a rate-determing step for the reduction reaction of each oxide could be considered to be the transfer process of lanthanum ion or oxygen ion in lanthanum oxide layer of reduction product.