Investigation of Cerium Reduction Efficiency by Grinding with Microwave Irradiation in Mechanochemical Processing

This study evaluated the efficiency of cerium reduction by grinding with microwave irradiation in mechanochemical processing. Grinding experiments with microwave irradiation were conducted using an agitating mixer. Since the structure of the ground samples was amorphous and the cerium concentration was much lower than those of other elements, the valence change and structural change of cerium after grinding with microwave irradiation were investigated using X-ray absorption fine structure (XAFS) analysis in the cerium K-edge. The X-ray absorption near-edge structure (XANES) analysis revealed that a portion of tetravalent cerium was reduced to trivalent cerium by grinding with microwave irradiation. In addition, it was confirmed by extended X-ray absorption fine structure (EXAFS) analysis that oxygen vacancies were produced as a result of the cerium reduction reaction. To evaluate the efficiency of cerium reduction efficiency, the percentage reduction by grinding with microwave irradiation was compared to that by planetary ball milling and microwave irradiation. As a result, it was revealed that the efficiency of cerium reduction via grinding with microwave irradiation was higher than that via microwave irradiation and the same as that via planetary ball milling. Moreover, a larger amount of tetravalent cerium could be reduced to trivalent cerium by grinding with microwave irradiation than when using planetary ball milling and microwave irradiation.