UO_(2+x)芯块低温烧结的活化机理

Active mechanism of low-temperature sintering to UO_(2+x) pellets

报道了UO2+x芯块低温烧结实验的结果。12组芯块在N2+CO2组成的部分氧化气氛下于立式钼丝炉中低温烧结。UO2芯块要获得密度为10.41g/cm3(94.98%理论密度)需在氢气氛中于2073～2273K下烧结,而UO2+x芯块实现该密度的烧结温度可降低400K以上。建立了超氧化铀缺陷模型来研究低温烧结的活化机理。研究发现铀离子扩散系数与气氛中氧分压或是UO2+x中x成正比。利用铀离子的扩散系数,可预测UO2+x芯块在1073、1273、1473和1673K温度下的烧结密度;还可算出x=0.04时,UO2+x芯块在部分氧化气氛下的理论烧成温度。计算所得烧结密度和烧成温度与实验结果符合得很好。

Low-temperature sintering experiments of UO2＋x pellets and the results were reported in this paper. 12 groups pellets were sintered in vertical molybdenum wire furnace with N2 ＋CO2 partially-oxidative atmos- phere. Densities which achieved 10.41g/cm3 （94.98% theoretical density） could be sintered at a much lower temperature （more than 400K） while UO2 pellets were sintered at 2073-2273K in hydrogen. A defect model of hyper-stoichiometry uranium dioxide was built for studying the active mechanism. The diffusion coefficient was positive to partial pressure of oxygen （P%） or excess oxygen ions （x in UO2＋x）. The sintered densities of UO2＋, pellets were predicted by diffusion coefficient of uranium ions at 1073, 1273, 1473 and 1673K. The theo- retical sintering temperature of UO2＋x in partially-oxidative atmosphere was also calculated when x was 0.04. The results of sintered densities and sintering temperature were agreed to experimental results very well.