UO_2-ZrO_2固溶体的形成机制和致密化规律（英文）

Solid Solution Formation and Densification Mechanism of UO_2-ZrO_2

采用溶胶-凝胶法制备了UO_2-ZrO_2芯块,分析了制备过程中芯块的固溶体的形成、微观组织结构和致密化行为。X射线衍射结果表明低于1600℃时UO_2-ZrO_2芯块中主要是四方结构的ZrO_2固溶体和面心立方结构的UO_2固溶体。随着烧结温度的增加,ZrO_2固溶体逐渐减少,UO_2固溶体不断增加,并伴有2θ的偏移。由于离子扩散速率和晶体结构不同,Zr元素易扩散至UO_2中,UO_2基体固溶ZrO_2同时不断长大,原ZrO_2的位置产生缺陷,使得芯块形成新的孔隙,芯块密度下降。烧结温度大于1650℃时,基体组织主要是是面心立方(U,Zr)O_2,晶粒尺寸迅速长大。

UO2-ZrO2 composite was prepared by Sol-gel. Solid solution formation,microstructure and densification of the composite were investigated and analyzed.X-Ray Diffraction results indicate that the UO2-ZrO2 is composed of both tetragonal ZrO2 solid solution and face-center cubic UO2 solid solution up to 1600℃.As the temperature increases,relative amount of ZrO2 solid solution in the composite decreases gradually while that of UO2 solid solution increase,with 2θshifting accompanying.Because of the different diffusion rate of uranium and zirconium,zirconium preferentially diffuses into the UO2 phase and the UO2 matrix expands to accept extra zirconium cations,leaving vacancies at the original ZrO2 site.The whole process brings in new pores in the pellets after sintering and results in the decreasing of density.Sintered above 1650℃,the major phase of the matrix is（U,Zr）O2,and The average grain size increases quickly.