Ce4+替代Pu4+的模拟固化体(Gd1-xCex)2Zr2O7+x的合成及结构演变

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Gd2Zr2O7中Gd具有很大的中子吸收截面,其烧绿石结构-缺陷萤石结构的转变能较低,使其成为理想的核废料固化基材.使用硝酸盐为原料,添加少量NaF作助熔剂,在较低温度下(和传统高温固相反应相比),合成了烧绿石型Gd2Zr2O7.以Ce4+模拟Pu4+,研究了Gd2Zr2O7对锕系核素的固化,并合成了系列模拟固化体(Gd1-xCex)2Zr2O7+x(0≤x≤0.6).采用粉末X射线衍射(XRD)对系列样品进行了表征.结果表明:随着x值的增大,样品从烧绿石结构向缺陷萤石结构转变,且晶胞大小基本保持恒定,但当x=0.6时,衍射峰明显宽化,晶格畸变比较严重,晶格稳定性降低.当x=1时,即用Ce4+完全取代Gd3+进行合成,不能得到Ce2Zr2O8,产物发生了相分离,为四方结构的(Zr0.88Ce0.12)O2和萤石结构的(Ce0.75Zr0.25)O2的混合物.模拟固化体的浸出率测试表明:当x≤0.2时,各元素浸出率均很低,但当x≥0.4时,各元素的浸出率明显升高,说明以Gd2Zr2O7作为固化Pu4+的基材,Pu4+掺入量不宜高于40%. Gd has a large neutron absorption cross-section in Gd2Zr2O7, and its pyrochlore structure-defect fluorite structure can be transformed into an ideal material for nuclear waste solidification.Using nitrate as a raw material and adding a small amount of NaF Flux, the pyrochlore Gd2Zr2O7 was synthesized at lower temperature (compared with the conventional high temperature solid state reaction) .Cu4 + simulated Pu4 + was used to study the curing of actinides by Gd2Zr2O7 and a series of simulated solidified bodies were synthesized Gd1-xCex) 2Zr2O7 + x (0≤x≤0.6) .A series of samples were characterized by X-ray diffraction (XRD) .The results showed that with the increase of x value, However, when x = 0.6, the diffraction peak is widened and the lattice distortion is more serious and the lattice stability is reduced. When x = 1, the complete replacement of Gd3 + with Ce4 + (Ce0.75Zr0.25) O2 with tetragonal structure and (Ce0.75Zr0.25) O2 with tetragonal structure were obtained.The results of the leaching rate of simulated solidified body showed that when the content of Ce2Zr2O8 was When x≤0.2, the leaching rate of each element is very low, but when x≥0.4, the leaching rate of each element obviously increases, indicating that with Gd2Zr2O7 The cured substrate Pu4 +, Pu4 + incorporated in an amount not higher than 40%.
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