Pu在Gd_2Zr_2O_7基质中的模拟固化:(Gd_(1–x)Ce_x)_2Zr_2O_(7+x)的热物理性能研究（英文）

Simulation of the Immobilization of Pu in the Gd_2Zr_2O_7 Matrix by Investigating the Thermophysical Properties of(Gd_(1-x) Cex)_2Zr_2O_(7+x)

采用高温固相反应,以NaF作助熔剂,在1000°C的温度下合成了锕系元素Pu的模拟固化体(Gd1–xCex)2Zr2O7+x(0≤x≤0.7).研究了模拟固化体的物相、热膨胀系数(TEC)、热导率(TC)随温度及组成的变化规律.粉末X射线衍射(XRD)测试结果表明:Gd2Zr2O7基质本身呈弱有序烧绿石结构,而用Ce4+取代Gd3+的模拟固化体都呈缺陷萤石结构.(Gd1–xCex)2Zr2O7+x的Ce(3d)X射线光电子能谱(XPS)有六个峰,结合能分别位于881.7,888.1,897.8,900.4,907.1,916.1 e V处,与Ce O2的XPS图谱非常相似,说明Ce为四价.随着温度的升高,所有样品的热膨胀系数总体上呈增大趋势.在室温至750°C附近,大部分样品的热导率随温度的升高而降低,之后热导率又呈小幅上升.在相同温度下,固化体(Gd1–xCex)2Zr2O7+x(0≤x≤0.7)的热膨胀系数及热导率随组成变化呈相同趋势:在0≤x≤0.1范围内随x的增大而增大,随后在x=0.1–0.7时逐渐减小.

Polycrystalline samples of（Gd1-x Cex）2Zr2O7＋x（0 ≤ x ≤ 0.7） were synthesized by solid-state reaction using NaF as a flux at 1000 °C to simulate Pu-immobilization in the Gd2Zr2O7 matrix. Phase transformation and variation of the thermal expansion coefficients（TECs） and thermal conductivities（TCs）of the samples with temperature and composition were investigated. Powder X-ray diffraction（XRD）patterns show that pure Gd2Zr2O7 has a weakly ordered pyrochlore structure, whereas Ce-containing samples（i.e., the Pu-simulated solidified samples） exhibit a defect fluorite structure even if x is as low as0.1. When x reaches 0.7, the XRD peaks of these samples widen. In the Ce 3d X-ray photoelectron spectrum（XPS） of（Gd1-x Cex）2Zr2O7＋x there are six peaks located at binding energies of 881.7, 888.1,897.8, 900.4, 907.1, and 916.1 e V, which are almost the same as the peaks of Ce O2. The Ce 3d XPS reveals that the Ce species in（Gd1-x Cex）2Zr2O7＋x are tetravalent. The TECs of（Gd1-x Cex）2Zr2O7＋x（0 ≤ x ≤0.7） generally increase with increasing temperature. At the same temperature, the TECs and TCs exhibit the same variation trend with the composition of the simulated solidified forms： they decrease from x = 0 to0.1 and then linearly increase from x = 0.1 to 0.7.