Gd1.6Nd0.4Zr2O7烧绿石的快速合成及其组织结构研究

为探索Gd₂Zr₂O₇烧绿石快速固化高放废物中锕系核素的新途径,实验用高温高压固相反应法在3～4GPa压力、1573～1673K温度范围内合成了Gd_1.6Nd_0.4Zr₂O₇烧绿石固化体,并利用X射线衍射仪、扫描电镜对样品进行了分析。结果表明：高温高压固相反应法可在极短时间（15min）内合成完全固溶的Gd_1.6Nd_0.4Zr₂O₇立方烧绿石固化体,较常用制备方法（一般合成时间不低于48h）快近200倍;用该技术合成的样品在常温常压下的相转变温度及压力得以显著提高,烧绿石相更趋稳定;样品晶格常数随Nd含量的增加及合成温度的升高而逐渐增大,随合成压力的增加而逐渐减小。这种快速高效的合成方法为未来开展高放核素的工业固化提供了一种新的技术途径和基本数据参考。     

阳离子有序相Ce2Zr2O7.97的石墨还原制备及其结构表征

采用石墨还原法探索了CeO₂-ZrO₂二元体系在不同还原温度、还原时间条件下的物相组成及结构,借助X射线衍射、红外振动光谱等手段对还原样品进行了物相表征及结构分析。实验结果表明：通过石墨还原能在较低温度（T_red＝1050 ℃）、较短时间（t＝24 h）内合成纯相Ce₂Zr₂O_7.97,较传统先还原（95%Ar+5%H₂,T_red≥1400℃,t＞48 h）后氧化（O₂或空气气氛）工艺更简单经济;Ce₂Zr₂O_7.97相能在1050～1300 ℃、24～72 h还原条件下稳定存在并保留至室温而不发生相分解,其机制可能归因于石墨所形成的弱还原环境;Ce₂Zr₂O_7.97相拥有与烧绿石Ce₂Zr₂O₇相近的有序阳离子亚晶胞结构,但由于其氧空位（O3、O4、O11）被大部分氧离子所填充,导致该相结构对称性降低。本文提出的石墨还原法制备富氧相Ce₂Zr₂O_7.97有望成为一种较传统制备工艺更简单经济的新方法,而Ce₂Zr₂O_7.97相能在还原气氛中稳定存在,可为An₂Zr₂O_7+x固化体的存放环境提供借鉴和参考。     

Gd2O3-Nd2O3-ZrO2-CeO2体系的高温固相反应研究

为研究Gd₂O₃-Nd₂O₃-ZrO₂-CeO₂四元氧化物体系的高温固相反应,以Gd₂O₃、Nd₂O₃、ZrO₂、CeO₂混合粉体为原材料,在1 673 K和1 773 K温度下煅烧24、48、72 h,分别制备了系列样品,并对合成样品进行了XRD和SEM分析。结果表明,合成产物为具有缺陷萤石相且伴有少量烧绿石相的Gd_2-xNd_xZr_2-xCe_xO₇（0≤x≤2）晶体化合物。随着煅烧温度的升高和煅烧时间的延长,产物中立方烧绿石相的化合物增多,晶粒尺寸变大,且有少量未知相生成。进而探讨了锆基陶瓷固化多核素的潜在应用,并提出了未来研究的相关热点问题。     

(Sr0.1Th0.2Nd0.3La0.2Gd0.2)2Zr2O7高熵烧绿石固化体的制备及化学稳定性

以金属硝酸盐为原材料,通过溶胶-喷雾热解-高温烧结法制备了(Sr_0.1Th_0.2Nd_0.3La_0.2Gd_0.2)₂Zr₂O₇高熵烧绿石固化体。利用X射线衍射(XRD)、扫描电镜(SEM)、Raman光谱对固化体结构进行表征,通过MCC-1浸出实验方法分析了固化体化学稳定性。研究结果表明：高熵烧绿石固化体为纯相高熵烧绿石结构,最佳烧结温度为1 500℃。随着烧结温度增加,固化体晶粒和密度明显增加。浸出实验结果显示：La、Gd、Zr、Nd元素42 d归一化浸出率为10^-6 g/(m²·d)量级,Sr、Th元素的42 d归一化浸出率分别为10^-5 g/(m²·d)和10^-3 g/(m²·d)量级,固化体表现出良好的化学稳定性。     

Er2Ti2O7烧绿石基玻璃陶瓷固化体的制备工艺研究

为获得含单一钛酸盐烧绿石的玻璃陶瓷固化体,本文以Er₂Ti₂O₇作为钛酸盐烧绿石代表,在传统的烧结法制备工艺基础上,通过热雾喷解和晶核掺入的技术改进,分别研究了烧结温度、烧结时间、玻璃与陶瓷晶核质量配比等参数对Er₂Ti₂O₇基玻璃陶瓷固化体物相及结构的影响规律。XRD结果表明：在不同的烧结温度、烧结时间和质量配比下,均能获得含单一Er₂Ti₂O₇烧绿石的玻璃陶瓷固化体,Er₂Ti₂O₇前驱体在玻璃中的相稳定性好,未发生相分解,玻璃组分亦未受陶瓷相的影响而析出第二相;玻璃组分对陶瓷颗粒存在张应力作用,玻璃含量越高,Er₂Ti₂O₇的晶胞常数越大;提高烧结温度和烧结时间均有利于增强固化体中Er₂Ti₂O₇的结构有序性,但烧结温度效果强于烧结时间。SEM结果表明：Er₂Ti₂O₇在玻璃基体上呈四方形生长,与玻璃界面清晰,相容性好。固化体的物性测试结果表明,玻璃组分占比将直接影响固化体的表观孔隙率和致密度。根据以上结果可知,新工艺制备的样品具有相纯度高、烧绿石相与玻璃相容性好、两相比例可调等优点,较好地解决了钛酸盐烧绿石在玻璃基体中易发生相分解的问题。     

人造岩石固化体SrCeTi2O7的合成与性能研究

采用⁸⁸Sr模拟放射性核素⁹⁰Sr,Ce⁴⁺模拟四价锕系放射性核素。以分析纯SrCO₃、CeO₂和TiO₂为主要原料,通过高温固相反应制备SrCeTi₂O₇人造岩石固化体。对固化体的烧成工艺、物理性能、晶体结构及微观形貌进行研究,并对固化体的热稳定性及抗浸出性能进行探讨。结果表明,选择配方n(SrCO₃)∶n(CeO₂)∶n(TiO₂)＝1∶1∶2,在1 450 ℃下保温5 h可合成结构致密、晶型发育完整的SrCeTi₂O₇人造岩石固化体;Dicvol程序指标化结果表明,该固化体化合物属四方晶系,晶胞参数为a＝0.387 33(4) nm,c＝0.388 07(5) nm;SrCeTi₂O₇人造岩石固化体具有良好的热稳定性,经高达800 ℃热处理后样品仍保持原有物相不变;PCT-B粉末浸泡法测试结果表明,SrCeTi₂O₇人造岩石固化体具有较好的抗浸出性能,浸泡周期28 d时Sr、Ce和Ti的浸出率分别为3.51×10^-4、8.23×10^-8和2.02×10^-7 g/(m²·d)。     

喷雾热解合成An_2Zr_2O_7(An=La、Nd)烧绿石及结构分析

锆基烧绿石An2Zr2O7以优异抗辐照性能和化学稳定性成为高放废物中锕系核素的理想固化基材。镧系核素常作为替代核素进行锕系核素的固化研究,实验以硝酸盐为原料,以三价的镧系元素(La、Nd)模拟锕系元素,采用sol-喷雾热解方法在1 200℃、6h内合成了(La、Nd)2Zr2O7烧绿石。采用粉末X射线衍射(XRD)、扫描电镜(SEM)、拉曼光谱分析方法对合成的样品进行了结构表征,结果表明:利用该方法合成了单一物相的烧绿石立方结构An2Zr2O7;相对于La2Zr2O7的烧绿石结构,Nd2Zr2O7烧绿石具有向萤石结构转变的趋势。该合成方法为目前的高放废液人造岩石固化提供了一定的技术基础。     

高温结晶合成Mn2O3@MoS2复合材料及其对铀的吸附性能

采用高温熔盐电解法合成了MoS₂,为了提高MoS₂对铀的吸附性能,以MoS₂为基底复合Mn₂O₃。MoS₂的片层结构有效地分散了Mn₂O₃的团聚,同时引进了亲铀氧基团。采用电子扫描显微镜及能谱(SEM & EDS)、X射线衍射仪(XRD)、Zeta电位仪等对Mn₂O₃@MoS₂复合材料进行了表征,表征结果表明,高温结晶合成的Mn₂O₃@MoS₂复合材料具有完整的微观形貌和稳定的晶体结构。通过静态吸附批实验探究了在不同变量下Mn₂O₃、MoS₂和Mn₂O₃@MoS₂三个材料对溶液中铀的吸附效果,结果表明,Mn₂O₃@MoS₂的吸附性能优于Mn₂O₃和MoS₂,在pH=5.5时,吸附平衡时间为90 min,吸附动力学遵循准二级动力学模型,吸附等温线符合Langmuir模型。Mn₂O₃@MoS₂的单层饱和吸附容量为117.5 mg/g,在293.15~318.15 K的温度梯度中,升温有利于吸附进行。     

Mo在Al2O3上的吸附、解吸性能及其与U、Sr、Cs、I等杂质元素的分离

目前国际⁹⁹Mo面临供应危机,急需新技术和新反应堆。医用同位素生产堆是以²³⁵UO₂(NO₃)₂溶液为燃料的专用反应堆,生产成本低、三废少、经济效益高。本工作利用Al₂O₃为分离材料,从模拟的医用同位素生产堆（MIPR）燃料溶液中分离和纯化Mo。结果表明,经两次分离,Mo的总回收率大于 60%, U、Sr、Cs、I等杂质可以被除去,采用Al₂O₃从MIPR燃料溶液中提取⁹⁹Mo工艺可行。     

Gd2Zr2-xCexO7(0.0≤x≤2.0)的制备与表征

为获得钆锆烧绿石基固化体固化Pu后的物理性能、物相变化及微观形貌,本研究用Ce⁴⁺模拟Pu⁴⁺,以Gd₂O₃、ZrO₂和CeO₂粉体为原料,采用高温固相法,制备不同固溶度（0～100%,按摩尔计）的系列钆锆烧绿石固化体,并对密度、硬度、物相和微观形貌等进行表征。结果表明：实验所得系列固化体的密度和硬度均随着x的增大而增大,硬度H_V与x满足关系式H_V＝661.272 73+223.936 36x（R²＝0.946 38）。在x＝0.0时,所得固化体为单一的烧绿石结构;在x＝0.2时,固化体从烧绿石结构转变为萤石型结构;在0.2≤x≤2.0范围内,固化体均为单一萤石型结构。固化体微观形貌不规则,呈板块状。     

Application of combined neutron diffraction and impedance spectroscopy for in-situ structure and conductivity studies of La2Mo2O9

In-situ neutron diffraction combined with AC impedance spectroscopy was applied successfully to investigate the correlation between crystal structure and electrical properties of the La₂Mo₂O₉ oxide ion conducting electrolyte material. Neutron diffraction patterns were collected as a function of temperature while the AC impedance spectra were recorded simultaneously using a modified sample environment to monitor the conductivity change of the sample. A close relationship between unit cell parameters and the bulk conductivity was observed, confirming that the oxygen transport is dependent on the lattice structure. With the transition from the low temperature alpha to the high temperature beta phase, expansion of the crystal structure makes more space available for oxygen transport, leading to a dramatic increase of the ionic conductivity. The successful application of this technique provides a new method to simultaneously investigate crystal structure and electrical properties in electro-ceramics in the future.     

Gd2Zr2O7 pyrochlore: Potential host matrix for some constituents of thoria based reactor’s waste

The present work explores the potential of Gd₂Zr₂O₇ for incorporation of ThO₂ and Al₂O₃ which are components of Advanced Heavy Water Reactors (AHWR) waste. XRD studies reveal that the compositions corresponding to y from 0.0 to 0.4 in Gd_2−yTh_yZr_2−yAl_yO₇ are single phasic in nature and beyond y > 0.4 the biphasic region starts. The solubility of thoria in Gd₂Zr₂O₇ pyrochlore could be enhanced by more than five times by simultaneous incorporation of alumina. The lattice parameter increases with increase in Th and Al content in the series. The r_A/r_B ratio increases with increase in Th and Al content in Gd₂Zr₂O₇ and in turn the degree order increases as has been seen by gradual increase in the intensity of superstructure peaks. Single phasic samples were investigated by Raman spectroscopy also. Thermal expansion behavior of single phasic samples was investigated by HT-XRD. In order to confirm the nature of the phases backscattered images have been recorded on all the samples.     

Alpha-decay induced amorphization of Cm-doped Gd2TiZrO7

The sample of pyrochlore-based ceramic doped with a ²⁴⁴Cm isotope with a target composition Gd_1.935Cm_0.065 TiZrO₇ was prepared by cold pressing and sintering. The pyrochlore structure phase was predominant in the sample but minor perovskite and gadolinium zirconate (ideally Gd₂Zr₂O_7−x) were also present. The Ti/Zr pyrochlore phase was rendered amorphous at a dose of 4.6 × 10¹⁸ α-decays/g (0.60 dpa). Volume expansion of the pyrochlore lattice was found to be 2.7 vol.% at a dose of 3.85 × 10¹⁸ α-decays/g.     

Review of A2B2O7 pyrochlore response to irradiation and pressure

This article reviews recent research on swift heavy-ion irradiations and high-pressure studies on pyrochlores of the Gd₂Zr_2−xTi_xO₇ binary [1], [2], [3] and [4]. Applying three complementary analytical techniques (synchrotron X-ray diffraction, Raman spectroscopy and transmission electron microscopy) allowed for the investigation of the response of pyrochlore to irradiation and/or pressure. The chemical composition of pyrochlore has a strong effect on the character and energetics of the type of structural modifications that can be obtained under pressure or irradiation: For Ti-rich pyrochlores, the crystalline-to-amorphous transition is the dominant process. When Zr is substituted for Ti, an order-disorder transformation to the defect-fluorite structure becomes the increasingly dominant process. Except for Gd₂Zr₂O₇, single ion tracks in pyrochlore consist of an amorphous core, surrounded by a crystalline, but disordered, defect-fluorite shell. This shell is surrounded by a defect-rich pyrochlore region. In contrast to similar effects observed when pressure or irradiation are applied separately, the response of the pyrochlore structure is significantly different when it is exposed simultaneously to pressure and irradiation. The combination of relativistic heavy ions with high pressure results in the formation of a new metastable pyrochlore phase. TEM and quantum-mechanical calculations suggest that these novel structural modifications are caused by the formation of nanocrystals and the modified energetics of nanomaterials.     

γ辐照联合H_2O_2处理污泥滤液的研究

采用60 Coγ射线辐照处理污泥滤液,通过对比处理前后化学需氧量(COD)、紫外可见吸光度和浑浊度的变化,研究了辐照处理中初始pH、初始H2O2浓度和吸收剂量对污泥滤液处理效果的影响。结果表明:在相同吸收剂量和初始H2O2浓度条件下,酸性条件更利于CODCr的降低;γ辐照联合H2O2处理存在显著协同效应,吸收剂量为18.75kGy、初始H2O2浓度为2mmol/L时,污泥滤液CODcr去除率达70.4%,浑浊度下降94.9%。     

MgO-pyrochlore composite as an inert matrix fuel: Neutronic and thermal characteristics

Inert matrix fuels are an important component of advanced nuclear fuel cycles, as they provide a means of utilizing plutonium and reducing the inventory of ‘minor’ actinides. We examine the neutronic and thermal characteristics of MgO-pyrochlore (A₂B₂O₇: La₂Zr₂O₇, Nd₂Zr₂O₇ and Y₂Sn₂O₇) composites as inert matrix fuels in boiling water reactors. By incorporating plutonium with resonance nuclides, such as Am, Np and Er, in the A-site of pyrochlore, the k_infvs. burn-up curves are shown to be similar to those of UO₂, although the Doppler coefficients are less negative than UO₂. The Pu depletion rates are 88-90% (²³⁹Pu) and 54-58% (total Pu) when the inert matrix fuels experience a burn-up equivalent of 45 GWd/tHM UO₂. Because of the high thermal conductivity of MgO, the center-line temperatures of the MgO-pyrochlore composites at 44.0 kW/m are lower than those of UO₂ pellets. After burn-up, the A-site cation composition is 15-35 at.% lower than that of the B-site cations in pyrochlore (e.g., A_1.84B_2.17O_7.00) due to the fission of Pu in the A-site and the presence of fission product elements in the A- and B-sites of the pyrochlore structure.     

Study on effects of swift heavy ion irradiation on the crystal structure in CeO2 doped with Gd2O3

To simulate the effects of Gd₂O₃-doping and high-energy fission products in UO₂, Gd₂O₃-doped CeO₂ pellets were irradiated with 200-MeV Xe¹⁴⁺ ions. Doping and irradiation effects were analyzed using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The lattice constant of CeO₂ decreases and the local structure is disordered with increased doping levels. However, the irradiation induces an expansion of the lattice and a disordering of atomic arrangement near the Gd atoms. The effects of the irradiation become more pronounced with increasing Gd₂O₃-dopant levels. Our results are compared with those of a study involving Er₂O₃-doped CeO₂.     

Ion beam analysis of partial lithium extraction of LiMn2O4 by chemical delithiation

Lithium manganese oxide, LiMn₂O₄, has been studied by many research groups. This material is a great candidate to be used as positive electrode in rechargeable lithium-ion batteries because of its low cost, abundant precursors and non-toxicity. LiMn₂O₄ has a spinel Fd-3m structure and shows a reversible extraction and insertion of lithium ions that is one of the most important characteristic of positive electrodes in rechargeable batteries.In this work, LiMn₂O₄ samples were synthesized by solid state reaction. A partial lithium removal was performed on this system by chemical delithiation using HCl aqueous solutions at different concentrations. Six partial-extracted compounds were obtained and characterized by Ion beam analysis (IBA) in order to obtain the Li concentrations. X-ray diffraction (XRD) and Rietveld analyses were also performed. A rigorous study of lithium contents is critical to analyze the structure properties of these compounds and samples production parameters. The IBA method used in this work was the analysis of energy spectra of elastic backscattered (EBS) proton from Mn, O and Li nuclei and the α-particles energy from the ⁷Li(p,α)⁴He nuclear reaction (NR).     

Enthalpy measurements of La2Te3O9 and La2Te4O11

Enthalpy increment measurements on La₂Te₃O₉(s) and La₂Te₄O₁₁(s) were carried out using a Calvet micro-calorimeter. The enthalpy values were analyzed using the non-linear curve fitting method. The dependence of enthalpy increments with temperature was given as: H°(T) − H°(298.15 K) (J mol⁻¹) = 360.70T + 0.00409T² + 133.568 × 10⁵/T − 149 923 (373 ? T (K) ? 936) for La₂Te₃O₉ and H°(T) − H°(298.15 K) (J mol⁻¹) = 331.927T + 0.0549T² + 29.3623 × 10⁵/T − 114 587 (373 ? T (K) ? 936) for La₂Te₄O₁₁.