粉末表面氧化对二氧化铀芯块烧结性能的影响

用SEM、XRD、BET和DSC TG、热膨胀仪等观察了UO₂粉末的形貌结构并研究粉末氧化前后的烧结性能,分析了UO₂粉末表面预氧化对二氧化铀芯块烧结性能的影响。结果表明,240℃×8 h是UO₂粉末预氧化表面改性的最佳工艺;粉末改性后表层为UO_2+x和少量U₃0₇,改性粉末压坯在氩气气氛中开始发生收缩的温度降低了530-600℃,平均线收缩率提高了1倍;在本氩气保护条件下,热膨胀试验后芯块的密度从8.52 g/cm³提高到9.44 g/cm³。采用本改性粉末,在1300℃×5 h/N2+5%CO₂-1500℃×1 h/H₂批试烧结,其密度达10.26 g/cm³,O/U比为2.013。     

Application of Microwave Radiation to Produce Uranium Dioxide Powder from Its Trioxide

Radiochemistry - The possibility of producing UO2 powder from UO3 using microwave radiation (power 300 W) in the presence of organic compounds with amino groups: carbohydrazide (CH),...     

Mo-8wt%Cu纳米复合粉末的制备和烧结

采用机械合金化法制备出Mo-8wt%Cu超细复合粉末,并对由该复合粉末所制得的压坯进行了液相烧结,利用SEM、XRD等分析手段对复合粉末的特性和烧结体的组织进行了表征和观察,实验结果表明,该方法制备的Mo-8wt%Cu超细复合粉末颗粒细小,平均粒径在300nm左右,高能球磨后的复合粉末由Mo-Cu过饱和固溶体相和Cu相组成,而且两相的晶粒度达到纳米级,其中Mo-Cu过饱和固溶体相的晶粒约为106nm,复合粉末具有很高的烧结特性,经高温烧结后合金致密度达到98.5%以上,而且金相组织分布均匀。     

Synthesis of High-Density Pellets of Uranium Dioxide by Spark Plasma Sintering in Dies of Different Types

A procedure for electric pulse consolidation of commercial UO₂ powders of various ceramic grades into high-density fuel pellets using dies of various types was studied. The influence of the parameters of spark plasma sintering (SPS) on the chemical composition of the initial powders and quality of ready UO₂ pellets was examined. The main advantages and drawbacks of the SPS process for consolidation of UO₂ powder in standard graphite dies were revealed. A novel alternative procedure for SPS of UO₂-based fuel pellets in Mo-based dies was suggested. High quality of the pellets (density 97.5–98.4% of theoretical, no C impurity, mean grain size no more than 3 μm) and mild sintering conditions (1100°С, 141.5 MPa, 25 min) make the process highly promising. The results obtained are of interest for the development and possible implementation of an industrial SPS process for production of ceramic nuclear fuel.     

二氧化铀粉末运输容器假想跌落事故下的安全设计与试验验证

目的 设计易裂变二氧化铀粉末运输容器,证明容器在最危险姿态下,可以满足9 m跌落的核临界、屏蔽安全和放射性物质包容相关设计准则。方法 设计外柔内刚的三层密封容器,内外壳之间填充聚氨酯减振吸能材料,建模分析容器多种姿态下的结构与功能材料动态响应,确定最危险跌落姿态。针对最危险工况开展实际跌落测试试验,证明容器在假想事故下的安全性。结果 容器在最危险跌落工况下,聚氨酯材料减振吸能效果与设计计算相符,中子吸收板、中子慢化板等功能材料位置和缺损量符合要求。二氧化铀粉末的密封性得以保障。结论 以有限元分析为基础的容器仿真分析与样机试验结果匹配度较高,试验样机通过了相关跌落试验,证明了容器在危险姿态下的9 m跌落安全性能。     

W-20wt%Cu超细复合粉末的制备和烧结

采用喷雾干燥-氢气还原法制备出W-20wt%Cu超细复合粉末,并对由该复合粉末所制得的压坯进行了高温烧结,利用SEM、XRD等分析手段对复合粉末的特性和烧结体的组织进行了表征和观察。实验结果表明,由该方法制备的W-20wt%Cu超细复合粉末颗粒细小,平均粒径在200nm左右;喷雾干燥后的氧化物复合粉末在还原后产生了新的合金相（Cu0.4W0.6）,还原后的复合粉末由Cu0.4W0.6相和Cu相组成,而且两相的晶粒度达到纳米级,其中Cu0.4W0.6相的晶粒约为33nm,Cu相的晶粒约为63nm;复合粉末具有很高的烧结特性,经高温烧结后合金致密度达到98%以上,而且金相组织分布均匀。     

Finite Element Simulation of Die Pressing and Sintering

Numerical simulation of die compaction and sintering is a promising tool for reducing development times and costs or optimizing production cycles. Finite element simulations allow qualitative and quantitative predictions of undesirable distortions after firing. Even qualitative predictions of crack formation are possible.     

U和UO2状态方程研究进展

铀和二氧化铀都是核科学与核工程中的重要材料,长期以来都不缺乏对它们的状态方程的研究.它们生产、存储和使用的环境复杂,涵盖宽温、宽压、强辐照、表面辐射、氦泡演化等极端条件,需要从实验和理论出发获取不同温度和压力下的材料物性,如晶体结构、相变行为、压缩性质、弹性性质与输运性质.此外,它们都属于强关联电子体系,拥有丰富的相图与奇特的物理性质,因此在实验与理论上研究它们的状态方程等物性具有极大的挑战性,该项研究一直属于前沿研究的热点.数十年来,人们采取各种实验手段,对铀和二氧化铀的热力学物性进行了测量;但由于铀及其化合物的特殊性质,相关实验研究工作仍存在一定程度上的困难.而另一方面,自1990年代以来,随着第一性原理方法的发展,使用密度泛函理论(DFT)方法对铀和二氧化铀物理性质展开计算的工作也不断涌现,不仅与实验工作相互验证,而且填补了实验条件无法企及的极端条件下的参数空白.随着计算机软硬件和数值算法的发展,相关DFT方法已经获得了较大突破,对铀和二氧化铀状态方程的描述也更为准确.其中,修正电子多体关联效应的动力学平均场方法(DMFT)以及修正声子振动能的平均场势方法(MFP)等算法是值得研究者进一步关注的.本文就20世纪以来对金属铀和二氧化铀实验和理论状态方程的研究进展进行了梳理,先后针对实验测量和理论计算两方面的晶体结构和相变行为、准静态压缩与冲击绝热压缩曲线、弹性力学、输运性质进行了概括总结,并探讨了二氧化铀晶体缺陷行为的相关研究工作.此外,本文还利用第一性原理方法对铀和二氧化铀的状态方程做了简要的计算,验证了已有公开文献中的结果,这将有助于后续研究.     

Preparation of Polycrystalline Singe-phase K0:3MoO3 by Hot Isostatic Pressing Sintering

Nearly single-phase and polycrystalline charge-density-wave compound K0.3MoO3 have been prepared by using a simple method. In this work, K2CO3 and MoOs were used as starting materials and reacted by hot isostatic pressing （HIP） sintering. The product is nearly single phase K0.3MoO3 determined by X-ray powder diffraction （XRD） and energy dispersive spectroscopy （EDS）. Measurement of temperature dependence of resistivity reveals that the transport property of polycrystalline K0.3MoO3 obviously differs from that of single crystal due to the grain boundaries and the anisotropic structure in this kind of compound.     

氢化钛粉烧结制备纯钛工艺研究

本实验选用氢化钛粉代替传统氢化脱氢(HDH)钛粉为原料,通过成型-烧结(脱氢)工艺制备纯钛。研究烧结温度和烧结时间对纯钛相对密度的影响,确定制备纯钛的最优工艺条件。最终确定氢化钛粉烧制备结纯钛的最优工艺条件为:升温速率为10 ℃/min,烧结温度为1 200 ℃,烧结时间为4 h。实验制备的烧结纯钛符合ASTM B348标准中等级4的规定,烧结件平均抗拉强度σ_b能够达到601.7 MPa,平均延伸率δ为20%,截面收缩率ψ平均为25.67%。     

苹果酸络合物沉淀法制备纳米二氧化钛粉体

提出了一种苹果酸络合物沉淀法制备高纯纳米二氧化钛粉体方法。使含有适量表面活性剂的Ti4+与C4H4O52-反应生成苹果酸钛络合物前驱体Ti2O2(OH)2C4H4O5·4H2O,经洗涤、干燥,在900℃下煅烧2h,得到纳米TiO2粉体。经XRD和TEM检测,产物纳米二氧化钛为金红石型结构,平均粒径为40nm。     

纳米复合WC-Co粉末的烧结研究进展

纳米复合WC-Co粉末的烧结是纳米晶WC-Co硬质合金制末的烧结研究进展,包括纳米复合粉末的烧结特性、烧结机理和常用的烧结方法.     

Evaporation and Condensation of Uranium Dioxide in an Electromagnetic Field

New physical phenomena related to the interaction of laser radiation with high evaporation materials, in particular with uranium dioxide, have been experimentally revealed by a subsecond heating technique. The first phenomenon, interpreted as an absorption flash, was observed in laser heating the sample and was manifested as a sharp drop in temperature on the heating curve. The second phenomenon, interpreted as a threshold condensation of vapor on the sample, was revealed during the cooling stage of the sample initially heated by laser radiation. This was manifested as an exothermal condensation peak on the cooling curve. The study of these phenomena has shown that there was a stable vapor zone above a sample in the field of laser radiation. The size and shape of the small particles produced due to laser evaporation and mainly formed in this vapor zone depended on the power of the laser radiation and the pressure of the inert gas. A change in the parameters of the vapor zone by changing the power of the laser radiation and the pressure of the inert gas gives the potential to produce nanoparticles of targeted sizes. Thus, the study of physical processes and mechanisms of forming nanoparticles of refractory materials at high temperatures motivates further development of the method of laser evaporation for producing nano-dimensional powders of targeted sizes and properties. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

埋碳烧结法制备碳/铝酸钙复合粉体及其微观表征

以有机酸钙(草酸钙、柠檬酸钙、硬脂酸钙)和氧化铝为原料,采用埋碳烧结法制备碳/铝酸钙复合粉体。借助X射线衍射仪(XRD)、拉曼光谱(Raman)和扫描电子显微镜(SEM),研究了烧结温度和有机酸钙种类对产物物相组成及显微结构的影响,通过粒度分析仪、热重分析仪对其性能进行检测。结果表明,烧结温度由1 200 ℃升至1 400 ℃,产物中C₁₂A₇逐渐转变为CA和CA₂,与以碳酸钙为钙源的试样相比,有机酸钙1 400 ℃烧结试样的CA₂含量较高;各试样拉曼光谱图中在1 350 cm-1和1 580 cm-1附近均出现了自由碳的D峰和G峰,表明各试样中均含有自由碳;SEM分析表明以柠檬酸钙为钙源和碳源的试样(1400-Cit)经1 400 ℃埋碳烧结后产物中自由碳弥散分布于铝酸钙中并被其包裹,形成球形复合粉体。利用氧化失重法测得1400-Cit试样的碳含量最高,其质量分数达5.98%。     

Features of Uranium Stereochemistry in Uranyl Oxofluorides

Radiochemistry - Crystal chemical analysis was carried out of compounds containing UO22+ ions in the structure, which coordinate fluorine and oxygen atoms. It was found that in 193 complexes of the...     

Sialon粉体的无压烧结

为获得致密的Sialon陶瓷材料,采用自制Sialon粉末,分别添加8.5％Al2O3-1.5％Y2O3和8.5％Si3N4-1.5％Y2O3(均为质量分数)系两种烧结助剂后进行充分混合,混合物粉末在钢模中冷压成两种压坯试样,然后在N2气氛中分别在1600℃保温4h和1550℃保温4h进行无压烧结.利用XRD、SEM等技术表征反应过程和产物特征.试样的体积密度分别达到最高值3.1 g/cm3和3.02 g/cm3;显微硬度分别为1639 HV/GPa0.5和1651 HV/GPa0.5.     

Oxidation of Uranium Dioxide with Manganates and Permanganates in Carbonate Solutions

Oxidation, dissolution of uranium dioxide with some alkali, alkaline-earth metal man-ganates and permanganates in carbonate solution was studied. The kinetics of decomposition of potassiummanganate and permanganate in solutions of some carbonates were studied spectrophotometrically in the range of pH from 7.8 to 13.0. It was found that the stability of MnO₄ ^- and MnO₄ ^2- ions and the pathways of their decomposition are governed by both pH and the nature of salts. The results of similar measurements in the presence of uranium dioxide showed that throughout the studied range of pH to the higher rate of conversion of KMnO₄ to K₂MnO₄ corresponds the higher rate of oxidation and dissolution of UO₂ in carbonate solution.