Combustion synthesis and thermal expansion measurements of the rare earth–uranium ternary oxides RE6UO12 (RE=La, Nd and Sm)

Rare earth–uranium ternary oxides were synthesized by a solution combustion route. The starting materials were the corresponding metal nitrates and urea. In these preparations, the metal nitrates act as oxidizer and urea as fuel. Highly exothermic decomposition of the metal nitrate–urea complexes on heating at about 500 K leads to a combustion process yielding RE₆UO₁₂ fine powders. Thermal expansion measurements of these compounds were carried out in the temperature range of 298–1173 K by high temperature X-ray powder diffractometry. The observed axial thermal expansion behaviour is explained on the basis of the crystal chemistry of the compounds.     

Synthesis and Characterization of Nano-sized Boron Powder Prepared by Plasma Torch

Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCl3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4.5:1, total feed of 4.9 m3/h, and plasma power of 25 kW. The samples were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and inductively coupled plasma - mass spectrometry (ICP-MS), inductively coupled plasma - atomic emission spectrometry (ICP-AES), inductive combustion infrared absorption (ICIA) and Infrared thermal conductivity of oxygen and nitrogen analyzer (ITCA). The results show that the boron powders have different crystal structures with higher dispersion and purity. The average diameter is about 50 nm, and the purity is 90.29% or so. This new technology can use simple process to produce high quality boron powders, and is feasible for industrial production.     

锆英石对三价锕系核素固化能力及抗γ射线辐照稳定性

为研究锆英石对三价锕系核素的固化效果及抗γ射线辐照稳定性,以Eu³⁺模拟三价锕系核素,ZrO₂、SiO₂和Eu₂O₃粉体为原料设计了包容量为25%～10%（摩尔分数）的锆英石固化体配方,在1500℃条件下保温22h进行固化体的制备,通过⁶⁰Co源γ射线辐照装置对固化体进行γ射线辐照实验。利用X射线衍射仪、激光拉曼光谱仪和扫描电子显微镜对所制备固化体及经γ射线辐照后固化体的物相、结构及微观形貌进行了分析。结果表明：固化体中虽加入了2.5%～10%的Eu₂O₃,但主物相仍以锆英石物相为主,均具有较高的结晶度,随着Eu₂O₃添加量的增加,变生程度略显增加;固化体经579.1kGy的γ射线辐照后主物相依然以锆英石物相为主,变生程度较辐照前略显增加,但依然具有较高的结晶度。     

Estimation of plasma parameters in the process of micro-scale powder plastic and characteristics of its products

The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I (696.54 nm) lines by optical emission spectroscopy (OES) in the process of plasma plastic, and the morphology and microstructure of tungsten (W) powders were investigated by scanning electron microscope (SEM) and x-ray Diffraction (XRD), respectively. The results show that the assumption of local thermodynamic equilibrium (LTE) was invalid at the end of the plasma jets, and earlier than this after the injection of tungsten powder. The temperature and electron density of the plasma jets were up to about T=6797 K with Q_c=50 slpm and n_e=1.05×10¹⁶ cm⁻³ with Q_s=115 slpm at Z=60 mm, respectively, and both dropped rapidly with the injected tungsten powders of 20 μm. After the plasma plastic process, the spherical tungsten powders were prepared and there were some satellite particles on the surface of the spherical products. The tungsten powders were both composed of a single equilibrium α-W phase with a body centered cubic (bbc) crystal structure before and after plasma treatment.     

Surface Treatment of Polypropylene Powders Using a Plasma Reactor with a Stirrer

A radio frequency argon plasma reactor with a stirrer was employed for the surface treatment of polypropylene (PP) powders. The changes in the superficial contact angle and the superficial composition of the un-treated and treated PP powders were analyzed by means of water contact angle (WCA) measurement, X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The water contact angle changed from the original value of 130.2° before plasma treatment to the value of 73.6° after treatment for 5 minutes. With the increase in plasma treating time, there were a decrease in the water contact angle and an increase in the content of oxygen containing polar functional groups (i.e., C-O, C=O and O-C=O). Both XPS and ATR-FTIR results indicated that the plasma treatment led to the formation of oxygen containing polar functional groups due to oxidation on the surface of the PP powders, and the trend of variation of the water contact angle with plasma treating time was related to the concentration of oxygen atom on the treated PP powders surface. Furthermore, the aging of the plasma-treated PP powders was investigated.     

Microstructural changes in adjusted uranium during thermal cycling

The changes in microstructure of adjusted uranium during thermal cycling between 400 and 600°C were examined using hardness measurements, back-reflection X-ray techniques, and optical and high-voltage electron microscopy. It was found that the changes in microstructure resulting from thermal cycling are similar to those occurring during conventional hotworking operations in many materials. The microstructures produced by cycling have some similarities to those induced by irradiation. The implications of these observations are discussed.     

模拟核素固化体ZrxCe1-xSiO4的制备和表征

为研究锆英石对放射性核素Pu(Ⅳ)的固化能力,选用Ce(Ⅳ)作为Pu(Ⅳ)的模拟替代物质,以ZrO₂、SiO₂和CeO₂粉体为原料,在1500 ℃条件下通过保温72 h进行Zr_xCe_1-xSiO₄（0≤x≤0.5）系列样品的制备。利用XRD对所获样品的物相和结构进行分析,并采用Rietveld结构精修方法对样品的晶胞参数进行精细化计算。结果表明：当0≤x≤0.05时,样品保持为锆英石相;当x>0.05时,有CeO₂物相出现。在锆英石相范围内,晶胞参数a、c、V与x之间符合线性关系。     

锆英石对模拟核素Ce~(4+)的固化能力

为研究锆英石对四价锕系核素的固化能力,利用Ce4+模拟四价锕系核素。以ZrO2、SiO2和CeO2粉体为原料设计了包容量为5%～20%(摩尔分数)的锆英石固化体配方,在1500℃下保温22h进行固化体的制备。利用X射线衍射仪、扫描电子显微镜、红外光谱仪和激光拉曼探针对所制备固化体的物相、结构及微观形貌进行了分析。研究结果表明:在固化体中虽加入了5%～20%的CeO2,但主物相仍以锆英石物相为主,且均具有较高的结晶度,随着CeO2添加量的增加,固化体的无序程度略显增强。     

Study on the RF inductively coupled plasma spheroidization of refractory W and W-Ta alloy powders

Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a formidable task. In this paper, spherical refractory metal powders processed by high-energy stir ball milling and RF inductively coupled plasma were investigated.By utilizing the technical route, pure spherical tungsten powders were prepared successfully, the flowability increased from 10.7 s/50 g to 5.5 s/50 g and apparent density increased from6.916 g cm~(-3) to 11.041 g cm~(-3). Alloying element tantalum can reduce the tendency to microcrack during tungsten laser melting and rapid solidification process. Spherical W-6 Ta(%wt)powders were prepared in this way, homogeneous dispersion of tantalum in a tungsten matrix occurred but a small amount of flake-like shape particles appeared after high-energy stir ball milling. The flake-like shape particles can hardly be spheroidized in subsequent RF inductively coupled plasma process, might result from the unique suspended state of flaky particles under complex electric and magnetic fields as well as plasma-particle heat exchange was different under various turbulence models. As a result, the flake-like shape particles cannot pass through the high-temperature area of thermal plasma torch and cannot be spheroidized properly.     

基于蒙特卡罗模拟的不同轴向长度不同晶体材料的PET灵敏度和散射分数研究

长轴向PET是未来PET的发展方向。本文根据NEMA NU2—2012标准利用蒙特卡罗模拟工具研究了不同轴向长度和不同晶体材料对PET灵敏度和散射分数的影响,并将模拟结果与实验结果进行了比较。结果表明,模拟结果与实验结果符合很好,验证了模拟的可靠性。灵敏度随轴向长度的增加而增加,但这种增加是非线性的,且在某一长度处变化最明显,不同的PET对应的灵敏度变化最明显的轴向长度也不同。灵敏度表现最好的晶体为LuAP,YAP晶体的灵敏度最低。晶体材料和轴向长度对散射分数均没有明显影响。     

Monte Carlo Simulation Study on Impact of AFOV and Crystal on Scatter Fraction and Sensitivity of PET

Long axial field of view (AFOV) PET is the development direction of future PET. The purpose of this paper is to simulate PET using GATE toolkit to evaluate scatter fraction (SF) and sensitivity for different AFOV and different crystal materials according to NEMA NU2-2012 protocol. The simulation results were compared with the experimental results. The simulation results are in accordance with experimental results, and the reliability of the simulation is verified. As the AFOV increases, the sensitivity also increases, but this increase is non-linear and changes most significantly at a certain length, and the axial length of the most obvious sensitivity change is different for different PET. The crystal with the best sensitivity is LuAP, and the YAP crystal has the lowest sensitivity. The crystal material and AFOV have no significant impact on the scatter fraction.     

立方烧绿石Gd_2Zr_2O_7的高温高压合成

为探索高温高压固相反应法合成Gd2Zr2O7烧绿石的可能性,以Gd2O3和ZrO2的混合粉体为原料,在5.2GPa压力、1473～1873K温度范围内进行了实验研究。通过XRD对合成样品进行了结构表征,结果证实,在5.2GPa和1873K条件下,保温保压30min,成功地合成出单一物相的、具有立方烧绿石结构的Gd2Zr2O7化合物。这种新的合成方法对于开展武器级多余钚和含钚高放废物固化具有重要的科学价值和实际意义。     

Investigation of plasma immersion ion implanted niobium oxide and titanium nitride films by nanohardness measurement

Plasma immersion ion implantation has to date mainly been used for surface and near-surface treatment of bulk material. On the other hand, it also allows for implantation into thin films. When rare gas ions are used this treatment may alter the microstructure of the films. Application of reactive ions additionally changes the composition and may lead to formation of compound phases such as oxides and nitrides. Thin films of niobium and titanium were deposited onto steel and silicon by electron beam evaporation. The films were then subjected to plasma immersion implantation. For niobium, an RF excited oxygen plasma was used. Titanium was treated with a nitrogen ECR microwave plasma. The resulting oxide and nitride films were analyzed by depth-sensing nanohardness measurements. The results were correlated with analytical findings from Rutherford backscattering and X-ray diffraction measurements. It turns out that nitrogen ion implantation into titanium yields an increase in hardness with increasing process time. By contrast, oxygen incorporation into niobium leads to a reduction in hardness which could be correlated with the oxygen content. With increasing amount of oxygen entering the film from the surface, the hardness decreases, starting from the surface and following the oxygen amount in depth.

Observed hardness profile and stoichiometry profile investigated by RBS exhibit the same multilayered structure.     

Synthesis and characterization of Li4SiO4 nano-powders by a water-based sol-gel process

The water-based sol-gel process for the synthesis of Li₄SiO₄ nano-powders was reported for the first time. LiOH·H₂O and aerosil SiO₂ were used as the starting materials with citric acid (C₆H₈O₇·H₂O) as the chelating agent. Li₄SiO₄ powders with particle size as small as 100 nm were successfully synthesized at the temperature as low as 675 °C. Phase analysis, morphology, sintering behavior of the powders and ionic conductivity of the sintered bodies were investigated systematically. The experimental results showed that the powders obtained by the water-based sol-gel process (SG) possessed excellent sinterability, exhibiting a linear shrinkage of 5.2% while sintered to 900 °C, more than 3 times that of the powders obtained by solid state reaction (SSR). The bulk conductivity of the SG sintered bodies was much higher than that of the SSR samples at the same testing temperature.     

Investigations of single crystal and polycrystalline metal mirrors under erosion conditions in TEXTOR

Metal mirrors are planned for optical diagnostic systems of ITER. However, erosion, deposition and particle implantation can change the performance of mirrors. Mirrors made from the single crystal (SC) materials are among the main candidates for use in ITER diagnostic systems operating under erosion-dominated conditions. Laboratory tests have confirmed good optical performance of SC mirrors under erosion, but the dedicated direct comparative test in tokamak environment was missing.Such a direct test was performed in TEXTOR. Single crystal molybdenum, tungsten and polycrystalline (PC) molybdenum mirrors were exposed under the same conditions in the SOL plasma of TEXTOR. Surface and optical properties of mirrors were characterized before and after exposure. Before exposure glow discharge cleaning in hydrogen restored the reflectivity of mirrors oxidized during storage on air.No significant changes in total reflectivity were observed for all mirrors after exposure. Drastic increase of diffuse reflectivity was measured for PC Mo mirror, no change for a SC one. Thus, specular reflectivity of single crystal is higher than of polycrystalline one. The most affected wavelength range is 250-1000 nm, no significant change of reflectivity was noticed in the range 1000-2000 nm. Negligible effect of the exposure on polarization characteristics was observed.     

Zr-Sn-Nb-Fe合金显微组织及耐腐蚀性能研究

将Zr-Sn-Nb-Fe合金样品冷轧后在500和560℃下分别保温不同时间,在350℃、16.8MPa、含70μg/gLi⁺的LiOH水溶液中腐蚀,500℃/100h样品的耐腐蚀性能最好。用透射电镜（TEM）研究了这些样品的显微组织和第二相,观测到随着保温时间延长,500℃下保温样品中的第二相由连续片层逐渐转变成带状分布的颗粒,保温时间达到100h时,基体内析出βNb。560℃下保温样品与500℃下保温样品有相似的组织转变过程,只是时间大幅缩短,保温仅10h时,基体已完全再结晶为等轴晶。     

Interfacial microstructures and hardness distributions of vacuum plasma spraying W-coated ODS ferritic steels for fusion plasma facing applications

In the present study, interfacial microstructures and hardness distributions of W-coated ODS steels as plasma facing structural materials were investigated. A vacuum plasma spraying (VPS) technique was employed to fabricate a W layer on the surface of the ODS ferritic steel substrates. The microstructural observations revealed that the VPS-W has very fine grains aligned toward the spraying direction, and a favorable interface between W and ODS ferritic steels by a mechanical inter-locking without an intermetallic layer. However, crack-type defects were found in VPS-W. Because a brittle inter-diffused layer does not exist at the joint interface, the hardness was gradually distributed in the joint region. After neutron irradiation, irradiation hardening significantly occurred in the VPS-W. However, the hardening of VPS-W was less than that of bulk W irradiated at 773 K. Thus, the VPS is considered to be one of the promising ways to join dissimilar materials between W and ODS steels, which can avoid the formation of an interfacial intermetallic layer and create favorable irradiation hardening resistance on the W coated layer.     

Comparative research of plasma-assisted milling and traditional milling in synthesizing AlN

In this paper, traditional milling and discharge plasma-assisted milling are employed to synthesize aluminum nitride (AlN) powder at nanometer scale by milling the mixture of aluminum and lithium hydroxide monohydrate. AlN powders can be generated in traditional milling and plasma-assisted milling in an hour milling time. Differential thermal analysis curves show that the reaction temperature of the powders treated by plasma-assisted milling is lower than that of traditional milling. These results indicate that plasma-assisted milling has higher efficiency in the synthesis of AlN, getting smaller crystallite size and activating powder. Moreover, an optical emission spectrum is employed to demonstrate the active species in plasma. The different formation process of AlN in the two-milling process, and the promotion effects of plasma in the milling process are discussed.     

Comparative research of plasma-assisted milling and traditional milling in synthesizing AIN

In this paper,traditional milling and discharge plasma-assisted milling are employed to synthesize aluminum nitride (AlN) powder at nanometer scale by milling the mixture of aluminum and lithium hydroxide monohydrate.AlN powders can be generated in traditional milling and plasma-assisted milling in an hour milling time.Differential thermal analysis curves show that the reaction temperature of the powders treated by plasma-assisted milling is lower than that of traditional milling.These results indicate that plasma-assisted milling has higher efficiency in the synthesis of AlN,getting smaller crystallite size and activating powder.Moreover,an optical emission spectrum is employed to demonstrate the active species in plasma.The different formation process of AlN in the two-milling process,and the promotion effects of plasma in the milling process are discussed.