Synthesis of Nano-Size AlN Powders by Carbothermal Reduction from Plasma-Assisted Ball Milling Precursor

Nano-size aluminum nitride(AlN) powders have been successfully synthesized with a high efficiency method through annealing from milling assisted by discharge plasma(p-milling)alumina(Al_2O_3) precursors. The characterization of the p-milling Al_2O_3 powders and the synthesized AlN are investigated. Compared to conventional ball milling(c-milling), it can be found that the precursors by p-milling have a finer grain size with a higher specific surface area,which lead to a faster reaction efficiency and higher conversion to Al N at lower temperatures. The activation energy of p-milling Al_2O_3 is found to be 371.5 kJ/mol, a value that is much less than the reported value of the unmilled and the conventional milled Al_2O_3. Meanwhile, the synthesized Al N powders have unique features, such as an irregular lamp-like morphology with uniform particle distribution and fine average particle size. The results are attributed to the unique synergistic effect of p-milling, which is the effect of deformation, fracture, and cold welding of Al_2O_3 powders resulting from ball milling, that will be enhanced due to the introduction of discharge plasma.     

Simulation of the effects of different substrates,temperature,and substrate roughness on the mechanical properties of Al_2O_3 coating as tritium penetration barrier

Residual thermal stress in the system is a serious problem that affects the application of tritium permeation barrier coatings in fusion reactors. The stress not only determines the adhesion between coating and substrate, but also changes the properties of the material. In this study,finite element analysis was used to investigate the relationship between the residual thermal stress and the mechanical properties of Al_2O_3 tritium penetration barrier systems. Moreover, the residual thermal stress influenced by factors such as different substrates, temperature, and substrate roughness was also analyzed. The calculation showed that the hardness and elastic modulus increased with increasing compressive stress. However, the hardness and elastic modulus decreased with increasing tensile stress. The systems composed of Al_2O_3 coatings and different substrates exhibited different trends in mechanical properties. As the temperature increased, the hardness and the elastic modulus increased in an Al_2O_3/316 L stainless steel system; the trend was opposite in an Al_2O_3/Si system.Apart from this, the roughness of the substrate surface in the system could magnify the change in hardness and elastic modulus of the coating. Results showed that all these factors led to variation in the mechanical properties of Al_2O_3 tritium permeation barrier systems. Thus, thedetailed reasons for the changes in mechanical properties of these materials need to be analyzed.     

316L不锈钢基材防氚渗透Al2O3涂层残余热应力分析

在聚变堆防氚渗透第一壁制备过程中,Al2O3涂层与316 L不锈钢基体间由于材料热膨胀系数的差异容易产生裂纹.本文利用有限元方法研究了AL2O3/316 L涂层制备过程中的残余应力的分布.结果表明在界面等区域存在严重的应力集中;涂层厚度、孔隙率大小以及涂层是否致密对残余应力水平有很大影响.涂层内部关键区域的残余应力水平,随着涂层厚度增加而增加;孔隙率不同对界面的残余应力分布趋势没有明显影响,但对应力值却有很大影响,孔隙率增大涂层残余应力最大值下降;相同厚度情况下致密Al2O3涂层所受压应力远大于多孔Al2O3涂层承受的残余应力.     

核电站废气中氢氧复合的研究(Ⅰ)——小型试验

为了适应我国核电发展的需要,进行了核电站废气中氢氧复合的研究。研制了适合于核电站工艺废气处理中氢氧复合用的高效催化剂,进行了氢氧复合各种工艺条件试验,确定了氧氧复合的最佳工艺条件。实验结果表明:含钯量为0.5％的Pd-Al_2O_3催化剂性能良好,氢氧复合率均很高,氢复合率>98.3％,氧复合率>99.9％。复合后尾气中氢氧含量很低,氧含量<3ppm,氢含量<400ppm(体积ppm)。在一定的工艺条件下完全能满足核电站工艺废气处理的要求。     

氚处理设备敷面材料的选择

本实验研究了15种金属和非金属材料表面对氚气的吸附、转化(为氚化物)和转移(进人体)的性能。结果表明,在所检查的7种金属材料中,氧化膜保存完好的硬铝吸附、转化和转移氚的能力较弱,氧化膜破坏后这种能力则大为增强;在8种非金属材料中,以聚四氟乙烯吸附、转化和转移氚的能力为最低,其次是聚乙烯和普通玻璃。氚处理设备应尽量选用硬铝、聚四氟乙烯、玻璃和聚乙烯作表面结构材料,或者用这些材料敷面,以减少工作人员对氚的吸收。     

A New Model for Exchange of Deuterium in Oxide Ceramics for Protium in Light Water Molecule at Room Temperature

For exchange of deuterium (D) in oxide ceramics for protium (H) in light water molecule at room temperature is proposed the one way diffusion model: absorption of proton and adsorption of OH^- due to dissociation of H₂O at the surface, diffusion of proton, release of deuteron in trapping site due to local molecular recombination with proton and the subsequent trapping of another proton into the vacant trapping site. The one way diffusion model has been formulated in form of the mass balance equations for free proton and both proton and deuteron trapped in trapping sites which include the rate constants of chemical reactions for proton described above. The solutions of the concentrations of deuterons retained and protons uptaken in the specimen have been fitted to the experimental data and the rate constants of the chemical reactions relevant to the D-H exchange have been determined. The rate constants of the chemical reactions are discussed. Moreover, potential applications of the one way diffusion model are discussed.     

An neutron generator-based NIPGA system for on-site analysis

Utilizing NIPGA, an experimental device for cement raw material analysis has been developed, with a 2.5 MeV D-D neutron generator, BGO detector and 2048 MCA. A linear regression was developed for calculating the data. A 6-month on-site application of the system showed that the CaO, SiO_2, Fe_2O_3 and Al_2O_3 analysis results agreed well with chemical analysis, within 0.40%, 0.40%, 0.50% and 0.50%, respectively.     

低温制备气相色谱法分离氢同位素

介绍了采用低温制备气相色谱法以Al2O3装填分离柱进行氢同位素分离的装置。研究了氢同位素分离色谱柱(Al2O3分离柱)的制备和操作步骤，并对其分离效果进行了讨论。实验结果表明：经分离、净化后，氘纯度可达99．9％以上。该装置具有结构简单、操作费用低、一次性投资少等优点，在那些对氢同位素纯度要求高，用量小的部门或实验室有良好的应用前景。该装置不仅可用于氢氘分离，还可用于氘氚分离。     

Influence of Different Surface Modifications on the Photovoltaic Performance and Dark Current of Dye-Sensitized Solar Cells

The TiO2 nanoporous film photoelectrode, as a crucial component of dye-sensitized solar cells, has been investigated. The photovoltaic properties and the dark current were studied by two surface modification methods. One was to apply a compact layer between the conductive glass substrate and nanoporous TiO2 film. Another was to produce TiO2 nanoparticles among the microstructure by TICl4 treatment. A suitable concentration and number of times for TICl4 treatment were found in our experiment. The dark current is suppressed by surface modifications, leading to a significant improvement in the solar cells performance. An excessive concentration of TICl4 will produce more surface states and introduce a larger dark current reversely. The dye is also regarded as a source of charge recombination in dark to some extent, due to an amount of surface protonations introduced by the interracial link in the conductive glass substrate/dye interface and dye/TiO2 interface.     

MHWRR屏冷系统缓蚀剂K2CrO4浓度确定及其缓蚀机理研究

应用经典的失重法研究确定MHWRR屏冷系统缓蚀剂K_2CrO_4的使用浓度和屏冷系统首次使用时表面预处理工艺。用表面分析技术、电化学测试法研究K_2CrO_4的缓蚀机理。K_2CrO_4为阳极型缓蚀剂。在碳钢表面形成的Cr_2O_3,Fe_2O_3或其它Fe-O-Cr化合物增补和强化了碳钢表面的抗蚀性。     

中子慢化材料特性研究

文章采用蒙特卡罗模拟计算方法分析铝、氧化铝和氟化铝3种慢化材料在清华大学试验核反应堆束流孔道内的慢化特性。研究给出了利用慢化材料实现超热中子辐射场的一般规律，并优选出适用于在该堆建立超热中子辐射场的最佳慢化材料是Al与AlF₃质量百分数比为2∶3的Al-AlF₃混合物。     

Model for Thickness Dependence of Radiation Charging in MOS Structures

The model considers charge buildup in MOS structures due to hole trapping in the oxide and the creation of sheet charge at the silicon interface. The contribution of hole trapping causes the flatband voltage to increase with thickness in a manner in which square and cube dependences are limiting cases. Experimental measurements on samples covering a 200 - 1000 ? range of oxide thickness are consistent with the model, using independently obtained values of hole-trapping parameters. An important finding of our experimental results is that a negative interface charge contribution due to surface states created during irradiation compensates most of the positive charge in the oxide at flatband. The tendency of the surface states to "track" the positive charge buildup in the oxide, for all thicknesses, applies both in creation during irradiation and in annihilation during annealing. An explanation is proposed based on the common defect origin of hole traps and potential surface states.     

一种中子管用的Al2O3自生靶

一、引言采用自生靶是提高中子管性能的首要措施,而自生靶的材料选择和工艺处理方法对其性能有很大影响。菲利普等公司用蒸发到银基片的钛膜作为自生靶材料;我们对氚-钛靶和钛膜自生靶也做过一些实验。但这种钛膜靶会因溅射损失而影响寿命。我们在实验中还发现,当工作束流较大,靶温升高时,钛层中的气体会迅速逸出,使管内气压难     

The Scintillation Mechanism in Thallium Doped Alkali Halides

In the scintillation mechanism for alkali iodides doped with thallous iodide: 1. Most of the luminescence, and possibly all of it, is from recombination and therefore energy transfer is predominantly from charge transport to thallium. 2. There are two modes of recombination at thallium which differ in the sequence of charge trapping at Tl+. The electron may be trapped before a mobile hole recombines with it, or the hole may be trapped before recombination with a free electron. 3. Thermal hole diffusion is an important process at room temperature and determines which mode a recombination event follows. 4. Both modes of recombination are active. 5. There is non-thermal hole trapping which is a significant part of the scintillator mechanism.     

Plasma Modified Polypropylene Membranes as the Lithium-Ion Battery Separators

To reduce the thermal shrinkage of the polymeric separators and improve the safety of the Li-ion batteries,plasma treatment and plasma enhanced vapor chemical deposition（PECVD）of SiO_x-like are carried out on polypropylene（PP）separators,respectively.Critical parameters for separator properties,such as the thermal shrinkage rate,porosity,wettability,and mechanical strength,are evaluated on the plasma treated PP membranes.O₂ plasma treatment is found to remarkably improve the wettability,porosity and electrolyte uptake.PECVD SiO_x-like coatings are found to be able to effectively reduce the thermal shrinkage rate of the membranes and increase the ionic conductivity.The electrolyte-philicity of the Si Ox-like coating surface can be tuned by the varying O₂ content in the gas mixture during the deposition.Though still acceptable,the mechanical strength is reduced after PECVD,which is due to the plasma etching.     

用于光电化学水分解的高光氢转换效率TiO2纳米棒阵列

半导体一维纳米材料具有独特的光电性质,且相对于零维纳米颗粒,具有良好的电子传输途径,因而在光电化学(PEC)分解水中有着重要的应用前景。TiO2纳米棒和纳米线已被证实具有优良的PEC性质。本文采用水热方法在氟掺杂二氧化锡导电玻璃(FTO)上制备了紧密规整的金红石型TiO2纳米棒阵列,研究了活化温度对TiO2纳米棒电极的光活性影响,并计算其光氢转换效率。该光氢转换效率高于同类报道的数据。     

Amyloid fibril-supported Pd nanoparticles as electrocatalyst for hydrogen peroxide reduction

Palladium nanoparticles(Pd NPs) were fabricated by using insulin amyloid fibrils(INSAFs) as biotemplates.Atomic force microscopy measurements showed that ultrasmall Pd NPs were well adsorbed and dispersed on surfaces of INSAFs. X-ray photoelectron spectroscopy confirmed the partial reduction of Pd ion into metallic Pd(0) probably due to the presence of Cys groups on surface of the insulin fibrils. The electrochemical performance of Pd/INSAFs to reduction of H_2O_2 was further evaluated by cyclic voltammetry. The remarkably high electrocatalytic activity, low detection limitation and excellent stability make the Pd/INSAFs a promising bio-nanoelectrocatalyst.     

复合换热管过冷沸腾换热实验与关联式评价

以去离子水为实验介质,在单面受热流密度条件下,开展了聚变装置偏滤器的过冷流动沸腾强化换热特性实验研究,将内肋强化换热技术与内插扭带结构相结合,利用两者的协同强化传热效应,设计出一种复合换热管。实验参数为：质量流速,992～4 960 kg/(m2·s);压力,04～2 MPa;入口过冷度,8701～11921 ℃;热流密度,1～163 MW/m2。对4种强化换热管（光管、内插扭带管、内螺纹肋管和复合换热管）的管内过冷流动沸腾换热特性和综合性能评价指标（PEC）进行了对比实验。结果表明：与其他3种管道相比,复合换热管的对流换热系数和PEC最高,传热特性最好。研究了复合换热管的扭带扰动比、螺距、压力和质量流速对管内两相流动对流换热系数的影响规律,发现对流换热系数与螺距、质量流速呈正比,与扭带扰动比、压力呈反比。最后对比了4个现有的过冷流动沸腾换热经验公式,并在无量纲模型基础上,增加了扰动比和螺径比（t/Dh）进行修正,利用非线性拟合方法提出了适合复合换热管过冷流动沸腾的努塞尔数新公式。     

Chemical and Structural Aspects of the Irradiation Behavior of SiO2 Films on Silicon

Similarly to vitreous silica, irradiation of Sio2 films on silicon releases bond strain by creating network defects and a small increase in density and a decrease in polarizability. In contrast, the density of quartz crystal decreases and its polarizability increases during irradiation. These effects are due to the basic trend of maximizing ?-bonding and minimizing bond strain in the Si-O network. From the irradiation-generated electron-hole pairs, the holes are trapped in narrow and localized ?-bands at ~0.4 eV above the SiO2 valence band while the electrons move rather freely. This hole trapping is an intrinsic property of the Si-O bond. Hole trapping also occurs at the Si/SiO2 interface where interface states are generated. It is suggested that this process involves breaking surface Si-H bonds. Results obtained with various analytical techniques demonstrate that hydrogen present in various forms in the oxide film plays a crucial and complex role in the irradiation behavior of Si/SiO2 interface structures.     

惯性约束聚变靶丸材料磁性聚苯乙烯的制备

聚苯乙烯(PS)是惯性约束聚变(ICF)实验中重要的靶丸材料,磁性聚苯乙烯材料有利于实现靶丸在辐射场中的无接触支撑。本工作以FeCl3、FeCl2和NaOH为原料,在分散剂的作用下,制得均匀分散的棕黑色Fe3O4磁流体,然后与苯乙烯聚合获得Fe3O4-聚苯乙烯磁性材料。激光粒度分布测试结果显示,所得磁流体的粒度小且分布均匀;XRD分析表明,磁流体中无其它杂相存在。此外,还对Fe3O4-聚苯乙烯磁性材料进行了DTA及FTIR分析。分析测试结果表明,采用本工作所设计的方法可合成出Fe3O4-聚苯乙烯磁性复合材料。