Homogeneous crystallization of the Lennard-Jones liquid. Structural analysis based on Delaunay simplices method

The crystallization process of a simple liquid upon slow cooling has been modeled by the Monte-Carlo method. The model contains 10,000 Lennard-Jones atoms in the model box with periodic boundary conditions. The model structure is investigated at different stages of crystallization using Delaunay simplices. The simplex belonging to one or another particular crystal structure was determined by the shape of the given simplex taking into account the shape of its neighboring simplices. Simplices typical of the fcc and hcp crystal structures, as well as of polytetrahedral aggregates, not typical of crystals, were studied. The analysis has shown that the “precursors” of a hcp structure are strongly dominating over the “precursors” of a fcc structure in liquid phase before the beginning of crystallization. When crystallization starts, small embryos of the fcc structure are observed; the simplices peculiar to hcp are present at that in great amount, but they are distributed over the sample more uniformly. As crystallization proceeds, the portion of the fcc phase grows faster than hcp. However, no unified crystal appears in our case of slow cooling of the model. A complex polycrystalline structure containing crystalline regions with multiple twinning, pentagonal prisms and elements of icosahedral structures arises instead.     

微波消解凯氏定氮法快速测定酱油中全氮

研究了凯氏定氮法测定酱油中全氮时样品的微波消解方法,进行了微波消解条件的选择及消解结果精密度试验,并与国家标准方法对比,验证了方法的准确度。试验结果表明,消解完全仪需20min,相对标准偏差均小于2%（n=7）,回收率范围为96%～103%,经t检验,微波溶样法与国家标准凯氏定氮法的测定结果无显著性差异。     

水热法合成K0.5Bi0.5TiO3纳米陶瓷粉体

K_0.5Bi_0.5TiO₃(KBT)nanocrystalline particles were hydrothermally synthesized from Bi(NO₃)₃·5H₂O, TiO₂ and KOH. The crystal phase, chemical composition and microstructure were characterized by XRD, XRF, Raman scattering spectroscopy and TEM. The results indicated that the products were pure perovskite structured K_0.5Bi_0.5TiO₃ with chemical stoichiometry and perovskite structure. The TEM observation revealed that the particles possessed a feature of cubic shape and a nano-scale of about 40 nm. The KBT ceramics sintered at 1 040 ℃ from hydrothermal powders show higher density and better electric properties than that prepared by a solid-state reaction method.     

气相法合成一维无机纳米材料的研究进展

一维无机纳米材料是研究电子传输行为、光学特性和力学机械性能等物性的尺寸和维度效应的理想系统，将在构筑纳米电子和光电子器件等集成线路和功能性元件的进程中充当非常重要的角色，已成为当前纳米材料科学领域的前沿和热点。本文将从一维无机纳米材料的合成、表征和物性研究等方面，结合近年来国内外的最新进展对这一新兴领域作一概述。     

Pt3Co核-Pt壳型纳米粒子的制备及磁性

Pt₃Co alloy nanoparticles were prepared by the reduction of H₂PtCl₆ and Co(OOCCH₃)₂ using NaBH₄ as a reducing agent. The Pt₃Co core-Pt shell nanoparticles (Pt₃Co@Pt) were synthesized using hydrogen absorption reduction and characterized by plasma-atomic emission spectrometry (ICP), transmission electron microscopy (TEM), X-ray diffraction (XRD) and SQUID magnetometer. The results show that average size of Pt₃Co@Pt nanoparticles is 3.6 nm with a standard deviation of 0.9 nm. Heating Pt₃Co nanoparticles in air at 700 ℃ for 1 h, Co in Pt₃Co nanoparticles was oxidized to Co₃O₄ and CoO; while no oxidation tendency was detected for Pt₃Co@Pt nanoparticles. The crystallize structure of Pt₃Co@Pt changed from the face centered cube (fcc) to the face centered tetragonal (fct) after the heating treatment. The coercivity of the heated Pt₃Co@Pt reached to 276 Oe at room temperature.     

不同方法掺杂Au对纳米α-Fe2O3气敏性能的影响

分别采用共沉淀法、浸渍法、紫外辐照法制备了掺杂不同Au含量的α-Fe2O3纳米粉体,并制作了旁热式厚膜型气敏元件.用XRD、TG-DTA和TEM技术对纳米晶的晶型、晶粒大小及形貌进行了表征.考察了掺杂方法、Au含量及焙烧温度对α-Fe2O3气敏性能的影响.结果表明,采用三种方法掺杂适量Au后,都使α-Fe2O3的气敏性有了显著提高,其中采用共沉淀法,在400℃焙烧的Au质量分数为1.5%的α-Fe2O3的气敏性最佳.     

二苯基二甲氧基硅烷单体制备空心微胶囊的模板合成方法研究

制备了直径在700～1500 nm范围内的空心聚硅氧烷微球. 在O/W型聚二苯基硅氧烷微乳模板核上, 加入一定比例的二苯基二甲氧基硅烷(D型官能团)和甲基三甲氧基硅烷(T型官能团)的有机硅单体, 使之围绕在模板核表面聚合交联形成核壳结构的聚硅氧烷微胶囊, 利用合适溶剂溶解透析的方法去除模板核得到空心微胶囊. 通过TEM和AFM测定考察, 讨论了体系的各反应条件对空心微球的形态结构和大小分布的影响.     

钒掺杂TiO2/AC负载催化剂的制备及光催化活性

以TiO2为主要成分的光催化剂的研究已日益受到人们的广泛关注[1-6]。但TiO2粉末的回收和流失问题难以解决,固定化TiO2负载催化剂的研制是解决这一问题的有效手段[2-6]。从实际应用的观点看,TiO2的光催化剂活性还有待进一步提高。研究发现,大多数过渡金属离子和少数非金属离子的     

Tautomerism of monochalcogenosilanoic acids CH3Si(O)XH (X = S,Se, Te) in the gas phase and in the polar and aprotic solution: An ab initio computational investigation

Computational investigations by an ab initio molecular orbital method (HF and MP2) with the 6‐311+G(d,p) and 6‐311++G(2df, 2pd) basis sets on the tautomerism of three monochalcogenosilanoic acids CH₃Si(?O)XH (X = S, Se, and Te) in the gas phase and a polar and aprotic solution tetrahydrofuran (THF) was undertaken. Calculated results show that the silanol forms CH₃Si(?X)OH are much more stable than the silanone forms CH₃Si(?O)XH in the gas‐phase, which is different from the monochalcogenocarboxylic acids, where the keto forms CH₃C(?O)XH are dominant. This situation may be attributed to the fact that the Si? O and O? H single bonds in the silanol forms are stronger than the Si? X and X? H single bonds in the silanone forms, respectively, even though the Si?X (X = S, Se, and Te) double bonds are much weaker than the Si?O double bond. These results indicate that the stability of the monochalcogenosilanoic acid tautomers is not determined by the double bond energies, contrary to the earlier explanation based on the incorrect assumption that the Si?S double bond is stronger than the S?O double bond for the tautomeric equilibrium of RSi(?O)SH (R?H, F, Cl, CH₃, OH, NH₂) to shift towards the thione forms [RSi(?S)OH]. The binding with CH₃OCH₃ enhances the preference of the silanol form in the tautomeric equilibrium, and meanwhile significantly lowers the tautomeric barriers by more than 34 kJ/mol in THF solution. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

A new linear method for analyzing four‐way multiblock tables: STATIS‐4

A new four‐way multiblock method is proposed to study the links between more than two sets of data tables (several multiblocks) measured on the same observations. This method, called STATIS‐4, generalizes the STATIS method to more than one set of matrices. In its first step, STATIS‐4 is searching for one consensus for each multiblock and a global consensus summarizing all the previous ones as good as possible. Some graphical representations can be made to visualize the proximities between the tables within a multiblock and to visualize those between all the multiblocks. Moreover, plots of the observations for each table, each multiblock and global observations can be made. The theory of STATIS‐4 and the algorithm used to obtain the optimal solutions are presented. Moreover, a real sensory dataset is studied with STATIS‐4. Copyright © 2008 John Wiley & Sons, Ltd.