从头计算方法比较TiSi2的C54相和C49相

采用平面波超软赝势描述多电子体系,利用密度泛函理论和广义梯度近似,计算出C54相和C49相TiSi2的晶格常数、体弹性模量、形成能、电子态密度(DOS)和Mulliken电荷布居等性质.通过比较这两种物质的性质,发现尽管两者形成能很相近,但C49相结构对称性差、体弹性模量小、熔点低, Ti原子d轨道的反键强、离子性弱.这些性质上的差异和C49相TiSi2在固相反应中优先形成有关.     

不相溶液体的性质和应用

文章综述了不相溶液体的性质和应用。一些关于不相溶液体在微尺度下的流动行为的研究表明,由于液体之间不同的黏度、密度和界面自由能,这种不相溶液体的流动行为不同于具有相似或相同性质的液体,因此在生物医学和化学工业中有着不可替代的作用。     

体育器材中碳纤维材料的密度泛函理论研究

基于密度泛函理论的第一性原理方法,研究了掺杂对碳纤维性质影响的微观机理.对碳纤维掺杂结构、电子性质及弹性模量进行分析,得出如下结论:Ⅰ型掺杂时碳纤维的形成能范围在4.79~20.03eV,Ⅱ型掺杂时的形成能在4.31~22.36eV.2种掺杂模型掺杂后结构未见明显变化,只是键长与层间距发生变化,由范德华力作用耦合C原子与不同原子半径的原子相互作用所导致.Ⅰ型Mg掺杂碳纤维后a方向的模量增加了2 833.11Gpa,Ⅱ型Mg掺杂时提升2 436.03GPa,Ⅰ型Al掺杂碳纤维后a方向的模量增加了1 624.86Gpa,弹性模量增长非常明显.对弹性模量明显增长的掺杂模型进行电子态密度分析,结果表明Al,Mg掺杂碳纤维结构在高弹性模量要求下更加稳定.由此可得,碳纤维材料中掺杂Al和Mg可以提高碳纤维材料弹性性能.     

氮化硅新相P6和P6＇的理论研究：一种研究陶瓷材料的新工具

在原子尺度上构建模型,采用密度泛函理论结合准谐波近似研究了氮化硅新相（P6和P6＇相）的点阵常数、弹性常数和弹性模量. 并使用β-Si3N4作基准材料来测试计算结果的准确性. 研究发现β-Si3N4的晶胞常数和弹性常数与实验值吻合相当好. 研究了P6和P6＇相在30～55 GPa的各向异性因子、脆性和力学稳定性,结果表明两相属于金属性和脆性材料,且晶体的脆性和各向异性都随着压强的升高而增大. β相在40 GPa和300 K时会转变成P6＇相. 当压强继续升高到53．2GPa时,P6＇相又转化成δ相．同时研究了氮化硅的热容、体积和体模量等性质随温度的变化规律．     

离子液体在多水相液液平衡体系中的作用

通过用短链离子液体(1-乙基-3-甲基咪唑溴盐[C2mim]Br、1-丁基-3-甲基咪唑溴盐[C4mim]Br)部分或全部取代SDS/DTAB/PEG/NaBr/H2O多水相体系中的无机盐NaBr,用长链离子液体十二烷基-3-甲基咪唑溴盐[C12mim]Br部分取代体系中阳离子表面活性剂DTAB,系统研究了离子液体在分相体系中的作用及其对分相体系性质的影响.研究表明,SDS/DTAB/PEG/NaBr/H2O混合体系形成的四水相体系可以看作"聚合物双水相"与"表面活性剂双水相"共存的结果.短链离子液体([C2mim]Br、[C4mim]Br)较强的亲水性能赋予其较强的盐析能力,在混合体系中表现出明显的盐效应,保证了四水相体系中"聚合物双水相"的存在.短链离子液体与聚合物之间的相互作用及其对表面活性剂之间相互作用的影响均不可忽略.对混合体系的相行为,共存多相的性质有重要的影响.而长链离子液体[C12mim]Br主要通过自身的疏水作用影响"表面活性剂双水相"的性质,充当表面活性剂的角色.然而,[C12mim]Br与DTAB分子结构上的差异,导致表面活性剂分子在"表面活性剂双水相"的两相重新分配,影响了对应两相的体积及萃取能力.可见,通过调节离子液体的烷基链长、混合体系中的含量等可获得具有特定性质的多水相体系.     

C60晶体在有序相的分子取向结构

以C60晶体中分子两种取向排列形成的双能级系统为基础,通过探讨C60晶体在有序相的热力学性质,得到了38o和98o两种取向排列的分子在晶体中均匀分布的结构稳定性结论.根据已报道的C60晶体在有序相两端点温度85 K 和260 K取向分布的实验结果,将较高的分子取向(38o)能级的概率转化成分数值1/6和3/8,得到了有序相两种取向分子在两温度端点的分布规律.当概率的分数值为1/4和1/3时,C60晶体将具有较大的结构稳定性和较小的介电损耗及内耗值,对应的温度分别为122.6和194.3 K.因而解释了介电实验结果出现异常的现象是由38o取向分子均匀分布的"规则-无规-规则"变化所造成的.     

新型手性近晶C相液晶共聚酯的设计与合成

以对苯二甲酰氯 ,2 ,5 二 [4 ((s) 2 甲基丁氧基 )苯甲酰氧基 ]对苯二酚和乙二醇、一缩乙二醇、二缩三乙二醇、三缩四乙二醇和聚乙二醇为单体 ,采用低温溶液缩聚方法 ,合成了一系列新的手性近晶C相串型液晶共聚酯 .共聚酯通过GPC、DSC、TG、WAXD、偏光显微镜和旋光仪等方法表征 .发现所有的共聚酯加热至各自的熔点以上都能形成液晶态 ,在液晶态可以观察到近晶相的焦锥织构 ,所有的手性化合物和共聚酯都有较高的旋光性 .通过变温X 射线衍射研究结合偏光显微镜观察和旋光分析证明它们为手性近晶C相 .所有共聚酯的熔融温度 (Tm)和各向同性温度 (Ti)随共聚酯中不同柔性链段长度的增加逐渐降低 ,液晶态温度范围变宽     

分光光度法研究水-乙醇体系析相萃取分离和富集PdBr2-4

用可见分光光度法研究了水-乙醇体系析相萃取分离和富集PdBr42-的行为及与一些金属离子分离的条件.结果表明,(NH4)2SO4能使乙醇的水溶液分成两相,在分相过程中,Pd(Ⅱ)与KBr生成的PdBr42-与质子化乙醇(C2H5OH2+)形成的缔合物[PdBr42-][C2H5OH2+]2能被乙醇相完全萃取.当乙醇、K...     

丙酸水相加氢反应中Ru负载量对C—C键断裂的影响

考察了(1.0%、4.0%、6.0%)Ru/ZrO2催化剂的丙酸水相加氢性能.采用N2物理吸附、CO脉冲化学吸附、H2程序升温还原(H2-TPR)、CO和丙酸吸附傅里叶变换红外光谱(FTIR)研究了Ru/ZrO2催化剂的物理化学性质.COFTIR表明,Ru负载量增加,催化剂表面Ru粒子的富电子程度增加,更接近金属Ru的本征特性.丙酸FTIR表明,丙酸分子在Ru/ZrO2催化剂表面经解离吸附主要形成丙酰基和丙酸盐物种.随Ru含量增加,丙酰基更容易发生脱羰反应,导致C—C键断裂.     

KBr-水-正丙醇体系中析相萃取分离富集Hg(Ⅱ)

研究了KBr-水-正丙醇析相萃取Hg(Ⅱ)的行为及与一些金属离子分离的条件.结果表明,( NH4)2SO4能使正丙醇的水溶液分成两相,在分相过程中,Hg(Ⅱ)与KBr生成的HgBr42 -与质子化正丙醇(C3H7OH2+)形成的缔合物[HgBr42-] [C3H7OH2+]2能被正丙醇相完全萃取.当溶液中KBr、( N...     

Kinetics of titanium silicide formation by rapid thermal processing

Summary Auger electron spectroscopy (depth profiling and line shape analysis), X-ray diffraction, and cross-sectional transmission electron microscopy were employed to investigate the kinetics of titanium silicide formation by rapid thermal annealing in N₂ and Ar ambients. A silicide is formed within only a few seconds at 620°–700°C. All the analysis techniques utilized reveal that the silicides primarily consist of sequential TiSi₂ and TiSi phases. The TiSi₂ is the metastable, poorly-conducting C49 modification. The TiSi₂ growth was evaluated quantitatively and was shown to be limited by diffusion of Si through the silicide. For annealing in N₂, the TiSi phase is stabilized compared to Ar annealing; additionally a titanium nitride forms near the surface and grows inward by another diffusion-limited process. When the TiSi and TiN reaction fronts approach the available Ti is consumed for these reactions; further silicide growth can only occur via complex phase transformations. The ratio of the activation energies for both diffusion processes was measured to be , in approximate agreement with literature data. The role of impurities for silicide growth will be discussed.

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Kinetik der Titansilizidbildung durch Kurzzeittempern

     

Ternary zirconium tin Antimonide ZrSn2-xSbx (0.2 < x < 0.8), different from the parent binaries ZrSn2 and ZrSb2

The new intermetallic phase ZrSn2-xSbx was prepared by arc-melting and annealing at 800 degrees C. It adopts the hexagonal CrSi2-type structure (Pearson symbol hP9, space group P6222 (or P6422), Z = 3, a = 5.51-5.53 A, c = 7.65-7.63 A) and exhibits a significant phase width (0.2 < x < 0.8). In contrast, the parent binary phases adopt different structures: ZrSn2 has the orthorhombic TiSi2-type structure, and ZrSb2 exists as two orthorhombic forms (alpha-ZrSb2, own type; "beta-ZrSb2", PbCl2-type). The structures of ZrSn2, ZrSn2-xSbx, and beta-ZrSb2 are distinguished by the stacking and distortion of nets with composition "ZrQ2" (Q = Sn, Sb). The CrSi2-type and TiSi2-type structures differ only minimally in energy, but interlayer Sb-Sb bonding is important in stabilizing the structure of beta-ZrSb2.     

制备高比表面多孔Ti-Si复合氧化物材料的新方法

Ti- Si复合氧化物多孔材料在异相催化、催化剂载体等方面引起了人们的普遍关注 .将具有痕量Ti的 Si O2 玻璃用于纤维、膜及光学玻璃的制造中 ,在较宽的温度范围内显现出较低的热膨胀系数 [1] .特定组成的 Ti- Si复合氧化物在一些酸催化反应中具有相当的活性 [2～ 6 ] ,如苯酚胺化、乙烯水合、丁烯异构化、 2 -异丙醇脱水、 1 ,2 -二氯乙烷分解等反应 .另一些组成的 Ti- Si复合氧化物多孔材料已被用于选择性氧化反应中 [7] .Ti- Si复合氧化物的物理化学性能与材料自身的组成及均匀性有关 ,常规的制备方法有共沉淀法 [2 ,3,5] 和溶胶 -凝…     

Synthesis of (+)-patulolide C via an asymmetric hydroformylation/macrocyclization cascade

A highly atom-economical total synthesis of (+)-patulolide C has been accomplished in three steps from the known (2R)-8-nonyn-2-ol in 49% overall yield and 93% de. A Rh(I)-catalyzed asymmetric hydroformylation (AHF)/ intramolecular Wittig olefination cascade was utilized to set the C4-hydroxyl stereochemistry and E-olefin geometry as well as form the macrolactone.     

Studies of Cephalosporin C Purification by Ultrafitration

Cephalosporin C was produced with fermentation technique. There are many impurities (mycelium, protein et al) in its fermentation liquor, which can be removed by ultrafitration membrane separation. The ultrafiltration technique has been used for purifying the fermentation liquid of antibiotics^[1-2],however, its application in extraction of Cephalosporin C from its fermentation liquor has not been reported. In this paper, we use Ultra-flo ultraflitration membrane system (concludes UF-54 pilot plant, flat board membrane module, thin composite membrane of 30 thousand reject molecular weight) to purify #1-#3 fermentation liquors of Cephalosporin C, which were not pretreated except acidification(pH=3).     

C59O的结构、电子光谱及NMR谱的理论预测

用INDO系列方法对C₆₀的取代产物C₅₉O进行几何构型优化,得到Cs对称性的稳定构型,以此构型为基础,计算并预测了C₅₉O的电子光谱和NMR谱.最后与C₅₉O的等电子分子体C₆₀^2-及C₆₀O进行了比较.     

Fabrication of titania and titania–silica aerogels using rapid supercritical extraction

Titania (TiO₂) and titania–silica (TiSi) aerogels are suitable for photocatalytic oxidation of volatile organic compounds for pollution mitigation; however, methods for fabricating these aerogels can be complex. In this work we describe the use of a rapid supercritical extraction (RSCE) technique to prepare TiO₂ and TiSi aerogels in as little as 8 h. The RSCE technique uses a metal mold and a four-step hydraulic hot press procedure to bring the solvents in the sol–gel pores to a supercritical state and control the supercritical fluid release process. Resulting TiO₂ aerogels were powdery with BET surface areas of 130–180 m²/g, pore volumes ~0.5 cm³/g and skeletal densities of 3.6 g/mL. Monolithic TiSi aerogels were made using two different methods. An impregnation process, in which titania precursor was added to a silica sol–gel, took 4–8 days to complete with a 7-h RSCE and resulted in translucent aerogels with high surface area (560–650 m²/g) and pore volume (2.0–2.6 cm³/g), bulk densities ranging from 0.1 to 0.4 g/mL and skeletal densities of 2.3 g/mL. A co-precursor method for preparing TiSi aerogels took 8 h to complete. The precursor chemical mixture was poured directly into the mold and processed in a 7-h RSCE process. The resulting aerogels were opaque, with high surface areas (510–580 m²/g), low bulk density (0.03 g/mL), skeletal densities of 2 g/mL and pore volumes of 2.6–3.5 cm³/g. Preliminary solar simulator studies show that TiO₂ and TiSi aerogels are capable of photocatalytic degradation of methylene blue in aqueous solution.     

Electronic polarizability and Judd-Ofelt parameters of Nd3+ and Er3+ ions in transparent crystallized glasses with nonlinear optical Ba2 TiSi2O8 nanocrystals

Transparent crystallized glasses consisting of nonlinear optical Ba(2)TiSi(2)O(8) nanocrystals are prepared in Eu(2)O(3)-, Nd(2)O(3)-, and Er(2)O(3)-doped 40BaO-20TiO(2)-40SiO(2) glasses by a conventional heat treatment method in order to clarify the optical properties of rare-earth (RE) ions in nanocrystals. The electronic polarizabilities of crystallized glasses are evaluated from the values of density and refractive index, and are found to decrease due to nanocrystallization, which indicates that the chemical bonding state in the crystallized glasses is more covalent compared to the precursor glasses. It is proposed from x-ray diffraction analyses and photoluminescence spectra of Eu(3+) ions that RE ions such as Nd(3+) and Eu(3+) are incorporated into Ba(2)TiSi(2)O(8) nanocrystals. The Judd-Ofelt parameters, Omega(t) (t=2, 4, and 6), of Nd(3+) and Er(3+) ions are evaluated from optical absorption spectra. It is observed that the Omega(2) parameter of Nd(3+) and Er(3+) increases largely due to nanocrystallization, suggesting that the site symmetry of Nd(3+) and Er(3+) ions in nanocrystallized glasses is largely distorted due to their incorporations into the Ba(2+) sites in Ba(2)TiSi(2)O(8) nanocrystals. The change in the Omega(4) and Omega(6) parameters due to nanocrystallization is small. It is proposed that nonlinear optical Ba(2)TiSi(2)O(8) nanocrystals including RE ions would have a high potential as active optical materials.     

C3v-symmetrical tribenzotriquinacenes as hosts for C60 and C70 in solution and in the solid state

Various tribenzotriquinacenes (TBTQs), most of which incorporate six functional groups at the periphery of their C3v-symmetrical, rigid and convex-concave molecular framework, have been studied with respect to their ability to form supramolecular complexes with the C60 and C70 fullerenes, either in the solid state or in solution. The hexabromo derivative Br6-TBTQ was cocrystallized with C60 as [Br6-TBTQ相似文献