Reactions of Magnesium and Titanium Alkoxides. Preparation and Characterization of Alkoxy-Derived Magnesium Titanate Powders and Ceramics

The interaction between magnesium and titanium alkoxides is studied in order to chose the best precursors for synthesis of MgTiO₃. No reaction between magnesium and titanium methoxides and isopropoxides occurs. The solubility diagrams for Mg(OR)₂-Ti(OR)₄-ROH, R = Et,-Bu at 20°C are studied. Magnesium ethoxotitanates of variable composition Mg_nTi_4-n (OEt)_16-2n2nEtOH (n=2.0-0) which are structural analogs of Ti₄(OR)₁₆ (R = Me, Et) are isolated. This is a quite unusual example of statistical distribution of heteroatoms in molecular structures of metal alkoxides. Among the systems of metal alkoxides with simple aliphatic radicals only Mg(OBu)₂-Ti(OBu)₄-BuOH gives a convenient precursor for the synthesis of MgTiO₃. A simple scheme of preparation of magnesium titanate from the alkoxide solutions is suggested. The phase purity of MgTiO₃ is to a considerable extent dependent on the hydrolysis conditions. The alkoxy-derived magnesium titanate is obtained in the form of a uniform fine powder, it can be sintered into dense ceramics in the temperature range of 1140–1220°C which is 150–200°C lower in comparison with the conventional powders.     

酚醛型吸附树脂在非水体系中对吡啶和N,N-二甲基苯胺的吸附性能研究

研究了酚醛型吸附树脂JDW 2在非水体系中对吡啶和N ,N 二甲基苯胺的静态吸附 .由实验结果推论正己烷中树脂对吡啶和N ,N 二甲基苯胺的吸附是以氢键吸附机理为主进行的 ,JDW 2酚醛型吸附树脂在正己烷中 ,等温吸附吡啶和N ,N 二甲基苯胺的平衡吸附数据符合Langmuir方程 ,相关系数在 0 99以上 ,因此 ,酚醛型吸附树脂在正己烷中吸附吡啶和N ,N 二甲基苯胺属单分子层吸附 ;同时对非水体系中乙醇或乙酸乙酯的含量对树脂吸附吡啶和N ,N 二甲基苯胺的影响进行了研究     

Weak Mixing in Interval Exchange Transformations of Periodic Type

Interval exchange transformations (IETs) are piecewise isometries of the interval, obtained permuting a certain number of subintervals. We give a condition on IETs in the special subclass of IETs with periodic Rauzy-Veech cocycle which guarantees weak mixing, i.e. the continuity of the spectrum. The proof involves the study of the associated spectral measures. The condition can be checked explicitly by computing a certain Galois group of a field related to the Ravzy-Veech cocycle. Explicit examples of weakly mixing IETs are constructed in the Appendix. *Dedicated to the memory of F.A. Berezin     

周期极化掺镁铌酸锂光学参量振荡器时域特性的实验研究

分别采用MOTORULA公司的硅基光电二极管探测器和JUDSON公司的InGaAs光电二极管探测器对泵浦光和信号光的脉宽进行了测量.研究了极化周期、工作温度以及抽运功率与周期极化掺镁铌酸锂光学参量振荡器输出的信号光脉冲宽度的作用关系.实验采用LD端面抽运的声光调Q Nd∶YVO4激光器作为抽运源,在晶体温度为30 ℃、极化周期为29.5 μm条件下,当抽运功率为1 008 mW时,获得了平均功率为238 mW的信号光输出,其光-光转换效率为23.6%,最窄脉冲宽度约为9.3 ns,相对抽运光脉宽被明显压窄.     

微含水量电解液中高管径比TiO2纳米管阵列的制备

通过阳极氧化法在微含水量为0.5wt%的NH₄F/乙二醇/H₂O酸性电解质体系中制备了管径大、高管径比的二氧化钛（TiO₂）纳米管阵列。采用SEM、XRD等测试手段对TiO₂纳米管阵列形貌及晶相进行表征,探讨了不同氧化时间、电压对纳米管阵列形貌的影响,微含水量下氧化电压可以适当增加,更容易得到规整的长纳米管阵列;通过测定样品的光电流和紫外-可见光漫反射吸收光谱,研究分析了含水量以及超声工艺对纳米管光吸收及光电流特性,微含水量下得到的纳米管阵列可见光吸收边红移至420nm,对480~700nm可见光有明显的光吸收,光电流显著增大;丙酮作为超声介质可有效去除纳米管阵列表面的集束,能进一步提高纳米管阵列的光电性能。     

基于有机-无机介孔二氧化硅杂化材料对Cu^2和Co2+的选择性测定

合成了一种有机-无机介孔二氧化硅杂化材料(SBA-15-Tpy),通过透射电镜显微镜、X射线衍射、热重分析和N_2吸附-解吸曲线对其进行表征,并基于该材料建立了在水中对Cu²⁺和Co²⁺的选择性识别。研究表明,SBA-15-Tpy与Cu²⁺和Co²⁺结合后会分别在800 nm和510 nm处产生新的吸收峰,加入其它金属离子后不发生明显的吸收峰值变化。在最优条件下,检测Cu²⁺和Co²⁺的线性范围分别为2.0~200.0μmol/L和10.0~200.0μmol/L,检出限分别为0.48μmol/L和4.28μmol/L。将上述方法用于江水中Cu²⁺和Co²⁺的测定,回收率在96.0%~108.5%之间。     

不同维度ZnO能带结构和电子态密度的研究

本文采用基于密度泛函理论的第一性原理计算方法来研究不同维度ZnO的能带结构和电子态密度.参考实验上的ZnO晶格参数构建不同维度的ZnO模型并进行结构优化后再计算能带结构和电子态密度.研究结果表明二维和三维ZnO都属于直接带隙半导体且二维ZnO的禁带宽度大于三维ZnO;从三维变到二维,ZnO的电子局域化程度变高且Zn 3d轨道电子从能量较低的能级向能量较高的能级跃迁.本文的研究展示了二维和三维ZnO能带结构和电子态密度的异同,为二维ZnO基的器件研究提供了一定的理论参考价值.     

气相色谱-质谱法测定甘蔗中除草剂残留量

提出了采用QuEChERS法提取净化,气相色谱-质谱法同时测定甘蔗中除草剂莠去津、乙草胺和莠灭净的残留量。采用DB-5MS毛细管柱分离,电子轰击离子源选择离子检测模式进行质谱测定。莠去津、乙草胺和莠灭净的检出限(3S/N)分别为0.001,0.002,0.001mg.kg-1。在3个浓度水平上对方法的回收率作了测定,测得回收率在88.0%～108.0%,相对标准偏差(n=6)在1.1%～6.9%之间。     

Hydrophobic Modification of Poly(Ethylene Terephthalate) with Epoxy-Modified Polysiloxane by Reactive Extrusion

Hydrophobic poly(ethylene terephthalate) (PET) was prepared by reactive blending of PET with double epoxy groups modified polysiloxane (diepsi) or multiepoxy groups modified polysiloxane (multiepsi). The structure of the modified PET was characterized by ¹H NMR and intrinsic viscosity. The grafted ratio of diepsi and multiepsi was 1.3 and 0.03 wt%, respectively. With the introduction of diepsi and multiepsi to PET, the water contact angle of modified PET increased from 73° to a maximum of 106°, showing the good hydrophobicity of the modified PET. The samples of modified PET were washed with different solvents and their water contact angles did not significantly decrease, indicating good durability of the hydrophobicity. Moreover, the films of modified PET prepared by solution casting (phenol and 1, 1, 2, 2-tetrachloroethane mixed solution) showed excellent hydrophobicity with the contact angle 151°. Scanning electron microscopy images showed the surface of the modified PET films to be rougher than those of unmodified PET because the introduction of polysiloxane to PET resulted in phase separation during the solvent evaporation process.     

Liquid–liquid extraction of neodymium (III) and europium (III) using synergic mixture of furosemide and tribenzylamine in benzyl alcohol

The extraction behavior of Nd(III) and Eu(III) with 0.05 mol dm⁻³ furosemide in benzyl alcohol as single acidic extractant and then with equimolar (0.05 mol dm⁻³) synergic mixture of furosemide as acidic extractant and tribenzylamine as neutral donor in benzyl alcohol has been studied from aqueous solutions of pH 1 to 6. The effect of various parameters and of various cations and anions on the extraction of these metal ions was investigated. The composition of the extracted adducts was determined by slope analysis method that came out to be [(M(FS)₂)⁺ (CH₃COO)⁻] and [M(FS)₃·3TBA] where M = Nd(III) and Eu(III).