电化学法沉积氧化锌晶须

应用阳极氧化法沉积氧化锌(ZnO)松针状晶须,SEM和XRD观察、表征样品形貌与结构.结果表明,电沉积氧化锌晶须直径为20～50 nm、长度200～300 nm、长径比10～15,纯度高,结晶度好,属六方晶系纤锌矿(JCPDS 36-1451).循环伏安法研究了该氧化锌结晶过程,并考察了电解液的锌酸盐[Zn(OH)4]2-浓度和基底表面氧化膜对晶须生成的影响.     

The Role of Oxygen Dissociation in Plasma Enhanced Chemical Vapor Deposition of Zinc Oxide from Oxygen and Diethyl Zinc

The influence of electron impact dissociation of oxygen on neutral chemistry was studied for plasma-enhanced chemical vapor deposition (PECVD) of zinc oxide using oxygen and diethyl zinc. Electron conditions in the reactor were estimated based on simulations of well-known Ar-O₂ plasmas, while the majority of the thermal chemistry was abstracted from the combustion literature. A rudimentary model of film growth was developed using the rate of oxygen dissociation as the lone adjustable parameter.n Model results were compared directly with experimental measurements of deposition rates and neutral species densities for a wide range of conditions. Good quantitative agreement between experiments and model were observed as a function of composition and rf power. The system is highly sensitive to the electron impact dissociation of oxygen, which creates the radical pool that drives the majority of the chemistry. The approach detailed here provides a framework for the development of models of oxide PECVD derived from other metalorganic precursors.     

Spherical Zinc Oxide Nano Particles from Zinc Acetate in the Precipitation Method

The liquid precipitation method using zinc acetate dihydrate was applied for the synthesis of uniform and spherical ZnO nanoparticles. The ultrafine zinc oxid was prepared in a water‐ethanol mixture solution. The solution containing zinc cation was soluble in water. The surface‐active agent triethanolamine (TEA) was soluble in ethanol. Then alkali precipitated by adding n‐propylamine. The spherical zinc oxide particle morphology was found to be highly dependent on the zinc salt concentration, ethanol‐water ratio, and the surface‐active agent additive. The process can produce white ZnO powder of 50–90 nm in size. The morphology of zinc oxide showed a powder shape by transmission electron microscopy (TEM), the crystallization phase structure of zinc oxide by X‐ray diffraction (XRD), and the zinc oxide remaining by using an organic analysis by infrared spectroscopy (IR).     

Effect of Zinc Oxide on Morphology and Mechanical Properties of Polyoxymethylene/Zinc Oxide Composites

This paper studies the effects of zinc oxide (ZnO) on morphology and mechanical properties of pure polyoxymethylene (POM) and POM/ZnO composites. POM/ZnO composites with varying concentration of ZnO were prepared by melt mixing technique in a twin screw extruder. The dispersion of ZnO particles on POM composites was studied by scanning electron microscope (SEM). It is observed that the dispersion of ZnO particles is relatively good. The mechanical properties of the composites such as tensile strength, stress at break, Young's modulus and impact strength were measured. Increasing content of ZnO up to 4.0 wt% increases the impact strength of POM. Addition of ZnO beyond 4.0 wt% decreases the impact strength. The composites containing ZnO content greater than 2.0 wt% show increased Young's Modulus. The tensile strength and stress at break decrease with increasing ZnO content. This may be due to the compatibility between ZnO and POM.     

锌铋复杂氧化物Bi2Zn5O8的合成及其晶体生长特性

利用硫酸锌、硝酸铋、氢氧化钠为原料在超声体系中反应合成锌铋复杂氧化物,考察了反应物料比和加料顺序对产物组成的影响.经X射线荧光及化学滴定确定了产物的分子式为Bi2Zn5O8,并由TEM、SEM和TG-DTA等方法对所得产物进行表征.TEM和SEM结果显示晶体呈枝蔓晶生长.     

硫酸锌晶体巧妙制法的实验探讨

在中学化学课本中,制取硫酸锌晶体时常采取蒸发结晶的方法,而做该实验时存在一些不足：所需的时间很长,不适宜在课堂上演示;蒸发液体时,所需要的化学仪器太多,课前携带不方便;蒸发结束后,蒸发皿中仅有白色的粉末,不能看到无色的硫酸锌晶体[1]。     

Vapor Phase Epitaxy of Nitride Films

GaN and related compounds are very promising materials for developing short wavelength light emitting devices, such as laser diode (LD) and light emitting diode (LED), high temperature and high power electronics. Commercially used nitride materials have been made by vapor phase epitaxy (VPE), including metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE). MOVPE is a widely used technique to fabricate semiconductor films. Its precise control of growth process, ability of handling multi large area wafers, and excellent reproducibility make it valuable in large-scale production of electronic and optoelectronic devices. VPE of nitrides has met several critical materials issues. Firstly, a high vapor pressure of nitrogen leads to the lack of bulk crystal of GaN. People have to use heteroepitaxy technique to produce GaN materials and devices, which makes high-density defects in GaN epilayers. Secondly, the high bonding energy of GaN and high stability of NH₃ require a high growth temperature. The high nitrogen vapor pressure at high growth temperature requires enhanced local precursor densities. Additionally, the growth chemistry of VPE of nitride materials is very complicated. Parasitic chemical reactions take place during the VPE growth and degrade the material quality. Finally, the physical process of VPE growth has not been well understood. Optimized production of nitride material is predicated on an understanding of how the film properties are affected by the initial processing sequence. Heteroepitaxy of nitrides is strongly influenced by the initial nucleation and growth sequence.     

ZnO及其含锌混合氧化物薄膜的充放电性能研究

从充放电性能、晶体结构等方面考察了包括粉末状的ZnO、脉冲激光沉积方法制备的ZnO薄膜和含锌混合氧化物薄膜的电化学性质.结果表明,ZnO粉末制备的电极的嵌入容量随退火温度的升高而增大,掺入其他氧化物可以明显改善ZnO薄膜的电化学性能,在Ar气氛中,基片温度为400℃时,沉积的靶子成分为Zn:B:P:Al=1:1:0.5:0.5(摩尔比)的含锌混合氧化物薄膜具有较高的可逆容量,且循环性能良好.     

Crystal Smectic-B Phase from a Mesomorphic Ferrocene Derivative

The thermal properties of two ferrocene derivatives, substituted by either one or two cholesteryloxycarbonyl units, were investigated. While the monosubstituted ferrocene derivative 1 was found to be non-mesomorphic, the disubstituted ferrocene derivative 2 exhibited a crystal smectic-B phase. This result shows that ferrocene-containing thermotropic liquid crystals, despite the bulkiness of the metallocene core, are not limited to disordered calamitic phases.     

超声波激活纳米氧化锌损伤牛血清白蛋白的研究

利用紫外-可见(UV-Vis)光谱和荧光光谱研究了超声波照射激活纳米氧化锌(ZnO)粒子对牛血清白蛋白(BSA)的损伤,并考查了超声波照射时间、纳米ZnO粉末加入量、溶液酸度和照射功率等因素对BSA分子损伤的影响。结果表明,对于体系温度为37.0±0.2 ℃和浓度为1.0×10^-5 mol·L^-1的BSA溶液,BSA的损伤程度随着超声波照射时间,纳米ZnO粉末加入量,溶液pH值和照射功率的增加而增大。此外,还初步探讨了超声波照射激活纳米ZnO粒子损伤BSA分子的机理,认为是声致发光和高热激发使纳米ZnO粒子产生·OH自由基,进而损伤BSA分子。     

纳米氧化锌的合成与表征

纳米氧化锌的合成与表征何勇宁，沈孝良，马礼敦（复旦大学分析测试中心上海２００４３３）关键词纳米材料，氧化锌，合成，表征制备纳米材料的方法很多，如蒸发冷凝法、化学气相沉积法、溶胶－凝胶法、超临界法、水热法及各种热分解法等。Ｌｉｕ等［２］用超声雾化热分解...     

EDTA滴定法测定含锌物料中氧化锌

采用氯化铵-氨水体系溶解试样,干过滤后,向移取的滤液中加入氯化钡和硫酸共沉淀铅离子,过滤分离硫酸铅沉淀,向滤液中加人抗坏血酸、氟化钾、硫代硫酸钠等掩蔽剂掩蔽少量干扰元素。在pH=5~6的乙酸-乙酸钠缓冲溶液中,以二甲酚橙为指示剂,用EDTA标准滴定溶液滴定测得结果为氧化锌、水溶性锌和镉合量,扣除由原子吸收光谱法测得的水溶性锌量和镉量,即为氧化锌量。对总氨浓度、氯化铵-氨水浓度比、溶液加入量、搅拌时间、共存离子干扰、精密度等进行了实验,建立了EDTA滴定法测定含锌物料中氧化锌物相的分析方法。实验证明,氧化锌含量在24%~83%时,方法精密度(RSD)为0.25%~0.54%,加标回收率在99%~104%,完全满足含锌物料中氧化锌的测定要求。     

High Performance Varistor Discs Obtained from Chemically Synthesized Doped Zinc Oxide Powder

The ceramic microstructure, the chemical homogeneity of specific dopants and the mechanical integrity of a varistor disc are critical parameters in determining the transient voltage suppression features of these devices. The material properties and overall quality of the starting ceramic powders used to produce such components are essential in achieving the desired properties. The present work describes a novel chemical method developed to produce doped zinc oxide powders and an industrial scale manufacturing process for the production of final varistor blocks for surge arrester applications. The results are compared with those obtained when using standard varistor powder made by the mixed oxide route is used. All the fundamental electrical properties of the discs have been determined and correlated with the relevant manufacturing steps.     

锌蒸气的氧化行为与氧化锌的结晶形貌

用热重法测定了不同气氛下锌蒸气的氧化动力学曲线,用扫描电镜跟踪观察分析了产物的结晶形貌,结果表明,氧化动力学遵守直线规律时,产物是无定形、颗粒状和单针状的ZnO;氧化动力学为抛物线规律时,产物是四针状或多针状的ZnO.动力学转变规律的原因是锌蒸气中气态锌原子与凝聚生成的锌液滴之间存在动态平衡,气态锌原子的氧化过程遵守直线规律;而锌液滴的氧化过程分为两个阶段,分别受收缩球状界面反应模型R₃和三维扩散模型D4动力学控制,表观活化能分别为106.3～108.2和114.2～117.3kJ/mol;扩散过程实际上是锌原子通过氧化膜层由里向外扩散,扩散系数D=2.46～9.70×10^-5cm²/s.     

Crystal growth of barium rhenates from hydroxide fluxes

Single crystals of two new barium rhenate compositions, Ba₁₆Re₆O₃₇ and Ba₁₀Re₃O₁₆(OH)₃, and of one new polymorph, orthorhombic Ba₅Re₂O₁₂, were grown out of a barium hydroxide flux in sealed silver tubes. Ba₁₆Re₆O₃₇ and Ba₁₀Re₃O₁₆(OH)₃ crystallize into the monoclinic C2/m system, with a = 20.577(4) Å, b = 5.8897(10) Å, c = 15.438 (3) Å, β = 92.255(10) ° and a = 1938342(9) Å, b = 5.8172(3) Å, c = 10.2925(5) Å, β = 91.7460(10) °, respectively. The orthorhombic polymorph of Ba₅Re₂O₁₂ crystallizes in the space group Pnma, with a = 19.6728(10) Å, b = 5.8491(3) Å and c = 10.4648(5) Å. All the three crystal structures are related and consist of a framework of BaO_x polyhedra (where x varies from six to twelve) with interpenetrating layers of ReO₆ octahedra.     

Vapor Pressure and Heat of Sublimation of Crystal Polymorphs

In order to determine the applicability of vapor pressure studies on polymorphic modifications, pairs of enantiotropically related modifications of caffeine, theophylline and carbamazepine were investigated. The studies were performed over a wide temperature range (71 to 191°C) and accordingly over a wide vapor pressure range (0.02 to 400 Pa) using an automatic instrument constructed on the basis of the gas saturation principle. This instrument enables an analytical determination of the main component and the impurities present by the chromatographic separation of the substances transported in the gas flow. Therefore, the real partial pressure of the main component can be measured. Due to the high precision of the applied method it was possible to determine partial pressure curves and the thermodynamic transition temperature — the point at which the vapor pressure of two crystal polymorphs is equal. The thermodynamic transition temperatures of caffeine and theophylline were determined to be 136 and 232°C, respectively. These values are in agreement with experimental or calculated values derived from DSC investigations but are more reliable. Vapor pressure measurements of carbamazepine are only meaningful in the low temperature range due to its decomposition at high temperatures. The thermodynamics, advantages and limits of vapor pressure determinations of polymorphic modifications are discussed.This revised version was published online in November 2005 with corrections to the Cover Date.     

甲醇在氧化锌表面吸附的研究

摘要用原位红外和脉冲实验研究了甲醇在氧化锌表面的吸附行为. FTIR结果表明, 甲醇吸附于氧化锌上易生成甲氧基, 且其生成量随着吸附温度的提高而增加. 进一步的研究结果表明, 甲氧基是由甲醇同氧化锌表面的羟基反应生成的, 将其暴露于水蒸汽中后很快消失. 脉冲实验发现, 氧化锌上脉冲甲醇时产生水, 再脉冲水则产生甲醇. 因此甲醇在氧化锌表面吸附生成甲氧基和水的反应是可逆的.