ZnO纳米线的制备及场发射特性的研究进展

从ZnO纳米线的生长机制出发,重点讨论了催化剂在制备过程中的作用,比较了采用VLS和VS不同机制生长ZnO纳米线的优缺点,并结合二者特点发现采用金属自催化将是制备高质量ZnO纳米线阵列的一种有效方法.分析了几种有利于提高其场发射性能的后处理方法,经过适当的后处理ZnO纳米线晶体的结构将更加完善,场发射开启场、阈值场将进一步降低,电流密度和场增强因子也将随之大大提高.     

不同温度和时间对SMAT黄铜基底生长ZnO纳米结构与形貌的影响

利用热氧化法,在不同氧化温度、保温时间条件下,在经过SMAT处理的Cu-Zn合金基底上生长出ZnO纳米线。采用X射线衍射、扫描电子显微镜、高分辨透射电子显微镜对样品结构、形貌进行了分析表征。结果表明:表面生长的纳米线为六方结构ZnO;氧化温度、保温时间对ZnO纳米线形貌有较大影响。总结了纳米线的生长机理。     

Ag掺杂ZnO纳米线酒敏性能的研究

利用浸渍法将ZnO纳米线浸渍于AgNO3溶液中制备了Ag 掺杂的ZnO纳米线.借助X射线衍射仪(XRD)和场发射扫描电子显微镜(FESEM)对纳米线的晶体结构和形貌进行了表征.结果表明纳米线既含面心立方结构的Ag又含有六方纤锌矿结构的ZnO.三维网络结构的ZnO纳米线被一层致密的Ag颗粒包裹并在其表面形成了大量的具有高比表面剂的孔洞结构.将纯的和Ag掺杂的ZnO 纳米线都作为酒敏传感材料,在酒精浓度为0.001%,工作温度为150～400℃的范围内测试了它们的气敏特性,结果显示,Ag掺杂的ZnO纳米线的酒精灵敏度比纯ZnO纳米线提高了14.在工作温度为350℃的条件下测试了它们的响应-恢复时间.气敏元件的酒敏特性主要归结于表面吸附效应.     

不同温度和时间对SMAT黄铜基底生长ZnO纳米结构与形貌的影响

利用热氧化法，在不同氧化温度、保温时间条件下，在经过SMAT处理的Cu—Zn合金基底上生长出ZnO纳米线。采用X射线衍射、扫描电子显微镜、高分辨透射电子显微镜对样品结构、形貌进行了分析表征。结果表明：表面生长的纳米线为六方结构ZnO；氧化温度、保温时间对ZnO纳米线形貌有较大影响。总结了纳米线的生长机理。     

Ag纳米粒子修饰ZnO纳米线特性研究

利用水溶液法制备ZnO纳米线,使用真空热蒸发方法用Ag对ZnO纳米线进行表面修饰。用场发射扫描电子显微镜(FESEM)、X射线衍射(XRD)仪、吸收谱仪分析它们的表面形貌、物相结构及光学性质,同时分析了其场发射性能。结果表明,随着Ag修饰量的增加,ZnO纳米线表面上的Ag纳米粒子分布会由稀疏逐步到致密,最后Ag的纳米粒子几乎连在一起。测量吸收谱线发现修饰后的ZnO纳米线的吸收能力变强,但存在一个临界值,当修饰量超过临界值后,ZnO纳米线的光吸收能力会减弱。对修饰后ZnO纳米线的场发射性能进行初步测试,结果表明适当量的Ag修饰可以有效降低ZnO纳米线的场发射开启电压。     

生长温度对热蒸发法制备ZnO纳米线的结构与发光性能影响

采用无金属催化剂的简单热蒸发法,在Si(100)衬底上不同生长温度下成功地制备了高密度和大长径比的单晶ZnO纳米线。分别利用X射线衍射仪(XRD)、扫描电子显微镜(SEM-EDS)、透射电子显微镜(TEM)及荧光光谱仪表征样品的结构和发光性质。XRD和TEM研究表明,所制备的样品为沿C轴择优取向生长的单晶ZnO纳米线,具有六方纤锌矿结构。SEM和TEM研究表明,生长温度对ZnO纳米线的形貌及长径比的影响较大。当生长温度为700℃时,制备得到长径比为300(长度约为15μm,直径约为50nm)的ZnO纳米线。低于600℃时,形成花状ZnO纳米锥或 纳 米 棒。高 于700℃时,形 成 小 长 径 比 的ZnO纳米棒。此外,室温光致发光(PL)谱上出现一个强而尖锐的紫外发射峰以及一个弱而宽泛的蓝光发射峰。采用的热蒸发法制备ZnO纳米线基于气-固(VS)生长机理且该生长方法可用于大规模、低成本制备高纯度的单晶ZnO纳米材料。     

生长温度对热蒸发法制备ZnO纳米线的结构与发光性能影响

采用无金属催化剂的简单热蒸发法,在Si(100)衬底上不同生长温度下成功地制备了高密度和大长径比的单晶ZnO纳米线。分别利用X射线衍射仪(XRD)、扫描电子显微镜(SEM-EDS)、透射电子显微镜(TEM)及荧光光谱仪表征样品的结构和发光性质。XRD和TEM研究表明,所制备的样品为沿c轴择优取向生长的单晶ZnO纳米线,具有六方纤锌矿结构。SEM和TEM研究表明,生长温度对ZnO纳米线的形貌及长径比的影响较大。当生长温度为700℃时,制备得到长径比为300(长度约为15μm,直径约为50nm)的ZnO纳米线;低于600℃时,形成花状ZnO纳米锥或纳米棒;高于700℃时,形成小长径比的ZnO纳米棒。此外,室温光致发光(PL)谱上出现一个强而尖锐的紫外发射峰以及一个弱而宽泛的蓝光发射峰。采用的热蒸发法制备ZnO纳米线基于气-固(VS)生长机理且该生长方法可用于大规模、低成本制备高纯度的单晶ZnO纳米材料。     

紫光激发提高Ag修饰的ZnO纳米线的气敏特性

为了提高ZnO纳米线的酒敏特性,利用紫光激发经浸渍法获得Ag修饰的ZnO纳米线.利用扫描电子显微镜（SEM）,X射线衍射仪（XRD）对修饰后的ZnO纳米线进行了晶体结构和形貌的表征.结果表明其晶体结构中既有六方纤锌矿结构的ZnO,又有面心立方的Ag.三维网络结构的ZnO纳米线的表面被一层致密的具有高孔隙率的Ag颗粒覆盖,使得ZnO纳米线具有更高的比表面积.纯ZnO纳米线和Ag修饰的ZnO纳米线都用作气敏基料,根据它们在酒精蒸气中紫光照射和无紫光照射条件下电阻的变化来测定它们的气敏特性.结果显示紫光照射下经质量分数为6%AgNO3修饰的ZnO纳米线对酒精蒸气的最大灵敏度由75.8提高到175.77.此过程中光催化氧化-还原反应起到了重要作用.     

具有四角状棒-线结构纳米氧化锌的制备和性能

用气相氧化法合成出具有纳米棒-线结构的ZnO纳米材料.扫描电子显微镜(SEM)、透射电子显微镜(TEM)观察和X射线衍射谱(XRD)的分析表明:四角状ZnO纳米材料具有六方纤锌矿晶体结构,在棒-线纳米结构中,每个角的长度为1～2 μm,纳米棒的直径为100～200 nm,纳米线的直径约为30 nm.用气-固(VS)生长机制解释了棒-线纳米结构的形成.与ZnO大块材料不同,四角状ZnO纳米棒-纳米线材料在室温下具有～380 nm波长的紫外发射和～520 nm波长的绿光发射,其机理是晶体中杂质与结构缺陷少,以及与其纳米尺度相联系的量子限域效应.     

ZnO/TiO_2复合纳米材料的制备及其在染料敏化太阳电池中的运用

本文在长有ZnO纳米粒子作为"种子层"的FTO基底上用水热合成法制备了取向高度一致的ZnO纳米线阵列,用TiCl4的异丙醇溶液在ZnO纳米线阵列的表面生长了纳米结构的TiO2。利用扫描电子显微镜、能量散射谱、X射线衍射分别表征纳米材料的形貌和结构,用Raman光谱研究了材料的晶格结构特性。染料敏化太阳电池的性能测试表明,与纯ZnO作为光阳极相比,ZnO/TiO2复合纳米材料作为光阳极的器件,开路电压和填充因子都得到了提高。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.