溶胶凝胶法制备钛酸锶钡(Ba1-xSrx)TiO3陶瓷及其介电性能的研究

采用硝酸钡、硝酸锶、钛酸丁酯和柠檬酸为原料的配合物溶胶凝胶方法制备了(Ba1-xSrx)TiO3(BST)陶瓷.实验结果表明,BST粉体合成温度及烧结温度分别为700及1250℃,均低于传统工艺的相应温度. Sr含量x≥0.40,(Ba1-xSrx)TiO3陶瓷的相结构为立方钙钛矿相;Sr含量x＜0.40,(Ba1-xSrx)TiO3陶瓷的相结构为四方钙钛矿型. (Ba1-xSrx)TiO3(0.5≤x≤0.70)陶瓷的电容率随温度变化曲线,说明存在由铁电四方相到顺电立方相的相变.且随锶(Sr)的摩尔量x的增加,(Ba1-xSrx)TiO3陶瓷样品的相变温度向低温方向移动,相变温度Tc的移动关系为Tc=394.1-272.6x(K).     

Ba0.6 Sr0.4 TiO3-ZnNb2O6复相微波介质陶瓷的结构与介电性能研究

以Ba0.6Sr0.4TiO3为基体材料,采用传统陶瓷制备工艺,制备了Ba0.6 Sr0.4 TiO3-ZnNb2O6(简称BSTZ)复相微波介质陶瓷.结果表明,BSTZ复相陶瓷可在1200℃烧结成瓷,烧结温度明显低于Ba0.6Sr0.4TiO3陶瓷的烧结温度,并反应生成新相BaNb3.6O10.在室温低频下,随ZnNb2O6含量的增加,BSTZ复相陶瓷的介电常数下降;在1.6kV/mm的直流偏压下,各BSTZ复相陶瓷的可调性随ZnNb2O6添加量增加而减小.     

新型的Sol-gel法制备Ba0.6Sr0.4TiO3铁电陶瓷

采用新型的Sol-gel工艺制备了Ba0.6Sr0.4TiO3(BST)超细粉体,将BST粉体进行压制和烧结,获得了晶粒尺寸在1μm以内的BST陶瓷块体.观察了BST陶瓷块体的结晶情况并测定了其电学性能.在Sol-gel工艺中,加入了有机大分子量聚乙烯吡咯烷酮(polyvinyl pyrrolidone,PVP)制备BST前驱体.实验结果表明PVP的加入可有效增加前驱体的稳定性和分散性,降低BST陶瓷的预烧温度约250℃,并在1200℃获得晶粒细小、致密的BST陶瓷.BST陶瓷,显示弥散相变特征.     

新型的Sol-gel法制备Ba0.6Sr0.4TiO3铁电陶瓷

采用新型的Sol-gel工艺制备了Ba0.6Sr0.4TiO3(BST)超细粉体,将BST粉体进行压制和烧结,获得了晶粒尺寸在1μm以内的BST陶瓷块体.观察了BST陶瓷块体的结晶情况并测定了其电学性能.在Sol-gel工艺中,加入了有机大分子量聚乙烯吡咯烷酮(polyvinyl pyrrolidone,PVP)制备BST前驱体.实验结果表明:PVP的加入可有效增加前驱体的稳定性和分散性,降低BST陶瓷的预烧温度约250℃,并在1200℃获得晶粒细小、致密的BST陶瓷.BST陶瓷,显示弥散相变特征.     

细晶Ba0.6Sr0.4TiO3(BST)陶瓷材料的制备与介电性能

采用改进的Sol-gel工艺和传统烧结技术制备了晶粒尺寸在0.15～10μm的Ba0.6Sr0.4TiO3(BST)陶瓷,观察了样品的显微结构,并对样品的介电性能进行了测试,分析了晶粒尺寸对材料介电性能的影响.实验结果表明:改进的Sol-gel工艺和两步烧结法可以有效地控制Ba0.6Sr0.4TiO3(BST)陶瓷的晶粒尺寸.晶粒尺寸的降低,材料的介电常数也随之下降,介电峰呈现明显的铁电-顺电弥散相变;但当陶瓷的晶粒尺寸＜1 μm,介电常数出现峰值,铁电相变温区变窄.     

表面活性剂对溶胶-凝胶法制备Ba0.6Sr0.4TiO3粉体的影响

钛酸锶钡(BST)陶瓷是一种性能优异的电容器材料、热敏材料和铁电压电材料,具有非常广阔的应用领域.采用溶胶-凝胶法合成了Ba0.6Sr0.4TiO3纳米粉体,通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)、激光粒度分析仪对粉体的物相组成、颗粒大小和形态进行了分析,利用红外光谱仪(FT-IR)研究了表面活性剂在合成纳米Ba0.6Sr0.4TiO3过程中的作用,并重点考察了表面活性剂对Ba0.6Sr0.4TiO3粉体性能的影响.研究结果表明,通过添加适量的表面活性剂能有效改善纳米钛酸锶钡粉体的表面性能,使纳米钛酸锶钡具有较好的分散性,可充分发挥材料的纳米效应.     

改进的sol-gel工艺制备细晶Ba0.6Sr0.4TiO3陶瓷及其介电性能的研究

用改进的sol-gel工艺制备了细晶钛酸锶钡(Ba0.6Sr0.4TiO3,BST)陶瓷块体,研究了BST陶瓷的结晶与介电性能.在这种改进sol-gel的工艺中,用传统的固相反应煅烧形成BST粉体,经高能球磨制备BST纳米陶瓷粉体,再将一定质量的纳米粉体加入到相同化学组成的BST的溶胶液中,经普球球磨12h后,制备成悬浮性好,分散均匀的浆料.浆料可用来制备BST陶瓷,并在1200℃保温2h烧结成瓷,结果显示,BST陶瓷块体结构致密,晶粒尺寸在0.15～2μm之间.分析了样品的介电性能和晶粒尺寸对材料介电性能的影响.介电温谱显示,在0℃,100kHz时,相对介电常数为2500,介电损耗为0.02;并且存在明显的弥散相变.     

Ln0.6Sr0.4 FeO3-δ(Ln=La、Nd、Ce)阴极材料的制备与表征

以甘氨酸-硝酸盐水溶液为前驱体合成了Sr掺杂的稀土铁酸盐Ln0.6Sr0.4FeO3-δ(Ln=La、Nd、Ce)粉体.对制备过程的化学键变化、样品的热稳定性、物相形成过程及导电性进行了表征.结果表明,甘氨酸-硝酸盐合成法成相温度低于1000℃.坯体烧结较粉状样品更有利于钙钛矿物相的形成,La0.6Sr0.4FeO3-δ及Nd0.6Sr0.4FeO3-δ坯体1000℃煅烧2h即可形成近乎单一的钙钛矿相(ABO3);Ce0.6 Sr0.4 FeO3-δ是CeO2立方萤石相和产物钙钛矿相共存,两相难分主次.合成样品低温下的导电行为符合小极化子导电机制;1200℃烧结的La0.6Sr0.4FeO3-δ样品在测试全温度范围内(450～800℃)电导率超过100S/cm,Nd0.6Sr0.4FeO3-δ在中温区(600～800℃)电导率＞60S/cm;Ce0.6Sr0.4FeO3-δ样品的电导率不理想.     

Si-B-O系BST玻璃陶瓷制备及介电弥散研究

采用硝酸钡、硝酸锶、钛酸丁酯、正硅酸乙脂和硼酸三正丁脂为原料的溶胶凝胶方法制备了Si-B-O系BaxSr1-xTiO3玻璃陶瓷。通过差热分析(DTA)、热失重(TG)、X射线衍射(XRD)分析Si-B-O系BST玻璃陶瓷超细粉体合成过程及其相结构变化。采用X射线衍射(XRD)、扫描电子显微镜(SEM)描述Si-B-O系BST玻璃陶瓷烧结体的相结构和显微组织结构变化。阻抗分析仪测量Si-B-O系BST玻璃陶瓷的-50～100℃介电温谱。实验结果表明：Si-B-O系BST玻璃陶瓷粉体的相结构为立方钙钛矿相结构,其合成温度为700℃．不存在第二相。Si-B-O系BST玻璃陶瓷的烧结温度低于传统工艺。Si-B-O系BST玻璃陶瓷的显微结构呈细晶结构。Si-B-O系BST玻璃陶瓷的介电常数ε随着烧结温度升高而增大．介电损耗tgδ随测试温度的增加而降低。随着晶粒平均尺寸的减小．Si-B-O系BST玻璃陶瓷样品的介电峰变低．平坦．宽化．存在介电峰弥散化的现象。     

(1-x)(K_(0.5)Na_(0.5))NbO_3-x(Sr_(0.4)Ba_(0.6))_(0.7)Bi_(0.2)TiO_3无铅铁电陶瓷介电性能研究

采用传统固相烧结法,在铌酸钾钠陶瓷基体中掺入Sr、Ba、Bi和Ti元素,制备了(1-x)(K0.5Na0.5)-NbO3-x(Sr0.4Ba0.6)0.7Bi0.2TiO3((1-x)KNN-xBSBT)(0.01≤x≤0.04)陶瓷。XRD测试结果表明,(1-x)KNNxBSBT(0.01≤x≤0.04)为纯钙钛矿相;介电温谱表明,(1-x)KNN-xBSBT为弛豫铁电体;0.97KNN-0.03BSBT陶瓷介电常数具有很好的温度稳定性,在室温至400℃介电常数变化很小。     

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.