热压烧结工艺对AlN陶瓷显微结构及性能的影响

以直接氮化法制备的AlN粉体为原材料,添加质量分数为5％ 的Y2O3做烧结助剂,采用热压烧结工艺制备AlN陶瓷.研究烧结温度和压力对AlN陶瓷显微结构、相对密度和热导率的影响.结果表明:随着烧结温度的升高,AlN陶瓷的晶粒长大,第二相逐渐增多,热导率和相对密度均为先增大后减小;随着压力的增大,AlN陶瓷的晶粒逐渐细小,气孔率减少,热导率和相对密度都显著增大.确定AlN陶瓷的最优烧结条件如下:温度为1800℃,压力为50 MPa.     

Li2O对SPS烧结AlN陶瓷致密化、显微结构和导热性的影响

研究了低温烧结助剂Li2O对SPS烧结AlN陶瓷烧结致密化过程、烧结体显微结构和导热性的影响.研究表明:在SPS烧结过程中,烧结助剂Li2O和Sm2O3(或Y2O3)的加入使AlN试样开始收缩并进入烧结初期阶段的温度从1550℃左右下降到1200℃以下;同时Li2O使AlN试样的烧结温度显著降低,完全致密化温度降低到1650℃左右.烧结体的显微结构表明:Li2O的加入有助于形成润湿性良好的液相,促进AlN陶瓷的液相烧结;但不利于快速烧结坯体中气体的扩散与逸出,使试样的致密度受到影响.同时,Li2O影响AlN晶粒的发育,使液相润湿性提高,晶界相均匀分布,增加了晶粒界面上的声子散射,对AlN材料的热导率产生不利影响.同时,添加1.0wt%Li2O和1.5wt%Sm2O3的AlN试样的热导率低于仅添加1.5wt%Sm2O3的试样.     

纳米复合助剂对氮化铝陶瓷烧结特性的影响

如何获得理想的氮化铝陶瓷是电子陶瓷材料研究领域的重要课题。本研究采用纳米复合添加剂Y2O3-La2O3,分别在1600℃、1650℃、1700℃、1750℃和1800℃下,无压烧结氮化铝陶瓷。测定并分析了AlN陶瓷的性能和微观结构。实验结果表明:烧结温度达到1750℃,就可获得致密烧结,此时AlN晶粒细小均匀,第二相Al2Y4O9、LaAlO3和Y2O3分布在AlN晶界,AlN晶粒内的氧含量很低,AlN陶瓷样品的热扩散率较高。     

复合助剂CaF2-Y2O3对AlN-BN复合陶瓷显微结构和热导性能的影响

用热压法制备了AlN-BN复合陶瓷材料,添加CaF2和Y2Os为烧结助剂,研究了烧结助剂的种类、含量以及不同保温时间对复合材料的物相组成、显微结构和热导率的影响.添加复合助剂(1～3)wt%Y2O3-3wt?F2的试样在保温过程中晶界相挥发明显,净化了复合材料的晶界,减少了复合材料中AlN晶格缺陷,获得了纯净的AlN-BN复合陶瓷.与单独添加CaF2助剂的试样相比,添加复合助剂的试样的介电性能没有明显下降,随复合助剂(1～3)wt%Y2O3-3wt?F2中Y2O3含量的增加,AlN-BN复合陶瓷的热导率显著提高.添加复合助剂3wt%Y2Os-3wt?F2的试样在1850℃下保温3h获得的热导率为132.7W·m-1·K-1.     

Y2O3和纳米AlN协同作用对氮化铝陶瓷烧结性能及热传导的影响

在微米氮化铝粉体中添加含量为4%的Y2O3和不同含量的纳米AlN粉体制备氮化铝陶瓷,研究了Y2O3和纳米AlN协同作用对微米氮化铝陶瓷烧结性能和热传导性能的影响。结果表明,Y2O3优先与纳米AlN粉体表面的Al2O3反应生成活性较高的第二相Al5Y3O12,相比于Y2O3与微米AlN粉体表面Al2O3反应生成的Al5Y3O12,具有更低的熔化温度及更好的流动性;同时,纳米AlN粉体的高比表面能也促进氮化铝陶瓷的致密化进程。二者的协同作用有效地促进氮化铝陶瓷的致密烧结,改善第二相的微观分布,从而能在较低的烧结温度下获得具有较高热导率的氮化铝陶瓷。当Y2O3和纳米AlN粉体的添加量(质量分数)分别为4%和1.5%时,在1800℃烧结得到的氮化铝陶瓷密度为3.26 g·cm-3,第二相以连续相的形式分布于氮化铝晶界处,热导率为151.75 W/(m.K)。     

以Al-B-C为烧结助剂的SiC陶瓷热压烧结工艺

以SiC超细粉末为原料,Al粉、B粉和碳黑为烧结助剂,采用热压烧结工艺制备了SiC陶瓷,重点研究了烧结助剂含量(4～13 wt％)对SiC陶瓷物相组成、致密度、断面结构及力学性能的影响.除SiC主晶相外,X射线衍射图还显示了Al8B4C7相的存在;当烧结助剂的含量从4 wt％增至13 wt％时,扫描电镜照片显示陶瓷断面形貌从疏松结构变成致密结构,存在晶粒拔出现象;陶瓷力学性能随着烧结助剂含量的增加先升高后降低.当烧结助剂含量为10 wt％时,SiC陶瓷的力学性能达到最高,抗弯强度为518.1 MPa,断裂韧性为4.98 MPa·m1/2.Al、B和C烧结助剂在1850℃烧结温度下形成的Al8B4C7液相促进晶粒间的重排和传质,并填充晶粒间的气孔,提高了陶瓷致密度.     

晶界相和晶界对AlN陶瓷热导率的影响

本文研究了掺杂CaO Y2 O3热压烧结和常压烧结AlN陶瓷的晶界相及其产生过程和除氧机制 ;分析了两种烧结工艺烧制的AlN陶瓷的晶界成份 ;测定了不同晶界相含量和晶界成份对应的AlN陶瓷的热导率     

热压烧结AlN(Y_2O_3)陶瓷热导率的温度关系

采用热压烧结技术,以Y2O3为烧结助剂制备AlN陶瓷。闪光法测试AlN陶瓷在室温~200℃的温度关系。结果表明,AlN陶瓷热导率随温度升高而降低;气孔对AlN陶瓷热导率随温度变化的速率有抑制作用,气孔率越小(致密度越高),热导率对温度变化越敏感;AlN陶瓷钇铝酸盐晶界相含量对热导率随温度变化的速率有促进作用,钇铝酸盐含量越高,热导率对温度变化越敏感。     

Al2O3透明陶瓷显微结构的研究

采用高纯Al2O3(＞99.9%)粉末为原料,用无压烧结工艺制备Al2O3透明陶瓷.研究了添加剂Y2O3、烧结温度、保温时间等对Al2O3透明陶瓷显微结构和光学性能的影响.实验结果表明,适量的Y2O3能够抑制Al2O3晶粒的生长,改善烧结性能,但添加量过多会使Al2O3陶瓷气孔略有增加.在1800℃烧结的样品密度接近理论密度,具有较好的光学性能.延长保温时间能够使晶粒长大的同时有效排除晶界处少量气孔.     

微波低温烧结制备氮化铝透明陶瓷

微波烧结(Microwave Sintering)是一种新型、高效的烧结技术, 具有传统烧结技术无可比拟的优越性. 本文在不添加任何烧结助剂的前提下, 采用高纯微米级氮化铝(AlN)粉, 在1700℃/2h的微波低温烧结工艺条件下制备出透明度较高的AlN透明陶瓷. 分析结果表明, 采用微波低温烧结工艺制备的AlN透明陶瓷晶粒尺寸细小(<10μm), 晶粒发育完善且分布均匀, 晶界平直光滑且无第二相分布, 从而证明用微波烧结可以实现AlN透明陶瓷的低温烧结.     

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.……     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

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.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.