纯稀土纳米晶Gd块体材料的结构与磁性

采用放电等离子烧结技术（简称SPS技术）及热处理制备了全致密纯稀土纳米晶Gd块体材料，研究了材料的微结构和磁性。X衍射结果表明材料在烧结过程中形成了一定程度的c轴织构。TEM观察显示，烧结态纳米晶Gd的平均晶粒尺度在10nm左右；热处理后，平均晶粒尺寸达到100nm。PPMS测试发现与粗晶Gd相比，纳米晶Gd的居里温度以及饱和磁化强度均有所下降。说明Gd的纳米化对其磁性具有重要影响。     

放电等离子快速烧结纳米3Y-TZP材

本文采用放电等离子烧结技术（ＳＰＳ）快速烧结结纳米３Ｙ－ＴＺＰ材料,利用ＳＰＳ技术快速烧结,可制备出完整、致密的３Ｙ－ＴＺＰ材料,在烧结温度为１３００℃,保温３ｍｉｎ条件下,相对密度达９８．２％,晶粒仅１００￣１３０ｎｍ,研究发现,材料的密度随烧结温度的变化趋势与一般快速烧结有明显区别;材料的晶粒随烧结温度的提高而长大,但长大幅度小于其他一些烧结方法所得的３Ｙ－ＴＺＰ材料,本研究对这些现象进行了理     

热压烧结制备纳米Y-TZP材料

本文研究了热压烧结制备纳米Ｙ－ＴＺＰ材料的过程．研究结果表明：热压烧结纳米Ｙ－ＴＺＰ材料有一些新的特点,主要是纳米Ｙ－ＴＺＰ材料在热压烧结时,由于软团聚未能有效地破碎;造成烧结过程中团聚体内部首先致密化,与基体之间产生张力,导致裂纹状大气孔的出现．同时因石墨模具的限制,热压时的外压不足以克服塑性滑移产生所需的“阈值”,因此大气孔无法“压碎”,使材料的烧结密度比相同温度下无压烧结还低．针对热压烧结纳米Ｙ－ＴＺＰ材料的局限性,采用热煅压烧结,可在１１００℃的低温下获得致密的纳米Ｙ－ＴＺＰ材料,晶粒大小仅８５ｎｍ左右。     

Cu纳米晶块体的制备及纳米晶粒长大动力学研究

采用高能球磨的方法制取金属纳米晶粉末，然后利用放电等离子烧结（SPS）技术制备出金属纳米晶块体材料。设计系列实验研究金属纳米晶材料的晶粒长大行为，获得了纳米晶粒长大的动力学规律。根据已有的工作基础和对实验结果的深入分析，确定动力学参数对稳定相晶粒长大行为的影响。实验发现了高能球磨配合SPS技术制备的Cu纳米晶块体发生快速晶粒长大的临界温度，并结合纳米晶界过剩体积与过剩自由能的关系，分析了纳米晶粒组织的能量因素对晶粒长大行为及动力学的影响。     

超细、纳米晶WC-Co硬质合金烧结技术的研究现状

WC-Co硬质合金因高硬、耐磨而在切削、釆矿和耐磨零件等领域广泛应用。研究发现,当WC晶粒尺寸小于0.5μm时(即超细、纳米晶WC-Co硬质合金),与普通硬质合金相比,材料的硬度和强度显著提高,其韧性也同样会有所提升。因此,晶粒细化有助于改善硬质合金的力学性能,从而延长其使用寿命。长期以来,有关硬质合金性能改善方面的研究多关注于从粉体出发,即通过采用超细纳米粉体和合理烧结工艺来实现超细晶和纳米结构硬质合金的制备。然而,在合金制备过程中其致密性与晶粒长大之间往往存在较为复杂的交互作用,如何保证在烧结过程中致密化的同时抑制WC晶粒长大是提高合金性能以及保证合金质量稳定性的关键技术问题之一。本文主要阐述了高温液相烧结制备超细、纳米晶WC-Co硬质合金过程中有关致密化和晶粒长大机制之间的关联性,从烧结工艺与添加剂两方面介绍了近年来国内外的研究现状。烧结工艺具体分为常规烧结工艺(主要包括氢气烧结、真空烧结和热等静压烧结等)和快速烧结工艺(主要包括微波烧结、放电等离子烧结、高频感应热烧结等),对比了上述烧结工艺之间的不同以及总结了不同烧结工艺的优缺点。在添加剂方面,重点介绍了过渡族碳化物和稀土元素对硬质合金烧结过程中晶粒生长的抑制作用,并在此基础上阐述了超细、纳米晶WC-Co硬质合金烧结技术的未来发展趋势。     

晶粒可控钛酸钡致密陶瓷的制备及表征

采用超重力反应沉淀法制备的纳米钛酸钡粉体和常规陶瓷工艺,通过控制烧结温度在 1200 ~1300℃,分别制备了晶粒尺寸 0.45~2.2μm的致密陶瓷。实验结果表明超重力反应沉淀法制备的粉体具有良好的烧结和介电性能。烧结温度为 1200℃时,相对密度即可达到95%,晶粒尺寸为 0.45μm,随烧结温度的升高,晶粒逐渐长大,未出现晶粒的异常长大现象,到1300℃相对密度和晶粒尺寸分别达到 97.7%和2.2μm。钛酸钡陶瓷介电性能有明显的粒度效应,晶粒在1.2μm左右时,室温介电常数达到最大(4143)。由于晶粒内部立方相成分的出现,包含更细晶粒的陶瓷(d=0.45μm)呈现低的介电常数。     

Si-Al-Zr-O系超微细晶复相陶瓷研究

回顾了目前Si-Al-Zr-O系超微细晶复相陶瓷的主要研究方法并分析了这些方法的特点.针对应用超微细粉致密化制备Si-Al-Zr-O系陶瓷材料存在的烧结温度高(一般高于1500℃),致密化难,增韧相种类有限且成本高等问题,提出了一种新的制备方法——非晶原位受控晶化法,在较低温度1100~1200℃下制得均匀、致密、高可靠性的Si-Al-Zr-O系超微细晶复相陶瓷.该方法能有效避免高温烧结以及烧结过程中纳米粉末的团聚和晶粒异常长大,实现显微结构的有效控制,是一种具有发展前景的制备技术.     

双A层MAX相Mo2Ga2C的热压烧结研究

本工作采用真空热压烧结的方法, 研究Mo₂Ga₂C粉体的烧结性能, 制备致密的Mo₂Ga₂C块体材料, 并且表征所制备材料的微观结构。实验发现750 ℃是合适的烧结温度, 过高的烧结温度(850 ℃)会导致样品分解, 主要产物为Mo₂C。在750 ℃烧结过程中, 随着烧结时间的延长, 样品的晶粒没有明显长大, 但是样品内部空隙显著变小, 内部织构增强, 相对密度明显提高。因为Mo₂Ga₂C晶体的片状结构, 热压烧结过程中, 部分片状晶粒会偏转, 导致烧结样品的多数晶粒的(00l)晶面会倾向垂直于热压方向。在750 ℃烧结8 h, 可以得到几乎完全致密(相对密度98.8%)的Mo₂Ga₂C块体材料。     

粉体表面包碳对3Y-TZP陶瓷烧结性能及微观结构的影响

采用对纳米氧化锆陶瓷粉体表面包碳,研究了在不同烧结工艺下,碳含量(0%～7.0%(wt))的变化对纳米氧化锆陶瓷烧结性能及微观结构的影响.分析结果表明:包裹少量碳能明显提高烧结活性,增大烧结坯密度.在本实验条件下,碳含量为1.5wt%的纳米氧化锆陶瓷在1250℃低温氧化气氛中烧结,可得到相对密度约为96%、晶粒尺寸约为85m的陶瓷体,此后随着碳含量的增加,致密度减小;采用真空烧结,由于碳没有被氧化,包裹层的存在阻止了晶界的扩散,延缓了陶瓷体烧结的致密化过程,烧结性能较差;同时碳的加入有效地抑制了晶粒的长大.     

纳米晶WC-Co硬质合金的研究现状

概述了国内外纳米晶硬质合金的发展现状.纳米晶WC-Co硬质合金制备的关键技术主要包括:优质纳米晶WC粉的制备和烧结过程中WC晶粒长大的控制.综述了优质纳米晶WC粉的特点和制备技术,以及目前国内外烧结过程中控制晶粒长大采取的主要措施:添加晶粒长大抑制剂、调整烧结工艺和开发新型烧结方法.列举了合金的实际应用领域,展望了纳米晶硬质合金的发展前景.     

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 ...     

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.     

The Influence of Nitrogen and Boron Implant into Silicon Substrate on the Phase and Internal Stress of c-BN Films

Cubic boron nitride(c-BN) film was deposited on a Si (100) substrate by the RF-magnetron sputtering.The mainly problems for fabrication of c-BN films are the low purity and high intrinsic compressive stress. In order to solve the two problems, the c-BN film with the buffer interlayer was deposited on the substrate which had been implanted with nitrogen and/or boron ions. The results show: the implantation of nitrogen ions can obviously increase c-BN content and reduce the internal stress slightly; while the implantation of boron shows no obvious improvement to the content of c-BN, which can reduce the internal stress in the film obviously. In addition, it is suggested that the implantation of nitrogen and boron shows the best result, which not only can increase the content of c-BN, but also reduce the internal stress in the c-BN film obviously.