高温等静压烧结Al2O3-ZrO2纳米陶瓷

本工作用化学共沉淀法制备了平均晶粒尺寸约２０ｍｍ的２０ｍｏｌ％Ａｌ２Ｏ３－ＺｒＯ２复合粉体,不含有Ｙ２Ｏ３作为四方氧化锆的稳定剂,粉体的煅烧温度为７５０℃,ＸＲＤ结果表明,粉体中含１００％立方氧化锆相,未发现有Ａｌ２Ｏ３结晶相存在。该粉体用高温等静压方法,在１０００℃和２００ＭＰａ的条件下烧结１ｈ,得到了平均尺寸为５０ｎｍ的致密陶瓷,样品密度为密度的９８％左右。     

氧化锆纳米粉体烧结性能研究

为了研究纳米氧化锆粉体的烧结性能,以4种不同粒度的氧化锆粉体为原料,在热分析仪上测试了室温～1000℃范围内坯体的形变量和热膨胀性能.采用1450℃恒温1～6 h的烧结工艺,制备了氧化锆陶瓷,并进行了性能表征.结果表明:粉料1次粒子粒径越小,其初始烧结温度越低;粉料的团聚粒径越小,分布越窄,坯体的烧结致密化越容易.     

低温制备高致密度细晶W-10％TiC复合材料

采用高能球磨结合真空热压的手段制备了W-10％（质量分数）TiC复合材料。采用扫描电镜、透射电镜和x射线衍射等对复合粉体及复合材料进行表征。结果表明，通过高能球磨得到了粒径均匀，平均粒径约为100nm的纳米复合粉体，粉体经过1700℃真空热压烧结后致密度达到99．1％，并且保持细晶结构（平均晶粒尺寸为0．8gm）。热压和高能球磨导致的机械活化以及引入的Fe、Ni等杂质是复合材料低温烧结达到高致密度的重要原因。     

低温烧结细晶Y-TZP

通过在Ｙ－ＴＺＰ中加入适量的硅酸盐玻璃添加剂,使其烧结温度明显降低,并且制备出具有细晶粒、高强度的四方相氧化锆增韧陶瓷材料．分析了添加剂含量及烧结温度与材料致密度、显微结构及力学性能的关系,发现在Ｙ－ＴＺＰ材料中加入１ｗｔ％的添加剂,可以使材料在１４００℃下烧结,氧化锆晶粒尺寸约为１００～２００ｎｍ;其抗折强度可达９５０ＭＰａ．     

纳米粉体干燥方法的研究

采用三种干燥方法：冷冻干燥、共沸蒸馏和烘箱干燥对溶胶-沉淀法制备的沉淀进行干燥处理,得到了立方相BaTiO₃纳米粉．研究发现：冷冻干燥和共沸蒸馏都能防止粉体中形成硬团聚,提高了烧结活性,其中冷冻干燥法效果更明显．文章同时对两种干燥方法防止硬团聚形成的机理进行了讨论．     

半导体SnO2纳米晶态粉体显微结构对气敏传感器性能的影响

用ＸＲＤ、ＳＥＭ手段分析了共沉淀工艺和水热合成技术制备的半导体ＳｎＯ２纳米晶态粉体及其厚膜陶瓷材料的显微结构,结果表明两种粉体的晶粒尺寸大约７ｎｍ,但两种粉体的ＸＲＤ照片差异较大。用水热合成技术制备的粉体其颗粒是由纳米晶粒团聚而成,颗凿尺寸大约３００ｎｍ左右,具有较大的表面活性,而具有较大的表面活性,而用共沉淀工艺制备的粉体,颗粒分布较宽,活性差。两种粉体的显微结构对厚膜陶瓷材料显微结构的形成和Ｓ     

电熔急冷工艺制备Ca—PSZ的特性分析

采用电熔融喷吹法制备不同氧化钙含量部分稳定氧化锆粉体（Ca—PSz），发现以该粉体为原料的制品在烧结过程中易出现开裂现象，采用阿基米德法和X射线衍射仪分析经不同温度和时间热处理的样品的密度和相组成寻找造成开裂的原因。研究发现：用熔融喷吹法制备的氧化钙部分稳定氧化锆粉体中稳定相一部分为Ca抖稳定氧化锆，一部分为粒径尺寸小于相变临界尺寸的无稳定剂介稳氧化锆；1200℃下热处理电熔喷吹法制备的部分稳定氧化锆粉体可促进其微观形貌的完善和晶粒的长大，提高样品密度；当热处理温度为1500℃，晶粒尺寸超过相变临界尺寸（〉14．34nm），样品中的介稳相氧化锆会分解生成单斜相氧化锆，导致样品稳定度和密度急剧降低。     

以碳酸氢铵为沉淀剂制备纳米钇铝石榴石粉体

以碳酸氢铵为沉淀剂,硝酸盐为原料,采用沉淀法,通过仔细控制沉淀过程的工艺参数,得到了煅烧后可直接生成纯相YAG的前驱体沉淀物,前驱体经过900℃煅烧即可获得纳米YAG粉体.BET,TEM和XRD的测试结果表明纳米YAG粉体的晶粒尺寸为67～175nm,晶粒形态为球形,分散性良好.粉体达到完全致密化的最低烧结温度为1450℃.所获得的粉体经过1700℃真空烧结3h,烧结体具有一定的透明度.研究表明,这种纳米YAG粉体所具有的良好烧结活性与粉体的纳米晶粒尺寸,球形晶粒形态及极佳的分散性有关.     

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.     

激光烧结快速制备自由形状纳米块体材料的试验研究

基于选区激光烧结快速成形技术，以纳米Al2O3粉体材料为研究对象，进行了自由形状纳米块体材料制备的研究。研究结果表明，在适当的工艺参数下，可制备出任意形状的Al2O3块体材料，材料内部组织结构致密，晶粒尺寸保持在40nm以内。与其他烧结方法相比，激光烧结制备的纳米材料晶粒尺寸更为细小，组织结构更为致密。     

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.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

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.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

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 ...