自韧Si_3N_4的显微结构控制及其性能研究

选择等摩尔Y_3O_3—La_2O_3为添加剂,利用自韧技术和热压方法制备Si_3N_4陶瓷,在最佳的工艺条件下,室温断裂韧性和强度分别为11～12.5MPa.m~(1/2)和900～1000MPa;1350℃时为22～24MPa.m~(1/2)和720～780MPa,韦伯模量为18.4～24.5。这些性能居国内领先、国际先进水平。 掌握了工艺参数和添加剂量对显微结构和力学性能的影响规律及显微结构和力学性能的相互关系。确定了获得高性能自韧Si_3N_4陶瓷的最优工艺和成分。分析表明,β-Si_3N_4晶粒的平均直径为1μm、长径比为7.5左右并且均匀分布时,对提高性能有利。 通过致密化、α→β相变和β-Si_3N_4晶体生长过程分析及动力学计算,揭示了β-Si_3N_4晶体在在不同方向上的生长规律。 研究发现裂纹偏转是主要的增韧机制,β-Si_3N_4棒状晶的拔出,裂纹分支和桥接也对K_(IC)值有所贡献。观察到β-Si_3N_4晶粒在[001]方向存在大量的生长台阶和〔210〕方向上的生长螺线。发现了螺线生长机制。晶体生长缺陷如β-Si_3N_4晶粒异常长大、表面微裂纹及晶粒分支等使性能下降。 实验结果表明,自韧Si_3N_4的氧化符合抛物线规律。1350℃、100h后强度保持率为75％,氧化增重为0.64mg/cm~2。氧化后表面生成的粗大方石英、Y_2Si_2O_7及La_2Si_2O_7等导致裂纹而使强度下降。热震后     

添加Mg、Y氧化物对Fe-Mo/Si3N4金属陶瓷微观组织与性能的影响

提出在Fe-Mo/Si_3N_4金属陶瓷中添加Mg、Y氧化物,在常压烧结条件下实现金属复合、晶须技术双重强韧化陶瓷,并研究了Mg、Y氧化物对Fe-Mo/Si_3N_4金属陶瓷的微观组织与性能的影响.结果表明:添加Mg、Y氧化物的Fe-Mo/Si_3N_4金属陶瓷,存在与Si_3N_4润湿性极好的金属Fe与MoSi_2相,颗粒状α-Si_3N_4转变成晶须条状β-Si_3N_4,烧结体致密且晶粒得到明显细化,各项性能得到大幅提升,实现了金属复合、晶须技术双重强韧化Si_3N_4陶瓷。     

日本氮化硅陶瓷的最近动向

氮化硅(St_3N_4)不是自然存在的,而是人工合成的一种化合物,它如同碳化硅、氮化硼、氮化铝等化合物一样,是一种具有广阔发展前途的工程结构陶瓷材料。Si_3N_4主要有两种晶体结构:六方晶系的β-Si_3N_4和三方晶系的α-Si_3N_4。低温时形成低温型的α-Si_3N_4和高温时形成高温型的β-Si_3N_4。从低温型的α-Si_3N_4转向高温型的β-Si_3N_4的相变温度     

NbSiN纳米复合膜的显微结构、超硬效应和机理的研究

采用NbSi复合靶,通过调节Nb与Si的比例,利用磁控溅射射频工艺,在单晶硅片上沉积不同Si含量的NbSiN纳米复合膜。利用X射线衍射仪、纳米压痕仪和高分辨透射电镜等,研究了Si含量对NbSiN纳米复合膜的微观结构和力学性能的影响。结果表明:随着薄膜中Si含量的增加,其结晶程度先升高,然后降低,硬度和弹性模量先增加后降低,当n(Si):n(Nb)=5:20时,NbSiN薄膜硬度和弹性模量均达到最大值33.6和297.2 GPa。微观组织观察表明,此时NbSiN薄膜内部形成Si_3N_4界面相包裹NbN纳米晶粒的纳米复合结构,Si_3N_4界面相呈结晶态协调相临NbN纳米晶粒间的位向差,并与NbN纳米晶粒之间形成共格外延生长,其微结构可用nc-NbN/c-Si_3N_4模型来表示,表明其超硬效应源于NbN基体相和Si_3N_4界面相之间形成的共格外延生长界面。     

R-α’-Sialon的形成和Si_3N_4AlN-R_2O_3(R=Nd、Sm、Gd、Dy、Er 和 Yb)系统的亚固相关系

实验测定了 Si_3N_4-AlN-R_2O_3(R=Nd、Sm、Gd、Dy、Er 和 Yb)六个系统的亚固相图.在这些系统中,α-Si_3N_4 都同各个0.1R_2O_3∶0.9AlN 分别形成有限固溶体.固溶体界限随着稀土元素原子序数的增加而扩大.β-Si_3N_4同各个 R-α′-Sialon 固溶体在1750℃处平衡。这些亚固相图,对于开发稀土氧化物在新型高温氮陶瓷结构材料中的应用,提供了依据.此外,发现了一个新化合物—Nd_2AlO_3N,它和已报导的 Sm_2AlO_3N 同样具有四方结构.     

烧结温度对反应烧结氮化硅铁复合材料 物相组成及力学性能的影响

以硅铁粉、Fe-Si_3N_4粉末、钛铁矿粉为原料,采用自蔓燃法制备Si_3N_4-Fe_3Si复合材料。将Si_3N_4-Fe_3Si复合材料试样在1 650,1 700,1 750和1 800℃氮气气氛下进行烧结。采用X射线衍射、红外光谱分析、扫描电镜、维氏硬度等探究了烧结温度对Si_3N_4-Fe_3Si复合材料试样密度、孔隙率、显微结构、物相组成、力学性能的影响,并采用差示扫描量热法(DSC)探究了硅铁-钛铁矿混合物的燃烧过程。结果表明,烧结温度对氮化硅铁复合材料的显微结构、力学性能有显著的影响,随着烧结温度的升高,试样的密度、维氏硬度均增大,Si_3N_4-Fe_3Si复合材料的致密性增加;但弯曲强度和断裂韧性随着温度升高先增大后减小,在1 750℃达到最大值。在1 750℃时,试样的密度、维氏硬度、弯曲强度和断裂韧性分别为3.33 g/cm~3、9.85 GPa、331 MPa和8.5 MPa·m~(1/2)。弯曲强度提高了56%,断裂韧性提高了102%,表现出良好的抗弯强度和断裂韧性。在1 750℃时, Si_3N_4-Fe_3Si烧结试样主要物相为β-Si_3N_4、Y_2Si_2O_7、Fe_3Si和少量的Al_2O_3,完成了α-Si_3N4向β-Si_3N_4的变相,Fe_3Si在高温烧结条件下稳定性良好。     

SiC_W含量对SiC_W/Si_3N_4复合陶瓷力学及高温微波性能影响

以α-Si_3N_4粉、β-SiC_W为原料,Al_2O_3、Y_2O_3为烧结助剂,采用凝胶注模工艺制备了SiC_W/Si_3N_4复合陶瓷材料,烧结温度为1 650℃,保温1.5h。研究了SiC_W加入含量对SiC_W/Si_3N_4复合陶瓷的微观结构、力学及常温/高温微波吸收性能的影响。结果表明:随着SiC_W含量的增加,SiC_W/Si_3N_4复合陶瓷的抗弯强度和断裂韧性都有先増后减的趋势,当含量为10wt%时,抗弯强度达到最大值505MPa,断裂韧性达9.515MPa·m1/2。常温介电常数在SiC_W含量为10wt%时,实部达最大值12,在12GHz最大吸收值为-21dB。高温介电常数随着SiC_W含量的增加有先增后减的趋势,在含量为10wt%时,实部达到最大值12.5。相比于纯Si_3N_4陶瓷,当SiC_W含量为10wt%时,SiC_W/Si_3N_4复合陶瓷在11.7GHz左右最大吸收可达-27dB,有效吸收频带(小于-5dB)为11.2~12.3GHz。     

掺稀土氧化物热压Si_3N_4中的玻璃相

高温 Si_3N_4材料正在发展成为一种热机和其它高温工程材料,在材料制备中为了得到充分致密的材料,需要加入少量添加剂。然而由于添加剂的存在,在制成材料晶界处形成玻璃相。因而 Si_3N_4材料的高温强度,断裂机理和蠕变动力学性能将受到玻璃相影响。本文主要研究并讨论了这类 Si_3N_4材料和经高温持久试验后材料中玻璃相发生变化     

(AlCrTiZrNb)N/Si3N4纳米多层膜的微观结构和力学性能研究

采用多靶磁控溅射系统,使用AlCrTiZrNb合金靶和Si靶制备了不同Si_3N_4厚度的(AlCrTiZrNb)N/Si_3N_4纳米多层膜,样品基底为单晶硅。通过X射线衍射仪(XRD)、高透射电子显微镜(HRTEM)、扫描电子显微镜(SEM)和纳米压痕仪对样品进行微观组织的表征和力学性能的测量。实验结果表明,随着Si_3N_4层厚度的增加,样品的结晶度和力学性能均先增加后减小,XRD图谱中出现面心立方相结构。在Si_3N_4层厚度为0.5 nm时,(111)衍射峰强度达到最大值。说明薄膜结晶度最强,薄膜的硬度和弹性模量也达到最高值,分别为30.6,298 GPa。通过对样品的横截面的形貌观察,发现当Si_3N_4层厚度为0.5 nm时,多层膜的多层结构生长良好。在(AlCrTiZrNb)N层的模板作用下,Si_3N_4层从非晶态转变为面心立方结构,与(AlCrTiZrNb)N层之间形成共格外延生长结构,(AlCrTiZrNb)N/Si_3N_4纳米多层膜的强化可归因于两调制层之间形成的共格界面。     

纳米氮化硅的表面修饰及分散稳定性研究

用γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH-570)对纳米氮化硅(Si_3N_4)粒子进行表面修饰,采用开炼混合和硫化工艺制得Si_3N_4/丁苯橡胶(SBR)纳米复合体系,通过红外光谱(FT-IR)、接触角仪、透射电镜(TEM)和橡胶加工分析仪(RPA)对改性前后纳米Si_3N_4粒子及纳米Si_3N_4/SBR复合体系在有机体系中的分散稳定性和力学性能进行分析。结果表明:KH-570分子链成功接枝在纳米Si_3N_4表面并急剧降低了纳米粒子的表面能,有效阻止纳米颗粒团聚,提高了纳米粒子在有机体系中的分散稳定性,改善了纳米复合材料的界面粘结,增强了复合材料的力学性能。制得的改性纳米Si_3N_4/SBR表面能为35.521J/m~2,比未改性纳米Si_3N_4的表面憎水性提高了3倍以上,储能模量达到600kPa,有效提高了纳米Si_3N_4/SBR复合材料的性能。     

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.     

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...     

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.     

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.     

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.     

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.……     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

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.