Combined-Stage Sintering Model

By focusing on the similarities between the three stages of sintering, a single equation is derived that quantifies sintering as a continuous process from beginning to end. The microstructure is characterized by two separate parameters representing geometry and scale. The dimensionless geometry parameter, denoted T, comprises five scaling factors that relate specific microstructural featuers (e.g., surface curvature) to the scale (grain diameter). Calculations of T from experimental data show (a) agreement with computer simulations of initial-stage sintering, (b) the effect of surface diffusion on T, and (c) changes in T with microstructural evolution during sintering. Application of the model to the design of firing schedules and the study of microstructural geometry effects on sintering is discussed.     

Changes in seebeck coefficient of Pt and Pt 10% Rh after use to 1700°C in High-purity polycrystalline alumina

A technique is presented that enables the effects of temperature on the Seebeck coefficient to be assessed for individual wires. The technique, involving a high-resolution thermoelectric scanning rig and a nonuniform conditioning furnace of known temperature profile, was applied to 0.5-mm-diameter wires of Pt and Pt 10% Rh. Changes were observed in Seebeck coefficient when these wires were used in high-purity twin-bore insulation for up to 200 h at temperatures over the range 500 to 1700°C. Contamination from the insulation was found to be transmitted by a vaporization process, having an activation energy of 3 eV. This caused changes of up to 0.14 V · °C^–1 in Pt and 0.01 V · °C^–1 in Pt 10% Rh. Rhodium transfer to the pure Pt wire changed its Seebeck coefficient by up to 5 V · °C^–1. The consequences of both processes for thermocouple pyrometry are presented.     

我国氧化铝工业现状及发展对策

在分析了国内外氧化铝工业的现状及差距的基础上，提出了发展我国氧化铝工业的六条战略措施及对策。     

Porous structures printed by fused deposition of granules processed from a novel polyamide/alumina-based system

Alumina ceramic porous structures were shaped by the fused deposition of alumina/polyamide 612 composite granules using an FDM 3D printer with a modified extruder to process granulated powder instead of a filament. The composite granules were prepared via thermally induced phase separation (TIPS). Firstly, in order to determine the proportion of polymer/solvent to be used in the TIPS process, different volume fractions of PA612 in dimethyl sulfoxide (DMSO) were studied (0.01 to 0.20), and the granules obtained were characterized by SEM, DSC, and Raman spectroscopy. Secondly, the addition of different ceramic loadings to the PA612/DMSO solution was studied with the aim of determining the amount to be used for preparing the composite granules by TIPS. In particular, the effect of the alumina content on the morphology and size of the obtained composite granules was studied. In addition, rheological properties (oscillatory and rotational tests) of the feed materials were studied. Finally, the printing conditions, including the nozzle temperature and nozzle diameter, and the extrusion process, were optimized in order to obtain porous structures with good quality. Alumina porous structures were successfully printed, debinded, and sintered. Adequate bonding between layers was achieved, and no defects at interfaces were detected.     

无机超细粉体改性锂离子电池隔膜的研究进展

综述了近年来无机超细粉体改性锂离子电池隔膜的研究进展,首先介绍了已在锂电隔膜改性上商业应用的Al₂O₃和AlOOH对传统聚烯烃膜和新型静电纺丝膜的改性方法和改性效果,随后又对常规无机材料TiO₂和SiO₂粉体对锂电隔膜的改性进行了叙述,最后对BN等非常规隔膜改性无机材料进行了简介;总结和讨论了无机材料改性后隔膜的组分、结构和性能对锂离子电池综合性能的影响,并对其无机材料改性锂电池隔膜的未来发展趋势进行了展望。     

煤粉炉粉煤灰提取氧化铝活化技术研究进展

介绍了近年来采用煤粉炉粉煤灰作为原料制备氧化铝的预处理活化工艺技术,指出了粉磨法、硫酸法、氯化钙法、铵盐法、碳酸盐法、氟化盐法、物理-化学联合活化法的优缺点及在工程转化过程中需重点关注的环节。虽然部分工艺技术实现了工业化,但因成本高等因素导致项目关停,建议粉煤灰综合利用研究方向应以工程转化难点问题为导向,理论研究与工程设计相结合,逐步探索出一条经济效益好、安全环保的粉煤灰制备氧化铝工业化路线。     

6061Al/Al2O3金属基复合材料组织和性能

以6061Al作为基质材料,利用液体冶金的搅拌铸造技术及挤压法制备Al₂O₃颗粒增强的金属基复合材料,选取6061Al添加3种质量分数为5%、10%和15%的Al₂O₃为研究对象,以改善6061Al/Al₂O₃复合材料的力学性能。通过SEM分析表明,Al₂O₃颗粒在6061Al金属基体中的分布相当均匀;由X射线衍射试验结果显示,复合材料中只有6061Al和Al₂O₃,且不会影响结晶性及6061Al的组织结构型态。试验结果表明,随着Al₂O₃添加量增加至15%,6061Al/Al₂O₃复合材料的硬度和抗拉强度均有较大提高,但伸长率略有下降,由于材料孔隙率的提升,致密度下降,从而引起材料的硬度略微下降;分析磨损量与Al₂O₃添加量及磨损率与滑动距离的关系,结果显示商用6061Al的磨损率最大,而6061Al/Al₂O₃(15%)复合材料的磨损量最小,并且磨损率最低,这是由于在6061Al中加入Al₂O₃颗粒,Al₂O₃颗粒的存在可以减少磨粒对基体的犁削作用,有效提高基体的耐磨性。深入探讨Al₂O₃颗粒增强的金属基复合材料,发现颗粒增强体以很细的粉末(一般在20 μm以下)加入到金属基中起到提高硬度、强度和耐磨性的作用;然而,Al₂O₃添加量越来越大时,其对6061Al系列材料的硬度、强度和耐磨耗性等性能将起到负面作用。     

Net shape formation of sub-micron alumina with reduced flaws by high-speed centrifugal compaction process

A new compacting method for powder materials is presented. High-Speed Centrifugal Compaction Process (HCP) utilizes centrifugal force of about 10,000 g for the compaction. HCP is suitable for net shape compaction of fine sub-micron and nano-powders. HCP possesses a unique compacting mechanism that is different from other colloidal processes including Pressure Casting (PC), and has a number of useful characteristics. HCP has a higher compacting speed than PC, wide applicability for net shape formation, as well as a defect removing function. Because of homogeneous and flawless green microstructure, HCP alumina shows superior sinterability and higher strength and hardness than most of other aluminas. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials“, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Preparation and mechanical properties of Fe_3Al/Al_2O_3 nano-/micro-composite

1　INTRODUCTIONAlumina(Al2 O3)ceramicsareoftenconsideredforstructuralapplications,duetotheirpropertiesofhighhardness ,chemicalandwearresistanceandgoodmechanicalpropertiesatroomandhightemperature .Thewellknownlimitationfortheseceramics ,how ever ,istheverylowtoughness .Recentstudieshaveshownsignificantimprovementsinmechanicalprop erties ,includingtoughness ,byaddingductilesecondphaseparticles ,suchasNi,Al,MoandCu[14 ] .Anincreaseof 80 % 333%inthefracturetoughnesshasbeenreportedforAl2 O3…