Compressive mechanical properties of partially sintered porous alumina of bimodal particle size system

This paper examined theoretically and experimentally packing behavior, sintering behavior and compressive mechanical properties of sintered bodies of the bimodal particle size system of 80 vol% large particles (351 nm diameter)–20 vol% small particles (156 nm diameter). The increased packing density as compared with the mono size system was explained by the packing of small particles in 6-coordinated pore spaces among large particles owing to the similar size relation between 6-coordinated spherical pore and small particle. The sintering between adjacent large particles dominated the whole shrinkage of the powder compact of the bimodal particle size system. However, the bimodal particle size system has a high grain growth rate because of the different curvatures of adjacent small and large particles. The derived theoretical equations for the compressive strengths of both mono size system and bimodal particle size system suggest that the increase in the grain boundary area and relative density by sintering dominate the compressive strength of a sintered porous alumina. The experimental compressive strengths were well explained by the proposed theoretical models. The strength of the bimodal particle size system was high at low sintering temperatures but was low at high sintering temperatures as compared with that of mono size system of large particles. This was explained by mainly the change of grain boundary area with grain growth. The stress–strain relationship of the bimodal particle size system showed an unique pseudo-ductile property. This was well explained by the curved inside stress distribution along the sample height. The inside stress decreases toward the bottom layer. The fracture of one layer of sintered grains over the top surface proceeds continuously with compressive time along the sample height when an applied stress reaches the critical fracture strength.     

纳米ZrO_2－Al_2O_3复合粉末注浆成型与烧结行为研究

平均粒径为２０ｎｍ的ＺｒＯ_２添加５～１５ｖｏｌ％的粒径为２００ｎｍ的Ａｌ_２Ｏ_３粉末注浆成型与烧结特性表现出与普通微米及亚微米级粉末不同的特性：浆料具有较低的含固量，粘度为５厘泊时为５５ｗｔ％；浆料呈微弱触变性：生坯具有较低相对密度，仅为理论值的３５．５％；少量Ａｌ_２Ｏ_３（５～１０ｖｏｌ％）促进复合材料的烧结，但也伴随着Ａｌ_２Ｏ_３晶粒异常长大。上述现象归因于纳米粉末具有非常高的比表面，粉末表面吸附大量紧吸附水不能被石膏模所排除，而粉末巨大的表面能促进了烧结过程中的质点扩散。     

Slip casting of highly concentrated ZnO suspensions: Rheological studies,two-step sintering and resistivity measurements

The paper presents research on elaboration of well dispersed and stable aqueous suspensions of ZnO fine powder. Within the work the influence of the type and concentration (0.2 wt% - 1.2 wt%) of selected dispersing agents (i.a. poly(acrylic acid)-based polyelectrolyte and tetramethylammonium hydroxide), solid loading (30 - 50 vol%) and milling time (1–3 h) on the rheological properties of the slurries was investigated. Two-step sintering (970/920 °C, 2 h) was applied to sinter the green bodies obtained by slip casting.The lowest viscosity of ZnO suspensions was obtained for the addition of 0.4 wt% of poly(acrylic acid)-based polyelectrolyte (PAA) and TMAH. ZnO suspension containing PAA had negative zeta potential in the whole pH range. The highest solid loading obtained in the study was 50 vol%. The applied two-step sintering allowed to obtain samples of high density (above 96% of TD) and homogeneous microstructure of average grain size of 640 nm. ZnO sintered bodies were characterized by different electric properties at the core part and outer part of the sample which was caused by the differences in concentration of oxygen vacancies.     

Microstructure,ionic conductivity and mechanical properties of tape-cast Li1.5Al0.5Ti1.5P3O12 electrolyte sheets

Free-standing Li_1.5Al_0.5Ti_1.5P₃O₁₂ electrolyte sheets with a thickness of 50–150 μm were prepared by tape casting followed by sintering at 850–1000 °C in air. While a sintering temperature of 850 °C was too low to achieve appreciable densification and grain growth, a peak relative density of 95% was obtained at 920 °C. At higher sintering temperatures, the microstructure changed from a bimodal grain size distribution towards exclusively large grains (> 10 μm), accompanied by a decrease in relative density (down to 86% at 1000 °C). In contrast, ionic conductivity increased with increasing sintering temperature, from 0.1 mS/cm at 920 °C to 0.3 mS/cm at 1000 °C. Sintering behavior was improved by adding 1.5% of amorphous silica to the slurry. In this way, almost full densification (99.8%) and an ionic conductivity of 0.2 mS/cm was achieved at 920 °C.Mechanical characterization was carried out on the almost fully densified material, yielding elastic modulus and hardness values of 109 and 8.7 GPa, respectively. The fracture strength and Weibull modulus were also characterized. The results confirm that densification and reduction of grain size improve the mechanical properties.     

P(VDF–HFP)/BST纳米复合薄膜的制备及介电、储能性能

采用溶液铸造法,以聚(偏氟乙烯–六氟丙烯)[P(VDF–HFP)]为基体、钛酸钡锶(BST)为填料制备了纳米薄膜材料。对薄膜的物相组成和微观形貌进行了表征,研究了BST含量对薄膜介电性能和储能性能的影响。结果表明,随着BST含量的增大,薄膜的介电常数显著上升,介电损耗在中、高频区域有所下降,击穿强度逐渐减小,薄膜的充电能量密度显著增大;介电常数的实测值与Maxwell-Wagner理论模型计算值基本吻合,表明填料和基体结合良好,薄膜材料内部组织均匀,无明显缺陷。此外,从实际应用的角度讲,外加电场强度低于800 kV/cm或介于800~2100 kV/cm时,为了获得最大的放电能量密度,应分别选用BST体积分数为30%或20%的P(VDF–HFP)/BST复合薄膜材料。     

The preparation of SiCP/Ag–Cu–Ti hybrid tapes and application in the joining of silicon carbide ceramics

Abstract

A novel method of tape casting to fabricate ceramic-particulate-reinforced composite filler alloy tapes with low organics (no more than 6?wt.%) was developed, with which SiC_P/Ag–Cu–Ti hybrid tapes were successfully prepared and used in joining of sintered silicon carbide ceramics. The stress rheometer, scanning electron microscopy and energy dispersive spectrometer were used to characterize the rheological properties of slurry and microstructure of green tapes and joints. The slurry for tape casting consists of dispersant, binder, solvent, a mixture of ceramics particulates and metal powders, and no plasticizer was added. Castor oil phosphate was proven the suitable dispersant for the slurry, and the content of dispersant, binder, solid loading was optimized as 3?wt.%, 2.6?wt.% and 26?vol.%, respectively. The fabricated hybrid tapes possess good ductility and uniform thickness. The SiC particulates were homogeneously distributed in the metal powders matrix in both sides of the green tapes, and the distribution was retained in the SiC/SiC joints.     

新型干法水泥熟料易磨性概论

基于国外的研究论点,对新型干法水泥熟料及配料进行试验实测对比。结果表明：熟料热工形成过程影响易磨性的主要因素是C2S含量,其他矿相、液相含量以及密度/升重的影响不明显;快冷熟料优于慢冷;水泥粉磨过程的影响取决于熟料及其配料原料的易磨性,挤压终粉磨、联合粉磨等工艺可以忽略所有影响易磨性的因素,易磨性试验可节能30%~60%以上。     

连铸中间包透气上水口的研制与应用

介绍了连铸中间包透气上水口的性能和种类及连铸工艺对透气上水口性能的要求。利用合成莫来石颗粒、α-Al     

连铸结晶器内非金属夹杂物运动行为模拟

通过联立求解Navier-Stokes方程和颗粒运动轨迹方程来确定非金属夹杂物在钢液中的上浮速度,对板坯结晶器内夹杂物的运动规律进行了模拟,并用个别实验结果进行了验证. 结果表明: 夹杂物颗粒粒径越大,浮力作用越明显,其下潜深度越小,停留时间缩短,夹杂物上浮的可能性越大. 为保证夹杂物顺利上浮至渣层被去除,在本计算条件下, 连铸机垂直段长度应大于2.5 m.     

中药有效成分快速检测方法的研究

指出实现中药成分快速分析的3个主要途径简化分析方法、高效分离技术和反应与分析的耦合,并对一些新型的分离分析方法在药物分析中的应用作了介绍,论述了它们在中药成分快速分析和质量控制中的前景.