镁基复合材料微区力学状态的有限元分析

弹性变形范围内,在采用三维有限元模型分析了颗粒增强Mg基复合材料(PRMMCs)中,颗粒的分布形态对材料微区力学状态的影响。结果表明,在保持颗粒长径比(2:1)和颗粒间距(d)不变的情况下,随着θ的变化,不存在颗粒断裂的危险,材料的主要失效方式为界面脱离和基体开裂。增强体相对夹角θ=15o时的结果优于其它情况,这更有利于充分发挥材料的性能。     

Gas—Liquid Mass Transfer Coefficient in Stirred Tank Reactors

Volumetric gas—liquid mass transfer coefficient (k_La) data available in the literature for larger tanks (T = 0.39 m to 2.7 m) have been analyzed on the basis of relative dispersion parameter, N/N_cd. It was observed that at a given superficial gas velocity (V_G), k_La values were approximately the same irrespective of geometric configuration (size of the tank, type and size of the impellers, type of the sparger, etc.) at a particular N/N_cd. A single correlation based on N/N_cd is presented which shows satisfactory agreement with the k_La data of different workers.     

细菌纤维素合成过程中的影响因素

研究了接种量、pH值、培养液深度、培养液表面积和发酵时间等因素对形成细菌纤维素膜的产量、厚度及比表面积的影响。结果表明:接种量在7%、初始pH值在5～6范围内细菌纤维素的产量最大;厚度主要取决于发酵时间和初始pH值;培养液表面积对单位面积细菌纤维素产量有比较大的影响;膜的比表面积与发酵时间的长短无关。     

不同活化剂对石油焦基活性炭孔结构的影响

以石油焦为原料 ,Na OH,KOH和 Na2 CO3 为活化剂制备活性炭 ,采用氮气吸附考察了不同活化剂对活性炭的比表面积、中孔和微孔孔径分布、孔容积及平均孔径等孔结构的影响 .结果表明 :KOH活化制备的活性炭包含 1 nm的微孔和 4nm的中孔 ,总孔容 0 .648cm3 /g,比表面积大 ;Na OH制备的活性炭以 1 nm的微孔为主 ,占总孔容 ( 0 .1 65 cm3 /g)的 98% ,平均孔径 1 .83nm;Na2 CO3 制备的活性炭以 4nm的中孔为主 ,占总孔容 ( 0 .1 43cm3 /g)的 68.5 % ,平均孔径 3.42 nm,比表面积小 .3种样品的孔径都呈现出多峰分布特征 .KOH和 Na2 CO3 活化制备的活性炭的 N2 吸附脱附曲线属于 型 ,Na OH活化制备的活性炭吸附脱附曲线属于 型 .     

气相法二氧化硅应用机理及特性

主要介绍了气相法二氧化硅在液态体系、干燥体系、固态体系中的作用机理；气相法二氧化硅在应用中的特殊性能；以及比表面积、pH、含水量、添加量、表面处理程度等气相法二氧化硅各项物理性能对应用性能的影响。     

Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization

Partially crystalline Si₃N₄, with nanosized crystals and a specific surface area greater than 200 m²/g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH₃ to 1000°C. This polymer does not contain N initially. Crystallization to high-purity α-Si₃N₄ proceeds with additional heating above 1400°C under N₂. The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000° to 1600°C under N₂, are consistent with an amorphous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400°C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes.     

An improved light attenuation technique for measuring large interfacial areas

A laser-based light attenuation technique was successfully used to measure interfacial areas as high as 5832 m²/m³ and Sauter mean bubble diameter varying between 50 and 5600 μm. Good agreement between this approach and the photographic technique was obtained particularly at low gas holdups.     

Surface Areas of Nitrated Hydrotalcites

Hydrotalcites in the nitrate form were prepared using microwave irradiation in the hydrotreatment step. The surface area (BET) of nitrated hydrotalcites was evaluated. Solids were characterized by atomic absorption, X-ray diffraction and BET analysis. Thermal pretreatment temperature determined the surface area of the hydrotalcites.     

反相微乳液聚合引发剂对聚丙烯酰胺分子质量影响的研究

分别以三种引发剂体系为引发剂,从引发机理出发,通过正交实验研究了丙烯酰胺反相微乳液聚合中引发剂种类、引发剂浓度、反应温度、单体浓度等对聚丙烯酰胺(PAM)相对分子质量的影响。结果表明,引发剂种类对水溶性PAM相对分子质量有显著的影响;过硫酸铵-亚硫酸氢钠和偶氮二异丁腈复合引发体系是合成高相对分子质量PAM的有效引发体系。该引发体系在反应温度为40℃,氧化还原引发剂与偶氮的质量比为1∶4,单体浓度为20%,引发剂浓度为0.3%,pH为9的最佳条件下合成的PAM相对分子量为1.44×107。     

微粉对矾土基超低水泥浇注料性能的影响

以高铝矾土熟料为主原料 ,加入 2 %的铝酸钙水泥及总量为 6 %的Al2 O3 微粉和SiO2 微粉 ,配制了矾土基超低水泥浇注料 ,研究了微粉对浇注料的烧结性能、力学性能及热震稳定性的影响。结果表明 :(1 )SiO2 微粉对浇注料的促烧结作用优于Al2 O3 微粉。这是因为与Al2 O3 微粉相比 ,由气相沉积生成的SiO2微粉的粒度小 ,比表面积大 ,活性较高。 (2 )随着SiO2微粉加入量的增加 ,在 1 1 0 0℃和 1 4 0 0℃处理后的常温强度以及在 1 30 0℃和 1 4 0 0℃下的高温抗折强度和抗热震性明显提高。这是由于引入的SiO2 微粉在高温下与Al2 O3 反应生成的针状莫来石穿插进入刚玉骨架 ,起着明显的强化和韧化作用