CHARAC TERIZATION OF TiAl POWDER PRODUCED BY MECHANICAL ALLOYING

The microstructure,alloying reaction and sintering behavior of the powder produced by Mechanical Al-loying(MA)for 8 h from 64 wt.-% Ti powder and 36 wt.-% Al powder were studied by scanning electronmicroscopy,optical microscopy,X-ray diffractometry,differential scanning calorimetry(DSC)and dilatometry.The mechanically alloyed powder partictes are Ti-Al composite particles.Thus,titanium aluminides can formeasily in the powder through diffusion during heat treatment.It is shown that the sintering behavior of this pow-der,different from the behaviors of TiAl alloy powder and mixed powder of 64 wt.-% Ti powder and 36 wt.-%Al powder,changes from expansion at temperatures below 1000℃ to shrinkage at temperatures above 1000℃.Homogeneously alloyed TiAl material with a density over 96% of the theoretical density can be produced fromthe mechanically alloyed powder by compaction-sintering.     

Characterization of ultrafine La x Sr1−x MnO3 powder prepared by spray pyrolysis

The characterization of La _x Sr_1−x MnO₃ powders produced by spray pyrolysis using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation, specific surface area (Brunauer-Emett-Teller), and particle size distribution measurements shows that the resultant large particles are loose agglomerates consisting of many small particles. However, the sintered tiny particles can form hard agglomerates, and the particle size increases remarkably. The structures of the powders before and after sintering were identified by x-ray diffraction (XRD). The study of the electrical property of the powder shows that the powder is a metallic conductor. In a reducing atmosphere, the powder can be decomposed. When the powder is cofired with yttria-stabilized zirconia 5% (YSZ) powder at 1200 °C for 5 h, no new phase is produced, and the powder remains a single provskite hexagonal-rhombohedral structure.     

测定银的新催化分光光度法研究──藏红T－碘化钾指示反应体系

根据银对藏红Ｔ与碘离子氧化还原反应的催化作用，建立了一种测定微量银的动力学光度法。方法的线性范围为０．５～４．０μｇ／ｍｌ，检测限为０．０２μｇ／ｍｌ。除Ｈｇ２＋严重干扰，Ｆｅ３＋、Ｃｒ６＋有轻度干扰外，其余常见的离子不影响测定。与常见测定银的动力学法相比，本法反应速度很快，且所有测定均可在室温下进行。     

氰化氢在终冷塔中气液两相之间转移的研究

分析了煤气中氰化氢的形成,论述了氰化氢在煤气和其冷凝液中的平衡机理,讨论了影响氰化氢相平衡的因素,研究了直接终冷、间接终冷时煤气中氰化氢的转移情况。     

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 .     

铁(Ⅲ)—苯芴酮—聚乙二醇辛基苯基醚显色反应的研究及应用

详细研究了非离子表面活性剂聚乙二醇辛基苯基醚（OP）存在下铁（Ⅲ）与苯芴酮的显色反应。结果表明铁（Ⅲ）与苯芴酮形成了蓝紫色的配合物，其最大吸收波长λmax为614nm，对比度（△λ）为74nm，摩尔吸光系数ε614为6．41×104L·emol(-1)·cm(-1)，铁量在0～16μg／25mL范围内服从比耳定律。所拟方法用于磷矿样中铁的分析与邻菲罗啉法结果一致。     

Electron Emission from Barium Strontium Titanate Ceramics

This paper focuses on understanding the influence of materials' properties on the ferroelectric electron emission. Ferroelectric ( x =1.0 and 0.8) and paraelectric ( x =0.67 and 0.5) compositions of barium strontium titanate (Ba _x Sr_{(1− x )}TiO₃) system were chosen for study based on their different ferroelectric and dielectric properties. Similar emission current waveforms were obtained from four compositions with negative triggering voltage applied to the rear electrode of the samples. It was difficult to explain the experimental results using the spontaneous polarization-switching model. The mechanism of electron emission from Ba _x Sr_{(1− x )}TiO₃ ceramics was ascertained to surface plasma emission.     

Analysis of the oscillatory behavior of double-walled carbon nanotube-based oscillators

Molecular dynamics simulations of oscillatory behaviors of double-walled carbon nanotube-based oscillators are performed. The second-generation empirical bond-order potential is used for the atomic interactions within a wall, and a registry-dependent and four different registry-independent van der Waals potentials are used for the atomic interactions between walls. It is found that the frequencies of the nanotube oscillators are sensitive to the choice of the van der Waals potentials. An almost non-decay oscillation is observed for the registry-dependent potential when there is no rocking motion. However, an apparent decay oscillation is observed when rocking motion occurs. A decay oscillation is observed for all registry-independent potentials even without rocking motion. Mechanisms leading to unstable oscillatory behavior are analyzed.     

PVC助剂的新进展

介绍了近年来聚氯乙烯助剂的研制、开发的现状和趋势。