High char‐yielding poly[acrylonitrile‐co‐(itaconic acid)‐co‐(methyl acrylate)]: synthesis and properties

Polyacrylonitrile terpolymers of various compositions consisting of acrylonitrile (AN), itaconic acid (IA) and methyl acrylate (MA) were synthesized by solution polymerization in dimethylsulfoxide. Increase in concentration of either IA or MA retarded the overall polymerization rate and the polymer molecular weight. The system consisting of AN + MA and varying IA concentration was more prone to retardation in comparison with the system composed of AN + IA with variable MA concentration. The retardation factors were quantified. Minor quantities of MA boost the reactivity of IA in the terpolymer system. The terpolymer was richer in MA vis‐à‐vis the feed. The thermal characteristics of the terpolymer were examined as a function of its composition. In contrast to the copolymer of AN and IA requiring 1–1.5 mol% IA, the terpolymer required an IA content of approximately 2.5 mol% for optimum thermal stability. The polymer with 90 mol% AN, 2.5 mol% IA and 7.5 mol% MA exhibited reasonably good char‐forming characteristics and thermal stability. The overall crystallinity and crystallite size of the polymers were found to decrease on incorporation of the comonomers. The ‘aromatization index’ of the copolymer increased with the temperature of pyrolysis through re‐organization of the tetrahydropyridine ladder structure. Copyright © 2005 Society of Chemical Industry     

Manufacture of carbon fibers from polyacrylonitrile precursors treated with CoSO4

Free‐radical solution copolymerization of itaconic acid and acrylonitrile was carried out in DMSO using azodiisobutyronitrile as an initiator, changing the feed rate of itaconic acid. The resulting polymerization solution was spun to form polyacrylonitrile (PAN) precursors of carbon fibers. The precursors were treated with a CoSO₄ aqueous solution on‐line. The structure and properties of untreated and treated PAN precursors and the resultant carbon fibers were characterized by SEM and TEM, a stabilization process, etc. It is suggested that CoSO₄ acts as a catalyst in the formation of a ladder structure and reduces the temperature of cyclization, and the carbon fibers developed from treated PAN fibers showed improvement in the tensile strength and the Young's modulus. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 153–158, 2002     

大电流监测信号提取的光收发及信号处理

近年来,大电流的监测成了人们十分关心的问题,这是由于大电流有强磁、高压、电流大等一系列的直接监测所不能克服的问题。这就需要把高压大电流的强电信号,经过提取后变成能在实验室中直接观测的弱电信号。为此,如何从高压大电流的信号中提取出随实时信号变化而实时变化的小信号就变成了一个关键问题。详细介绍了监测信号提取的光收发电路原理和后续信号处理电路,分析了各部分的作用,给出了必要的分析结果。     

尿素对以硝酸铝和葡萄糖为原料合成氮化铝粉末反应过程中相变及反应速率的影响

以硝酸铝(Al(NO3)3·9H2O)和葡萄糖(C6H12O6·H2O)为原料,利用碳热还原法制备氮化铝粉末,研究了尿素对前驱物的制备及前驱物氮化反应的影响,研究发现添加尿素合成的前驱物和未添加尿素合成的前驱物在氮化反应过程中相变和反应速率存在较大差异。在没有添加尿素合成的前驱物的氮化反应过程中,出现了γ-Al2O3、α-Al2O3、AlON和AIN相,该前驱物的反应速率慢,完全氮化需要在1600℃下才能完成。对于添加尿素合成的前驱物而言,在其氮化反应过程中仅出现了γ-Al2O3和AIN相,没有α-Al2O3和AlON的生成,AIN直接由γ-Al2O3氮化生成,该前驱物的氮化反应速率快,氮化反应温度低,在1400℃下即可实现完全氮化。分析讨论了两种前驱物的氮化反应速率不同的主要原因,并利用XRD、SEM等分析方法对粉末进行了表征。     

红外警戒系统作战环境的计算机仿真

文中论述了红外警戒系统视景仿真研究的主要内容，给出了仿真软件流程。探讨了满足红外警戒系统全方位、多目标视景生成的实时性方法。     

Low-pressure pyrolysis studies of a new phosphorus precursor: Tertiarybutylbis(dimethylamino)phosphine

The low pressure decomposition of tertiarybutylbis(dimethylamino) phosphine, (t-Bu)P(NMe₂)₂, (TBBDMAP), has been studied on quartz and deposited GaP and InP surfaces. This new phosphorus precursor has been found to pyrolyze on quartz surfaces at much lower temperatures than the related compounds tertiarybutylphosphine, (t-Bu)PH₂, (TBP) and tris(dimethylamino)phosphorus, P(NMe₂)₃, (TDMAP). In contrast to the results obtained for TDMAP, GaP and InP surfaces decrease the decomposition temperature of TBBDMAP only slightly. The TBBDMAP reaction products were dimethylamine, methylmethyleneimine, and isobutylene, consistent with previous pyrolysis studies of TBP and TDMAP.     

激光对抗技术发展动态

激光对抗主要包括激光侦察告警、激光无源干扰和有源干扰，以及激光防护几方面。本文概述了激光对抗技术的发展。     

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.     

正交试验法在PAN原丝纺丝工艺中的应用

利用正交设计方法确定了PAN湿法纺丝过程中影响原丝性能最主要的因素。结果表明 :以计量泵转速、凝固浴温度、负拉伸以及蒸汽拉伸倍数作为考察对象 ,影响原丝性能的最显著因素是蒸汽拉伸倍数 ,其次是负拉伸。以负拉伸、第二拉伸、第三拉伸以及蒸汽拉伸的倍数作为考察对象 ,影响原丝性能最显著的是蒸汽拉伸倍数 ,负拉伸几乎没有影响。利用正交实验结果 ,适当调节蒸汽拉伸倍数 ,制得强度为 6.5～ 7.0cN/dtex ,线密度为 1.1～ 1.3dtex的原丝     

二甲基亚砜一步法碳纤维用聚丙烯腈原丝生产工艺

叙述了二甲基亚砜一步法（高转化）高强碳纤维用聚丙烯腈原丝生产的工艺流程。着重讨论了聚合、纺丝的工艺控制。以及工艺控制对聚丙烯腈原丝和最终碳纤维性能的影响。按此工艺生产的聚丙烯腈原丝的质量完全符合高强碳纤维生产的需要。