Study of stability of high‐temperature polyimides using TG/MS technique

The oxidative stability of the carbon fiber‐reinforced composite of polyimide was examined, in real time, using the evolved gas analysis techniques. Off‐gas degradation products suggested the onset temperature for chain scissions to be fairly low at about 190–220°C. Based on the off‐gas products present and the trend of their release, the composite degradation mechanism appeared to be similar between 190 and 371°C, thereby marking 371°C to be the highest accelerated aging temperature for its long‐term lifetime prediction. Beyond 371°C, different degradation mechanisms would apply. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1219–1227, 2002     

明胶中过氧化物的控制

在用药用明胶为主要原料生产药用空心胶囊的生产中,由于明胶中的过氧化物对胶囊中各种色素的颜色具有氧化褪色作用,胶囊产品放置时间过长,其颜色就会发生变化,加上药品自身安全性的要求等原因,故国内引进的外国胶囊生产线对明胶原料中的过氧化物含量的要求特别严格,要求明胶中不得检出过氧化物成分.尽管目前我国药典和轻工行业对药用明胶标准未作过氧化物含量的规定,相信很多生产药用空心胶囊的厂家对此项目都有内控标准,如本胶囊公司就规定,凡对购进的明胶均不得检出过氧化物成分,否则一律退货.笔者相信,不久的将业,药用明胶的标准修订肯定会增加过氧化物含量的规定.为此,明胶生产企业就必须在明胶生产中严格控制过氧化物的含量,使其达到客户的要求.     

淤浆法HDPE装置低聚物不能结片原因探析

分析了淤浆法HDPE装置低聚物不能结片的原因,并提出了相应的工艺处理措施。     

Surface photografting polymerization of vinyl acetate,maleic anhydride,and their charge‐transfer complex. VI. Charge‐transfer complex (2)

The photografting copolymerization of a low‐density polyethylene/vinyl acetate (VAC)–maleic anhydride (MAH) binary monomer system was studied from the perspective of dynamics. The total conversion percentage (CP) and grafting conversion percentage (CG) were measured by gravimetry. On the basis of plots of CP and CG as functions of the polymerization time, the total polymerization rate (RP) and grafting polymerization rate (RG) were calculated. In addition, the apparent activation energy (E_a) and the reaction orders of the photografting polymerization under different reaction conditions, such as the total monomer concentration and the concentration of benzophenone (BP), were determined also. The results showed that, in comparison with the photografting polymerization of the two single monomers (VAC and MAH), RP and RG noticeably increased for the VAC–MAH binary monomer system. When the total monomer concentration was kept at 4M, the apparent E_a's of the three photografting polymerization systems were as follows: for VAC ([MAH]/[VAC] = 0/4), E_a's for the total polymerization and grafting polymerization were 41.00 and 43.90 kJ/mol, respectively; for MAH ([MAH]/[VAC] = 4/0, E_a's were 39.65 and 43.23 kJ/mol, respectively; and for the VAC–MAH binary monomer system, E_a's were 34.35 and 40.32 kJ/mol, respectively. These results suggested that the polymerization of the binary system occurred more readily than the other two. The reaction orders of RP with respect to the total monomer concentration of the monomers and the concentration of BP were 1.34 and 0.81, respectively. According to these investigations, it could be inferred that in the binary monomer system, both the free monomers and charge‐transfer complex took part in the polymerization; to the termination of the propagating chains, two possible pathways, unimolecular termination and bimolecular termination, coexisted in this binary monomer system. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 910–915, 2005     

Al2O3／TiB2／SiCW陶瓷刀具加工镍基合金时的磨损机理研究

研究了Ａｌ２Ｏ３／ＴｉＢ２／ＳｉＣＷ陶瓷刀具加工Ｉｎｃｏｎｅｌ７１８镍基合金时的切削性能和磨损机理。结果表明；在低速切削条件下，Ａｌ２Ｏ３／ＴｉＢ２／ＳｉＣＷ和硬质合金刀具的抗后刀面磨损的能力相差不大；而在高速切削条件下，前者的抗后刀面磨能力远高于后者。     

结晶性高聚物作为相变材料的应用

本文研究了结晶性高聚物聚乙烯及其共混物作为相变材料对模拟发热体铜片热量的吸收作用，由于相变的吸热，铜片的温度在一定时间范围内保持在一个定值。选择不同的相变材料，可使这种温度平台出现在不同的温度范围，不共晶的共混物可有两个以上的温度平台，提高了降温效果。     

Comprehensive Benefit Evaluation System for Low-Impact Development of Urban Stormwater Management Measures

In recent years, plenty of simulation research about the low impact development(LID) control effect has emerged, but studies on scheme comparison and evaluation are lacking. In this study, a comprehensive benefit evaluation system for LID, including environmental, economic, and social benefits, was established on the basis of Analytic Hierarchy Process(AHP) and urban storm water model. Above all, benefit identification, quantitative evaluation and scheme comparison of single LID measures were obtained according to site investigation, simulated calculation and theoretical analysis. Whereafter, LID combination plans were designed based on single LID measures with high comprehensive benefit values, and their comprehensive benefits were evaluated to obtain the optimal plan. Then, based on well-founded system combined with Storm Water Management Model (SWMM), the design and optimization of LID were conducted, with a case in Xi’an, China. It turned out that the preferential order of the LID single measures according to the comprehensive benefit was: bio-retention > rain barrels > low-elevation greenbelt > green roofs > permeable pavement. Five LID combination plans were designed based on bio-retention, rain barrels, low-elevation greenbelt, and green roofs. Evaluation results showed that plan I (bio-retention and green roofs) was the optimal LID combination plan.     

20＂通径中压球阀的设计和三维数值模拟

介绍了通径为20＂（1＂=25．4mm）的大口径中压球阀阀体、新型C形金属密封环组件等的结构设计；在阀座与球体之间采用整体碟形弹簧和新型阀座密封填料，以保证高压密封，提高使用寿命；阀芯采用空心球体结构和分段冲压成形加工工艺，有效地保证了球体的加工精度和质量，降低了生产成本；在结构设计中，充分考虑了球阀的密封、防火、启闭传动及制造工艺的要求；对其中结构复杂的球阀阀体和空心球形阀芯进行了强度计算和ANSYS应力、应变模拟分析计算，二者计算结果一致，并认为阀体的厚度由其大开孔处局部应力的整体补强确定。     

A study on structure and electrochemical properties of (La, Ce, Pr, Nd)2MgNi9 hydrogen storage electrode alloys

(La, Ce, Pr, Nd)₂MgNi₉ hydrogen storage alloys were prepared through induction melting followed by a long annealing treatment. The structure and electrochemical properties of annealed alloys have been investigated by orthogonal design experiments. Both the individual effects of each substituting element and their interaction in alloys were studied systemically. It has been shown that the structure of main phase in alloys belongs to PuNi₃-type with a space group R-3m. Substituting rare-earth elements have a significant effect on both the phase structure of alloys and microstructure. The anisotropic change in the crystal structure of alloys can cause the acceleration of pulverization of alloy particles and result in the deterioration of the cyclic stability of alloy electrodes. Misch metals can raise the plateau pressure of hydrogen absorption/desorption. The discharge capacity of alloy ranges from 342.97 to 380.68 mAh g⁻¹ depending on the sort and content of substituting elements. Both cerium and neodymium can obviously reduce the discharge capacity of alloy electrodes. When compared to the La₂MgNi₉ alloy electrode, mish metals can significantly improve the high rate dischargeability of alloy electrodes. The improvement of the kinetic characteristic of alloy electrodes mainly results from the increase of the hydrogen diffusion rate in alloy bulk.     

底吹钢包两相区两段模型

在考虑雷诺应力的基础上，建立了底吹钢包中气液两相区流体流动的两段模型。这一模型可用于计算近喷嘴处和浮羽流区各截面处两相流的平均速度、速度分布、流股直径和平均含气率等．数值计算表明：理论含气率与实验值符合很好．计算还表明：平均含气率和平均速度随高度的增大而减小，但流股直径随高度的增大而增大．另一方面，平均速度随初始供气量的增大而增大，而抽引比则随供气量增大而减小．通过两段模型可很好地描述喷嘴处气液流的行为．