微孔聚丙烯中空纤维膜

以熔融纺丝－冷却拉伸与热致相分离两种制备微孔聚丙烯中空纤维的意义、原理、过程、影响因素等进行了评述。     

低温热致相分离法制备聚偏氟乙烯中空纤维多孔膜的研究

提出了一种低温热致相分离成膜方法(L- TIPS),通过干-湿法纺丝工艺制备了聚偏氟乙烯( PVDF)中空纤维多孔膜,考察了非溶剂致相分离法(NIPS)和热致相分离法(TIPS)两种成膜机理的竞争关系对膜形态结构和性能的影响.结果表明:低温热致相分离法在制备PVDF中空纤维膜的过程中同时发生了非溶剂致相分离机理和热致相分离机理,与单纯非溶剂致相分离机理成膜相比,膜断面未出现大的空穴,仅有少量指状孔,中部为球状结构,内外表面均有皮层,增强了膜的抗污染性能和强度;铸膜液浊点温度与凝固浴温差越大,壁厚越厚,热致相分离作用越明显,非溶剂致相分离作用相对减弱,膜的纯水通量和强度均有所提高,卵清蛋白截留率变化不大;低温热致相分离法比传统热致相分离法制膜温度低,能够添加常用的亲水性高分子添加剂(PVP、PEG、PVA).     

热致相分离制备聚丙烯微孔膜微观结构的研究

对热致相分离制备的聚丙烯中空纤维微孔膜微观结构进行了分析研究．研究表明，通过改变稀释剂、聚丙烯浓度和成核剂种类及浓度，可以改变聚丙烯微孔膜的形态、孔结构和孔径大小．     

TIPS法iPP中空纤维膜的拉伸性能研究

通过熔融共混等规聚丙烯(iPP)/邻苯二甲酸二丁酯(DBP)/邻苯二甲酸二辛酯(DOP)体系,采用热致相分离法(TIPS)制备iPP中空纤维膜,且在不同的拉伸温度及拉伸比下对中空纤维膜进行拉伸研究.对膜结构与透过性能进行了表征.采用环境扫描电子显微镜(SEM)对膜的内、外表面以及截面结构进行观测,发现拉伸后膜外表面的皮层以及膜结构得到有效改善.使用电子式万能试验机对中空纤维膜的拉伸强度进行了测试.随着拉伸温度和拉伸比的增加,膜的孔隙率、纯水通量以及拉伸强度均呈现先增大后减小的趋势.膜的孔隙率最大可提高35.3％,纯水通量提高了286.9％,拉伸强度可提高至6.86 MPa.nano-SiO2(纳米SiO2)添加的杂化膜经过拉伸后,孔隙率增大了46.8％,纯水通量提高了416.1％,拉伸强度提高了181.9％.研究表明:通过对iPP中空纤维膜进行拉伸处理,可以优化膜结构,并改善了膜表面皮层以及透过性能.     

聚丙烯构型对疏水微孔膜的性能影响及共混膜制备研究

以分子构型对聚丙烯疏水微孔膜在热致相分离制膜过程中的影响规律为研究对象,考查了3种分子构型的聚丙烯成膜后的微观形态和综合分离性能.结果表明:由于热致相分离制膜过程中不同分子构型的聚丙烯的结晶行为不同,等规聚丙烯(iPP)易于形成规则的蜂窝状球晶,具有较好的平均孔径,而无规聚丙烯(aPP)和间规聚丙烯(sPP)易于形成致密的蜂窝状结构,等规聚丙烯和无规聚丙烯两种结构共混膜增大了等规聚丙烯的平均孔径和孔隙率,有助于提高其通量及机械稳定性,等规聚丙烯和无规聚丙烯共混膜渗透通量达20.30 kg/(m~2·h),截留率均超过99.99%.     

热致相分离制膜条件对聚丙烯平板微孔膜结构的影响

以热致相分离法制备了聚丙烯平板微孔膜.研究了铸膜液中聚丙烯浓度、熔体指数、稀释剂和成核剂种类及含量、凝固浴温度等制膜因素及条件对膜结构的影响.采用扫描电子显微镜观测制备膜的断面及表面结构,并基于热力学和结晶动力学理论对聚丙烯成膜过程机理进行探讨,结果表明:制膜条件对聚丙烯平板微孔膜的结构影响明显.     

复合热致相分离制膜方法

系统介绍了北京坎普尔环保技术有限公司自主创新研发成功的复合热致相分离(complex Thermally Induced Phase Separation,简称为c-TIPS)制膜方法,并与经典的热致相分离(TIPS)制膜方法和修正热致相分离(m-TIPS)制膜方法作了比较.c-TIPS法以水溶性良溶剂和水溶性添加剂组成的混合物作为"复合稀释剂",在加热搅拌罐中,于聚合物熔点(Tm)以下的温度(一般为90～170℃)下形成聚合物/复合稀释剂体系的均相溶液,在相同温度或低5～10℃的温度下纺丝,通过控制芯液和冷却液的组成,利用同时或先后发生的热致相分离(TIPS)和非溶剂致相分离(NIPS)过程的复合相分离过程,制备了强度高、通量大、外表面有皮层(超滤膜)和没有皮层(微滤膜)的新型中空纤维(毛细管)多孔膜.该方法适用于几乎所有半结晶性和非结晶性制膜材料,例如,PVDF,PES,PS,PVC,PAN,PMMA,CA,等,所得膜的综合性能大大优于用NIPS法制备的同样材料的膜性能.     

聚丙烯中空纤维膜耐氧化改性及膜蒸馏的应用研究

聚丙烯中空纤维膜在纯水预处理、制药纯化分离、饮料酒水浓缩、工业废液回收等领域有广泛的应用.为了提高聚丙烯基中空纤维膜的耐氧化性与使用寿命,本研究通过添加抗氧剂和改进成型工艺来制备高性能聚丙烯中空纤维膜.具体探讨了最佳抗氧剂添加量对膜抗氧化性的影响,经过氧化实验36 h后,添加0.4%抗氧剂1076可使聚丙烯中空纤维膜的水接触角提高67%,同时拉伸强度降低10%,最大伸长率降低15.4%.在膜蒸馏实验中,添加0.3%抗氧剂1010的耐氧化聚丙烯中空纤维膜在运行30 h后,对Al³⁺的截留率依旧可达99.7%.总之,抗氧剂的添加显著提高了聚丙烯中空纤维膜在膜蒸馏应用中的截留性质和使用寿命.     

热致相分离法制备聚偏氟乙烯微孔膜的研究

热致相分离法是一种制备聚合物微孔材料的有效方法.介绍了聚合物初始浓度、稀释剂、降温速率、成核剂、萃取剂等因素对热致相分离法制备聚偏氟乙烯(PVDF)微孔材料的影响,并对热致相分离法制备聚偏氟乙烯(PVDF)微孔膜的最新研究进展进行了介绍.     

热致相分离法制备聚醚醚酮中空纤维膜

以聚醚醚酮(PEEK)、聚醚酰亚胺(PEI)为原料,采用熔融纺丝-热致相分离法成功的制备出PEEK中空纤维膜,并详细研究了膜成型条件对膜结构与力学性能的影响,测试了PEI含量为60%的最大中空度下膜的渗透性能。结果表明,通过控制中空纤维的成型条件可以控制中空纤维膜的中空度、壁厚等结构;PEI含量高,空气层高度低,拉伸比大时纤维中空度高,壁厚小;拉伸比和空气层高度对膜孔径的影响并不大,而PEI的含量是影响膜孔径的最主要因素,当PEI含量从40%提升到60%时,孔径从6.1 nm提升到6.9 nm;PEEK与PEI两者相容性好,形成双连续的海绵状孔结构;力学性能表明,PEI含量是影响力学性能的主要因素,当PEI含量从40%提升到60%时,膜强度从0.396 c N/dtex降低到0.267c N/dtex。     

Study on unsymmetrical phenomena of vapor cooled current leads

Unsymmetrical phenomena of gas flow and temperature distributions between a pair of vapor cooled current leads (VCCL) often occur in superconducting systems, which makes the VCCL depart from the optimum operating status, consequently results in an increased heat leak to the cryostat and even a destroyed safety operating condition of the VCCL. To analyze this problem, a numerical model for the VCCL was built, which is based on the conservation equation of energy for the solid and the conservation equations of mass, momentum, and energy for the fluid. With this model, unsymmetrical phenomena between a pair of VCCL were analyzed. Unbalanced gas flow distribution in a single multi-channel VCCL was also studied. Some conclusions were made for the design of VCCL, and a new type of VCCL with combined positive and negative poles and a helical cross section structure was developed. Test results showed that the unsymmetrical phenomena can be well restrained by using the new type of VCCL.     

LY12铝合金表面有机-无机杂化膜特性研究

作为-种有机-无机杂化材料,倍半硅氧烷(SSO)近年来被发现其具有良好的防腐性能,并有望成为传统的防腐材料-铬酸盐转化膜的替代物.本文用乙烯基三甲氧基硅烷(VMS)通过溶胶凝胶法制得了SSO,并涂敷于LY12铝合金表面.用(EIS)对不同水解时间下制得的VMS膜层的结构进行了表征.水解3d所获得的VMS在不同固化时间下的EIS谱图上出现了一个新的时间常数,证实了在VMS膜层与铝合金基体之间产生了一个新的中间层.根据实际的可能性,该层包含Al-O-Si,膜层与基体以化学键合;然而,完全水解的VMS膜层的EIS谱图中没有这个新的时间常数.不同水解时间的VMS膜层的EIS谱图表明为获得致密的膜层且与基体间以化学键合,VMS需在本文反应条件下水解3d.     

Study on cross section of high temperature superconducting coil

It is in particular of importance for HTS coils to secure a larger central magnetic field and/or a large stored energy with shorter length of HTS tapes. The critical current of an HTS tape depends on both the flux density and the flux angle against tapes. From this point, the performance improvement of HTS coils is taken into account with an analytical model. The minimum volume coil derived from the Fabry Factor constant curve is taken concerning the original coil shape, which is often employed in low temperature superconducting coils. The coil critical current was analyzed in consideration of the anisotropic properties of the tape.The electric field of HTS tapes in the coil was calculated at the coil critical current and the high electric field portion were cut out. The optimal coil cross section is obtained by iterating this calculation process. As a result, the critical current and the stored energy density of the coil were improved. The stored energy density increased about 17% and the central magnetic field was almost kept constant regardless of 19% reduction of HTS tapes, as compared with the original coil with the rectangular cross section.     

Investigation on the internal thermal link of pulse tube refrigerators

Within a pulse tube refrigerator (PTR) in coaxial configuration the pulse tube is located inside the regenerator matrix in axial direction. An internal thermal contact between these two main components of the coldfinger occurs. The experimental investigation of the direction and the quantity of transferred heat is in focus of this paper. Intermediate cooling of the regenerator by the corresponding part of its own pulse tube can improve the cooling performance of a PTR. Therefore, a well-adapted geometrical arrangement between the pulse tube and the regenerator is essential, considering the temperature distribution inside the coldfinger. We deduce design parameters to optimise the configuration of coaxial PTRs.     

聚乙烯吡咯烷酮对羟基磷灰石结晶和形貌的影响

采用化学均相沉淀法,在水热条件下以Ca(NO3)2.4H2O和(NH4)2HPO4为原料,合成了具有特殊形貌的羟基磷灰石(HA)微球。在合成过程中加入聚乙烯吡咯烷酮(PVP)为模板剂,研究了PVP的加入和浓度对HA晶体形貌和粒径的影响。结果表明,PVP的加入改变了HA晶体的生长方式,颗粒是由针片状HA晶体组成的微球;HA颗粒的形貌和粒径可以通过调节PVP浓度来控制,当PVP浓度从0%(质量分数,下同)增加到12%时,HA颗粒的形貌逐渐由不规则的絮状团聚物转变为规整的微球,组成微球的结构单元也随PVP浓度的变化有所不同。     

PMMA单分子膜成膜特性研究

研究了ＰＭＭＡ单分子膜的成膜特性及其结构．结果表明，ＰＭＭＡ能够在较大的表面压范围内形成稳定的单分子膜，并且具有不可重复压缩性、表面压力的各向异性和松驰特性．ＴＥＭ照片显示，ＰＭＭＡ分子链在单分子膜中是有序平行排列的     

Effect of convection heat transfer on the design of vapor-cooled current leads

A general optimization method for vapor-cooled current leads is presented with taking into account the effect of convection heat transfer and extended surfaces. This analytical work is considered as a unified design method, since one formulation calculates the minimum heat load and the corresponding optimal design condition for arbitrary heat transfer condition, spanning two limiting cases—the zero convection (or conduction-cooled leads) and the perfect heat transfer. It is clearly shown that the augmentation of the convective cooling can reduce the heat load to a certain extent, but the optimum lead parameter required to minimize the heat load for the finite heat transfer may not exist between the two limiting values. A new dimensionless parameter called the Ch number is introduced to conveniently incorporate the convection effect into the optimization. The present method is demonstrated for two specific lead designs that have been recently developed for 10 kA level of applications.     

偏振模色散对高速光码的影响

研究一阶、二阶偏振模色散（PMD）对10 Gb/s和40 Gb/s的光传输系统性能的影响，考虑PMD的统计特性，基于基本偏振态（PSP）理论数值模拟了非归零码（NRZ）和归零码（RZ）在传输过程中产生的脉冲畸变以及系统Q值的变化。结果表明，传输速率越高PMD对系统性能的影响越显著，二阶PMD也将不可忽略。另外，RZ码传输性能明显优于NRZ码并且可通过预啁啾进行改善。     

Effect of precipitation on post-heat-treated Inconel 625 alloy after friction stir welding

This study evaluated the mechanical properties of friction stir welded and post-heat-treated Inconel 625 alloy. Friction stir welding (FSW) was performed at rotation and traveling speeds of 200 rpm and 100 mm/min, respectively; heat treatment was carried out after welding at 700 °C for 100 h in vacuum. As a result, the application of FSW on Inconel 625 alloy led to the grain refinement in the stir zone, which resulted in increase in mechanical properties than those of the base material. Especially, applying heat treatment after FSW led to the improvement of mechanical properties of the welds; microhardness and tensile strength increased by more than 30% and 50%, respectively, as compared to FSW alone.     

The effect of pre-straining on the mechanical behaviour of self-piercing riveted aluminium alloy sheets

Self-piercing riveting as an alternative joining method to spot-welding has attracted considerable interest from the automotive industry and has been widely used in aluminium intensive vehicles. Pressing and stamping are important processes in automotive production and result in additional straining on the vehicle body sheet material. It is therefore important to have knowledge of the effect of sheet pre-straining on the quality of the self-piercing riveted joints and on the mechanical behaviour of the riveted aluminium alloy sheets. This paper reports the influence of sheet pre-straining on the static and fatigue behaviour of self-piercing riveted aluminium alloy sheet. Wrought aluminium alloy sheet, NG5754 with a nominal thickness value of 2 mm was used to obtain pre-strained NG5754 sheets with pre-straining levels of 3%, 5% and 10%. Pairs of pre-strained NG5754 sheets were joined to create single-riveted lap joints which subsequently underwent lap-shear and fatigue testing. Microscopic inspection showed that the joint quality was satisfactory despite the increasing sheet straining levels. The results showed that by increasing the pre-straining level up to 10%, the shear and fatigue strength also increased. The rate of increase of the static and fatigue strength differed as the pre-straining levels varied.