PIP法制备Cf/SiC复合材料过程中碳纤维的化学损伤

对先驱体聚碳硅烷浸渍裂解工艺(PIP)制备Cf/SiC复合材料过程中碳纤维损伤严重的问题, 系统地分析了在Cf/SiC复合材料制备过程中先驱体裂解对碳纤维的化学损伤. 研究结果表明, PIP工艺中碳纤维的化学损伤包括界面反应和基体向碳纤维内部的扩散反应. 其中聚碳硅烷(PCS)中的活性基团和碳纤维的化学反应并不严重, 而微量的氧气和杂质对碳纤维的化学损伤影响很大; 基体中硅等元素可向碳纤维内部扩散, 随着高温处理时间的延长而加深, 并形成脆性的界面层, 使碳纤维截面积减小. 在第一周期浸渍裂解过程中, 先驱体对碳纤维的化学损伤很少, 在后续周期中, 随着基体致密度的提高, 碳纤维的化学损伤有所增加.      

碳纤维的表面处理及其特性

碳纤维复合材料是一种低密度、高比强度、高比刚度,耐热、耐烧融的新材料。从七十年代初问世以来,已经得到了广泛的研究和应用,至今,仍处于迅速发展阶段中。作为结构材料使用,在复合材料的特性中,层间剪切强度是重要的。就一种树脂(聚酯、环氧、聚酰胺等)和特定碳纤维所制成的复合材料而言,其层间剪切强度主要取决于树脂与纤维两相间的粘结性能。碳纤维表面处理的根本目的,则在于改善两相间的粘结,以提高碳纤维复合材料的层间剪切强发。本文着重介绍若干表面处理方法和有关碳纤维表面特性及其对复合材料性能的影响。     

钡铁氧体包覆碳纤维的制备及毫米波衰减性能

通过溶胶凝胶法,在碳纤维表面均匀包覆了一层厚度约为1 μm的钡铁氧体(BaFe₁₂O₁₉)。采用SEM、FTIR、XRD、XPS等技术对碳纤维/钡铁氧体复合材料的组成、结构、性能进行了表征和分析。利用8 mm波雷达装置测试了碳纤维、碳纤维/钡铁氧体复合材料的毫米波衰减性能。实验结果表明：由于碳纤维/钡铁氧体复合材料兼具电损耗和磁损耗吸收,其8 mm波衰减性能明显优于单纯的碳纤维。     

苎麻纤维布和碳纤维布混杂铺层复合材料力学和阻尼性能研究

将具有优异阻尼减振性能的纯天然苎麻纤维布与力学性能较好的碳纤维布混杂铺层,利用VRAM(真空吸注成型)工艺制备了环氧树脂基结构阻尼复合材料.首先考察了复合材料的力学性能,包括动态力学性能、静态力学性能和冲击断裂韧性;其次通过共振频率和阻尼因子评价了复合材料的阻尼减振性能.结果表明,通过苎麻纤维布/碳纤维布的混杂铺层能够平衡力学性能和阻尼性能之间的矛盾,可根据实际应用需求实现材料阻尼性能和力学性能的可控调节,充分发挥复合材料可设计性强的优势.其中"RCRCR"型铺层复合材料的损耗因子达到0.0057,比纯碳纤维布复合材料的0.0018提高了2.2倍,而拉伸强度和拉伸模量分别达到381.6 MPa和21.5 GPa,比纯苎麻纤维板提高了4.6倍和97.2%.最后,对混杂铺层复合材料的结构进行分析并针对阻尼性能进行有限元模拟,探讨了不同铺层方式影响复合材料力学性能和阻尼性能的规律,并对其他混杂铺层的复合材料的共振频率和损耗因子进行预测,为结构阻尼材料的设计提供一定的参考依据.     

增大有机复合材料层间抗剪强度的方法

D.A.Jaworski等人利用碳纤维在浸渍树脂前先进行溴化的方法,可使碳纤维和环氧树脂组成的复合材料层间抗剪强度增加。从而可以提高这类复合材料     

短碳纤维增强聚芳醚酮断面形态的研究

复合材料的强度是通过基体和纤维之间的应力传递获得的．这种传递可通过基体和纤维之间机械的、物理的和化学的结合来实现．因此,复合材料的界面结合很重要,它直接影响碳纤维在复合材料中的增强效率．短纤维在基体中由于其末端较多,其内部更易形成应力集中［１～４］．...     

高亲水性环氧树脂的制备及对碳纤维的表面处理

在三乙胺催化下,以己二酸和环氧树脂制备了己二酸改性环氧树脂(AAEP),通过考察反应温度等因素对己二酸转化率和AAEP环氧值的影响,得到了AAEP合成的最佳条件.用傅里叶变换红外光谱和核磁共振对AAEP进行了表征.用KOH中和AAEP得到己二酸改性环氧树脂钾盐(AAEPK),测试了AAEPK乳液的性质和AAEPK处理后碳纤维的分散性,并通过场发射扫描电子显微镜和X射线光电子能谱对碳纤维的表面形貌和基团进行了研究.结果表明,AAEPK具有高亲水性,适用于碳纤维处理剂,当AAEPK的浓度和吸附量分别为1.0%(质量分数)和3.0 mg/g时,处理剂可在纤维表面均匀分布,使得碳纤维在树脂基体中的分散性得到改善.研究了处理剂对碳纤维/环氧树脂复合材料弯曲和剪切性能的影响,发现处理后碳纤维短丝/环氧树脂复合材料的弯曲强度和碳纤维布/环氧树脂复合材料的层间剪切强度较未处理的试样分别增加了168%和113%,说明AAEPK处理后碳纤维在基体中分散性和黏结性的提高是碳纤维/环氧树脂复合材料力学性能提高的主要原因.     

超临界流体回收碳纤维树脂复合材料

碳纤维树脂复合材料回收再利用是碳纤维产业可持续发展的重要一环,因此受到学术界及产业界的广泛关注。 超临界流体回收碳纤维方法是一种高效、清洁,并且对碳纤维性能损伤较小的回收方法。 本文回顾了超临界流体回收碳纤维树脂复合材料研究进展,系统讨论超临界体系、反应条件、催化剂等对树脂降解率、回收碳纤维性能的影响,并对超临界流体回收碳纤维树脂复合材料的未来发展进行了展望。     

聚醚醚酮/碳纤维复合材料的界面结构以及结晶形态的研究

本文采用扫描电子显微镜观察经氩等离子刻蚀后PEEK/碳纤维复合材料的界面层结构和PEEK树脂的结晶形态。无论是从熔体还是从橡胶体结晶,PEEK树脂的结晶都是从碳纤维表面诱导开始,最后形成横穿晶体结构。在高碳纤维含量的复合材料中,PEEK的球晶尺寸主要由碳纤维之间的距离控制,受温度的影响较小。在PEEK/碳纤维复合材料的结晶过程中,第一片晶片在碳纤维表面取向生长方式为:晶体的ā轴(厚度方向)平行于维纤径 向。b轴(晶片生长方向)与纤维最小圆截面的切线重合,(?)轴(垂直晶片平面的方向)平行于纤维轴向。由于球晶成核过程是取向生长,因而生成的球晶也按一定的方式取向。     

等离子接枝处理的CF/PAA复合材料层间剪切强度及其形貌研究

采用等离子技术对碳纤维(CF)进行接枝芳基乙炔(PAA)处理,研究了影响CF／PAA复合材料层间剪切强度(ILSS)的因素。结果表明,经等离子接枝PAA处理后,复合材料的ILSS有了很大提高。SEM显示经接枝处理后CF和PAA树脂之间的界面结合紧密,改善了复合材料的界面结合性能。     

Oxidative charge transport through DNA in nucleosome core particles

Eukaryotic DNA is packaged into nucleosomes, made up of 146 bp of DNA wrapped around a core of histone proteins. We used photoexcited rhodium intercalators to explore DNA charge transport within these assemblies. Although histone proteins inhibit intercalation of the rhodium complex within the core particle, they do not prevent 5'-GG-3' oxidation, the signature of oxidative charge transport through DNA. Moreover, using rhodium intercalators tethered to the 5' terminus of the DNA, we found that guanine bases within the nucleosome can be oxidized from a distance of 24 bp. Histone binding did not affect the pattern and extent of this oxidation. Therefore, although the structure of the nucleosome core particle generally protects DNA from damage by solution-borne molecules, packaging within the nucleosome does not protect DNA from charge transfer damage through the base pair stack.     

Auger spectrum of a water molecule after single and double core ionization

The high intensity of free electron lasers opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules, radiation damage induced by absorption of high intense x-ray radiation is not yet fully understood. One of the striking effects which occurs under intense x-ray illumination is the creation of double core ionized molecules in considerable quantity. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From the MD trajectories, photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schro?dinger equations. These rates served to solve the master equations for the populations of the relevant electronic states. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were incoherently accumulated according to the obtained time-dependent populations, thus neglecting possible interference effects between different decay pathways. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint in the resulting electron emission spectra. The lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime.     

DNA damage in nucleosomes

Eukaryotic genomic DNA is packed into chromatin, whose fundamental structural unit is the nucleosome. As DNA-histone protein complexes, nucleosomes show different properties toward exogenous and endogenous DNA-damaging agents. This review summarizes nucleosome DNA damage due to different sources, including alkylating agents, radicals, UV radiation and reactive DNA damage intermediates. In most cases, the histone core protects the associated DNA against damage via its structure and/or scavenging of damaging agents. In contrast, histones react with damaged DNA and, in some instances, catalyze DNA damage in the nucleosome. The biological consequence of nucleosome DNA damage and future prospects in this field are briefly discussed.     

Amides and Heparin‐Like Polymer Co‐Functionalized Graphene Oxide Based Core @ Polyethersulfone Based Shell Beads for Bilirubin Adsorption

Excessive bilirubin in the body of patient with liver dysfunction or metabolic obstruction may cause jaundice with irreversible brain damage, and new type of adsorbent for bilirubin is under frequent investigation. Herein, graphene oxide based core @ polyethersulfone‐based shell beads are fabricated by phase inversion method, amides and heparin‐like polymer are introduced to functionalize the core‐shell beads. The beads are successfully prepared with obvious core‐shell structure, adequate thermostability and porous shell. Clotting times and protein adsorption are investigated to inspect the hemocompatibility property of the beads. The adsorption of bilirubin is systematically investigated by evaluating the effects of contacting time, initial concentration and temperature on the adsorption, which exhibits improved bilirubin adsorption amount for the beads with amides contained cores or/and shells. It is worth believing that the amides and heparin‐like polymer co‐functionalized core‐shell beads may be utilized in the field of hemoperfusion for bilirubin adsorption.     

Isolation and characteristics of the PSI-LHCI-LHCII supercomplex under high light

We developed a novel method for the isolation of the PSI-LHCI-LHCII complex from spinach leaves. The supercomplex was resolved into a core complex (CPI), LHCII trimers, LHCI dimers and LHCII monomers using green gel electrophoresis. We then investigate changes in the fluorescence and absorption spectra of PSI-LHCI-LHCII under high light. In addition, we compared light-induced denaturation of the core protein subunits in both PSI-LHCI and PSI-LHCI-LHCII. Differences in denaturation and photochemical activity indicated that binding of LHCII increased the photosensitivity of the PSI core. Increased energy delivered to the PSI core during illumination accelerated damage to the core complex.     

Damage control of DNA in nucleosome core particles: when a histone's loving, protective embrace is just not good enough

Packaging DNA into nucleosome core particles generally offers protection from damage by molecules diffusing in solution. However, on page 403 of this issue, Barton and coworkers report that although noncovalently bound, activated Rh (Rhodium) does not readily bind within nucleosomal DNA, activated Rh that is covalently tethered to the 5' terminus of a histone-associated oligonucleotide oxidizes guanine bases from a distance of up to 24 base pairs, demonstrating that histones do not protect DNA from long-range damage from the transport of charge through stacked bases. This implies that oxidative damage generated on DNA in vivo may spread from an initially damaged site to distal sites. Once created, such sites may persist and be resistant to repair because of the protective packaging by histones; they thus may result in permanent mutations.     

核壳结构催化剂Cr-Zn@SiO2@SAPO-34催化合成气直接转化制低碳烃的性能

合成气直接转化高选择性制烃类产物仍是巨大的挑战.本文合成了以Cr-Zn氧化物为核, SiO2为中间过渡层,再通过原位水热合成覆盖一层SAPO-34分子筛为壳的核壳结构催化剂.合成气转化反应结果显示,与纯Cr-Zn金属氧化物相比,核壳结构催化剂将产物分布由甲醇和甲烷移动至C2–C4烃(所有烃类产物中占66.9%).这表明核壳结构催化剂用于合成气一步法直接转化制液化石油气的反应具有可行性,但是催化剂结构和组成有待于进一步优化,以提高其催化反应性能.     

Ultraviolet radiation-induced limitation to epilithic microbial growth in arid deserts--dosimetric experiments in the hyperarid core of the Atacama Desert

Experiments were conducted during November 2003 in the dry core of the Atacama Desert, Yungay, Chile to test the hypothesis that UV radiation, in environments where liquid water is not available, and thus enzymatic repair of UV-induced damage is inhibited, can prevent epilithic colonization. Novel dosimeters made from the cryptoendolithic, desiccation and radiation-resistant cyanobacterium Chroococcidiopsis sp. isolated from the dry Negev desert, Israel, showed that monolayers of this organism were killed within one day. The diurnal profile of microbial loss of viability was investigated with dosimeters of Bacillus subtilis, which similarly showed cell death within one day. Soil grains obtained from south of Yungay where liquid water is more abundant and transported to the hyperarid core showed killing of indigenous vegetative organisms within one day. Gypsum and mineral grain coverings of 1mm were sufficient to prevent measurable UV-induced damage of Chroococcidiopsis and B. subtilis after 8d exposure. These results show that under extreme desiccation and an ambient UV flux the surface of rocks can potentially be rendered sterile, but that millimetre thick mineral coverings can protect organisms from UV-induced killing, consistent with the observed patterns of lithophytic colonization in the Atacama Desert. These data further show that UV radiation can be an important limiting factor in surface biological rock weathering in arid regions.     

Multiple light scattering and cavitation in two phase tough polymers

In glassy polymers toughened by inclusion of nanometric rubber particles, the high impact strength is due to cavitation of the rubber particles followed by the appearance of microshear bands in the glassy matrix. These materials are mostly opalescent or even opaque, which renders difficult any optical investigation of the damage process. Simple light scattering techniques were employed in earlier work to study the onset of damage in transparent toughened polymers. As demonstrated in one previous paper, multiple light scattering can be employed to further investigate opaque materials and hence highly damaged polymers. Coherent light backscattering in strongly opaque materials arises from the fact that an incident light beam, if not absorbed, is scattered successively by several scatterers before emerging again at the front surface of the body. The so‐called coherent backscattering cone may be analyzed in terms of the size, shape, and density of the scatterers. In the present work, this technique was applied to a semicrystalline polymer and to rubber toughened PMMA containing core‐shell (hard core) particles, an initially transparent material which becomes progressively opaque in the course of mechanical damage under stress. During the damage process, both the number of cavitated particles and their individual void fraction may increase, and a cavitated particle acts as a light scatterer of cross‐section proportional to its void content. The weakness of such scattering techniques resides in the fact that the light scattering pattern is determined by the product of the density of the scatterers and their scattering cross‐section. Consequently, the number of damaged particles cannot be separated from the particle void content. This study describes a new method based on the superposition of small elastic unloadings on the main tensile strain. During these unloadings, the number of damaged particles remains constant but their optical cross‐section changes, thus leading to a supplementary equation describing the scattering properties of the body. Hence, the number of cavitated particles and their individual void fraction may be calculated separately from the experimental data. Since the use of coherent light backscattering to investigate damage mechanisms in polymers is relatively new, the paper also recalls the basic principles of multiple light scattering. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 113–126, 1999     

Antiproliferation- and Apoptosis-Inducible Effects of a Novel Nitrated [6,6,6]Tricycle Derivative (SK2) on Oral Cancer Cells

The benzo-fused dioxabicyclo[3.3.1]nonane core is the central framework in several natural products. Using this core, we had developed a novel nitrated [6,6,6]tricycle-derived compound containing an n-butyloxy group, namely, SK2. The anticancer potential of SK2 was not assessed. This study aimed to determine the antiproliferative function and investigated possible mechanisms of SK2 acting on oral cancer cells. SK2 preferentially killed oral cancer cells but caused no harmful effect on non-malignant oral cells. After the SK2 exposure of oral cancer cells, cells in the sub-G1 phase accumulated. This apoptosis-like outcome of SK2 treatment was validated to be apoptosis via observing an increasing annexin V population. Mechanistically, apoptosis signalers such as pancaspase, caspases 8, caspase 9, and caspase 3 were activated by SK2 in oral cancer cells. SK2 induced oxidative-stress-associated changes. Furthermore, SK2 caused DNA damage (γH2AX and 8-hydroxy-2′-deoxyguanosine). In conclusion, a novel nitrated [6,6,6]tricycle-derived compound, SK2, exhibits a preferential antiproliferative effect on oral cancer cells, accompanied by apoptosis, oxidative stress, and DNA damage.