Sorption of Water by Aromatic Polyamides

Protection of Metals and Physical Chemistry of Surfaces - Isotherms of water-vapor sorption by aramid fibers and films of various nature were determined by static sorption methods. Structural and...     

Preparation and Characterization of Nickel-Coated Carbon Fibers by Electroplating

Electroplating technique was applied to coat carbon fibers with nickel. Before plating, the initial fibers were pretreated to improve the wettability in bath. The electroplating parameters were optimized to obtain high-quality nickel-coated carbon fibers, and the effects on plating were studied. The coated carbon fibers were characterized by SEM, XRD, and XPS. The coatings are uniform, smooth, bright, and adherent to carbon fibers not only along length but also along the diameter of the filaments, and mainly composed of pure nickel. Metal-carbon-oxygen bonds are present at the interface between nickel coatings and fibers, which provides the interfacial binding force. The results of performance tests showed that the nickel-coated fibers possess a good bonding strength not less than 78.5 kPa, and exhibit excellent oxidation resistance at high temperature. Compared with the initial fibers, the wettability with aluminum is also improved obviously.     

碳纤维负载Pd-TiO2光催化材料的制备及表征

以PAN基碳纤维为载体,采用溶胶-凝胶法制备碳纤维负载TiO2的光催化材料(TiO2/CF),用常温氧化-还原法在其表面沉积贵金属Pd粒子对其改性,制备碳纤维负载Pd-TiO2的光催化材料(Pd-TiO2/CF).XRD分析表明:采用溶胶-凝胶法在碳纤维表面形成了锐钛矿型TiO2.选择偶氮类染料酸性橙Ⅱ作为光催化降解目标物,用紫外吸收光谱分析等TiO2负载量的TiO2/CF,Pd-TiO2/CF和粉末型TiO2的光催化活性.结果表明:TiO2在负载条件下光催化活性有所下降;Pd粒子沉积可有效提高光催化活性;对于酸性橙Ⅱ溶液,Pd-TiO2/CF光催化活性较TiO2/CF、粉末型TiO2均有显著提高.     

Tensile Properties and Fracture Behavior of Different Carbon Nanotube-Grafted Polyacrylonitrile-Based Carbon Fibers

The tensile properties and fracture behavior of different carbon nanotube (CNT)-grafted polyacrylonitrile-based (T1000GB) single carbon fibers were investigated. Grafting of CNTs was achieved via chemical vapor deposition (CVD). When Fe(C₅H₅)₂ (also applied via CVD) was used as the catalyst, the tensile strength and Weibull modulus of the carbon fibers were improved, possibly due to the growth of dense CNT networks on the carbon fibers, which may have led to a reduction in the number of strength-limiting defects. Separately, at lower concentrations of an Fe(NO₃)₃·9H₂O catalyst in ethanol, which was applied via dipping, the tensile strength of CNT-grafted fibers was nearly identical to that of the as-received fibers, although the Weibull modulus was higher. For higher concentrations of the Fe(NO₃)₃·9H₂O catalyst, however, the tensile strength and the Weibull modulus were lower than those for the as-received material. Although the density of the CNT network increased with the concentration of the Fe(NO₃)₃·9H₂O catalyst in the ethanol solution, heating of the ethanolic Fe(NO₃)₃·9H₂O catalyst solution generated nitric acid (HNO₃) due to decomposition, which damaged the fiber surfaces, resulting in an increase in the number of flaws and consequently a reduction in the tensile strength. Therefore, the tensile strength and Weibull modulus of CNT-grafted carbon fibers vary due to the combination of these effects and as a function of the catalyst concentration.     

Tensile Properties of Polyimide Composites Incorporating Carbon Nanotubes-Grafted and Polyimide-Coated Carbon Fibers

The tensile properties and fracture behavior of polyimide composite bundles incorporating carbon nanotubes-grafted (CNT-grafted) and polyimide-coated (PI-coated) high-tensile-strength polyacrylonitrile (PAN)-based (T1000GB), and high-modulus pitch-based (K13D) carbon fibers were investigated. The CNT were grown on the surface of the carbon fibers by chemical vapor deposition. The pyromellitic dianhydride/4,4′-oxydianiline PI nanolayer coating was deposited on the surface of the carbon fiber by high-temperature vapor deposition polymerization. The results clearly demonstrate that CNT grafting and PI coating were effective for improving the Weibull modulus of T1000GB PAN-based and K13D pitch-based carbon fiber bundle composites. In addition, the average tensile strength of the PI-coated T1000GB carbon fiber bundle composites was also higher than that of the as-received carbon fiber bundle composites, while the average tensile strength of the CNT-grafted T1000GB, K13D, and the PI-coated K13D carbon fiber bundle composites was similar to that of the as-received carbon fiber bundle composites.     

Characterization and Oxidation Behavior of Rayon-Derived Carbon Fibers

Rayon-derived fibers are the central constituent of reinforced carbon/carbon (RCC) composites. Optical, scanning electron, and transmission electron microscopy were used to characterize the as-fabricated fibers and the fibers after oxidation. Oxidation rates were measured with weight loss techniques in air and oxygen. The as-received fibers are ~10 μm in diameter and characterized by grooves or crenulations around the edges. Below 800 °C, in the reaction-controlled region, preferential attack began in the crenulations and appeared to occur down fissures in the fibers.     

碳纤维表面熔盐反应制备TiC涂层

采用熔盐反应法在碳纤维表面反应形成了TiC涂层,利用XPS,XRD和SEM对涂层的化学组成、相组成和微观结构进行了分析和表征,研究了反应温度和保温时间对涂层厚度和形貌的影响.结果表明:碳纤维表面形成的是含有少量自由碳的TiC涂层,涂层形貌与原碳纤维表面形貌相似;TiC涂层的厚度随反应温度、保温时间的增加而增加,在700...     

Study of Oxidation of Carbon Fibers Using Resistance Measurement

Thermogravimetric analysis (TGA) is a useful and frequently used quantitative analysis technique to study the oxidation kinetics and mechanism of carbon fibers (CFs). An alternative method involving the resistance measurement of CFs during oxidation is proposed to study the oxidation behavior of CFs in this study, which might be also applied to other carbon materials. Experimental results from resistance measurements at different oxidation temperatures show qualitative consistency with those obtained using the TGA technique for the same type of fiber. A comparison between these two techniques is discussed.     

Oxidation Mechanisms of Copper and Nickel Coated Carbon Fibers

Differential-Thermal Analysis (DTA) and X-ray diffraction analysis were applied to determine the mechanisms of high-temperature oxidation of copper- and nickel-coated carbon fibers. Both kinds of coatings were deposited by electroless plating onto the fiber surface. The as-deposited copper film was crystalline, whereas the nickel coating consisted of an amorphous Ni–P alloy. Coated fibers were heated from room temperature to 900 °C in air at 10 °C min^?1. For the copper coating, the main oxidation product formed at low temperatures was Cu₂O, while at higher temperatures was CuO. The crystallization of Ni–P took place at 280–360 °C with the formation of Ni and Ni₃P. The final compounds were NiO, Ni₂P and Ni₃(PO₄)₂. After complete oxidation of the carbon fibers, copper and nickel-oxidized microtubes were obtained. Besides, while copper reduced the temperature of the fiber oxidation, nickel coatings increased the minimum temperature needed for this reaction.     

碳纤维表面化学镀Ni-B的初步研究

采用正交试验方法对碳纤维(CF)表面化学镀Ni-B进行了初步研究。找出了影响CF化学镀Ni-B的主要因素,得到了CF化学镀Ni-B的较佳配方及其工艺条件。镀Ni-B后CF在500℃～700℃之间热处理后,其拉伸强度仅有很小的下降。     

碳纤维增强铝基复合材料熔体真空除气

为解决搅拌铸造法制备的碳纤维增强铝基复合材料气孔率过高对材料性能的破坏问题,在熔体搅拌混合结束后,增加真空除气的工艺减少复合材料中的气体。采用阿基米德法测量了复合材料铸锭的相对密度,研究了碳纤维增强A356合金基复合材料熔体在0.03MPa的真空度下,真空炉温度、除气时间对复合材料铸锭致密度的影响。结果表明,当炉温为700℃、除气2min,即可将复合材料铸锭的气孔率降低至2%以下。通过扫描电镜观察了复合材料铸锭的组织,结果显示界面完好,未发现气孔。     

电化学氧化对碳纤维表面电化学性质的影响

碳纤维表面呈现化学惰性,缺乏活性官能团,限制了碳纤维作为电化学分析电极的应用.目前,许多手段被用于碳纤维的表面改性处理.采用电化学氧化方法,在磷酸溶液中对碳纤维进行了处理,并进行了红外光谱和循环伏安试验.结果发现:处理后碳纤维的表面接上了活性官能团,大量活性碳原子被剥离出来.在K4Fe(CN)6加KCl、FeSO4加HClO4两组混合溶液体系中的电化学响应明显改善,适合作为电化学分析电极.     

Sorption Reaction of Chromium(VI) Ions with Carbon Adsorbents

Protection of Metals and Physical Chemistry of Surfaces - The sorption interaction of chromium(VI) ions with carbon adsorbents was studied by the physicochemical methods of energy dispersive X-ray...     

水分子诱导类金刚石薄膜表面的变化

利用等离子体增强化学气相沉积技术在单晶硅表面制备了类金刚石(DLC)薄膜,并将其分别浸泡在经磁场处理和未经磁场处理的去离子水中。利用X射线光电子能谱仪、原位纳米力学测试系统和高速摩擦磨损测试仪分析和比较在水和磁化水中浸泡后DLC薄膜表面的变化情况。结果表明:磁场作用将改变经过DLC薄膜表面微孔或缺陷渗进薄膜内的水分子个数,进而诱导DLC薄膜表面发生变化。在含水环境中,比如液体水中,水分子参与反应并诱导C=C键朝向C-C或C-H键转化,并且氢原子将进入薄膜内中和膜内自由基,进而导致其硬度,摩擦因数升高。     

碳纤维在高温下的结构、性能演变研究

针对碳纤维在碳／碳烧蚀防热复合材料中应用的基础问题,论述了不同碳纤维结构、成分、表面特征,及其力学性能和热物理性能的高温演变规律,揭示了碳纤维灰分含量对碳纤维力学性能和热氧化性能的影响。确定了在碳／碳复合材料复合成型过程中,碳纤维结构受基体碳影响的变化规律和碳纤维表面特征对碳／碳材料宏观力学性能的影响。阐明了碳／碳复合材料中碳纤维的力学性能对纤维发生折断烧蚀的阻碍作用和通过控制碳／碳成型最高温度实现提高性能的途径。     

Raman Strain Sensing and Interfacial Stress Transfer of Hierarchical CNT-Coated Carbon Fibers

Hierarchical reinforcements of carbon fibers (CFs) coated with carbon nanotubes (CNTs) were produced via two different methodologies, namely chemical vapor deposition (CVD) and wet chemical treatment. These advanced smart structural materials are possible candidates for inherent strain sensing and improved interfacial properties when incorporated in the volume of structural fiber-reinforced polymer composites. The morphology and wetting properties of the hierarchical CFs were evaluated via SEM and contact angle measurements. Enhanced values in the strain-induced Raman sensing ability of the hierarchical reinforcement produced via CVD in comparison with the uncoated fibers were measured at single fiber level. The residual stress transfer profiles of both the hierarchical and the uncoated carbon fibers were also evaluated using the Raman spectroscopy in order to evaluate the phase interaction in the hierarchical structure. Compressive residual stresses in the order of 1.5 GPa were found to act on the CF surfaces, while tensile residual stresses were measured for both the CNT-coated systems. The effects of the preparation process of the CNT coatings on the residual stress profiles were also prominent, with the CVD-grown coatings resulting in higher tensile residual stresses, 1.76 GPa instead of 1.22 GPa for the coatings produced via wet chemical treatment. The change in the residual stress profiles established the interaction between the CFs and the CNTs via an anchoring mechanism which significantly altered the stress field at the vicinity of the interface.     

Oxidation Behavior of PAN-based Carbon Fibers and the Effect on Mechanical Properties

PAN-based carbon fibers were oxidized both in dry air and wet air in the temperature range of 400–600 °C. Kinetic laws are established that follow an Arrhenius-type temperature dependence. Oxidised fiber surfaces were investigated by SEM and AFM. Oxidation leads to the modification of surface morphology with the disappearance of the axial striations initially present. Then, residual properties were evaluated by failure tests in tension on single-filaments. Oxidation has a dramatic effect even for a low level of weight loss. The tensile failure stresses are reduced by 25–40 % for a mass loss of 2.5–5 %. This excessive embrittlement is more related to the creation of new defects by oxidation than a significant reduction in fiber cross-section area.     

Sorption of water by polyacrylic acid

The interaction of polyacrylic acid with water is reported. Water, which is consumed by polyacrylic acid in a wide range of humidities is found to exist in two states, i.e., statistically dissolved in the matrix (Flory-Huggins mode) and in cluster form. No retention due to the sorption on active sites according to Langmuir’s mode is detected.     

Processing of Carbon Fibers Reinforced Mg Matrix Composites Via Pre-infiltration with Al

Mg-C composites offer a suitable alternative to Al alloys while allowing for a significant weight reduction, but their production can be impaired by the poor wettability of C substrates by Mg. In this study, a new “liquid” processing route has been investigated. By making use of the well-known effect of a pre-treatment of the C fibers with an aqueous solution of K₂ZrF₆ in favoring spontaneous wetting of C with Al, C yarns have been pre-impregnated with Al and the feasibility of further using them as reinforcements in Mg matrix composites has been assessed. More particularly, it has thus been shown that the, under the thermal conditions involved in the process, C fibers did not suffer damage due to chemical reaction with Al, and also that special care should be taken to control the surface condition of the pre-infiltrated yarns.     

不同纺丝工艺国产高强中模碳纤维及其复合材料性能对比

目的 进一步探究国产不同纺丝工艺高强中模碳纤维及其复合材料的相关性能,并验证干喷湿纺工艺碳纤维的表面状态及其复合材料性能。方法 针对干喷湿纺的GW800G和湿喷湿纺的CCF800H两种碳纤维及其复合材料,采用场发射环境扫描电子显微镜(FESEM)、原子力显微镜(AFM)、X射线光电子能谱仪(XPS)、X射线衍射仪(XRD)和动态接触角测量仪表征其表面形貌、表面化学特性以及表面能,对两种碳纤维的微观表面性能以及微观结构进行对比分析,并与相同的高温环氧树脂复合,通过热压罐成型技术制成层合板,进一步表征两种复合材料的力学性能,并观察了复合材料90°拉伸和90°弯曲破坏试样断面形貌。结果 GW800G碳纤维表面形貌较光滑,CCF800H碳纤维表面粗糙度较大且凹槽明显。GW800G碳纤维和CCF800H碳纤维表面化学活性较高和表面能均较高,表面活性碳原子比例分别达到了34.11%和33.24%,表面能分别达到了36.92 mJ/m²和40.08 mJ/m²,二者水平差距较小。同时两种碳纤维的微晶结构相似,GW800G碳纤维具有更高的石墨化程度。这些特点...