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。     

NiSO_4改性对聚丙烯腈原丝及其碳纤维结构与性能的影响

碳纤维具有高比强度、高比模量、导电、耐热、自润滑等优异的综合性能,在纤维增强复合材料中得到了广泛的应用.可制备碳纤维的前驱体有人造丝、沥青、聚丙烯腈纤维、木质素、聚乙烯纤维、聚苯并噻唑(PBO)纤维等.但大多数高强碳纤维目前仍然是由聚丙烯腈纤维制备的,同时,许多工作都集中在更进一步提高碳纤维的机械性能.特别是在我国, 碳纤维质量与某些发达国家相比,还有较大的差距,急需解决的问题就是如何尽快研制出高力学性能的碳纤维.采用氨基硅氧烷、脂肪族羧酸[1]、CuCl[2]、KMnO 4[3]、CoCl2[4]等有机或无机化学试剂对聚丙烯腈原丝进行化学处理, 以改进最终碳纤维的结构与性能是一种有效的方法.国内在这方面的研究还很少.文献[1 ～4]中所采用的方法都是利用商业聚丙烯腈原丝在碳化前进行洗油、浸渍、洗涤烘干处理 ,增加了碳纤维制备的工序,同时,原丝损伤较大,在连续生产中难以适用.我们在原丝连续制备的同时采用NiSO4溶液浸渍处理聚丙烯腈纤维,本文主要研究了采用NiSO4浸渍改性后聚丙烯腈原丝及其碳纤维的结构与性能.研究表明,采用NiSO4在线浸渍改性聚丙烯腈原丝,生产工艺简单,且能有效地改进最终碳纤维的结构与性能.     

甲基异丙苯氧化速率模型

甲基异丙苯液相氧化虽为一慢反应,但工业上只在接近(不完全是)动力学控制条件下进行。因此,动力学模型需经校正再应用。本文在工艺条件考察及动力学研究的基础上,就传质因素、氧浓度及异构体组成对氧化的影响进行定量关联,求得相应的校正系数。建立了以动力学方程为基础并对上述因素进行校正的氧化速率模型。它可用于工业氧化(非动力学控制)情况。用此模型所得计算结果与实验值相符合。     

气相生长碳纤维对环氧树脂固化反应的影响及其复合物固化动力学研究

用示差扫描量热方法研究了气相生长碳纤维作为填料对4,4′-二氨基二苯甲烷四缩水甘油环氧树脂(TGDDM)/4,4′-二氨基二苯基砜(DDS)等温固化反应的影响.与纯环氧树脂一样,气相生长碳纤维复合物的固化反应也属于自催化反应类型.气相生长碳纤维对环氧树脂的固化反应动力学影响很小.固化反应的过程可以用一种修正过的自催化动力学模型来描述,在整个固化反应过程中纯TGDDM/DDS环氧树脂及其气相生长碳纤维复合物模型拟合得到的结果和实验数据相当一致.     

次亚磷酸根在镍电极上的电氧化机理与动力学

用电化学质谱(EMS)和动力学模型分析等方法研究了次亚磷酸根在镍电极上的电化学氧化机理和动力学.研究表明，次亚磷酸根的电化学氧化是通过从P－H键脱离一个原子H，形成磷中心自由基(PHO2－•)，而磷中心自由基(PHO2－•)进一步进行电化学反应形成最终产物亚磷酸。利用该模型，推导出相关动力学方程并通过与实验数据拟合获得动力学参数.结果表明，该模型能很好地模拟次亚磷酸根在镍电极上的电化学氧化过程.     

VPO催化氧化正丁烷反应动力学

VPO催化氧化正丁烷制顺酐是目前唯一实现工业化的低碳烷烃选择氧化反应。本文介绍了VPO催化机理和主要的反应网络,综述了国内外反应动力学的研究进展情况。根据人们对正丁烷氧化反应机理的不断认知及动力学模型的完整性,首次将正丁烷氧化制顺酐反应动力学的发展分为探索期、成型期和拓展期三个时期,并阐释了每个时期的特征和典型模型。探索期特征是仅考虑反应物在催化剂表面的吸附行为,成型期特征是充分考虑了产物对反应的抑制作用,拓展期特征是考虑了催化剂氧化度不断变化的动态过程并将不同氧气形式之间的相互变化引入动态模型中。从时空多尺度角度研究动力学和传递之间的相互作用是正丁烷选择氧化反应动力学下一步的研究重点,也是未来动力学研究的发展方向。     

高性能纳米碳材料改性Cu/ZnO/Al2O3甲醇水蒸汽重整制氢催化剂

由铜基催化剂催化甲醇水蒸汽重整制氢是有效解决车载燃料电池等制氢需求的潜在途径．但传统铜基催化剂对该反应的低温催化活性及制氢选择性均不理想．近年来碳纳米管及活性碳纤维等因具有独特的纳米孔结构、高比表面积和优异的吸附性能作为潜在的新型催化材料而备受关注．     

锌蒸气的氧化行为与氧化锌的结晶形貌

用热重法测定了不同气氛下锌蒸气的氧化动力学曲线,用扫描电镜跟踪观察分析了产物的结晶形貌,结果表明,氧化动力学遵守直线规律时,产物是无定形、颗粒状和单针状的ZnO;氧化动力学为抛物线规律时,产物是四针状或多针状的ZnO.动力学转变规律的原因是锌蒸气中气态锌原子与凝聚生成的锌液滴之间存在动态平衡,气态锌原子的氧化过程遵守直线规律;而锌液滴的氧化过程分为两个阶段,分别受收缩球状界面反应模型R₃和三维扩散模型D4动力学控制,表观活化能分别为106.3～108.2和114.2～117.3kJ/mol;扩散过程实际上是锌原子通过氧化膜层由里向外扩散,扩散系数D=2.46～9.70×10^-5cm²/s.     

氧化还原活性碳纤维的研究进展

就氧化还原碳纤维的制备及其结构、影响氧化还原容量的因素、氧化还原机理等方面进行了综述，并做了研究前景展望。     

离子的胶体状态与其电化学储能极限

阳离子氧化还原化学是电化学储能技术中最核心的储能机理,如何高效快速利用氧化还原活性阳离子是发展兼具高功率密度与高能量密度储电技术的关键。 处于胶体状态的阳离子可形成热力学平衡态和非平衡态,具有高反应活性和低离子迁移势垒,展现出独特的电化学特性。 本文着重介绍氧化还原活性阳离子的胶体状态与其在电化学储能上的应用,并从热力学和动力学方面阐述其储能机理,以及活性胶体离子电极和超级电容电池的构筑。 利用胶体的高比表面积、高离子吸附能力和荷电离子梯度分布等特性,创造性地构筑胶体超级电容电池,解决了现有电化学储能电极材料体系中高容量与高功率不能兼具的问题,同时开拓了胶体体系新的应用方向。     

碳纤维的抗氧化处理

用硼化合物对碳纤维进行抗氧化处理,提高了纤维的高温抗氧化性能。用热分析、电子显显微镜、表面电子能谱和X射线衍射等进行了研究,结果表明:碳纤维经过硼化合物处理后,氧化活化能提高123.4%,热氧化分解点提高268℃,高温使用寿命提高许多倍,但物理机械性能变化不大。     

Surface characterization and electrical property of carbon fibers modified by air oxidation

Polyacrylonitrile‐based carbon fibers were modified by oxidation in air, and a systematic study of surface groups and surface resistance at different treated temperatures was made. Progressive fiber weight loss occurred with increasing extents of air oxidation, and it was approximately proportional to the extent of air oxidation from the onset of oxidation up to 400 °C. At this point 4.4% of the initial fiber weight had been lost. A faster loss of weight occurred as the extent of air oxidation increased from 400 °C to 700 °C. X‐ray photoelectron spectroscopy studies (C 1s and O 1s) indicated that the oxygen/carbon atomic ratio rose rapidly from 2.64% (as‐received carbon fiber) to 42.83% as the oxidation temperature was increased to 400 °C. Fourier transform infrared spectra showed the relative intensity of the peaks at about 3440 cm^?1 from ―OH stretching vibrations and at 1634 cm^?1 from ―C?O stretching vibrations increased significantly at 400 °C. FESEM micrographs showed that as‐received fibers show relatively smooth surface. With oxidation temperature increasing, the fiber surface was rougher. The surface resistance of treated carbon fibers decreased obviously with increasing oxidation temperatures. The most decrease was about 100% at 400 °C. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of low current density electrochemical oxidation on the properties of carbon fiber‐reinforced epoxy resin composites

Changes in surface physicochemical structures of polyacrylonitrile‐based carbon fibers resulted from low current density electrochemical oxidation were monitored by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The relationship between the interlaminar shear strength (ILSS) values of carbon fiber‐reinforced polymers (CFRPs) and carbon fiber surface chemistry including elemental ratios and the relative content of oxygen‐containing functional groups were researched. SEM results revealed that the electrochemical oxidation got rid of surface contaminants generated during the production process. XPS analysis showed that the relative contents of oxygen and nitrogen increased by 446% and 202%, respectively, after the electrochemical oxidation. Carbon fiber surface chemistry was of paramount importance to the interfacial properties of CFRPs. The higher the carbon fiber surface activity, the better the interfacial bonding was, and an increase in the acidic‐group contents was responsible for a higher ILSS value. However, when the current density increased to 1.0 A/m², the interfacial bonding between carbon fiber and the epoxy resin became weak which led to the decline in ILSS values. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and electrocoating of indole-thiophene comonomer on carbon fiber microelectrode, and surface topography by AFM

5,2-Thiophenylindole(5,2 In-Th) comonomer is synthesized by means of palladium catalyzed Stille cross-coupling reaction with an aim of obtaining extensively conjugated, low oxidation potential comonomer relative to its corresponding monomer. The comonomer is characterized by UV-Visible, FTIR, and NMR spectroscopic techniques, and the resulting conjugated copolymer exhibited the properties of both polyindole and polythiophene (having low oxidation potential and high conductivity).5,2 In-Th comonomer was electropolymerized onto carbon fiber microelectrodes. The copolymer was electrochemically coated (grafted) onto micron size carbon fiber by constant potential electrolysis and cyclic voltammetry (CV) and the resulting nanosize thin films of polymers were characterized using atomic force microscopy (AFM), and FTIR spectroscopy. The efficiency of the electrocopolymerization process on the carbon fiber surfaces under preparative constant current electrolysis and potentiodynamic conditions, was evaluated in order to ascertain the effects of copolymer thickness, dopant and morphology.     

Electrooxidation of Phenylhydrazine on Carbon Electrodes

Electrochemical behavior of phenylhydrazine on glassy carbon and carbon fiber in a neutral aqueous solution is studied with differential voltammetry and potentiostatic oxidation. The fiber surface has a considerable catalytic effect, and the oxidation products depend on the fiber potential. The application of carbon fiber as an electrode material in electrochemical purification of waste water from phenylhydrazine is considered.     

A review of heat treatment on polyacrylonitrile fiber

Developing carbon fiber from polyacrylonitrile (PAN) based fiber is generally subjected to three processes namely stabilization, carbonization, and graphitization under controlled conditions. The PAN fiber is first stretched and simultaneously oxidized in a temperature range of 200-300 °C. This treatment converts thermoplastic PAN to a non-plastic cyclic or a ladder compound. After oxidation, the fibers are carbonized at about 1000 °C in inert atmosphere which is usually nitrogen. Then, in order to improve the ordering and orientation of the crystallites in the direction of the fiber axis, the fiber must be heated at about 1500-3000 °C until the polymer contains 92-100%. High temperature process generally leads to higher modulus fibers which expel impurities in the chain as volatile by-products. During heating treatment, the fiber shrinks in diameter, builds the structure into a large structure and upgrades the strength by removing the initial nitrogen content of PAN precursor and the timing of nitrogen. With better-controlled condition, the strength of the fiber can achieve up to 400 GPa after this pyrolysis process.     

新型碳纤维负载直接乙醇燃料电池Pt-SnO_2阳极催化剂的性能研究

采用静电纺丝技术制备了碳纤维基纳米Pt-SnO2阳极催化剂(Pt/Sn原子比为3)。通过X射线衍射(XRD)、红外光谱(FT-IR)、扫描电子显微镜(SEM)等技术对该催化剂进行了表征,并采用循环伏安法对其在乙醇燃料电池中的阳极催化活性进行了评价。结果表明,纳米Pt-SnO2催化剂均匀地分散在碳纤维骨架上;随着烧结温度的升高,碳纤维载体的致密度越高、导电性能越好。电催化性能测试表明,烧结温度为800℃时催化剂的峰电流密度最大,达到0.11 A/cm2,抗中毒能力也最强。单电池的发电性能表明,在一定的乙醇浓度下,1.0 mL/min进样流速具有最优的发电效率。     

Study of oxidation properties and decomposition kinetics of three-dimensional (3-D) braided carbon fiber

The XRD, SEM, isothermal oxidation-weight loss and non-isothermal thermogravimetry (TG)-differential thermogravimetry (DTG) were used to study the oxidation properties and oxidation decomposition kinetics of three-dimensional (3-D) braided carbon fiber (abbreviated as fiber). The results showed that the non-isothermal oxidation process of fiber exhibited self-catalytic characteristic. The kinetic parameters and oxidation mechanism of fiber were studied through analyzing the TG and DTG data by differential and integral methods. The oxidation mechanism was random nucleation, the kinetic parameters were: lg A=10.299 min⁻¹; E_a=156.29 kJ mol⁻¹.     

环氧树脂在碳纤维表面的浸润行为

利用场发射环境扫描电境(FESEM)测定了室温下环氧树脂在单纤维表面的接触角,观测并计算了环氧树脂液滴在单根碳纤维表面的接触角随温度的变化,结果表明接触角随温度升高明显降低,说明升高温度有利于改善环氧树脂对碳纤维的浸润性能.用液滴形状分析仪(DSA)在垂直和平行于纤维排列方向上观测了不同温度下单向排列碳纤维集束表面环氧树脂的铺展过程,发现在不同方向上观测到的接触角差别较大,其中垂直于纤维排列方向上观测到的接触角随温度的变化与环氧树脂在单根碳纤维表面的接触角变化基本一致,说明环氧树脂在平行于纤维束方向的接触角真正代表其浸润性能.     

Influence of an oxidation of the carbon fiber surface by boiling nitric acid on the adhesion strength in carbon fiber‐acrylate composites cured by electron beam

A time‐dependent oxidation of carbon fibers in boiling nitric acid was used to investigate the influence of a modification of the fiber surface properties on the adhesion strength with an acrylate resin cured by electron beam (EB). For each time of treatment, a characterization of the surface topography and the surface chemistry was done (topography at a micrometric and nanometric scale, specific surface area, temperature programmed desorption, X‐ray photoelectron spectroscopy analysis). The oxidation of the fiber surface in boiling nitric acid created a rough surface, which significantly increased the specific surface area, and also generated a high density of hydroxyl groups, carboxylic acids and lactones in comparison to untreated fibers. The adhesion strength with the acrylate resin cured by EB was measured by a pull‐out test. For comparison, an isothermal ultraviolet curing of the matrix was also investigated. The value of the interfacial shear strength, determined by the Greszczuk's model, was increased by the oxidation of the carbon fiber surface for both curing processes, but lower values were systemically obtained with EB curing. Copyright © 2012 John Wiley & Sons, Ltd.