Microstructure of carbon fiber preform and distribution of pyrolytic carbon by chemical vapor infiltration

The carbon/carbon composites were made by chemical vapor infiltration(CVI) with needled felt preform. The distribution of the pyrolytic carbon in the carbon fiber preform was studied by polarized light microscope (PLM) and scanning electronic microscope(SEM). The experimental results indicate that the amount of pyrolytic carbon deposited on the surface of chopped carbon fiber is more than that on the surface of long carbon fiber. The reason is the different porosity between the layer of chopped carbon fiber and long carbon fiber. The carbon precursor gas which passes through the part of chopped carbon fibers decomposes and deposits on the surface of chopped carbon fiber. The pyrolytic carbon on the surface of long carbon fibers is produced by the carbon precursor gas diffusing from the chopped fiber and the Z-d fiber. Uniform pore distribution and porosity in preform are necessary for producing C/C composites with high properties.     

Application of X-ray phase-contrast imaging technique in the study of pyrocarbon-coated zirconia kernels

X-ray in-line phase-contrast imaging is an emerging technique made practical by high brilliance synchrotron X-ray sources and high-performance X-ray detectors. This technique is capable of providing improved contrast along with edge enhancement for weakly absorbing samples and hence it is of immense value in study of materials like carbon fiber, carbon composite, etc. This technique is also very useful for determination of coating thickness, uniformity of pyrocarbon coating on the fuel kernel particles. The applications of such fuel kernel particles demand a high-quality of uniformity and precise thickness. The thickness and uniformity of such coatings depends upon several parameters of the system during their preparation. In this paper, we have explored the use of X-ray phase-contrast techniques for the measurement of coating thickness and its uniformity. We present the results of such experiments on SiC and pyrocarbon (PyC)-coated zirconia micro-spheres. This information may be of importance in optimization of the various parameters during the deposition process. The results bring out the importance of the X-ray phase-contrast technique in materials research.     

碳纤维的化学镀铜

本文提出一种碳纤维的化学镀铜技术,研究了各种工艺参数对镀层特性的影响。结果表明,使用化学镀技术在碳纤维表面镀铜是成功的,镀层均匀、连续;镀铜速率主要受镀液中HCHO的浓度控制。应用此镀铜碳纤维成功地制造出碳纤维增强铝基复合材料。     

铁镍磁性涂层碳纤维软磁性能及电磁屏蔽效能的研究

目的制备兼具良好电磁屏蔽效能和软磁性能的新型屏蔽材料。方法采用化学镀的方法在碳纤维表面制备FeNi合金涂层和Ni涂层。运用SEM、EDS、XRD分析涂层碳纤维的形貌、成分和镀层结构。通过VSM研究其软磁性能。采用万用表测量其电阻并计算电导率。利用网络矢量分析仪测量其电磁参数并计算其电磁屏蔽效能,进而对FeNi合金涂层碳纤维和Ni涂层碳纤维的上述性能进行对比。结果金属镀层均匀且晶粒细小。FeNi合金涂层碳纤维的矫顽力为29.25 Oe,饱和磁化强度为25.61 emu/g。在7.92~18 GHz频率范围内,FeNi合金涂层碳纤维的电磁屏蔽效能均在30 dB以上,峰值为40.79 dB。结论金属涂层能使碳纤维具有软磁性能,并能有效地调整其电磁参数,进而显著提高其电磁屏蔽效能。与Ni涂层碳纤维相比,FeNi合金涂层碳纤维的上述性能更加优异。该研究为兼具良好电磁屏蔽效能和软磁性能的新型屏蔽材料的制备提供了新方案。     

Development and microstructure optimization of atmospheric plasma-sprayed NiO/YSZ anode coatings for SOFCs

In this paper, preparation and characterization of porous anode layers with uniform phase distribution are discussed for solid oxide fuel cell (SOFC) application. The Ni/8YSZ cermet coatings were fabricated by atmospheric plasma spray (APS) process using oxidized nickel coated graphite (Ni-graphite) and 8 mol% yittria — stabilized zirconia (8YSZ) blend as feedstock. To control the microstructure of the coating, the nickel coated graphite with low density was used as a starting feedstock instead of conventional pure nickel (Ni) powder. To balance the conductivity, uniform porosity, and structural stability of the coatings, the effects of process parameters such as hydrogen gas flow rate, stand off distance and pore formation precursor (graphite) addition on the microstructures of the resulting coatings are investigated. The results show that the anode coatings with high conductivity, structural stability and porosity could be deposited with moderate hydrogen gas flow rate and short stand off distance.     

无钯镀镍碳纤维增强Sn-3.0Ag-0.5Cu复合钎料的制备

采用化学镀法在碳纤维表面制备无钯镍镀层,用粉末冶金法制备了以镀镍碳纤维为增强相的Sn-3.0Ag-0.5Cu复合钎料,借助于SEM、EDS、OM等检测手段对其微观组织进行分析,研究镀镍碳纤维含量对复合钎料微观组织和基本性能的影响。结果表明:镀镍碳纤维主要分布在复合钎料的晶界处;随着复合钎料中镀镍碳纤维含量的增加,其弥散度逐渐降低,熔点变化不大;当镀镍碳纤维含量(质量分数)大于1%时,镀镍碳纤维在晶界处的团聚现象严重,复合钎料的电阻率显著升高。添加1%的镀镍碳纤维有助于减小液态复合钎料在助焊剂界面和Cu基板处的表面张力,降低钎料基体的电流密度,使得复合钎料的润湿性提高,电阻率有所降低。     

Protective ceramic multilayer coatings for carbon fibers

Uniform, adherent, crack-free and non-bridging HfC and HfC/SiC coatings on carbon fibers have been synthesized by a reactive CVD (RCVD) process at low temperatures. To fabricate SiC coating on HfC-coated carbon fiber, an alternative approach using unsaturated organosilicon polymer solution was also proposed. The schemes describing the formation of carbide coatings on carbon fibers by RCVD and transformation of unsaturated organosilicon polymers into silicon carbide are discussed. The HfC and HfC/SiC coatings were studied by SEM, EDS and XPS techniques. Coatings are composed of hafnium, silicon and carbon as the main constituents and oxygen and fluorine as contaminants. As was proposed, the composition of the coatings is affected by several factors, among them a chemical attack of coated fibers by gaseous oxygen- and fluorine-containing by-products can be considered as dominant ones. The duplex HfC/SiC-coated carbon fibers exhibit more oxidation resistance at elevated temperatures than the initial and HfC-coated carbon fibers.     

Amorphous carbon coated stainless separator for PEFCs

An SUS316L stainless steel separator was coated with amorphous carbon by using an electron cyclotron resonance (ECR) plasma sputtering technique, and used in a polymer electrolyte fuel cell (PEFC). Characteristics of this carbon film were investigated with Raman spectroscopy and XPS. Quantitative depth profiles and chemical depth profiles of the deposited carbon layer were measured with GD-OES and XPS, respectively. The contact resistivity between a carbon paper and the carbon coated SUS316L steel was also measured. The performance of PEFC single cells assembled with carbon coated SUS316L separators, uncoated SUS316L separators, and conventional carbon separators were compared. The results revealed that an assembled PEFC having carbon coated SUS316L separators provided better performance than one having uncoated SUS316L, and the PEFC showed comparable performance to one having conventional carbon separators.     

Study of thermal degradation behavior of dense and nanostructured silicon carbide coated carbon fibers in oxidative environments

The oxidation resistive properties of bare, dense SiC and nanostructured SiC coated carbon fibers were examined in different oxidative environments from room temperature to 1350 °C. Chemical vapor deposition process was used for the preparation of dense and nanostructured silicon carbide (SiC) coating on carbon fiber using methyltrichlorosilane. SEM, TEM and XRD analysis inferred dense and nanostructured β SiC coatings. The dense and nanostructured SiC coated carbon fibers have shown much improved oxidation property in oxygen as well as in static air environment. Possible mechanism of oxidation behavior of dense and nanostructured SiC coated carbon fibers and role of SiO₂ have been discussed.     

炭纤维增强镁基复合材料的制备

对炭纤维进行了表面化学镀镍处理并通过扫描电镜(SEM)评价了炭纤维化镀层。利用粉末冶金热挤压方法制备了短切炭纤维增强镁合金复合材料并通过超景深金相显微镜观察了纤维在复合材料中的分布。研究了材料中炭纤维含量为0～4%时对复合材料的影响。结果表明,镀镍炭纤维在复合体中均匀分散,炭纤维质量分数为4.0%的镁预制体采用压制压力为420MPa,烧结温度为550℃,保温0.5h后在480℃用280MPa的压力进行热挤压得到的复合材料力学性能较佳。     

In-situ processing of carbon coatings on the surface of SiC-based fibers

Carbon coatings have been formed on the surface of free carbon containing Tyranno ZMI and Nicalon SiC-based fibers by reaction with chlorine gas (chlorination) in the temperature range 550-675 °C. The kinetics and growth mechanisms have been investigated for both fibers. Results have shown that, for similar experimental conditions, the reactivity of both fibers displayed noticeable discrepancies. It has thus been observed that the Nicalon fiber was more prone to chlorine-based treatment and displayed a thicker carbon coating than the ZMI fiber. These results have also revealed that, in both cases, these thicknesses can be closely monitored by physical parameters such as temperature and aging duration. The nature of the obtained coating has also been investigated by various experimental devices. AES, SEM and TEM analyses have thus evidenced that these carbon coatings were uniform and well adherent whereas AFM showed that the chlorine-based treatments resulted in a nanometer-range roughness at the fiber surface. Adsorption gas analyses also revealed a microporosity coupled with a high specific surface area. The chemical composition of the final products was determined by XPS and Mass Spectroscopy. Finally, the oxidation behavior which was investigated by thermogravimetric analysis revealed that oxidation occurs at a quite low temperature (225 °C).     

不锈钢纤维烧结毡在微生物燃料电池阳极中的研究进展

详细介绍了不锈钢纤维烧结毡在微生物燃料电池阳极中的应用现状及前景.不锈钢纤维烧结毡是采用微米级的不锈钢纤维经无纺铺制、叠配、真空烧结而成.它是由不同丝径的纤维形成的一种三维金属多孔材料,具有机械强度高、渗透性能好、导电性好、吸附能力强、耐腐蚀、耐高温、易加工等优点,在高效微生物燃料电池阳极材料方面呈现出了巨大的应用价值...     

Preparation and characterization of sol–gel derived zirconia coated carbon fiber

Zirconia coated carbon fiber for thermal and oxidation protection was prepared through a sol–gel technique. A zirconia sol was synthesized with the zirconium oxychloride, ammonia and polyethylene glycol, each of them acting as the zirconium resource, precipitant and surfactant. The morphology, phase composition and thermal properties of the zirconia coated carbon fiber were evaluated by SEM, EDS, XRD and TG-DTA. The increase of dipping cycles can raise the thickness of the coating, while attaching more ZrO₂ crystals on the coating surface. Mass variations of the 3 mol% YSZ and 2 mol% YSZ coated carbon fibers at 800 °C are 20% and 40%, less than the 70% of the uncoated carbon fiber.     

碳纤维表面 h-BN 耐高温涂层的制备及表征

目的在碳纤维表面制备六方氮化硼涂层,以提高纤维的抗氧化、耐高温性能,拓宽其在高温领域的应用。方法以硼酸、尿素、氨气和氮气作为原始材料,先通过浸渍法在碳纤维表面涂覆硼酸和尿素的混合溶液,然后将其放置在氨气和氮气氛围中进行高温热解。采用电子显微镜分析涂层的形貌,观察涂层与碳纤维的结合是否良好;采用傅里叶红外光谱、X射线电子能谱及X射线衍射等测试技术对涂层的成分和结构进行表征。结果碳纤维表面的涂层连续,形貌良好。红外光谱中,在1399,799 cm-1处存在B—N键和B—N—B键的特征峰。X射线衍射图谱中,在43.64°和53.93°存在六方氮化硼(001)晶面和(004)晶面的特征峰。X射线电子能谱分析表明,涂层中存在O,B,C和N四种元素,且B与N的原子比接近1∶1。结论实验中成功制备了h-BN涂层碳纤维,且涂层和碳纤维结合较好。涂层中的h-BN结晶度良好,纯度较高,但少量氧化物的存在会对h-BN涂层碳纤维耐高温性的提升有所影响,如何进一步提高h-BN涂层的纯度有待研究。     

高密度预制体制备炭/炭复合材料的弯曲力学性能与断裂机制

以丙烯作为碳源,氮气作为载气,采用初始密度为0.94g/cm3三维正交PAN基12K炭纤维预制体,利用自制的快速CVI炉制备基体热解炭结构为带状结构的C/C复合材料。力学性能测试结果表明,材料的弯曲断裂特征与制备过程中受到的高温热处理次数有关。从载荷-位移曲线来看,当C/C复合材料经过两次热处理时,C/C复合材料呈明显假塑性断裂特征。当C/C复合材料经过三次热处理时,载荷-位移曲线趋于稳定平滑,抗弯强度降低。从C/C复合材料断面的SEM图可以观察到材料断裂可以分为层间断裂和层内断裂,而层内断裂又因热解炭填充密度变化呈明显的分区断裂。由于热解炭和纤维含量在C/C复合材料中分布的差异,材料在不同的区域表现出不同的断裂特征,从而使得材料具备良好的弯曲强度同时具有一定的韧性特征。     

Influence of corrosion on the interface between zinc phosphate steel fiber and cement

The interface bond between steel fibers and concrete matrix is a key factor influencing bearing capacity of steel fiber reinforced concrete (SFRC). In order to improve the interface bond strength and corrosion resistance, a kind of method was put forward by depositing zinc phosphate (ZnPh) coating on steel fiber surface in this paper. The corrosion behavior was investigated in 5% NaCl solution by using linear polarization measurement. Microstructure analysis (SEM and EDX) and fiber pull‐out test in combination with linear polarization measurement were carried out. The results prove that ZnPh coatings fabricated on the carbon steel surface can not only protect steel fiber against corrosion, but also enhance the mechanical interlocking bonds between fibers and matrix.     

Oxidation protection of carbon fibers by a reaction sintered nanostructured SiC coating

A nanostructured SiC coating was prepared on the surface of carbon fibers by slurry coating and in situ reaction sintering. Phases of the coating were identified by X-ray diffraction, and features and structure were investigated by scanning electron microscopy and transmission electron microscopy. The oxidation resistant properties of the carbon fibers with and without the SiC coating were studied using isothermal oxidation. The results show that the nanostructured SiC coating was uniform and its coverage was complete. The oxidation activation energy of the fibers increased about 25% and the oxidation resistant of the coated fibers increases significantly.     

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.     

碳纤维表面改性对Cf/Mg复合材料微观组织和界面的影响

研究在碳纤维表面分别用化学法镀Ni和溶胶-凝胶法涂SiO2两种涂层,用真空压力浸渗法制备Cf/Mg复合材料.用SEM、EDS和TEM对Cf/Mg复合材料微观组织和界面特征进行分析.结果表明:无涂层的碳纤维与Mg基体浸润性较差,碳纤维在Cf/Mg复合材料微观组织巾分布不均匀,界面结合强度较弱.碳纤维表面包覆Ni或SiO2涂层改善了碳纤维与Mg基体的润湿性;包覆Ni涂层的碳纤维在Mg基体中分布均匀,并在其界面处生成金属间化合物Mg2Ni,界面为强结合;碳纤维表面的SiO2涂层与Mg进行少量的反应生成MgO和Si,界面结合好.能很好地传递载荷.     

Photocatalytic activity of anatase thin films coated cotton fibers prepared via a microwave assisted liquid phase deposition process

Nanocrystalline titanium dioxide thin films in the anatase phase was successfully coated on cotton fibers via a simple microwave (MW) assisted liquid phase deposition (MW-LPD) process with hexafluorotitanate ammonium (NH₄)₂TiF₆ as precursor. Compared with the conventional LPD processes, the MW-LPD technique could provide quickly high yield and crystallinity in a diluted precursor solution at a low temperature. Microwave irradiation penetrated and simultaneously heated the bulk of the material and led to higher heating efficiency with faster processing. The X-ray diffraction (XRD) and selected-area electron diffraction (SAED) studies on these powders indicated that the powders obtained with MW irradiation have much higher crystallinity with a single phase anatase. Scanning electron microscopy (SEM) images showed the information of continuous layers of titania on cotton fibers. UV-vis analyses revealed the coated titania produced an excellent UV protection of the coated fiber. The fibers with anatase coatings showed high photocatalytic property and better repetition on the photodegradation of methylene blue (MB).