硼玻璃抗氧化炭材料研究

硼硅酸盐玻璃在高温下对炭材料以及炭／炭复合材料具有较好保护作用。本文对生成这种成本较低的硼硅酸盐玻璃膜的原料硅粉、三氧化二硼等进行了研究，并试着寻找能够生成致密、连续、牢固的保护膜的方法。实验表明硅粉、三氧化二硼在900℃～1100℃保护效果较差。     

炭／炭复合材料的氧化行为与防护

本文评论了炭/炭复合材料在空气中的氧化行为。讨论了氧化硼、基质抑制剂和玻璃状涂层对炭/炭复合材料氧化反应的抑制。     

抗氧化炭石墨材料的研究及高温氧化行为

采用了改善炭石墨材料基体抗氧化性能和用磷酸无机高分子复合盐处理后的内外结合的方法制备了一种抗氧化炭石墨材料。这种材料的特点是保持着炭石墨材料基体的特性如自润滑性,耐磨性、硬度、强度等,适用于高温富氧条件下长时间工作的动密封材料。参照ASTM─1179—91测试了650℃下空气中100小时的氧化失重。其氧化行为的分析结果表明,这种抗氧化石墨材料在650℃下空气中氧化失重达5％的时间为65小时,此时的氧化速率为4．4mg／g·hr。氧化60小时以后,氧化失重速率随时间的延长而迅速增加,出现了一个转折点。     

炭砖试样的氧化行为

研究了含Si粉的炭砖试样与不含Si粉的炭砖试样的CO2氧化行为2。结果发现：在炭砖中加入Si粉可明显降低其与CO2反应的速率,并使氧化反应的表观活化能大大提高。     

毡体热处理对炭/炭复合材料氧化行为的影响

将炭纤维毡体进行两组不同温度的高温热处理，然后采用化学气相沉积工艺制备炭／炭复合材料，考察了两组材料在不同温度、时间下的氧化失重率，利用X射线衍射技术分析了炭纤维的石墨化度，采用扫描电子显微镜观察了氧化前、后炭／炭复合材料的形貌，探讨了两组材料的氧化反应过程及其氧化行为差异的原因。     

炭材料的制法

炭材料制备工艺的特点是通过汽相沉积法在炭／炭复合材料表面涂覆第一层炭，然后，在此表面上用化学汽相沉积法，用陶瓷或用陶瓷和炭的混合物制成第二层涂履层，至少使第一层涂覆层的炭的热物理性能或者是机械物理性能两者中之一发生连续的或阶式的变化。     

4种炭素材料的抗氧化性能研究

在熔炼炉中对电极石墨、模压石墨、挤压石墨、等静压石墨4种炭素材料从室温逐渐加热至700℃,并在一定温度下保温1h,测其质量,绘制材料质量变化曲线图,以质量变化表征其抗氧化性的强弱.通过SEM、XRD等手段分析这几种炭素材料抗氧化性差异的本质原因.研究表明,这4种炭素材料的抗氧化性强弱顺序为等静压石墨、电极石墨、挤压石墨、模压石墨,影响石墨材料的抗氧化性能主要因素有石墨材料的石墨化程度、晶体结构缺陷、体积密度及杂质含量等.     

炭质材料在活化过硫酸盐高级氧化技术中的应用进展

在应用过硫酸盐高级氧化技术降解有机污染物的过程中,开发经济、高效、安全的新型活化技术至关重要并成为目前的研究热点。近年来,炭质材料凭借其自身独特的优势及发展前景迅速受到广泛的关注,有望成为应用于高级氧化技术的新一代绿色催化剂。本文综述了近几年来国内外关于各种炭质材料在活化过硫酸盐氧化技术中的研究应用进展,包括活性炭活化、不同类型的生物炭活化、表面化学改性炭材料活化、杂原子改性炭材料活化、炭材料负载金属及金属氧化物活化以及炭材料与其他技术耦合活化过硫酸盐降解有机污染物的研究现状,并探讨了该技术在应用过程中的运行成本问题,最后提出了该技术目前面临的问题及未来发展方向,期望为促进炭质材料活化过硫酸盐高级氧化技术的进一步推广和应用提供参考。     

Borate treatment of carbon fibers and carbon/carbon composites for improved oxidation resistance

Carbon fibers and carbon/carbon composites have been treated with borate additives and then cured at 500–600°C to produce a continuous film of boron oxide on all exposed surfaces.This treatment has been found to be highly effective in retarding oxidation of the carbonaceous substrate for extended periods in flowing air at temperatures up to 1000°C. At higher temperatures, and in the presence of water vapor, borate species were appreciably volatile and the oxidation protection provided by the coatings was less effective.     

Microstructure effects on the electrochemical corrosion of carbon materials and carbon-supported Pt catalysts

The electrochemical corrosion behavior of a set of porous carbonaceous materials of interest as catalyst supports for polymer electrolyte membrane fuel cells was examined in 2 M H₂SO₄ at 80 °C at constant electrode potential of 1.2 V vs. RHE. Correlations have been observed between the specific rates of corrosion of carbon materials and carbon-supported Pt catalysts on the one hand and their substructural characteristics derived from X-ray diffraction analysis on the other hand. Carbon supports of the Sibunit family and catalytic filamentous carbons possess lower specific (i.e., surface area normalized) corrosion currents compared to conventional furnace black Vulcan XC-72 and better stabilize Pt nanoparticles.     

Study of chemical bonds in carbon and boron materials by EPMA

This paper describes the study of chemical bonds in carbon and boron materials (single-crystalline graphite, natural diamond, boron carbide and pure boron) by electron probe microanalysis. BK and CK X-ray emission spectra of the investigated materials are presented and discussed.     

Influence of boron on structure and oxidation behavior of graphite fiber, P120

P120 fibers, derived from mesophase pitch, were substitutionally doped with boron in the concentration ranges of 200-4600 ppm. An oxidation study was carried out in dry air at 973, 1023, and 1073 K at 95 kPa. Boron is preferentially positioned into the less disordered core region and in the external surface area (skin) of the fiber. Upon oxidation these regions are preferentially protected. Oxidation rates decreased by a factor up to 3, varying with boron concentration, burn-off level and oxidation temperature. The activation energy of oxidation increased from 151 kJ/mol for heat-treated P120 fibers to 180 kJ/mol for fibers with 3300 ppm B, then decreased to 122 kJ/mol for fibers containing 4600 ppm of boron. The observed decrease in oxidation rate is directly attributed to the location and concentration of boron. Boron doping inhibits oxidation by blocking specific active sites. It is proposed that 1000 ppm B as a threshold concentration at which the electronic, chemical, and physical (structural) behavior could be modified.     

炭/炭复合材料抗氧化研究现状

总结了炭/炭复合材料抗氧化研究现状,重点介绍了抗氧化涂层的制备方法,包括包埋浸渍法、化学气相沉积(CVD)、溶胶-凝胶法(Sol-Gel)和水热电沉积法以及近几年针对抗氧化涂层开裂问题各国学者的最新研究成果。提出了炭/炭复合材料抗氧化研究今后努力的方向。     

Hard boron rich boron nitride nanoglasses

Boron‐rich amorphous boron nitride (B_xN_1?x, 0.55 ≤ x ≤ 0.95) alloys are generated by means of ab initio molecular dynamics simulations and their local structure, mechanical properties and electronic structure are exposed. BN:B phase separations are perceived in all amorphous networks, suggesting that these materials can serve as nanoglass ceramics. The sp² hybridization is the main building unit in the BN‐rich regions for low boron concentrations, and the models carry locally the signature of the two‐dimensional hexagonal BN structure. The amorphous states having both sp² and sp³ hybridizations form for boron contents between 70% and 80%. At higher boron concentrations, sp³ hybridization with a fraction of ~90%‐98% is detected as seen in the cubic or wurtize BN crystals. In the boron rich regions, the ideal and defective pentagonal pyramids emerge at 60% boron content, and the first complete B₁₂ molecule develops at 70% boron concentration. In addition to the B₁₂ icosahedron, the formation of a cage‐like B₁₆ molecule is, for the first time, discovered in some amorphous alloys. The isolated B₁₆ molecule is, however, found to be unstable. The Vickers harness calculations reveal that some of these amorphous alloys can serve as hard materials. When their electron properties are considered, all amorphous materials are predicted to be semiconducting.     

The role of substitutional boron in carbon oxidation

An experimental and theoretical study of carbon oxidation in the presence of substitutionally doped boron has been carried out. The effects of boron loading, reaction temperature and degree of burnoff were analyzed for a range of carbon materials. Both inhibiting and catalytic effects were observed. Several semiempirical molecular orbital modeling approaches were used in an attempt to rationalize these intriguing experimental findings in terms of electronic effects in the graphene layer. In particular, a critical analysis of the key adjustable parameters was performed. The oxidation results were discussed in terms of a balance between three potentially competing effects of substitutional boron: (a) reduced total electron density; (b) decreased contribution of delocalized π electrons to the electron density of the remaining carbon atoms; and (c) σ electron localization on carbon atoms due to the higher electronegativity of carbon with respect to boron.     

Preferential distribution and oxidation inhibiting/catalytic effects of boron in carbon fiber reinforced carbon (CFRC) composites

Two different batches of CFRC composites were prepared in the absence/presence of B with the expectation of increasing oxidation stability and improving the processing compatibility of CFRC composites in commercial applications. The composites were examined to reveal the nature of substitutional B in oxidation, crystallinity and distribution preference in the composites. Substitutional B acts both a catalyst and an inhibitor in carbon oxidation, depending on the content and the extent of carbon burn-off reaction. Crystallinity increases with the incorporation of B, as expected; d₀₀₂ decreases, and L_c and L_a increase. Boron prefers to be distributed in the less ordered structure; non-graphitizable PAN-based carbon fibers have higher B contents than graphitizable coal-tar pitch, but processing conditions can change this preference. The incorporation of B in CFRC composites seems to be beneficial for improving the potential ability of the composites in applications by increasing crystallinity and oxidation stability.