石墨化处理对高压浸渍碳化碳/碳复合材料抗氧化性能的影响

用超高压液相浸渍和碳化,经石墨化处理制备了毡基碳／碳复合材料。采用等温氧化实验,系统研究了所得试样在不同温度(773～1 173 K)条件下的氧化动力学行为;用X射线衍射和扫描电子显微镜检验观察了石墨化处理前后毡基碳／碳复合材料的氧化形貌和微观结构。结果表明：石墨化处理可明显的提高毡基碳／碳复合材料的抗氧化性能;毡基碳／碳复合材料的基体在氧化反应中优先氧化,氧化反应速率随温度的升高而增大;在高于或低于临界温度973 K时,毡基碳／碳复合材料的氧化反应分别受2种不同的机制控制,其反应活化能E,在石墨化前分别为7.91×10~4 J／mol和2.80×10~4J／mol,石墨化后分别为1.08×10~5J／mol和4.42×10~4J／mol。     

高炉炉缸炭砖的抗氧化性能

借助于热力学分析和氧化性能实验,研究了高炉炉缸用炭砖在空气气氛下的氧化行为和氧化动力学。结果表明,炭砖的质量损失主要来自于石墨C氧化,质量损失量随温度升高、保温时间延长而增大。炭砖的氧化过程属于连续型氧化,而非保护型氧化。在800~1 200℃时,氧化过程的控速环节为碳氧界面反应控速,氧化反应的活化能为5 586.76 J/mol。石墨C氧化将导致炭砖内部形成多气孔的氧化层,随温度升高和时间增加,氧化层面积增大,材料耐压强度和密度降低。     

原位气相生长碳纳米纤维改性炭/炭复合材料研究

采用化学气相沉积(CVD)法在不同密度的炭/炭复合材料表面原位生长碳纳米纤维(CNFs),探究不同工艺参数对CNFs微观形貌的影响规律,寻求最优化工艺。以原位生长CNFs改性C/C复合材料和纯C/C复合材料为研究对象,描述了CNFs的生长机制,并分别对2种试样进行石墨化度、力学性能和导热性能的检测分析,研究CNFs增强C/C复合材料性能的改性机理。结果表明:当催化剂前驱体Ni(NO_3)_2溶液的浓度为0.10 mol/L,裂解温度为650~700℃,反应时间为30~45 min时,所制备的CNFs直径细小均匀,一般为30~60 nm,长径比大,呈网状分布,分散性好。相同密度下,CNFs-C/C复合材料的弯曲强度达到166.29 MPa,比纯C/C复合材料(131.73 MPa)提高了26.2%,弯曲性能显著提升。原位生长CNFs改性C/C复合材料的室温z轴热导率为14.50 W/(m·K),是纯C/C复合材料的1.85倍。     

热解炭结构对C/C复合材料热物理性能影响

炭布叠层为预制体，采用等温CVI工艺制备出炭/炭（C/C）复合材料。通过调节丙烯与氢气的比例得到热解炭结构分别为粗糙层（RL），光滑层（SL），各向同性（ISO）的三种C/C复合材料，研究了热解炭组织结构对C/C复合材料热导率的影响，讨论了C/C复合材料的导热机理。结果表明：RL织构C/C复合材料的热导率无论是在平行方向还是在垂直方向上都明显高于SL和ISO织构C/C复合材料，在两个方向上，RL织构C/C复合材料的最大热导率比SL织构C/C复合材料分别大41.0%和31.7%，是ISO织构C/C复合材料的2倍多，且3种C/C复合材料的热导率随温度的升高呈现不同的变化趋势。     

基体炭种类对C/C复合材料电导率的影响分析

使用炭毡为增强体分别制备了热解炭基、树脂炭基、沥青炭基和热解炭/树脂炭双基体、树脂炭/沥青炭双基体C/C复合材料,比较研究了复合材料的电导率与不同先驱体含量的关系。结果表明,不同前驱体C/C复合材料电导率有较大的差异,热解炭基C/C复合材料的电导率是沥青炭基C/C复合材料和树脂炭基C/C复合材料电导率近3倍,热解炭和沥青炭双基体C/C复合材料的电导率符合简单并联混合法则,树脂炭和沥青炭双基体C/C复合材料的电导率随树脂炭质量分数的增加而减小。     

Pt/C催化氧化甲醛和甲酸反应动力学研究

目前草甘膦工业生产母液含大量甲醛,今采用Pt/C催化剂在反应过程中催化氧化甲醛以期提高母液循环套用效率。运用自制Pt/C催化剂研究甲醛和甲酸的氧化反应及其动力学。XRD和TEM测定表明,Pt/C催化剂中Pt的平均粒径为1.4 nm,分散性较好。消除内、外扩散影响后在反应压力0.6 MPa、搅拌转速800 r×min~(-1)、氧气流量120 mL×min~(-1)及反应温度323.15~353.15 K的条件下进行甲醛和甲酸氧化反应动力学实验,建立本征动力学模型并运用实验数据进行拟合计算得到动力学参数,甲醛氧化生成甲酸反应活化能为36.04 k J×mol~(-1),甲酸氧化反应活化能为19.93 k J×mol~(-1),甲醛与甲酸的吸附热分别为-60.26 k J×mol~(-1)和-39.96 k J×mol~(-1)。     

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。     

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。     

碳/碳复合材料氧化的研究进展

碳/碳(C/C)复合材料因比重轻、导电导热快等优异性能,成为航空航天领域应用的理想材料,但在643K以上温度的含氧环境中,碳/碳(C/C)复合材料易发生氧化而导致失效,因此,研究C/C复合材料的抗氧化性能非常必要。本文对C/C复合材料的氧化过程进行了总结,氧化过程主要是低温段的碳氧化学反应控制和高温段的氧气经边界层与碳反应的扩散控制。目前,针对C/C复合材料的抗氧化性弱的问题,有研究者提出,基体改性和涂层防护是提高材料抗氧化能力的主要方法。本文综述了静态氧化和高温氧化烧蚀的最新研究进展,从相关的研究进展可知,该材料的应用环境较为单一,为此本文基于海洋腐蚀环境,分析了C/C复合材料的氧化过程。     

催化氧化葡萄糖制葡萄糖酸的动力学

以Au/C为催化剂,在间歇反应釜中考察了搅拌速率、催化剂粒径和反应温度对催化氧化葡萄糖制备葡萄糖酸的影响,并利用Aspen Plus软件中内置的LHHW动力学方程对实验数据进行拟合.结果表明,Au/C催化葡萄糖合成葡萄糖酸反应的活化能和指前因子分别为8.5× 104 J/mol和3.2× 1011 mol/(g·s)....     

炭/炭复合材料抗氧化研究进展

C／C复合材料的高温氧化性能限制了其在高温领域的广泛应用。本文简要介绍了C／C复合材料的氧。化机理及两种主要的抗氧化技术，即抗氧化涂层技术和内部抗氧化技术，并就涂层的结构和发展趋势作了简要介绍。介绍了添加抑制剂磷和硼对C／C复合材料的高温氧化抑制，重点分析了将硼引入C／C复合材料的方法及硼在其中的接触氧化抑制和优先分配。对C／C复合材料的最新进展情况作了简要介绍，并对C／C复合材料高温抗氧化的研究方向提出自己的看法。     

碳／碳复合材料的性能和应用进展

碳／碳（C／C）复合材料是以碳为基体,碳纤维增强的复合材料,具有高比强度、高比模量、耐高温、耐腐蚀、耐疲劳、抗蠕变、导电、传热和膨胀系数小等一系列优异性能,既可作为结构材料承载重荷,又可作为功能材料发挥作用。同时,碳／碳（C／C）复合材料是一种能在超高温条件下工作的高温结构材料,所以在航空航天领域具有广阔的应用前景。本文综述了碳／碳（C／C）复合材料的制备相应力学、热学性能,化学性能和其在各领域的应用进展。     

Siliconization elimination for SiC coated C/C composites by a pyrolytic carbon coating and the consequent improvement of the mechanical property and oxidation resistances

Carbon/carbon (C/C) composites have a wide application as the thermal structure materials because of their excellent properties at high temperatures. However, C/C composites are easily oxidized in oxygen-containing environment, which limits their potential applications to a great degree. Silicon carbide (SiC) ceramic coating fabricated via pack cementation (PC) was considered as an effective way to protect C/C composites against oxidation. But the mechanical properties of C/C composites were severely damaged due to chemical reaction between the molten silicon and C/C substrate during the preparation of SiC coating by PC. In order to eliminate the siliconization erosion, a pyrolytic carbon (PyC) coating was pre-prepared on C/C composites by the chemical vapor infiltration (CVI) prior to the fabrication of SiC coating. Due to the retardation effect of PyC coating on siliconization erosion, the flexural strength retention of the SiC coated C/C composites with PyC coating increased from 46.27 % to 107.95 % compared with the specimen without PyC coating. Furthermore, the presence of homogeneous and defect-free PyC coating was beneficial to fabricate a compact SiC coating without silicon phase by sufficiently reacting with molten silicon during PC. Therefore, the SiC coated C/C composites with PyC coating had better oxidation resistances under dynamic (between room temperature and 1773 K) and static conditions in air at different temperatures (1773?1973 K).     

Microstructure,thermophysical properties,and ablation resistance of C/HfC-ZrC-SiC composites

Carbon/carbon composites modified by HfC-ZrC-SiC were fabricated by reactive melt infiltration with the aim of improving their ablation resistance for application in aerothermal environments. Their microstructure, thermophysical and ablation properties were investigated. Results show that the thermal diffusivity decreases with increasing temperature for all composites. The thermal conductivity of the C/HfC-ZrC-SiC composites decreasing with increasing HfC molar fraction is related to decreased grain size and increased porosity, which impede phonon interaction and increase the phonon scattering. High HfC content effectively improves the oxidation and ablation resistance of the composites. C/HfC-ZrC-SiC composites containing 8.8?mol.% HfC exhibited the best ablation resistance owing to a compact and continuous HfO₂-ZrO₂ mixed layer that formed on the ablated surface.     

A Si–Mo–W Coating to Protect SiC-Coated Carbon/Carbon Composites Against Oxidation

In order to protect carbon/carbon (C/C) composites against oxidation, a Si–Mo–W coating was prepared on the surface of SiC-coated C/C composites by a simple reaction method. The microstructures of the as-received coating were characterized by scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy analyses. The results show that the SiC/Si–Mo–W coating can protect C/C composites from oxidation in air at 1673 K for 220 h with a mass loss of 0.003%, and at 1773 K for 252 h with a mass gain of 1.56%. The excellent oxidation-resistant property of the SiC/Si–Mo–W coating at 1673–1773 K is attributed to the formation of SiO₂ film on the coating surface. The mass loss of the coated C/C composites during the oxidation test at 1873 K in air primarily resulted from the reaction of C/C substrate and oxygen diffusing through the penetration cracks in the coating.     

Advances in oxidation and ablation resistance of high and ultra-high temperature ceramics modified or coated carbon/carbon composites

Carbon/carbon (C/C) composites are considered as one of the most promising materials in structural applications owing to their excellent mechanical properties at high temperature. However, C/C composites are susceptible to high-temperature oxidation. Matrix modification and coating technology with ultra-high temperature ceramics (UHTCs) have proved to be highly effective to improve the oxidation and ablation resistance of C/C composites. In this paper, recent advances in oxidation and ablation resistance of C/C composites were firstly reviewed, with attention to oxidation and ablation properties of C/C composites coated or modified with UHTCs. Then, several new methods in improving oxidation and ablation resistance were discussed, such as by using nanostructures to toughen UHTCs coatings or carbon matrix and the combination of matrix modification and coating technology. In addition, relevant ablation tests with scaled models were also briefly introduced. Finally, some open problems and future challenges were highlighted in the development and application of these materials.     

A Review on Wear and Friction Performance of Carbon–Carbon Composites at High Temperature

Carbon–carbon (C/C) composite is one of the best ceramic matrix composite due to its high mechanical properties and applications at control environments in various sectors. Carbon–carbon composite is made of woven carbon fibers; carbonaceous polymers and hydrocarbons are used as matrix precursors. These composites generally have densities <2.0 g/cm³ even after densification. C/C composites have good frictional properties and thermal conductivity at high temperature. Also C/C composite can be used as brake pads in high‐speed vehicles. In spite of various applications, C/C composites are very much prone to oxidation at high temperature. Therefore, C/C composites must be protected from oxidation for the use at high temperature.     

纳米碳管和纳米二氧化硅修饰玻碳电极示差脉冲伏安法测微量铜

本文用纳米碳管和纳米二氧化硅修饰的玻碳电极以1mol/LH2SO4为底液测定Cu^2＋,方法是先在-0．5V进行预还原120s,然后用示差脉冲伏安法进行阳极扫描,发现在-0．04V（vs．SCE）处出现铜的氧化峰,且峰电流与Cu^2＋的浓度在5．0×10^-8～1．0×10^-2mol/L范围内呈良好的线性关系,该方法的检出下限为1．0×10^--8mol/L。用标准加入法测得回收率范围为92．3％～104．2％,相对标准偏差（RSD）为3．5％。将此电极用于实际样品的测定,取得较好的结果。     

Oxidation behavior and protection of carbon/carbon composites prepared using rapid directional diffused CVI techniques

The oxidation kinetics of carbon/carbon (C/C) composites prepared using a rapid directional diffused (RDD) CVI process were studied. The results showed that the Arrhenius curve for the RDD CVI C/C composites consists of two straight lines, the intercept of which is at about 700 °C at the linear oxidation stage. The oxidation rates are controlled by the surface reaction at 600-700 °C, and the corresponding activation energy is 121 kJ/mol. Between 700 and 800 °C, the oxidation rates are dominated by chemical reaction and diffusion, and the relevant activation energy is 80 kJ/mol. SEM investigation showed that the oxidation starts with original pores on the C/C composite surface with the carbon fiber and matrix oxidized simultaneously. An inexpensive and easily pasted coating containing epoxy organic silicon resin, borates, refractory particulates, etc. was developed. After isothermal temperature, thermal cycle and immersion water oxidation tests, the coating was demonstrated to exhibit good oxidation-resistance properties. The oxidation-resistant mechanism of the coating is discussed.     

炭纤维增强炭基复合材料的界面

炭纤维增强炭基（炭／炭）复合材料中的界面直接影响材料的力学、热物理、抗氧化等性能。深入对炭／炭界面的研究,对于改进材料结构,提高材料性能意义重大。因此对炭／炭复合材料界面研究的意义、方法、现状作了介绍,并展望了研究的发展趋向。