炭／炭复合材料用基体前驱体的研究动态

介绍了几种炭／炭复合材料的基体前驱体的性质及制备方法。指出研制低成本、高性能、工艺性好的基体前驱体材料是研制低成本、高性能的炭／炭复合材料的关键。     

不同炭基体对炭/炭复合材料力学性能的影响

结合化学气相沉积（CVD）和前驱体浸渍裂解工艺,分别以丙烯、糠酮树脂和煤沥青为前驱体制备了密度在1.85g/cm3以上的三维炭/炭（C/C）复合材料,对比研究了沥青炭、热解炭+沥青炭以及热解炭+树脂炭结构（分别为A、B、C组）的等三种不同炭基体C/C复合材料的增密效率与力学性能,采用排水法表征C/C复合材料的孔隙率及密度,利用扫描电镜进行炭基体的微观结构表征,采用万用电子力学试验机进行拉伸强度、压缩强度、剪切强度等力学性能表征。结果表明,在热解炭质量含量相同的前提下,树脂浸渍裂解增密速率低于沥青浸渍裂解工艺,树脂炭基体孔隙率低于沥青炭基体。不同炭基体结构的C/C复合材料力学性能次序为：热解炭+树脂炭双元炭基体最高,纯沥青炭基体次之,热解炭+沥青炭双元炭基体最低,分析原因为热解炭与树脂炭双元炭基体的界面结合强度高,而沥青炭为混乱无序碳结构,热解炭和沥青炭双元炭基体界面结合强度弱,因此力学强度最低。     

Ni/SiO2催化制备炭/炭复合材料研究

利用常规化学气相渗透工艺，在针刺炭布预制体中添加3．5％，4．O％Ni／SiO2负载型金属催化剂，以丙烯作碳源气体，在750-900℃下，经过100h的沉积，炭／炭（C／C）复合材料的密度达到1．65g／cm^3，其催化沉积炭的速率比不舍催化剂时提高了3倍以上。该材料经高温处理后，氧化失重率低，氧化起始温度高。应用扫描电镜（SEM），X射线衍射分析（XRD）和光学显微镜观察了基体炭的形貌，分析了催化沉积炭和抗氧化机理。实验结果证明，用该催化化学气相渗透法制备C／C复合材料，周期短，成本低，抗氧化性能好。     

炭/炭复合材料的热物理性能

综述了炭／炭复合材料的热物理性能及其影响因素。炭／炭复合材料热导率的大小由炭纤维的类型、取向、体积分数以及基体的结构类型决定，热处理工艺也对它有很大的影响。炭／炭复合材料的热导率随温度升高一般先升高后降低。炭／炭复合材料在低温时具有负热膨胀系数，影响其这一性能的因素除了坯体结构和基体     

一种新型炭／炭复合材料的快速致密化工艺探

通过对化学液气相快速致密化这种新型炭／炭复合材料快速制备工艺的步研究,以PAN基炭毡为预制体,低分子液态烃为碳源前驱体,采用电磁感应加热,在900℃－1100℃温度内,3小时制备了密度为1．78g/cm^3的炭／炭复合材料。研究结果表明此工艺较传统工艺的致密化周期缩短了100倍以上,同时指出这种工艺快速致密化预制体的机制是由于预制体内存在较高温度梯度和碳源扩散过程受控于化学反应力学。     

炭基体结构状态对C/C复合材料抗烧蚀性能的影响

碳基体在C／C复合材料的组成中占有很大的比重，因此炭基体不同的结构状态往往对C／C复合材料的各项性能有显著的影响。本文利用不同的原料和加工工艺制备出了三种具有不同炭基体的C／C复合材料，这三种碳基体分别是热解炭，沥青炭以及解热炭－树脂炭混合炭基体。对这三种材料多项性能的测试结果表明，炭基体的结构状态如石墨化度，炭片层结构的取向度的不同对C／C复合材料的各项性能均有显著的影响；基本趋势是C／C材料的石墨化度越高，材料的导电性能，导热性能以及抗烧蚀性能越好，压缩强度越低。三种炭基体中沥青炭基体沿纤维轴向的取向度最低，其抗烧蚀性能最差。     

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。     

化学气相沉积(CVD)炭/碳复合材料(C/C)研究现状

主要介绍了炭／炭复合材料（C／C）的化学气相沉积（CVD0制备方法及其影响因素，以及热解炭的组织与沉积机理。概括了VCD的基本方法，如等温法、压差法、热梯度法等。分析了温度、气流速率、气体浓度、预制体及孔隙的形状大小状况等对CVD过程的影响。列举了热解炭的组织，包括光滑层、粗糙层、各向同性体碳以及它们的变体，并对其生长特征及性能进行了较详细的描述。综述了热解炭的沉积机理，典型的有分子沉积、固态沉积、液滴沉积机理等。     

预制体结构对炭／炭复合材料力学性能影响

四种用于制备炭／炭（C／C）复合材料的预制体，即1K发布叠层坯体（1#坯体），3K发布叠层坯体（4#坯体），发市 炭纸叠层坯体（2#坯体），特殊炭毡 发布叠层坯体（3#坯本），并探索了预制体结构对C／C复合材料力学性能影响．研究表明：用1#坯体制备的C／C复合材料弯曲强度最高，2#坏体制备的材料弯曲强度最低，随著炭纤维（CF）体积含量的增加，用四种坯体制备的材料弯曲强度增大。确定了弯曲强度的优化配方．     

钨酚醛树脂连接炭/炭复合材料的工艺研究

以钨酚醛树脂为原料基体，添加适量的钨粉，对炭／炭复合材料进行连接试验，测试了不同温度处理后连接处的室温剪切强度。结果表明，经1500℃处理后连接处仍保持较高的连接强度，最高可达16．1MP。。利用XRD和SEM研究了接头的组成和形貌，并探讨了钨粉含量及热处理温度对接头强度的影响。     

碳/碳复合材料等温化学气相渗透工艺模糊系统建模

等温化学气相渗透(chemical vapor infiltration，CVI)是制备陶瓷基和碳基复合材料重要的传统工艺，该工艺主要的不足之处是周期极长，因此，优化工艺参数、提高沉积效率是目前等温CVI工艺研究的重点。在实验样本的基础上，利用遗传算法来自动获取和优化模糊规则，从而建立了碳／碳复合材料等温CVI工艺模糊系统。通过系统对训练样本和测试样本的输出，可以看出：系统具有较高的精度和泛化能力。利用该系统，得到了沉积温度、纤维体积分数和沉积室压强等参数对等温CVI工艺的影响规律，对实际生产中CVI工艺的制定有指导意义。     

结构炭/炭复合材料力学性能及微观结构研究

采用四向编织、快速化学气相渗透致密化新工艺制备了炭／炭复合材料,其弯曲强度达３２０ＭＰａ。分析研究了这种材料的力学性能特征。利用ＳＥＭ和高分辨ＴＥＭ分析了基体炭、炭纤维／基体灰界面的精细结构,发现炭纤维呈单根被基体炭包围,基体现灰呈层片状,为二维有序的乱层石墨结构;在炭纤维与基体炭之间存在着过渡相,这一过渡相厚度的约几十纳米,随着与炭纤维之间距离的增大,它们之间形成的夹角由小变大,这一过渡相即为炭     

KOH-浸渍-还原法在炭纤维表面制备不同金属纳米催化剂涂层及其应用

为了催化炭纤维原位生长纳米炭纤维／纳米碳管，研究纳米炭纤维／纳米碳管在炭／炭复合材料中的应用，采用KOH-浸渍-还原法在炭纤维上制备纳米催化剂颗粒。首先用KOH处理炭纤维改变其形貌，然后将炭纤维分别在硝酸钴和硝酸镍催化剂前驱体溶液中浸渍，干燥，再用H2气还原制得催化剂颗粒，最后催化热解CO在炭纤维上原位生长纳米炭纤维／纳米碳管。结果表明：KOH处理能使炭纤维表面变得凹凸不平，有效的阻止了催化剂前驱体液体的流动，使涂层均匀；浸渍-还原法能获得粒径小、均匀、适合纳米炭纤维生长的金属颗粒；与Co纳米颗粒相比，Ni分散效果和催化效果更好。     

CVI工艺参数对C／C复合材料均匀致密化的影响

CVI工艺参数对炭／炭（carbon／carbon,C／C）复合材料的致密化速率、密度分布和性能有重要的影响,通过控制工艺参数可以在保证致密化速率的同时获得密度均匀分布的C／C复合材料,本文讨论了AS／VR比值、碳源气体、碳源气体分压、沉积温度和气体滞留时间对C／C复合材料均匀致密化的影响及这几个工艺参数的协同作用。     

化学液相气化渗透法制备炭/炭复合材料研究的进展

综合评述了化学液相气化渗透(chemical liquid vapor infiltration, CLVI)法制备炭/炭(C/C)复合材料的研究.概述了CLVI法的工艺特点及其快速致密的原理,并分别从预制体形状、发热体加热方式、前驱体种类等方面介绍了近年来各种改进的CLVI工艺.分析了制备方式、温度以及前驱体种类等对热解炭微观结构的影响.展望了CLVI法制备C/C复合材料的发展趋势.综合分析表明:目前,CLVI法尚不能满足应用于工业化生产的要求,今后将向多试样沉积、低能量消耗、前驱体高利用率等方向发展.     

Properties of Si/SiC ceramic composite subjected to chemical vapour infiltration

Si/SiC ceramic composite was prepared by infiltration of liquid silicon into carbon preforms that was made from cotton fabric and phenolic resin. This composite was subjected to the chemical vapour infiltration (CVI), using methyltrichlorosilane as a precursor gas. The effect of infiltration time on densification and mechanical properties was studied. Results show a significant improvement in density by pore closure. Flexural strength increases with increasing infiltration time. However, beyond 60 h of infiltration, the strength improvement was insignificant. The high temperature oxidation resistance of the above ceramics was also studied. The CVI treated samples show considerable resistance to oxidation compared to untreated samples. Thermogravimetric analysis also confirmed the better oxidation resistance of the CVI treated samples.     

Morphology and anti-ablation properties of PIP Cf/C–SiC composites with different CVI carbon content under 4.2 MW/m2 heat flux oxy-acetylene test

In this work, the needled carbon fiber preforms were used to make seven groups of carbon/carbon composite billets with different matrix carbon contents by controlling the processing time of chemical vapor infiltration (CVI). C_f/C–SiC composites were prepared by infiltration of SiC into these C/C composites billets using polycarbosilane (PCS) through precursor infiltration and pyrolysis (PIP). After oxy-acetylene torch testing (heat flux of 4.2 MW/m²) for 200s, 300s and 400s, respectively, it revealed that the anti-ablation properties of the C_f/C–SiC composite samples were enhanced by a higher content of SiC matrix. Additionally, specimens bearing longer duration tests showed a trend of lower average ablation rates. The lowest linear ablation rate is 0.008 mm/s and the mass ablation rate is 0.0019 g/s for those high SiC content samples tested for 400s. The SEM images of the tested samples showed the mechanism and the non-linear process of ablation resistance progression.     

Kinetics of pyrolytic carbon infiltration for the preparation of ceramic/carbon and carbon/carbon composites

Carbon/carbon and zeolite/carbon composites have been prepared by pyrolytic carbon infiltration of organic and inorganic substrates with different porous structures. The chemical vapour infiltration kinetics of these substrates has been studied in a thermogravimetric system at atmospheric pressure, using benzene as pyrolytic carbon precursor. The rate of pyrolytic carbon infiltration seems to depend on the porosity of the substrate available to the pyrolytic carbon precursor, irrespective of the nature of the substrate studied. Activation energy values of about 180 kJ/mol were found for the different substrates used in the temperature range of 700-800 °C, where the cracking reaction of benzene takes place, predominantly, in a heterogeneous form. At higher temperatures homogeneous reactions compete with heterogeneous ones and higher values of activation energies (280-380 kJ/mol) were obtained. The oxidation of the pyrolytic carbon deposited on the different substrates studied takes place in the same range of temperature, which suggests the presence of a similar pyrolytic carbon structure on substrates of different nature or a similar accessibility to the deposited layer.     

Catalytic graphitization of templated mesoporous carbons

Graphitic porous carbons with a wide variety of textural properties were obtained by using a silica xerogel as template and a phenolic resin as carbon precursor. The synthetic procedure used to prepare them was as follows: (a) infiltration of the porosity of silica by a solution containing phenolic resin, (b) carbonization of the silica-resin composite, (c) removal of the silica skeleton, (d) impregnation of the templated porous carbon with a metallic salt and (e) catalytic graphitization of the impregnated carbon by heat treatment at 900 °C. The graphitization of the carbons thus prepared varies as a function of the carbonization temperature used and the type of metal employed as catalyst (Fe, Ni or Mn). The porous characteristics of these materials change greatly with the temperatures used during the carbonization step. These graphitized carbons exhibit high electrical conductivities up to two orders larger than those obtained for the non-graphitized samples.     

Microstructures and tribological properties of carbon/carbon-boron nitride composites fabricated by powdered additives and chemical vapor infiltration

The carbon fiber reinforced/carbon-boron nitride (C/C-BN) dual matrix composites were fabricated via adding hexagonal boron nitride (h-BN) powders into the needled carbon felt and subsequent chemical vapor infiltration (CVI) process. An experimental investigation was performed to study the influences of BN volume content on the microstructures and tribological properties of C/C-BN composites. The results indicate that the pyrolytic carbon (PyC) in the C/C-BN composites is regenerative laminar (ReL) due to the inducement of BN powders during CVI process, whereas the PyC in the C/C composite is classic smooth laminar. Additionally, the friction coefficients of C/C-BN composites with three different BN contents in volume fractions (4.5, 9 and 13.5 vol%) are all higher compared to the reference C/C composite (0.22). Note that the highest coefficient of friction (0.29) is obtained when the BN volume content in the C/C-BN composite is 9 vol%. Moreover, the linear and mass wear rates of C/C-BN composites as well as the 30CrSiMoVA counterparts are significantly decreased with the increase of BN volume content. The favorable friction and wear properties of C/C-BN composites are attributed to the synergistic effect induced by the ReL PyC and BN. The microstructural variation of C/C composites modified by h-BN could improve the compatibility between the C/C-BN composites and 30CrSiMoVA counterpart, resulting in an enhanced adhesive attraction between the wear debris and the surface of 30CrSiMoVA counterpart. Furthermore, the investigations concerning the friction surfaces indicate that the formation of sheet-like friction films with large areas are more easily to occur on the surfaces of 30CrSiMoVA counterparts mating with the C/C-BN composites rather than mating with the C/C composite.