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。     

影响C／C复合材料中热解炭结构的工艺因素

热解炭结构是影响C／C复合材料性能的重要因素,通过工艺条件的控制可以得到理想的热解炭结构,文章综述了影响C／C复合材料中热解炭结构的几类工艺因素,并对其作用机理进行阐述。     

C/C复合材料中基体炭的微观结构表征

采用扫描电子显微镜、金相偏光显微镜对不同结构基体炭，包括热解炭、沥青炭、树脂炭进行形貌表征和分析。通过试验观察到热解炭的微观结构主要分为粗糙层结构、光滑层结构、过渡层结构和各向同性结构，热解炭表面为球冠形结构；沥青炭的主要形貌结构主要有镶嵌型结构，区域与镶嵌并存结构，区域与流线型并存结构，流线型结构；树脂碳的结构主要为表面光滑的块状结构。     

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。     

化学气相渗（CVI）C／SiC复合材料性能控制

本研究用化学气相渗技术制备了四种Ｃ／ＳｉＣ复合材料：在ＣＨ３ＳｉＣｌ３＋Ｈ２（普通）＋Ａｒ（高纯）系统中制各了两种材料：材料Ａ为１Ｋ炭布层叠无热解炭界面层，材料Ｂ为１Ｋ炭布层叠有热解炭界面层；在ＣＨ３ＳｉＣｌ３＋Ｈ２（高纯）＋Ａｒ（高纯）系统中制备了另两种材料：材料Ｃ和材料Ｄ分别为１Ｋ、Ｔ３００炭布层叠有热解炭界面层．分别对其中每两种材料进行了相互比较，研究了骨架纤维、界面层及基体对整个复合材料性能的影响；通过控制上述三方面因素可以对Ｃ／ＳｉＣ复合材料的总体结构进行设计从而控制其材料最终性能。     

多晶硅炉热场用C/C复合材料的硅化腐蚀失效机理

以2D叠层炭布为增强体的炭/炭（C/C）复合材料作为多晶硅炉用热场盖板,对其在硅液/硅蒸汽共同作用下的硅化腐蚀失效机理进行了研究。通过多功能密度测试仪、扫描电子显微镜（SEM）和X射线衍射仪（XRD）分析了硅化作用对C/C复合材料致密度、微观结构及物相组成的影响,并对侵蚀后的C/C复合材料失效机理进行了分析。结果表明：硅化侵蚀后的C/C复合材料致密度高,存在大量的Si元素,生成了大量的β-SiC,且微观缺陷较多,层间开裂严重,呈现脆性断裂模式。理论分析发现,高温下单位摩尔质量的热解炭和单位摩尔质量的硅发生反应生成单位摩尔质量的SiC后,总体积膨胀约为单位摩尔热解炭体积的6.3倍,不同物相间的热失配导致热应力集中,引起C/C复合材料变形开裂失效,裂纹产生的扩散通道加剧了硅液/硅蒸汽对C/C复合材料的硅化侵蚀作用。     

C/C刹车盘制备工艺的研究

选择整体针刺毡为预制体，致密化工艺采用气相沉积(CVD)，以天然气和丙烷的混合气体为原料，制备C／C刹车盘。其热解炭以粗糙体为主，摩擦曲线平稳，没有湿态衰减，沉积时间短。     

C/C复合材料CVI致密化过程及影响因素研究进展

综述了C/C复合材料CvI致密化过程中,气相反应、表面反应和扩散共同作用控制热解炭沉积的特点;讨论了沉积温度、气体压力、碳源气体种类、滞留时间、预制体等因素的影响.     

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。     

化学气相沉积致密针刺C/C复合材料的结构及力学性能研究

以T300炭纤维无纬布、网胎为原材料,层叠针刺成型炭纤维预制体,并采用化学气相沉积工艺对预制体进行致密,制成密度为1.55 g/cm3的针刺C/C复合材料。对针刺C/C复合材料的微观结构进行了观察分析,并对材料力学性能进行了测试。结果表明:化学气相沉积致密的针刺C/C复合材料呈现出以层间大量垂直纤维束为节点的类钉板状网状结构,这种特殊结构使材料层间结合更好,材料整个结构更加紧密;针刺C/C复合材料内部纤维被沉积形成的热解炭所包裹,热解炭的织构类型为光滑层(SL)和粗糙层(RL)并存;针刺C/C复合材料的各项力学性能均达到了较高水平,并且高温力学性能比常温力学性能有了很大幅度的提高。     

高性能C/C复合材料制备工艺研究

对制备C/C复合材料的化学气相渗透工艺进行了系统的实验研究,着重分析了热解碳的沉积过程。研究表明,在化学气相渗透的初始阶段,热解碳主要在碳纤维表面沉积,并与碳纤维之间形成了界面结合;随后,热解碳的沉积继续填充碳纤维预制体内部的气孔。这一过程有助于缓解纤维与陶瓷基体之间的界面应力。研究表明,通过调节热解碳的沉积时间可以得到具有一定密度梯度的C/C复合材料。     

炭／炭复合材料CVI致密化技术的研究与发展

详细介绍了CVI理论的建立和发展,并在此基础上,对化学气相渗透中的气相组成与显微结构变化的关系,即气相组成变化对热解炭显微结构的影响进行了全面的分析。在介绍化学气相渗透技术发展的同时对化学气相渗透技术的最新进展进行了综述,特别是详细介绍了强制流动CVI、限域变温强制流动CVI、等离子体增强等温(或热梯度)低压CVI、HCVI技术、液相气化CVI等CVI新技术近几年来的最新发展,并在文后对未来化学气相渗透技术的发展进行了展望。     

针刺炭纤维预制体结构单元对C/C复合材料性能的影响

采用6K炭纤维无纬布/网胎交替叠层及12K炭纤维无纬布/网胎交替叠层,在针刺工艺,致密化、热处理工艺完全相同的情况下,制备了密度为1.8g/cm3的热解炭/树脂炭双元基体的两种C/C复合材料产品,考察了针刺预制体结构单元对C/C复合材料性能的影响.结果表明,两种C/C复合材料的热学（垂直方向导热系数）、电学性能及石墨化度基本相当;而针刺6K炭纤维无纬布/网胎预制体C/C复合材料的拉伸、弯曲、压缩、层间剪切强度分别为127MPa,189MPa,263MPa,24.6MPa;其平行方向导热系数为54.6W/m＆#183;K,比常规针刺12K炭纤维无纬布/网胎预制体C/C复合材料相应提高了38％,32.2％,32.8％,38.9％,21％,彰显了细化针刺预制体结构单元对C/C复合材料力学性能的显著影响.     

Reaction Mechanism and Microstructure Development of Zr–Si Alloyed Melt‐Infiltrated ZrC‐Modified C/C Composite

ZrC ceramic modified‐C/C composite is prepared by a quick and low‐cost reactive melt infiltration process with a Zr‐Si8.8 alloy. Reaction kinetics and mechanism of pyrolytic carbon with the infiltrated Zr‐Si8.8 alloy are investigated. A continuous ZrC layer is found to be formed around pyrolytic carbon due to the in situ reaction and its thickness parabolically increases with an increase in reaction time period. Zr concentration in the alloyed melts decreases due to the reaction between Zr and pyrolytic carbon and Zr₂Si phase precipitates from the residual alloyed melts. A model for the growth of ZrC layer is established to describe the reaction kinetics of pyrolytic carbon with Zr‐Si8.8 alloy. The calculated thickness of the reaction‐formed ZrC layer is in good agreement with the experimental data. Based on the Arrhenius equation, the activation energy of the reaction between carbon and Zr‐Si8.8 alloy is 313.2 KJ/mol, smaller than that of the reaction between carbon and pure zirconium. The microstructure of the reactive melt‐infiltrated ZrC‐modified C/C composite is characterized by optical microscope, SEM, EDS, XRD, and TEM. The mechanism of the reaction between pyrolytic carbon and Zr‐Si8.8 alloy is discussed on the basis of the characterization results and phase diagram. A schematic is proposed to understand the reaction mechanism between pyrolytic carbon and Zr‐Si8.8 alloy and microstructure development of the ZrC‐modified C/C composite.     

高炭树脂芳基乙炔聚合物炭化过程研究(Ⅱ)

通过XRD、FTIR和DTA等分析方法研究了芳基乙炔聚合物的炭化过程,结果表明:芳基乙炔聚合物的炭化过程可大致分为3个阶段;炭化温度在350～500℃时,聚合物结构变化较小;炭化温度在500～600℃时,聚合物主链结构被完全破坏,并转变为玻璃炭结构;炭化温度在600～900℃时,随炭化温度的增加,炭化物由玻璃炭结构逐渐向乱层石墨结构转变。     

Microstructure and mechanical performance evolution of C/C–ZrC composites exposed to oxyacetylene flame

C/C–ZrC composites were prepared by isothermal chemical vapor infiltration (ICVI) combined with reactive melt infiltration (RMI). The ablation behavior of the C/C–ZrC was investigated using an oxyacetylene flame. The effect of ablation time on the microstructure and mechanical property evolution of the composite was studied. The results showed that as the ablation time prolonged, the linear and mass ablation rates of the composite increased firstly and then stabilized. After 15 s ablation, the flexural strength and modulus of the C/C–ZrC were interestingly increased by 141.8% and 40.9%, which reached 138.42 MPa and 6.45 GPa, respectively. During ablation, the preferential oxidation effect of ZrC could mitigate the oxidation of pyrolytic carbon (PyC) and carbon fibers, and the volume change induced by the ZrC →ZrO₂ phase transformation could weaken its bonding with PyC, which was beneficial for releasing the internal residual stresses of the C/C–ZrC and then contributed to the mechanical performance improvement.     

Effect of HfC nanowires grown on carbon fibers on the microstructure and thermophysical properties of C/C composites

One-dimensional (1D) hafnium carbide nanowires (HfCnws) were grown in situ on carbon fibers (CFs) via a Ni-assisted pyrolysis method of organometallic polymer precursor. Scanning electron microscopy (SEM), transmission electron microscope (TEM), polarized-light optical microscopy (PLM), and Raman were used to analyze the effect of HfCnws on the microstructure of pyrolytic carbon (PyC). The specific heat capacity (HC), thermal diffusivity (TD), thermal conductivity (TC), and coefficient of thermal expansion (CTE) of HfCnws-C/C composites were also investigated. Results show that HfCnws wrapped by carbon nanosheet were successfully synthesized. The diameter of HfCnws is about 30 nm and the thickness of carbon nanosheet is about 10 nm, which could induce the formation of isotropic (ISO) PyC. After introducing HfCnws, the TD and CTE of HfCnws-C/C composites were increased. Ni2HfCnws-C/C composites show a higher TC and TD, and the CTE increased with the increasing content of HfCnws.     

W2C/AC催化快速热解松木磨木木质素

以活性炭（AC）为载体制备了不同钨负载量的W₂C/AC催化剂,将其和松木磨木木质素（MWL）机械混合后进行Py-GC/MS（快速热解-气相色谱/质谱联用）实验,考察了钨负载量、催化剂/MWL比例对产物分布的影响,并通过外标法对主要产物（芳烃类和酚类）的真实产率进行了定量分析。结果表明,W₂C/AC催化剂可有效促进木质素的热解解聚生成单酚类产物,并对酚类产物具有脱羰基、脱甲氧基、脱羟基以及加氢的效果,从而促进稳定的酚类产物（不含羰基、甲氧基和不饱和碳碳双键）和芳烃类产物的生成。在4种W₂C/AC催化剂中,10%-W₂C/AC的催化效果最佳,在催化剂/MWL比例为5时热解产物总产率达到最大值,此时芳烃类和酚类产物的总产率由无催化剂时的21.2 mg·g^-1和151.0 mg·g^-1增加至102.1 mg·g^-1和191.1 mg·g^-1。     

限域变温强制流动CVI工艺制备C／C复合材料的组织及力学性能特点研究

分析了采用限域变温强制流动CVI工艺制备C/C复合材料的组织及力学性能的特点,结合C/C复合材料的组织形成规律和组织对性能的影响规律,详细研究了在同一工艺条件下所获得的具有不同组织和不同力学性能的C/C复合材料的力学性能及组织分布规律,并从微观组织结构的角度对力学性能的变化规律给予解释。     

Influence of the deposition parameters on the texture of pyrolytic carbon layers deposited on planar substrates

Pyrolytic carbon layers were deposited from methane on planar substrates (pyrolytic boron nitride) at various residence times, methane pressures and deposition temperatures. The depositions were performed in a cavity oriented perpendicular to the gas flow. The small surface area/reactor volume ratio of the reactor geometry allows depositions in the growth and nucleation mechanism. Transmission electron microscopy was applied to study the texture and microstructure of the carbon layers. A texture transition from medium- to high-textured pyrolytic carbon occurs as a result of increasing residence times, methane pressures and temperatures. Improved textures are generally correlated with increasing deposition rates, which are not necessarily constant during long-term depositions. Lower textures are observed in the vicinity of the substrate interface that are attributed to the influence of the substrate morphology and microstructure.