The effect of graphite addition on the mechanical and tribological properties of pitch-based granular carbon composites

The present work deals with the effect of graphite addition on selected mechanical and tribological properties of pitch-based granular carbon composites. Three pitches (a commercial impregnating coal tar pitch, an air-blown pitch and a thermally treated coal tar pitch) and anthracite particles as reinforcing material were used to prepare carbon composites to be tested as carbon brake pads. These carbon composites show good compression strength (from 25.8 to 94.2 MPa) but unstable and high friction coefficients (>0.5). Experimental results have showed that small amounts of graphite addition (2.5 and 5.0 wt%) lead to carbon materials with more stable and lower friction coefficient (<0.3). So, graphite addition promoted the reduction in the wear rate. Finally, compressive strength of carbon composites prepared with modified pitches significantly increases after addition of small amounts of graphite with values from 94 to 128.8 MPa.     

A comparative study of the characteristics of baked carbon mixes employing different filler materials

A study of the physical characteristics of baked carbon mixes employing calcined petroleum coke, coal-tar pitch coke, metallurgical coke and anthracite coal has been made to explore their relative suitability and area of application. It is revealed that petroleum coke and pitch coke lead to a carbon product of almost the same density and electrical resistivity. However, the crushing strength of the product employing pitch coke is 1 1/2 times that of the one employing petroleum coke. The carbon product produced from the metallurgical coke is found to be slightly inferior in respect of density and electrical resistivity and slightly superior in respect of crushing strength when compared with that made from petroleum coke. The use of anthracite coal results in a carbon product of significantly lower density and much higher electrical resistivity than that of the product using the petroleum coke. However, the strength of the anthracite coal-based carbons is found to be nearly double that of the petroleum coke-based carbons. Thus, the significance of the present study lies in the fact that the above findings help one to estimate a possible filler composition for a carbon product possessing the desirable critical characteristics.     

沥青基碳/碳复合材料的组织特性

以 １Ｋ ＰＡＮ基碳纤维为增强体、以调制中温煤沥青为基体前躯体,分别在常压下和高压（４０ＭＰａ、８０ＭＰａ）下制备出了沥青基碳／碳复合材料。借助偏光显微镜对碳／碳复合材料试样进行的微观组织的观察发现,碳基体中既有域组织,也有镶嵌组织,而焦炭主要为细镶嵌组织．偏光试样经过酸液氧化腐蚀处理后,利用电子显微镜对其扫描观察,发现各向异性区域呈现出流线组织特征,流线纹路的疏密与沥青碳化时的压力有关．压力越高,纹路越密实,表明碳层面的取向性也就越好．     

碳/碳复合材料基体用中间相沥青

中间相沥青具有高残碳率、高密度、低的密度变化及易石墨化等优点 ,是较理想的碳 /碳 (C/C)复合材料基体前驱体。本文从 C/ C复合材料制备工艺的角度 ,阐述了制备 C/ C复合材料用的中间相沥青的主要特性 ,其中包括中间相沥青的流动性、在碳化过程中的稳定化、微观结构以及中间相沥青基 C/ C复合材料的界面结构。     

为化剂对沥青浸渍性能的影响

通过采用常压热缩聚、压力热缩聚、硫氧化等常规工艺和以呋喃树脂、均四甲苯和石油沥青为共炭化剂进行共炭化的方法对煤沥青改性,比较了不同工艺和不同共炭化剂对改善沥青浸渍剂综合性能的效果,希望提高沥青浸渍剂产炭率的同时使沥青仍保持良好的流动性。研究结果表明,硫氧化法使沥青产生了过度的交联,很高软化点的沥青只具有较低的产炭率水平;压力热缩聚可以得到综合性能较好的浸渍剂沥青。而通过选用合适的共炭化剂,可以进一步改善沥青浸渍剂的综合性能;石油沥青共炭化在经济上具有一定的优势。     

不同煤焦油沥青与吡啶烷的反应性能的比较

以三种不同的煤焦油沥青为原料,分别与吡啶硼烷反应制备了硼取代中间相沥青。比较了它们的软化点、残炭值、四氢呋喃不溶物（THFI）以及中间相的偏光显微结构。发现煤焦油沥青不同所得结果有显著差别：较高软化点的沥青与吡啶硼烷的反应活性较强,而相同软化点的净化煤焦油沥青与吡啶硼烷具有更强的反应性,所得中间相沥青的软化点,残炭值及四氢呋喃不溶物的含量较高,其偏光显微结构也证实了这一点。     

粒状增强体种类对沥青基炭复合材料性能的影响

采用普通液压机及新型的模压半炭化成型工艺,在大气环境下制备出了高密度、低成本、应用广的三种焦炭(冶金焦、沥青焦Ⅰ和沥青焦Ⅱ)颗粒增强的沥青基炭复合材料(简称PCCs).通过对PCCs材料先后进行快速焙烧处理,沥青浸渍-炭化致密化处理和高温石墨化(2373K)处理,制得了PCC材料的焙烧样品、致密化样品和石墨化样品.通过力学性能试验,SEM和XRD等方法,研究了增强体焦炭颗粒的种类对沥青基炭复合材料的体积密度和抗压强度的影响.结果表明:PCCs材料抗压强度的高低,除了与其体积密度相关外,还与其所采用的增强体焦炭颗粒的耐压强度、微观结构和表面状态有密切的关系.焦炭颗粒的耐压强度愈高、表面越粗糙、开孔孔隙越多,其对沥青基炭复合材料的增强作用也就越显著.无论PCCs材料是焙烧样品、致密化样品、还是石墨化样品,用磨碎冶金焦制备的PCCs材料的三种样品的抗压强度最大,用沥青焦Ⅱ制备的PCCs材料的次之,用沥青焦Ⅰ制备的CRPCC材料的最小.粒状增强体的种类对CRPCC材料的力学性能不仅具有非常重要的影响,而且其强度也具有一定的遗传性.     

炭化压力对沥青成焦形貌及航空刹车用C/C复合材料浸渍增密效果的影响

将武钢中温沥青和太钢高温沥青在不同压力下炭化，进一步对所得沥青焦进行了高温热处理，利用扫描电子显微镜（SEM）和光学显微镜观察所得沥青焦形貌。结果表明；低压炭化时，沥青焦体积密度小，疏松、多大孔，主要为流线区域型各向异性结构；高压炭化时，沥青焦体积密度明显变大，孔变小且均匀分布，主要为小区域和细镶嵌型各向异笥显微结构。考察了不同炭化压力对浸渍增密航空刹车用C／C复合材料的增密效率的影响，结果显示，对整个沥青而言的宏观残炭率明显高于只针对样品而言的实际残炭率，因此有必要进行高压浸渍／炭化实现快速增密。利用XRD和显微硬度测试仪检测了不同炭化压力所得沥青焦热处理后的石墨化度和显微硬度，发现高压下形成的沥青炭更难于石墨化，但石墨化度与显微硬度的热处理后的粗糙层（RL）CVD炭有较好的可比性。     

工艺条件对硼取代聚芳烃中间相沥青性能的影响

以煤焦油沥青和吡啶硼烷为原料采用加压热缩聚工艺制备硼取代聚芳烃中间相沥青,考察了硼添加量,反应温度和反应时间对中国间相沥青的收率、软化点、残炭值、四氢呋喃的的含量以及硼含量的影响。发现在同一热缩聚条件下随硼添加量的增加,中间相沥青的收率降低,但其软化点、残炭值及四氢呋喃不溶物却相应提高,８０％～９０％的硼被保留在反应产物中,对于相同的硼添加量,反应温度的提高及反应时间的延长对中间相沥青的收率和性能     

前驱体对炭泡沫孔结构的影响

分别以煤沥青、石油中间相沥青和AR沥青为前驱体制备炭泡沫材料。采用GPC测定前驱体分子量,SEM观察所制炭泡沫的孔结构,光学显微镜测量所制炭泡沫的孔径及其分布。结果发现,由于煤焦油沥青不含中间相,且QI含量较高,导致在实验条件下不能直接制备出合格的炭泡沫。以石油中间相沥青和AR沥青为原料均能制备出具有分布均匀开孔结构,且微观各向异性的炭泡沫。由AR沥青制备的炭泡沫呈现平均孔径较小(212μm)、孔壁较薄、孔径分布较窄(180μm~300μm)、开孔率较高、以及韧带排列较规整等特点,表明低QI含量、低分子量且分布较窄的前驱体有利于发泡。     

Carbonization of coal-tar pitch into lump needle coke in a tube bomb

The carbonization of coal-tar pitches and their QI (quinoline insoluble)-free fractions was studied by evaluating their lump cokes produced in a tube bomb at various temperatures (470 to 550° C) and pressures (0 to 75 kg cm^–2 gauge). The lump coke from QI-free fractions had a comparable anisotropic development and coefficient of thermal expansion (CTE). The carbonization temperature and pressure were found to influence strongly the properties of the cokes. At the highest temperature of 550° C, the most appropriate pressure for the best needle coke was 15 kg cm^–2 G (gauge). Either higher or lower pressure increased the CTE value of coke. In contrast, at a moderate temperature of 500° C, the higher pressure produced the better coke. At the lowest temperature of 470° C, it took 10 h to complete the carbonization, and the lowest pressure allowed the best extent of uniaxial arrangement. Among the cokes prepared under the present conditions, the Carbonization at 500° C under 40 kg cm^–2 G produced the best needle coke with a CTE value as low as 0.1 × 10^–6° C^–1. The carbonization scheme leading into the needle coke is discussed for a better understanding of how the carbonization temperature and pressure cooperatively influence the quality of the resultant coke, in relation to the carbonization reactivity of coal-tar pitch.     

Influence of coal tar pitch coating on the properties of micro and nano SiC incorporated carbon–ceramic composites

Carbon-micro or nano silicon carbide–boron carbide (C-micro or nanoSiC–B₄C) composites were prepared by heating the mixtures of green coke and carbon black as carbon source, boron carbide and silicon at temperature of 1,400 °C. Green coke reacts with silicon to give micron sized silicon carbide while the reaction between silicon and carbon black gives nano silicon carbide in the resulting carbon–ceramic composites. The green coke was coated with a suitable coal tar pitch material and used to develop carbon-(micro or nano) silicon carbide–boron carbide composites in a separate lot. The composites were characterized for various properties including oxidation resistance. It was observed that both types of composites made from uncoated as well as pitch-coated green coke exhibited good oxidation resistance at 800–1,200 °C. The density and bending strength of composites developed with pitch-coated green coke improved significantly due to the enhanced binding of the constituents by the pitch.     

具有中间相沥青过渡层的炭/炭复合材料的微观结构与力学性能

采用液相浸渍-炭化和CVI复合工艺, 制备出在炭纤维和热解炭之间具有中间相沥青过渡层的炭/炭复合材料, 借助偏光显微镜、扫描电镜、透射电镜以及力学性能测试研究了所制备的炭/炭复合材料的微观结构与力学性能. 结果表明: 在偏光显微镜下中间相沥青炭的光学活性高于热解炭的光学活性, 中间相沥青炭在SEM和TEM下均呈片层条带状结构, 热解炭在SEM下呈“皱褶状”片层结构, 在TEM下为粒状结构; 在HRTEM下, 中间相沥青炭、热解炭和炭纤维的晶化程度依次降低. 在加载过程中, 材料内部多层次的界面通过改变裂纹扩展路径而延缓其扩展速度, 在断口形貌上体现出锯齿状的断裂形式, 纤维拔出长度适中, 材料表现出韧性破坏的断裂特征. 材料具有较高的力学性能, 抗弯强度达到244MPa, 断裂韧性达到9.7MPa·m^1/2.     

高密度石墨泡沫及其石蜡复合材料的热物理性能(英文)

以中间相沥青和添加中间相炭微球的沥青为原料,调整发泡压力和发泡温度制备沥青泡沫,经1273K炭化和2973K石墨化,制备了高密度石墨泡沫。为了进一步提高石墨泡沫的密度,采用573 K的沥青反复浸渍炭化未添加中间相炭微球的沥青在1273K下所制的泡沫炭,再经2973K石墨化获得增密度后的石墨泡沫。而后制备了相应石墨泡沫/石蜡复合材料。研究了石墨泡沫热物理性能的影响因素和石墨泡沫/石蜡复合材料的热行为。研究表明:沥青组分、发泡温度和发泡压力决定了石墨泡沫的结构和热物理性能,而石墨泡沫的热导率决定了复合材料的热行为。与石蜡相比,石墨泡沫/石蜡复合材料的热扩散系数提高了768至1588倍。石墨泡沫/石蜡复合材料的潜热与石蜡的质量分数成正比。该复合材料是快速响应电子散热材料的良好选择。     

一维高导热C/C复合材料的制备研究

以三种沥青作为基体前驱体, 实验室自制的AR中间相沥青基纤维为增强体, 通过500℃热压成型, 随后经炭化和石墨化处理制备出一维炭/炭(C/C)复合材料。研究了前驱体沥青种类和热处理温度对复合材料导热性能的影响, 并采用扫描电子显微镜和偏光显微镜对其石墨化样品的形貌和微观结构进行表征。结果表明; C/C复合材料在沿纤维轴向的室温热扩散系数和导热率均随热处理温度的升高而逐渐增大; 由AR沥青作为基体前驱体所制备的C/C复合材料具有更加明显的沿纤维轴向取向的石墨层状结构以及最好的导热性能, 其3000℃石墨化样品沿纤维轴向的室温热扩散系数和导热率分别达到594.5 mm²/s和734.4 W/(m·K)。     

添加剂对煤沥青的改性作用及沥青焦性能的影响

通过考察添加剂加入量与煤沥青的甲苯不溶物含量、软化点、析焦量以及所得沥焦的抗氧化性和石墨化活性的关系,探讨了添加剂对煤沥青的改性作用及其对沥青焦性能的影响。实验结果表明：在煤沥青中加入适当的添加剂可提高煤沥青的甲苯不溶物含量和析焦量,加入添加剂的煤沥青炭化后所得沥青焦的抗氧化性和石墨化活性均得到显著提高,但氧化残余物含量有所上升。该沥青焦经2300℃高温石墨化处理后仍表现出优良的抗氧化性。     

Carbonization and graphitization of meso-carbon microbeads prepared by the emulsion method

Meso-carbon microbeads (MCB) prepared from coal-tar and fluid catalytic cracking (FCC)-decant oil pitches by an emulsion method were carbonized and graphitized. When using the thermosetting process as a pretreatment, the weight gain of MCB by oxidation was approximately 5 wt%, and Fourier transform-infrared measurement showed that the oxidation occurred mainly at aliphatic components in MCB. In the course of carbonization, a heat treatment at 700°C eliminated the C-H groups and the oxygen-containing functional groups, which had remained partly at 500°C. MCB were fairly graphitizable, considering the high values of obtained from X-ray diffraction measurement. The surface of MCB, which had been originally smooth, became slightly irregular during carbonization, and deformation in the shape of MCB was observed after the graphitization process. These are due to the anisotropic growth and shrinkage of the mesophase structure.     

Blending mesophase pitch to improve its properties as a precursor for carbon fibre Part 1 Blending of PVC pitch into coal tar and petroleum-derived mesophase pitches

The blending of mesophase pitch with isotropic PVC pitch was studied to improve their properties as a precursor for carbon fibre. PVC pitch prepared at 420° C which remained almost isotropic was found to be miscible with coal tar-derived mesophase pitch without reducing the anisotropic content and spinnability. The tensile strength of pitch fibres remained unchanged by the blending; however, the reactivity for stabilization was enhanced. The resultant carbon fibres from the blend exhibited slightly higher tensile strength. In contrast, petroleum-derived mesophase pitch failed to dissolve the PVC pitch, leaving a number of isotropic droplets. The structural factors of mesophase pitches with regard to their compatibility with PVC pitches are briefly discussed.     

原料配比对石墨材料热传导性能的影响

以煅烧石油焦和煤沥青为基本原料，采用热压工艺制备了一系列石墨材料，考察了煅烧石油焦填料的粒度分布以及粘结剂用量对石墨材料的传导性能的影响，并阐明了粘结剂与填料粒子在热混捏与热压过程中相互作用原理。结果表明：石墨材料的传导性能不仅依赖于原料种类，粒度，而且与其质量配比有关，有最佳原料配比所制备的块状石墨具有高密度，低孔率，低电阻以及高导热等特点；填料煅烧石油焦颗粒以及粘结剂用量的过多或过少，都不利于石墨材料的传导性能，本文填料中最佳煅烧石油焦颗粒用量为25%，原料中最佳粘结剂含量为25%。     

The effect of zirconium addition on the microstructure and properties of chopped carbon fiber/carbon composites

Carbon/carbon composites containing zirconium were prepared using chopped carbon fiber, mesophase pitch and Zr powder by the traditional process including molding, carbonization, densification and graphitization. The influence of Zr on the microstructure and properties of the composites were investigated. Results show that Zr can improve the interface bonding, promote more perfect and larger crystallites and enhance the conductive/mechanical properties of the composites. The high in-plane thermal conductivity of 464 W/(m K) and excellent bending strength of 83.6 MPa was obtained for a Zr content of 13.9 wt% at heat treatment temperature(HTT) of 2500 °C. However the conductive/mechanical properties of the composites decrease dramatically for an higher HTT of 3000 °C. SEM micrograph of the fracture surface for the composites shows that lower disorder crystallite arrangement of fiber and carbon matrix come into being in the composites during HTT of 3000 °C, which should be responsible for the low properties. Correlation between the content of Zr and the microstructure and properties are discussed.