【作者】 袁观明；

【导师】 李轩科；

【作者基本信息】 武汉科技大学 ， 化学工艺， 2012， 博士

【摘要】 炭材料（如炭纤维、C/C复合材料、石墨材料等）具有低密度、低热膨胀系数、优异的机械性能和较高的热导率等优点，是近年来热管理领域里最具发展前景的一类导热材料。但是炭材料内部石墨晶体的特殊性（各向异性）和多样性（微晶尺寸及其取向不同）决定了其导热性能大相径庭，从一般石墨材料的70~150W/m.K到气相生长炭纤维轴向的1950W/m.K不等。因此控制炭材料内部石墨微晶尺寸、取向及其连续性是提高其特定方向室温热导率的关键。本论文以萘系中间相沥青为原料，通过熔融纺丝制备了毫米宽度的带状沥青纤维，经预氧化、炭化和石墨化处理得到石墨层片高度取向的高导热带状石墨纤维。选择氧化稳定化并低温热处理后的带状纤维与中间相沥青粘结剂进行复合再中温（500oC）热压制备一维带状纤维/C复合材料，此材料经后续炭化和石墨化处理得到石墨层片沿带状纤维长度方向高度择优取向的一维高导热C/C复合材料。同时利用中间相沥青为粘结剂和廉价易得的高结晶度天然鳞片石墨为骨料，采用相同的成型和热处理工艺制备了高定向高导热石墨材料。研究工作取得的主要结论如下：1、中间相沥青基带状纤维的制备、表征及其性能测试（1）以中间相沥青为原料，采用熔融纺丝工艺制备出表面光洁平整、宽度（0.3~1.5mm）和厚度（15~30μm）可控的带状沥青纤维。带状沥青纤维经220~260oC氧化稳定化“固定”住了带状纤维的形貌和结构，在随后高温炭化和石墨化过程中带状纤维内部石墨微晶生长发育，其微晶尺寸逐渐变大，微晶三维有序堆积结构逐步完善，石墨层片沿带状纤维主平面高度取向。而且带状纤维在高温热处理过程中保持其带状形态，不发生变形（劈裂、褶皱和卷曲），有效克服了径向辐射状圆形纤维的易劈裂难题。（2）热处理温度对带状纤维的抗氧化性能和力学性能有显著影响，热处理温度越高，带状纤维的结晶度和石墨化度越高，其抗氧化性能越好。2800~3000oC石墨化带状纤维的抗氧性能明显优于K-1100石墨纤维。1.5mm宽带状纤维低温（400~700oC）热处理后的力学性能较低，经过1000oC炭化处理后其力学性能明显提高，拉伸强度和弹性模量分别达到了876MPa和109GPa，经3000oC石墨化处理后带状纤维的拉伸强度和弹性模量进一步提高至2.53GPa和421GPa。（3）随着热处理温度的提高，带状纤维的轴向导电性能不断提高。1.5mm宽带状纤维经3000~3200oC石墨化后其室温轴向电阻率仅为1.05~1.08μ.m，比K-1100石墨纤维的室温轴向电阻率（1.17μ.m）低。根据中间相沥青基炭纤维的导电导热关联式计算得到1.5mm宽带状纤维的室温轴向热导率可达1100~1200W/m.K。2、一维高导热带状纤维/C复合材料的制备、表征及其性能测试（1）以单向铺排带状纤维为基体材料，在其表面均匀涂覆适量的中间相沥青粘结剂，经500oC一次热压成型再高温炭化、石墨化处理，可以制备较高体积密度的一维带状纤维/C复合材料。随着热处理温度的不断提高，复合材料的体积密度逐渐增加。500oC热压成型样品的体积密度约为1.2~1.3g/cm~3，1000oC炭化处理后其体积显著收缩，密度增至1.7~1.8g/cm~3，3000oC石墨化后材料的体积密度达到了1.85~1.90g/cm~3。（2）XRD、PLM和SEM测试分析表明，1.5mm宽带状纤维/C复合材料具有明显的结构各向异性，带状纤维在复合材料中单向有序排布，其主平面沿热压方向有序堆积，内部石墨层片沿带状纤维长度方向高度择优取向。电阻率和热扩散系数测试表明，该复合材料具有显著的电学和热学各向异性，沿带状纤维长度方向具有优异的导电和导热性能。3000oC石墨化复合材料沿带状纤维长度方向和带状纤维主平面堆积方向的室温电阻率分别为1.5μ.m和22.2μ.m，其相应热导率为862W/m.K和11W/m.K。热处理温度对复合材料沿带状纤维长度方向的室温热扩散系数和热导率有重要影响，热处理温度越高，其热传导性能越好。复合材料沿带状纤维长度方向的室温热导率与其热处理温度和体积密度之间有着良好的线性关联，其相关系数（0.98和0.95）较高。（3）带状纤维的宽度和纤维的截面形态对复合材料的体积密度、室温热扩散系数和热导率有重要影响。0.5mm和0.3mm窄带状纤维/C复合材料的体积密度较高（1.88~1.91g/cm~3），沿带状纤维长度方向的室温热扩散系数和热导率分别为570~580mm~2/s和820~830W/m.K；圆形纤维/C复合材料的体积密度较低（1.70g/cm~3），沿纤维长度方向的室温热扩散系数和热导率分别为554mm~2/s和707W/m.K。虽然1.5mm宽带状纤维/C复合材料的体积密度（1.86g/cm~3）稍低，但是沿带状纤维长度方向的热扩散系数（618mm~2/s）明显较高，因此相应热导率（862W/m.K）也较高。3、天然鳞片石墨基高导热石墨材料的制备、表征及其性能测试（1）以天然鳞片石墨和中间相沥青分别为骨料和粘结剂，采用500oC一次热压成型再高温热处理可以制备较高体积密度的石墨块。鳞片石墨粒径、中间相沥青粘结剂用量、热压压力和热处理温度等对石墨块的体积密度有一定的影响，86wt.%天然鳞片石墨（+32目）和14wt.%中间相沥青混合料经10MPa压强热模压成型的炭块经2800oC石墨化后其体积密度达到1.91g/m3以上。（2）XRD、PLM和SEM测试分析表明，制备的石墨块具有明显的结构各向异性，天然鳞片石墨主平面沿热压方向高度有序堆积排列。除体积密度和比热容外，石墨块其它物理性能（如力学性能、导电性能、导热性能）具有明显的各向异性，在垂直和平行热压方向存在较大差异。（3）石墨块沿垂直热压方向的室温电阻率受天然鳞片石墨粒径、中间相沥青粘结剂用量和热处理温度的影响较大。2800oC石墨化后的石墨块沿垂直热压方向具有优异的导电和导热性能，其室温电阻率和热导率分别达到了1.45μ.m和622W/m.K，而在平行热压方向的室温电阻率和热导率分别为8.35μ.m和25W/m.K。该石墨块在垂直热压方向的耐压强度（11.3MPa）和抗弯强度（7.7MPa）较低。（4）除热处理温度、中间相沥青粘结剂的用量和晶体取向对石墨块的热导率有非常明显的影响以外，其它因素（如测试环境温度、天然鳞片石墨的粒度、不同的沥青粘结剂、热压成型温度、掺杂处理等）也会影响石墨材料的热导率。4、高导热炭材料的导热导电性能关联及其导热机理初步探讨（1）带状炭（石墨）纤维及其一维C/C复合材料的室温轴向热导率与其轴向电阻率、石墨化度和石墨微晶参数（d002、Lc、La）密切关联，其相关系数都较高（≥0.91）。石墨块沿垂直热压方向的室温热导率与此方向的电阻率关联度不大，但是和沥青粘结剂衍生石墨的微晶参数（Lc、La）有一定关联，其相关系数（0.46和0.64）较低。（2）由带状纤维室温轴向热导率和电阻率的关联式可知：3000oC石墨化带状纤维的室温轴向热导率达到了1084~1174W/m.K。利用一维C/C复合材料的热导率混合计算公式反推3000oC石墨化带状纤维的室温轴向热导率可达到1136W/m.K，这表明利用带状纤维轴向电阻率来计算其轴向热导率是有效可行的。采用这两种方法预测C/C复合材料沿带状纤维长度方向的室温热导率有望达到890~920W/m.K。（3）3种高导热炭材料（带状纤维、C/C复合材料、石墨材料）的导热机理分析表明：炭材料热传导性能受样品热处理温度、石墨化度、微晶参数和晶体取向的影响较大。炭材料内部石墨微晶的尺寸大小是决定其导热性能高低的主要内在因素之一，其沿垂直热压方向的室温热导率与石墨微晶平面大小La成正比。更多还原

【Abstract】 Owing to their low density, low thermal expansion coefficient, excellent mechanical propertiesand high thermal conductivity, carbon materials (such as carbon fibers, C/C composites, graphitematerials, etc.) become the most promising materials in thermal management field in recentyears. However, the particularity (anisotropy) and diversity (differentia of micro-crystallite sizeand graphitic crystal orientation) of carbon materials lead to their room-temperature thermalconductivities varying widely from70~150W/m.K (general graphite materials) to1950W/m.K(vapor grown carbon fibers). Therefore, the control of the size, orientation and continuity ofgraphite crystals in carbon materials is very important for enhancing the room-temperaturethermal conductivity along a specific direction. In this thesis, ribbon-shaped pitch fibers withwidth in milimeter-scale were prepared by a melt-spinning method using a naphthalene-basedmesophase pitch as a raw material, and highly oriented ribbon-shaped graphite fibers with highthermal conductivity were otained through pre-oxidation, carbonization and graphitization.One-dimensional C/C composites were prepared by a hot-pressing method at about500oC usingthe unidirectional stacked ribbon-shaped fibers (after stabilization and low temperature treatment)as matrix and mesophase pitch as binder. The C/C composites with high thermal conductivitywere obtained by subsequent carbonization and graphitization treatment, in which carbon layersof the ribbon-shaped graphite fibers show highly preferred orientation parallel to the longitudinaldirection of the ribbon fibers. Graphite materials with natural graphite flake with highlypreferred orientation perpendicular to the hot-pressing direction were also prepared by a similarhot-pressing and heat treatment process using mesophase pitch and natural flake graphite withhigh crystallinity as raw materials. The main conclusions of the work were obatined as follows:1. Preparation, characterization and property measurements of mesophase pitch-based ribbonfibers(1) Using mesophase pitch as a raw material, ribbon-shaped pitch fibers with a flat and smoothsurface and controllable width (0.3~1.5mm) and thickness (15~30μm) were prepared by amelt-spinning method. The morphology and structure of the ribbon-shaped pitch fibers werefixed through oxidation stabilization at220~260oC for a certain time. During the followingcarbonization and graphitization treatment, the internal graphitic crystals of ribbon fibersgradually grows and develops, the crystal size gradually becomes larger, and as a result athree-dimensional ordered stacking structure of micro-crystals becomes complete. Thegraphitic layers possess a higher degree of orientation parallel to the main plane of ribbonfibers. Ribbon-shaped fibers keep their ribbon shape and do not deform (split, fold or crimp)during the whole high-temperature carbonization and graphitization process. It can overcomethe problem of easy splitting of round-shaped carbon fibers with a radial texture after hightemperature heat treatment.(2) The heat treatment temperature has an obvious influence on the anti-oxidation property andmechanical properties of ribbon-shaped carbon fibers. The crystallization degree andgraphitization degree of the ribbon-shaped carbon fibers gradually increase with the increase of heat treatment temperature, which results in a better oxidation resistance of the ribbonfibers after graphitization treatment. The anti-oxidation property of the ribbon-shaped fibersgraphitized at2800~3000oC is significantly better than that of the K-1100fibers. Themechanical properties of the ribbon-shaped pitch fibers with a width of1.5mm carbonized atlow temperature (400~700oC) are relatively low. The tensile strength and elastic modulus ofthe ribbon-shaped fibers carbonized at1000oC reach876MPa and109GPa, which furtherincrease to2.53GPa and421GPa after graphitized at3000oC.(3) The axial electric conductivity of ribbon-shaped fibers gradually improves with the increaseof heat treatment temperature. The axial room-temperature electrical resistivity of the ribbonfibers with a width of1.5mm graphitized at3000~3200oC is as low as1.05~1.08μ.m,which is lower than that of the K-1100fibers (1.17μ.m). The axial room-temperaturethermal conductivity of the ribbon fibers graphitized at3000oC calculated by the universalcorrelation of electrical resistivity and thermal conductivity of mesophase pitch-based carbonfibers is up to1100~1200W/m.K.2. Preparation, characterization and property measurements of one-dimensional ribbon fiber/Ccomposites with high thermal conductivity(1) Using the unidirectional stacked ribbon-shaped fibers as a matrix material, followed bycoating mesophase pitch binder on them, ribbon fiber/C composite materials with high bulkdensity were fabricated through one-step hot-press molding at about500oC and subsequentcarbonization and graphitization treatment. As the heat treatment temperature rises, the bulkdensity of the composites gradually increases. The bulk density of the hot-pressed sample atabout500oC is only about1.2~1.3g/cm3, which increases to1.7~1.8g/cm3after thecarbonization treatment at1000oC due to the significant volume shrinkage, and furtherincreases to1.85~1.90g/cm3after the graphitization treatment at3000oC.(2) XRD, PLM and SEM analyses show that the1.5mm wide ribbon fiber/C composite blockprepared exhibits a structural anisotropy. Ribbon-shaped fibers have been unidirectionallydistributed in the composite block and the main planes of the ribbon fibers are orderlyaccumulated along the hot-pressing direction. The internal graphitic layers possess a higherdegree of preferred orientation parallel to the longitudinal direction of the ribbon fibers. Theribbon fiber/C composite block shows obvious electrical and thermal anisotropy and hasexcellent electrical and thermal conductivities along the longitudinal direction of the ribbonfibers. The room-temperature electrical resistivities of the composite sample graphitized at3000oC along the longitudinal direction of the ribbon fibers and along the ribbon fiberaccumulation direction are1.5μ.m and22.2μ.m, respectively. The correspondingroom-temperature thermal conductivities of the sample are862W/m.K and11W/m.K. Heattreatment temperatures have an obvious influence on the thermal diffusivity and thermalconductivity of the composites. The thermal conductivity of the composites increases withthe increasing of heat treatment temperature. There is a good linear correlation between theroom-temperature thermal conductivity of the composite along the longitudinal direction ofthe ribbon fibers and its heat treatment temperature and bulk density, the correlation coefficients (0.98and0.95) of which are both high.(3) The width of the ribbon fibers and transversal shape of fibers have a big influence on thebulk density, the room-temperature thermal diffusivity and thermal conductivity of C/Ccomposites along the longitudinal direction of the ribbon fibers. Narrow (0.5mm and0.3mmwide) ribbon fibers/C composite has a high bulk density (1.88~1.91g/cm3), and theirroom-temperature thermal diffusivity and thermal conductivity along the longitudinaldirection of the ribbon fibers reach570~580mm2/s and820~830W/m.K, respectively.However, a round-shaped fiber/C composite has a lower bulk density (1.70g/cm3), and itsthermal diffusivity and thermal conductivity along the longitudinal direction of the ribbonfibers at room temperature are554mm2/s and707W/m.K. The bulk density of the wide (1.5mm) ribbon fiber/C composite is1.86g/cm3, lower than that of the narrow ribbon fibers/Ccomposite, but the former has a significantly larger thermal diffusivity (618mm2/s) andthermal conductivity (862W/m.K).3. Preparation, characterization and performance testing of graphite materials with high thermalconductivity made with natural flake graphite(1) Using natural flake graphite and mesophase pitch powder as bone-material and binder,graphite blocks with a high bulk density were prepared through a hot-pressing method at about500oC and subsequent heat treatment at high temperature. Flake graphite particle size, themesophae pitch binder content, hot-pressing pressure and heat treatment temperature have acertain impact on the bulk density of the graphite block. The bulk density of the graphiteblocks made with86wt.%natural flake graphite (+32mesh) and14wt.%mesophase pitchpowder hot-pressed at about10MPa pressure is above1.91g/m3after2800oC graphitizationtreatment.(2) XRD, PLM and SEM analyses show that the prepared carbon (graphite) blocks have anobvious structural anisotropy, and the natural flake graphite has been stacked orderly alongthe hot-pressing direction. Except the bulk density and specific heat capacity, other physicalproperties (such as mechanical properties, electrical property, and thermal property) of thegraphite block have an obvious anisotropy. There is a significant difference between thevertical and parallel to the hot-pressing direction.(3) The particle size of natural flake graphite, mesophase pitch binder content and heat treatmenttemperature have a great influence on the room-temperature electrical resistivity of graphiteblocks along the direction perpendicular to the hot-pressing direction. The graphite blocksafter treatment at2800oC show good electrical and thermal conductivity along the directionperpendicular to the hot-pressing direction. Their room-temperature electrical resistivity andthermal conductivity are1.45μ.m and622W/m.K, respectively. However, along thedirection parallel to the hot-pressing direction, the room-temperature electrical resistivity andthermal conductivity are8.35μ.m and25W/m.K, respectively. The compressive andbending strengths of the graphite blocks are relatively low, which are1.3MPa and7.7MPa,respectively.(4) Except heat treatment temperature, the content of mesophase pitch binder and graphitic crystal orientation, other factors (such as the environmental testing temperature, thegranularity of the natural graphite flakes, the properties of pitch binder, hot-pressingtemperature and doping treatment, etc.) have also influences on the room-temperaturethermal conductivity of the graphite blocks along the direction perpendicular to thehot-pressing direction.4. Discussion on the thermal conductivity of carbon materials associated with its electricalconductivity and thermal conductivity mechanism(1) For ribbon-shaped carbon (graphite) fibers and their one dimensional C/C composites, theaxial room-temperature thermal conductivity has close relationships with the axial electricalresistivity, degree of graphitization and graphitic micro-crystallite parameters (d002, Lc, La).The correlation coefficients are all as high as above0.91. There is no obvious relationshipbetween the room-temperature thermal conductivity and electrical resistivity of graphiteblocks along the direction perpendicular to the hot-pressing direction, but theroom-temperature thermal conductivity of graphite blocks in the direction has some weakrelevance with the pitch binder derived graphitic micro-crystallite parameters (Lc and La).The correlation coefficients are0.46and0.64, respectively.(2) The axial room-temperature thermal conductivity of the ribbon-shaped fibers graphitized at3000oC reach1084~1174W/m.K calculated according to the relationship between the axialthermal conductivity and electrical resistivity of ribbon-shaped fibers, which is up to1136W/mK through back-calculating by thermal conductivity mixed formula for one dimensionalC/C composites. It is feasible to estimate the axial thermal conductivity of ribbon fibers bytesting the electrical resistivity. The room-temperature thermal conductivity of C/Ccomposites along the longitudinal direction of fiber is expected to reach890~920W/m.Kaccording to both methods.(3) The thermal conduction mechanism analyses of three kinds of carbon materials(Ribbon-shaped fibers, C/C composites and graphite materials) with high thermalconductivity show that heat treatment temperature, graphitization degree, micro-crystalliteparameters and crystal orientation have significant influences on the thermal conductivity ofcarbon materials. The micro-crystallite size of carbon materials is one of the most importantinternal factors impacting the thermal conductivity of the carbon materials. Theroom-temperature thermal conductivity along the direction perpendicular to the hot-pressingdirection is proportional to the micro-crystallite coherence length La measured by X-raydiffraction.更多还原