炭前驱体形态对C/C复合材料导热系数的影响

INFLUNCE OF ARRANGING STRUCTURE OF CARBON PRECURSOR ON THERMAL CONDUCTIVITY OF C/C COMPOSITES

利用热塑性中间相沥青为黏结剂,短炭纤维为增强体,一步热压成型制备C/C导热复合材料.采用SEM和偏光显微镜观察等分析手段,研究了2∶1,2.5∶1和3∶1三种不同管径比对C/C复合材料的影响.结果表明:通过热压模具空腔结构的改变可以引起炭前驱体挤出形态的变化,使得轴向基体炭有序生长与短炭纤维增强体呈现有序排列.其中间相液晶分子垂直和平行于模压压力方向均排列成纤维状长程有序结构,短切纤维呈现出与压力平行方向排布.当空腔管径比为3∶1,轴向导热系数由86.2 W/(m.K)增大至115.5 W/(m.K),各向异性比由1.6减小为1.2.由此所得块体C/C复合材料具有显著的二维取向结构,轴径向导热系数趋于平衡.

C/C composites have broad application prospects in some particular fields. To prepare C/C composites with hot-pressing mold, thermoplastic mesophase pitches used as bind- ers, kneading with short carbon fibers were moulded from RT to 650℃. Then after process of carbonization（1 000℃） and graphitization（2 700 ℃）, C/C composites with thermal conductivity were prepared. The experiment showed that the extrusion structure of carbon precursor changed with structure of cavity in the mould, which made matrix carbon in the axial direction growing orderly and short carbon fibers（SCFs） for the heat transmission medium arranging orderly in the matrix carbon. After observed through polarizing microscope and scanning electron microscope （SEM）, the mesophase pitch liquid crystal moleculars presented fibrous long-range order structure both in two-dimension directions. In addition, SCFs were distributed parallel to the hotpressing direction. When the ratio of tube cavity was 3 ： 1, thermal conductivity of C/C composites in axial direction increased from 86.2 W/（m ·K） to 115.5 W/（m·K） and the anisotropy ratio of thermal conductivity decreased from 1.6 to 1.2 C/C. Composites obtained from this method, had obvious two-dimensional orientation structure, which made the coefficient of thermal conductivity in two-dimension direction balanced.