炭纤维物理性能对C/C复合材料氧化性能的影响

用相同牌号的T700炭布长纤维和炭毡短纤维交替叠层作为坯体，通过化学气相沉积（CVD）法生产二维C／C复合材料，尽管两种纤维具有很相近的结构和石墨化度，并经历相同的热处理过程，但同一C／C试样在随后的变温氧化和等温氧化过程中存在两个主要的氧化方向，一个是热解炭基体优先于炭布氧化，另一个是炭毡纤维优先于炭基体氧化。研究表明，两种纤维的物理性能（如表面积、孔径分布和总孔体积）有显著差别，即两种纤维的微孔结构和孔径分布有很大差别，从3－10nm，炭毡纤维的分布峰值比炭布纤维大得多，炭毡纤维的累积吸附孔体积的增长也比炭布纤维快，而且炭毡纤维的最大孔径比炭布纤维的大得多。正是这些因素使得炭布纤维比炭毡纤维具有更强的抗氧化性，导致了其抗氧化和氧化活性的明显不同。因此，即使炭布纤维和炭毡纤维具有相同的结构，并经过同样的热处理过程，在被用作坯体生产C／C复合材料前，应仔细考虑其物理性能。

EFFECT OF PHYSICAL PROPERTIES OF CARBON FIBERS ON THE OXIDATION OF C/C COMPOSITES

The same brand T700 carbon cloth long fiber and carbon felt short fiber were used as substrate to produce 2D carbon carbon composite by chemical vapor deposition (CVD) method. Though these two kinds of carbon fibers had the very similar structural order, graphitization degree and same thermal history, the oxidation test showed quite different behavior: the oxidation occurred firstly at the interface between the fibers and the carbon matrix, then toward two directions, one was the pyrolytic carbon consumption occured before the onset of oxidation of the carbon cloth substrate, the other was the carbon felt fiber consumption occured before the onset of oxidation of the pyrolytic carbon matrix. Investigation showed that the significant difference of physical properties (such as surface area, pore size distribution and total pore volume) leaded to obviously two different oxidation resistance and oxidation reactivity of the two fibers. The pore size distributions of the two fiber were significantly different : from 3nm to 10nm, the distribution peak value of the carbon felt fiber was much larger than that of the carbon cloth fiber. And there was a quicker increase of the cumulative pore volume of the carbon felt fiber than that of the carbon cloth fiber. At the same time, the largest pore diameter of the carbon felt fiber was much larger than that of the carbon cloth fiber. These factors resulted in a higher oxidation resistance of the carbon cloth fiber than that of the carbonfelt fiber. So physical properties of carbon cloth fiber and felt fiber should be taken into account before they were used as substrate in C/C composites production even though they have same thermal history and structural order.