Selective Infiltration of Fine Pores in Molecular Size by Use of CVI

化学气相渗透现在被用来生产航空航天应用的先进材料。它也适用于碳材料，以提高其抗氧化性。本文对电极级石墨、电极级炭、焦炭和活性碳等几种炭进行了甲烷热解，用氮气吸附方法研究了细孔：亚微孔(直径1.5 nm)、微孔(d&lt；2 nm)、中孔(d&lt；50 nm)的结构变化。这些细孔被认为对氧化动力学有重要作用，因为在内燃烧的情况下，氧化主要发生在这样的细孔中，因为它们的比表面积比大孔(d&gt；50 nm)大。测量结果表明，浸渍的活性碳的微孔尺寸极大地减小。此外，在氧化过程中，这些孔的开孔率被减缓到原始样品的约三分之一。因此，微孔的形成归因于活性碳和其他碳的抗氧化性的提高。用压汞计测得的大孔的变化与细孔的变化进行了比较，但认为对抗氧化性的提高影响不大。

Chemical vapor infiltration is now being used to produce advanced materials for aerospace applications. It is also applicable to carbons to enhance the resisitance against oxidation. In the present study, methane pyrolysis was conducted for several kinds of carbons such as electrode-grade graphite electrode-grade carbon, coke and activated charcoal.The structural change of the fine pores : submicropore (diameter<1.5nm), micropore (d<2nm), mesopore (d<50nm), was investigated by use of nitrogen adsorption method. Those fine pores oreconsidered to have an important role for oxidation kinetics because in the case of inner burning, oxidation is considered mainly to occur in such fine pores due to their larger specific surface area comparing to those of macropores (d>50nm).The measured results indicates that the size of micropores decreases extremely for the infiltrated activated charcoal. Additionally, the opening rate of these pores are retarded to about 1/3 of the original sample during the oxidation. Therefore, it is concluded that the micro pores are attributed to the enhancement of oxidation resistance for activated charcoal as well as other carbons.The change of macropores measured by mercury porosimeter is compared with that of fine pores but is considered to have little effect on the enhancement of resistance.