Revista de ciencias e ingeniería de materiales

Developing a Practical Chemical Process to Prepare Boron-Doped Carbon (CBx) Materials with High Thermal-Oxidative Stability

Abstract

Joseph Vandy Sengeh, Wei Zhu, Houxiang Li and T. C. Mike Chung*

This paper discusses a new method to prepare boron doped carbon (CBx) material with some substitutional boron atoms homogeneously distributed in the highly graphitic structure. The chemistry involves a mesophase boron-doped pitch (B-Pitch) prepared by mixing a borane reagent (i.e., dichlorophenylacetylborane) with petroleum pitch at 400°C. The resulting mesophase B-Pitch was further diluted with the starting pitch to adjust its softening temperature and melt viscosity, they are essential during the preparation of C/C composites. A resulting B-Pitch/Pitch blended precursor with 3.3 mol% B content and a softening temperature of 300°C was directly converted to CBx CBx CBx CBx B2O3 surface layer to slow down the oxygen diffusion into the matrix and stability. CBx) CBx at 2300°C under argon atmosphere, showing a char yield of 81%. The presence of a small percentage of B atoms in this B-Pitch/Pitch precursor catalyzes the carbonization/graphitization to form a highly graphitic CBx structure. Compared to synthetic graphite, which is stable in air up to 500°C, the resulting CBx shows higher thermal-oxidative stability. In air at 600°C, no weight loss was observed after 6 hours. At 700°C and 800°C, there was no detectable weight loss for 80 minutes. Evidently, the homogeneous distribution of B atoms in the CBx matrix is essential in continuously providing a protective B2O3 surface layer to slow down the oxygen diffusion into the matrix and delay the thermal/oxidative degradation process. Overall, this new precursor technology may offer the C/C composite manufacturing with reduced pyrolysis cycles and increased thermal/oxidative stability in high temperature applications.