Graphitization of Glass-like Carbon by Boron Carbide Additives

Abstract

The graphitization of glass-like carbon by boron carbide was investigated.The pieces of the glass-like carbon were buried in boron carbide powder and hot-pressed under the pressure of 19.6 MPa at 2200°C.Boron distribution, texture change and graphitization of hot-pressed glass-like carbon were measured.
The hot-pressed glass-like carbons could be generally classified into three zones from the distribution and the concentration of boron.These zones were named as phase 1, 2 and 3 in order from the region contacted with boron carbide toward the center of glass-like carbon matrix.Characteristics of each phase are as follows.
Phase 1 shows granular texture consisted of carbon grains and boron carbide ones. Boron also existed in carbon as a solid solution.The carbon have three dimensional ordered structure.
In phase 2, boron existed only in carbon as a solid solution.The region located at the side contacted with phase 1 showed optical anisotropic texture.The major part of the region located at the side contacted with phase 3 showed a homogeneous and optical isotropic texture.
In phase 3, boron could not be almost detected and the major part showed the same optical isotropic texture as that of original glass-like carbon.
In phase 1 boron content was generally scattered from 2 to 10 wt% and in which boron solid-soluted in carbon was about 1-2 wt%.In phase 2 boron content showed the maximum value of 1-2 wt% at the boundary region with phase 1, and it decreased with approaching toward phase 3.
It was considered that graphitization of glass-like carbon hot-pressed in boron carbide powder at 2200°C was proceeded by the diffusion of boron forming boron carbide and three zones above mentioned were formed in consequence of the content of boron which diffused into glass-like carbon at 2200°C.