Structural Change in Natural Graphite heat-treated with Boron Carbide

Abstract

Structural change in natural graphite power heat-treated with boron carbide power under a pressure of 19.6 MPa was investigated as functions of heat-treatment temperature from 1400 to 2300°C and content of boron carbide from 0 to 50 wt%.Above 2000°C, d (002) and d (110) remarkably changed, (006) peak remarkably broad-ened and the lattice strain (ec) increased with increasing temperature and with increasing boron carbide content.Raman band at 1360 cm-1 also appeared.From these experimental results, it was concluded that the three dimensional ordered structure of graphite began to change into a disorderedstate above 2000°C when boron carbide coexisted with. The disordering was found to be caused by boron atom diffusion into substitutional or interstitial position in graphite structure.The amount of substitution-ally diffused boron was estimated to be about 1-2 atom% at 2000-2300°C and this diffusion was thought to induce the decrease of d (002) and increase of d (110). Interstitial diffusion of boron began to start after substitution when boron existed in excess of the solubility limit. Interstitial insertion of boron was thought to induce the increase of d (002) but had no effect on d (110).