Intercalation of bromine into natural graphite the effect of oxidation and residual bromine on the rate and amount of uptake

Abstract

Intercalation of bromine at 20°C into spectroscopic grade SP-1 natural graphite flakes oxidized previously to four levels of burn-off has been studied. The threshold pressure, equilibrium amounts taken up at relative pressures up to 0.95, and the diffusion coefficient for bromine uptake are little affected by graphite oxidation at all burn-off s studied (up to 46.1%). However the time after bromine exposure at the threshold pressure at which rapid bromine intercalation commences monotonically decreases with increasing burn-off. It is suggested that during this initial time period, bromine entering the graphite is essentially fully ionized, whereas bromine entering later, and rapidly, is not ionized. Oxidation affects the subsequent thermal stability of the intercalated bromine and the composition of the residue compound formed following heating to 950°C. Rates of uptake and amount of bromine intercalated subsequently on the residue compounds are dependent upon their Br C ratio and how the residual compounds were formed.