Kinetic Studies of Fluorination of Graphite in Diffusion Controlled Region

Abstract

Our previous work revealed that the curve of the weight increase vs.time in the fluorination of graphite by fluorine gas consisted of four parts. The mechanism of the final part was studied in this paper by means of the thermobalance specially designed for fluorine gas. The flaky graphites from Madagnscar ores with the 800 μ of mean diameter were used for the sample. Experiments have been carried out under the fluorine pressure of 50, 100 and 200 mmHg in the temperature range from 500 to 600 C.
The relationship between the degree of transformation, x, and reaction time, t, was expressed by a modified Jander's equation, [1-(1-x)1/2]2=kt. The reaction rate, k, was proportional to square root of fluorine pressure. The apparent activation energy was found to be 26 ± 1kcal/mol. The reaction rate was depressed when the fluorination of graphite crystal proceeded about 6 μ from edge plane. The time required for the formation of final compound (C:F=1:1) depended upon the diameter of graphite particle. The experimental results indicated that the rate-determining point of the reaction lay in the transfer step of fluorine molecules through the fluorinated layer of the graphite.