The oxidation of porus carbon: the development of porosity of a cellulose carbon by reaction with oxygen

Abstract

The work reported in the thesis is an examination of the influence of temperature of activation on the development of microporosity in a polymer carbon. It involves the investigation of the rate of reaction with oxygen over the temperature range 400 - 726 C and the measurement of the porosity produced by adsorptive methods. It was concluded from experimental activation energies obtained for the reaction that the temperature ranges 400 - 460 C and 480 - 726 C were in Zones II and III respectively of the classification of Heddon and Wicke*. These conclusions were supported by investigation of the influence of partial pressure of oxygen, sample weight and crucible geometry on the rate of reaction. Analysis of adsorption isotherms shows that the development of porosity depends on the temperature of activation. In Zone III where reaction is on the external surface of the carbon there is little or no development of porosity whereas in Zone II where the reaction occurs within the pores of the carbon, substantial development of porosity occurs. A method for the determination of the thermodynamic criterion, ΔS < 0, for the applicability of the Dubinin Theory to the adsorption isotherms was developed. Application of the Dubinin Equation to the regions of the isotherms where the Thermodynamic criterion was shown to apply gave lines that were not generally straight as originally postulated. However analysis of the results in terms of the Dubinin Equation in general confirmed the effects of temperature of activation on the development of porosity. Comparison of oxygen and carbon dioxide as activating gasses was made by reference to Rowan’s work and showed that under comparable conditions of activation carbon dioxide is a more efficient activating gas.