Kinetics of Oxidation of Beneficiated Indian Graphite

Graphite occurs in nature along with other minerals and impurities with lowfixed carbon. With adoption of crushing, grinding and beneficiation, percentage of fixed carbon increases and consequently high purity graphite obtained with repeated beneficiation. In India mainly three sources of graphite are used and they are palamau, Jharkhand, bolangir of Orissa and Shivaganga of Tamilnadu. After physico chemical evaluation of these graphites, oxidation behaviour was studied in DTA/TGA apparatus by controlling the atmosphere to study their reaction kinetics and finding out the activation energy required for each specific condition. Three temperature1s of oxidation were selected keeping in mind the oxidation peak obtained in DT/TG analysis. 

Kinetic models for all three graphite samples upto a certain temperature show rate is controlled by reaction of carbon with gas at the interface. Reaction at higher temperature shows partial shifting from chemical reaction to diffusion reaction through the pore decarburised zone. Phase boundary controlled, Contracting disc phase boundary controlled and two dimensional diffusion controlled reaction model have been identified as probable model for graphite oxidation. Formation of decarburised zone gives rise to different activation energy resulting from chemical reaction at lower temperature and diffusion reaction at higher temperatures. Activation energy values show two different slopes corresponds to changing of mechanism. Activation energy values also show variable values with respect to particle size variations.