Effects of pyrite impurity in initial graphite on properties ofresidual graphite bisulfate prepared in CrO3-H2SO4 system

摘要

A number of residual graphite bisulfates were prepared from Ukrainian natural flaky graphites of a varied particle sizerndistribution by oxidation with concentrated sulfuric and chromic acids. The expanding coefficient of the products is loweredrnwith a decrease in particle size of the initial graphite. This effect was ascribed to pyrite which predominantly concentrates inrnthe smallest-sized graphite particles. Pyrite is a powerful reducing agent, which requires up to 6 mol of chromium trioxide forrnits oxidation and even a small proportion of the pyrite will render oxidizing agent inoperative in the intercalation process. Inrnorder to verify adverse effect of the pyrite on the properties of residual graphite bisulfate, a number of graphite mixtures withrnvarying content of the natural pyrite were subjected to intercalation. It was found that increased amount of the pyrite addedrncauses a decrease in the intercalant content of the end product and its expanding coefficient due to partial consumption of thernoxidizer in the side reactions. Removal of the small-sized particles from the initial graphite gives rise to improvement inrnproperties of the finished product.