The Corrosion of Carbon Black Anodes in Alkaline Electrolyte: III . The Effect of Graphitization on the Corrosion Resistance of Furnace Blacks

A selection of furnace black carbons of varying surface area and industry type were heat treated in purified helium at 2700°C and the corrosion resistance was measured under conditions of oxygen evolution in 30% at 55°C. The extent of graphitization was determined qualitatively by x‐ray diffraction and by transmission electron microscopy (TEM). Separate linear correlations of the corrosion rate per unit mass with the BET surface area were observed for furnace blacks and for graphitized furnace blacks, with the rate for the graphitized blacks being a factor of ca. 2.5 lower on a unit area basis. The correlations had a relatively high standard deviation, however, indicating that BET area was probably not the only physical property affecting the corrosion rate. TEM analysis of the carbons after extended corrosion indicated a strong preferential attack of the ungraphitized regions, i.e. , much greater selectivity than the factor of 2.5 indicated by the BET correlation. A unifying correlation was observed for both the furnace blacks and their graphitized forms using the corrosion rate per unit mass and the iodine adsorption number. It was concluded that there are specific sites on the carbon surface (titrated by iodide) that serve as the initiators for dissolution of carbon atoms from the bulk of the material. One particular type of furnace black, SRF (N774), appears to be an especially good precursor for forming a highly graphitized and very corrosion resistant carbon black.