Chlorine corrosion of graphites and technical carbons – I. Reaction with gaseous chlorine at elevated temperatures

Abstract

AbstractGraphite and graphitized technical carbons are used for the construction of chemical apparatus and equipment, which handle chlorine at higher temperatures. Technical carbons are attacked at temperatures above 500°C by chlorine with seizable rate so that they cannot be assumed to be stable at elevated temperatures although thermodynamically carbon in chlorine atmosphere becomes more stable as the temperature increases. The erosive/corrosive degradation of a number of technical carbons, including glassy carbons, by chlorine has been investigated in the temperature range 600 to 800°C. Chlorine corrosion has been compared with the corrosive action of oxygen, mixtures of oxygen and chlorine, carbon dioxide and mixtures of CO2 and chlorine. Chlorine corrosion is the slowest degradation process of all. Between 600 and 800°C the weight loss of these carbons in chlorine atmosphere is much slower than mass transfer limited and is kinetically controlled and its rate increases up to 0.5 mm/year at the highest temperature (800°C). Combustion in oxygen atmosphere is by five orders of magnitude faster than chlorine attack on carbon.Chlorine in presence of oxygen decelerates the combustion rate a lot, but chlorine has almost no influence on the rate of CO2‐attack on technical carbons. The detailed structure of different technical carbons bears only little on chlorine corrosion rates whereas it has an influence on the combustion rate with oxygen. A number of chlorinated aromatic olefines and compounds like octachlorostyrene and hexachlorobenzene are formed as byproducts of the chlorine attack on carbons. The main products are CCl4 and C2Cl4. A second paper will deal with anodic corrosion of Cl2‐evolving carbon anodes.