Carbons and Graphites, Reactivity of

Abstract

In this review article, the impact of reactivity on the most important applications of carbon and graphite materials are discussed. Utilization of carbon and graphite materials in many important applications is limited by their oxidation resistance. When exposed to air (oxygen) at high temperatures, these materials oxidize quite readily. In contrast to the behavior of many other materials, however, the products of oxidation are not stable at high temperatures and the mechanical properties of carbons may thus deteriorate. The topic discussed in this article is the ease of oxidation, or gasification reactivity, of carbons and graphite. More specifically, we are interested in the relative formation of gaseous products (carbon monoxide (CO) and/or carbon dioxide (CO2)) versus the solid oxides. These oxides are more appropriately referred to as stable carbon–oxygen surface complexes. We define ‘reactivity’ as the rate of reaction, for example, percent carbon gasified per hour, under specified conditions of temperature and oxygen partial pressure. Reactivity in O2 is the primary focus, because of carbon’s greatest affinity for this ubiquitous gas, but most of the arguments presented here are equally applicable to other oxidizing gases of interest (e.g., CO2, H2O, N2O, NO). In addition to reviewing the kinetics of the relevant reactions, including their sometimes unavoidable catalysis and often desirable inhibition, we discuss briefly the key aspects of thermodynamics and heat and mass transport phenomena.