THE MECHANISM AND KINETICS OF THE NIOBIUM-CARBON REACTION UNDER SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS-LIKE CONDITIONS

The mechanism and kinetics of the chemical reaction between Nb(s) and C(s) under self-propagating high-temperature synthesis (SHS)-like (or combustion synthesis-like) conditions have been studied. Experiments w ere designed and conducted in order to produce a transport-resistance- free reaction between Nb and C under time-temperature conditions that are characteristic of the combustion synthesis process. To do so, a re action couple, consisting of carbon and either a thin niobium foil or a fine niobium wire, was used. The effects of the temperature history and the formation of a liquid phase on the reaction were studied. In a ddition, theoretical experiments of the reaction were also conducted. The results showed that at high temperatures, layered niobium carbide phases formed in a direction that was parallel to the original carbon- niobium interface. As might be expected, local melting played a very s ignificant role in the reactions. The mechanism and kinetics of these reactions provide a fundamental understanding of the manner and rate b y which a powder-based Nb/C SHS process takes place, and, by extension , to a large, general class of solid-solid material synthesis processe s that are based on the SHS (or combustion synthesis) process.