Avaliation of gas phase kinetics of the carburization and deactivation reactions aimed to produce NbC

The gas phase kinetic study referent the carburization of NbO2 to NbC is presented in this paper. The reaction took place in a rotating cylinder reactor, with rotation velocity (r) of 5 rpm, at temperatures of 1148, 1173 and 1223 K, gas phase flow of 4.033 x 10(-6) m(3)/s and Nb2O5 initial mass of 0.004 kg. The reaction mechanism is represented by the reduction of Nb2O5 into NbO2 (first reaction), followed by the carburization of NbO2 into NbC (second reaction). In this work the kinetic model of gas phase was carried out for the second reaction which is represented by two steps: the first regards the consumption of CH4 and second, the deactivation of NbO2. From chromatographic analysis of the gas products at the reactor outlet, the molar consumption of CH4 with reaction time was determined. The results showed the kinetic behavior in the first step represented by a pseudo-first-order model and in the second step by first-order deactivation models. In the present study, it was determined the kinetic constant (k), the activation energy (E) of the first and second steps, the velocity constant for deactivation k' and the decline constant k(d) that expresses the deactivation factor of NbO2. Statistical parameters showed satisfactory agreement between the experimental data and those predicted by the model. (C) 2012 Elsevier B.V. All rights reserved.