Mechanism of the reduction of carbon/alumina powder mixture in a flowing nitrogen stream

Abstract

The mechanism of the reduction of carbon/alumina powder mixture in a flowing nitrogen stream was studied. Five steps were found to be involved in the overall reaction.

$$\begin{gathered} Al_2 O_{3f} (s) + 2C_f (s)\mathop \to \limits^{k_1 } Al_2 O(g) + 2CO(g) \hfill \\ Al_2 O(g) + solid surface\mathop \rightleftharpoons \limits_{k_2^\prime }^{k_2 } [Al_2 O]_s \hfill \\ [Al_2 O]_s + CO(g) + N_2 (g)\mathop \to \limits^{k_3 } 2AlN(s) + CO_2 (g) \hfill \\ CO_2 (g) + C_f (s)\mathop \rightleftharpoons \limits_{k_4^\prime }^{k_4 } CO(g) + [O]_c \hfill \\ [O]_c \mathop \to \limits^{k_5 } CO(g) \hfill \\ \end{gathered}$$

The consumption rates of Al₂O₃ and carbon, and the production rate of AIN, were determined to be

$$\begin{gathered} \frac{{d[Al_2 O_3 ]}}{{dt}} = - 143.88(1 + m)exp( - 290 580/RT) [Al_2 O_3 ][C]^2 / \hfill \\ \left\{ {1 + 5.83 x 10^{14} exp( - 427 497/RT)\frac{{[CO_2 ]}}{{[CO]}}} \right\}^2 kg mol s^{ - 1} m^{ - 3} \hfill \\ \frac{{d[C]}}{{dt}} = - 409.504 exp ( - 254 500/RT) [Al_2 O_3 ][C]^2 / \hfill \\ \left\{ {1 + 5.83 x 10^{14} \exp ( - 427 497/RT)\frac{{[CO_2 ]}}{{[CO]}}} \right\}^2 kg mol s^{ - 1} m^{ - 3} \hfill \\ \frac{{d[AlN]}}{{dt}} = 53.24(1 + m) exp( - 290 580/RT) [Al_2 O_3 ][C]^2 / \hfill \\ \left\{ {1 + 5.83 x 10^{14} exp( - 427 497/RT)\frac{{[CO_2 ]}}{{[CO]}}} \right\}^2 kg mol s^{ - 1} m^{ - 3} \hfill \\ \end{gathered}$$

in the temperature range 1648–1825 K.