OXIDATION BEHAVIOR OF N-CONTAINING MELILITE SOLID-SOLUTIONS ND2SI3-XALXO3-X(XN4)

Four compositions of N-containing Nd-melilite solid solution (Nd-MI) N d2Si3-xAlxO3+xN4-x (x = 0, 0.3, 0.6, 1.0) prepared by hot-pressing tec hnique were oxidized at 1000 degrees C or 1250 degrees C (only for x = 1.0) for 20 h in air in a TG unit. The phase compositions, densities, oxidation products, oxidation curves and microstructures of the sampl es were compared. The oxidation curves obtained indicate that the weig ht gains per unit area decrease obviously with increasing the Al subst itution in Nd-MI, which is in good agreement with the corresponding ch anges in morphologies of the oxide-scale and cross-section of the samp les, i.e, the cracks vary with the increase of Al content of Nd-M', fr om large to small, and transit to pores. The oxidation mechanism of Nd -M' was also discussed. (C) 1998 Published by Elsevier Science Limited . All rights reserved.