Corrosion behaviour of aluminium nitride in liquid aluminium: Influence of the microstructure

The intrinsic characteristics of sintered aluminium nitride (mechanical, thermal, chemical) facilitate their use in production of heater element protection tubes for molten aluminium industries. Two kinds of industrial materials are characterised from the mechanical and thermal point of view. Moreover the samples' microstructure is observed before and after corrosion tests in liquid aluminium alloy (dipped finger method). The two batches exhibit identical mechanical properties and the thermal conductivity decreases from 170 Wm(-1) K-1 at room temperature to 35 W m(-1) K-1 at 1000 degrees C. Conversely, the distribution of the secondary phase (YAG) depends on the material. Despite the microstructure differences revealed by scanning (SEM) and transmission (TEM) electron microscopy, no corrosion is observed after 2000 h tests in molten aluminium alloy. These results confirm that AlN could be a good candidate for this application. (C) 1997 Elsevier Science Limited.