Microporous layer structure in oxidized aluminium nitride polycrystals

This study examined interfacial microstructure of a polycrystalline aluminium nitride (AlN). The AlN was thermally oxidized at an elevated temperature (1450 °C) in ambient air prior to the microstructural examination. A porous, thin-film structure was found at the interface where the oxidation took place. Thickness of the porous layer was about a few hundreds of nanometre. An energy dispersive spectrometry (EDS) revealed that the interfacial composition was yttrium-rich, indicating that the selection of sintering additives is critically important to the formation of the interfacial layer. This porous structure may be detrimental to the adhesive properties of the oxide scale.