J. Sappei’s research while affiliated with Mines Saint-Étienne and other places

By reaction between transition (γ) aluminas from boehmite and ammonia (T ≈ 1000-1100°C), up to 1%wt nitrogen can be fixed in the form of a γ-aluminum oxynitride layer on γ-Al2O3 surface grains. This layer delays the polymorphic transformation of γ- into α-Al2O3. For higher nitrogen contents, aluminum nitride appears. An application can be the preparation of partially nitrided Al2O3 powder in γ-AlON and /or AlN, that can lead to γ-AlON single phase or Al2O3-γ-AlON composites. Such composites, obtained by γ-Al2O3 partially nitrided in AlON, present γ-AlON along grain boundaries; that microstructure is efficient in increasing the composite wear resistance.

The action of ammonia on boehmite was studied in the temperature range 900–1200°C. This reaction begins at about 900°C and leads to the formation of a γ aluminium oxynitride (γ AlON) layer on the γ alumina grains. This layer retards the allotropic transformation of γ into αAl2O3. Starting from boehmite, it is not possible to get more than 1% wt N in the form of γ AlON. For higher nitrogen contents, aluminium nitride appears. An application can be the preparation of partially nitrided alumina powders containing γ AlON and/or AlN that can lead to either Al2O3AlN composites or single phase γ AlON ceramics.