Reaction Bonded AlN (RBAN) Advanced Non Oxide Ceramics

The nitridation of RBAN samples proceed by both solid-gas and liquid-gas reactions depend on the morphology and average particle size of Al starting powder. The reaction rate was found been increased by decreasing average particle size of the Al and by choosing the flake-like morphology. The temperature at which nitriding reaction occurs depends on the Al average particle size and morphology. The compared respective results show a major influence of the AlN/Al ratio. It seemed that the optimum AlN/Al weight ratio should be 75/25 wt%. Due to the smaller particle size and morphology of the flake -like morphology of Al starting powder as compared to equi-axed one, however the nucleation period in flake-like morphology Al maybe shorter. The change in the microstructural parameters resulting from the Al powder particle size distribution and morphology also affects the mechanical properties of RBAN samples. Fracture strength increases with decreasing porosity, pore size and by using the flake-like morphology. In order to make high strength materials it is desirable to have a homogeneous microstructure with a narrow pore size distribution and small pores.