High pressure combustion synthesis of aluminum nitride

We report initial results on the synthesis of monolithic aluminum nitride by burning Al–AlN mixtures in high pressure nitrogen. The objective is to synthesize economically large, near-theoretical density AlN parts. In this work, we begin with compacted mixtures of 10 μm Al and 3 μm AlN powder formed into 7.62 cm diameter by 3.81 cm thick disks having densities up to 60% of theoretical. Then, at N₂ pressures up to 180 MPa (26 000 psi), we ignite the disk on one face. The fraction of Al converted to AlN, density, and severity of macroscopic cracking vary with N₂ pressure and heat transfer from the sample. Presently, products are inhomogeneous, showing regions of relatively high porosity, regions with no porosity but with AlN in a matrix of Al, and regions of nearly theoretical density AlN.