Transparent, Polycrystalline Cubic Aluminum Oxide

The stringent mechanicalthermal and broadband electromagnetic wave transmission requirements for sensing mechanisms of the future require optimized and new material concepts. Aluminum oxide-based ceramics and single crystals are strong contenders for these applications, but exhibit significant directional variation anisotropy in properties. This barrier to utilization has been eliminated by an AMMRC-invented material - sintered polycrystalline nitrogen- stabilized cubic aluminum oxide ALON. This material has been fabricated into dense, transparent bodies with isotropic properties Knoop 100 hardness of 1800, elastic modulus of 46,000,000 psi, a dielectric constant and loss tangent, respectively, at 10 MHz of 8.56 and 0.0004, trivial oxidation in air up to 1200 C, an IR cutoff at 5.2 micrometer, and an average thermal expansion coefficient alpha of 0.000,007 per C 25 C-1000 C. These properties suggest greatly improved performance in many other Al2O3 applications. Successful fabrication of ALON was preceded by the determination of the high temperature phase equilibria and crystal chemistry of aluminum oxynitride spinels in the Al2O3-AlN system.