Transparent glass ceramic - based on alumina phosphorus pentoxide with boric oxide nucleating agent

摘要

Ceremic contains >=50% of fine grained pref. 30 mu, randomly orientated crystallites in a glassy phase and has compsn. 50-80 wt. % P2O5, 5-20% B2O3, 10-30% Al2O3. MgO, CaO and/or ZnO may be added to improve physical and electrical properties, usually at the expense of transparency. Pref. prepn. comprises melting, casting, annealing 450-650 degrees C, nucleating at 500-700 degrees C for1/j to 2 hrs. and crystallising at 650-1050 degrees C, for 1/i to 4 hrs. Resistant to alkali metal vapours and used for high temp. lamps and metal ceramic seals.