Tungsten and Molybdenum Metallizings of High-Alumina Ceramics

Abstract

The metallizing of high-Al2O3 ceramics (purity>99%) with W or Mo was investigated by painting W, Mo, H2WO4 or H2MoO4 powder on the Al2O3 substrate and heating at 1400°C in H2 or Ar. When heated in H2, where H2WO4 and H2MoO4 were reduced to W and Mo, the bonding of W and Mo coatings to Al2O3 was very weak for all metal sources. This may be explained by the insufficient amount of glass component, mainly SiO2, in Al2O3 substrate to bond metal phase. When heated in Ar, on the other hand, H2WO4 gave W coating tightly bonded to Al2O3, although H2MoO4 did not form Mo coating. The metallic W may be produced by the thermal decomposition of W-oxide in Ar and bound to the substrate with a glass phase formed by the reaction between W-oxide and Al2O3. When Ni was joined to the substrate above the melting point, a large gap was observed at the interface between Ni and non-metallized Al2O3 substrate. On the other hand, Ni adhered tightly to W-metallized Al2O3 substrate, indicating that W phase played a role as an intermediate bonding layer between Ni and Al2O3.