Translucent Aluminum Oxide-to-Niobium Metal Seals Using a Crystalline Solder in the System CaO-Al₂O₃-MgO-B₂O₃

Abstract

Translucent aluminum oxide-to-niobium metal seals were formed by using an oxide solder and interfaces between the materials were examined by an optical microscope and an electron probe microanalyzer.
The oxide solder used for this experiment was a crystalline solder and was composed of crystals of CaO, Al₂O₃, MgO and B₂O₃, and contained no alkali.
The results were as follows:
(1) Vacuum tight seals were formed by this technique.
(2) The solder which turned into a glass-ceramic composite by sealing operation contained 3CaO⋅Al₂O₃, CaO⋅Al₂O₃ and MgO⋅Al₂O₃ as main constituent phases.
(3) B₂O₃ in the solder was very useful in improving adhesion.
(4) The intermediate layer about 10μ thick was formed at translucent aluminum oxidesolder interface.
(5) Thickness of the intermediate layer at niobium metal-solder interface was less than 1μ. This was in contrast to the case of solder containing Na₂O and K₂O which had formed intermediate layer 10μ thick in the author's previous experiment.
(6) Transition layers with concentration gradients of Al and Nb were formed in the solder at the ceramic-solder and metal-solder interfaces, respectively. These layers were expected to be useful in reducing sealing stress and in improving adhesion.