New Techniques in Glass-to-Metal Sealing

The new techniques in glass-to-metal sealing described in the paper include accurate and controlled oxidation of the metal, and the powder-glassing method of making seals. The accompanying experimental data refer to Kovar, since most of the laboratory work has been on glass-to-Kovar seals. Data are presented for Kovar oxidized at a number of controlled temperatures and varying times. Excellent adherence of glass to Kovar is obtained with a weight gain of about 0.0003 to 0.0007 grams per square centimeter regardless of temperature of oxidation. With preoxidation, any tendency for peeling or flaking shows up readily on cooling to room temperature. This condition is undesirable, since it indicates subsequent poor glass-to-metal adherence. The powder-glassing method of making seals consists of grinding the glass, suspending the powdered glass in a suitable liquid, applying it to the prepared metal, and fusing to form a thin glass layer. The glass tube or bulb is subsequently joined to this layer as a glass-to-glass seal. Several examples of applications are given, one of them pertaining to multisection blanks employing butt seals. Hypotheses on the function of H2baking of Kovar, the adherence of glass to Kovar, and the nature of the oxidation process of Kovar are presented.