Soft Magnetic - Controlled Expansion - The thermal expansion characteristics of this group of alloys are used in several ways. For glass-to-metal sealing applications, the thermal expansion characteristics of glass and metal are closely matched and the metal must also have an oxide which fluxes at high temperature with the glass to provide a hermetic and mechanically sound joint. The most common applications are attachment of metallic parts to the internal of TV and cathode ray tubes, and also certain lamp bulb bases.