METALLIZATION (Continued.)

The process of joining alumina to metal commences, after preparatory cleaning, with the application of refractory metal paint onto the alumina surface. The paint is applied by spray, brush, roller or screen print, the actual method chosen being dependent upon the component size, shape and production quantities.

Various types of paint are employed, dependent upon the method of application and the grade of alumina. All the metallizing paints are prepared from the basic constituents, under close quality control, by Ceramic Seals Limited. In order to bond the refractory metal layer into the ceramic the components are sintered in a reducing atmosphere at temperatures up to 2000°C. The sintered metal layer is then nickel plated to provide a wetting interface for the subsequent brazing operations. The brazed joint will be hermetic and will remain so even after repeated heating cycles. Other techniques of joining ceramic-to-metal and ceramic to ceramic such as Active Braze Alloys, without prior metallization, are available if required.

When requested, metallized or metallized and glazed ceramics, to customer's individual specification can be supplied. Metallizing sapphire viewpoints and lenses is a speciality.