Effect of double oxide layer on metal-glass sealing

One of the main requirements of a metal-glass sealing is hermeticity along with mechanical strength of the metal-glass bond. For this purpose. the the rmal expansion coefficient of the metal needs to be as close as possible to the glass expansion coefficient to limit stress development in the glass. Second, an oxide layer should be developed on the metal surface that works as an interface. for the transition from glass properties, gradually, to me tal properties. For these purposes, a ferritic stainless steel stabilized w ith titanium has been developed. The thermal coefficient expansion of the m etal was measured using a Chevenard differential dilatometer. To evaluate a dhesion of the oxide film on the metal, oxide spallation after deformation has been performed. Scanning electron microscopy (SEM) was done to determin e the oxide structure and X-ray photoelectron spectroscopy (XPS) was perfor med to analyze the superficial composition of the oxide. It is shown that c hromium affects the thermal expansion coefficient of the metal. A study of the oxide film Formed by a thermal treatment under wet hydrogen atmosphere is presented. During this thermal treatment a double oxide layer is built u p. The outer layer, made of a spinel type MnCr2O4 with titanium oxide in th e extreme surface, dissolves in the glass. The inner layer, made of a chrom ia scale ensures the mechanical cohesion. Moreover, it is shown that silico n contained in the steel segregates at the metal-oxide interface and decrea ses metal-oxide adhesion, and consequently metal-glass sealing. (C) 2000 El sevier Science B.V. All rights reserved.