Interfacial reaction in anodically bonded joints during receiving reverse voltage

A voltage in the opposite direction to that of anodic bonding was applied to anodically bonded joints of Fe and Kovar alloys to borosilicate glass at a temperature at which thermal diffusion of the alkali ions in the glass was activated. Disjunction of the bond interfaces occurred in the Kovar/glass joints. On the other hand, the Fe/glass joints retained cohesion of their bond interface after a long application of the reverse voltage. In an as-bonded Kovar alloy/glass joint, a reaction layer of a crystalline Fe oxide was found at the bond interface. The content of Fe in Kovar alloy adjacent to the bond interface decreased. The oxide layer was formed by the reaction between Fe from the Kovar alloy and O from the alkali ion depletion layer in the glass. The reaction layer in an Fe/glass joint was of amorphous Fe–Si oxide. This layer was much thicker than the reaction layer in the Kovar/glass joint. After application of the reverse voltage, Fe in the amorphous oxide layer in Fe/glass was substituted by alkali ions. It was suggested that this process mitigated concentration of alkali ions at the bond interface and prevented disjunction of Fe/glass joints by the reverse voltage.