Zinc diffusion affects the chemical stability of the borosilicate glass and AISI 304 interface

Abstract To guarantee the long-term service of glass-to-metal seals, the interface between glass and metal should possess stable chemical bonding. This study presents a strategy to improve the chemical stability of glass/oxide/metal interfaces. Borosilicate glasses with different ZnO contents (0, 3.8 and 7.6 wt%) were joined to AISI 304 metal housings. A layered structure oxide film, consisting of a continuous outer spinel oxide layer, an inner layer of Cr2O3 and a discontinuous SiO2 region, was obtained through the pre-oxidation of AISI 304 before sealing. The morphology and chemistry of the glass/oxide/metal interface in the joined samples were systematically investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The results revealed that Zn2+ diffused into the spinel oxide layer, leading to a Zn-rich layer during the sealing process. Additionally, the distribution of Zn2+ in the spinel oxide layer became more uniform as the ZnO content increased. The joined samples also underwent a thermal aging treatment, and the results indicated that the Zn-rich layer can act as a barrier to ionic diffusion, improving the chemical stability of the glass/oxide/metal interface.