The effectiveness of SnCl2 and SnCl4 in the sensitization of soda lime silicate glass for silver mirror production was investigated using XPS. Precleaned glasses treated with 2.5 × 10-3 M solutions of either SnCl2 or SnCl4 showed similar levels of tin uptake (3 to 5 at%) that could not be removed by extensive rinsing in distilled water. Oxidation states of the bound tin were not easily distinguished by XPS measurements, however their chemical reactivities were quite dissimilar. Upon exposure of the sensitized glass surfaces to ammoniacal silver nitrate, approximately two silver atoms became attached per surface tin atom for the SnCl2-treated specimens. In contrast, most of the tin was lost from the SnCl4-treated glass surfaces after identical treatment. Approximately one silver atom became bound per remaining three tin atoms in the latter case. Auger parameter data indicated that the ionic character of the silver-tin bond was greater than that of metallic silver but less than that of the silver-oxygen bond in either silver oxide or ion-exchanged silver in the glass. An oxidation-reduction mechanism is proposed for the sensitization reaction of silver with surface stannous ions that is consistent with XPS results.
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