Phase Equilibria in the System Ca0-PbO-SiOZ 157 Na,CO,j, and NaOH also indicates that an etching mechanism is predominant because Na is still present on all treated surfaces. Also, the Na,CO, and NaOH treatments were sufficient to remove the SO,-rich skin developed during fire-polishing, since the Ca and Mg in the bulk are now detectable. Electron micrographs (Figs. 8(A), 8(B), and 8(C)) indicate that the fire-polished surfaces are less planar than those obtained from the acid treatments ( Fig. 8 ( 0 ) ) and that residues are present on all surfaces treated in alkaline solutions. IV. ConclusionsThe combined techniques ofXPS and TEM of surface replicas of chemically and physically treated soda-lime glass surfaces clearly demonstrate that large variations in surface composition relative to the bulk glass result. Large surface compositional differences can exist without apparent microstructural differences and are readily detectable by XPS. The suggestion that the heated soda-lime glass acquires a surface film of Na,O in the range of 400" to 700°C'4 is supported by XPS data for the vacuum heat-treated surfaces. In general, the XPS results show that treatment in dilute acids and water results in a nearly pure SiO, surface, fire-polishing yields an Si0,-enriched surface, and dilute bases leach some of the network modifiers. There is little correlation between XPS and surface topography as determined by TEM. With the exception of firepolished surfaces, all treatments render the surface susceptible to the attachment of atmospheric COP; prolonged treatment results in the formation of alkali and alkaline-earth carbonates. These are the familiar weathering products of soda-lime as well as other glass surfaces. Direct surface analysis by XPS is in essential agreement with the inferred composition of soda-lime glass surfaces, as determined by chemical analysis of leachates.

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