Weathering of float glass exposed outdoors in an urban area

To study the weathering of soda-lime-silica float glass exposed to a polluted, urban environment, an outdoor exposure experiment was conducted in Paris. Both 'tin hath' and 'air' faces were exposed in two locations: sheltered and unsheltered locations from the rain. Samples were withdrawn after one, two, six, 12 and 24 months and analysed by SIMS. EPMA, FTIR spectroscopy and SEM. Analyses show the formation of leached layers some tens of nanometers thick as a consequence of exposure. For all exposure modes the surfaces were depleted in sodium and, to a lesser extent, calcium, and relatively enriched in silica. In general, unsheltered samples are more weathered than their sheltered homologues, and the 'air side' appears more weathered than the 'tin bath' side. For all the samples the thickness of the leached layer grows over time. Hydration of this layer is clearly detected by SIMS which revealed hydrogen enrichment in the uppermost surface. Beside the uniform leaching process, the samples seem to undergo other localised weathering phenomena. Indeed some hollow and jagged areas, observed by SEM might be interpreted as evidence of local corrosion phenomena.