ATOMIC-FORCE MICROSCOPY AND X-RAY PHOTOELECTRON-SPECTROSCOPY INVESTIGATION OF THE ONSET OF REACTIONS ON ALKALI SILICATE GLASS SURFACES

Atomic force microscopy was used to measure forces acting on a sharp t ungsten tip as it was brought into contact with silica and 30 mol% bin ary alkali silicate glasses. Experiments were performed in controlled atmospheres and under vacuum. Attractive forces and liquid-layer thick nesses were found to vary markedly between the glasses, and heterogene ity was observed on the binary alkali silicates analyzed in vacuo. Air or wet carbon dioxide exposure resulted in the penetration of the tip into a soft surface layer on the alkali silicates. In addition, liqui d layer formation on the alkali silicates was found to be promoted by exposure to water vapor in the order lithium < sodium < potassium. X-r ay photoelectron spectroscopy indicated that reaction between the pota ssium silicate surface and water vapor occurred on exposure to only 10 (-4) torr (1 torr = 1.33 x 10(2) Pa) water. Surface segregation and le aching of potassium occurred under the same conditions.