6533b832fe1ef96bd129a226

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Changes of lead silicate glasses induced by leaching

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Abstract The structural differences in the surface region between freshly fractured and leached silicate glasses containing 16.7, 18.8 and 44.4 mol% PbO, respectively, were investigated by photoelectron spectroscopy (XPS). The optical properties and the thicknesses of leached layers were determined by reflection measurements. The binding energies of the O1s signal components for untreated samples can be ascribed to non-bridging (NBO) and bridging (BO) oxygen and oxygen associated with lead as network former (OPb). The binding energy of OPb was found to be 529.1 ± 0.2 eV. For quantitative conclusions, relative XPS sensitivity factors were determined for oxygen, silicon and lead in these glasses. The experimental NBO/BO/OPb ratio found is in good agreement with the NBO/BO/OPb ratio calculated by use of the `discrete bond model' (DBM). Leaching causes a removal of about 90% of the glass modifiers. The O1s signal of silanol groups and other O–H bonds formed appears at a higher binding energy as compared with the BO signal. Whereas the glasses with smaller Pb contents exhibit thin and well confined leached layers, on the glass with the larger Pb content a structured thick layer is formed. Its thickness growth follows a t -dependence expected for a diffusion controlled process. Pb at network forming sites is more stable with respect to leaching than network modifying Pb. After the removal of Pb from network modifying sites, in addition to the formation of silanol and other O–H bonds a rebinding between Si tetrahedra is found resulting in an increased density of the leached layer.