Reactions between sol–gel coatings and some technical glass substrates during consolidation

SiO2 and Na2O–SiO2 coatings have been applied on float glass and other technical glass substrates by a sol–gel dip-coating process. After drying and baking these films at temperatures up to 500 °C and for times up to 1020 min, the in-depth profiles of the different constituents were measured by secondary neutral mass spectrometry (SNMS). Sn, Al, and Si turned out to be immobile, whereas a diffusion coefficient of ≈10−17 cm2/s could be evaluated for Mg at 500 °C for the transport from float glass into the films. Ca diffused a little faster, however, especially for the Na2O–SiO2 films a saddle point and finally a peak occurred in the interface region. This interface peak was even stronger for Na, showing quite anomalous profiles. The mechanism of this peak formation is explained mainly as an up-hill diffusion process. According to this model at the interface non-bridging –O− ions are formed, whose electroneutrality has to be maintained by mobile cations like Na+ and Ca2+, even diffusing against their own concentration gradient. The other glass substrates, two borofloat glasses and an alkali-poor display glass showed similar but less pronounced effects.