Formation and properties of sol-gel derived, alkali resistant, CaO-BaO-Si-2-TiO2 coatings

Glass substrates were dip coated with CaO-BaO-SiO2-TiO2 system sols which w ere stabilised by chelation with acetic acid. Infrared absorption spectra w ere taken to understand the processes of sol formation and gel to glass tra nsition. The change in surface composition of coated substrates due to imme rsion in alkaline solution up to 144 h was characterized by scanning electr on microscopy (SEM) and atom absorption spectrophotometry analysis. It was found that alkali corrosion of the coated substrate results in the formatio n of insoluble TiO2 rich film and sodium and calcium silicate crystals. The reaction between the coating and hydroxyl ions was suppressed by a TiO2 ri ch film. On the other hand silicate crystals etched the surface during grow th to give rise to etched pits which cause dissolution of the oxides of Si, Ca and Na of the substrates as immersion time increased. However; the anti corrosion coating was an Effective barrier against alkali attack since the coating was not detached from the glass surface during alkali immersion. It was also shown that alkali durability depends on the composition of the co ating.