ON THE INTERACTION OF SILICA XEROGEL THIN-FILMS WITH OXIDIZED ALUMINUM OR PHOSPHATE COATINGS ON STEEL

XPS has been used to study the interaction between very thin layers of silica deposited by the sol-gel technique and coatings on metals of the simple oxide or the phosphate type. Samples were measured as-received and after vacuum heating at 150-350-degrees-C. It has been found that silica xerogel below 500-degrees-C reacts with alumina and nickel oxide to form silicates. Compared with simple iron or zinc phosphates, mixed zinc-iron phosphate coatings are more stable against heating and contain much more phosphorus. In this case silica surface deposits (1) reduced mass transfer and the ability for phosphate coating reconstruction, (2) limited phosphorus and/or water removal from the surface and (3) enhanced zinc segregation towards the surface.