Production of SiO2–P2O5–CaO–(Na2O) structured films

The sol-gel method is used to obtain from film-forming solutions, based on solutions of tetra-ethyl-ortho-silicate and phosphoric acid with addition of calcium and sodium salts, thin structured films in the systems SiO2–P2O5–CaO–(Na2O) with the following content by weight (wt.%): 10 – 85 SiO2, 5 – 40 P2O5, 10 – 50 CaO, and 10 Na2O. The physical-chemical processes in solutions giving rise to a transition of the true solutions into colloidal solutions via successive sol and gel states are studied. A criterion is established for the film-forming power: the viscosity of the solutions. The critical value of the viscosity for obtaining high-quality films is determined. Oxide systems form in films during kilning to temperature 600°C. The structure of the films is investigated by means of infrared spectroscopy, atomic-force microscopy, and x-ray phase analysis. The surface of the films is characterized by an extended relief and porosity, so that it should have high adhesion properties. The thickness of the films obtained does not exceed 90 nm.