Influence of the H2O Teos ratio on the preparation of SiO2 thin coatings by the sol-gel dipping method

Thin oxide coatings bay be prepared from solutions of alkoxides by the solgel method. The procedure consists in the application of a thin liquid layer of solution on the substrate and in the subsequent gelation of this coating. A final heat treatment transforms the gel into a glass or a ceramic. The liquid fila may be deposited by different ways; in the present work the dip-coating technique was used. A study on the different physical and chemical parameters which influence the quality and the thickness of silica coatings on glass substrates was started with the purpose of understanding and controlling the sol-gel dipcoating process. In this paper the first results concerning the role of water in the solution are presented. Solutions with different H2O/alkoxide ratios were prepared and used to coat glass slides. It was observed that the possibility of obtaining good quality coatings depends on the physical properties of the solutions, such as viscosity and surface tension, as well as on the chemical properties (gelation time). Data are presented on the influence of the withdrawal speed on the fila thickness in function of the water content. © 1989.