Chemical and microstructural characterization of sol-gel coatings in the ZrO2-SiO2 system

Sol-gel films and thin coatings are useful materials to be applied in a wide variety of optical devices. Particularly, sol-gel coatings behave as appropriate hosts for organic dyes that can be used as optical sensitive dopants. With the aim to check hydrolytic resistance and optical quality of sol-gel matrices to be used in further sensor applications, coatings in the ZrO2-SiO2 system have been prepared. Different starting precursors were used and several heat treatments were performed. Multilayer coatings were also obtained in the 50ZrO(2). 50SiO(2) composition. Hydrolytic resistance tests at room temperature were carried out. Influence of thermal densification degree of coatings upon hydrolytic resistance was evaluated by determining the ultraviolet (UV) absorption edge. Microstructure of samples before and after resistance tests were observed by transmission and scanning electron microscopy. Results indicate that the effect of treatment temperature is the main variable affecting chemical durability of samples. The presence of organics and residual water also played an important role, together with the percentage of ZrO2 and the use of organic-inorganic precursors. Conditions in which cracks appeared upon coatings were also discussed, as well as their influence on the results of further hydrolytic resistance tests. (C) 2001 Elsevier Science B.V. All rights reserved.