History and principles of the sol-gel process, and some new multicomponent oxide coatings

Certain historical facts are discussed regarding the principles of the sol-gel process and some new applications are mentioned. Forty years ago Geffcken and Bergen prepared single oxide coatings by the sol-gel process and Schroeder developed a thin film physics. The first products appeared on the market in 1953 and large scale production in 1959 with automotive rear-view mirrors, later anti-reflection coatings and sunshielding windows were introduced using TiO2 and SiO2. Dislich and Hinz elaborated the chemical basis for the preparation of multicomponent oxides, glasses, glass ceramics and crystalline substances in 1969 and published their results in 1971. So from 1971 on it was known that any type of multicomponent oxide can be synthesized using the alkoxides of the different elements by the sol-gel process. Of the three steps; complexation, hydrolysis, polycondensation, it is the first step that has been newly introduced. The first product on the market now for some years is a silicate phosphate layer which improves the hydrolytic stability of optical glasses, used in laser protective filters manufactured by the Deutsche Spezial Glas AG. An 8-component glass ceramic (Si, Al, P, Li, Mg, Na, Ti, Zr) and a crystalline cadmium stannate layer (Cd2SnO4 have been prepared.