Helmut Dislich

Glassy and crystalline systems from gels: Chemical basis and technical application

Abstract After a period of twelve years development of sol-gel-derived glasses, glass ceramics and ceramics, there are some new products or processes which could possibly be “scaled up” for technical application. For economical reasons, they must have special “sol-gel advantages”. Such sol-gel-advantages are described and then connected with the properties which these special products and procedures must have. A review of other sol-gel fields, using literature and patents until 1982, is also presented. The most interesting fields seem to be: preforms for communication fibres, technical fibres drawn from solution (possibly, unsupported films), hollow spheres for nuclear fuels, catalytic effects and, last not least, coatings. Coatings are the oldest sol-gel products which have derived new impetus from multicomponent oxide syntheses. In this field, heat mirror coatings on float glass, necessary for energy saving windows, are of the greatest interest. The general widening of the chemical basis is the natural well of future products.

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

Abstract 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 TiO 2 and SiO 2 . 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 (Cd 2 SnO 4 have been prepared.

Sol-Gel 1984 → 2004 (?)

Abstract The future of sol-gel will show “tailor-made” products with better-defined compositions (also stoichiometric), higher homogeneity and purity, and more controlled processes at lower temperatures. The higher the sol-gel specific advantage is, the higher the future chance. Prognosis for special ceramics should be especially good. “Heavy” industrial procedures will not be replaced. Some fields of interest are described in this sense.

Sol-gel: Science, processes and products

Abstract The connection between science, processes and products in the sol-gel field is shown. This determines what advantages sol-gel processes have and can have in the future. But it also makes clear some disadvantages which have to be circumvented for industrial use. Therefore, future products based on the sol-gel process must have product or process advantages.

Anti-reflecting light-scattering coatings via the sol-gel-procedure

Abstract After a simplified description of usual AR-coating procedures a sol-gel cold-spray procedure is described. A dispersion of SiO2 (Aerosil®) in an alcoholic solution of partly condensed silica acid ester is sprayed onto the front of a television screen and converted by hydrolysis and polycondensation into a transparent silica layer, in which silica particles are embedded. The optical quality of this coating is comparable with an acid-etched glass surface.