Antireflective coatings for glass , Graded index.

Glass compositions and process conditions by which broad band gradedindex antreflective films can be produced on glass surfaces have been developed. The end use for the treated glass sheet is as cover plates for flat plate solar-thermal collectors; thus, cost issues dictated that the process conditions fall within constraints imposed by the float glass process.To accomplish this objective, both the film formation process and the characteristics of the graded-index films were investigated in detail. A model, borosilicate glass was used for initial work that served to verify experimental procedures, to confirm essential features of the film forming process and to determine whether the porous surface film and the phase separated structure of the host glass had an adverse effect on mechanical properties. Glasses and film surfaces were characterized chemically (atomic absorption, Auger and SIMS), microstructurally (SEM, TEM and replica microscopy), by weight loss, by specific surface area (BET), by small angle X-ray scattering (SAXS) and optically.Based on the results with the borosilicate glass, a candidate soda-limesilica glass composition was defined that satisfied the phase separation and float glass process criteria. Heat treatments were defined for the glass that produced appropriate microstructures and selective etchants were defined that produced porous films by selective dissolution.U.S. Dept. of Energy