Protection des verres d'optique et miroirs aluminiés

Abstract
The object of this study is the behaviour of films as used for increasing or decreasing the reflectivity of glass, and of films likely to be used for protection of metallic deposits, when they are exposed to an atmosphere containing sea-air, at a temperature of 35°C, during a time sufficient to cause deterioration. The conclusions are as follows. The fluorides used either as protecting films or for anti-reflection treatment, have a poor resistance, magnesium fluoride giving the best results, but being practically destroyed after about ten days. Silicium and especially silicium monoxyde are practically unalterable when deposited on glass. They give by far the best protection for reflecting surfaces of metallic aluminium. But this protection disappears eventually owing to breaking of the protective layer which forms an increasing number of fissures through which the attack of the subjacent metal takes place. The difficulty is apparent with all the substances deposited on metal, and in particular with TiO2. Aluminium films of sufficient thickness obtained under very good conditions of vacuum and cleanliness, on which the natural protective alumina film is formed by exposure to air for one month show also good resistance. Processes of rapid formation of the protective film of Al2O3 chemical means have given moderate results.