Vapor-phase deposition of fluorine glass

Details Vapor-phase deposition of fluorine glass Vapor-phase deposition of fluorine glass

1993-11-29

1994-11-01

Beck, Shrive

Coating processes

Coating by vapor, gas, or smoke

Base includes an inorganic compound containing silicon or...

4272551, 65DIG16, 428432, 428691, C23C 1622, B32B 1700

Patent

active

053606370

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the vapor phase deposition of a fluoride containing glass on a substrate, as well as to the resulting vitreous composition deposited on a substrate.
It is known that certain mixtures of metallic fluorides have the property of yielding vitrifiable composition. Glasses based on metallic fluorides are generally called fluoride containing glasses.
Fluoride containing glasses have the property of presenting a broad window of transparency (wavelengths generally ranging from 0.3 to 8 micrometers) and in particular an ultra-transparency in the intermediate infrared, clearly greater than that of silica.
The field of use of fluoride containing glasses can then extend from long distance telecommunications using optic fibers at very weak losses, to laser fibers employed in microsurgery.
It is known that the preparation of optic fibers require very high purity materials. In particular, certain cations such as iron, cobalt, nickel etc. must not be present in an amount greater than 10 to 50 parts per million, in order to obtain optic fibers having very weak losses.
The classic process of producing pieces of fluoride containing glasses by fusion and tempering causes significant pollution by contact with the containers employed for the fusion and casting.
It is then very important to be able to prepare fluoride containing glasses by vapor phase deposition in order to avoid such disadvantages.
However, conventional techniques of vapor phase deposition are not useful because of the chemical complexity of vitreous fluoride systems.
In effect fluoride containing glasses admit of at least four constituents. Now, if the composition of the vapor in equilibrium above binary mixtures can generally be foreseen, the introduction of other constituents renders the evaporation more complex and the theoretic ratios of the constituents of the vapor phase are no longer respected. In general, the molten mixture is enriched in one or more constituents less volatile than the others so that the modification of the composition of the liquid being evaporated rapidly leads to departing from the thermic field of the liquidus. It has been observed then that evaporation ceases and that the composition present in the crucible crystallizes.
It is thus that the vapor phase deposition of a glass, based on zirconium fluoride, has been attempted without success; see for example H. Poignant et Coll., Mat. Science Forum, 5, 79-84 (1985).
It has now been discovered that it is possible to vapor phase deposit certain fluoride containing vitreous compositions by melting the constituents of the glass to be deposited in a receptor bath constituted by a molten mixture of fluorides forming itself a vitrifiable composition constituted of elements less volatile than the fluorides of the glass to be deposited. This technique avoids the difficulties encountered in the direct evaporation method, for it has been discovered that the composition of the "reception glass" remains essentially constant, or in any case varies sufficiently little so that it is possible to maintain the bath in the liquid state. It has been found that these results can be obtained when the composition of the reception bath is a vitrifiable composition, that is to say a composition having a behavior analogous to that of a eutectic mixture.
The present invention thus relates to a process for the vapor phase deposition of a fluoride containing glass on a substrate, the said fluoride containing glass having the following composition (in mole %; total 100%) vapors coming from a molten bath of the metallic fluoride comprising a reception bath having the following composition (in mole %; total 100%) ingredients of the fluoride containing glass to be deposited.
In particular embodiments of the invention the process can still exhibit characteristics, taken singly or in combination, which are explained hereafter.
The initial proportion in mass of the reception bath with respect to the total mass of the initial bath, is sufficiently significant to maintain a suf

REFERENCES:
patent: 4328318 (1982-05-01), Miranday et al.
patent: 4521523 (1985-06-01), Aubourg et al.
patent: 4610708 (1986-09-01), Sarhangi et al.
Glass Technology vol. 28, No. 1, Feb. 1, 1987, H. Poignant et al. "The preparation of fluoride glass single mode fibres".
Material Science Forum, vols. 32-33, 1988, Trans Tech Publications, B. Boulard et al: "Chemical vapour deposition of fluorides, molecular dynamics simulation of amorphous systems", pp. 61-68.
Revue de Physique Appliquee, vol. 21, No. 11, Nov. 1986, J. Lucas: "Les nouveaux verres", pp. 683-687.
Patent Abstract of Japan, Volum 9, No. 324 (C-320,-(2047), 19 Dec. 1985.

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