Geo-Centers, Inc.

Chester Fisher

Danh C Tran

A method of making fluoride glasses produces fluoride glass having such low OH and low oxide content that the extrinsic optical absorbance caused by the OH vibration at 2.9.mu. is eliminated or substantially reduced. In the method, a glass charge is placed in a capped crucible and dry argon gas is caused to flow through the capped crucible while the temperature is raised to melt the charge. Thereafter, while the dry argon gas flow is continued, the temperature in the furnace is held constant for a time sufficient to obtain a homogenous melt in which all crystalline materials are dissolved. The temperature is then lowered to a value between the glass crystalization temperature and the sublimation temperature of ZrF.sub.4 and then, at isothermal conditions, the flow of dry argon gas is replaced by a flow of SF.sub.6 gas or by a flow of CF.sub.4 gas. At the lowered temperature, the SF.sub.6 or CF.sub.4 gas flow is maintained for a time sufficient to eliminate or greatly reduce OH and oxides in the glass melt. Thereafter, the melt is allowed to cool in a still water-free environment.

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Columbia, MD, United States of America

Chester Fisher