Method for Preparing Reduced Tungsten Oxide

The present invention relates to a novel method for preparing a solid, reduced, amorphous tungsten oxide. More particularly, it relates to a method for eifecting alkali metal borohydride reduction of a tungstate solution under controlled pH conditions and at ambient temperatures whereby a solid, amorphous precipitate com prising reduced tungsten oxide is recovered.

It is well known that the reduction of solid tungsten trioxide can be effected by means of hydrogen in a closed reaction vessel at elevated temperatures, usually in the range from about 300 C. to about 800 C., and under a positive pressure. Unfortunately, the utilization of elevated temperatures and autogenous pressures substantially increases the cost for preparing reduced tungsten oxide. In addition, a need exists for eifecting the coprecipitation of tungsten with other metallic substances. This cannot be accomplished, if the other substance is adversely affected by elevated temperatures. Hence, attempts have been made to carry out the reduction of a tungstate ion at ambient temperatures and pressures to prepare a useable precipitate. None has been successful. For instance, the treatment of ammonium metatungstate solution with sodium borohydride under alkaline conditions does not result in any reaction. Similarly, recoverable solid product is not obtained when ammonium metatungstate is treated with sodium borohydride under acid conditions. Employing the latter technique, only colloidal tungsten blue, in contradistinction to a precipitate, is formed. If a method for reducing tungsten trioxide in solution to recover a solid, reduced, amorphous tungsten oxide could be found which is inexpensive and straightforward, such a method would fill a long-felt need in the art.

It is, therefore, a principal object of the present invention to obtain recoverable solid, reduced, amorphous tungsten oxide from a tungstate solution. It is a further object of the invention to provide a procedure whereby reduced tungsten oxide is obtained in solid, amorphous form utilizing ambient temperatures and atmospheric pressures. Other objects and advantages will be noted from the ensuing detailed description.

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