Freeze-Drying of Ammonium Paratungstate

The preparation of ammonium paratungstate by freeze-drying is one of the methods of industrial production of tungsten products. Ammonium paratungstate freeze-drying method is essentially the principle of ammonium tungstate solution as the freeze-drying method of raw materials, its rapid rapid freezing.

At this point, ammonium paratungstate and water crystallize almost simultaneously. The product is then subjected to vacuum and the frozen crystals are warmed slightly to sublimate the water and free ammonia in the frozen crystals to achieve the preparation of ammonium paratungstate. Ammonium paratungstate products obtained by freeze-drying method showed a hollow needle-like structure. The ammonium paratungstate had a fine particle size and a uniform particle size distribution.

Freeze crystallization is one of the key steps of ammonium paratungstate freeze-drying method. The ammonium paratungstate freeze-drying process is as follows: a certain concentration of ammonium tungstate solution, placed on the metal plate. After the rapid use of liquid nitrogen method, the product was frozen to give frozen. The frozen product is then placed in a 5 to 6 L capacity freeze-drying apparatus, sublimed and dewatered at a vacuum of 50 to 100 microns. Finally, 11 parts of aqueous ammonium paratungstate were obtained. Ammonium paratungstate powder or tungsten composite powder obtained by the freeze-drying method has a fine particle size, a very uniform particle size distribution, and excellent control of product composition and impurities.

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