Hydrothermal Preparation of Pyrochlore Tungsten Oxide

Pyrochlore tungsten oxide as an important tungsten compound form, may be used for gaschromic, electrochromic, photochromic materials, catalysis, batteries and other fields. Pyrochlore tungsten oxide preparation method using soft chemical synthesis method and hydrothermal synthesis method.

Soft chemical synthesis with APT as precursor, refluxing in acid glycol solution, thus, [(NH₄)₂O]W₂O₆ (x = 0.5), products by ion exchange and dehydration, obtained pyrochlore tungsten oxide. Soft chemical synthesis method is early preparation of pyrochlore tungsten oxide, the reaction efficiency is low, is not suitable for large scale application.

Hydrothermal synthesis method includes adding hydrochloric acid in Na₂WO₄ solution was acidified by hydrothermal reaction, preparation of pyrochlore tungsten oxide, at present, the preparation of pyrochlore tungsten oxide by hydrothermal synthesis method is based on the system of sodium tungstate and the pyrochlore tungsten oxide has higher sodium and other impurities. Because of the structure of pyrochlore tungsten oxide special, impurity content is difficult to decline, severely affected the quality of products.

Some scholars have improved the hydrothermal method, and can directly from the ammonium tungstate solution preparation pyrochlore type tungsten oxide, the method steps are:

1) Adding tungstate type tungsten oxide seed into ammonium tungstate solution to obtain ammonium tungstate slurry;

2) The resulting ammonium tungstate slurry was placed in a reaction vessel, closed after hydrothermal reaction;

3) The slurry obtained after the hydrothermal reaction is cooled and solid-liquid separated, and the resulting solid is washed and dried, and part of the slurry is returned to the step 1) for the seed crystal, and the rest is the pyrochlore-type tungsten oxide product.

Hydrothermal method from ammonium tungstate solution preparation of pyrochlore tungsten oxide, compared with inorganic or organic acid solution to adjust the pH preparation of pyrochlore tungsten oxide process from sodium tungstate solution, using ammonium tungstate solution system, its wide range of applications, easy and mainstream tungsten metallurgy combination, easy to use; the system of adding the pyrochlore tungsten oxide crystal, can accelerate the reaction rate, and the seeds can be recycled; hydrothermal reaction system closed, in which ammonia and ammonium carbonate were retained in the crystallization solution, can recycling, do not pollute the environment.

• < Prev
• Next >