Traditional preparation method of blue tungsten oxide contains APT calcinaton method, APT mild hydrogen reducing method and inner reducing method. APT calcination method principle is during heating process, keep negative pressure in furnace to prevent air goes in, APT decompose of generating ammonia can split out hydrogen and nitrogen, the mild reducing atmosphere should be kept in furnace, the final product is blue tungsten oxide. Besides that, in order to adjust phase composition of product, ammonia gas can be injected in furnace.
Blue tungsten oxide phase composition is depended on the chosen non-oxidative system, which means if some kind of phase composition of blue tungsten oxide is needed, by controlling temperature and non-oxidative atmosphere, the product can be easily obtained. Below chart shows phase composition of APT decomposed under different atmosphere.