Compared with the ordinary tungsten oxide, hollow porous tungsten oxide sphere because of the larger specific surface area, thus to has the significant size, surface, quantum size and macroscopic quantum tunneling effect, and thereby to expand the application areas, which can be used as a solar absorption, stealth and photocatalytic materials and gas sensitive materials of NO_x, H₂S and NH₃ etc. Ammonium metatungstate (AMT) is an important intermediate compound in tungsten production industry, the excellent raw material for manufacturing tungsten oxide, tungsten powder, tungsten carbide powder and other tungsten products. 

 

A study was taking the ammonium metatungstate solution or a mixture of AMT and ammonium tungstate solution as raw material, to produce hollow porous tungsten oxide sphere through a combination of spray drying method and heat treatment, its technological process is: Preparing ammonium metatungstate solution or a mixture solution of AMT and ammonium tungstate, with the concentration of 200 g/L, then to prepare AMT or mixture of AMT and ammonium tungstate hollow powder; after putting the powder in a furnace to calcine for15-180 min under the temperature of 400-1000℃, we finally get made hollow porous tungsten oxide ball. Its properties are as follows: 

1. The concentration of AMT and ammonium tungstate mixture solution is 200g/L, the mass ratio of AMT and ammonium tungstate is 4:1~1~4, heat treatment temperature is 400~1000°C, time of heat preservation is 15~180 min. 

2. The spray drying method is using the ammonium tungstate solution, the concentration is 200 g/L, the heat treatment temperature of 400~1000°C, time of heat preservation for 15 ~ 180 min. Because when the temperature is below 400°C, the crystal growth speed is to slow and hard to generate porous; however, when the temperature is higher than 1000°C, the too fast growth speed of crystal will cause the nanosize particle of tungsten oxide hard to control, and thus it will easily get the coarse tungsten oxide particle which will reduce the specific surface area. While, when the heat preservation time is less than 15 minutes, the crystal growth is not completely; but when the holding time is higher than 180 min, it will come out combination of crystal and cause the coarse tungsten oxide particle.