WO3 nanopowders were synthesized by using an aged-hydrothermal route. A saturated aqueous solution of ammonium metatungstate [(NH4)10W12O41xH2O] (0.15 mol of W) was prepared and acidified with HNO3 (2.2 N) to produce ~5 pH. The product was kept in a hermetically sealed Teflon container with stirring for one week at 60 °C. Then 5 ml of aged solution was transferred into a Teflon-lined stainless steel autoclave and heated at 170 °C for 48 h. The material obtained was filtered, washed with deionized water and dried in air at room temperature and finally calcined at 400 °C.

 

Thick films of nanostructure h-WO3 were prepared by using an screen printing technique. In the present process, thixotropic paste was formulated by mixing the synthesized h-WO3 powder with ethyl cellulose (as a temporary binder) in a mixture of butyl carbitol acetate and turpineol organic solvents. The ratio of h-WO3 to ethyl cellulose was kept at 95:05. The ratio of inorganic to organic part was kept as 75:25 in formulating the pastes. The thixotropic pastes were screen printed on a glass substrate in the desired patterns. The as-prepared films were fired at 400 °C for 2 h. The prepared thick films were called as pure h-WO3 thick films.