Characterization and butanol/ethanol sensing properties of mixed tungsten oxide and copper tungstate films obtained by spray-sol-gel

Mixed WO3-CuWO4 films have been prepared from an aqueous solution of copper sulfate and polytungsten gel with a molar ratio of Cu/W from 0 to 100%. These solutions were sprayed on to alumina substrates at 220 deg. C. The obtained films were amorphous and crystallized after annealing at 300 deg. C in air for 3 h. The annealed films were composed of a mixture of CuWO4 and WO3 phases. The film obtained from a solution with an equimolar ratio of Cu/W was pure CuWO4. The pure WO3 films obtained have high surface 'irregularities', such as porosity. These surface 'irregularities' in the films were maintained or even increased as Cu/W molar ratio augments in the starting solution up to 10%. The gas sensitivity to butanol and ethanol vapors is also enhanced when the CuWO4 phase increases in the film by up to 7-10%; with further increments to this proportion the detection sensitivity decreases, so compromises are approximately 7-10%. The gas sensitivity of pure CuWO4 was lower than that of pure WO3