Large scale production of spherical WO3 powder with ultrasonic spray pyrolysis assisted by sol–gel method for hydrogen detection

Abstract

Abstract The spherical WO 3 powder was prepared by a facile ultrasonic spray pyrolysis process assisted by a sol–gel method. The thermal analysis of tungsten oxide precipitate indicated that there is 10% weight loss in the temperature range of 25–350 °C with two distinct steps, which correspond to the loss of the interlayer water molecules and the coordinated water molecules. The crystal structure and morphology have been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the XRD peaks for the obtained sample can be indexed to the orthorhombic WO 3 ·H 2 O and triclinic WO 3 with the crystal water being eliminated after heat treatment. The particle size distribution was characterized by laser particle size analyzer and the result shows a double distribution; 50% of the total volume is composed of particles which are smaller than 0.74 μm. The d.c. electrical response to hydrogen of the spin-coating thick film sensor has been measured in the temperature range from 200 °C to 300 °C. The results indicate that the sensor performs as a n-type semiconductor, and it shows the maximum and minimum responses at 200 °C and 300 °C, respectively, with nearly linear dependence on the hydrogen gas concentration.