Electrical and humidity sensing properties of Chromium(III) oxide-tungsten(VI) oxide composites

The composite made from the mixture of Cr2O3 and WO3 for humidity sensing properties are described in detail. The sintered Cr2O3 (COWO-10), WO3 (COWO-01), and the composites of CO and WO in the mole ratio 1:1, 1:2,2:1, 3:2, and 1:4, respectively in the form of a disc of 10 mm diameter were subjected to do conductance measurements over the temperature range 373-673 K from which activation energies were determined. The Brunauer-Emmett-Teller (BET) surface adsorption studies showed that the radius of the pore sizes were found to,be distributed from 10-45 Angstrom. The pore specific volume was calculated to be 0.01 cm(3) gm(-1), which was further evidenced by scanning electron microscopic photographs. As the composites having micropores are preferred for the humidity sensing properties, the composites were subjected to do resistance measurements as a function of relative humidity in the range of 5-98% RH, achieved by different water vapor buffers thermostated at room temperature. The sensitivity factor, S-f (R-5%/R-98%) measured at 25 C revealed that COWO-14 has the highest humidity sensitivity factor of 14039( 977). The response and recovery time for this humidity sensing composite was also studied. (C) 2003 Elsevier Science B.V. All rights reserved.