Sintering and humidity-sensitive behaviour of the ZnCr2O4-K2CrO4 ceramic system

Solid state reaction at elevated temperatures and the sintering behaviour of zinc chromite formed by zinc oxide and chromite oxide were investigated. Crystalline structure, surface and fractured morphologies and humidity-sensitivity characteristics of ZnCr2O4-K2CrO4-CuO were studied. The fired ceramic body, which proved to be mainly constructed from ZnCr2O4 spinel grains, was porous. The humidity characteristics of the sensor showed that the resistance decreased as a logarithmic function with an increase in humidity. The resistance values obtained were about 6 x 10(9) Omega and 3 x 10(4) Omega at 25 and 93% relative humidity (RH), respectively. Based on a.c. impedance measurements, an equivalent circuit associated with a network of resistors together with series capacitors has been suggested. It is assumed that such an equivalent circuit model of the sensor under the moist conditions represents the sensing mechanism as a diffusion process.