Humidity Sensing Behavior of Nano-Particle Size Magnesium Chromites Derived from the Tannery Wastewater

The aim of this work is recovery the chromium content from the tannery wastewater to decrease the environmental pollution. Also, benefit the extracted chromium compound by study their electrical behavior to be used as humidity sensor device. The chromium content was extracted as a solid power by using MgO for precipitation. The prepared dry powder was characterized by different process. The results of the characterizations indicate that the chromium content precipitated as MgCr2O4. The efficiency of separation reaches to 99.98%. The crystalline size was calculated by applying Scherer equation, the calculation indicate that the MgCr2O4 formed in nano-sized particles and affected markedly with calcinations. As the calcination temperatures increase from 300 to 900 °C the crystalline size increases from 44.1 to 70.6 nm, this may due to growth the crystals by calcinations. To study the evaluation of MgCr2O4 as relative humidity (RH) sensors, the dried samples were exposed to different humidities between 22 to 92%. The electrical behaviors of humidity samples were measured to investigate the humidity sensing. AC conductivity of both the dry and the humidity samples indicate that the conductivity increases as the humidity increase from 27 to 80 RH%. The variation of conductivity for both dried and humidity samples shows that as the humidity increases from 22 to 80, the conductivity increases while above 80% the conductivity greatly increase. From the dependence of the electrical properties of MgCr2O4 on water content, it may conclude that, MgCr2O4 can be used as humidity sensors between 27 to 90%.