Manufacturing of tin oxide pellets and their application for CO and C3H8 gas sensors

Tin oxide (SnO2) powders were obtained by the homogeneous precipitation method from a 0.4 M starting solution prepared from tin chloride as tin precursor and urea as precipitation agent. The SnO2 powders were ball milled at 4, 6 and 8 h and two different speeds, 300 and 400 rpm. Structural analysis was performed by X-Ray diffraction (XRD) to confirm the SnO2 rutile phase. In this work the crystallite size variation with respect to milling time and speed has been studied by using the High Resolution Transmission Electron Microscopy (HRTEM). Further, the powders milled at 400 rpm for 6 h were put in a stainless steel die and pressed with a pressing machine to manufacture thin pellets. After several experimental trials stable SnO2 pellets were formed by pressing with 16 tons for 90 min. Silver contacts were deposited on the pellets surface by the thermal evaporation technique. The sensing properties of these pellets were measured at different carbon monoxide (CO) and propane (C3H8) concentrations and operation temperatures. Powders with a uniform crystallite size, around 25 nm, were obtained after a ball milling process for 6 h at 400 rpm. Effects of CO and C3H8 concentration and the measuring temperatures on the gas sensing properties are also reported in this work.