Manufacture of Ag, Cr and Cu-doped ZnO pellets for gas sensor applications

Starting from a mixture of zinc acetate and potassium hydroxide, zinc oxide (ZnO) powders were prepared by the homogenous precipitation method. The powders were calcined at 800°C for 2h, and subsequently milled in a planetary ball milling during 8 h at a constant speed of 400 rpm. The crystalline phase was determined from X-Ray diffraction (XRD). The morphology of the particles was analyzed by using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). From XRD results the wurtzite structure of ZnO was corroborated. SEM images showed a homogenous distribution of the particle size, whereas from TEM analysis the particle size was determined with a higher precision. From the milled and calcined powders, a mixture of ZnO powders with alumina (Al₂O₃) was developed at different weight ratios for manufacturing 1 mm thick pellets. After measuring the sensing properties of undoped pellets, the [ZnO]/[Al₂O₃] ratio presenting the maximum sensitivity was taken as reference, and then, doped by impregnation pellets were manufactured to analyze the dopant effect. Three different dopants were used, namely, Cu, Ag, and Cr. The sensing properties of the pellets were tested in an atmosphere of propane, 500 ppm, and different operation temperatures, 200 and 300°C.