Microstructural Characterization and Gas Sensing Properties of Solution Precursor Plasma-Sprayed Zinc Oxide (ZnO) Nanostructured Coatings

ZnO nanostructured coatings have been prepared on Al₂O₃ substrates fitted with Au electrodes on one side and a Pt heater on the other, forming a solid-state gas sensor. The coatings were deposited by solution precursor plasma spraying (SPPS) using aqueous zinc acetate as the precursor solution. FE-SEM images show that the coatings are nanostructured with grain sizes of 50-100 nm. Surface morphology and grain size were found to be influenced by the flow rate of H₂ in the plasma forming gas. The gas sensing function was characterized by measuring the electrical resistance of the coating in the presence of NO₂ gas, showing good sensitivity down to the sub-ppm range.