Preparation of nanostructured Zn-Cr-O spinel powders by ultrasonic spray pyrolysis

Abstract

Ultrasonic spray pyrolysis (1.7 MHz) has been applied for the generation of zinc chromium oxide submicronic (470 nm) particles from the corresponding metal nitrate solution. Heterogeneous gas-liquid/solid chemical reactions occurred in dispersed systems (aerosols) at 1173 K with the residence time ranging from 3 to 6 s. Such a synthesis method enables a high surface reaction and stoichiometric retention at the droplet scale that is of special importance when functional materials with sensing properties are considered. Consequently, homogeneous distributions of the constituting elements and zinc to chromium atomic ratio of about 0.7 are proved by EMAX analysis. The particle morphology, revealed mostly as a composite structure, comprised of primary crystallites smaller than 70 nm. The particle crystalline structure, phase content and decomposition behavior were analyzed in accordance with various methods of analysis (X-ray powder diffraction (XRD). differential scanning calorimetry (DSC). differential thermal analysis (DTA), scanning electron microscopy with X-ray microanalyser (SEM-EMAX)) and discussed in terms of precursor chemistry and process parameters.