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

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 o ccurred in dispersed systems (aerosols) at 1173 K with the residence time r anging from 3 to 6 s. Such a synthesis method enables a high surface reacti on and stoichiometric retention at the droplet scale that is of special imp ortance when functional materials with sensing properties are considered. C onsequently, homogeneous distributions of the constituting elements and zin c to chromium atomic ratio of about 0.7 are proved by EMAX analysis. The pa rticle morphology, revealed mostly as a composite structure, comprised of p rimary 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 s canning calorimetry (DSC). differential thermal analysis (DTA), scanning el ectron microscopy with X-ray microanalyser (SEM-EMAX)) and discussed in ter ms of precursor chemistry and process parameters. (C) 2001 Elsevier Science Ltd. All rights reserved.