Spray pyrolysis of YBCO precursors

Acetate, nitrate, and oxalate precursors for YBCO have been spray pyrolyzed under different conditions. Shelled and nonhollow microparticles were obtained from acetate and nitrate precursors, while nonhollow agglomerates were obtained from the oxalate suspension. At low furnace temperatures, the temperature and residence time of the particles were insufficient for complete decomposition of the precursors leading to Cu2O and Cu metal in the product. At 900 °C and above, reduced forms of CuO were not detected by x-ray measurements, and up to ∼60 wt.% YBCO was obtained. An approximate model predicting the particle and gas temperatures along the reactor under different operating conditions was developed. The model demonstrates that under the experimental conditions used here, the absorbed radiation heat by the particles from the furnace walls is significant in heating the gas. The gas and the particle temperatures are fairly close due to the effective heat transfer to the particles. At furnace temperatures of 700 °C, the maximum predicted particle temperature is about 500 °C (for ∼1 s). This explains the incomplete reactions obtained under these conditions. Above 900 °C the reactions are predicted to be complete within the first half of the furnace, leaving sufficient residence time for partial conversion into YBCO. Finally, an approximate expression predicting the relative contribution to the gas heating by the walls and the aerosol has been developed.