Synthesis of yttria nano-powders by the precipitation method: The influence of ammonium hydrogen carbonate to metal ions molar ratio and ammonium sulfate addition

Yttria (Y2O3) nano-powders were synthesized by the normal-strike precipitation method. The influences of R (NH4HCO3/M3+, molar ratio) and ammonium sulfate addition were studied throughout the preparation process. Several analytic techniques such as XRD, TG/DSC, SEM and FTIR were used to determine the characteristics of the precursors and Y2O3 powders. It was found that morphologies and phases of the precursors were evidently influenced by the R value. The phases of the precursors were Y2(CO3)3·2.79H2O when R was 3-4, while the composition of the precursors with R = 4-5 was (NH4)aY(OH)b(CO3)c·xH2O. Homogeneous needle-flake shaped particles composed of coadjacent grains with diameters of about 70 nm were obtained as the R = 3-4. The rhombohedral flake-shaped particles were the products with R = 5-6. The mechanism of the influence of R value on the precipitation of the precursor was also investigated in this work. Pure Y2O3 nano-powders were obtained by calcining the precursors at 1000 °C for 4 h regardless of what the R value was. Sulfate ions affect not only dispersion of nanopowders, but also their grain size. Results obtained in this work are contributed to the controllable synthesis of yttria powders.