Monodispersed Sc₂O₃ precursor particles via homogeneous precipitation: Synthesis, thermal decomposition, and the effects of supporting anions on powder properties

Monodispersed Sc₂O₃ precursor particles were synthesized by the urea-based homogeneous precipitation method, with an investigation into the effects of supporting anions (NO₃⁻, Cl⁻, and SO4 ²⁻) on powder properties. Characterizations of the powders were achieved by elemental analysis, x-ray diffractometry, Fourier transform infrared, differential thermal analysis/thermogravimetry, high-resolution scanning electron microscopy, and the Brunauer-Emmett-Teller method. Unlike other rare earths, Sc3+ does not precipitate as basic carbonate but instead forms hydrated γ-ScOOH from either nitrate or chloride solution. Particles of the hydrated γ-ScOOH are pumpkin-shaped (approximately 1.0 μm) and are made up of thin-platelike crystallites emanating from a common axis. The presence of complexing SO₄²⁻ changes the reaction chemistry toward Sc₂O₃ powders, leading to basic sulfate [Sc(OH)_1.6(SO4)_0.7 η H₂O] precursor particles having hexagonal morphology (approximately 10 μm in diameter and 0.5 μm in thickness). The hydrated γ-ScOOH directly converts to Sc₂O₃ by calcination at 400 °C or above, while the basic sulfate transforms to oxide at temperatures ≥ 900 °C via an amorphous state and a Sc₂(SO₄)₃ intermediate. The effect of SO₄²⁻ on powder morphologies and reaction chemistry is discussed. Nanocrystalline Sc₂O₃ powders comprising monodispersed particles were obtained via thermal decomposition of the precursors.