Wet‐Chemical Routes Leading to Scandia Nanopowders

Two wet‐chemical routes have been used to synthesize Sc 2 O 3 nanopowders from nitrate solutions employing ammonia water (AW) and ammonium hydrogen carbonate (AHC) as the precipitants. The precursors and the resultant oxides are characterized by elemental analysis, X‐ray diffractometry, differential thermal analysis/thermogravimetry, high‐resolution scanning electron microscopy, and Brunauer‐Emmett‐Teller analysis. Crystalline γ‐ScOOH· n H 2 O ( n ≈ 0.5) is the only phase obtained by the AW method. This phase dehydrates to Sc 2 O 3 at ∼400°C, yielding hard aggregated nanocrystalline Sc 2 O 3 powders. Three types of precursors have been synthesized by the AHC method, depending on the AHC/Sc 3+ molar ratio ( R ): amorphous basic carbonate [Sc(OH)CO 3 ·H 2 O] at R ≤ 3, crystalline double carbonate [(NH 4 )Sc(CO 3 ) 2 ·H 2 O] at R ≥ 4, and a mixture of the two phases at 3 < R < 4. Among these precursors, only the basic carbonate shows spherical particle morphology, ultrafine particle size (∼50 nm), and weak agglomeration. Sc 2 O 3 nanopowders (∼28 nm) with high surface area (∼49 m 2 /g) have been prepared by calcining the basic carbonate at 700°C for 2 h.