Fabrication of transparent Sc₂O₃ ceramics with powders thermally pyrolyzed from sulfate

Scandia (Sc₂O₃) is a ceramic material that shows interesting thermal and optical properties, but is difficult to grow as single crystals. As an alternative, in this work we fabricated polycrystalline Sc₂O₃ transparent ceramics via vacuum sintering, using powders thermally pyrolyzed at 1200 °C from a scandium sulfate salt, Sc₂(SO₄)₃ · 7.8H₂O, that we prepared. Characterization of the powders was achieved by differential thermal analysis/thermogravimetry, x-ray diffractometry, Brunauer–Emmett–Teller analysis, and field-emission scanning electron microscopy. Sintering behaviors of the Sc₂O₃ powders were studied in air via dilatometry. The sulfate salt transforms to oxide at temperatures ≥1000 °C, and the best pyrolysis temperature for transparent ceramics fabrication is 1200 °C, at which the resultant Sc₂O₃ powder is good in dispersion, ultrafine in particle size (∼80 nm), and almost free from residual sulfur. Transparent ceramics were fabricated from this powder via vacuum sintering at 1625 °C or above. The ceramics sintered at 1700 °C for 4 h exhibit an in-line transmittance of approximately 56–58% in the visible light region at a sample thickness of 1.0 mm.