Fabrication, sintering behavior and mechanical properties of calcium oxide doped yttrium oxide refractory via aqueous gel casting method

Abstract

Yttrium oxide is an ideal choice for titanium aluminum alloy melting and casting, its wider use is hindered by sintering challenges and low thermal shock resistance. To address this, we propose a gel casting method for calcium oxide-doped yttrium oxide production. We pretreated yttrium oxide with phosphoric acid to prevented hydrolysis and adjusted the isoelectric point of yttrium oxide to match calcium carbonate's. Anions from calcium carbonate increased slurry solid content (up to 58 vol%) while maintaining low viscosity (57.78 mPa·s at 40 s−1 shear rate). After sintering at 1650 °C for 2 h, the material showed a flexural strength of 78 MPa, with a 90% retention rate after thermal shock test. The introduction of calcium oxide induced lattice distortion, improving mechanical properties by aiding sintering and grain boundary diffusion. XPS and STEM analysis confirmed random replacement of Y3+ by Ca2+ at the C2 position with 1 wt% doping.