This study systematically explores, for the first time, the relationships among sintering behavior, physico-mechanical properties, microstructure, and radiation shielding of reactive alumina ceramics. High-purity reactive α-Al₂O₃ powder with bimodal particle size distribution was pressurelessly sintered at 1550–1600 °C for 1–3 h. Nearly full densification (≥ 99% theoretical density) was achieved at 1550 °C–3 h and above. XRD and SEM–EDX confirmed single-phase corundum (α-Al₂O₃) formation. Increasing sintering temperature and dwell time enhanced densification and grain coarsening. The highest hardness (18.37 ± 0.45 GPa) occurred at 1550 °C–1 h, while the best fracture toughness (4.19 ± 0.62 MPa·m^1/2) and flexural strength (387 ± 37 MPa) were obtained at 1600 °C–3 h. Crack deflection, bridging, branching, and nanopore-related mechanisms contributed to toughness improvement. Color values (L ≈ 90–95, a ≈ 0–1.7, b ≈ 9–12, ΔE ≈ 0–3.8) showed high stability. The best γ-ray shielding was achieved at 1600 °C–3 h, with linear attenuation coefficients of 29.959 cm⁻¹ (0.662 MeV), 22.789 cm⁻¹ (1.173 MeV), and 21.351 cm⁻¹ (1.332 MeV). These results indicate that reactive α-Al₂O₃ ceramics can be readily densified, offering excellent mechanical performance and radiation attenuation for advanced shielding panels and blocks.

Keywords: Al₂O₃, Radiation shielding, Reactive alumina, Physico-mechanical properties, Solid-state sintering.