Effect of Simultaneous Addition of Three Sintering Aids: magnesium, lanthanum, and zirconium oxide on the Mechanical and optical properties of Alumina Ceramics fabricated by SPS Method

This study investigates the synergistic effects of a novel triplex sintering aid system—magnesium oxide (MgO), lanthanum oxide (La₂O₃), and zirconium oxide (ZrO₂)—on the mechanical and optical properties of transparent alumina ceramics fabricated using spark plasma sintering (SPS). The specimens were sintered at 1350°C for 10 minutes under 70 MPa pressure. The sample with the highest zirconia content (sample Z: 100L100M300Z) achieved a bulk density of 3.94 g/cm³, corresponding to 99.9% of the theoretical density of alumina. This sample exhibited an infrared transmission of 71.4% at 5 µm and a visible transmittance of 32% at 750 nm, surpassing values reported for single or dual sintering aid systems. Mechanical testing revealed a microhardness of 19.34 ± 0.1 GPa and a fracture toughness of 5.24 MPa.m⁰·⁵ for sample Z. Additionally, this sample demonstrated the highest flexural strength of 356.83 MPa, attributed to its finer grain size, reduced porosity, and the synergistic effects of the triplex sintering aids. The results demonstrate a promising pathway for producing high-performance transparent alumina ceramics with tailored properties for demanding optical and mechanical applications.