Effect of Added Mullite Whisker on Properties of Lithium Aluminosilicate (LAS) Glass-Ceramics Prepared for Dental Restoration

In this work, lithium aluminosilicate (LAS) glass-ceramics were prepared from lithium disilicate glass powder and mullite whiskers. Lithium disilicate glass powder (28.6Li-68.6Si-2K-0.8La, mol.%) with contents of 5, 10 and 15 wt.% mullite whiskers were hot-pressed at 860 °C for 1 h. The effects of added mullite on phase composition, microstructure, mechanical properties, coefficient of thermal expansion (CTE) and translucency were systematically studied. Also, the mechanism for phase transformation and grain growth was discussed. The LAS glass-ceramic samples exhibited relative densities above 98% with main crystalline phases of lithium disilicate (Li2Si2O5, LD), lithium silicate (Li2SiO3, LM), and β-spodumene (LiAlSi2O6). The β-spodumene whiskers were in-situ synthesized through the reaction between mullite whiskers and glass matrix. As β-spodumene fraction rose, lithium disilicate crystals content decreased and that of lithium silicate increased, resulting in declined bending strength and improved fracture toughness. The composite containing 10 wt.% mullite whisker showed optimal performance with bending strength above 300 MPa and fracture toughness of 2.7 MPa·m1/2. The formation of β-spodumene in the obtained composite declined CTE, with values ranging from 10.5×106 °C-1 for LD glass-ceramic to 6.03×10-6 °C-1 for LAS glass-ceramic doped with 15 wt.% mullite whiskers. Finally, though the real in-line transmission of obtained glass-ceramic composites declined as β-spodumene content rose, the specimens containing less than 10 wt.% mullite whiskers showed favorable translucency, which would suit applications in dental restoration.