Magnesium aluminate spinel ceramics infiltrated with lanthanum-glass for dental applications

In this work, porous ceramic substrates based on magnesium aluminate spinel (MAS), Mg${}_2$Al${}_2$O${}_4$, were infiltrated with a lanthanum-rich glass for applications as dental ceramic material. The substrates were fabricated by uniaxial compaction of the spinel powder at 100 MPa for 60 s and sintering at 1 550 °C, 1 600 °C or 1 650 °C for 2 h. The porosity of the substrates after sintering varied between 17 vol.% and 24 vol.%. The substrates were then infiltrated with a lanthanum-rich glass at 1 140 °C for 2 h. After infiltration, dense ceramics were obtained, while hardness, fracture toughness and flexural strength varied from 850 to 1 000 HV, 2.8 to 3.5 MPa · m${}^{1/2}$ and 235 to 305 MPa, respectively, as a function of glass content. Theoretical calculations indicate that the amount of infiltrated secondary glassy phase should be about 17 vol.%, in order to obtain the highest crack propagation resistance.