The effect of rare-earth oxide addition on the hot-pressing of magnesium silicon nitride

The effect of rare-earth oxide addition (1–5 mass% of Ln2O3 addition; Ln=Y, La, Nd, Sm, Gd, Dy, Er, and Yb) on the properties of hot-pressed (1550 °C, 90 min, 31 MPa) magnesium silicon nitride (MgSiN2) compact (ceramic) has been investigated. The role of rare-earth oxide addition on the relative density was classified as follows: (i) positive effect (Y2O3, La2O3, and Yb2O3 addition), (ii) no appreciable effect (Nd2O3 and Er2O3 addition), and (iii) negative effect (Sm2O3, Gd2O3, and Dy2O3 addition). The grain sizes of the MgSiN2 ceramics with rare-earth oxide addition were almost comparable to or slightly smaller than those of the pure MgSiN2 ceramic. The average Vickers hardness of the MgSiN2 ceramic with 1 mass% of Y2O3 addition showed the highest value (21.5 GPa) amongst the MgSiN2 ceramics with rare-earth oxide addition. The thermal conductivity of the MgSiN2 ceramic had a maximum for the case of 1 mass% of Yb2O3 addition (26.6 W·m−1·K−1) and was believed to be the highest value so far reported for MgSiN2 ceramic. It was concluded that the relative density and Vickers hardness were best enhanced through the use of Y2O3 addition, whereas the addition of Yb2O3 was most suitable for enhancing the thermal conductivity.