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

Abstract

Abstract The effect of rare-earth oxide addition (1–5 mass% of Ln 2 O 3 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 (MgSiN 2 ) compact (ceramic) has been investigated. The role of rare-earth oxide addition on the relative density was classified as follows: (i) positive effect (Y 2 O 3 , La 2 O 3 , and Yb 2 O 3 addition), (ii) no appreciable effect (Nd 2 O 3 and Er 2 O 3 addition), and (iii) negative effect (Sm 2 O 3 , Gd 2 O 3 , and Dy 2 O 3 addition). The grain sizes of the MgSiN 2 ceramics with rare-earth oxide addition were almost comparable to or slightly smaller than those of the pure MgSiN 2 ceramic. The average Vickers hardness of the MgSiN 2 ceramic with 1 mass% of Y 2 O 3 addition showed the highest value (21.5 GPa) amongst the MgSiN 2 ceramics with rare-earth oxide addition. The thermal conductivity of the MgSiN 2 ceramic had a maximum for the case of 1 mass% of Yb 2 O 3 addition (26.6 W·m −1 ·K −1 ) and was believed to be the highest value so far reported for MgSiN 2 ceramic. It was concluded that the relative density and Vickers hardness were best enhanced through the use of Y 2 O 3 addition, whereas the addition of Yb 2 O 3 was most suitable for enhancing the thermal conductivity.