Microwave Sintering of Mullite-Nd2O3 Composites: Investigation of Microstructure and Mechanical Properties
We investigated the effect of microwave sintering temperature on the densification, microstructure, and mechanical properties of mullite-Nd2O3 composites. The calcined mullite precursors prepared from aluminum nitrate nonahydrate and tetraethyl orthosilicate with and without 10 wt.% Nd2O3 were sintered with microwave fast heating processes at temperatures of 1400, 1500 and 1600°C without a holding time. The XRD results revealed cristobalite, alumina, and mullite as the dominant crystalline phases in the sintered samples without Nd2O3, and the quantity of mullite increased with increasing sintering temperature. The addition of Nd2O3 led to the elimination of cristobalite peaks with increasing the temperature from 1400 to 1500°C. The composites showed higher relative density compared with mullite ceramic, probably due to increased absorption of microwave energy by Nd2O3. The highest Vickers hardness (13.9?±?0.2 GPa), bending strength (387?±?22 MPa), and fracture toughness (4.81?±?0.1 MPa.m0.5) were found in the mullite composite sintered at 1600°C. The good mechanical properties of mullite-Nd2O3 composite seem to be due to the formation of worm-shaped fibers in the Al2O3-SiO2-Nd2O3 ternary system in the microstructure of the composite.