High thermal stability of microwave sintered low-εr β-eucryptite materials

Low-temperature sinterable microwave LiAlSiO-based solid-state material was investigated with regard to microwave dielectric properties as functions of the sintering temperature. β-eucryptite materials and alumina-reinforced β-eucryptite composites were sintered by microwave technology at 1100°C and 1200°C. The combination of fast heating and the dramatic reduction in cycle time, along with the non-conventional heating source, opens the way to produce materials with desired multifunctional properties. The microstructure and crystalline composition of the materials were characterised, and the mechanical, thermal and microwave dielectric behaviours were analysed. X-ray diffraction showed good chemical stability in materials without between-phase reactions during the microwave sintering process. The excellent mechanical (∼8 GPa of hardness and ∼100 GPa of Young's modulus), thermal (-0.23·10 K) and microwave dielectric properties (ε =4.10; Q=1494) were obtained from the LAS/AlO composites sintered at a very low temperature (1100°C). The results achieved show the possibility of designing ceramic nanocomposites at low sintering temperatures using microwave technology with near-zero thermal expansion coefficients, high mechanical and chemical stability and low dielectric properties.