Effects of SiO2-Al2O3-Y2O3sintering additives on mechanical and thermal performance of MgO based porous ceramics

Abstract

MgO-CaO-Fe₂O₃-x wt.% SiO₂-y wt.% Al₂O₃-z wt.%Y₂O₃ (3≤x≤15, 0≤y≤12, 0≤z≤12) porous ceramics are prepared by the organic foam template method and the mechanical and thermal performance are investigated. The XRD results illustrate that the main phase is MgO, and the secondary phases include MgSiO₃, MgAl₂O₄, and Y₂O₃. The Mg-O-Si and Mg-O-Y peaks are observed in FTIR spectrum, indicating the successful incorporation of additives. The results from mercury intrusion porosimetry show that the porous ceramic is mainly macro-pores, with few meso-pores distributed on the skeleton, which effectively increase total porosity. The SiO₂ doping changes the fracture manner of MgO-CaO-Fe₂O₃ ceramic from intergranular to transcrystalline, co-addition of Al₂O₃ can promote the formation of MgAl₂O₄ spinel that distribute at the grain boundary and decrease grain size of MgO, and the Y₂O₃ could enable uniform grain size distribution, which disperse external forces evenly to improve the mechanical properties. The MgO composite ceramic synthesized by organic foam template method, due to the high total porosity ~85%, exhibits thermal conductivity below 0.07 W/(m·K), which is almost independent of SiO₂-Al₂O₃-Y₂O₃ doping concentration. Typically, the MgO-2.5 wt.% CaO-1 wt.% Fe₂O₃-3 wt.% SiO₂-0.3 wt.% Al₂O₃-6 wt.% Y₂O₃ porous ceramics exhibit total porosity of 84.6%, compressive strength of 4.3 MPa, and thermal conductivity of 0.063 W/(m·K). Benefiting from their outstanding compressive strength and low thermal conductivity, the MgO based porous composite ceramics exhibit significant potential for application as building insulation materials.