Effect of core-shell microspheres as pore-forming agent on the properties of porous alumina ceramics

The porous alumina ceramics with closed pores were fabricated using C@Al₂O₃ microspheres as pore-forming agent. The closed pores with a diameter about 5 μm were successfully obtained in the dense matrix, owing to the additive C@Al₂O₃ microspheres. Different amount of C@Al₂O₃ microspheres was added to investigate the effects of closed pores on thermal, dielectric and mechanical properties. With the increasing microspheres amount, the closed porosity of alumina ceramics ranges from 5.82 to 14.5%, the thermal conductivity decreases continuously at the temperature ranging from 30 to 1200 °C, and the flexural strength and fracture roughness decrease. As the closed porosity increases, the real permittivity decreases, while the tangent loss has a slight increase. When the mass ratio of C@Al₂O₃ microspheres is 10 wt.%, the porous alumina ceramics with the thermal conductivity (13.07–3.8 W·m^{− 1}·K^{− 1}), the flexural strength (97.05 ± 18 MPa), and the fracture roughness (2.65 ± 0.13 MPa·m^1/2) can be obtained.