Facile Method for Preparing Hierarchical Al₂O₃-Glass Foam Ceramics with Superior Thermal Insulating Property

Porous ceramics are good candidates for thermal-insulating materials. Glass is a low-cost material that possesses low intrinsic thermal conductivity of less than 10 W·m^-1·K^-1. However, the mechanical strength of a homogeneous glass material is fairly low. We, in this work, have fabricated Al₂O₃-hollow glass sphere (HGS) foam ceramics with a facile particle-stabilized foaming method. The obtained foam ceramic presents a hierarchical microstructure that is rare to be seen elsewhere using this foaming technique. The foaming system contains two types of particles having opposite charges, and the particle-stabilized foaming mechanism is hence discussed. The optimal sample possesses a porosity above 94% with a thermal conductivity as low as 0.0244 W/m·K, which reaches the level of superinsulating materials. The compressive strengths of the foam ceramics range from 0.07 to 0.83 MPa. The effective medium theory model is used to calculate the thermal conductivities as reference. The deviation of the theoretical values from the experimental ones are derived from the effect of the hierarchical microstructure of the foams. The results of this work may deepen one's understanding and pave new ways for the particle-stabilized foaming technique. The unique microstructure of the ceramic may also shed some light on fabricating superior thermal-insulating ceramic materials.