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

Abstract

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.

3D Printing of Hollow Microspheres into Strong Hierarchical Porous Ceramics

“…Both types of hollow microspheres have been exploited for the fabrication of thermal insulators, impact absorbers, as well as lightweight concrete and composite materials, also known as syntactic foams. [ 10 ] Using such hollow microspheres as pore formers in conventional manufacturing processes has enabled the fabrication of porous ceramics [ 11 ] with enhanced thermal insulation properties [ 12 ] and low dielectric constant. [ 13 ] Introducing such microspheres as building blocks in colloidal inks for extrusion‐based printing could open new opportunities for the design and manufacturing of hierarchical ceramics with pores at multiple length scales.…”

3D Printable Ultra‐Highly Porous and Mechanically Strong Foam Materials for Multiple Applications

“…[29,30] This facile strategy can be readily exploited to make highly porous ceramic materials using a broad range of inorganic raw materials. [31][32][33][34][35][36] By adjusting the interfacial tensions between liquid-gas, solid-liquid, and solid-gas through tuning the hydrophobicity of the particle surfaces, stable foams can be formed rapidly by applying vigorous stirring to the system. Macroporous ceramics are usually formed with a pore diameter of 10-100 µm.…”