Preparation of porous halloysite nanotube ceramics with high porosity and low thermal conductivity by foam-gelcasting

Abstract In this study, porous halloysite nanotube ceramics were prepared by the foam-gelcasting method using sodium carboxymethyl cellulose (CMC) as a foam stabilising agent, Isobam 104 as a dispersant and triethanolamine lauryl sulphate (TLS) as a foaming agent, respectively. Then, the effects of firing temperature on the phase composition, microstructure, and pore size distribution of porous halloysite nanotube ceramics were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunner-Emmet-Teller (BET), thermogravimetry (TG) and differential scanning calorimetry (DSC). The results showed that the prepared porous ceramics contained both mesopores (10–50 nm) and macropores (100–300 μm). As the firing temperature rose, the linear shrinkage and compressive strength of samples increased, while the porosity decreased. When the porosity was as high as 75.7%, the samples still remained the compressive strength of 1.1 MPa, and had the lowest thermal conductivity, reaching 0.194 W/(m·K) (at a testing temperature of 100 °C).