Thermophysical Properties and Microstructure Analysis of Geopolymer Foam Coating

Geopolymer foam has good thermal insulation properties. Due to its numerous open pores, geopolymer foam requires a protective coating to prevent environmental moisture penetration. In this study, a novel inorganic high-temperature-resistant coating specifically designed for geopolymer foam substrates was developed. The coatings were prepared via solid–liquid biphase blending at room temperature. The coating ratio design, process preparation, basic physical properties, water resistance, alkali resistance, high-temperature resistance, microscopic characterization, and thermal stability were examined. The results showed that the thermal conductivity of the best coating was 0.0536 W/(m·K) and the coating retained 95% of its original mass at 600°C. Observing the X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) results, it was found that the changes of lithium silicate solution (Li2O·nSiO2; LS) concentration, sodium silicate solution (Na2O·nSiO2; NS) concentration, and hollow microsphere (HM) dosage had no effect on the material composition, backbone structure, and functional groups of the coatings. The thermogravimetric (TG) results showed that the mass retention was still 94–97% at 1,000°C, which indicated that the samples had good high-temperature resistance and thermal stability. This coating exhibited rapid drying, fast film formation, excellent adhesion, a smooth/glossy surface, thermal stability at 600°C, and consistent performance. Applied using the slurry-coating technique, this method demonstrated practical constructability and promising application prospects.