Preparation and Thermal Protection Performance of a Lightweight Inorganic Coating for High-Temperature Applications

The increasing demand for thermal protection materials in new energy vehicle (NEV) systems has stimulated the development of lightweight coatings capable of simultaneously providing thermal insulation and fire resistance. In this study, a lightweight ceramic-like inorganic coating was prepared by incorporating hollow glass microspheres (HGMs), expanded vermiculite, and ceramic fibers into a sodium silicate matrix. The expanded vermiculite/ceramic-fiber ratio and coating thickness were varied to evaluate their effects on thermal protection. Among the investigated formulations, Formulation C showed the lowest mean thermal conductivity, with a value of 0.0649 ± 0.0004 W m−1 K−1 for the 1-mm-thick C-1 coating. The apparent density of the representative Formulation C coating was 0.54 ± 0.02 g cm−3 (n = 3). During representative single-specimen direct butane-flame exposure tests, the spatially averaged backside temperature of the 2-mm-thick C-2 specimen was 147.1 °C after 600 s, compared with 420.1 °C for the uncoated aluminum plate, corresponding to a temperature difference of 273.0 °C. Cross-sectional SEM showed non-uniform structural evolution after flame exposure, with more pronounced morphological changes near the flame-facing region and greater retention of microspherical structures in the inner region. The representative Formulation C coating also retained more than 80% of its mass at 800 °C in both nitrogen and air. These results indicate that the combined presence of HGMs, expanded vermiculite, ceramic fibers, and the sodium silicate matrix provides effective resistance to heat transfer under high-temperature exposure. The coating therefore offers a lightweight inorganic approach for high-temperature thermal protection.