Employment of mixed silicate particles with improved expansion capacity in a developed silicon-based intumescent coating

Abstract Silicone-based coatings with solid-expandable agents have gained increased interest to investigate more organic–inorganic concepts for fire-protective coatings. In this work, a relatively unexplored concept of inherently intumescent alkali silicate particles incorporated in silicone binder is presented. The particles are chemically modified to consist of combinations of alkali silicate cations (Li, Na, and K) that are previously reported to exhibit significantly higher expansion than the individual alkali silicates as intumescent agent. The formulations were exposed to a hydrocarbon fire scenario in a lab-scale furnace showcasing comparable and even better fire protection than a commercial epoxy-based intumescent coating. Here, char expansions of more than 500% were obtained with relatively low thermal conductivity. The thermal behavior was mapped by thermogravimetry, hot-stage digital microscopy, and rheometer revealing solid expansion of the alkali silicate particles before the decomposition of the silicone. The entrapment of formed amorphous silica in the silicate matrix provided a solid char with distinct layer characterized by the alkali silicate particles. The char surface consisted of silicate melt, while the hollow, solid-expanded silicate particles were more evident toward the bottom of the char. Hereby, the work presents great modification options for alkali silicate particles as intumescing agents in silicone binders in the suggestion of alternative intumescent concepts to the traditional organic based.