Preparation and thermal properties of fire resistant metakaolin-based geopolymer-type coatings

Geopolymer-type coatings prepared by using an industrially available sodium silicate solution (SiO2:Na2O = 3.1) and metakaolin were applied to steel substrates. The coatings exhibited excellent adhesion to steel substrates achieving greater than 3.5 MPa tensile stress. Dissolution of the coating in water after 72 h of static testing varied between 12.8 and 34.5 wt.% depending on the water content of initial formulations. Coating formulations showed up to 3% thermal expansion after heating to 800 °C. Coatings maintained high structural integrity with steel substrates when subjected to a heat treatment by a gas torch and formulations calcined at 1000 °C for 1 h showed an X-ray amorphous structure.