Development and Optimization of a High-Temperature Geopolymer Based Adhesive for Metallic Substrates

Geopolymers (GPs) are defined as a unique class of inorganic polymers synthesized through polycondensation of monomeric Al and Si species into a complex 3D framework. Due to their good mechanical properties, fire resistance, and low thermal conductivity, much research has been conducted on possible use in construction materials and in fire resistant coatings. Despite the abundance of research on geopolymer based coatings on metallic substrates, very little research has been done on the adhesive properties at both room and high temperature of geopolymer gels on metallic substrates. In this work, substrates adhered with geopolymer based adhesives were analyzed for surface wettability, adhesive layer thickness, lap shear and tensile strength at room and elevated temperatures. In addition, photographic analysis was conducted through use of optical and electron microscopy with Energy-Dispersive X-Ray Spectroscopy (EDS). Results of testing are conclusive in showing that geopolymer based adhesives are comparable in tensile and shear strengths to alternative commercially available polymer adhesives at room temperature, while maintaining good performance after exposure to elevated temperatures, i.e., up to 800 °C. Exposure to elevated temperatures appears to cracking in the geopolymer matrix without delamination due to thermal expansion mismatch, leading to a reduced strength adhesive without complete debonding or failure. In addition, it was shown that a Si-O-M oxygen bridge develops between the Si in the geopolymer gel and the metal (M) oxide on the surface leading to increased strength