Compressive property of geopolymer based syntactic foams

Syntactic foams were developed in the early 60's and are widely applied to aerospace and submarine industry now. It is a special kind of composite materials which can be synthesized in a mechanical way by mixing hollow particles (the filler) with a resin system (the binder). Geopolymers are amorphous binder materials with three-dimensional structure resulting from the polymerization of aluminosilicate monomers in an alkaline solution. The composition of the final geopolymers can be altered by various factors, such as SiO₂/Al₂O₃ ratio, concentration of alkaline solution, water content etc. In this work, an alkali aluminosilicates binder, known as geopolymer, was first used as the matrix of syntactic foams. It was prepared from metakaolin, as aluminosilicatic raw powder, and alkaline solution. Three types of hollow microspheres, Ex-lites (ceramic), K1 (glass) and BJO-0930 (phenolic) were used as the fillers. The effect of each type of sphere on the compressive property of the syntactic foam was studied. The addition of Ex-lites and K1 microspheres not only created the interfacial bonding between the microspheres and the matrix, but also altered the molar ratio of Al:Si due to the chemical interaction between spheres and alkaline solution. The volume fraction and chemical compositions of the microspheres also play the important roles in the compressive property of the syntactic foams.