Geopolymer: Room-Temperature Ceramic Matrix for Composites

Geopolymers are semiamorphous three-dimensional networks of polymeric sodium, potassium, lithium and magnesium silico-aluminates of the poly(sialate) type (Si-O-Al-O-) or of the poly(sia1ate-siloxo) type (Si-O-Al-OSi-O-). Geopoly-mers harden at room temperature (between 20 and 120°C) and are rather similar to thermosetting organic resins, but are stable up to 1200/1400°C without shrinkage. Hardening medium involves the chemical reaction of alumino-silicate oxides (Al3+ in N-fold coordination) with alkali polysilicates yielding polymeric Si-O-Al bonds. A wide range of alkaline resistant inorganic reinforcements have been combined with geopolymer matrices (in particular Sic fiber) through skills of the reinforced plastics/composites industry, yielding the nonburning, nonsmoking, nontoxic benefits of ceramics without that industry's high temperature, high energy processing. Sic Fiber/K-poly(sia1ate-siloxo) matrix composite shaped and hardened at 70°C (158°F) for 1 h 30 min develops flexural mean strengths of at least 380 MPa which remains unchanged after firing at 450°C (842°F), 700°C (1292°F). and 900°C (1652°F).