Preparation and characterization of K-PSS geopolymer

The three key molar ratios influencing the synthesis of potassium type poly-sialate-siloxo (K-PSS) geopolymer: n(SiO₂)/n(Al₂O₃), n(K₂O)/n(Al₂O₃), and n (H₂O)/n(K₂O) are systematically investigated in accordance with orthogonal design principle. Based on compressive strength and infrared spectra, the effects of the three molar ratios are analyzed quantitatively on the macro-and micro-scales, finally obtaining the optimum mixture proportion. Additionally, X-ray diffraction, infrared spectra and nuclear magnetic resonance with magic angle spinning measurements show that infrared spectrum peak at 1086 cm^-1 caused by the stretching vibration of [SiO₄] tetrahedra shifted to lower wavenumber around 1033 cm^-1, and the 6-fold Al was transformed into 4-fold coordination during the synthesis of geopolymer. The Al exists in the form of 4-fold coordination and connects with SiO₄ tetrahedra, finally forming amorphous geopolymeric products with framework configuration. Correspondingly the Si exists in the form of SiQ⁴(4Al) and SiQ⁴(2Al) units. No oligomers such isolated or small group building blocks are found.