Synthesis and characterization of metakaolin-based crystalline phase sodium aluminum silicon oxide geopolymers using concentrated alkaline medium

Abstract

Crystalline phase geopolymers that include sodium aluminum silicon oxide were produced with high concentrations of NaOH activator in metakaolin–sodium silicate solution at 80 °C. Low-temperature geopolymerization provided these first-ever reported crystalline geopolymers when high NaOH concentration 12–15 M was used for the aqueous metakaolin medium. By changing the NaOH activator concentration to 10 M, amorphous geopolymers were formed, but crystalline geopolymers of sodium aluminum silicon oxide appeared in the NaOH concentration range. The crystalline phase had dense morphology of the formed bulk ceramics, respectively exhibiting 8.4 ± 0.5 MPa compressive strength at weight ratios of solid/liquid (S/L) and Na2SiO3/NaOH of mixtures for 0.45 and 1.0.