Hydrothermal synthesis of 11 Å tobermorite – Effect of adding metakaolin to the basic compound

Abstract

Different amounts and types of metakaolin were analyzed and applied for the hydrothermal synthesis of 11 Å tobermorite. All synthesized samples were investigated by means of powder XRD combined with Rietveld refinement. Al-substituted 11 Å tobermorite was successfully synthesized on the basis of a broad range of compounds characterized by a varying content of metakaolin. Katoite was present depending on the amount of supplied Al3+, which was determined by the dosage of metakaolin. Minor crystalline components included in the two types of metakaolin sources varied greatly in their reactivity under hydrothermal conditions. Despite a different degree of purity, the two types of metakaolin showed corresponding effects at moderate dosages but contrary effects at higher dosages as for the synthesis of 11 Å tobermorite. The domain morphology of tobermorite could be associated with Al3+ incorporation for low dosages of metakaolin represented by up to 2 wt.-% Al2O3 in the dry mix. By contrast, Al3+ affected tobermorite lattice parameters at equivalent and even at higher dosages with c reaching 22.95 Å at 12 wt.-% Al2O3 in the dry mix.