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

Different amounts and types of metakaolin were analyzed and applied for the hydrothermal synthesis of 11 angstrom tobermorite. All synthesized samples were investigated by means of powder XRD combined with Rietveld refinement. Al-substituted 11 angstrom 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 angstrom 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 angstrom at 12 wt.-% Al2O3 in the dry mix.