• Hydrothermal synthesis of hydrogarnet and tobermorite at 175 °C from kaolinite and metakaolinite in the CaO–Al2O3–SiO2–H2O system: A comparative study.

      Rios, Carlos A.; Williams, Craig D.; Fullen, Michael A. (Amsterdam: Elsevier, 2009)
      The hydrothermal synthesis of hydrogarnet and tobermorite from kaolinite and metakaolinite was examined at 175 °C for 24 h in the CaO–Al2O3–SiO2–H2O (CASH) system, which is important in cement science and especially in cement chemistry and is closely related to the pozzolanic reaction, the CaO-aggregate reaction and the glass fibre reinforcement of hardened cement. Starting mixtures were prepared with molar ratios Al/(Si + Al) = 0.10–0.13 and Ca/(Si + Al) = 1.00–7.00. The hydration products were characterized by X-ray diffraction, scanning electron microscopy, Fourier transformed infrared spectroscopy, Magic Angle Spinning Nuclear Magnetic Resonance and thermogravimetric analysis in order to elucidate their mineral chemistry and microstructure. Results reveal that several poorly crystalline materials were formed, with un-reacted Ca(OH)2 appearing at shorter reaction times. Hydrogarnet always tended to form more rapidly than tobermorite. It was transformed into aluminium-substituted tobermorite with curing time. CaO is present in the further reaction with SiO2 forming calcium silicate hydrates, and released Al3+ ions were inserted into tobermorite.
    • Synthesis of Zeolites and Zeotypes by Hydrothermal transformation of Kaolinite and Metakaolinite.

      Rios, Carlos A.; Williams, Craig D.; Maple, Martin J. (Bucaramanga, Colombia: Universidad de Pamplona, 2007)
      The synthesis of zeolitic materials by hydrothermal transformation of kaolinite and metakaolinite in NaOH solutions of various concentrations was investigated between 100 and 200 degrees C, over different reaction times, using in some cases precipitated SiO2 or organic templates. Materials were obtained, including clathrasils: cancrinite (CAN), sodalite (SOD), and Linde Type A (LTA), faujasite (FAU), NaP1 (GIS), analcime (ANA) and nepheline hydrate I (JBW) zeolites. In general, co-crystallization of CAN and SOD, likely via an unstable LTA zeolite intermediate, was observed after dissolution of kaolinite at low temperature; although the feldspathoids tend to be unstable at high temperature. LTA zeolite was synthesized after metakaolinite reaction, with minor amount of FAU zeolite, ANA and SOD. Solids were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA).