Kinetics and Mechanism of Hydrothermal Reaction between Alite and Quartz

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  • HARADA Michiaki
    Department of Mineral Industry, School of Science and Engineering, Waseda University
  • HAGIWARA Yoshikazu
    Department of Mineral Industry, School of Science and Engineering, Waseda University
  • NGUYEN Van Hoang
  • ASAGA Kiyoshi
    Department of Inorganic Materials, Faculty of Engineering, Tokyo Institute of Technology
  • DAIMON Masaki
    Department of Inorganic Materials, Faculty of Engineering, Tokyo Institute of Technology

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Other Title
  • エーライト‐石英系水熱反応の速度と機構
  • エーライトー セキエイケイ スイネツ ハンノウ ノ ソクド ト キコウ

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A kinetic study was made on the hydrothermal reaction between alite and quartz. Synthesized alite powders with 3900cm2/g in surface area, or mixtures of the alite and quartz of 6-10μm in particle diameter were pelletized at various ratio. The pellets were autoclaved at 181°C under saturated vapor pressure for 0.5-72h. The hydrothermally treated samples were characterized by XRD and SEM. Unreacted alite, unreacted quartz, free lime and combined water of samples were determined, The chemical composition of the products and rate of the reaction were calculated from the experimental data.<br>In the alite-H2O system, C-S-H with high CaO/SiO2 ratio and Ca(OH)2 were producedd at early stage of the reaction, and then C3SH1.5 was produced. When small amount of SiO2 was introduced (CaO/SiO2=1.5), C3SH1.5 was disapeared during the reaction proceeded and final products were C-S-H and Ca(OH)2. In the case of CaO/SiO2=0.8, C3SH1.5 was not produced from early stage and produced Ca(OH)2 reacted again with SiO2 to form C-S-H with the composition similar to tobermorite. Even when the large amount of SiO2 was introduced (CaO/SiO2=0.5), the product with lower CaO/SiO2 ratio, such as gyrolite, was not formed, and C-S-H and unreacted SiO2 were observed.<br>The reaction of alite was controlled by diffusion through the product layer arround each alite grain. The reaction of quartz was controlled by dissolution at early stage and by diffusion at later stage. The uneven surfaces of alite grain were observed at early stages, suggesting that the dissolution rate of alite varied depending on crystal surfaces.

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