繊維状3CaO・Al2O3・3CaCO3・32H2Oの合成と性質

安江 任, 金井 謙介, 小嶋 芳行, 荒井 康夫

doi:10.2109/jcersj.100.1053

As one of the serial studies on fibrous calcium compounds, the synthesis of fibrous C₃A⋅3CaCO₃⋅32H₂O was studied by adding CaCl₂ solution (6-21×10^-3mol dm^-3) to the solution prepared by introducing CO₂ gas or by adding Na₂CO₃ solution (CO₃^2-concentration: 1-5×10^-3mol dm^-3) into NaAlO₂ solution (7-22×10^-3mol dm^-3). Characteristics of the product obtained by liquid-phase reaction in CaCl₂-NaAlO₂-CO₂ and CaCl₂-NaAlO₂-Na₂CO₃ systems were determined by means of X-ray diffraction, thermal analysis (TG-DTA), scanning electron microscopy, infrared spectroscopy and chemical analysis. The formation of fibrous C₃A⋅3CaCO₃⋅32H₂O was affected remarkably by synthetic conditions such as pH, initial Ca/Al atomic ratio and concentration of CO₃^2-ion. When the concentration of CO₃^2-was 1-3×10^-3mol dm^-3, the initial Ca/Al atomic ratio to form fibrous crystals of C₃A⋅3CaCO₃⋅32H₂O was less than 0.3 in CaCl₂-NaAlO₂-CO₂ system and less than 2.0 in CaCl₂-NaAlO₂-Na₂CO₃ system. Thus, the fibrous crystals were stable at pH above 11.7. Therefore, when the initial Ca/Al atomic ratio exceeds 0.3 in the system of CaCl₂-NaAlO₂-CO₂, pH because less than 11.7, yielding no fibrous crystals. While, the reaction in CaCl₂-NaAlO₂-Na₂CO₃ system to form the fibrous crystals progressed successfully because the pH value was kept over 11.7 even in the initial Ca/Al atomic ratio 0.3-2.0. It was confirmed that fibrous C₃A⋅3CaCO₃ 32H₂O crystallized as high crystalline fibers with aspect ratios above 300 elongated parallel to c-axis in hexagonal through an unstable amorphous phase which was precipitated in the initial step. The fibrous shape was stable in heating up to 300°C. Furthermore, the packing state of the fibrous crystals as filler for paper was discussed.

繊維状3CaO・Al<sub>2</sub>O<sub>3</sub>・3CaCO<sub>3</sub>・32H<sub>2</sub>Oの合成と性質

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