アルコキシド法によるAl^<3+>置換型トバモライトの合成と性質

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The preparation of glasses, fibers and ultra-fine powders for fine-ceramic materials by the alkoxide method has recently attracted special interest. Tobermorite is generally synthesized by hydrothermal reaction under saturated steam pressure of 10 kgf/cm^2 above 180℃ in inhomogeneous suspension of CaO(solid)-SiO_2(solid)-H_2O(liquid) system. A study was made to investigate the synthesis of Al^<3+>-substituted tobermorite at a low temperature (95℃) under atmospheric pressure by using homogeneous mixed solutions of the CaCl_2-Si(OC_2H_5)_4-AlCl_3-C_2H_5OH-H_2O system. The thermal behavior and cation exchange for the Al^<3+>-substituted tobermorite were carried out by means of X-ray diffraction, thermal analysis (TG-DTA), infrared spectroscopy and chemical analysis. The procedure for the synthesis of Al^<3+>-substituted tobermorite consisted of deposition of a CSH gel from homogeneous mixed solutions (Ca/Si atomic ratio: 1.0, Al/(Al+Si) atomic ratio: 0.03-0.20) by adding KOH solution and the crystallization of the gel by aging at 95℃ under atmospheric pressure for 5 days. A basal spacing due to (002) plane in tobermorite was affected by the Al/(Al + Si) atomic ratio; 10.7 Å below the atomic ratio of 0.03 and 11.3 Å in the atomic ratio of 0.05-0.20. The crystallization of Al^<3+>-substituted tobermorite was much accelerated in the range of the Al/(Al + Si) atomic ratio of 0.05-0.10 but converted to the CSH gel over the atomic ratio of 0.20. A basal spacing expanded with increasing Al^<3+>-substituted for Si^<4+> in silicate ion chains of tobermorite dependent on the substitution of greater Al^<3+> than Si^<4+> in size and the limitation for this substitution were approximately 18% as Al^<3+>. Consequently, Al^<3+>-substituted tobermorite included much K^+ which was supplied to neutralize the electric charge happened by the substitution. The capacity of cation exchange for K^+⇔Na^+ of Al^<3+>-substituted tobermorite increased with increasing amount of substituted Al^<3+>. The maximum capacity was 80-90 meq/100 g. Even in the case of the CSH gel, the capacity indicated the same values but in the exchange capacity per unit-surface, the former showed higher value than the latter.
社団法人日本セラミックス協会の論文
1991-09-01

アルコキシド法によるAl^<3+>置換型トバモライトの合成と性質

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