Effects of Wet Air on Formation and Thermal Stability of 12CaO⋅7Al<sub>2</sub>O<sub>3</sub>

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  • SANGO Hiroyuki
    Department of General Education, Faculty of Science and Engineering, Nihon University
  • MIYAKAWA Tsugio
    Department of General Education, Faculty of Science and Engineering, Nihon University
  • YASUE Tamotsu
    Department of Industrial Chemistry, Faculty of Science and Engineering, Nihon University
  • ARAI Yasuo
    Department of Industrial Chemistry, Faculty of Science and Engineering, Nihon University

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  • 12CaO・7Al<sub>2</sub>O<sub>3</sub>の生成と熱安定性に及ぼす湿分の影響
  • 12CaO 7Al2O3 ノ セイセイ ト ネツ アンテイセイ ニ オヨボス

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Abstract

Effects of wet air on the formation and thermal stability of 12CaO⋅7Al2O3(C12A7) were studied in atmospheres with controlled water vapor content. The formation process of C12A7 in fired products was examined by X-ray powder diffraction and the water included in 11CaO⋅7Al2O3⋅Ca(OH)2(C11A7⋅Ca(OH)2) was identified by means of Fourier transform infrared spectrophotometer (FT-IR). Anhydrous C12A7 was prepared in dry atmosphere at temperatures above 1150°C. On the other hand, C11A7⋅Ca(OH)2 including hydroxide ions was formed at above 1000°C in flowing wet air and the humidity accelerated the formation of the hydrate. It was difficult to make the distinction of X-ray diffraction patterns between C12A7 and C11A7⋅Ca(OH)2, but the stretching vibration band of O-H at about 3560cm-1 measured by means of FT-IR enabled to identify the hydrate. In a flow of dried helium gas, the hydrate C11A7⋅Ca(OH)2 decomposed into 5CaO⋅3Al2O3(C5A3) with dehydration when it was heated in the temperature range of 1100 to 1250°C. At temperatures above 1250°C, C5A3 changed into C12A7. On the contrary, C5A3 changed into C11A7⋅Ca(OH)2 by heating at about 1100°C in a flow of wet air.

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