Thermodynamics and kinetics of hydroxide ion formation in 12CaO·7Al 4O 3

Katsuro Hayashi, Masahiro Hirano, Hideo Hosono

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96 Citations (Scopus)


We have examined the thermodynamics and kinetics of hydroxide (OH) ions that formed in cages of 12CaO·7Al 2O 3 (C12A7) with nanoporous structures. It is confirmed using thermogravimetric-evolved gas analyses (TG-EGA) that hydration in C12A7 is mediated by a reaction between an oxide (O 2-) ion in the cage and an H 2O molecule in the atmosphere to form two OH - ions in the cages. To simply and exactly quantify the OH - content from infrared absorption measurements of OH-stretching band, we propose a method combined with a thermodynamic analysis, allowing the simultaneous determination of the molar extinction coefficient of the OH-band, enthalpy, and entropy for the hydration. Hydration enthalpy in C12A7 is extremely high compared with other oxides and was enhanced by the marked instability of O 2- ion in the cage. Consequently, high solubility of OH - ion is retained up to unusually high temperatures. Furthermore, we determined diffusion coefficients of species relevant to the hydration process and demonstrated that inward diffusion of OH - ions is the rate-determining process.

Original languageEnglish
Pages (from-to)11900-11906
Number of pages7
JournalJournal of Physical Chemistry B
Issue number24
Publication statusPublished - Jun 23 2005
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry


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