Thermodynamic properties and hydration behavior of ye'elimite

Author(s): B. Lothenbach, Charles Geiger, Edgar Dachs, F. Winnefeld, A. Pisch
Abstract: Ye'elimite occurs in nature and in calcium sulfoaluminate cements. The thermodynamic properties of synthetic orthorhombic ye'elimite, Ca4Al6O12SO4, were determined experimentally using low-temperature relaxation calorimetry and at higher temperatures using differential scanning calorimetry and drop calorimetry. The heat capacity, Cp, of 480 J/mol/K and standard entropy, S◦, of 487 J/mol/K at 298 K were measured. These values compare well with those calculated by density functional theory. Heat of dissolution measurements give an enthalpy of formation, ΔfH◦, of -8382.5 kJ/mol for ye'elimite. Heat of reaction measurements for nano-crystalline Al(OH)3 give ΔfH◦ = 1276 kJ/mol. The resulting calorimetric-based enthalpies were used to calculate the degree of ye'elemite hydration. A solubility product, KS0,ye'elimite, of 10^-1.4 at 298 K was calculatedfrom the enthalpy and entropy values. Pore solution composition indicates the presence of a hydroxylated surfacelayer on ye'elimite, which results in a lower solubility with K_S0,surface ≈10¹⁹ for the reaction Ca₄Al₆O₁₂SO₄ +12H₂O⁰ → 4Ca₂+ + 6Al(OH)^-4 + SO^2-₄
Organisation(s): Department of Mineralogy and Crystallography
External organisation(s): Eidgenössische Materialprüfungs- und Forschungsanstalt, Université Joseph-Fourier (Grenoble-I), Paris-Lodron Universität Salzburg
Journal: Cement and concrete research
Volume: 162
No. of pages: 15
ISSN: 0008-8846
DOI: https://doi.org/10.1016/j.cemconres.2022.106995
Publication date: 12-2022
Peer reviewed: Yes
Austrian Fields of Science 2012: 105116 Mineralogy, 203024 Thermodynamics
Keywords
ASJC Scopus subject areas: General Materials Science, Building and Construction
Portal url: https://ucrisportal.univie.ac.at/en/publications/c997d08c-7b3e-477b-8be6-299e8521e41e

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