Physicochemical Study of Titanium-bearing GarnetsстатьяИсследовательская статья
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Дата последнего поиска статьи во внешних источниках: 18 мая 2022 г.
Аннотация:Four samples of natural Ti-bearing garnets from Odihincha Maimecha-Kotui alkaline province (Krasnoyarsk Krai, Russia) were studied using electron microprobe analysis, powder X-ray diffraction, FTIR, Raman and Mössbauer spectroscopy, thermal analysis. The enthalpies of formation from the elements were determined with a high-temperature heat-flux Tian-Calvet microcalorimeter by means of the melt solution calorimetry. The values of ΔfH0el(298.15 K) were found for the first time to be: −5861.1 ± 11.3 kJ/mol for (Ca3.00Na0.02Fe2+0.01)(Fe3+1.42Ti4+0.26Al0.21Mg0.04Fe2+0.03Mn2+0.01)[(Si2.85Fe3+0.13)O11.92(OH)0.08]; −5915.2 ± 9.0 kJ/mol for Ca3.01(Fe3+1.27Ti4+0.57Mg0.05Fe2+0.03Mn2+0.01)[(Si2.69Al0.16Fe3+0.13Ti4+0.01)O11.96(OH)0.04]; −5902.5 ± 9.1 kJ/mol for (Ca2.97Mn2+0.02Fe2+0.01)(Fe3+1.20Ti4+0.64Mg0.05Fe2+0.04)[(Si2.64Fe3+0.23Al0.11Ti4+0.01)O11.96(OH)0.04]; and −5945.7 ± 10.2 kJ/mol for (Ca2.90Na0.04Fe2+0.03Mn2+0.02Mg0.01)(Fe3+0.97Ti4+0.71Mg0.13Zr0.08Fe2+0.05) [(Si2.33Fe3+0.32Ti4+0.24Al0.07)O11.84(OH)0.16]. Using the obtained values of the formation enthalpies and of estimated entropies, the standard Gibbs free energies of formation of these garnets were calculated. Finally, the enthalpies of the formation of the end-members of the isomorphic schorlomite-morimotoite series were derived. The obtained thermodynamic constants were used for the quantitative modeling of stability fields of these minerals.