A comprehensive physicochemical study of fluorwavellite Al3 (PO4) 2. 1 (OH) 1. 9F0. 8⋅5. 5H2O (from the Ulytau region, Kazakhstan) was carried out using powder X-ray diffraction, electron probe microanalysis, FTIR, Raman and EPR spectroscopy, and thermogravimetry. The enthalpy of formation of the studied fluorwavellite from elements was determined for the first time using high-temperature melt solution calorimetry in a Calvet microcalorimeter (–6606 ± 12 kJ/mol). The value of its standard entropy was estimated and the Gibbs energy of formation was calculated (483. 4 J/ (mol K) and –5941 ± 12 kJ/mol, respectively). The thermodynamic constants of the end members of the isomorphic series wavellite Al3 (PO4) 2 (OH) 3⋅5H2O–fluorwavellite Al3 (PO4) 2 (OH) 2F⋅5H2O were estimated: { ₅}H{₄₋}^0 (298. 15 K) = –6328 ± 12 and –6435 ± 12 kJ/mol, S0 (298. 15 K) = 464. 3 and 463. 0 J/ (mol K), { ₅}G{₄₋}^0 (298. 15 K) = –5674 ± 12 and –5801 ± 12 kJ/mol, respectively.
Gritsenko et al. (Sun,) studied this question.