A calorimetric and thermodynamic investigation of strontium fluorapatite Sr10PO46F2. (January 2022)

• Record Type: Journal Article
• Authors: Lelet, Maxim I.; Mikhailov, Dmitry A.; Lyakaev, Denis V.; Lelet, Julia N.; Fukina, Diana G.
• Is Part Of: Journal of chemical thermodynamics. Volume 164(2022)
• Publication Date: 2022-01
• Subjects: Calorimetry -- Heat Capacity -- Entropy -- Enthalpy -- Heat of Formation -- Gibbs function of formation -- Apatite -- Strontium; Thermodynamics -- Periodicals; Thermochemistry -- Periodicals; Thermodynamique -- Périodiques; Thermochimie -- Périodiques; Thermochemistry; Thermodynamics; Periodicals; 541.369
• DOI: 10.1016/j.jct.2021.106636
• Languages: English
• ISSNs: 0021-9614

Abstract

Highlights: The temperature dependence of isobaric heat capacity for Strontium Fluorapatite S r 10 P O 4 6 F 2 was investigated in the temperature range T = 6.8 K–651.7 K. The enthalpy of formation for Strontium Fluorapatite S r 10 P O 4 6 F 2 have been determined at T = 298.15 K. The standard thermodynamic functions of formation at T = 298.15 K for Strontium Fluorapatite S r 10 P O 4 6 F 2 have been calculated. The optimized synthesis technique for Strontium Fluorapatite S r 10 P O 4 6 F 2 was developed by the authors of the article based on the classical sol–gel process. Abstract: A calorimetric and thermodynamic investigation of one of the representatives of full-substituted fluorapatites, strontium-substituted fluorapatite { S r 10 P O 4 6 F 2 }, was undertaken. The phase was synthesized according to the technique developed by the authors of the article based on the classical sol–gel process. The synthetic product was characterized by X-ray powder diffraction (XRD), X-ray fluorescence analysis (XRF), Scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and Differential thermal/gravimetric analysis (DTA-TG). The enthalpy of formation of the phase was determined using HNO3 -solution calorimetry giving Δ f H m o ( T = 298.15 K, S r 10 P O 4 6 F 2, c r ) = ( - 13721 ± 8 ) k J ∙ m o l - 1 . The low-temperature heat capacity, C p, m o, was measured using adiabatic calorimetry from T = (6.8 to 307.0) K. The high-temperature heat capacity, C p, m o, was measured using DSC calorimetry from T = (306.7 to 651.7) K. Using these C p, m o ( T ) data, the third law entropy at T = 298.15 K, S m o, is calculated as (938.7 ± 3.8) J∙K −1 ∙mol −1 . This new experimental result, together with literature data, are used to calculate the Gibbs energy of formation, Δ f G m o, giving: Δ f G m o ( T = 298.15 K, S r 10 P O 4 6 F 2, c r ) = ( - 13000 ± 9 ) k J ∙ m o l - 1 . Smoothed C p, m o T values between T → 0 K and T = 650 K are presented, along with values for S m o and the functions [ H m o T - H m o 0 ] and [ G m o T - G m o 0 ] . Thermodynamic stability of cation-substituted fluorapatites, M 10 P O 4 6 F 2 with M = Ca, Ba, Sr, Mg, was analyzed based on literature and experimental data.