Title: A calorimetric and thermodynamic investigation of strontium fluorapatite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si27.svg"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="bold">S</mml:mi><mml:mi mathvariant="bold">r</mml:mi></mml:mrow><mml:mn>10</mml:mn></mml:msub><mml:msub><mml:mfenced open="(" close=")"><mml:mrow><mml:mi mathvariant="normal">P</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:mfenced><mml:mn>6</…
Abstract: A calorimetric and thermodynamic investigation of one of the representatives of full-substituted fluorapatites, strontium-substituted fluorapatite {Sr10PO46F2}, 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 ΔfHmo(T=298.15K,Sr10PO46F2,cr)=(-13721±8)kJ∙mol-1. The low-temperature heat capacity, Cp,mo, was measured using adiabatic calorimetry from T = (6.8 to 307.0) K. The high-temperature heat capacity, Cp,mo, was measured using DSC calorimetry from T = (306.7 to 651.7) K. Using these Cp,mo(T) data, the third law entropy at T = 298.15 K, Smo, 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, ΔfGmo, giving: ΔfGmo(T=298.15K,Sr10PO46F2,cr)=(-13000±9)kJ∙mol-1. Smoothed Cp,moT values between T → 0 K and T = 650 K are presented, along with values for Smo and the functions [HmoT-Hmo0] and [GmoT-Gmo0]. Thermodynamic stability of cation-substituted fluorapatites, M10PO46F2 with M = Ca, Ba, Sr, Mg, was analyzed based on literature and experimental data.
Publication Year: 2021
Publication Date: 2021-09-27
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 1
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