Determination of solid solutions composition in the SrSO₄ • 0,5H₂O – KCe(SO₄)₂ • H₂O system by X-ray fluorescence analysis

The chemical composition of solid solutions samples in the SrSO₄ · 0.5H₂O – KCe(SO₄)₂ · H₂O system, synthesized by coprecipitation from aqueous solutions of KNO₃, Sr(NO₃)₂, Ce(NO₃)₃ and H₂SO₄ was studied using X-ray fluorescence analysis. Power approximation functions of calibration dependences of concentration on intensity were used to determine the content of potassium, strontium and cerium (III) sulfates. The coefficients of calibration dependences and their metrological characteristics, such as standard errors s_e and determination coefficients r², were calculated using the least squares method. In the range of determined concentrations (% wt.) K₂SO₄ 5.324 – 22.54, SrSO₄ 11.10 – 89.26, Ce₂(SO₄)₃ 9.243 – 73.32 the standard error for concentration estimation was 0.03, 0.01, 0.02, respectively. The chemical composition of solid solutions was described by the assumed formula K_xSr_{2 – 2x}Ce_x(SO₄)₂ · H₂O, where 0 < x < 1. The X-ray difraction analysis confirmed the presence of a wide existence region of stable solid solutions formed by unstable isostructural trigonal phases SrSO₄ · 0.5H₂O and KCe(SO₄)₂ · H₂O. Stabilization of solid solutions was achieved as a result of heterovalent substitution of cations 2Sr²⁺ ↔ Ce³⁺ + K⁺ in a sulfate anion ambience. Cascade diffraction patterns of 12 solid solution samples and 4 individual compounds — orthorhombic modification of SrSO₄, trigonal modifications of SrSO₄ · 0.5H₂O and KCe(SO₄)₂ · H₂O, monoclinic modification of KCe(SO₄)₂ · H₂O — were presented in this article. The arrangement of reflections in the diffraction patterns of SrSO₄ · 0.5H₂O, KCe(SO₄)₂ · H₂O and solid solutions was completely identical. When changing the chemical composition of solid solution samples, the unit cell parameters remained virtually unchanged. The obtained results indicated the fundamental possibility of using X-ray fluorescence analysis for accurate determination of chemical composition of solid solutions samples in SrSO₄ · 0.5H₂O – KCe(SO₄)₂ · H₂O system.

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