Liquid and crystallized phases stability in the sub-system H3PO4H4P2O7: Experimental determination and modeling

•Systematic investigation of solid-liquid equilibria (SLE) of H3PO4H4P2O7.•Analytical representation of liquidus curves using Quasi-ideal model.•Delimitation of the stability range of ortho- and pyrophosphoric acid (I and II). The study of the system formed by ortho- and pyrophosphoric acid was resu...

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Published in:Thermochimica acta 2024-10, Vol.740, p.179837, Article 179837
Main Authors: Mouhib, Mohamed, Chiriac, Rodica, Toche, François, Counioux, Jean-Jacques, Saab, Joseph, Kaddami, Mohammed, Goutaudier, Christelle
Format: Article
Language:English
Subjects:
H3PO4
H4P2O7
Polymorphism
Solid-liquid equilibria
Superphosphoric acid
WPA
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Summary:•Systematic investigation of solid-liquid equilibria (SLE) of H3PO4H4P2O7.•Analytical representation of liquidus curves using Quasi-ideal model.•Delimitation of the stability range of ortho- and pyrophosphoric acid (I and II). The study of the system formed by ortho- and pyrophosphoric acid was resumed in order to understand the crystallization conditions of these two compounds and to highlight the existence of their possible polymorphism. To this end, the solid-liquid equilibria (SLE) of pyrophosphoric acid was studied in depth. Contradictions in literature data were resolved through systematic experimentation: solubility measurements, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Calorimetric measurements confirmed the existence of two crystalline forms of pyrophosphoric acid, and their stability domains were determined. Furthermore, thermodynamic modeling of the SLE has led to a consistent and refined representation of the observed phenomena. In particular, the transition temperature from low-temperature (form I) to high-temperature form (form II) of pyrophosphoric acid was determined at 298.4 K and the coordinates of the eutectic point common between H3PO4 and H4P2O7 (I) were precisely determined. Modeling also confirms the non-negligible quantity of triphosphoric acid in the liquid state throughout virtually the entire compositional range. Finally, X-ray powder diffraction data were used to determine the cell parameters and space group of pyrophosphoric acid using EXPO 2014 software. [Display omitted]
ISSN:0040-6031
DOI:10.1016/j.tca.2024.179837