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<p>The thermodynamic properties of Ca<sub>3</sub>P<sub>2</sub>O<sub>8</sub> at high temperatures were investigated using the CaO–SiO<sub>2</sub>–P<sub>2</sub>O<sub>5</sub> ternary phase relationship. The standard formation Gibbs energy of Ca<sub>3</sub>P<sub>2</sub>O<sub>8</sub> was measured at 1473 K to 1573 K by applying a chemical equilibrium method to the Ca<sub>3</sub>P<sub>2</sub>O<sub>8</sub> + CaSiO<sub>3</sub> + SiO<sub>2</sub> and Mg<sub>3</sub>P<sub>2</sub>O<sub>8</sub> + MgO oxide mixtures. The latter was used as a reference system for calibration to minimize intrinsic experimental errors. Additionally, a third-law analysis revealed excellent consistency between the measured Gibbs energy and literature data for the heat capacity and heat of formation of Ca<sub>3</sub>P<sub>2</sub>O<sub>8</sub>. Consequently, the standard Gibbs energy of formation of Ca<sub>3</sub>P<sub>2</sub>O<sub>8</sub> from CaO, P<sub>2</sub>, and O<sub>2</sub> was established as follows: <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(3\text{CaO}\left(\text{s}\right)+{\text{P}}_{2}\left(\text{g}\right)+\left(5/2\right){\text{O}}_{2}\left(\text{g}\right)={\text{Ca}}_{3}{\text{P}}_{2}{\text{O}}_{8}\left(\text{s}\right)\Delta {G}^{\circ}/\text{kJ}\, {\text{mol}}^{-1}=-2306+0.562 T\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>3</mn> <mtext>CaO</mtext> <mfenced close=")" open="("> <mtext>s</mtext> </mfenced> <mo>+</mo> <msub> <mtext>P</mtext> <mn>2</mn> </msub> <mfenced close=")" open="("> <mtext>g</mtext> </mfenced> <mo>+</mo> <mfenced close=")" open="("> <mn>5</mn> <mo stretchy="false">/</mo> <mn>2</mn> </mfenced> <msub> <mtext>O</mtext> <mn>2</mn> </msub> <mfenced close=")" open="("> <mtext>g</mtext> </mfenced> <mo>=</mo> <msub> <mtext>Ca</mtext> <mn>3</mn> </msub> <msub> <mtext>P</mtext> <mn>2</mn> </msub> <msub> <mtext>O</mtext> <mn>8</mn> </msub> <mfenced close=")" open="("> <mtext>s</mtext> </mfenced> <mi mathvariant="normal">Δ</mi> <msup> <mrow> <mi>G</mi> </mrow> <mo>∘</mo> </msup> <mo stretchy="false">/</mo> <mtext>kJ</mtext> <mspace width="0.166667em" /> <msup> <mrow> <mtext>mol</mtext> </mrow> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mo>=</mo> <mo>-</mo> <mn>2306</mn> <mo>+</mo> <mn>0.562</mn> <mi>T</mi> </mrow> </math></EquationSource> </InlineEquation>.</p>

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Measurement of Thermodynamic Property of Tri-calcium Phosphate Using Phase Relation in the CaO–SiO2–P2O5 Ternary System

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  • 发表日期：

    2026年2月17日

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  • Keijiro Saito,
  • Kazuki Morita,
  • Masakatsu Hasegawa

摘要

The thermodynamic properties of Ca3P2O8 at high temperatures were investigated using the CaO–SiO2–P2O5 ternary phase relationship. The standard formation Gibbs energy of Ca3P2O8 was measured at 1473 K to 1573 K by applying a chemical equilibrium method to the Ca3P2O8 + CaSiO3 + SiO2 and Mg3P2O8 + MgO oxide mixtures. The latter was used as a reference system for calibration to minimize intrinsic experimental errors. Additionally, a third-law analysis revealed excellent consistency between the measured Gibbs energy and literature data for the heat capacity and heat of formation of Ca3P2O8. Consequently, the standard Gibbs energy of formation of Ca3P2O8 from CaO, P2, and O2 was established as follows: \(3\text{CaO}\left(\text{s}\right)+{\text{P}}_{2}\left(\text{g}\right)+\left(5/2\right){\text{O}}_{2}\left(\text{g}\right)={\text{Ca}}_{3}{\text{P}}_{2}{\text{O}}_{8}\left(\text{s}\right)\Delta {G}^{\circ}/\text{kJ}\, {\text{mol}}^{-1}=-2306+0.562 T\) 3 CaO s + P 2 g + 5 / 2 O 2 g = Ca 3 P 2 O 8 s Δ G ∘ / kJ mol - 1 = - 2306 + 0.562 T .