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Abstract <p>The variable-composition compounds Bi(Al<sub>1–<i>x</i></sub>Fe<sub><i>x</i></sub>)<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub> with an alunite-type structure were obtained by hydrothermal synthesis in the Bi<sub>2</sub>O<sub>3</sub>–Al<sub>2</sub>O<sub>3</sub>–Fe<sub>2</sub>O<sub>3</sub>–P<sub>2</sub>O<sub>5</sub>–H<sub>2</sub>O system. Using experimental data on the miscibility limits of components in (1–<i>x</i>)BiAl<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>–<i>x</i>BiFe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>, parameters of the subregular solution model were determined (<i>Q</i><sub>1</sub> = 6.395, <i>Q</i><sub>2</sub> = 8.987 kJ/mol) and the curves for spinodal and binodal decomposition of solid solutions with alunite-type structure were calculated. According to thermodynamic calculations, the compounds BiAl<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub> and BiFe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub> can be formed at temperatures above 122 and 170°C, respectively, which is consistent with the experimental data obtained in the present study, indicating the absence of compounds with alunite-type structure at 160°C in the 0.8 &lt; <i>x</i> ≤ 1 range.</p>

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Formation of Alunite-type Compounds in the Bi2O3–Al2O3–Fe2O3–P2O5–H2O System under Hydrothermal Conditions

  • 期刊论文

  • 发表日期：

    2025年7月1日

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  • D. P. Elovikov,
  • O. V. Proskurina,
  • V. V. Gusarov

摘要

Abstract

The variable-composition compounds Bi(Al1–xFex)3(PO4)2(OH)6 with an alunite-type structure were obtained by hydrothermal synthesis in the Bi2O3–Al2O3–Fe2O3–P2O5–H2O system. Using experimental data on the miscibility limits of components in (1–x)BiAl3(PO4)2(OH)6–xBiFe3(PO4)2(OH)6, parameters of the subregular solution model were determined (Q1 = 6.395, Q2 = 8.987 kJ/mol) and the curves for spinodal and binodal decomposition of solid solutions with alunite-type structure were calculated. According to thermodynamic calculations, the compounds BiAl3(PO4)2(OH)6 and BiFe3(PO4)2(OH)6 can be formed at temperatures above 122 and 170°C, respectively, which is consistent with the experimental data obtained in the present study, indicating the absence of compounds with alunite-type structure at 160°C in the 0.8 < x ≤ 1 range.