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<p>Alumina-rich magnesia–alumina spinel (MgAl<sub>2</sub>O<sub>4</sub>) is increasingly used as a high-performance ceramic in extreme-service environments, yet the temperature dependence of its exsolution equilibrium has not been quantified; and this information is essential for optimizing in-situ toughening of refractory castables. This study systematically elucidates the isothermal exsolution kinetics and equilibrium limits of an 85-grade, alumina-rich spinel between 1100 and 1600&#xa0;°C. Using a 325-mesh electrofused feedstock and dwell times ranging from 0.5&#xa0;h to 7 d, we quantified phase abundances and lattice stoichiometries by Rietveld refinement of X-ray diffraction data coupled with energy-dispersive X-ray spectroscopy. Below 1300&#xa0;°C the lattice remains supersaturated for up to 7 d without detectable α-Al<sub>2</sub>O<sub>3</sub> precipitation, establishing 1300&#xa0;°C as the minimum kinetic threshold for measurable exsolution. The maximum extent of exsolution (lowest residual Al<sub>2</sub>O<sub>3</sub>, 78.3 wt.%) is attained at 1300&#xa0;°C. Between 1400 and 1600&#xa0;°C the equilibrium Al<sub>2</sub>O<sub>3</sub> content of the spinel phase is essentially constant at 80 wt.%, indicating that the extent of equilibrium exsolution becomes insensitive to temperature above 1400&#xa0;°C. In contrast, the time required to reach this equilibrium state decreases with increasing temperature, from 12&#xa0;h at 1300&#xa0;°C to 0.5&#xa0;h at 1600&#xa0;°C, which is related to the acceleration of Al<sup>3+</sup> lattice diffusion.</p>

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Effect of different heat-treatment temperatures on the exsolution equilibrium of 85-alumina-rich spinel

  • 期刊论文

  • 发表日期：

    2026年2月24日

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  • Xiaogai Sun,
  • Zhongzhuang Zhang,
  • Kaiwei Ye,
  • Huixia Jia,
  • Guotian Ye,
  • Yuandong Mu

摘要

Alumina-rich magnesia–alumina spinel (MgAl2O4) is increasingly used as a high-performance ceramic in extreme-service environments, yet the temperature dependence of its exsolution equilibrium has not been quantified; and this information is essential for optimizing in-situ toughening of refractory castables. This study systematically elucidates the isothermal exsolution kinetics and equilibrium limits of an 85-grade, alumina-rich spinel between 1100 and 1600 °C. Using a 325-mesh electrofused feedstock and dwell times ranging from 0.5 h to 7 d, we quantified phase abundances and lattice stoichiometries by Rietveld refinement of X-ray diffraction data coupled with energy-dispersive X-ray spectroscopy. Below 1300 °C the lattice remains supersaturated for up to 7 d without detectable α-Al2O3 precipitation, establishing 1300 °C as the minimum kinetic threshold for measurable exsolution. The maximum extent of exsolution (lowest residual Al2O3, 78.3 wt.%) is attained at 1300 °C. Between 1400 and 1600 °C the equilibrium Al2O3 content of the spinel phase is essentially constant at 80 wt.%, indicating that the extent of equilibrium exsolution becomes insensitive to temperature above 1400 °C. In contrast, the time required to reach this equilibrium state decreases with increasing temperature, from 12 h at 1300 °C to 0.5 h at 1600 °C, which is related to the acceleration of Al3+ lattice diffusion.