Study of phase formation in the CaO–MgO–Al₂O₃ system

Significant interest in the ternary CaO-MgO-Al2O3 system in materials science is due to the unique combination of functional properties of calcium and magnesium aluminates. A particular scientific focus is the challenge of forming a compound with the composition CaMgAl10O17. Its stoichiometry logically follows from the structural analogy with the well-studied and widely used barium and strontium aluminates (BaMgAl10O17 and SrMgAl10O17), which demonstrate high efficiency as host matrices for phosphors. While there are sporadic indications in the scientific literature regarding the possibility of synthesizing this compound, reliable data unambiguously confirming its stable existence are currently lacking. In this work, calcium-magnesium aluminate was synthesized using the solution combustion method followed by annealing in the temperature range of 550-1300 °C. The synthesis products were analyzed using thermal analysis, IR spectroscopy, and X-ray phase analysis with full-profile Rietveld refinement. It was established that under the investigated conditions, the target compound CaMgAl10O17 does not form as a thermodynamically stable phase. The main products of high-temperature annealing are calcium hexaaluminate (CaAl12O19), magnesium aluminate (MgAl2O4), and calcium dialuminate (CaAl4O7). The content of the presumed calcium-magnesium aluminate phase does not exceed 6%. Contribution of the authors: the authors contributed equally to this article. The authors declare no conflicts of interests.

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