Phase evolution and thermal behaviors of the solid-state reaction between SrCO ₃ and Al ₂O ₃ to form SrAl ₂O ₄ under air and CO ₂-air atmospheres

The solid-state reactions between SrCO ₃ and Al ₂O ₃ forming SrAl ₂O ₄ under air and CO ₂-air atmospheres were investigated. The solid-state reaction between SrCO ₃ and Al ₂O ₃ under a CO ₂ atmosphere can be separated into multiple reaction stages. The first stage is attributed to the formation of SrAl ₂O ₄ resulting from the reaction between SrCO ₃ and Al ₂O ₃. The diffusion of Al ₂O ₃ through the product layer then takes place to continue the reaction. At a higher temperature, the Sr ₃Al ₂O ₆ formation reaction occurs due to the chemical reaction between SrCO ₃ and SrAl ₂O ₄. The SrCO ₃ is thermally finally decomposed. The resulting SrO may diffuse rapidly through the product layer, producing pure SrAl ₂O ₄ formation via a complicated diffusion process at a much higher temperature. These reaction stages occur at very close temperatures under an air atmosphere, leading to a complex reaction between the solids in air.