Phase Evolution During Formation of SrAl ₂ O ₄ from SrCO ₃ and α‐Al ₂ O ₃ /AlOOH

Abstract

Through the execution of experimental investigation, thermogravimetry, X‐ray diffractometry, Fourier transform‐infrared spectrometry, transmission electron microscopy, and energy‐dispersive spectrometry, a variant reaction mechanism model was proposed for the solid‐state reaction between SrCO 3 and Al 2 O 3 /AlOOH for formation of SrAl 2 O 4 material. The solid‐state reaction is observed to be dependent on the calcination temperature. At temperatures lower than the transformation temperature of SrCO 3 from orthorhombic to hexagonal (920°C), the reaction is attributed to the interfacial reaction between SrCO 3 and alumina. Conversely, at temperatures higher than that, the solid‐state reaction is dominated by the diffusion of Al 3+ ions into the SrCO 3 lattice. In this mechanism, two metastable species, hexagonal SrCO 3 and hexagonal SrAl 2 O 4 , were observed. The activation energies of SrCO 3 decomposition in the solid‐state reaction also support these results. The interfacial reaction at low temperatures is characterized by a high activation energy of ∼130 kJ/mol; whereas, in the reaction at higher temperatures, the activation energy of SrCO 3 decomposition decreases to 34 kJ/mol.