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• The high-throughput express diagnostics realized using quantitative infrared thermography (QIRT) allows us to identify the amorphous phase in polymorphic alumina by the analysis of hydration-dehydration-induced thermal effects. • Unlike crystalline alumina, the amorphous one produces a pronounced excess heating in the hydration process. • In a humid atmosphere, the solid-state exothermic chemical reaction of the oxide transformation into crystalline hydroxide takes place • The pseudoboehmite phase formation during the rehydration process occurs exclusively due to the amorphous alumina interaction with water. Dispersed alumina is one of the main materials used in adsorption and catalytic technologies. However, some poorly controlled factors (exposure to the atmosphere, etc.) can change the oxide phase composition and morphology. Hence, it follows that the development of robust approaches to characterizing the material structure is a topical problem. In this study, the ability of high-performance quantitative infrared thermography (QIRT) to identify the amorphous phase in polymorphic alumina by the analysis of hydration-dehydration-induced thermal effects is demonstrated. The QIRT-obtained findings were verified by a comparison with the XRD patterns measured on the same samples. It is revealed that, in a humid atmosphere, the solid-state exothermic chemical reaction of the oxide transformation into crystalline hydroxide takes place, and, unlike crystalline alumina, the amorphous one produces a pronounced excess heating in this process. Moreover, it is found that the pseudoboehmite phase formation during the rehydration process occurs exclusively due to the amorphous alumina interaction with water. It is shown for the first time that the high-throughput express diagnostics realized using QIRT allows us to determine the amorphous phase content in dispersed alumina and, potentially, in other materials for which this problem is relevant. [Display omitted] [ABSTRACT FROM AUTHOR]