Obtenção de LaMnO3 via decomposição térmica de 8-hidroxiquinolinatos

Abstract

The synthesis of manganites has been the subject of study due to the variation of its magnetic, electrical and catalytic properties. The variation in methodology, interferes in the physical and chemical properties of the formed compound. Among the manganites, we can highlight the lanthanum manganite (LaMnO3), which is a perovskite and that has several applications, such as solid oxide fuel cells, catalysts, among others. There are several methodologies available in the literature to synthesize LaMnO3 such as, sol-gel, coprecipitation, synthesis by thermal decomposition, mechanosynthesis, among others. Therefore, the present study aims to propose a new methodology of synthesis for LaMnO3 by the thermodecomposition of solid chelates synthesized simultaneously with 8-Hydroxyquinoline (8-HQ) chelating. In this way, the work can be divided into three stages, the first is the synthesis of the chelate, which was performed by mixing metallic nitrates with 8-HQ under controlled conditions of elevation of the pH by varying the speed of addition of ammonium hydroxide (NH4OH). Subsequently, the precipitates were filtered, washed, dried and then characterized by XRD, FTIR, SEM and Atomic Absorption. The second stage, refers to the study of thermal behavior performed by TGA, DTG and DTA. In the third stage, the precipitates were calcined at temperatures of 400, 500, 600, 700, 800, 900 and 1000 °C, and characterized by XRD, SEM and EDS. Based on the analyzes, it was possible to verify that the formation of the solid chelates Mn and La occurred, that the speed of addition of NH4OH interferes in the morphology of the chelates, the conditions of thermal decomposition in synthetic air don’t significantly interfere in the formation of the final product and compositional analyzes and crystallographic studies confirmed the formation of the proposed oxide. Finally, the methodology stood out as a very promising alternative in obtaining LaMnO3 powders due to the simplicity of the method and the results obtained.