Síntese e caracterização de perovskitas de lantânio preparadas pelo método do citrato amorfo modificado

Abstract

Hydrogen is considered an important energy carrier for the XXI century. One of the processes involved in the production are the catalytic membrane reactors (CMR, Catalytic Membrane Reactor). This device is responsible for the production of synthesis gas (CO + H2) by the partial oxidation of fuels, such as methane. The families of LnMO3 perovskites (Ln = rare earth, M = transition metal) and its derived compositions represent an important class of materials with different electroceramic and of great interest from a technological standpoint properties, and may also be used for the manufacture of reactors membrane. In this context, this work aims at the synthesis and characterization of perovskite-type La0,6Sr0,4MO3 (M = Co, Mn, Fe) prepared by the amorphous citrate modified technique derived from the Pechini process. For the definition of synthetic samples of cobaltite doped lanthanum strontium (La0,6Sr0,4 CoO3) and manganite doped with strontium (La0,6Sr0,4MnO3) lanthanum procedure univariate and multivariate type 2x2 plans were made. While for the sample of lanthanum ferrite (LaFeO3) A slightly different approach was used. The main parameters (variables) considered in planning were: molar mass of hydroxyethyl cellulose (HEC), citric acid ratio: metal cation (AC:CM); drying temperature of the gel, and finally, temperature and time of calcination of the precursor. From the type of planning done in each case it was possible to define the most suitable conditions for obtaining a single-phase material, as well as a smaller crystallite size. The characterization techniques used were X-ray diffraction, thermal analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A notable aspect of this work is the sensitivity of the crystallographic phase obtained depending on the synthesis conditions. For this reason, knowledge of the chemical species present during the synthesis step is paramount to be obtained a material with appropriate characteristics.