Ca1−xSrxMnO3−δ granules, pellets, foams: Influence of fabrication conditions and microstructure on oxidation kinetics

Abstract

Microstructure and oxidation kinetics are closely intertwined factors that significantly influence the behavior of materials in oxidative environments. This relationship is of particular importance for redox materials such as ${\mathrm{Ca}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_{3-\delta }$, where reversible oxygen ions exchange and oxidation state shifts are key to their functionality. In the first study, scanning electron microscope (SEM) was used to examine how varying Sr content affects the morphology and microstructure of ${\mathrm{Ca}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_{3-\delta }$ powder compositions. The results indicate that increasing Sr content leads to smaller particle sizes and improved particle size homogeneity. Granules with Sr concentrations ranging from 0 % to 40 % exhibit notable changes in morphology. However, the microporosity and d50 vary slightly across the samples in a non-monotonic manner, with no clear trend emerging with respect to Sr concentration. The second study investigates how macrostructural forms, such as foams and pellets, impact oxidation kinetics in ${\mathrm{Ca}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{MnO}}_{3-\delta }$. Parameters including particle size distribution of the raw material, overall microporosity, and structural characteristics of these macrostructures were analyzed for their effect on oxidation rates. Findings reveal that macrostructural configuration, alongside microstructural features like microporosity, significantly impacts oxidation kinetics. These studies collectively underscore the critical relationship between dopant concentration, microstructural characteristics, and structural morphology in determining the oxidative behavior of ${\mathrm{Ca}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_{3-\delta }$, providing key insights into optimizing material performance in redox environments.