Sol-gel synthesis of Mn1.5Co1.5O4 spinel nano powders for coating applications

Mn1.5Co1.5O4 oxide spinels are widely used as protective coatings for stainless steel interconnects within planar solid oxide fuel cell stacks. Containing both cubic and tetragonal crystalline phases, these Mn/Co oxide spinels exhibit favorable thermal stability and electronic conductivity for the SOFC interconnect application. Slurry-based coating applications of Mn/Co oxides require precursor powders, which can benefit from being nano-structured. In this study, the sol-gel synthesis of nanocrystalline Mn1.5Co1.5O4 spinel is investigated. The decomposition of sol-gel precursors, as well as the crystalline phase structures and microstructures of the product Mn1.5Co1.5O4 are characterized by differential thermal and thermogravimetric (DTA/TG) analysis, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The effects of various sol-gel annealing temperatures (T), treatment times (t), and citrate-to-metal ratios (Rc) are evaluated. Results suggest that nanocrystalline Mn1.5Co1.5O4 spinel can be synthesized around 1050 °C, and that T = 1050 °C, t = 6 h and Rc = 2 are optimum conditions for producing the smallest grain size. Image analysis of TEM results shows that the size of Mn1.5Co1.5O4 crystallites increases with increasing temperature, with average particle sizes ranging from ∼70 nm to ∼1 μm. Selected area diffraction pattern (SADP) of Mn1.5Co1.5O4 spinel synthesized at 800 °C confirms the dual (cubic/tetragonal) structure of Mn1.5Co1.5O4.