Lanthanum chromite (LaCrO3), Lanthanum manganite (LaMnO3) and 40% strontium doped lanthanum cobalt iron oxide, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF-6428) are perovskite oxides which are widely used as interconnect or cathode materials in solid oxide fuel cells(SOFCs) due to their high electrical conductivity, good oxygen reduction kinetics, and good chemical stability. The solid state reaction route is the most commonly used method for synthesis of these materials. However, the solid state reaction method usually involves long-time mixing and high synthesis temperature (typically, >1200 ºC), which makes it time-consuming and costly. Molten salt synthesis, which occurs at much lower temperatures (350 ºC – 550 ºC) can offer better particle size and compositional control and reduced energy usage during materials synthesis.
In this study, LaCrO3, LaMnO3, and LSCF were synthesized in a molten salt eutectic of LiCl-KCl. A range of reaction temperature from 370 ºC to 600 ºC was investigated. It was found that a pure LaMnO3 perovskite phase can be formed at as 400 ºC using the molten salt method and that LSCF powders were successfully synthesized at 500 ºC. When forming LaCrO3 using the molten salt method, LaOCl was also formed at or above 400 ºC. The X-ray diffraction (XRD) results show this is an attractive alternative route of synthesis to decrease the reaction temperature. Both Scanning Electron Microscopy (SEM) images and XRD patterns for LaCrO3 showed that only cubic structures were formed at low temperature (400 ºC and 450 ºC) and then hexagonal structures started to appear at temperatures above 500 ºC. The molten salt synthesis method was then used to prepare core-shell structures with LaCrO3 or LSCF particles as the core and LaMnO3 as the shell. Core-shell structures were characterized by Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscope (STEM) and Energy Dispersive X-ray Spectroscopy (EDS). It was found that the expected core-shell structures were successfully formed with the overall cubic structures.
Therefore, the molten salt synthesis method is a feasible method to decrease the operation temperature and form the core-shell structure.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/27012 |
| Date | 02 November 2017 |
| Creators | Zhu, Yuexing |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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