| Phase Formation Investigation In Mechanochemical Synthesis Of Nanostructured Strontium-Doped Lanthanum Manganite |
| کد مقاله : 1062-THFC |
| نویسندگان |
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هما تمدن *، امیر مقصودی پور پژوهشگاه مواد و انرژی |
| چکیده مقاله |
| Abstract The possibility to use perovskite oxides -as cathodes- should lead to an extreme decrease of solid oxide fuel cell (SOFC) operation temperature. In this research, the structural and physical properties of lanthanum strontium manganite have been investigated. The procedure is as follows. First, La0.8Sr0.2MnO3 is synthesized by implementing the mechanochemical method, then the dried mixture powders ground at room temperature using a high-energy ball mill. The effect of grinding time and speed on the structural properties and phase behavior of Sr-doped LaMnO3 system was explored as well. Structural parameters of compounds have been determined by X-ray diffraction (XRD), which confirmed that the uncontaminated and Nano crystallite lanthanum strontium manganite powder with perovskite structure and cubic symmetry has been prepared. The other results consisting of Brunauer, Emmett and Teller (BET) data and scanning electron microscopy (SEM) strongly indicated that grinding time has a drastic impact on mechanochemical synthesis of strontium-doped lanthanum manganite. Grinding time improvement led to Nano crystallite size, distribution and structural characteristics modification. Keywords: solid oxide fuel cell cathode, strontium-doped lanthanum manganite, mechanochemical synthesis, nano crystallite, phase structure Results, discussion and conclusion The XRD patterns of not-ground samples are shown in Fig. 1. A close look at this figure reveals that the characteristic potential split diffraction lines closely match with coarse powder. As can be seen there is a tendency to monoclinic structure formation in not-milled samples which are directly heated in relatively high temperatures. This tendency is identical to that of the LSM and due to a decrease in disorder by changing the symmetry from orthorhombic to monoclinic. Fig. 2 indicates the X-ray patterns of ground samples of LSM with 220 rpm and calcined at 900oC . It can be detected that even at high grinding time (72h) and following calcination at 900oC for 2 hours in air, the peak splitting was observed in all of the diffraction patterns. The diffraction patterns of milled powder with 300 rpm and calcined at 600oC are illustrated in Fig. 3. For the samples which milled for 12 hours and more than that, the diffraction peaks indexed well to perovskite structure with cubic symmetry. This suggested that Sr2+ was successfully incorporated into the A-site (Lanthanum situation) of the LSM lattice. Due to the peak intensity increment, the amount of cubic phase LSM with perovskite lattice increased with grinding time at 300 rpm constant speed and calcination temperature of 600oC . The results of this research showed that diffraction patterns of LSM broadened out by increasing milling time up to 48 hours. Also the final product was a homogenous LSM phase with perovskite structure and cubic symmetry which obtained in a single-step method using low rotational speed (300 rpm) and relative low milling time (12h) without any additional treatment. |
| کلیدواژه ها |
| solid oxide fuel cell cathode, strontium-doped lanthanum manganite, mechanochemical synthesis, nano crystallite, phase structure |
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