Berlin 2012 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 13: Magnetic Materials
MA 13.13: Vortrag
Montag, 26. März 2012, 18:15–18:30, H 0112
Study of the mechanisms of the Thermal Decomposition reaction in the magnetocaloric system La(Fe,Si,Co)13 — •Konrad Löwe1, Jian Liu1, Hossein Sepehri-Amin2, Kazuhiro Hono2, Matthias Katter3, and Oliver Gutfleisch4,1 — 1IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany — 2NIMS, 1-2-1 Sengen, Tsukuba 305-0047 Japan — 3Vacuumschmelze GmbH u Co. KG, Grüner Weg 37, 63450 Hanau, Germany — 4TU Darmstadt, Institute for Materials Science, Petersenstr. 23 64287 Darmstadt, Germany
We report on the influence of the Co content in the magnetocaloric system La(Fe,Si,Co)13 on the Thermal Decomposition (TD) reaction. In the course of the reaction, the magnetocaloric La(Fe,Si,Co)13 phase reversibly decomposes into α-Fe(Co,Si) and the intermetallic LaFeSi phase, thus greatly enhancing the mechanical properties and therefore the machinability of the compound. The addition of Co significantly speeds up the reaction kinetics. The optimum temperature range for the TD was determined to be 973 - 1073 K, whereas the lower and upper limit lies at 873 K and 1173 K, respectively. With electron microscopy a pearlitic microstructure (lamellae) has been found in the decomposed state, indicating a eutectoid-type phase reaction. The thickness of the lamellae is about 20-30 nm in LaFe12Si and decreases with increasing Co content. Also the pearlite seems to be more ordered with addition of Co. 3DAP measurements show the enrichment of Co in both the α-Fe(Co,Si) and the LaFeSi lamellae. We conclude that the addition of Co somehow changes the pearlitic growth mechanisms, which is the main reason for the greatly enhanced TD kinetics.