Modifizierung der Werkstoffe auf Basis von Magnesiumsilicid mit Hilfe der Spark-Plasma-Synthese (English shop)

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The extensive investigations of selected Mg2Si-based materials within this work reveal new avenues for the application of the SPS technique in both basic and applied research and provide crucial new material for the characterisation of the Li compounds Li2xMg2-xX (X = Si, Ge, Sn, Pb).
Building on previous work and the results presented here, new possibilities arise both for synthesis based on the SPS process (in combination with powder production, powder processing and a corresponding tool design) and for an optimisation of the material properties of composite materials by using this technique.

The ternary phases Mg2Si1−xXx (X = Ge, Sn, Pb) and Mg2−x/2Si1−xSbx
In this work, the powder-metallurgical preparation of the phases Mg2Si1-xXx (X = Ge, Sn and Pb) and of the phase Mg2−x/2Si1-xSbx was achieved for the first time by means of the SPS technique from ball-milled powder mixtures (MgH2, Si, X).

The ternary phases Li2xMg2−xX (X = Si, Ge, Sn, Pb)
The incorporation of Li into Mg2Si was investigated in this work for the first time by the SPS solid-state reaction from LiH, MgH2 and Si. The synthesis of the Li-poor Li2xMg2−xSi phases is already achieved at temperatures of max. 700 °C.
Melt synthesis of these extremely air- and moisture-sensitive samples was carried out from the elements under an argon protective atmosphere with subsequent heat treatment at 200 °C. In this way, three different cubic Li2xMg2−xSi phases with 0 < x < 0.8 can be found on the Mg2Si-rich side of the ternary system. With increasing Li content, two structural transformations can be determined by X-ray diffraction, starting from the space group for Mg2Si to and , with the formation of a superstructure with a′ = 2a.
With increasing Li content in Li2xMg2−xSi, the properties change. The transition from the semiconducting to the metallic state could be demonstrated for the first time in this work.
In analogy to Li2xMg2−xSi, the phases Li2xMg2−xX (X = Ge, Sn, Pb) could be characterised. Intercalation of Li in Mg2X is not possible.

The composite materials based on Mg2Si
The brittle material behaviour of Mg2Si samples can be reduced by a powder-metallurgically produced composite material with Mg.

The SPS technique
Based on previous work, the distribution of current, density and temperature during the SPS process within the sample and the tool could be assessed in this work through the use of MgH2.