科研之友
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摘要
A polycrystalline higher manganese silicide (HMS) material has been sintered from an aluminium-enriched gas-phase atomized powder using spark plasma sintering (SPS). After tailoring the SPS parameters, the polycrystal is almost fully dense, mainly constituted by the Mn15Si26 HMS phase and the average grain size is around 10 mu m. Transmission electron microscopy investigations coupled to energy dispersive X-ray spectroscopy (EDS) measurements show that: (i) alumina is segregated at grain boundaries and multiple points; (ii) a small amount of residual silicon is homogeneously distributed in the sintered microstructure; (iii) intragranular nanometre-sized inclusions (averaged diameter around 20 nm, concentration of 8.9 x 10(-4) inclusions/nm(2)) are observed in most of the individual grains constituting the polycrystal. Some are crystalline and made of metallic MnSi, some are residual holes/gas bubbles entrapped into the sintered microstructure during the manufacturing step; (iv) each individual grain contains around I at.% of aluminium that is dispersed in the Mn15Si26 elemental lattice and then acts possibly as a dopant. Thermoelectrical properties of the sintered material have been investigated in the 20-700 degrees C temperature range and compared to the literature. The material exhibits the desired P-type conduction, the Seebeck coefficient has a high value for all the temperature range and in the same time the thermal conductivity is especially low. It is postulated that aluminium doping and the presence of nanometre-sized inclusions in the sintered microstructure are responsible for the dimensionless figure of merit (ZT) around 0.7 measured at 500 degrees C. Such a value, obtained on a sample manufactured with a very simple process, is the best one ever reported for this kind of material.
- 出版日期2015-1-5
