Synthesis of nanoscale SmFe intermetallic phases by a reduction-diffusion process of a powder mixture of Sm2O3-CaH2-Fe
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This study investigates the synthesis of SmFe intermetallic compounds by a solid state reduction-diffusion process (R-D process) using a mixture of Sm2O3-CaH2 ball-milled powders and Fe nanopowders. The Sm2O3-CaH2-Fe mixed powders were subjected to heat treatment under a switched gas atmosphere from Ar-5 vol.%H2 to a vacuum atmosphere during the R-D process at 800 οC. It was found that the SmFe intermetallic phases of Sm2Fe17 and SmFe3 were effectively formed in a switched gas atmosphere and observed on the surface of the sintered Fe nanopowder agglomerate. This formation occurred because the sintering of agglomerated Fe nanopowders occurred at a low temperature of about 500 οC earlier before the Sm dissociated from SmH2 was diffused into the sintered Fe nanopowders agglomerate during the R-D process. The Sm2Fe17 phase of the target alloy was identified having a rhombohedral Th2Zn17-type (2:17 R) structure with a grain size of 400-800 nm. It is expected that the Sm2Fe17 nanopowders can be effectively fabricated by controlling the initial powder characteristics such as size refinement and mixing homogeneity
Abstract
This study investigates the synthesis of SmFe intermetallic compounds by a solid state reduction-diffusion process (R-D process) using a mixture of Sm2O3-CaH2 ball-milled powders and Fe nanopowders. The Sm2O3-CaH2-Fe mixed powders were subjected to heat treatment under a switched gas atmosphere from Ar-5 vol.%H2 to a vacuum atmosphere during the R-D process at 800 οC. It was found that the SmFe intermetallic phases of Sm2Fe17 and SmFe3 were effectively formed in a switched gas atmosphere and observed on the surface of the sintered Fe nanopowder agglomerate. This formation occurred because the sintering of agglomerated Fe nanopowders occurred at a low temperature of about 500 οC earlier before the Sm dissociated from SmH2 was diffused into the sintered Fe nanopowders agglomerate during the R-D process. The Sm2Fe17 phase of the target alloy was identified having a rhombohedral Th2Zn17-type (2:17 R) structure with a grain size of 400-800 nm. It is expected that the Sm2Fe17 nanopowders can be effectively fabricated by controlling the initial powder characteristics such as size refinement and mixing homogeneity
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