Abstract
To clarify the mechanism of the formation of LaNi5 by the reduction-diffusion (RD) process, two kinds of experiments were carried out: (1) briquets consisting of La2O3, CaH2, and Ni wires were heated at 1300 K in the RD experiment; and (2) Ni wire was immersed into an Ni-La-Ca melt with a composition on the Ni-side liquidus surface at 1300 K. On the surface of Ni, LaNi5 grew and the formation of CaNi5 was also observed between the LaNi5 and Ni in the RD reaction; both layers grew in accordance with a parabolic rate law. Even in the reaction of Ni wire with an Ni-La-Ca ternary melt of low Ca concentrations, CaNi5 initially grew on the nickel surface before LaNi5 was formed, and the Ca in CaNi5 was replaced with La to form LaNi5. The reason for the initial formation of CaNi5 was discussed using molecular orbital calculations. These calculations show that the preferential and temporary formation of CaNi5 and the final production of LaNi5 can be explained by the electronic structures of Ni alloys containing Ca or La and those of the compounds, CaNi5 and LaNi5, respectively.
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Tanabe, T., Asaki, Z. Formation mechanism of LaNi5 in the reduction-diffusion process. Metall Mater Trans B 29, 331–338 (1998). https://doi.org/10.1007/s11663-998-0110-2
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DOI: https://doi.org/10.1007/s11663-998-0110-2