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Content archived on 2024-04-16



The optimum basic alloy composition among the rare-earth iron nitrides and rare-earth iron carbides was confirmed to be Sm2Fe17N3. A good basic understanding of the role of nitrogen in these interstitial intermetallics has been developed and the nature of the low-temperature gas-solid reaction clarified. The use of the range of precursors for introducing C, N or H, or a combination of them into intermetallics has been developed by CNRS and TCD. Gas-solid reactions on the > kg scale have been conducted by RP.

Progress in magnet development has matched expectations in most areas, nevertheless the development of a technically and commercially competitive processing route for Sm2Fe17N3 magnets remains problematic. The technology for producing isotropic nanocrystalline Sm-Fe-N powder on an advanced laboratory scale has been developed by Siemens. The powder has a high coercivity (iHc > 2 MA/m), a limited remanence (Jr approximately equals 0.75 T) due to its isotropic nature but excellent thermal stability of both properties.

Monocrystalline coercive powder has been developed by VAC and TCD. The fine powder (approximately equals 2 um) can be used for anisotropic bonded magnets and laboratory polymer bonded magnets produced by TCD have iHc = 0.7 MA/m, Jr = 0.9 T and (BH)max = 110 kJ/m{3}. Zinc-bonded magnets produced in industrial conditions by VAC have iHc = 1.1 MA/M, Jr = 0.77 T and (BH)max = 97 kJ/m{3}. The main problems have been related to texturing and densification of the magnets, which are technically important because the useful magnetic values scale with the remanence or the remanence squared.
Following the discovery of a new family of interstitial rare earth iron nitrides by the prime partner in early 1990 and the achievement of remarkable hysteresis in the mechanically-allowed samarium compound by one of the main industrial partners (Siemens), a coherent programma of research is proposed involving a rare-earth supplier (Rh degreesne Poulenc), a major magnet manufacturer (Vacuumschmelze) and two specialized research institutes. The aim is to develop a new generation of rare-earth iron permanent magnets based on Sm2Fe17N3-9.

Two approaches will be advanced in parallel : the one involves nanocrystalline powder produced by mechanical alloying or melt spinning, which may be textured before processing into bonded or compacted magnets; the other uses monocrystalline powder which may be oriented in a magnetic field and fabricated into polymer- or metal-bonded magnets. Both approaches promise a low-cost processing route to magnets that integrate form and function.

Magnet development will be supported by research to optimize the new alloys with respect to microstructure, magnetic performance and cost, and to upscale the gas-phase nitrogenation reaction. Materials and magnets will be extensively tested in various working environments.


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University of Dublin - Trinity College
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