The Raw Materials Summit 2019: connecting innovation in the Raw Materials Sector

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Isomorphs in model molecular liquids

Isomorphs are curves in the phase diagram along which a number of static and dynamic quantities are invariant in reduced units. A liquid has good isomorphs if and only if it is strongly correlating, i.e., the equilibrium virial/potential energy fluctuations are more than 90% correlated in the NVT ensemble. This paper generalizes isomorphs to liquids composed of rigid molecules and study the isomorphs of two systems of small rigid molecules, the asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for both systems we find that the isochoric heat capacity, the excess entropy, the reduced molecular center-of-mass self part of the intermediate scattering function, the reduced molecular center-of-mass radial distribution function to a good approximation are invariant along an isomorph. In agreement with theory, we also find that an instantaneous change of temperature and density from an equilibrated state point to another isomorphic state point leads to no relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be more approximative than those of the asymmetric dumbbell model, which is consistent with the OTP model being less strongly correlating. For both models we find "master isomorphs", i.e., isomorphs have identical shape in the virial/potential energy phase diagram.Comment: 20 page

A systematic study of HDDR processing conditions for the recycling of end-of-life Nd-Fe-B magnets

Scrap rare earth permanent magnets from various sources and applications were collected and processed for recycling using hydrogen decrepitation (HD) and hydrogenation disproportionation desorption and recombination (HDDR) processes. The effects of the principle HDDR processing parameters hydrogen pressure, hydrogen desorption rate and temperatures on the magnetic properties of the recycled materials have been investigated systematically. The optimum hydrogen pressures required for the complete disproportionation of the various magnet compositions were determined. We found that a hydrogen heat treatment composed of two steps (780 °C and 840 °C) and a moderate desorption rate can be used for the magnets having a higher Dy and Co content to obtain high quality anisotropic HDDR powders for resin bonded magnet production

Efficient recycling of rare earth permanent magnets: Applications and present situation

Many advanced technologies are based on the use of functional materials. Due to their chemical composition and microstructure these materials offer certain macroscopic properties useful for their specific applications. Modern vehicles contain a large number of electronic micromotors, electric actuators and powertrains are widely used also in the mechanical engineering industry. Audio devices and hard disks have become an integral part of the private as well as of the business life. For the future more and more energy will be produced via wind power and electric mobility will replace present mobility technologies, which are based on fossil fuels [1]

Seltene Erden - Seltenerdhaltige Permanentmagnete effizient recyceln

Viele moderne Technologien basieren auf dem Einsatz funktionaler Materialien, die aufgrund ihrer chemischen Zusammensetzung und ihrer Mikrostruktur für die jeweiligen Anwendungen spezielle makroskopische Eigenschaften aufweisen

Ce and La as substitutes for Nd in Nd2Fe14B-based melt-spun alloys and hot-deformed magnets: A comparison of structural and magnetic properties

Ce and La as very cheap rare-earth elements were used to substitute Nd in nanocrystalline melt-spun ribbons of nominal compositions (Nd1−xREx)13.6FebalCo6.6Ga0.6B5.6 (x = 0, 0.1, 0.2, … 1 for RE = Ce) and (x = 0, 0.1, 0.2, … 0.5 for RE = La). Ce substitution gradually decreased the Nd2Fe14B lattice constants and produced CeFe2 segregation from x = 0.7. La substitution led to lattice expansion along the c-axis and induced segregation of α-Fe and Nd2Fe17 at x = 0.5. Grain coarsening was observed in the Ce-substituted samples while La was found to suppress grain growth. Cerium worsened the magnetic properties of as-spun powders after an initial improvement in (Nd0.9Ce0.1)13.6FebalCo6.6Ga0.6B5.6 alloy which showed a coercivity (µ0Hc) of 1.54 T and a remanence (Br) of 0.81 T. Coercivity dropped with increasing La concentration but remanence increased from 0.73 T in the base composition to 0.88 T at x = 0.3. The Curie temperatures (TC) showed a slight decrease in both cases until x = 0.4. It then dropped abruptly for increasing Ce fractions and increased at x = 0.5 La. For x = 0.2 and 0.3 Ce and x = 0.2 La fractions, the melt-spun samples were further processed by hot-pressing and hot-deformation. The hot-pressed (Nd0.8La0.2)13.6FebalCo6.6Ga0.6B5.6 alloy measured lower coercivity but increased remanence comparing to the Ce-substituted alloys. However, this composition responded poorly to hot-deformation, severe cracking being induced in the process. Due to enhanced hot-workability, best magnetic properties were obtained after deformation for the (Nd0.7Ce0.3)13.6FebalCo6.6Ga0.6B5.6 alloy (µ0Hc = 1.09 T, Br = 0.97 T and energy product (BH)max = 170 kJ/m3)