John Speight

Life Cycle Inventory of the Production of Rare Earths and the Subsequent Production of NdFeB Rare Earth Permanent Magnets

Neodymium is one of the more critical rare earth elements with respect to current availability and is most often used in high performance magnets. In this paper, we compare the virgin production route of these magnets with two hypothetical recycling processes in terms of environmental impact. The first recycling process looks at manual dismantling of computer hard disk drives (HDDs) combined with a novel hydrogen based recycling process. The second process assumes HDDs are shredded. Our life cycle assessment is based both on up to date literature and on our own experimental data. Because the production process of neodymium oxide is generic to all rare earths, we also report the life cycle inventory data for the production of rare earth oxides separately. We conclude that recycling of neodymium, especially via manual dismantling, is preferable to primary production, with some environmental indicators showing an order of magnitude improvement. The choice of recycling technology is also important with respect to resource recovery. While manual disassembly allows in principle for all magnetic material to be recovered, shredding leads to very low recovery rates (<10%).

Magnets in medicine

Abstract As permanent magnet materials have developed, attempts have been made to take advantage of their improved properties in medical applications. Uses of magnets in medical applications range from their simple use for retention, through orthopaedics and fracture healing, to magnetomotive artificial hearts and pioneering brain surgery, where magnets are used to guide catheters. Magnets also find use in applications such as magnetic resonance imaging (MRI) scanners and drug delivery systems. This overview, based on an extensive review of the literature, chronicles the development of magnets in medicine and summarises areas where future research will be beneficial.

A zinc coating method for Nd–Fe–B magnets

Abstract A newly developed Low Pressure Pack Sublimation (LPPS) process has been used to coat fully dense Nd–Fe–B sintered magnets with zinc. The process was based on a form of sherardizing where the component to be coated is placed in a rotating chamber at 390°C in a mixture of sand and zinc dust. However, during the LPPS process, a moderate vacuum is applied and the chamber is not rotated. LPPS produced an adherent surface coating, which, when placed in a corrosive environment, displayed superior performance in terms of weight loss and reduction in magnetic properties compared to those exhibited by the commercially electroplated and uncoated samples. The severe corrosion conditions were imposed using an autoclave (100°C, 1bar pressure and saturated humidity). The composition and characteristics of the surface layers were examined using optical analysis, XRD and Scanning Electron Microscopy. Under the conditions employed in these studies, the LPPS process produced a small reduction in remanence and coercivity (≈10% and ≈5% respectively) by changing the surface conditions of the magnets. The reduction in properties was found to be related to coating thickness and temperature effects. By the use of LPPS a cheap and effective barrier to corrosion has been produced.

Pd–Cu–M (M = Y, Ti, Zr, V, Nb, and Ni) Alloys for the Hydrogen Separation Membrane

Self-supported fcc Pd-Cu-M (M = Y, Ti, Zr, V, Nb, and Ni) alloys were studied as potential hydrogen purification membranes. The effects of small additions (1-2.6 at. %) of these elements on the structure, hydrogen solubility, diffusivity, and permeability were examined. Structural analyses by X-ray diffraction (XRD) showed the fcc phase for all alloys with induced textures from cold rolling. Heat treatment at 650 °C for 96 h led to the reorientation in all alloys except the Pd-Cu-Zr alloy, exhibiting the possibility to enhance the structural stability by Zr addition. Hydrogen solubility was almost doubled in the ternary alloys containing Y and Zr compared to Pd65.1Cu34.9 alloy at 300 °C. It was noted that hydrogen diffusivity is decreased upon additions of these elements compared to the Pd65.1Cu34.9 alloy, with the Pd-Cu-Zr alloy showing the lowest hydrogen diffusivity. However, the comparable hydrogen permeability of the Pd-Cu-Zr alloy with the corresponding binary alloy, as well as its highest hydrogen permeability among the studied ternary alloys at temperatures higher than 300 °C, suggested that hydrogen permeation of these alloys within the fcc phase is mainly dominated by hydrogen solubility. Hydrogen flux variations of all ternary alloys were studied and compared with the Pd65.1Cu34.9 alloy under 1000 ppm of H2S + H2 feed gas. Pd-Cu-Zr alloy showed superior resistance to the sulfur poisoning probably due to the less favorable H2S-surface interaction and more importantly slower rate of bulk sulfidation as a result of improved structural stability upon Zr addition. Therefore, Pd-Cu-Zr alloys may offer new potential hydrogen purification membranes with improved chemical stability and hydrogen permeation compared to the binary fcc Pd-Cu alloys.

Suitability of Amorphous Thin–Film Alloys for Hydrogen Purification

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Joint second prize low pressure pack sublimation: newly developed zinc coating process

Abstract The LPPS process has been developed to coat Nd–Fe–B magnets and related alloy powders. The process is similar to sherardising, except that the coating chamber is static and evacuated to a moderate vacuum (10-1 torr). Compared to sherardising, LPPS achieves lighter coloured coatings and enhanced coating uniformity and has the ability to coat reactive ferrous materials such as Nd–Fe–B magnets. The corrosion protection provided by LPPS zinc is equivalent to that obtained with conventional sherardising. Using SEM, XRD, and SIMS analysis, the mechanism for both sherardising and LPPS has been shown to be the interaction of zinc vapour with ferrous substrates to form Fe–Zn intermediate phases (δ, ξ, and γ). At a given temperature, the zinc vapour pressure, chamber pressure, surface preparation of the component, and substrate material have been found to influence the rate of layer growth and final intermediate phase mixtures. Activation energy and thermodynamic analysis suggest that in galvanising, galvannealing, sherardising, and LPPS, Fe–Zn phase formation is dominated by the inward diffusion of zinc. For LPPS zinc coated Nd–Fe–B magnets, the same mechanism applies and leads to a complex mixture of (Nd–Fe–B)–Zn phases. The ‘black zinc’ layers seen occasionally with sherardising and LPPS have been shown to be associated with residual oxygen present in the deposition chamber. Black zinc surfaces have high optical absorbance as a result of their finely divided nature. Recent work on extending LPPS to coat magnet powders is also presented.