Allan Walton

Reversible Interpenetration in a Metal-Organic Framework Triggered by Ligand Removal and Addition

Interpenetration is known for the structures of many minerals and ice; most notably for ice, it exists in doubly interpenetrating (VI, VII, and VIII) and non-interpenetrating (Ih) forms with the latter being porous and having nearly half of the density of the former. In synthetic materials, specifically in metal–organic frameworks (MOFs), interpenetration is generally considered undesirable because it reduces porosity. However, on the contrary, many advantageous properties also arise when MOFs are interpenetrated, such as selective guest capture, stepwise gas adsorption, enhanced framework robustness, photoluminescence control, and guest-responsive porosity. Therefore, various strategies have been suggested to control interpenetration during synthesis. However, once these extended network materials are prepared as interpenetrating or non-interpenetrating structures, the degree of interpenetration generally remains unchanged, because numerous chemical bonds must be broken and subsequently reformed in a very concerted way during the process unlike some interlocked coordination compounds in solution (Figure 1a).

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%).

Characterisation of porous hydrogen storage materials: carbons, zeolites, MOFs and PIMs

Porous materials adsorb H2 through physisorption, a process which typically has a rather low enthalpy of adsorption (e.g. ca. 4 to 7 kJ mol(-1) for MOFs), thus requiring cryogenic temperatures for hydrogen storage. In this paper, we consider some of the issues associated with the accurate characterisation of the hydrogen adsorption properties of microporous materials. We present comparative gravimetric hydrogen sorption data over a range of temperatures for different microporous materials including an activated carbon, a zeolite, two MOFs and a microporous organic polymer. Hydrogen adsorption isotherms were used to calculate the enthalpy of adsorption as a function of hydrogen uptake, and to monitor the temperature dependence of the uptake of hydrogen. Under the conditions investigated, it was found that the Tóth equation provided better fits to the absolute isotherms compared to the Sips (Langmuir-Freundlich) equation at low pressures, whereas it appeared to overestimate the maximum saturation capacity. The isosteric enthalpy of adsorption was calculated by either: fitting the Sips and Tóth equations to the adsorption isotherms and then applying the Clausius-Clapeyron equation; or by using a multiparameter Virial-type adsorption isotherm equation. It was found that the calculated enthalpy of adsorption depended strongly upon the method employed and the temperature and pressure range used. It is shown that a usable capacity can be calculated from the variable temperature isotherms for all materials by defining a working pressure range (e.g. 2 to 15 bar) over which the material will be used.

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.

Low temperature hydrogenation properties of platinum group metal treated, nickel metal hydride electrode alloy

Nickel metal hydride batteries are now an established technology, being used in a wide range of applications. One problem that has been identified with the technology is the poor high rate capability of these batteries, and therefore in a number of circumstances nickel cadmium batteries are still the preferred energy source. One option to resolve this problem has been to surface treat the materials with platinum group metals. This treatment produces cells that show great promise in applications such as the power tool, industrial and automotive markets. The current work describes the surface treatment of metal hydride electrode alloys with a wider variety of platinum metal combinations to assess the rate performance of these materials at ambient and near-zero temperatures. It is observed that the treatment improves the activity of the cells at low temperatures, supporting the view that the surface energy of the electrode alloy is a strong contender as the rate-determining feature of these materials. In addition to this conclusion, the data suggest that these cells would withstand the harsh constraints when used as an automotive starter battery.

MgH2 → Mg phase transformation driven by a high-energy electron beam: An in situ transmission electron microscopy study

The dynamics of a phase change have been studied using the electron beam in a transmission electron microscope to transform MgH2 into Mg. The study involved selected-area diffraction and electron-energy-loss spectroscopy (EELS). The orientation relation ( and ), obtained from the electron diffraction study, has been used to propose a model for the movements of magnesium atoms during the phase change. The in situ EELS results have been compared with the existing H-desorption model. The study aims to describe the sorption dynamics of hydrogen in MgH2, which is a base material for a number of promising hydrogen storage systems.

Identification and recovery of rare-earth permanent magnets from waste electrical and electronic equipment

Nd-Fe-B permanent magnets are a strategic material for a number of emerging technologies. They are a key component in the most energy efficient electric motors and generators, thus, they are vital for energy technologies, industrial applications and automation, and future forms of mobility. Rare earth elements (REEs) such as neodymium, dysprosium and praseodymium are also found in waste electrical and electronic equipment (WEEE) in volumes that grow with the technological evolution, and are marked as critical elements by the European Commission due to their high economic importance combined with significant supply risks. Recycling could be a good approach to compensate for the lack of rare earths (REs) on the market. However, less than 1% of REs are currently being recycled, mainly because of non-existing collection logistics, lack of information about the quantity of RE materials available for recycling and recycling-unfriendly product designs. To improve these lack of information, different waste streams of electrical and electronic equipment from an industrial recycling plant were analyzed in order to localize, identify and collect RE permanent magnets of the Nd-Fe-B type. This particular type of magnets were mainly found in hard disk drives (HDDs) from laptops and desktop computers, as well as in loudspeakers from compact products such as flat screen TVs, PC screens, and laptops. Since HDDs have been investigated thoroughly by many authors, this study focusses on other potential Nd-Fe-B resources in electronic waste. The study includes a systematic survey of the chemical composition of the Nd-Fe-B magnets found in the selected waste streams, which illustrates the evolution of the Nd-Fe-B alloys over the years. The study also provides an overview over the types of magnets integrated in different waste electric and electronic equipment.

High coercivity, anisotropic, heavy rare earth-free Nd-Fe-B by Flash Spark Plasma Sintering

In the drive to reduce the critical Heavy Rare Earth (HRE) content of magnets for green technologies, HRE-free Nd-Fe-B has become an attractive option. HRE is added to Nd-Fe-B to enhance the high temperature performance of the magnets. To produce similar high temperature properties without HRE, a crystallographically textured nanoscale grain structure is ideal; and this conventionally requires expensive “die upset” processing routes. Here, a Flash Spark Plasma Sintering (FSPS) process has been applied to a Dy-free Nd30.0Fe61.8Co5.8Ga0.6Al0.1B0.9 melt spun powder (MQU-F, neo Magnequench). Rapid sinter-forging of a green compact to near theoretical density was achieved during the 10 s process, and therefore represents a quick and efficient means of producing die-upset Nd-Fe-B material. The microstructure of the FSPS samples was investigated by SEM and TEM imaging, and the observations were used to guide the optimisation of the process. The most optimal sample is compared directly to commercially die-upset forged (MQIII-F) material made from the same MQU-F powder. It is shown that the grain size of the FSPS material is halved in comparison to the MQIII-F material, leading to a 14% increase in coercivity (1438 kA m−1) and matched remanence (1.16 T) giving a BHmax of 230 kJ m−3.

Hydrogen storage properties of nanostructured graphite-based materials

Ball milling is an effective way of producing defective and nanostructured graphite. In this work, graphite was milled under 3 bar hydrogen in a tungsten carbide milling pot, and the effect of milling conditions on the microstructure and hydrogen storage properties was investigated by TGA-Mass Spectrometry, XRD, SEM and Raman spectroscopy. After milling for 10 hours, 5.5 wt% hydrogen was released upon heating under argon to 990°C. After milling for 40 hours, the graphite became significantly more disordered, and the amount of hydrogen desorbed upon heating decreased.

Production and Application of HPMS Recycled Bonded Permanent Magnets for a Traction Motor Application

Due to the volatility of the cost and sustainability concerns associated with the rare-earth permanent magnets, alternative product designs using less or no rare-earth contents have, recently, gained popularity. Another method to address this need is to apply a magnet recycling process, such as the novel hydrogen processing of magnetic scrap (HPMS) which can be applied to the end-of-life products such as hard drive disks. Despite the growing research on the background science of different recycling techniques, a practical make, use and evaluation of recycled magnets in a real-life application, is rarely attended. To address this gap, in this paper and for the first time, the viability of the HPMS recycled magnets for use in a permanent magnet traction motor is investigated. On this basis, a detailed description and testing of the recycling process and the magnet production for a customized traction motor design is provided. Furthermore, the behavior of the motor using the final magnet product is analyzed using simulations and prototype testing. Based on the results, the proposed recycled magnets satisfy the overall requirements, while demonstrating similar or better electromagnetic performance compared to the alternative low-cost ferrite magnets.