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Hydrogen separation membranes based on a heated metal foil of a palladium alloy, offer excellent permeability for hydrogen as a result of the solution-diffusion mechanism. Here, the possibility to separate hydrogen from the mixture of Natural Gas (NG) and hydrogen (NG+H2) with various NG concentrations using Pd, PdCu53 and PdAg24 hydrogen purification membranes is demonstrated. Hydrogen concentrations above ∼25% (for Pd and PdCu53) and ∼15% (for PdAg24) were required for the hydrogen separation to proceed at 400 °C and 5 bar pressure differential. Hydrogen permeability of the studied alloys could be almost fully recovered after switching the feed gas to pure hydrogen, indicating no significant interaction between the natural gas components and the membranes surface at the current experimental condition. Hydrogen flux of the membranes at various pressure differential was measured and no changes in the hydrogen permeation mechanism could be noticed under (NG 50%+H2) mixture. The hydrogen separation capability of the membranes is suggested to be mainly controlled by the operating temperature and the hydrogen partial pressure.

Amorphous alloys are of particular interest due to their less susceptibility to hydrogen embrittlement and corrosion, superior mechanical properties and more importantly lower cost compared to the Pd–based crystalline membranes. Amorphous thin films of Zr40.5Ni59.5, Zr56.2Cu43.8, Zr30Cu57.7Y12.3, and Zr32Cu57.3Ti10.7 alloys are fabricated by the magnetron sputtering method. All alloys are thermally stable until above 400 °C under an inert atmosphere. Nevertheless, the thermal stabilities of all alloys are reduced by almost more than 150 °C under hydrogen with exception of the Zr40.5Ni59.5 alloy showing comparable thermal stability under hydrogen and inert. Structural analyses by XRD under hydrogen and an inert atmosphere reveal decomposition of the studied amorphous alloys during the crystallisation process, leading to severe phase separation for Ni and Cu in Zr40.5Ni59.5 and Zr56.2Cu43.8 alloys. Such a phase separation seems to have an influence on the crystallisation path and products. However, Cu phase separation seems to be mitigated in Zr30Cu57.7Y12.3, and Zr32Cu57.3Ti10.7 alloys despite their higher Cu content compared to Zr56.2Cu43.8 alloy. The surface segregation tendency of Cu results in surface crystallisation in the Zr56.2Cu43.8 alloy, whilst bulk nucleation and growth dominates the crystallisation process in the other alloys, evident by the non–isothermal kinetic studies. The calculated activation energies show that more energy is required for nucleation compared to the growth process in the Zr40.5Ni59.5 and Zr56.2Cu43.8 alloys, whilst is the opposite case in Zr30Cu57.7Y12.3, and Zr32Cu57.3Ti10.7 alloys.

Surface topography and hydrogen permeation properties of Porous Stainless Steel (PSS) substrates for thin films deposition of Pd-based hydrogen separation membrane were investigated. Hydrogen permeance through the as received PSS substrates demonstrated a wide range, despite a similar average surface pore size of ~15 µm determined by SEM and confocal laser microscopy analyses. The surface pores of the PSS substrates were modified by impregnation of varying amounts of tungsten (W) powder. Maximum hydrogen flux reduction of 28% suggested that W has a limited effect on the hydrogen permeation through the PSS substrate. Therefore, it appears that hydrogen transport through PSS substrates is mainly controlled by the substrate geometrical factor ( e τ ), that is the ratio of the porosity to tortuosity. In addition, tungsten was shown to inhibit the iron inter-diffusion between the PSS substrate and the deposited Pd60Cu40 film at temperature as high as 800 °C. Thus, tungsten layer also serves as an effective inter-diffusion barrier. The variation in the permeance between the nominally similar PSS substrates indicates the importance to independently assess the hydrogen transport characteristics of each of the components in a composite membrane.

Neodymium iron boron (NdFeB) magnets are used in a number of important applications, such as generators in gearless wind turbines, motors in electric vehicles and electronic goods (e.g.— computer hard disk drives, HDD). Hydrogen can be used as a processing gas to separate and recycle scrap sintered Nd-Fe-B magnets from end-of-life products to form a powder suitable for recycling. However, the magnets are likely to have been exposed to atmospheric conditions prior to processing, and any oxidation could lead to activation problems for the hydrogen decrepitation reaction. Many previous studies on the oxidation of NdFeB magnets have been performed at elevated temperatures; however, few studies have been formed under atmospheric conditions. In this paper a combination of 3-D laser confocal microscopy and Raman spectroscopy have been used to assess the composition, morphology and rate of oxidation/corrosion on scrap sintered NdFeB magnets. Confocal microscopy has been employed to measure the growth of surface reaction products at room temperature, immediately after exposure to air. The results showed that there was a significant height increase at the triple junctions of the Nd-rich grain boundaries. Using Raman spectroscopy, the product was shown to consist of Nd 2 O 3 and formed only on the Nd-rich triple junctions. The diffusion coefficient of the triple junction reaction product growth at 20 °C was determined to be approximately 4 × 10 −13 cm 2 /sec. This value is several orders of magnitude larger than values derived from the diffusion controlled oxide growth observations at elevated temperatures in the literature. This indicates that the growth of the room temperature oxidation products are likely defect enhanced processes at the NdFeB triple junctions.

Pd 60 Cu 40 wt% (Pd 47.3 Cu 52.7 at%) membranes were surface modified by depositing Pd thin films of three different thicknesses (~100, 800 and 1400 nm) on to one side of a range of as-received Pd 60 Cu 40 wt% cold-rolled foils via magnetron sputtering. The hydrogen permeability of the membranes was then measured and compared to the uncoated material. The Pd 60 Cu 40 wt% membrane coated with a 1400 nm thick Pd thin film positioned on the feed side (445 kPa of hydrogen pressure) during hydrogen permeability measurements and cycled between 50 and 450 °C achieved the highest hydrogen permeability of 1.09×10 −8 mol m − 1 s −1 Pa −0.5 at 450 °C in the third cycle. This is a 58% increase on the value measured for the as-received Pd 60 Cu 40 wt% membrane under the same conditions. This improvement can be attributed to a Pd-rich Pd–Cu face centred cubic (FCC) phase forming through interdiffusion between the Pd thin film and bulk Pd–Cu membrane as a result of the test conditions used during hydrogen permeability measurements. This introduces a larger hydrogen concentration gradient across the membrane due to the relatively high hydrogen solubility of the Pd-rich Pd–Cu FCC phase resulting in the observed increase in permeability. The Pd 60 Cu 40 wt% membranes coated with a ~1400 nm and ~800 nm thick Pd thin film retained an almost pure Pd surface throughout cycling between 50 and 450 °C with a feed and permeate hydrogen pressure of 445 and 100 kPa, respectively. For the deposition technique and test conditions used throughout this work, these surface modified Pd–Cu membranes appear to stabilise the Pd thin films upon cycling across the critical temperature of 295 °;C.

Amorphous hydrogen separation membranes are under development because of their resistance to hydrogen embrittlement, improved mechanical properties, resistance to corrosion and most importantly lower intrinsic cost. The Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUBMSIP) is a versatile technique for deposition of high quality thin-films of almost any composition, while enabling the control of film size, thickness and shape. In this work, it was demonstrated that thin-films (∼3–6 μm) of amorphous Zr 40.5 Ni 59.5 , Zr 54 Cu 46 and Zr 30 Cu 57.5 Y 12.5 could be deposited onto glass substrates by the CFUBMSIP technique. XRD measurements only showed one broad peak for each alloy, with a peak centred between 36° and 42° 2 θ , indicating that the films were amorphous. Surface analysis by SEM and confocal microscopy suggest deposition of continuous films. The thermal stability of the films appears to be mainly governed by the alloying elements and their compositions. However, the measured activation energies indicated that the nucleation and growth mechanism in the magnetron sputtered films may be different from that reported for melt-spun amorphous alloys with similar compositions.

The effects of the addition of small amount of Zr (less than 2 at%) to the fcc phase of the Pd-Cu hydrogen separation alloy were investigated. Hydrogen flux variations in Pd-Cu and Pd-Cu-Zr alloys in the presence of 1000 ppm H2S + H2 feed gas showed a marked effect of Zr addition in improving the resistance to sulphur poisoning.

Pd–Cu alloys are of potential interest for use as hydrogen purification membranes, but have relatively low permeability compared to the commercially used alloys such as Pd–Ag. In this work, the effects of partial Ag substitution on the hydrogen diffusivity, solubility and the permeability of Pd–Cu membranes with a bcc structure have been investigated. With the addition of 2.3 and 3.9 at% Ag to Pd–Cu, lattice expansions of 0.11% and 0.35% were observed. Structural analyses by in-situ XRD showed that the bcc structure of the 2.3 at% Ag alloy is retained upon heating to 600 °C, whereas an fcc phase forms in the 3.9 at% Ag alloy resulting in a mixed (bcc+fcc) structure. Whilst the diffusion coefficients between 350 and 400 °C for both Pd–Cu–Ag ternary samples were shown to be lower than their binary alloys (which had similar structures), higher solubility values were obtained. The lower diffusion coefficients of the ternary alloys are related to an increase in the diffusion activation barrier in the presence of Ag, and the higher solubility values may be attributed to the lattice expansion and high Ag–H chemical interaction. Hydrogen permeation measurements showed that an enhancement in the hydrogen solubility of the bcc phase Pd45.8Cu51.9Ag2.3, does not have a substantial effect on the permeability of the membrane. In contrast, for the Pd45.1Cu51Ag3.9 sample with a mixed (bcc+fcc) phase, higher hydrogen solubility can lead to a remarkable improvement in permeability. Hence, it is suggested that the hydrogen permeability in the bcc phase is mainly controlled by hydrogen diffusion, and the solubility enhancement can only significantly improve the hydrogen permeability when the fcc phase is present.

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 ...

We report the discovery of a new, chemical route for ‘activating’ the hydrogen store MgH2, that results in highly effective hydrogen uptake/release characteristics, comparable to those obtained from mechanically-milled material.

We have investigated the use of zeolites as potential hydrogen storage materials. The zeolites A, X, Y and RHO, which encompass a range of different pore geometries and compositions, were synthesised by hydrothermal methods, and different cation-exchanged forms were prepared through ion-exchange from aqueous metal nitrate solutions. The phase composition and crystallinity of samples were interrogated by powder X-ray diffraction. Scanning electron microscopy revealed cubic crystals of zeolites both before and after ion-exchange. Hydrogen adsorption capacities were measured using a constant pressure Thermogravimetric Analyser; data were obtained over a range of pressures from 0 to 15 bar and isothermally at temperatures from -196 to 300 °C. The results showed that hydrogen uptake in zeolites is strongly dependent upon temperature, and also on framework and cation type. Surface area measurements were also carried out on these materials and the results used to interpret the hydrogen adsorption data. © 2003 Elsevier B.V. All rights reserved.

The hydrogen storage properties of zeolites X, Y, A and Rho containing various exchangeable cations have been investigated. All hydrogen storage capacities were measured at a temperature of -196° C and a pressure range of 0-15 bar, using a constant pressure thermogravimetric analyser. The results show that, zeolites exhibit diverse behaviour with respect to hydrogen uptake, dependent on both the framework structure and the nature of the cations present. A major factor influencing uptake is the available void space: in zeolites A and Rho pore blocking by large extraframework cations is a major factor restricting hydrogen uptake, but in zeolites X and Y, blocking does not occur. This study also suggests that cations may act as binding sites for hydrogen molecules. For zeolites X and Y, hydrogen uptake relates closely to the measured BET surface area. The highest gravimetric storage capacity of 2.19 wt.% was obtained for CaX. Volumetric storage densities of up to 31.0 kg H 2/m3 (143 H2 molecules/unit cell) and 30.2 kg H2/m3 (144 H2 molecules/unit cell) were achieved for CaX and KX, respectively. © 2005 Elsevier B.V. All rights reserved.

Common bermudagrass [Cynodon dactylon (L.) Pers.] was harvested from two producer sites (Latta and Stephens) with high soil-test P (286 and 153 ppm, respectively) to assess the effects of N fertilization on P uptake and potential removal in hay or silage. Ammonium nitrate was applied in split applications each year at rates totaling 0, 56, 112, 168, 224, 280, or 336 kg/ha of actual N. At the Stephens site in Yr 1, cumulative DM yield increased linearly (P 0.10) between concentration of P and N fertilization rate (overall mean = 0.40%), but concentrations of P declined in linear (P

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.

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%).

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.

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, galvan...

The room temperature lattice spacing variations across the intra-rare-earth alloy systems, Ce-Ho, Pr-Ho and Nd-Sm have been determined. Certain common characteristics of these variations have been identified such as a constant axial ratio c a within the composition ranges of the double hexagonal alloys. Extrapolation of the spacings of the double hexagonal Nd-Sm alloys gave the spacings of a double hexagonal form of samarium; these show excellent agreement with the spacings of a recently reported double hexagonal form of this metal. The compositional variations of the a and c spacings of a number of cerium intra-rare-earth alloys have been correlated with the mean atomic number Z m of the alloy.

The influence of small of HC1 on the thermal aging behaviour of Ti-Au, Ti-Pd-Au and Ti-Pt-Au metallizations on tantalum nitride resistor films has been investigated. Test samples consisted of unpatterned Ta2N resistor films on glass and Al2O3 ceramic substrates coated with conductor film, and 4 mil wide Ta2N resistors covered intermittently with conductor metallization strips. Test conditions covered temperatures between 100° and 400°C and two concentrations of air/HC1 mixtures (5:1 and 10 ppm) were used for the aging environments. The progress of the degradation of the metallizations has been followed using electrical measurements, pull strength of thermocompression bonded leads, optical and scanning electron microscopy, electron diffraction and microprobe analysis. It has been shown that the rate of degradation depends on the type of metallization, the substrate material, pattern geometry, aging temperature and environment. The major mode of degradation under the conditions of the present work is corrosion of the Ti bonding layer, the final corrosion product being the rutile and anatase modifications of TiO2. Intermediate layers of Pd and Pt in Ti-Au metallizations result in a significantly lower rate of corrosion. Possible mechanisms for the protective effect of the intermediate layers are discussed.

The lattice spacings of a selection of alloys in the systems Ce-Nd, Ce-Sm, Ce-Tb and Pr-Tb, have been determined. For the Ce-Nd, Ce-Tb and Pr-Tb systems, the room-temperature magnetic susceptibilities of certain alloys have been determined. Extrapolation of the atomic volume/composition plots of alloys with the double hexagonal structure in the Ce-Nd, Ce-Sm and Ce-Tb systems to 100 at.% Ce indicates that the apparent atomic volume of cerium in these alloys exceeds that of β-Ce, and that this atomic volume corresponds to an effective valency of 3 for the cerium atoms. In the close-packed hexagonal, terbium-rich, Ce-Tb alloys, the cerium atoms again appear to be in an expanded form corresponding to a valency of 3. These results are discussed in terms of the tendency for cerium to adopt the same valency as that of the solvent metal.

Lattice spacing and magnetic susceptibility measurements have been made for Sm-type alloys in the GdLa, GdCe, GdPr and GdNd systems, in both the equilibrium and liquid quenched states. In all cases the liquid quenched alloys adopt the the close-packed hexagonal structure. Magnetic ordering, with incomplete cancellation of the atomic moments, has been observed in all the alloys at low temperatures (7 K ). The magnetic ordering is discussed in terms of interactions between the constituent moments of the alloys.

Conditions for the scanning e-beam activation of P and As implanted source and drain junctions in production NMOS Si gate devices have been established. MOS devices with e-beam annealed, As-implanted, source and drain regions have been produced. The transistor parameters are found to be close to those of furnace annealed control devices, but e-beam annealed devices exbibit a smaller short-channel effect.

Nanocrystalline Mg-based compounds are attractive hydrogen storage materials. Further improved sorption kinetics can be combined with the intrinsically high storage capacity when using alloy additions or catalysts. In this work, platinum group metals (PGMs) have been employed to surface modify Mg- or Mg 2 Ni-based compounds. Nanocrystalline powders have been synthesised by high energy ball milling in hydrogen or argon atmospheres. The effects of co-milling time with the PGM, the use of pre-hydrided Mg for inert milling and blending with minor amounts of Ni are investigated. Gravimetric and thermal desorption studies combined with microstructural analysis using HRSEM and XRD demonstrate the usefulness of nanocrystallinity, thermodynamic destabilisation of the hydride and the catalytic properties of PGMs resulting in much reduced desorption temperatures. Reactively milled Mg 2 Ni co-milled for 1 h with Ru shows an onset temperature of hydrogen desorption as low as 80 °C.

Beam power per unit area and exposure time are the predominant factors in defining implant anneal conditions for the multiple scan electron beam annealing technique. A theoretical analysis is presented which agrees with experimental results. Carrier concentration profiles confirm that the implant becomes electrically active without diffusion.

The fabrication and c.w. operation of planar proton-isolated diffused junction and Schottky-barrier GaAs IMPATT diodes are described. The diodes have shown a maximum efficiency of 13.5% and output power of 315 mW in the Q band. Planar diodes appear to be superior to mesa devices formed from identical material.

Scanning-electron-beam annealing of ion-implanted silicon p+-n junctions over a range of beam power and exposure conditions is described. Electrical measurements have shown that electron-beam annealing can produce diode characteristics close to those of similar thermally annealed structures.