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Combined sulfur and nitrogen (S ​= ​12.9 ​at.%, N ​= ​9.9 ​at.%) rich carbons are synthesized for potassium ion anode applications. The low-surface-area carbons (56 ​m2 ​g−1) have sulfur covalently bonded to the structure, with minimum unbound “free” sulfur. This allows for exceptional rate capability and stability: Capacities of 437, 234 and 72 mAh g−1 are achieved at 0.1, 1 and 10 ​A ​g−1, with 75% retention at 2 ​A ​g−1 after 3000 cycles. These are among the most favorable capacity-cyclability combinations reported in potassium ion battery carbon literature. As a proof of principle, the carbons are incorporated into a potassium ion capacitor with state-of-the-art energy and power (e.g. 110 ​W ​h ​kg−1 at 244 ​W ​kg −1). According to XPS analysis, the reaction of nitrogen with K+ is distinct from that of K+ with sulfur. The N and N–O moieties undergo a series of complex multi-voltage reactions that result in both reversible and irreversible changes to their structure. The K–S reactions involve a combination of reversible adsorption and reversible formation of sulfides, thiosulfate and sulfate. GITT and EIS analysis indicate that incorporation of S into the N-rich carbon increases the K+ solid-state diffusion coefficient by factors ranging from ~3 to 8, depending on the voltage. The diffusivities are asymmetric with charging vs. discharging, signifying distinct reaction pathways. The covalently bound sulfur also has a positive influence on the solid electrolyte interphase (SEI) formation, at early and at prolonged cycling.

We report a bifunctional sodium metal battery (SMB) and lithium metal battery (LMB) cathode based on 63 wt.%SeS covalently bonded to a co-pyrolyzed polyacrylonitrile (PAN) host, termed “SeSPAN”. This dense, low surface area, fully-amorphous electrode offers a highly favorable combination of reversible capacity, rate capability, and cycling life: At a fast charging rate of 1 A g−1, the reversible capacities with Na and Li are 632 and 749 mAh g−1 (based on active SeS), with cycle 1 CE of 81% in both cases. At an ultra-fast charging rate of 4 A g−1 (∼5C) the reversible capacities with Na and Li are 453 and 604 mAh g−1. Li-SeSPAN degrades 3% at cycle 500, while with Na-SeSPAN degrades by 17% after 150 cycles at 0.5 A g−1. Both Na and Li cells display a uniquely low voltage hysteresis (210 and 200 mV at a current density of 0.2 A g−1), indicative of facile charge-discharge kinetics. Analysis of the post-cycled anodes shows negligible S or Se crossover, with neither species being detected in the Li-SEI after extended cycling.

This review focuses on carbon-based sodium ion battery (NIB) negative electrodes, emphasizing the internal structure – Na storage mechanisms – electrochemical performance relations. We bring a unique vantage to the ever-expanding field of NIB anode literature: To quantify the critical emphasis on the structure – properties interdependence, we provide comprehensive data comparisons of representative published studies. This is accomplished through a series of “Master Plots”, which rather than focusing on an individual publication, combine the data by broad features first outlined in the taxonomy section. The advantage of such an approach is that it transcends the paper-to-paper differences in electrochemical performance in a given class of anodes, providing generalizable comparisons that are statistically significant. For instance, we manage to demonstrate that, while N-doped carbons have a slight advantage in terms of capacity, their rate performance at higher currents is unchanged over that of undoped carbons. To our knowledge such broad high-level data analysis has not been done in past reviews on either NIB or LIB carbon anodes. Furthermore, we also discuss a wide range of individual microstructures and chemistries, offering critical analysis when appropriate.

Crystallographic features, physical properties and ionic release from yttria stabilized zirconia (YSZ) in suspension were studied by means of XRD, TEM, light-scattering particle size, BET, ICP and zeta potential analysis. It was found that Zr, Y, Na, and to a lesser extent Ca, Hf and Pd leach from 8 mol% YSZ powder. The impurities present increase the zeta potential of suspensions made from as-received YSZ. A trace amount of tetragonal phase observed in 8 mol% YSZ persists following washing and calcination–milling. Dislocations and crystallographic defects together with fractured crystals which form during milling of the calcined powder should lead to the formation of more broken bonds; as a result the surface of the particles can support higher surface charge density. Washing and calcination–milling lead to a shift of the isoelectric point of 8 mol% YSZ from pH 8.4 to pH 6.3 and 6.8, respectively. Due to higher chemical stability and previously shown positive impacts on microstructure and performance of fuel cells, use of calcined YSZ can be more advantageous than as received powder.

Fouling of metal heat-transfer surfaces employed in crude oil refining operations, driven by inorganic corrosion products, is not well understood. Here we employ a range of advanced analytical techniques, including TEM, SEM, FIB and XRD to systematically document the interdependent corrosion – fouling processes of three refinery metallurgies: a carbon steel, a (P91) 9Cr–1Mo steel, and a 347 stainless steel. We utilize two representative crude oil blends, testing at a metal surface temperature of 490 °C and an oil bath temperature of 290 °C. For the three metallurgies there is a mechanistic similarity of the fouling phenomenon, which begins with sulfidic corrosion of the metal surface and progresses to coking. It is observed that after 1 h of testing, carbon steel samples actually fouled somewhat less than the P91, which was initially unexpected since the latter is considered a more sulfidic corrosion resistant alloy. TEM and SEM analyses demonstrate that there is poor adhesion of the sulfide layer on the carbon steel, which we hypothesize results in the metal surface effectively self-cleaning. Despite being the most resistant to sulfidic corrosion and to fouling, the stainless steel nevertheless forms a thin Fe–Cr–Mn rich inner sulfide and a thicker Fe-rich outer sulfide. We also examine the role of volatiles (reactor pressure), and demonstrate that fouling rates drop off with successive tests on the same oil batch. This is attributed to a gradual exhaustion of S-containing species that react at high temperature to sulfide the metal surface, which in turn catalyze the growth of the organic coke.

Nanolayered composites based on Fe and Mg serve as insightful model systems for understanding a wide range of hydrogen storage materials. We examined the stability of the multilayered thin-film structure Si (substrate)/Ta/Mg/Fe/Ta/Pd after deuterium absorption and desorption and after annealing the specimen at 250 °C. We employed two complementary techniques for analysis: neutron reflectometry and analytical transmission electron microscopy. The neutron reflectometry provides evidence that interdiffusion is significant at 250 °C, but with the film general structure still in place. In contrast, after deuterium absorption and desorption at the same temperature, the changes of the film structure are more severe, such that the Mg/Fe/Ta/Pd layers appear to be fully intermixed, with only the bottom Ta layer remaining intact. Electron microscopy observations indicate that annealing at 250 °C has caused a phase transformation to form Mg 5 Pd 2 at the upper sections of the Mg layer, with the general periodicity of the sample still maintained, in accordance with the reflectometry measurements. In the desorbed state, the layers show substantial variations in local thicknesses, with thicker regions containing a range of Mg–Pd compounds and the thinner portions remaining primarily Mg. This degradation sequence occurs despite the Fe layer remaining chemically unchanged. We provide a mechanistic description regarding the observed evolution of the multilayered structure during annealing and deuterium cycling.

Hydrothermal carbonization followed by chemical activation is utilized to convert paper pulp mill sludge biowaste into high surface area (up to 2980 m2 g-1) carbons. This synthesis process employs an otherwise unusable byproduct of paper manufacturing that is generated in thousands of tons per year. The textural properties of the carbons are tunable by the activation process, yielding controlled levels of micro and mesoporosity. The electrochemical results for the optimized carbon are very promising. An organic electrolyte yields a maximum capacitance of 166 F g-1, and a Ragone curve with 30 W h kg-1 at 57 W kg-1 and 20 W h kg-1 at 5450 W kg-1. Two ionic liquid electrolytes result in maximum capacitances of 180-190 F g-1 with up to 62% retention between 2 and 200 mV s-1. The ionic liquids yielded energy density-power density combinations of 51 W h kg-1 at 375 W kg -1 and 26-31 W h kg-1 at 6760-7000 W kg-1. After 5000 plus charge-discharge cycles the capacitance retention is as high at 91%. The scan rate dependence of the surface area normalized capacitance highlights the rich interplay of the electrolyte ions with pores of various sizes. © 2013 Elsevier Ltd. All rights reserved.

The exceptional strength and distinct deformation physics exhibited by pure ultrafine-grained and nanocrystalline metals in comparison to their microcrystalline counterparts have been ascribed to the dominant influence of grain boundaries in accommodating plastic flow. Such grain-boundary-mediated mechanisms can be augmented by additional strengthening in nanocrystalline alloys via solute and precipitate interactions with dislocations, although its potency is a function of the changes in the elastic properties of the alloyed material. In this study, we investigate the elastic and plastic properties of Al1−xMox alloys (0 ⩽ x ⩽ 0.32) by tensile testing of sputter-deposited freestanding thin films. Isotropic elastic constants and strength are measured over the composition range for which three microstructural regimes are identified, including solid solutions, face-centered cubic and amorphous phase mixtures and body-centered cubic (bcc)/amorphous mixtures. Whereas the bulk modulus is measured to follow the rule of mixtures over the Mo composition range, the Young’s and shear moduli do not. Poisson’s ratio is non-monotonic with increasing Mo content, showing a discontinuous change at the onset of the bcc/amorphous two-phase region. The strengthening measured in alloyed thin films can be adequately predicted in the solid solution regime only by combining solute strengthening with a grain boundary pinning model. The single-step co-sputtering procedure presented here results in diversity of alloy compositions and microstructures, offering a promising avenue for tailoring the mechanical behavior of thin films.

Magnesium hydride combined with a new bimetallic Nb–V catalyst displays remarkably rapid and stable low temperature (200 °C) hydrogen storage kinetics, even after 500 full volumetric absorption/desorption cycles. The system is also able to fairly rapidly absorb hydrogen at room temperature at a pressure of 1 bar. This unprecedented absorption behavior was demonstrated for 20 cycles. We employed extensive cryo-stage transmission electron microscopy (TEM) analysis on fully and partially sorbed materials to provide insight into the rapid Mg to MgH2 phase transformation. After extended cycling of what was initially a 1.5 μm thick fully dense alloy film, the sample structure becomes analogous to that of a weakly agglomerated nanocomposite powder. The cycled Mg–V–Nb structure consists of a dense distribution of catalytic Nb–V nanocrystallites covering the surfaces of larger Mg and MgH2 particles. The partially absorbed 20 °C and 200 °C microstructures both show this morphology. TEM results combined with Johnson–Mehl–Avrami-type kinetic analysis point to the surface catalyst distribution and stability against coarsening as being a key influence on the two-stage hydriding kinetics. Remarkably, the mean size of the Nb0.5V0.5H nanocrystallites stays essentially invariant throughout cycling; it is 3 nm after 45 cycles and 4 nm after 500 cycles. A mechanistic description is provided for the cycling-induced microstructural evolution in the ternary alloy as well as in the binary baselines.

There is growing interest in the large scale cyclotron production of 99m Tc via the 100 Mo(p,2n) 99m Tc reaction. While the use and recycling of cyclotron-irradiated enriched molybdenum targets has been reported previously in the context of 94m Tc production, to the best of our knowledge, previous recycling studies have been limited to the use of oxide targets. To facilitate reuse of high-power enriched 100 Mo targets, this work presents and evaluates a strategy for recycling of enriched metallic molybdenum. For the irradiated 100 Mo targets in this study, an overall metal to metal recovery of 87% is reported. Evaluation of “new” and “recycled” 100 Mo revealed no changes in the molybdenum isotopic composition (as measured via ICP-MS). For similar irradiation conditions of “new” and “recycled” 100 Mo, (i.e. target thicknesses, irradiation time, and energy), comparable levels of 94g Tc, 95g Tc, and 96g Tc contaminants were observed. Comparable QC specifications (i.e. aluminum ion concentration, pH, and radiochemical purity) were also reported. We finally note that [ 99m Tc]–MDP images obtained by comparing MDP labelled with generator-based 99m Tc vs. 99m Tc obtained following the irradiation of recycled 100 Mo demonstrated comparable biodistribution. With the goal of producing large quantities of 99m Tc, the proposed methodology demonstrates that efficient recycling of enriched metallic 100 Mo targets is feasible and effective.

In order to assess the potential application of electrocatalytic hydrogenation to petroleum fractions, as an alternative to high-pressure hydrotreating, we studied the conversion of a series of model compounds. Naphthalene, 1-methyl naphthalene, quinoline, carbazole, and dibenzothiophene were reacted in a flow cell over sulfur-resistant tungsten disulfide/glassy carbon electrodes. Raney nickel was used as a reference catalytic electrode material. The reactants were dissolved in a solution of ionic liquid and water, to provide high solubility of reactant, high conductivity, and protons for electrochemical hydrogenation. Both quinoline and carbazole were hydrogenated on WS 2 /glassy carbon cathodes in the presence of thiophene, but the initial current efficiencies were less than 10%. Conversion of naphthalene was detected, but the initial current efficiency was only 1.8%. Conversion of 1-methyl naphthalene and dibenzothiophene was not detected over this electrode material. Raney nickel gave higher conversion rates and current efficiencies for quinoline, carbazole, and naphthalene, but only traces of product from 1-methylnaphthalene were detected. These results indicate that current efficiency and sustained conversion rates for alkylaromatics and heteroaromatics must be improved considerably in order for electrocatalytic hydrogenation to compete with conventional hydrotreating.

We examined the deuterium absorption and desorption of 55 nm thick Mg films alloyed with Fe and Cr using in-situ neutron reflectometry. The Mg alloy films were covered with bimetallic catalyst layers and could be fully absorbed at room temperature at a pressure of 8 mbar. The NR experiments revealed a deuterium gradient within the Mg alloy layers during absorption and a large deuterium uptake up to a D/M ratio of about 0.45 before the layer started to expand and form magnesium deuteride (MgD 2 ). Our NR data suggest that the catalytic effect of the Fe–Cr alloy is based on the avoidance of the formation of a blocking MgD 2 layer in the early stages of the absorption process leading to a fast hydrogen absorption kinetics.

We studied the catalytic effects of Titanium, Iron and FeTi intermetallic on the desorption kinetics of magnesium hydride. In order to separate the catalytic effects of each element from additional synergistic and alloying effects, Mg-Ti and Mg-Fe mixtures were studied as a baseline for Mg-Fe-Ti elemental and Mg-(FeTi) intermetallic composites. Sub-micron dimensions for MgH 2 particles and excellent nanoscale catalyst dispersion was achieved by high-energy ball-milling as confirmed by analytical electron microscopy techniques. The composites containing Fe shows desorption temperature of 170 K lower than as-received MgH 2 powder, which makes it suitable to be cycled at relatively low temperature of 523 K. Furthermore, the low cycling temperature prevents the formation of Mg 2FeH 6. In sorption cycling tests, Mg-10% Ti and Mg-10% (FeTi), after about 5 activation cycles, show fast desorption kinetics initially, but the kinetics also degrade faster than for all other composites, eventually slowing down by a factor of 7 and 4, respectively. The ternary Mg-Fe-Ti composite shows best performance. With the highest BET surface area of 40 m 2/g, it also shows much less degradation during cycling. This is attributed to titanium hydride acting as a size control agent preventing agglomeration of particles; while Fe works as a very strong catalyst with uniform and nanoscale dispersion on the surface of MgH 2 particles. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

This paper describes the microstructural evolution of Mg–FeTi mutlilayered hydrogen storage materials during extended cycling. A 28 nm Mg–5 nm FeTi multilayer has comparable performance to a cosputtered material with an equivalent composition (Mg–10%Fe–10%Ti), which is included as a baseline case. At 200 °C, the FeTi layers act as a barrier, preventing agglomeration of Mg particles. At 300 °C, the initial structure of the multilayer is preserved up to 35 cycles, followed by fracturing of the Mg layers in the in-plane direction and progressive delamination of the FeTi layers as observed by electron microscopy. Concurrently, an increase in the Mg grain size was observed from 32 to 76 nm between cycles 35 and 300. As a result, the absorption kinetics deteriorate with cycling, although 90% of the total capacity is still absorbed within 2 min after as many as 300 cycles. The desorption kinetics, on the other hand, remain rapid and stable, and complete desorption of 4.6 wt.% H is achieved in 1.5 min at ambient desorption pressure. In addition to showing good hydrogen storage performance, multilayers are an excellent model system for studying the relation between microstructure and hydrogen absorption/desorption kinetics.

This paper describes the hydrogen storage properties of Magnesium rich ternary Mg-Ni-Cu films of 1.5 μm thickness using binary Mg-Ni and Mg-Cu as baselines, and aims to elucidate the precise influences of alloying element Cu on the hydrogen sorption kinetics, thermodynamics and cycleability. Mg-rich Mg-Ni-(Cu) alloys show two stages during absorption. The first stage due to the absorption of Mg not alloyed in the form of Mg2Ni and Mg2Cu, hereafter denoted as free-Mg, is very quick, but the second one due to the absorption of intermetallic Mg2Ni and/or Mg2Cu is significantly slower. This sequence is confirmed by XRD characterizations at different absorption stages. The rapid first stage absorption is mainly catalyzed by the intermetallic phase, Mg2Ni. Cu substitution improves the desorption kinetics, but severely decreases the kinetics of the second absorption stage. Failure to completely absorb Mg2Cu to MgH2 and MgCu2 in consecutive absorption cycles leads to complete loss of desorption-ability in binary Mg-15 at.%Cu. XRD combined with TEM shows that segregation of Mg2Cu towards the grain boundaries is responsible for this. Pressure-Composition Isotherms are used to examine the thermodynamic properties of the alloys. The thermodynamic properties of the Low-Temperature (LT-) Mg2NiH4 are determined for the first time experimentally, and are found to be ΔH = −78.6 kJ/mol H2 and ΔS = −147.83 J/K-mol H2. It is found that the Cu substitution has no influence on the plateau pressure of MgH2 from free-Mg phase, but slightly increases the plateau pressure of LT-Mg2NiH4.

We have tested the hydrogen storage cycling behavior of bulk centimeter-scale magnesium - titanium and magnesium - stainless steel multilayer composites synthesized by accumulative roll-bonding (ARB). Roll-bonding of either titanium or stainless steel with magnesium allows the reversible hydrogen sorption of the resulting composite at 350°C. Identically roll-bonded pure magnesium can hardly be absorbed at this temperature. In the composites, the kinetics of the first cycle of absorption (also called "activation") improves with increased number of fold and roll (FR) operations. With increasing FR operations the distribution of the Ti phase is progressively refined, and the shape of the absorption curve no longer remains sigmoidal. Increasing the loading amount of the second phase also accelerates the kinetics. This holds true up to a threshold limit. Microscopy analysis performed on 1-2 wt.% hydrogen absorbed composites demonstrates that MgH 2 formed exclusively on various heterogeneous nucleation sites. During activation, MgH 2 nucleation occurred at the Mg-hard phase interfaces. During the subsequent absorption cycles, heterogeneous nucleation primarily occurred in the vicinity of "internal" free surfaces such as cracks. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Vitreous carbon supported tungsten sulfide (WS 2 ) nanoparticle catalysts were synthesized by fully sulfiding thin films of W. This support–catalyst combination was shown to be successful at hydrogenating 2-cyclohexen-1-one in the presence of sulfur. A well-known hydrogenation catalyst consisting of a nickel film, used as a baseline, was found to be completely ineffective in an identical solution. Catalyst samples with a nominal W thickness of 2 nm, produced the largest hydrogenation product yields with the highest efficiencies. SEM and XPS analyses confirm that this nominal thickness corresponds to a dense distribution of nano-scale WS 2 particles templated on the carbon substrate. We envision the WS 2 –carbon system becoming a catalyst of choice for electrocatalytic hydrogenation in a sulfur-rich environment.

We investigate, via both experiment and simulation, the effects of self-shadowing on the growth of faceted polycrystalline thin films. Faceted aluminum thin films were sputtered and the anomalous scaling behaviour of their surfaces was characterized. To understand the causes of this anomalous behavior, growth of faceted thin films was simulated by coupling a level set construction to a ballistic deposition model. The angular distribution function of deposition flux was varied to control the degree of self-shadowing. We show how differing degrees of self-shadowing strongly modify film surface morphologies and compare these results with experimental findings.

Cryo-stage transmission electron microscopy (TEM), supported by Density Functional Theory (DFT), is employed to explore the microstructure of magnesium hydride (MgH2) powders. Mechanical milling results in deformation twinning of the hydride. The crystallography of the twins is established. DFT analysis shows that the twin unit cell is just as thermodynamically stable as the undeformed α-MgH2 matrix. It is hypothesized that the twins contribute significantly to the observed milling-induced kinetic enhancement by acting as high diffusivity paths for hydrogen. Energy-filtered TEM analysis on partially desorbed MgH2 demonstrates that nucleation and growth of metallic magnesium occurs non-uniformly. Larger powder particles are a composite of isolated magnesium grains heterogeneously nucleated on the remaining hydride. Smaller particles are either fully transformed to magnesium or remain entirely a hydride. There is little evidence for any “core–shell” structure. It is also shown that in situ hydrogen desorption in the TEM is not representative of the elevated-temperature ex situ sequence.

This study focused on hydrogen sorption properties of 1.5 μm thick Mg-based films with Al, Fe and Ti as alloying elements. The binary alloys are used to establish as baseline case for the ternary Mg–Al–Ti, Mg–Fe–Ti and Mg–Al–Fe compositions. We show that the ternary alloys in particular display remarkable sorption behavior: at 200 °C the films are capable of absorbing 4–6 wt% hydrogen in seconds, and desorbing in minutes. Furthermore, this sorption behavior is stable over cycling for the Mg–Al–Ti and Mg–Fe–Ti alloys. Even after 100 absorption/desorption cycles, no degradation in capacity or kinetics is observed. For Mg–Al–Fe, the properties are clearly worse compared to the other ternary combinations. These differences are explained by considering the properties of all the different phases present during cycling in terms of their hydrogen affinity and catalytic activity. Based on these considerations, some general design principles for Mg-based hydrogen storage alloys are suggested.

We analyzed the elevated temperature volumetric hydrogen sorption behavior of magnesium thin films catalyzed by nano-scale bi-layers of Pd/Ta, Pd/Nb, Pd/Ti and Pd/Fe. Sorption of magnesium catalyzed by pure Pd was determined as a baseline. Sorption cycling demonstrated that when utilizing pure Pd and the Pd/Fe bi-layer catalysts the sorption kinetics of the Mg films rapidly degraded. However with the Pd/Nb, Pd/Ti and Pd/Ta bi-layer catalysts the composite remained cycleable. After multiple sorption cycles the Pd/Nb and Pd/Ti catalyst combinations possessed the fastest kinetics. X-ray diffraction analysis showed that NbH0.5 and TiH2 are formed during testing. Basic thermodynamic analysis indicates that NbH0.5 and TiH2 should be stable both during absorption and during desorption. We believe that this is why Nb and Ti are the most effective intermediate layers: The elements form stable hydrides at the Mg surfaces preventing complete Pd-Mg interdiffusion and/or acting as hydrogen catalysts and pumps.

We investigate the bulk and surface features of the crystalline–amorphous transitions in binary Al–Mo alloy thin films as a function of Mo composition using transmission electron microscopy, X-ray diffraction and atomic force microscopy analysis, as well as thermodynamic modeling. Of the alloys tested, the minimum in the root mean square (rms) surface roughness and correlation length occurs at the Al–32 at.% Mo composition, which corresponds to the maximum volume fraction of the amorphous phase and the minimum volume fraction of the body centered cubic nanocrystallites. The rms surface roughness of the 32 at.% Mo films is on the order of a single nanometer, compared with nearly 80 nm for the 50 at.% Mo film. A structure–zone map is constructed to relate the surface morphology of the films to their bulk microstructure. A thermodynamic model developed by Miedema and coworkers was used to predict the general trends observed in the microstructural evolution as a function of film composition.

The main focus of this work was the use of cryo-stage transmission electron microscopy (TEM) to elucidate features of the milled MgH 2 powder microstructure not accessible via “conventional” hydride characterization techniques such as X-ray analysis. We chose a classic problem in hydride research: the effect of high energy milling on the microstructure and the desorption properties of magnesium hydride (MgH 2 ) powder. High-energy mechanical milling provided for marked hydrogen desorption enhancement, while subsequent annealing reduced and ultimately eliminated it. Milling created a significant amount of microstrain in the α-MgH 2 . It also reduced the particle size and changed the size distribution to be multi-modal. Milling reduced α-MgH 2 grain size by a factor of two, which can be considered a fairly minor effect. Post-milling anneals completely eliminated the microstrain, increased the grain size to a similar value as the as-received powder, and smoothed the particle size distribution. Using TEM we were able to image the individual hydride grains within the powder particles. TEM analysis of the milled microstructure identified a high density of nano-scale twins within the hydride grains. Annealing reduced the twin density and coarsened their size. Elasticity analysis indicates that the energy stored by the accumulated dislocations as the result of the milling is negligible compared to the heat of the hydride formation.

We have used a level set construction to simulate the growth of faceted polycrystalline thin films in 2 + 1 dimensions using the van der Drift model. The evolution of several different crystal geometries into their self-similar late-stage surfaces is described. Each simulation resulted in a columnar microstructure and growth statistics including grain diameter and area, RMS surface roughness and surface texture were collected at each time step. We describe the dependence of each of these statistical measures upon the crystal geometry.

The formation of metal nanoclusters, nanodots and nanowires are the subject of intense current scientific and engineering interest. We report a new, simple and apparently economical technique to generate high concentrations of supported metal nanoparticles using sedimentary chabazite. This technique can be applied particularly well in the generation of relatively uniform supported silver nanodots. High densities of silver nanoparticles on the order of 1–5 nm, centered in the regime of 3 nm, are formed on sedimentary chabazite surfaces by the assemblage of exchanged silver cations thermally reduced to metal under a wide range of conditions including heating in air. Twenty (20) weight percent or more of a zeolite nanosilver composite material may be composed of these supported silver nanoparticles. Semi-synthetic, aluminum enriched chabazite allows the preparation of metal nanoparticles at even higher levels of concentration, up to 40% or more of the weight of the composite. We know of no other technique that can generate such high concentrations of uniform silver nanoparticles so easily, reproducibly and economically. Preliminary experiments indicate that a range of other metals, such as copper and nickel, may form equivalent chabazite induced and supported nanoparticles under appropriate reducing conditions.

This work details some aspects of the microstructure–properties–processing relations in spot friction welded (also known as friction stir spot welded) 6111 Al sheets, joined in a lap configuration. We have shown that the tool pin penetration depth has a strong effect on the failure mode of the joined samples and a lesser effect on the joint shear strength. With increasing tool pin penetration depth, and consequently with increasing depth of the tool shoulder pressing into the top sample, the failure mode in a lap-shear test changes from brittle and concentrated near the pin hole, to ductile and away from the weld towards the base metal. The sheet interface under the tool shoulder consists four regions; a region where there is no contact at all between the two surfaces, a region where only a mechanical bond (“kissing bond”) exists, a region where there is partial metallurgical bond, and a region with full metallurgical bonding. There is evidence that during welding the Fe–Si–Mn–Cu inclusions present in the as-received material are swept towards the joint interface, thus degrading the joint quality. The aluminum in the partially metallurgically bonded region, in the fully metallurgically bonded region and under the tool pin is fully recrystallized. In these regions, the presence of low angle grain boundaries indicates that additional deformation has occurred after recrystallized grains were formed. It is thus likely that recrystallization has occurred dynamically during the welding process. The material under the shoulder (a portion of the non-contacting region, the “kissing bond”, the partial metallurgical and the full metallurgical regions) has a significantly larger grain size than under the pin, as well as a different texture.

Atom probe tomography and high resolution transmission electron microscopy have been employed to reveal clustering of Si and Ge atoms in ternary Al–Si–Ge. No such clusters were observed in binary Al–Si. The clusters were on the order of five nanometers in diameter and contained Si, Ge and Al. This confirms a previous hypothesis that postulates the existence of such clusters due to atomic mismatch strain compensation between the Si and Ge atoms in an Al solid solution.

This work explores the effects of elevated temperature on the physical and chemical properties of nanocrystalline silver, and relates it to previously observed thermally induced changes in biological activity [Taylor PL et al. Biomaterials, in press, doi:10.1016/j.biomaterials.2005.05.040]. Microstructural evolution of nanocrystalline silver dressings, heat-treated for 24 h at temperatures from 23 to 110 degrees C, was studied in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). These analyses indicated that silver nanocrystalline coatings undergo significant changes in structure when exposed to elevated temperature. XRD analysis showed a rapid increase in crystallite size above 75 degrees C along with decomposition of crystalline silver oxide (Ag2O) at the onset of crystallite growth. SEM imaging showed a loss of fine features and sintering of the structure at elevated temperatures. The XPS data indicated that silver-oxygen bonds disappeared completely, with the initial decomposition occurring between 23 and 37 degrees C, and total oxygen in the coating decreased from 16-17% to 6.5% over the temperature range of 75-110 degrees C. A comparison of these results to the data of Taylor et al. [Biomaterials, in press, doi:10.1016/j.biomaterials.2005.05.040] indicates that the unique biological properties of nanocrystalline silver are related to its nanostructure. This should guide future development of therapeutic nanocrystalline silver delivery systems.

We have characterized the elevated temperature (190 °C) precipitation sequence near the grain boundaries of an AlCuSiGe alloy, comparing these results to the binary AlCu and the ternary AlSiGe. In the quaternary alloy, there is a graded microstructure that evolves with increasing distance from the boundaries, which is generally a superposition of the precipitate-free-zones (PFZs) in the binary AlCu and in the ternary AlSiGe. After aging for 3 h, this graded area consists of an approximately 140 nm wide region that is entirely precipitate free, followed by a 400 nm wide region that is denuded of Si–Ge and θ′ precipitates. Rather than containing the (Si–Ge)–θ′ pairs observed in the bulk, this 400 nm wide region contains only homogeneously nucleated θ′′. Only in the overaged condition (144 h) are the near grain boundary θ′′ replaced by a coarse distribution of large plate-like θ′. In the alloys, the solute depleted zones are much narrower than the total length of the PFZ. For example, in both AlCu and AlCuSiGe, the Cu depleted zone is only 30 nm wide. This underscores the need for vacancies during precipitation of not only θ′ and Si–Ge, but of θ′′ as well.

The principal focus of this work is to explain precipitation in Al–1 at.%Si–1at%Ge. The microstructure is characterized using conventional and high resolution transmission electron microscopy, as well as energy dispersive X-ray spectroscopy. The first precipitates to come out of solid solution have a cube–cube orientation relationship with the matrix. High resolution TEM demonstrated that all the precipitates start out, and remain multiply twinned throughout the aging treatment. Any twinned section of the precipitate no longer maintains a low index interface with the matrix, and consequently goes from a crystallographic to a spherical interface with the matrix. This explains the equiaxed shape of the Si–Ge precipitates. There is a variation in the stoichiometry of the precipitates, with the mean composition being Si–44.5 at.%Ge. It is also shown that in Al–Si–Ge it is not possible to achieve satisfactory hardness through conventional heat treatment. This result is explained in terms of sluggish precipitation of the diamond-cubic Si–Ge phase coupled with particle coarsening.