Hydrogen is a promising energy carrier for replacing fossil fuels, and hydrogen production via hydrogen evolution reaction (HER) is an environmentally friendly option if electrocatalysts with low overpotentials and longterm stability are used. In this work, the electrocatalytic performance of Pt 57.5 Cu 14.7 Ni 5.3 P 22.5 bulk metallic glass (BMG) with flat, micro-patterned, and nano-patterned surfaces for HER in 0.5 M H2SO4 is studied. The nano patterned Pt-BMG demonstrates outstanding long-term stability and self-improving behavior with a final over potential of 150 mV and a Tafel slope of 42 mV dec-1 after 1000 linear sweep voltammetry (LSV) cycles, which is respectively 42 % and 37 % lower than in the first LSV cycle. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) indicate the formation of a layer of CuO/Cu2O foam deposited on top of the nano-patterned surface during the stability test of 1000 LSV cycles. A three-step process is proposed to explain the formation of CuxO foam via dynamic hydrogen bubble templating (DHBT) electrodeposition from dissolution of the Pt-BMG without using copper salt. This work provides a method to create CuxO foams that could be used for various applications. Moreover, nano-patterned BMGs with DHBT deposition offer a feasible strategy to synthesize metal or metal-oxide foams.

Small quantities of crystalline domains created in an amorphous matrix are seen as an active driver for enhanced properties in bulk metallic glasses (BMGs). We investigated partial crystallization and phase transformations through a series of isotherms at 370 degrees C performed on amorphous Pd-based BMG samples with the nominal composition of Pd 43 Cu 27 Ni 10 P 20 (Pd-BMG) and a density of 9.425 g/cm3. X-ray based methods such as X-ray diffraction (XRD) and phase enhanced micro-computed tomography (mu-CT) have been pushed to their limits for studying atomic structure and morphology, while time available before crystallization has additionally been investigated via differential scanning calorimetry (DSC), and are combined with optical microscopy (OM), scanning electron microscopy (SEM), and hardness measurements for their mechanical properties. We reveal that Pd-based BMG samples isothermally treated at 370 degrees C start to crystallize after 20 min and still undergo phase transformations and recrystallization even after being fully crystalline after 60 min of the isothermal treatment. Interestingly, 3D phase enhanced micro-computed tomography shows a clear separation of two domains of slightly different densities. We highlight X-ray tomographic scans, allowing the 3D spatial visualization of extremely low-density contrast in different material domains, thus providing a multi-scale physical description of the Pd-BMG system. Interesting is the fact, that the re-crystallization is not homogenous and the crystalline domains can reach large size of (100-200 mu m) in an amorphous matrix.

Cryogenic thermal cycling (CTC) is an effective treatment for improving the room-temperature plasticity and toughness in metallic glasses. Despite considerable attention to characterizing the effects of CTC, they remain poorly understood. A prominent example is that, contrary to expectation, the stored energy in a metallic glass first rises, and then decreases, as CTC progresses. In this work, CTC is applied to bulk metallic glasses based on Pd, Pt, Ti, or Zr. The effects on calorimetric and mechanical properties are evaluated. Critically, CTC-induced effects, at whatever stage, are found to decay over about one week at room temperature after CTC, returning the properties to those of the as-cast glass. A model is proposed for CTC-induced effects, treating them as analogous to the accumulation of anelastic strain. The implications for analysis of existing data, and for future research on CTC effects, are highlighted.

This study investigates the potential of microalloying to control the ion release of a palladium-based metallic glass (Pd-MG). Silver and gallium are used as microalloying elements known for their antibacterial properties. Studies of ion-release kinetics, thermal and mechanical properties, formability, and corrosion behavior show that microalloying is a viable strategy to control ion release from metallic glasses. There is potential to maintain the optimal physical properties of metallic glasses while enhancing their antibacterial functionalities and biocompatibility. The study opens avenues for the development of advanced implant materials with improved mechanical strength, durability, and increased antibacterial response.

Recently, a new thermally activated distortion with amplification (TADA) effect has been reported in red gold alloys caused by the A1 -> L1(0) phase transformation. The macroscopic amplification is due to the persistence of variant selection nucleated under stress but growing in stress-free condition. In this work, we show that the TADA effect can generate a compressive force whose absolute value exceeds 40 MPa in bending and uniaxial loading. Complementary EBSD analyses indicate that the compressive force has no influence on the variant selection initiated under tension. This result confirms that the A1 -> L1(0) disorderorder phase transformation is diffusive, thermodynamically of 1st order, displacive and crystallographically continuous. The TADA force may be exploited for actuators. (C) 2022 The Authors. Published by Elsevier B.V.

Variant selection during the A1→L10 transformation in a polycrystalline red gold alloy close to equiatomic Au-Cu composition has been extensively studied by Electron Backscatter Diffraction (EBSD) in our previous work. The use of a mathematical description of the lattice distortion and the maximal work criterion allowed us to quantify the degree of selection. With the same approach, we investigate here an interesting shape distortion effect, discovered twenty years ago in equiatomic AuCu-Ga. The shape distortion of thin samples placed in bending condition and then heat-treated under stress is studied in details. The singular shape memory effect and the remarkable distortion amplification, which we call TADA effect, are explored by monitoring the sample radius of curvature and the advancement of the transformation. The underlying mechanisms of variant selection are revealed by EBSD analysis across the samples. The experimental crystallographic variant selection distribution is compared with the expected profile calculated with the Euler-Bernoulli beam theory. The good agreement demonstrates that variant selection during the transformation is at the origin of the macroscopic distortion of red gold alloys. The TADA effect was found to occur when external stresses are released, and strongly depends on the stress at the initial stage of the transformation. This unusual effect is assumed to result from the persistence of variant selection throughout the transformation.

The A0→L10 phase transformation, which appears in red gold alloys with compositions close to Au-Cu, is well known as diffusive. However, a shape memory effect has been reported in these alloys, which must involve variant selection during a displacive transformation. Therefore, in this work, the variant selection is studied by EBSD in a polycrystalline red gold alloy heat treated under 4-point bending. For the first time, the L10 domains could be identified by EBSD despite their c/a ratio close to unity and their nanometric scale. The orientation relationship between parent and daughter phases was determined and the mechanical work of the variant formation calculated from both the lattice distortion and the experimental orientations. The maximal work criterion, initially introduced for variant selection in martensitic transformations, was applied on large-scale areas with statistical data and it provided quantitative results on the degree of variant selection in both tension and compression.

Here we present measurements of surface tension and viscosity of the bulk glass-forming alloy Pd43Cu27Ni10P20 performed during containerless processing under reduced gravity. We applied the oscillating drop method in an electromagnetic levitation facility on board of parabolic flights. The measured viscosity exhibits a pronounced temperature dependence following an Arrhenius law over a temperature range from 1100 K to 1450 K. Together with literature values of viscosity at lower temperatures, the viscosity of Pd43Cu27Ni10P20 can be well described by a free volume model. X-ray diffraction analysis on the material retrieved after the parabolic flights confirm the glassy nature after vitrification of the bulk samples and thus the absence of crystallization during processing over a wide temperature range.

A shape-memory effect is known to appear in red gold alloys with compositions close to Au–Cu. The aim of this paper is to study by electron backscatter diffraction (EBSD) the variant selection in the A1 → L1 0 transformation occurring under stress, in bending conditions. The L1 0 domains are successfully identified by this technique despite the c / a ratio being close to unity. The orientation relationship between the cubic and tetragonal phases is determined by a careful analysis of the EBSD data. The distortion of the lattice for each variant is then modelled and calculated from the experimental orientations. The mechanical work associated with the transformation is computed from the lattice distortion by neglecting the obliquity. Finally, the distribution of this mechanical work is compared with the case of a uniform distribution of all variants, in order to evaluate the extent of variant selection. The maximal work criterion, often used for martensitic transformations, enabled quantification of the variant selection phenomenon.

This study describes investigations of continuous casting for the bulk metallic glass-forming alloys Pd43Ni10Cu27P20 and Pt57.3Cu14.6Ni5.3P22.8, respectively. Continuous casting of the Pd-based alloy readily produced fully amorphous rods of 10 mm diameter and > 500 mm length. In contrast, the Pt-based alloy always underwent crystallization during the casting process, even at smaller rod diameters down to 2 mm. In search of the reason for this difference, we simulated the process using ProCAST. Via adapting the heat transfer coefficients for all the relevant interfaces of the continuous casting setup we obtained good agreement between the experimental temperature data and the simulations. The calculations revealed that the maximum cooling rates achievable with this industrial setup ranged from 15 K/s to 17 K/s. This is well above the critical cooling rate for glass formation of the Pd-based alloy, but below that of the Pt-based alloy, as inferred from literature data and corroborated by fast differential scanning calorimetry. These findings illustrate how detailed casting simulations can predict the feasibility of semi-industrial bulk metallic glass production techniques.

The evaluation of the biological safety and degradation of materials is quite important for risk assessment in various biomedical applications. In this study, two procedures were followed to characterize the corrosion resistance of different Ti-based alloys. The first one consisted of performing specific electrochemical tests (open circuit potential, linear resistance polarization, Tafel plots, potentiodynamic polarization) in order to highlight their behavior to the general and localized corrosion. The static and dynamic fatigue cycles combined with crevice corrosion conducted on a new prototype have completed the study. The second procedure followed was a cations extraction investigation (by inductively coupled plasma mass spectrometry) in order to verify the ionic permeability of the oxides layers formed on the surfaces. Optical and scanning electron microscopy were used for surface analysis. It was noticed that in these two electrolytes, the bulk Ti-based alloys presented an almost similar general corrosion behavior. The small differences of behavior for Ti6Al4V scaffolds were correlated to the surface oxidation and roughness (owing to the selective laser melting process). The Ti alloys presented no traces of localized corrosion at the end of the test. The fatigue cycles revealed that a strong and adhesive oxides film was formed during the static cycles (difficult to remove even during the depassivation steps). The concentration of cations released was at the detection limit, revealing very good passivation films, in adequacy with the all the other results.

A series of noble metal high entropy alloys with up to six constituent elements has been produced by casting. PtPdRhIrCuNi forms single-phase face-centered cubic solid solution, and its stability is confirmed by annealing experiments. This alloy deforms homogeneously to ~30% to a high ultimate compression strength of 1839MPa. We discuss rules for the formation of single-phase solid solution.

The bending plasticity of Pd-based and Pt-based bulk metallic glasses (BMGs) is compared. Low cooling rates obtained during bulk casting render Pd-BMG (Pd43Cu27Ni10P20) brittle, whereas Pt-BMG (Pt57.5Cu14.7Ni5.3P22.5) retains high plasticity at all cooling rates. The ratio of the shear modulus (G) to the bulk modulus (B) in the two alloys is similar (similar to 0.2). A previously proposed critical G/B value of 0.41 for tough to brittle transition is not supported by our findings, which rather suggest an alloy specific critical G/B. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

New palladium-aluminium-based alloys with promising potential for application in the areas of jewellery and watchmaking are presented. Aparticular emphasis is placed on the mechanical behaviour of ternary palladium-aluminium-ruthenium (PdAlRu) alloys with 95 wt.% Pd. The new alloys combine high plasticity with high hardness relative to common Pd alloys. The low work-hardening rate enables cold working in excess of 95% reduction without intermediate annealing. The hardness (Vickers pyramid indentation) ranges from 100 HV to 300 HV in the annealed condition, depending on the Al:Ru ratio. Their whiteness in terms of colour coordinates is compared with platinum and white gold. The feasibility of porcelain fusion to PdAlRu for decorative purposes is also demonstrated.

Ambient ammonia concentrations, mainly originating from agricultural activities, have increased in the last few decades in Europe. As a consequence, critical loads on oligotrophic ecosystems such as forests and mires are greatly exceeded. Monitoring of ambient ammonia concentrations is necessary in order to investigate source-receptor relationships. Measuring ambient ammonia concentrations continuously with high time resolution is very expensive and cost-efficient systems are required. Where time resolution is of minor importance, several cost-effective systems, mainly dry denuder and passive samplers, can be applied. In this paper the Zürcher passive sampler, a diffusive sampling system, is presented. It is a Palmes type sampler with an acidic solution as absorbent and is easy to handle. It was tested at 46 sites in Switzerland over one year. The average concentration in ambient air was 2.5 microg m(-3) +/- 0.4 microg m(-3). The average of the blank values were 0.21 microg m(-3). The detection limit (double the standard deviation of the blank values) was 0.36 microg m(-3). Three passive samplers were exposed at each site and each period. The mean standard deviation of these triplicate measurements was 9.5%. Compared with a discontinuous tubular denuder system and a continuous annular denuder system, the deviation was less than 10%. The Zürcher passive sampler is a useful and cost-efficient tool to determine long-term average ammonia concentrations (one- to four-week periods) in ambient air for mean concentrations above 1 microg m(-3).

The effect of additions of C, Si, Ca, Sc and La at levels of 0.1, 0.3 and 1.0 atomic percent on the glass forming ability of the alloy Zr52.5Cu17.9Ni14.6Al10Ti5 has been investigated by means of metallography, X-ray diffraction and oxygen analysis using wedge shaped castings. In the original alloy, a very marked influence of oxygen on the glass forming ability is observed even at low concentrations. Low amounts of additional elements were found to influence the glass forming ability significantly. Adding Se to alloys containing 100-120 ppm oxygen increases the glass forming ability from 4.5 to 10 mm in terms of amorphous ingot thickness. These results were confirmed with additional samples, and best glass forming ability was found with additions of 0.03% to 0.06% Sc. The maximum amorphous thickness in the wedges as measured by metallography correlates within an accuracy of about I mm with that measured by X-ray diffraction over a wide range of modified alloys. A possible mechanism for the enhancement of glass formation through these dopants, and reasons for their effectiveness over only a limited concentration range, are discussed using results from differential scanning calorimetry and differential thermal analysis on a series of samples with different Sc concentrations.

Concentration profiles of N 2 O in a grassland soil and dynamic response curves to disturbance of the soil concentration (relaxation curves) were measured with a new membrane tube technique. Diffusive properties of the soil were derived from 222 Rn measurements. The mathematical analysis of the relaxation curves yielded N 2 O uptake rates U soil diffusivities D s , scale lengths z * , and production rates P at different levels under the surface. The following ranges were found during 2 days of measurements: D s = (0.4–5) × 10 −7 m 2 s −1 , U = (1–20) × 10 −4 s −1 , z * = 0.7–2.8 cm, and P = 0.02–4.4 ppb s −1 . These values were used to reproduce the measured N 2 O concentration profiles with a one‐dimensional diffusive transport model of N 2 O in the soil air‐filled pore space and to deduce flux profiles. Bidirectional fluxes occurred with small deposition fluxes up to a few ppt ms −1 during intensive growing phases of the grass. Uptake rates were high enough that N 2 O produced at greater depth did not reach the atmosphere.