Abstract Magnetic signals in igneous rocks arise from assemblages of iron‐oxide bearing minerals that differ in for example, size, shape, and chemistry. Paleomagnetic measurements on bulk samples measure millions of such grains simultaneously, producing a statistical ensemble of the magnetic moments of the individual grains. Scanning magnetometry techniques such as the Quantum Diamond Microscope (QDM) measure magnetic signals on micrometer scales, allowing the identification of magnetic moments of individual grains in a sample using for example, Micromagnetic Tomography (MMT). Here we produce a grain‐size distribution of iron‐oxides in a typical Hawaiian basalt from the superparamagnetic threshold (∼40 nm) to grains with a diameter of 10 µm. This grain‐size distribution is obtained by combining FIB‐SEM and MicroCT data from sister specimens, and normalizing them to the mineral surface area of non‐magnetic minerals. Then we use this grain‐size distribution to determine the contributions of individual magnetic carriers to bulk magnetic measurements and surface magnetometry. We found that measurements on bulk samples are sensitive to relatively small grain sizes in the realm of single domain or vortex states (<200 nm), while signals in surface magnetometry arise mainly from larger grains with diameters >1 µm. This implies that bulk measurements cannot be compared straightforwardly to signals from surface magnetometry from the same sample. Moreover, our observations explain why MMT results are insensitive to the presence of many small grains in a sample that intuitively should hamper their outcome.

&lt;p&gt;Micromagnetic tomography (MMT) is a new promising paleomagnetic technique that obtains magnetic moments for individual iron-oxides. These magnetic moments are inferred from surface magnetometry data obtained with quantum diamond microscopy (QDM), and iron-oxide positions determined with micro X-Ray computed tomography (MicroCT). Different to classical techniques, MMT does not depend on bulk measurements of samples. This makes it possible to only select the most reliable magnetic recorders. To make this improvement possible, MMT first has to deal with the presence of undetected magnetic carriers in basaltic rock samples used in previous MMT studies. Although particles smaller than 1 &amp;#181;m are good recorders of the magnetic field and may be visible in surface magnetometry, they are not detected by MicroCT. This violates one of the foundations of MMT and may disturb magnetic moments of other detected grains. However, it is currently unknown how many of these small disturbing particles are present in Hawaiian basaltic samples. We know that the smallest disturbing grains have a diameter of around 40 nm, since particles smaller than this threshold become superparamagnetic and cannot store magnetic signals. For this reason we want to obtain a grain-size distribution for iron-oxides from 20 nm to 10 &amp;#181;m to cover the complete range of grains that are capable of storing Earth&amp;#8217;s magnetic field. This requires a combination of FIBSEM slice-and-view and MicroCT techniques; FIBSEM detects single and pseudo-single domain grains with sizes between 20 nm and 1 &amp;#181;m and MicroCT detects multi-domain grains with sizes larger than 1 &amp;#181;m. Subsequently, FIBSEM and MicroCT data are combined to obtain the full spectrum of grain sizes. Unfortunately, grains are not uniformly distributed in the samples, so a scaling by volume would not produce a realistic spectrum. Therefore, based on observations that iron-oxides grains cluster on the interfaces of other minerals, we calculated how many times FIBSEM mineral interfaces from FIBSEM data fit the mineral interfaces from MicroCT data. Then, this factor is used to scale the FIBSEM iron-oxides to MicroCT iron-oxides and to obtain a complete distribution of all grain sizes. Interestingly, this distribution shows a clear peak in grain size at 70-80 nm. Furthermore, the smallest grain fraction is fitted a lognormal trend, but the fraction larger than 0.18 &amp;#181;m are fitted an exponential decay trend. With these trendlines in place we have finally acquired a realistic set of boundary conditions for the distribution of iron-oxide particles in basaltic rocks. This enables us to populate models with a realistic distribution of particles, which ultimately may shed light on the disturbing presence of small iron-oxides in MMT results. If we know the effect of these disturbances, we will understand which grains MMT can solve with highest certainty, ultimately leading to paleomagnetic interpretations on grain scale.&lt;/p&gt;

Micromagnetic tomography (MMT) aims to go beyond paleomagnetic measurements on bulk samples by obtaining magnetic moments for individual iron-oxide grains present in a sample. To obtain accurate MMT results all magnetic sources and all their magnetic signals should be known. Small particles (<<1 µm) are often not detected by MicroCT analyses, but do have a magnetic signal, and therefore hamper obtaining reliable MMT results. Currently it is unknown how many of these small ‘ghost grains’ are present in basaltic samples. Here we aim to obtain a realistic grain-size distribution for iron-oxides in a typical Hawaiian basalt. We characterize the entire grain-size range of interest to paleomagnetism, from the superparamagnetic threshold of ∼40 nm to multidomain grains with sizes up to 10 μm. This requires a combination of FIB-SEM slice-and-view and MicroCT techniques: FIB-SEM characterizes the grains between 20 nm and 1 μm and MicroCT detects iron-oxides >750 nm. The FIB-SEM and MicroCT data are combined through normalizing the grain-size distribution using the surface area of non-magnetic minerals that are characterised in both datasets. Then, a lognormal-like grain-size distribution is acquired for the entire grain-size range. Our dataset enables future studies to populate (MMT) models with a realistic distribution of even the smallest iron-oxide grains, which ultimately may shed light on the confounding influence of such ghost grains on MMT results.

The rapidly growing Li-ion battery (LIB) industry is struggling to find feasible methods to recycle end-of-life batteries as well as identify new applications for the recycled materials. The current study demonstrates a promising strategy to enhance the value of the LIB waste anode and cathode components as a raw material for electrocatalyst production. Recovered graphite and cobalt from spent LIBs (SLIBs) are used to obtain active, low cost, and stable nonprecious metal-based electrocatalysts for oxygen reduction reaction (ORR). SLIB graphite has been turned into graphite oxide which is thereafter codoped with Co and nitrogen to prepare an active electrocatalyst toward ORR with the onset potential of 0.98 V (vs RHE) in alkaline media. Extensive characterization is carried out on the compound, identifying the key factor driving the performance in the synergistic combination of cobalt and nitrogen. The material was successfully benchmarked against a commercial 19.8% platinum catalyst, showing comparable performance and a superior tolerance to methanol. The demonstrated ability to recycle LIBs into industrially relevant electrocatalysts can lead the way to a fully sustainable lifecycle for energy-storage solutions.

A rhenium promoted Fischer-Tropsch (FT) cobalt catalyst supported on gamma-Al2O3 has been investigated by Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD), before and after reduction. Electron diffraction, High Resolution TEM and Electron Energy Loss Spectroscopy were used to confirm the oxidation state. Cobalt aggregate, particle and crystallite sizes have been studied in detail and measured by TEM and XRD. A cobalt particle size of 10.0 +/- 2.4 nm obtained from bright field TEM images for the reduced material is consistent with the XRD analysis of the calcined catalyst. After reduction dark field TEM imaging gave a volume-weighted crystallite size of 7.5 +/- 2.5 nm, which is close to the value obtained by XRD. The particles had lost the parallel orientation and physical continuity within the alumina pore structure that were present before reduction. The latter was confirmed by electron tomography. Lamellae identified with the presence of Hexagonal Close Packed cobalt were observed in the predominantly Face Centred Cubic particles.

The conversion efficiency of solar energy in semiconductors is fundamentally limited by ultrafast hot-carrier relaxation processes, and slowing down these processes is critical for improved energy harvesting. Here we report formamidinium tin iodide (FASnI 3 ) nanocrystals where quantum confinement effects yield an evolution from a continuous band structure to separate energy states with decreasing nanocrystal size, as observed by transient absorption spectroscopy. The appearance of separate energy levels slows down the relaxation of hot carriers by two orders of magnitude at low injected carrier densities (<1 carrier pair per nanoparticle). The observed build up time of the ground-state bleach at the band edge is two orders of magnitude slower in FASnI 3 nanocrystals than in lead halide perovskite bulk and nanocrystals, which we attribute to a phonon bottleneck effect. Our results highlight the promise of lead-free perovskite nanocrystals for high-efficiency photovoltaic applications operating above the Shockley–Queisser limit.

Ni and Fe are excellent catalysts for carbon formation, and industrial alloys are therefore susceptible to metal dusting corrosion; a costly issue in e.g. synthesis gas manufacture. The objective of this work is to better understand the initial reaction phenomena leading to metal dusting, and thereby minimize the corrosion through optimum alloy selection and pretreatment. Pre-oxidized alloy 601 samples were subjected to carburizing gaseous environments at 750 C, and carbon formation and surface oxide layer development were investigated by SEM, optical microscopy, AES and Raman spectroscopy. Thin (S)TEM/EDS cross-section lamellae were prepared by Focussed Ion Beam milling. Beyond the initial incubation period, less carbon is formed under 10% CO/Ar than under synthesis gas with finite low carbon activity. Cr2O3 evolves as a thin surface oxide layer with only CO reacting and more ordered carbon develops with increasing exposure time. In contrast, oxidation yields (Ni, Fe, Cr)3O4 spinel formation while the materializing carbon remains its disorder during prolonged exposure to synthesis gas. The metal dusting corrosion rate is hence lowered due to Cr2O3 stabilization, while the spinel represents an unstable redox state that continuously yields new carbon. A fine-grained alloy surface structure is also found beneficial to the Cr2O3 formation.

Stress corrosion cracking (SCC) in Cu-free Al-Zn-Mg (7xxx) aluminium alloys limits its use in many applications. In this work, we study in detail the microstructure of a peak and slightly overaged condition in an AA7003 alloy using transmission- and scanning electron microscopy in order to provide a comprehensive understanding of the microstructural features related to SCC. The SCC properties have been assessed using the double cantilever beam method and slow strain rate tensile tests. Grain boundary particles, precipitate free zones, and matrix precipitates have been studied. A difference in the SCC properties is established between the two ageing conditions. The dominating difference is the size and orientation of the hardening phases. Possible explanations correlating the microstructure and SCC properties are discussed.

Understanding the role of iron and the nature of the active sites in nitrogen-doped carbon nanomaterials is vital for their future application as oxygen reduction electrocatalysts in fuel cells. In this paper, porphyrin-like Fe-N-4 sites have been identified in nitrogen-doped carbon nanofibers (N-CNFs) grown from iron nanoparticles by chemical vapor deposition (CVD). Acid treatment of the N-CNFs removed the iron growth particles and about 50% of the nitrogen groups from the pristine N-CNFs, without affecting the oxygen reduction performance. Performing electron energy loss spectroscopy (EELS) on the acid treated and annealed N-CNFs confirmed that the CVD synthesis method leads to iron being atomically incorporated into the N-CNF structure. Furthermore, Xray absorption near-edge structure (XANES) analysis of the Fe K-edge indicates that the iron atoms are stabilized by four nitrogen atoms, reminiscent of the Fe-N-4 structure found in porphyrins. An evolution of the XANES spectrum was observed when performing the measurements under mildly reducing conditions, which was explained by oxygen being adsorbed on the Fe-N-4 sites at room temperature. The Fe-N-4 moieties embedded in the N-CNFs were resistant to acid leaching and the results suggest that these Fe-N-4 sites are active sites for the oxygen reduction in N-CNFs.

Precipitation behavior in an industrially extruded AA7003 alloy has been studied using Transmission Electron Microscopy (TEM) together with Differential Scanning Calorimetry (DSC). Air Cooling (AC) after solution heat treatment results in quench induced heterogeneous precipitation of both β-Mg2Si and η-MgZn2 phases. Detailed TEM characterisation of resulting nanoscale precipitates after AC, or Water Quenching (WQ), and subsequent artificial ageing demonstrate that η′ and η2 hardening precipitates dominate in T6, whereas the overaged T7 state contains η2 and η1, where the latter accounts for approximately 50% of the relative phase fraction. The T7 state in addition forms 6xxx-type hardening precipitates only after WQ. Results presented here are expected to be relevant for any Si containing 7xxx alloy and open new possibilities for development of hybrid 6xxx- and 7xxx series aluminium alloys. This is discussed with respect to potential influence on mechanical- and corrosion properties.

The purpose of this work is to understand the role of Cu in the propagation mechanism of IGC on extruded alloy AA6005-T5. The constituent Cu segregates as a Cu-rich nanolayer, together with the formation of a solute depleted zone, along the grain boundaries during thermomechanical processing of the alloy. While the alpha-phase particles corrode in acidified chloride test solution, additional Cu becomes enriched as nanoscale particles and layer segments by dealloying on the external surface and fissure walls formed by IGC. While the grain-boundary layer functions as the internal cathode, enriched Cu acts as effective external cathodes in IGC propagation.

The paper presents a fundamental study of the properties and functions of well-defined Ni-Ag surface alloys in methane decomposition and steam reforming, aiming at providing a better understanding of the principle for manipulating the catalytic activity of steam reforming and suppressing carbon formation. A better insight of structure-property relationship was obtained by a kinetic study of the reactions on well-defined surface Ni-Ag alloys, which were synthesized by surface redox reaction to selectively introduce Ag atoms into the surface of Ni particles supported on hydrotalcite derived support. The effects of Ni surface alloy with Ag are three-folds in general. Replacement of Ni by Ag reduces the number of active site exponentially with increasing Ag site coverage. Ag site is not only inactive, but also significantly reduces the activity of adjacent Ni sites for methane activation in both methane decomposition and steam reforming. The third effect is to block the active sites for the nucleation and growth of the filamentous carbon. The rate of methane activation at Ni step sites was found to be 16-19 times of that on Ni terrace sites. The carbon formation rate decreased linearly with Ag site coverage and the effect of Ag is divided into two regions. At low Ag site coverages (0 to 0.055), Ag atoms preferentially deposit on Ni step sites, which has a significant effect on the methane activation compared to Ag atoms on the Ni terrace sites. The results reveal that the effects of Ag site on the carbon formation in the two regions are mostly caused by the different effects of Ag on the activity of Ni step sites and terrace sites, respectively, rather than the different ensemble sizes for carbon formation proposed in the literature.

As part of an extensive research program to study recent, unexpected intergranular corrosion (IGC) on 6xxx series aluminum alloys (AlMgSi), this paper investigates the mechanism of initiation and early propagation of IGC on the extruded AA6005-T5 alloy with small Cu content (0.1 wt%) by use of advanced electron microscopy techniques applied for near surface characterization. Corrosion testing was restricted to the accelerated IGC test according to the standard BS ISO 11846, involving exposure to acidified chloride solution. The effect of modifying the as-received extruded surface by metallographic polishing, argon sputtering, and alkaline etching was investigated. Initiation of IGC was delayed on the as-received surface compared to the modified surface, caused by the presence of an approximately 8 nm thick crystalline oxide layer formed during extrusion. IGC initiated at the primary alpha-Al(Fe, Cu, Mn) Si particles for all types of surfaces. However, these particles corroded rapidly in the test solution forming a residue of Cu and Si on the exposed particle surface. This phenomenon, as well as enrichment of Cu on the Al matrix surface by dealloying, contributed increasingly to the formation of new effective cathodic sites and continuing propagation of IGC. The AlMgSiCu (Q) phase, present as primary and secondary particles, was relatively inert against both oxidation and reduction. (C) The Author(s) 2019. Published by ECS.

We report here on the optical response of elliptical gold particles arranged in a rectangular lattice on glass and probed at non-normal incidence in reflection using spectroscopic Mueller matrix ellipsometry in the energy range 0.73-5.9 eV. The surface plasmon resonances, reshaped near the Rayleigh anomalies, are mapped out by full azimuthal rotation of the sample. The experimental Mueller matrices are discussed, and interpretation is supported by finite element modeling of the Mueller-Jones matrix elements, which allows for identification of the dipolar and multipolar responses observed in the experimental spectra. The data show a strong polarization conversion around the surface plasmon resonances as a function of the azimuthal angle of incidence, also reshaped near the Rayleigh lines. An effective strong circular diattenuation is observed from the recorded Mueller matrix. We further argue the importance of Mueller matrix ellipsometry for metrology in the manufacture of metasurfaces, for understanding the effect of the lattice in metasurface design, and finally in validating computational methods. (C) 2019 Optical Society of America

Melt quenched metal-organic framework (MOF) glasses define a new category of glass, distinct from metallic, organic, and inorganic glasses, owing to the dominant role of metal-ligand coordination bonding. The mechanical properties of glasses in general are important given their application in protective coatings and display technologies, though little is known about MOF glasses in this respect. The experimental elucidation of key properties such as their scratch resistance has been limited by the lack of processing methodologies capable of producing bulk glass samples. Here, nanoindentation was used to investigate the Young's modulus and hardness of four melt-quenched glasses formed from zeolitic imidazolate frameworks (ZIF): agZIF-4, agZIF-62, agZIF-76, and agZIF-76-mbIm. The creep resistance of the melt-quenched glasses was studied via strain-rate jump (SRJ) tests and through constant load and hold (CLH) indentation creep experiments. Values for the strain-rate sensitivity were found to be close to those for other glassy polymers and Se-rich GeSe chalcogenide glasses. Vacuum hot-pressing of agZIF-62 resulted in an inhomogeneous bulk sample containing the glass and amorphous non-melt-quenched aZIF-62. Remelting and annealing, however, resulted in the fabrication of a transparent, bubble-free bulk specimen, which allowed the first scratch testing experiments to be performed on an MOF glass.

Glasses formed by melt quenching metal–organic frameworks (MOFs) are attracting growing attention because they exhibit an improved processability compared with their crystalline counterparts. Melt quenched MOF glasses also define a new category of glass, distinct from metallic, organic and inorganic glasses, owning to the role that metal-ligand coordination bonding plays in their three-dimensional structures. The mechanical properties of glasses in general are of importance given their application in protective coatings, display technologies and screens. Little, however, is known about the mechanical behavior of MOF-glasses, and experimental elucidation of key properties such as their scratch resistance has been limited by the lack of processing methodologies capable of producing bulk glass samples. Here, nanoindentation was used to investigate the Young’s modulus and hardness of four melt-quenched glasses formed from zeolitic imidazolate frameworks (ZIF): agZIF-4, agZIF-62, agZIF-76 and agZIF-76-mbIm. The creep resistance of the melt-quenched glasses was studied via strain-rate jump (SRJ) tests, and through constant load and hold (CLH) indentation creep experiments. Values for the strain-rate sensitivity were found to be close to those for other glassy polymers and Se-rich GeSe chalcogenide glasses. One glass, agZIF-62, was used to explore two strategies for the preparation of bulk glass samples, i.e. (i) vacuum hot-pressing and (ii) remelting and annealing. Vacuum hot-pressing resulted in an inhomogeneous bulk sample containing the glass and amorphous, non-melt quenched aZIF-62. Remelting and annealing however, resulted in the fabrication of a transparent, bubble-free, bulk specimen, which allowed the first scratch testing experiments to be performed on a MOF-glass. The results are of high significance for potential applications of MOF-glasses.

The long term effect of up to 10 ppm H2S was studied for Fischer–Tropsch conversion of syngas by catalytic testing at 240 °C, 5 bar, H2/CO = 2.1 and GHSV = 2400 Nml/gcat h. Sulphur was dosed after ~ 300 or ~ 1000 h time on stream and the effect was monitored using on-line GC. The activity declined, and the effect correlated to the concentration of H2S in the feed. However, dosing after ~ 1000 h caused a stronger effect than dosing after ~ 300 h. The effects of sulphur are significant with respect to operational risks and mitigation but are substantially less severe than for a standard Co-based catalyst operated at 20 bar for wax production. The spent catalyst consisted of a mixture of cubic (Co, Mn)O, hexagonal Co, Co2C and sulphurous deposits; mainly MnSO4. It could not be concluded that sulphur had a direct effect on product selectivity, but it may have impacted water-gas-shift activity, and sudden changes in shift activity was found to correlate to changes in hydrocarbon selectivity.

Gaining an insight into the interface structure resulting from the interaction between metal nanoparticles and their supports, particularly under relevant reaction conditions, has been an important topic in heterogeneous catalysis and materials science. In this contribution, the active sites and interfaces of Pt sub-nanocrystals supported on carbon nanofibers (CNFs) are investigated and visualized at the atomic level by highly integrated X-ray absorption near-edge structure, X-ray absorption fine structure (EXAFS), and molecular dynamics (MD) simulations based on a reactive force field. Experimental and theoretical results indicate that the surface structure of the CNFs is one of the key parameters that governs the metal-support interface structure, which in turn determines the metal-support interaction strength and the structural properties of Pt clusters, including cluster size, Pt coordination number, and Pt-Pt bond length. Owing to the strong interaction between Pt and CNFs, sub-nanometer-sized Pt clusters are stabilized on CNFs. The Pt-Pt coordination number determined from EXAFS suggests Pt clusters of similar to 1 nm size are deposited on platelet-type CNFs (p-CNFs), whereas clusters smaller than 0.6 nm are supported on fishbone-type CNFs (f-CNFs). The catalysts exhibit high selectivity toward CO oxidation at relatively low temperatures in the presence of H-2, and their activity is related to the Pt coordination number and Pt-Pt bond length. The Pt clusters on the p-CNFs with relatively high coordination number have much higher activity than those on f-CNFs. The combined EXAFS analysis and MD simulations provide a better understanding of the catalyst properties at the atomic level and pave the way to use the CNF structure as a platform to tune the Pt particle size and metal activity through manipulating the metal-support interaction.