Wavelength Dispersive X-ray Spectroscopy Research Articles

Predicting the Average Composition of an AlFeNiTiVZr-Cr Alloy with Machine Learning and X-ray Spectroscopy

A multi-principal element alloy (MPEA) is a type of metallic alloy that is composed of multiple metallic elements, with each element making up a significant portion of the alloy. In this study, the initial atomic percentage of elements in an (AlFeNiTiVZr)1-xCrx MPEA alloy as a function of the position on the surface was investigated using machine learning algorithms. Given the absence of a linear relationship between the atomic percentage of elements and their location on the surface, it is not possible to discern any clear association from the dataset. To overcome this non-linear relationship, the prediction of the atomic percentage of elements was accomplished using both decision tree (DT) and random forest (RF) regression models. The models were compared, and the results were found to be consistent with the experimental findings (a coefficient of determination R2 of 0.98 is obtained with the DT algorithm and 0.99 with the RF one). This research demonstrates the potential of machine learning algorithms in the analysis of wavelength-dispersive X-ray spectroscopy (WDS) datasets.

Influence of annealing time on the microstructure and properties of additively manufactured X2CrNiMoN25–7–4 duplex stainless steel: Experiment and simulation

Duplex stainless steels (DSS) manufactured additively using the powder bed fusion – laser beam/metal (PBF-LB/M) process exhibit a predominantly ferritic microstructure due to the process inherent ultrahigh cooling rates. In this microstructural constitution, the high potential of a balanced two-phase ferritic-austenitic microstructure typical for DSS is not exploited, which is why these steels are subsequently heat-treated. The present study focuses precisely on this heat treatment considering PBF-LB/M-processed X2CrNiMoN25–7–4 DSS solution annealed at different times and aims to explain the influence of the as-built microstructure on the phase formation during solution annealing as a function of heat-treatment time and how different annealing times affect the mechanical and corrosive properties. The as-built microstructure was investigated using electron backscattered diffraction (EBSD), X-ray diffraction (XRD), and atom probe tomography (APT) and the subsequently solution annealed ones using EBSD, XRD, secondary electron microscopy (SEM), energy dispersive (EDS) and wavelength dispersive X-ray spectrometry (WDS). Additionally, the results were compared to DICTRA® simulations. The corrosive properties were examined by potentiodynamic measurements in 0.5 molar sulfuric acid, whereas the mechanical properties were characterized by tensile testing. The ferritic microstructure in the as-built condition is characterized by a supersaturation with nitrogen, accompanied by the formation of nanoscale Cr2N. During heat treatment, these precipitates serve as nucleation sites for austenite formation, so that a balanced, ferritic-austenitic microstructure is already achieved after 3 min. Compared to longer annealing times (5 and 60 min), the highest strength and corrosion resistance is obtained with an annealing time of 3 min, as longer times result in grain coarsening.

Elemental Compositions of Enamel or Dentin in Human and Bovine Teeth Differ from Murine Teeth.

Teeth with different chemical compositions can show vastly different physical properties, so knowledge of elemental composition is required to use animal teeth as substitutes for human teeth in research. In vitro, energy dispersive X-ray spectroscopy (EDX), improved by calibration standards and Si3N4-window material, enables determining local elemental compositions of inorganic and organic compounds without sample destruction. Six human molars, bovine incisors, murine incisors, and murine molars were analyzed. EDX-field scans and line scans were analyzed for elements Ca, P, O, C, N, F, Na, Mg, Fe, Cl, and S. Furthermore, Ca/P- and Ca/N-Ratios were calculated. The presence of iron in murine incisor enamel was investigated using additional wavelength dispersive X-ray spectroscopy measurements (WDX) near the enamel surface. Bovine and human enamel and dentin revealed close similarities regarding elemental composition. The median (25-75% percentiles) of At%Ca was 21.1 (20.8-21.3) in human enamel, 21.0 (20.7-21.2) in bovine enamel, and in murine enamel, 18.3 (17.85-18.88) for molars and 18.35 (18.00-18.75) for incisors. In dentin, murine teeth revealed a higher At%Ca compared to human and bovine teeth. Significant differences between human and bovine teeth were found for nitrogen in dentin, with a median of 4.5 (3.3-5) At%N for human dentin and 2.7 (2.3-3.2) At%N for bovine dentin. The Ca/P-Ratio was the highest in human and bovine enamel, which did not differ significantly. Enamel from murine molars had a higher Ca/P-Ratio than murine incisors and the highest Ca/P-Ratio in dentin was observed for human teeth and murine molars (1.49). WDX revealed iron in the outer 10 µm of pre- and post-eruptive enamel of murine incisors. Pre- and post-eruptive enamel on murine incisors only differed significantly in At%Ca (p = 0.041) and At%P (p = 0.026) with both At% higher in the pre-eruptive enamel. Murine teeth differ significantly from human and bovine teeth in terms of the elemental composition of enamel and dentin.

Organic preservation of vase-shaped microfossils from the late Tonian Chuar Group, Grand Canyon, Arizona, USA.

Vase-shaped microfossils (VSMs) are found globally in middle Neoproterozoic (800-730 Ma) marine strata and represent the earliest evidence for testate (shell-forming) amoebozoans. VSM tests are hypothesized to have been originally organic in life but are most commonly preserved as secondary mineralized casts and molds. A few reports, however, suggest possible organic preservation. Here, we test the hypothesis that VSMs from shales of the lower Walcott Member of the Chuar Group, Grand Canyon, Arizona, contain original organic material, as reported by B. Bloeser in her pioneering studies of Chuar VSMs. We identified VSMs from two thin section samples of Walcott Member black shales in transmitted light microscopy and used scanning electron microscopy to image VSMs. Carbonaceous material is found within the internal cavity of all VSM tests from both samples and is interpreted as bitumen mobilized from Walcott shales likely during the Cretaceous. Energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) reveal that VSM test walls contain mostly carbon, iron, and sulfur, while silica is present only in the surrounding matrix. Raman spectroscopy was used to compare the thermal maturity of carbonaceous material within the samples and indicated the presence of pyrite and jarosite within fossil material. X-ray absorption spectroscopy revealed the presence of reduced organic sulfur species within the carbonaceous test walls, the carbonaceous material found within test cavities, and in the sedimentary matrix, suggesting that organic matter sulfurization occurred within the Walcott shales. Our suite of spectroscopic analyses reveals that Walcott VSM test walls are organic and sometimes secondarily pyritized (with the pyrite variably oxidized to jarosite). Both preservation modes can occur at a millimeter spatial scale within sample material, and at times even within a single specimen. We propose that sulfurization within the Walcott Shales promoted organic preservation, and furthermore, the ratio of iron to labile VSM organic material controlled the extent of pyrite replacement. Based on our evidence, we conclude that the VSMs are preserved with original organic test material, and speculate that organic VSMs may often go unrecognized, given their light-colored, translucent appearance in transmitted light.

Influence of additive-derived reaction layers on white etching crack failure of SAE 52100 bearing steel under rolling contact loading

It is a common observation that rolling bearings fail due to the formation of white etching areas and white etching cracks (WEA/WEC). Branching crack networks beneath the surface and an altered microstructure known as WEA are characteristics of the failure mode. Therefore, the WEA-related cracks are known as WEC. In order to shed more light on this so far not fully understood phenomenon, the present study focussed on the role of specific oil additives and their influence on the formation of reaction layers and how these possibly affect the WEA/WEC formation. For this purpose, comprehensive tests were conducted on a three-ring-on-roller test rig using two different fully formulated oil lubricants with samples of SAE 52100 bearing steel. A subsequent carried out analysis by wavelength dispersive X-ray spectroscopy (WDX) and transmission electron microscopy (TEM) revealed the differences in the formed additive-derived reaction layers. While a known WEA/WEC-critical oil formulation, containing the two additives zinc dithiophosphate (ZDDP) and overbased calcium sulfonate (OBCaSul), did not result in any significant formation of reaction layers during mixed / boundary lubrication at an oil influx temperature of 95 °C, an oil formulation containing barium and phosphorus performed excellent in this respect. This finding is related to the observation that provocation of WEA/WEC failures in our experiment was always unsuccessful when the barium- and phosphorus-containing oil was used. The use of barium phosphate containing lubricants could therefore be an effective measure to prevent or significantly delay WEA/WEC damage to bearings.

TEM study of ∼PbCr2S4 columnar misfit phases

The disordered structure of the columnar misfit ​∼ ​PbCr2S4 phase (∼ character indicates that it is close to the stoichiometric composition but slightly away) has been revealed by means of transmission electron microscopy (TEM) varied techniques such as selected area electron diffraction (SAED), high-resolution TEM (HRTEM), dark-field TEM and high-angle annular dark field (HAADF) in scanning-transmision (STEM) mode. The structure consists of a hexagonal framework (Cr21S36), with unit cell parameters a0 ​= ​b0 ​= ​21.407 (1) Å and c0 ​= ​3.476 (1), and with hexagonal (Pb6Cr2S6) and trigonal columns (Pb3S) with the same a and b parameters and different c: c3 ​= ​3.98 Å; c6 ​= ​5.62 ​Å, measured by electron diffraction. While the framework exhibit no crystalline disorder, the arrangement of the two types of columns is disordered. This disorder is shown by electron diffraction as diffuse scattering planes which are perpendicular to the framework c axis and parallel to the a∗b∗ plane. While the disorder between hexagonal columns is due to the lack of correlation between different columns, we observe in the trigonal columns also the presence of intra-columnar atomic disorder. X-ray wavelength dispersive spectroscopy (XWDS) analyses produce Pb0.81(1)Cr2S3.97(6) composition. TEM imaging techniques suggest lack of correlation between trigonal columns as the cause for the observed disorder as well as inside-the-column structural disorder in Pb3S trigonal columns.

Interplay between solidification microsegregation and complex precipitation in a γ/γ’ cobalt-based superalloy elaborated by directed energy deposition

This study examines the segregations and the precipitation appearing during the solidification path of a Co-Ni-Al-W-Ta-Ti-Cr γ/γ’ cobalt-based superalloy processed by directed energy deposition (DED). Observations reveal characteristic elements partitioning in the liquid during additive manufacturing. Due to this microsegregation, complex multiphase precipitation occurs and the various precipitates are identified and characterized in a cobalt-based superalloy fabricated by DED. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to investigate the spatial distribution and nature of the various phases detected in the as-fabricated microstructure. Energy dispersive X-ray spectrometry (EDS), wavelength dispersive X-ray spectrometry (WDS), and electron energy loss spectroscopy (EELS) are coupled with a fine analysis of the diffraction patterns to identify the different phases decorating the interdendritic regions. These characterizations allow the identification of different submicronic precipitates: Al 2 O 3 , (Ta,Ti)(N,C), HfO 2 , Cr 3 B 2 and (Ti,Zr,Hf) 2 SC. The solidification sequence is discussed at light of the experimental results. This work provides a first understanding of the interplay between solidification segregations and the formation of second phase precipitation in a cobalt-based superalloy processed by DED. • A cobalt-based superalloy was processed by Direct Energy Deposition. • Solidification segregations lead to the precipitation of interdendritic phases. • Automated crystallographic orientation mapping and chemical analyses were used. • Various interdendritic phases have been identified: oxides (Al 2 O 3 and HfO 2 ), carbonitrides (Ta, Ti)(N, C), sulphocarbides (Ti, Zr, Hf) 2 SC, and borides Cr 3 B 2 . • The solidification path can be established based on the experimental observations.

Microbial Activity and Neomorphism Influence the Composition and Microfabric of Ooids From Great Salt Lake, UT

The sediment along the shorelines of Great Salt Lake (GSL), Utah is dominated by ooids, concentrically-coated carbonate sand grains. Two characteristics differentiate GSL ooids from typical modern marine ooids: well-developed radial aragonite microfabrics and the ubiquitous occurrence of a Mg-silicate phase. The radial microfabrics have formed the basis of conceptual models applied to understand the formation of radial fabrics in ancient ooids, but the formation of the Mg-silicates, and the relationship between Mg-silicates and radial aragonite crystals have received little attention. The occurrence of Mg-silicates in GSL ooids is surprising because GSL lake water pH is ~8.3, too low for Mg-silicate precipitation (requires pH>8.7). We use transmitted light microscopy, element mapping via wavelength-dispersive x-ray spectroscopy with electron microprobe, scanning electron microscopy, and synchrotron x-ray fluorescence (XRF) mapping and sulfur K-edge absorption spectroscopy to explore the spatial relationships between the mineral phases in GSL ooids. We observe large euhedral aragonite crystals penetrating Mg-silicate zones and cutting across laminar cortices, suggesting that the characteristic radial aragonitic fabrics in GSL ooids, traditionally interpreted as a primary structure, are enhanced, or in some cases entirely created via neomorphism. XRF maps reveal that Mg-silicate zones co-occur with elemental sulfur (S0), which we interpret as a metabolic intermediate of microbial sulfur cycling. This co-occurrence supports our hypothesis that microbial sulfur cycling plays a key role in the formation of GSL ooids by locally shifting pH beyond the threshold for Mg-silicate precipitation. This compositional fingerprint could serve as a biosignature in ancient lacustrine strata where Mg-silicates co-occur with carbonate minerals.

Saccoite, Ca2Mn+32F(OH)8⋅0.5(SO4), a new, microporous mineral from the Kalahari Manganese Field, South Africa

AbstractSaccoite, Ca2Mn3+2F(OH)8⋅0.5(SO4), is a new mineral found at the N'Chwaning III mine, Kalahari Manganese Field, Northern Cape Province, Republic of South Africa. It occurs as fillings of voids in hydrothermally altered manganese ore (comprising mostly of bixbyite and baryte). Further associated minor minerals are braunite, gypsum, chlorite, sturmanite and ettringite. Saccoite forms small needles, felted crystal masses or crusts. The new mineral is olive green, transparent, with white streak and vitreous lustre. No luminescence is observed. Saccoite is uniaxial (–) with refractive indices at 589(1) nm of ω = 1.705(5) and ɛ = 1.684(2). Pleochroism is distinct, i.e. bluish green (ω) and yellowish green (ɛ). The chemical composition was studied by means of an electron probe micro-analyser (EPMA) using wavelength-dispersive X-ray spectrometry (WDS). The empirical mineral formula is Ca2.06Mn3+1.78Cu0.10Mg0.07F0.97(OH)8.02(SO4)0.39. The unit-cell dimensions of saccoite (space group P4/ncc) are a = 12.834(3) Å, c = 5.622(2) Å, V = 926.0(4) Å3), and the calculated mass density is 2.73 g⋅cm–3. Saccoite exhibits a heteropolyhedral framework structure that is composed of edge- and corner sharing CaF2(OH)6 and M(OH)6 polyhedra (M = Mn3+ and Cu2+) with large channels along [001], which host disordered and only partially occupied groups, especially SO42–. The hydrogen atoms of the OH groups point into the channel to form hydrogen bonds with the channel anions. Ca–F distances are ~2.3 Å, the Ca–OH distances in the range of 2.44–2.58 Ǻ, and the M(OH)6 octahedron is strongly 4+2 Jahn-Teller distorted (4 × ~1.92 Å, 2 × 2.27 Å). The F atom is tetrahedrally coordinated to calcium atoms. The strongest lines in the powder X-ray diffraction pattern [d in Å (relative intensity) (hkl)] are: 9.0735 (35) (110), 4.5370 (95) (220), 4.0644 (20) (310), 3.0105 (100) (321), 2.8117 (20) (002), 2.7242 (75) (411), 1.9755 (35) (611), and 1.8142 (20) (550).

Magnetically Recoverable Silica-Decorated Ferromagnetic-Nanoceria Nanocatalysts and Their Use with O- and N-Butyloxycarbonylation Reaction via Solvent-Free Condition.

Silica-decorated ferrite nanoparticles, a new kind, coated with ceric ammonium nitrate (CAN), have been prepared successfully by simple coprecipitation techniques. Powder X-ray diffraction spectroscopy (PXRD), Fourier transform-infrared spectroscopy (FT-IR), field emission-scanning electron microscope (FE-SEM), wavelength-dispersive X-ray spectroscopy (WDX), energy-dispersive spectroscopy (EDS), inductive coupled plasma-optical emission spectroscopy (ICP-OES), and thermogravimetric analysis (TGA) techniques were used to characterize these nanoparticles. The catalysts are further studied for catalytic activity in solvent-free conditions. Importantly, these nanoparticles have been collected from the reaction mixture using an external magnet and recycled up to minimum of 15 cycles with no substantial loss of catalytic characteristics.

Improving the accuracy of alpha particle induced X-ray emission analysis: The role of multiple ionization K X-ray satellites

Wavelength-dispersive X-ray spectrometry is used to examine the influence of multiple ionization satellites induced by 3–5 MeV energy helium ion beams upon the accuracy of particle-induced X-ray emission analysis (PIXE). The work extends our prior study of elements magnesium, aluminum and silicon and their oxides to elements phosphorus, chlorine, potassium, calcium, titanium and chromium and, for the latter two, their oxides. Fitting of the spectra with Voigtian peaks enables construction of a database that comprises the mean energies and the relative intensities of up to four distinct satellite groupings. This database provides an empirical means for inclusion of one peak per satellite group when modelling energy-dispersive spectra. This is a useful step towards improving the accuracy of PIXE analysis of materials using helium beams; an example of this is provided using a spectrum recorded by the Curiosity rover on Mars.

Revealing the degradation mechanism of the lanthanum nickelates based double‐layer electrodes during long‐term tests in contact with chromium‐containing steel interconnects

This paper focuses on the long-term tests for 1000 hours of different Membrane-Electrode-Interconnect Assemblies (MEIAs), consisting of a steel interconnect and an asymmetrical solid electrochemical cell based on the Ce0.8Sm0.2O2−δ electrolyte, the double-layer working electrode with the La2NiO4+δ – Ce0.8Sm0.2O2−δ composite functional layer and the LaNi0.6Fe0.4O3−δ current collector layer, and the platinum reference electrode (O2, LaNi0.6Fe0.4O3−δ|La2NiO4+δ – Ce0.8Sm0.2O2−δ|Ce0.8Sm0.2O2−δ|Pt, O2). These tests were carried out on MEIAs with two types of Cr-based stainless steels, Crofer 22 APU and 08X17T, with and without protective coatings at 850°C in air. The electrochemical performance of MEIAs was studied without polarization as well as under cathodic and anodic polarization (current density was 0.5 A cm−2) by means of electrochemical impedance spectroscopy (EIS) and the distribution of relaxation times method (DRT). It was found that the proposed protective coatings for the stainless steels inhibit chromium poisoning without polarization and under anodic polarization: for Crofer 22 APU the degradation of the polarization resistance after ~1100 hours of exposure was 0.35 ± 0.05 Ω cm2, and for 08X17T it was from 0.40 ± 0.05 Ω cm2. In the case of cathodic polarization, the degradation of the polarization resistance remained at a very high level, comparable to uncoated samples: for Crofer 22 APU and 08X17T with coatings, it was about 0.6 to 0.8 Ω cm2 after ~1100 hours. Post-test analysis of the microstructure and chemical composition of the interconnect - double-layer electrode interface was carried out using scanning electron microscopy (SEM), wavelength dispersive X-ray spectrometry (WDS), and respective image analysis of the obtained data. The influence of chromium poisoning on the degradation was considered for different stages of the electrode performance. It was demonstrated that chromium predominantly accumulates in the current collector layer in the case of anodic polarization and in the functional layer in the cases of open circuit and cathodic polarization. For the first time, a combined electrochemical-chemical degradation mechanism of the La2NiO4+δ – Ce0.8Sm0.2O2−δ functional layer was discussed. Highlights Long-term tests of Membrane-Electrode-Inteconnect Assembles (MEIAs) were done. Chromium poisoning was detected on MEIAs with the interconnects without coating. Cathodic polarization terminates the protective properties of the coatings. Chromium poisoning decreases electrode activity to oxygen exchange and diffusivity. A combined electrochemical-chemical degradation mechanism of the functional layer was revealed.

Microstructure and properties of WC-11.5%Fe-4%NbH-0.5%C cemented carbides produced by spark plasma sintering

This study investigates the influence of milling parameters and sintering cycle on the microstructure and properties of cemented carbides with an overal WC–11.5wt%Fe–4wt%NbH–0.5wt%C starting powder composition. The raw material powders were milled and mixed in a ring mill or planetary ball mill and sintered at 1150, 1200 or 1250 °C using spark plasma sintering (SPS). The cemented carbide density, Vickers hardness and fracture toughness were evaluated. The microstructure was investigated by optical and scanning electron microscopy using wavelength dispersive X-ray spectroscopy for elemental mapping. The transition from NbH to NbC was identified for all sintered materials. Moreover, microstructural gradients were formed creating bi-layered structured materials with higher hardness edges and tougher cores. The highest microstructural homogeneity and hardness were found for planetary ball milled starting powder sintered at 1250 °C. For these samples, the highest density recorded was 13.69 g/cm3, which also obtained highest hardness values of 1620 Hv and 1589 Hv, on the surface and center regions, respectively.

Effect of disease duration on the distribution of otosclerotic foci within the stapes based on scanning electron microscopy analysis

Introduction: Otosclerosis is characterized by the presence of abnormal resorption and recalcification of the endochondral layer of the temporal bone, which is not observed in healthy subjects. The result of the alternating occurrence of both processes is the appearance of disorganized and, over time, dense, sclerotic bone tissue underlying the clinical manifestation of the otosclerotic process. Aim: The aim of the work is the chemical analysis of otosclerotic foci of the stapes superstructure with the use of a scanning electron microscope. Material and methods: Patients operated for the first time due to otosclerosis were analyzed. The removed stirrup suprastructures were examined in a Scanning Electron Microscope (SEM) using microanalytical techniques (WDXS – Wavelength-dispersive X-ray spectroscopy TEXS – Transition Element X-ray Spectrometer) and diffraction techniques (2D EBSD – Electron Backscatter Diffraction). Results: In patients with a short medical history, a statistically significant difference in calcium (Ca) concentration was found between the anterior and posterior cruses of stapes. Along with the duration of the disease, a statistically significant difference in calcium (Ca) concentration was observed between the stapes head and its cruses. In the course of the disease, degradation of the microstructure of the stapes bone tissue was observed in a scanning electron microscope. Conclusions: (A) As the otosclerotic process progresses, significant changes in the chemical composition between the individual parts of the stapes superstructure are observed; (B) The observed biochemical changes are accompanied by changes in the microstructure of bone tissue observed in SEM.

Characterization of stone tesserae from “The Indian Triumph of Dionysus” Mosaic (Casignana, Reggio Calabria, Italy)

Abstract The archaeological site of Casignana (Reggio Calabria) represents one of the most important Roman sites of Southern Italy thanks to its extension and refinement of its mosaics such as the “Indian Triumph of Dionysus”. Its stylistic complexity is related also to the wide range of polychrome stone tesserae used. For this reason, a minero-petrographic and geochemical characterization of some tesserae was carried out by Polarized Optical Microscopy (POM), Scanning Electron Microscope (SEM), and Electron probe microanalyzer combined with wavelength dispersive X-ray spectroscopy (EPMA-WDS). The results suggested the heterogeneity of the stone tesserae in terms of petrographic features and the probable provenance from both local and not sites.

Structure, electrical, and optical properties of reactively sputter-deposited Ta—Al—N thin films

We report on the influence of Al content on the structural, electrical, and optical properties of polycrystalline ternary Ta—Al—N thin films. Ta1−xAlxNy thin films with x up to 0.69 and 0.92 ≤ y ≤ 1.22 were deposited on silicon substrates by means of direct current reactive magnetron co-sputtering from elemental Ta and Al targets. The elemental composition, crystal structure, bonding state, and electrical and optical properties of the deposited films were characterized using wavelength-dispersive x-ray spectrometry, x-ray diffraction, x-ray photoelectron spectroscopy, four-point probe electrical resistance, and spectroscopic ellipsometry (SE), respectively. The real part (ɛ1) and imaginary part (ɛ2) of the dielectric constants were derived from the SE data, which were simulated and fitted by using a Drude and Lorentz oscillator models. The Ta1−xAlxNy films are characterized by a compact microstructure, which becomes more columnar with increasing Al content. It is found that the incorporation of Al into TaN lattice results in the stabilization of cubic Ta1−xAlxNy solid solutions up to x = 0.40, while a hexagonal phase is formed for 0.48 ≤ x ≤ 0.69. This structural transition is accompanied by a change in the chemical bonding state, high electrical resistivity (8–10 mΩ cm), and semi-transparent character. Ternary Ta1−xAlxNy alloys with a small amount of Al (x = 0.02 and 0.06) show superior electrical and optical conductivities compared to a binary TaN compound, making them appealing material candidates for UV plasmonic applications.

Influence of carbon content on fatigue strength of cemented carbides

In this study, the influence of carbon content on fatigue strength of fine grade cemented carbides (WC-12Co) was investigated. Thereby, the carbon content was varied systematically in the two- and three-phase region. Specimens from the different alloys were fabricated and tested in flat bending fatigue experiments. Results show no significant influence of the carbon content as long as no graphite was precipitated. In accordance with findings in the literature, the fatigue strength decreases significantly when graphite precipitations occur. Both, wavelength dispersive x-ray spectroscopy (WDS) and energy dispersive spectroscopy (EDS) were used for analysis of the chemical composition of the binder phase. No significant influence of the global carbon content on the morphology of WC-grains as well as the local carbon content in the cobalt-binder was found.

Widespread mineralization of soft‐bodied insects in Cretaceous amber

Fossilized tree resin, or amber, commonly contains fossils of animals, plants and microorganisms. These inclusions have generally been interpreted as hollow moulds or mummified remains coated or filled with carbonaceous material. Here, we provide the first report of calcified and silicified insects in amber from the mid-Cretaceous Kachin (Burmese) amber. Data from light microscopy, scanning electron microscopy (SEM), energy-dispersive and wavelength-dispersive X-ray spectroscopy (EDX and WDX), X-ray micro-computed tomography (Micro-CT) and Raman spectroscopy show that these Kachin fossils owe their preservation to multiple diagenetic mineralization processes. The labile tissues (e.g. eyes, wings and trachea) mainly consist of calcite, chalcedony and quartz with minor amounts of carbonaceous material, pyrite, iron oxide and phyllosilicate minerals. Calcite, quartz and chalcedony also occur in cracks as void-filling cements, indicating that the minerals formed from chemical species that entered the fossil inclusions through cracks in the resin. The results demonstrate that resin and amber are not always closed systems. Fluids (e.g. sediment pore water, diagenetic fluid and ground water) at different burial stages have chances to interact with amber throughout its geological history and affect the preservational quality and morphological fidelity of its fossil inclusions.

Visualization of structural changes and degradation of porphyrin-based battery electrodes

We present FIB/SEM tomography combined with an optimized embedding procedure and osmium tetroxide staining to trace and visualize the initial self-conditioning step as well as degradation processes of [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP) composite electrodes for the first time. Staining with osmium tetroxide allowed visualizing chemical changes of the active CuDEPP material. Four composite electrode samples prior and after cycling with different cycle numbers in LiPF6 electrolyte (i.e., pristine, one, 200 and 2000 charging cycles) were investigated and for all samples 3D reconstructions with a voxel size of 7.15 × 7.15 × 20 nm3 were performed. The samples were further analyzed by wavelength-dispersive X-ray (WDX) spectroscopy revealing the insertion of the electrolyte into the active material of the electrode. The formation of an interphase adjacent to the inner pore space of the active CuDEPP material could be unambiguously identified. In addition, Raman spectroscopy results confirmed the self-conditioning and degradation processes of the metalloporphyrin complex.

MoS2 oxidative etching caught in the act: formation of single (MoO3) n molecules.

We report the presence of sub-nm MoO x clusters formed on basal planes of the 2H MoS2 crystals during thermal oxidative etching in air at a temperature of 370 °C. Using high resolution non-contact atomic force microscopy (AFM) we provide a histogram of their preferred heights. The AFM results combined with density functional theory (DFT) simulations show remarkably well that the MoO x clusters are predominantly single MoO3 molecules and their dimers at the sulfur vacancies. Additional Raman spectroscopy, and energy and wavelength dispersive X-ray spectroscopies as well as Kelvin probe AFM investigations confirmed the presence of the MoO3/MoO x species covering the MoS2 surface only sparsely. The X-ray absorption near edge spectroscopy data confirm the MoO3 stoichiometry. Taken together, our results show that oxidative etching and removal of Mo atoms at the atomic level follow predominantly via formation of single MoO3 molecules. Such findings confirm the previously only proposed oxidative etching stoichiometry.