Hollow-core photonics crystal fiber for CO2 leakage monitoring
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Results for “core crystallization”
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Operando Bragg Coherent Diffraction Imaging of LiNi 0.8 Mn 0.1 Co 0.1 O 2 Primary Particles within Commercially Printed NMC811 Electrode Sheets
Due to complex degradation mechanisms, disparities between the theoretical and practical capacities of lithium-ion battery cathode materials persist. Specifically, Ni-rich chemistries such as LiNi 0.8 Mn 0.1 Co 0.1 O 2 (or NMC811) are one of the most promising choices for automotive applications; however, they continue to suffer severe degradation during operation that is poorly understood, thus challenging to mitigate. Here in this paper we use operando Bragg coherent diffraction imaging for 4D analysis of these mechanisms by inspecting the individual crystals within primary particles at various states of charge (SoC). Although some crystals were relatively homogeneous, we consistently observed non-uniform distributions of inter- and intracrystal strain at all measured SoC. Pristine structures may already possess heterogeneities capable of triggering crystal splitting and subsequently particle cracking. During low-voltage charging (2.7–3.5 V), crystal splitting may still occur even during minimal bulk deintercalation activity; and during discharging, rotational effects within parallel domains appear to be the precursor for the nucleation of screw dislocations at the crystal core. Ultimately, this discovery of the central role of crystal grain splitting in the charge/discharge dynamics may have ramifications across length scales that affect macroscopic performance loss during real-world battery operation.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Fluid Mixing during Phase Separation in Crystallizing White Dwarfs
Abstract Accurate models of cooling white dwarfs must treat the energy released as their cores crystallize. This phase transition slows the cooling by releasing latent heat and also gravitational energy, which results from phase separation: liquid C is released from the solid C/O core, driving an outward carbon flux. The Gaia color–magnitude diagram provides striking confirmation of this theory by revealing a mass-dependent overdensity of white dwarfs, indicating slowed cooling at the expected location. However, the observed overdensity is enhanced relative to the models. Additionally, it is associated with increased magnetism, suggesting a link between crystallization and magnetic field generation. Recent works aimed at explaining an enhanced cooling delay and magnetic field generation employ a uniform mixing prescription that assumes large-scale turbulent motions; we show here that these calculations are not self-consistent. We also show that thermohaline mixing is most likely efficient enough to provide the required chemical redistribution during C/O phase separation, and that the resulting velocities and mixing lengths are much smaller than previous estimates. These reduced fluid motions cannot generate measurable magnetic fields, suggesting any link with crystallization needs to invoke a separate mechanism. Finally, this mixing alters the chemical profiles, which in turn affects the frequencies of the pulsation modes.
79 ASTRONOMY AND ASTROPHYSICS↗
Explosive volcanism and the compositions of the cores of differentiated asteroids
Eleven iron meteorite groups showing correlations between Ni and siderophile trace elements that are predictable by distribution coefficients between liquid and solid metal of fractionally crystallizing metal magmas, are interpreted to be fragments of the fractionally crystallized cores of 11 differentiated asteroids. Many of these groups crystallized from S-depleted magmas which we propose resulted from removal of the first partial melt (a Fe,Ni-FeS cotectic) by explosive pyroclastic volcanism. It is shown that these dense, negatively buoyant melts can be driven to asteroidal surfaces by the combination of an excess pressure in the melt and the presence of buoyant bubbles of gas which decrease the bulk density of the melt. It is also shown that in typical asteroidal materials, veins will form which grow into dikes and serve as pathways for migration of melt and gas to asteroidal surfaces. Since cotectic Fe,Ni-FeS melt consists of about 85 wt. percent FeS and 15 wt. percent Fe,Ni, removal of small volumes of eutectic melts results in major loss of S but only minor loss of Fe,Ni, thus leaving sufficient Fe,Ni to form sizeable asteroidal cores.
Keil, Klaus↗
Explosive volcanism and the compositions of cores of differentiated asteroids
Eleven iron meteorite groups show correlations between Ni and siderophile trace elements that are predictable by distribution coefficients between liquid and solid metal in fractionally crystallizing metal magmas. These meteorites are interpreted to be fragments of the fractionally crystallized cores of eleven differentiated asteroids. Many of these groups crystallized from S-depleted magmas which we propose resulted from removal of the first partial melt (the Fe,Ni-FeS cotectic melt) by explosive pyroclastic volcanism of the type envisaged by Wilson and Keil (1991). We show that these dense, negatively buoyant melts can be driven to asteroidal surfaces due to the presence of excess pressure in the melt and the presence of buoyant bubbles of gas which decrease the density of the melt. We also show that, in typical asteroidal materials, veins will form which grow into dikes and serve as pathways for migration of melt and gas to asteroidal surfaces. Since cotectic Fe, Ni-FeS melt consists of about 85 wt pct FeS and 15 wt pct Fe, Ni, removal of small volumes of eutectic melts results in major loss of S but only minor loss of Fe,Ni, thus leaving sufficient Fe,Ni to form sizeable asteroidal cores.
Keil, Klaus↗
Dynamic Control of Refractive Index During Pulsed-Laser-Deposited Waveguide Growth
Engineering the optical properties of waveguides is important for the optimization of their guided optical mode characteristics. Here, we document the dynamic control of the refractive index and composition of crystalline films, via the substrate temperature, during pulsed-laser-deposition growth of Er(1%)-doped yttrium gallium garnet on <100>-orientated single-crystal yttrium aluminium garnet. An increasing substrate temperature is observed to reduce the gallium content in the grown film, with a corresponding reduction of refractive index. We demonstrate the ability to accurately control the refractive index via this technique and use it to grow a complex multi-core crystal waveguide. Our results highlight the potential of using pulsed laser deposition to fabricate crystal films with bespoke optical properties and thus engineer passive and active waveguide devices in situ.
Temperature↗
A Groundmass Composition for EET 79001A Using a Novel Microprobe Technique for Estimating Bulk Compositions. Lithology A as an Impact Melt?
Petrologic investigation of the shergottites has been hampered by the fact that most of these meteorites are partial cumulates. Two lines of inquiry have been used to evaluate the compositions of parental liquids: (i) perform melting experiments at different pressures and temperatures until the compositions of cumulate crystal cores are reproduced [e.g., 1]; and (ii) use point-counting techniques to reconstruct the compositions of intercumulus liquids [e.g., 2]. The second of these methods is hampered by the approximate nature of the technique. In effect, element maps are used to construct mineral modes; and average mineral compositions are then converted into bulk compositions. This method works well when the mineral phases are homogeneous [3]. However, when minerals are zoned, with narrow rims contributing disproportionately to the mineral volume, this method becomes problematic. Decisions need to be made about the average composition of the various zones within crystals. And, further, the proportions of those zones also need to be defined. We have developed a new microprobe technique to see whether the point-count method of determining intercumulus liquid composition is realistic. In our technique, the approximating decisions of earlier methods are unnecessary because each pixel of our x-ray maps is turned into a complete eleven-element quantitative analysis. The success or failure of our technique can then be determined by experimentation. As discussed earlier, experiments on our point-count composition can then be used to see whether experimental liquidus phases successfully reproduce natural mineral compositions. Regardless of our ultimate outcome in retrieving shergottite parent liquids, we believe our pixel-bypixel analysis technique represents a giant step forward in documenting thin-section modes and compositions. For a third time, we have analyzed the groundmass composition of EET 79001, 68 [Eg]. The first estimate of Eg was made by [4] and later modified by [5], to take phase diagram considerations into account. The Eg composition of [4] was too olivine normative to be the true Eg composition, because the ,68 groundmass contains no forsteritic olivine. A later mapping by [2] basically reconfirmed the modifications of [5]. However, even the modified composition of [5] has olivine on the liquidus for ~50 C before low-Ca pyroxene appears [6].
Jones, John H.↗
MESA Isochrones and Stellar Tracks (MIST). III. The White Dwarf Cooling Sequence
We present a substantial update to the MESA Isochrones and Stellar Tracks (MIST) library, extending the MIST model grids and isochrones down the white dwarf (WD) cooling sequence with realistic physics for WD cooling timescales. This work provides a large grid of MESA models for carbon–oxygen core WDs with hydrogen atmospheres (spectral type DA/DC), descended from full prior stellar evolution calculations. The model tracks, isochrones, and WD cooling timescale contours are available on the MIST project website and at doi:10.5281/zenodo.15242047. Our WD models provide a very large, publicly available grid with detailed physics for WD cooling timescales: realistic interior and envelope compositions, with element diffusion and heavy-element sedimentation, nuclear burning at the base of the WD hydrogen envelope, core crystallization, and C/O phase separation. As a large grid of open-source stellar evolution models, these WD models provide both out-of-the-box model tracks for comparison with observations and a framework for building further WD models to investigate variations in WD physics.
Astronomy and AstroPhysics↗
Chemical abrasion: the mechanics of zircon dissolution
Chemical abrasion is a technique that combines thermal annealing and partial dissolution in hydrofluoric acid (HF) to selectively remove radiation-damaged portions of zircon crystals prior to U–Pb isotopic analysis, and it is applied ubiquitously to zircon prior to U–Pb isotope dilution thermal ionization mass spectrometry (ID-TIMS). The mechanics of zircon dissolution in HF and the impact of different leaching conditions on the zircon structure, however, are poorly resolved. We present a microstructural investigation that integrates microscale X-ray computed tomography (µCT), scanning electron microscopy, and Raman spectroscopy to evaluate zircon dissolution in HF. We show that µCT is an effective tool for imaging metamictization and complex dissolution networks in three dimensions. Acid frequently reaches crystal interiors via fractures spatially associated with radiation damage zoning and inclusions to dissolve soluble high-U zones, some inclusions, and material around fractures, leaving behind a more crystalline zircon residue. Other acid paths to crystal cores include the dissolution of surface-reaching inclusions and the percolation of acid across zones with high defect densities. In highly crystalline samples dissolution is crystallographically controlled with dissolution proceeding almost exclusively along the c axis. Increasing the leaching temperature from 180 to 210 °C results in deeper etching textures, wider acid paths, more complex internal dissolution networks, and greater volume losses. How a grain dissolves strongly depends on its initial radiation damage content and defect distribution as well as the size and position of inclusions. As such, the effectiveness of any chemical abrasion protocol for ID-TIMS U–Pb geochronology is likely sample-dependent. We also briefly discuss the implications of our findings for deep-time (U-Th)/He thermochronology.
58 GEOSCIENCES↗
Nebular condensation of Ga, Ge and Sb and the chemical classification of iron meteorites
The quantization of the Ga and Ge contents in iron meteorites, which is used as a key parameter in the chemical classification of iron meteorites, is discussed in terms of nebular condensation. The calculation of nebular equilibrium condensation is examined, taking into account the dependence of the activity coefficient on temperature and composition, and recent calculations of the condensation temperatures of Ga, Ge, Sb, Au, As and Cu are presented, noting that Ge is the most volatile siderophile, followed by Ga and Sb. The narrow intragroup ranges of Ga and Ge are interpreted in terms of minimal fractionation during core crystallization, while the larger ranges of Sb are attributed to its significantly smaller solid/liquid distribution coefficient in IIIAB meteorites.
Wai, C. M.↗
Chemical fractionations in group IIIAB iron meteorites - Origin by dendritic crystallization of an asteroidal core
Results of an investigation of the crystallization history of the asteroidal core that produced nearly 200 iron meteorites of group IIIAB are presented. The accuracy of the published distribution of coefficients between solid and liquid metal for seven elements and their dependence on the concentrations of S and P are critically assessed to develop a nonideal fractional crystallization model that reproduces all of the major features of the overall chemical trends in group IIIAB. It is suggested that the apparent distribution coefficient of S was was much higher than its equilibrium value (not greater than 0.01) and that it increased during crystallization. In the present preferred model the apparent distribution coefficient for S increases from 0.6 to 0.8, while the S concentration of the liquid increases from 6 to 13 wt pct. It is inferred that light S-rich liquid accumulates preferentially at the top of the core and in structural traps formed by the advancing solid.
Haack, Henning↗
Prediction of crystal structures and motifs in the Fe–Mg–O system at Earth’s core pressures
Abstract Fe, Mg, and O are among the most abundant elements in terrestrial planets. While the behavior of the Fe–O, Mg–O, and Fe–Mg binary systems under pressure have been investigated, there are still very few studies of the Fe–Mg–O ternary system at relevant Earth’s core and super-Earth’s mantle pressures. Here, we use the adaptive genetic algorithm (AGA) to study ternary Fe x Mg y O z phases in a wide range of stoichiometries at 200 GPa and 350 GPa. We discovered three dynamically stable phases with stoichiometries FeMg 2 O 4 , Fe 2 MgO 4, and FeMg 3 O 4 with lower enthalpy than any known combination of Fe–Mg–O high-pressure compounds at 350 GPa. With the discovery of these phases, we construct the Fe–Mg–O ternary convex hull. We further clarify the composition- and pressure-dependence of structural motifs with the analysis of the AGA-found stable and metastable structures. Analysis of binary and ternary stable phases suggest that O, Mg, or both could stabilize a BCC iron alloy at inner core pressures.
Wang, Renhai↗
Massive Chromite in the Brenham Pallasite and the Fractionation of Cr During the Crystallization of Asteroidal Cores
Large (greater than or equal to 2 mm) chromite grains are present in IIIAB iron meteorites and in the main-group a pallasites (PMG), closely related to high-Au IIIAB irons, Pallasites seem to have formed by the intrusion of a highly evolved metallic magma from a IIIAB-like core into fragmented olivine of the overlying dunite mantle. High Cr contents are commonly encountered during the analyses of metallic samples of high-Au IIIAB irons and main-group pallasites, an indication that Cr contents were high in the intruding liquid and that Cr behaved as an incompatible element during the crystallization of the IIIAB magma, contrary to expectations based on the negative IIIAB Cr-Ni and Cr-Au trends among low-Au IIIAB irons. In a region about 10 cm across in the Brenham main-group pallasite massive chromite fills the interstices between olivine grains, the site normally occupied by metal in Brenham and other pallasites. The massive chromite may have formed as a late cumulus phase; because Fe-Ni was also crystallizing, its absence in the chromite-rich region suggests a separation associated with differences in liquid buoyancy. The coexisting chromite and olivine are zoned; in the olivine FeO is highest in pallasitic (olivine-metal) regions, lowest in rims adjacent to chromite, and intermediate in the cores of these olivines. Chromite shows the opposite zoning, with the highest FeO contents at grain edges adjacent to olivine. The observed gradients are those expected to form by Fe-Mg exchange between olivine and chromite during slow cooling at subsolidus temperatures. Compared to normal Brenham, contents of phosphoran olivine and phosphates are higher in the chromitic pallasitic region. We also report data for large-to-massive chromites present in PMG Molong and in high-Au IIIAB Bear Creek that, like Brenham, formed from a highly evolved magma. The Bear Creek chromite has a much lower Mg content than that in the pallasites, implying that, in the PMG, the Mg was extracted from the olivine during high-temperature reaction with the precipitating chromite. There are other circumstantial arguments indicating that Cr was incompatible in the metal during the crystallization of the IIIAB magma, with the concentration in die residual magma rising from an initial value of about 300 micrograms/g to a value around 700 micrograms/g when Bear Creek and Brenham were formed. We consider possible explanations for these negative Cr-Au and Cr-Ni trends and find the most probable one to be that they reflect sampling artefacts resulting from analysts avoiding visible chromite (and the commonly associated phase FeS) when choosing metal samples.
Wasson, John T.↗
Advanced Simulation of ITER Core X-ray Crystal Spectroscopy
X-Ray Simulation Analysis (XRSA) is an analytical ray-tracing mixed code developed specifically for the ITER Core X-Ray Crystal Spectroscopy (XRCS-Core) diagnostic, which employs a dual-reflection configuration incorporating multiple pre-reflectors made of Highly Oriented Pyrolytic Graphite (HOPG) and spherically curved analyzing crystals. The ITER XRCS-Core is designed for high spectral resolution measurement in specific wavelength ranges, including narrow bands around 1.354 Å for W 64+ , 2.19 Å for Xe 51+ , and 2.555 Å for Xe 44+ and Xe 47+ , enabling diagnostic capability across a broad electron temperature range in the ITER plasma. XRSA facilitates efficient simulation of the spectral performance of this complex X-ray spectroscopic system. Recent updates to the XRSA code have incorporated two critical effects: auto-focusing, which specifically applies to HOPG, and polarization. These two effects are particularly important in the dual-reflection configuration used in the ITER XRCS-Core system to provide more accurate modeling results. Here, simulations conducted with the updated code demonstrate that polarization has a substantial impact on the performance of the dual-reflection system. Additionally, the combined influence of polarization and system layout introduces performance variations across channels through the same crystal.
Computer graphics↗
Atomic-scale in situ observation of electron beam and heat induced crystallization of Ge nanoparticles and transformation of Ag@Ge core-shell nanocrystals
Crystallization of amorphous materials by thermal annealing has been investigated for numerous applications in the fields of nanotechnology, such as thin-film transistors and thermoelectric devices. The phase transition and shape evolution of amorphous germanium (Ge) and Ag@Ge core–shell nanoparticles with average diameters of 10 and 12 nm, respectively, were investigated by high-energy electron beam irradiation and in situ heating within a transmission electron microscope. The transition of a single Ge amorphous nanoparticle to the crystalline diamond cubic structure at the atomic scale was clearly demonstrated. Depending on the heating temperature, a hollow Ge structure can be maintained or transformed into a solid Ge nanocrystal through a diffusive process during the amorphous to crystalline phase transition. Selected area diffraction patterns were obtained to confirm the crystallization process. In addition, the thermal stability of Ag@Ge core–shell nanoparticles with an average core of 7.4 and a 2.1 nm Ge shell was studied by applying the same beam conditions and temperatures. The results show that at a moderate temperature (e.g., 385 °C), the amorphous Ge shell can completely crystallize while maintaining the well-defined core–shell structure, while at a high temperature (e.g., 545 °C), the high thermal energy enables a freely diffusive process of both Ag and Ge atoms on the carbon support film and leads to transformation into a phase segregated Ag–Ge Janus nanoparticle with a clear interface between the Ag and Ge domains. In conclusion, this study provides a protocol as well as insight into the thermal stability and strain relief mechanism of complex nanostructures at the single nanoparticle level with atomic resolution.
36 MATERIALS SCIENCE↗
Induced Anisotropy in FeCo-Based Nanocrystalline Ferromagnetic Alloys (HITPERM) by Very High Field Annealing
Very high magnetic field annealing is shown to affect the magnetic anisotropy in FeCo-base nanocrystalline soft ferromagnetic alloys. Alloys of composition Fe(44.5)Co(44.5)Zr(7)B(4) were prepared by melt spinning into amorphous ribbons, then wound to form toroidal bobbin cores. One set of cores was crystallized in a zero field at 600 deg. C for 1 h, then, field annealed at 17 tesla (T) at 480 deg. C for 1 h. Another set was crystallized in a 17-T field at 480 deg. C for 1 h. Field orientation was transverse to the magnetic path of the toroidal cores. An induced anisotropy is indicated by a sheared hysteresis loop. Sensitive torque magnetometry measurements with a Si cantilever sensor indicated a strong, uniaxial, longitudinal easy axis in the zero-field-crystallized sample. The source is most likely magnetoelastic anisotropy, caused by the residual stress from nanocrystallization and the nonzero magnetostriction coefficient for this material. The magnetostrictive coefficient lambda(5) is measured to be 36 ppm by a strain gage technique. Field annealing reduces the magnitude of the induced anisotropy. Core loss measurements were made in the zero-field-crystallized, zero-field-crystallized- than-field-annealed, and field-crystallized states. Core loss is reduced 30%-50% (depending on frequency) by field annealing. X-ray diffraction reveals no evidence of crystalline texture or orientation that would cause the induced anisotropy. Diffusional pair ordering is thought to be the cause of the induced anisotropy. However, reannealing the samples in the absence of a magnetic field at 480 deg. C does not completely remove the induced anisotropy.
FERROMAGNETIC ALLOYS↗
Carbon Solubility in Silicon-Iron-Bearing Metals during Core Formation on Mercury
Recent results obtained from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft showed the surface of Mercury has high S abundances (approximately 4 wt%) and low Iron(II) Oxide abundances (less than 2 wt%). Based on these extreme values, the oxygen fugacity of Mercury's surface materials was estimated to be approximately 3 to 7 log(sub 10) units below the IW buffer (Delta IW-3 to Delta IW-7). This highly reducing nature of the planet has resulted in a large core and relatively thin mantle, extending to only approximately 420 km depth (corresponding to a core-mantle boundary pressure of approximately 4-7 GPa) within the planet. Furthermore, MESSENGER results have suggested the presence of carbon on the surface of the planet. Previous experimental results from have also suggested the possibility of a primary floatation crust on Mercury composed of graphite, produced after a global magma ocean event. With these exotic conditions of this compositional end-member planet, it begs the question, what is the core composition of Mercury? Although no definitive conclusion has been reached, previous studies have made advances towards answering this question. Riner et al. and Chen et al. looked at iron sulfide systems and implemented various crystallization and layered core scenarios to try and determine the composition and structure of Mercury's core. Malavergne et al. examined core crystallization scenarios in the presence of sulfur and silicon. Hauck et al. used the most recent geophysical constraints from the MESSENGER spacecraft to model the internal structure of Mercury, including the core, in a iron-sulfur-silicon system. More recently, Chabot et al. conducted a series of metal-silicate partitioning experiments in a iron-sulfur-silicon system. These results showed the core of Mercury has the potential to contain more than 15 wt% silicon. However, with the newest results from MESSENGER's low altitude campaign, carbon is another potential light element that could be incorporated into Mercury's core. The goal of this study is to determine the carbon concentration at graphite saturation in various silicon-iron bearing metals relevant to possible mercurian core compositions. Future experiments will include the addition of sulfur into these metals.
Vander Kaaden, Kathleen E.↗