Diffusion Of Sulfur Research Articles

Sulfur Diffusion Studies Imitating Recycled Ground-Rubber-Containing Compounds

In-rubber properties of vulcanizates deteriorate in the presence of incorporated recycled ground rubber (GR). This behavior is partly explained by a possible diffusion of sulfur from the rubber matrix into the GR. Therefore, the sulfur concentration and, thus, the crosslink density in the matrix are reduced. This phenomenon was further investigated in this research work using two spatially resolved methods that supplement each other: the diffusion of soluble sulfur in GR-containing compounds was locally investigated via Micro X-Ray Fluorescence analysis. Viscoelastic properties were also determined spatially by the Micro Dynamic-Mechanical Indentation method. Combining the results of both methods, local concentrations of sulfur were related to local viscoelastic properties, revealing great differences in crosslink density at the interface between the GR and matrix material. In this way, it is shown that sulfur is capable of diffusing several mm, which locally doubles its concentration with respect to the sulfur content of the compound formulation. This, in turn, negatively impacts the homogeneity of crosslink density in both the matrix and GR, revealing a local increase in the elastic stiffness of 100 %. In addition, it was found that the vulcanization characteristics of the used polymers determine the amount of sulfur diffusion and, thus, the change in viscoelastic properties.

A distinct role of microstructure on hot corrosion behaviour of additively manufactured IN718

The effect of LPBF-IN718 microstructure on hot corrosion behavior was studied at 650 °C. H-IN718 with <001> oriented grains demonstrate more weight changes than V-IN718 with <110> oriented grains. Detailed characterization analysis corroborates that Rapp-Goto fluxing and sulphidation mechanisms are operating in LPBF-IN718 with 3SM. Further, GDOES confirms the sulphur gradient existence between Air/3SM and 3SM/H-IN718 interfaces. It suggests that <001> oriented grains serve as preferred sites for ion adsorption and reactions, which might facilitate the sulfur diffusion more effectively than other grain orientations. As a result, oxy-anions generated during sulfidation enhance the fluxing mechanism, increasing weight gain in H-IN718.

One-pot Synthesis of High-capacity Sulfur Cathodes via In-situ Polymerization of a Porous Imine-based Polymer.

Lithium-ion batteries, essential for electronics and electric vehicles, predominantly use cathodes made from critical materials like cobalt. Sulfur-based cathodes, offering a high theoretical capacity of 1675mAhg-1 and environmental advantages due to sulfur's abundance and lower toxicity, present a more sustainable alternative. However, state-of-the-art sulfur-based electrodes do not reach the theoretical capacities, mainly because conventional electrode production relies on mixing of components into weakly coordinated slurries. Consequently, sulfur's mobility leads to battery degradation - an effect known as the "sulfur-shuttle". This study introduces a solution by developing a microporous, covalently-bonded, imine-based polymer network grown in-situ around sulfur particles on the current collector. The polymer network (i) enables selective transport of electrolyte and Li-ions through pores of defined size, and (ii) acts as a robust host to retain the active component of the electrode (sulfur species). The resulting cathode has superior rate performance from 0.1C (1360mAhg-1) to 3C (807mAhg-1). Demonstrating a high-performance, sustainable sulfur cathode produced via a simple one-pot process, our research underlines the potential of microporous polymers in addressing sulfur diffusion issues, paving the way for sulfur electrodes as viable alternatives to traditional metal-based cathodes.

Ein‐Topf‐Synthese von Schwefelkathoden mit hoher Kapazität durch In situ‐Polymerisation eines porösen Polymers auf Iminbasis

AbstractLithium‐Ionen‐Batterien, die für elektronische Geräte und Elektrofahrzeuge unerlässlich sind, verwenden hauptsächlich Kathoden aus kritischen Materialien wie Kobalt. Eine nachhaltigere Alternative sind Kathoden auf Schwefelbasis, die eine hohe theoretische Kapazität von 1675 mAh g−1 und Umweltvorteile bieten, da Schwefel reichlich vorhanden und weniger toxisch ist. Moderne Elektroden auf Schwefelbasis erreichen die theoretische Kapazität jedoch nicht, vor allem weil die herkömmliche Elektrodenherstellung auf dem Mischen der Komponenten zu schwach koordinierten Aufschlämmungen beruht. Infolgedessen führt die Mobilität des Schwefels zu einer Degradation der Batterie – ein Effekt, der als „Schwefel‐Shuttle“ bekannt ist. Diese Studie stellt eine Lösung vor, indem ein mikroporöses, kovalent gebundenes, iminbasiertes Polymernetzwerk entwickelt wird, das in situ um die Schwefelpartikel auf dem Stromkollektor wächst. Das Polymernetzwerk (i) ermöglicht den selektiven Transport von Elektrolyt und Li‐Ionen durch Poren definierter Größe und (ii) fungiert als robuster Wirt, um die aktive Komponente der Elektrode (Schwefelspezies) zurückzuhalten. Die resultierende Kathode hat eine überlegene Leistung von 0,1 C (1360 mAh g−1) bis 3 C (807 mAh g−1). Mit der Demonstration einer leistungsstarken, langlebigen Schwefelkathode, die in einem einfachen Eintopfverfahren hergestellt wurde, unterstreicht unsere Forschung das Potenzial mikroporöser Polymere bei der Lösung von Schwefeldiffusionsproblemen und ebnet den Weg für Schwefelelektroden als praktikable Alternative zu herkömmlichen Kathoden auf Metallbasis.

SpuBase: Solar Wind Ion Sputter Database for Modeling Purposes

We supply the modelers with a database, SpuBase (doi:10.5281/zenodo.10783295), that is based on the latest approach for obtaining solar wind ion sputter yields in agreement with experimental sputter data outlined in Jäggi et al. We include an overview of sputter results for typical Lunar and Hermean surfaces. To obtain total sputter yields for any given surface, we perform a mass balance of individual mineral sputter yields. For a set of impact angles, the angular and energy distribution data are scaled according to the sputter yield, summed up and fitted to obtain one probability distribution for each chemical element involved. Comparison of the results from different geochemical terranes on the Moon and Mercury has shown that variations in the abundance of silicates result in comparable energy and angular distribution data owing to the underlying model assumptions. The inclusion of sulfides relevant for Mercury, however, significantly affects the energy and angular distributions of sputtered particles. The application of the damage-driven sulfur diffusion rate in FeS in all sulfur-bearing minerals results in 35 times lower sulfur yields on average and a less prominent forward sputtering of sulfur at grazing incidence angles.

Facile diffusion of sulfur and fluorine into a-IGTO thin films for high-performance and reliability of transparent amorphous oxide semiconductor thin-film transistors

Facile diffusion of sulfur and fluorine into a-IGTO thin films for high-performance and reliability of transparent amorphous oxide semiconductor thin-film transistors

Surface Diffusion on Ag(100) and Cu(100) Electrodes in the Presence of Low Coverage Halides

Atomic-scale processes at the electrochemical interface are of great importance to not only the fundamental research of electrochemistry, but also the newly developing technologies including energy conversion and bottom-up nanofabrication. In particular, the surface-active additive, such as halides, can strongly affect these processes, hence change the micro or macro behaviors of the studied system. For example, adding halides to the electrolyte is a feasible way to change the shape of the synthesized nanoparticles [1]. Besides, the modification of catalytic activity and selectivity by halide-containing electrolyte in CO2 electrochemical reduction on Cu surface has also been reported [2]. Therefore, a detailed and quantitative study of the electrochemical interface processes in the presence of co-adsorbed halides species may pave the way for more efficient design of electrochemistry-related procedures. Surface diffusion of adsorbates on the electrode is one of these processes, playing an important role e.g. in electrocatalysis, and electrochemical metal deposition or dissolution. Video-rate scanning tunneling microscope (Video-STM) in an electrochemical environment enables the recording of real-time videos of atomic-scale motion on electrode surfaces, which makes the observation and quantification of surface diffusion of individual adsorbed atoms and molecules possible [3].Halides form strongly adsorbed c(2x2) structures on various metal surfaces at the positive end of the double layer range. Our previous studies revealed a significant potential dependence of the surface diffusion of sulfur on Cu(100) and Ag(100) electrodes in the presence of close-packed c(2x2) halide adlayers [3,4]. In this range, sulfur atoms diffuse by hopping between neighboring sites of the c(2x2) lattice. The mobility of the atoms exponentially decreases with increasing potential, following a linear relationship between the potential and the diffusion barrier. More specifically, for a given system, the change of the diffusion barrier with the potential can be attributed to the change in the surface dipole moment along the diffusion path. Further studies demonstrated that the potential-dependence is independent of the diffusing species, which means that the co-adsorbed halides may dominate the change of the dipole moment.Here, instead of the c(2x2) potential range, the surface diffusion is studied in the negative potential range of Br-covered Ag(100), where Br forms a highly mobile lattice gas on the surface and the coverage increases with potential. Sulfur diffusion via hopping between neighboring sites of the (1x1) Ag substrate lattice was observed. Surprisingly, the diffusion rates increase with increasing potential, suggesting a different diffusion mechanism in the presence of low coverage halides. However, there is a wide potential gap between (1x1) and c(2x2) range, where quantitative Video-STM studies are difficult due to the high mobility of sulfur atoms at room temperature. Therefore, we also collected diffusion data at low temperature, which show the same potential dependence as the room temperature data, apart from a reduced mobility. These experiments allowed to show that the crossover between increasing and decreasing diffusion rates with potential indeed occurs at the phase transition between the disordered and the c(2x2) ordered Br adlayer, resulting in a maximum diffusion rate near the onset of Br adlayer ordering.In addition, the diffusion of CH3Sad on c(2x2)-Brad covered Cu(100) was studied to test the hypothesis that the inverted potential dependence (the diffusion rates increase with increasing potential in the ordered coverage range) of Sad diffusion on this surface is attributed to a Br-induced exchange diffusion [5]. The methyl group should inhibit the exchange of sulfur with a Cu surface atom and thus suppress an exchange mechanism for steric reasons. We therefore expect that the diffusion of CH3Sad on c(2x2)-Brad covered Cu(100) shows the same potential dependence as the diffusion of Sad and CH3Sad on c(2x2)-Clad covered Cu(100) [6-7], that is, a decrease of the diffusion rate with increasing potential.We acknowledge financial support by the Deutsche Forschungsgemeinschaft via project no. 504552981.

Measurement of Surface Diffusion at Electrochemical Interfaces Using in Situ Linear Optical Diffraction

Surface diffusion processes play an important role in many reactions at electrode surfaces and are of relevance to electrocatalysis, electrodeposition, and many other areas. Such processes have therefore been extensively studied on solids under vacuum conditions with a variety of different methods. In sharp contrast, only few studies exist to measure surface diffusion in electrochemical environment due to the lack of suitable methodology. We aim on partially filling this gap by introducing the all-optical in situ LOD methodology, which allows to measure surface diffusion rates over a wide range and thus overcomes limitations of established methods that are mostly restricted to slow diffusion rates. The method is based on the generation of a periodic spatial modulation of adsorbates using two interfering laser pulses. The subsequent equilibration of this pattern and thus the diffusion rate of adsorbates is probed by the linear optical diffraction (LOD) signal from a second laser.First proof-of-principle measurements were performed on sulfur diffusion on the Pt(111) electrode. For this purpose, the optical and electrochemical properties of this systems were investigated first, including studies of the optical reflectance change induced by chemisorbed sulfur (Sad) and investigations of the Sad oxidation mechanism. The subsequent studies of Sad surface diffusion revealed potential and coverage dependent diffusion rates which were at least an order of magnitude faster than under vacuum conditions. Supported by numerical simulations, the implications of strong adsorbate-adsorbate interaction combined with different grating modulation depths to the temporal evolution of the LOD signal were demonstrated and data accuracy and pitfalls of the method were discussed.Kattwinkel and Magnussen, ACS Meas. Sci. Au, in press (2023), https://doi.org/10.1021/acsmeasuresciau.2c00066Kattwinkel and Magnussen, Electrochimica Acta 434, 141297 (2022), https://doi.org/10.1016/j.electacta.2022.141297

Desulfurization Behavior of FeNi-Based Expansion Alloy Melt Using CaO-SiO2-MgO-Al2O3-CaF2 Slag

The effects of slag components on the sulfur distribution ratio {(wt.%S)/[wt.%S]} were analyzed using thermodynamic calculations. On this basis, the effects of the slag with different binary basicities (wt.% CaO/wt.% SiO2 = 3.0, 5.0, 7.0, 9.0 and 11.0) and Al2O3 contents (wt.% Al2O3 = 12, 16, 20 and 24) on the desulfurization behavior were investigated. The results show that the binary basicity and Al2O3 content were the main factors that affected the desulfurization. And an increase in the binary basicity and a decrease in the content of Al2O3, increase the sulfide capacity of the slag. In the early stage of the smelting process, the desulfurization process was limited due to the high content of oxides, such as FeO and MnO in the slag, and the sulfur content in the alloy melt reached 35 ppm. After the final deoxidation of the Si-Ca alloy, the desulfurization rate was significantly increased, and the maximum desulfurization rate reached 44.12%. During the ladle standing, the sulfur content in the alloy melt changed little because of the limitation of kinetics. The rate-limiting step of the desulfurization process was the diffusion of sulfur in the alloy melt.

Effect of trace sulfur on the hot corrosion resistance of Ni-base single crystal superalloy

The effect of sulfur on the hot corrosion resistance of Ni-base single crystal superalloy was investigated in Na2SO4 salt at 900 °C in static air. The results indicate that the corrosion resistance of the superalloy is significantly degraded even with several ppm contents of sulfur in the alloy. High sulfur content in the alloy causes the oxide layer to bulge and significantly shortens the corrosion incubation period. The accelerated corrosion process is attributed to the outward diffusion of sulfur from the alloy promoting S segregation at the oxide/metal interface and hence favors crack premature initiation.

Analysis of CdSe as an alternative buffer layer for Sb2Se3 solar cells

In this work, for the first time, CdSe is applied as a buffer layer on thermally evaporated Sb2Se3-based solar cells on superstrate configuration. The influence of this buffer layer on the growth of Sb2Se3 and the performance of the finished devices have been analyzed and compared with the typical CdS/Sb2Se3 junction.Selenium vacancies in Sb2Se3 thin film act as recombination centres, for this reason applying an excessive amount of Se is beneficial to the performance of the devices. In the case of the CdS/Sb2Se3 structure, the high concentration gradient enhances the selenium diffusion into the CdS and the sulphur diffusion into the Sb2Se3 resulting in an increased number of defects. The replacement of CdS with CdSe would allow us to avoid this detrimental effect.In this work, we show that CdSe improves the external quantum efficiency in the entire light spectrum, increasing the average current density of the devices up to 2 mA/cm2 in comparison to CdS/Sb2Se3. Also, the fill factor improves while the Voc slightly decreases due to the narrower band gap. Moreover, CdSe/Sb2Se3 samples demonstrate excellent stability under accelerated stability tests.

Molecular simulation study of liquid sulfur adsorption and diffusion in calcite nanoscale slits under varying temperature and pressure conditions

In the late stages of extensive development of high-sulfur carbonate gas reservoirs, pressure decline leads to sulfur enrichment, and when the temperature exceeds sulfur's melting point, sulfur precipitates in a liquid form, severely restricting the exploitation of high-sulfur carbonate gas reservoirs. However, the adsorption mechanism of sulfur deposition remains poorly understood. In this study, we investigated the microscopic adsorption mechanism of liquid sulfur in calcite nanopores using molecular simulation methods. Our research revealed that liquid sulfur adsorption in calcite nanopores is primarily influenced by pore size. When the pore size is less than 160 Å, multilayer adsorption dominates, with a single-layer sulfur film thickness of approximately 5 Å. At the nanoscale, 1 g of calcite with a 40 Å nanopore structure exhibits excess adsorption of liquid sulfur ranging from 0.00734 to 0.0279 g. As pressure increases, the adsorption of two or more layers intensifies, while the diffusion coefficient decreases. Conversely, as temperature rises, the density of each layer decreases, and the diffusion coefficient increases. Simultaneously, the diffusion coefficient of liquid sulfur in calcite slits exhibits a power function increase as the pore size enlarges. Under a pressure of 15 MPa, when the temperature increases from 420 K to 480 K, the diffusion coefficient increases from 6.96 × 10−11 m²/s to 3.51 × 10−10 m²/s. This study provides valuable insights into the adsorption and diffusion behavior of liquid sulfur in calcite nanopores, which can inform the development of high-sulfur carbonate reservoirs.

Characteristics of product layer and effects of sulfur-bearing ions on pyrite leaching in sodium aluminate solutions

During the utilization of high-sulfur bauxite by the Bayer process, the pyrite will react with sodium aluminate solution and generate various sulfur-bearing ions, however, the effect of these ions on pyrite leaching is seldom studied. This work clarifies the reaction mechanism of pyrite in various sulfur-bearing sodium aluminate solutions by characterizing electrochemistry and the product layers. The results show that the sulfur leaching efficiency are 48.0, 56.2, 23.1, 90.6 and 58.3 % in sulfur-free, S2-, S2O32-, SO32- and SO42--bearing sodium aluminate solutions at 260 °C for 40 min, respectively. With the disproportionation of S2O32- and accumulation of products, a dense sulfur-rich layer formed on the surface of pyrite retards the diffusion of sulfur into solution. However, the presence of SO32- can catalyze the transformation of pyrite into hematite plates, forming a loose layer which accelerates the diffusion of S2- and S2O32- into solution. In the presence of S2- and SO42-, the formation of easily removed products from surface slightly promote the reaction between pyrite and sodium aluminate solution.

Sulphur diffusion through a growing chromia scale and effects of water vapour

Fe-30Cr (wt%) alloy was exposed to Ar-0.5%SO2 and Ar-10%H2O-0.5%SO2 gases at 650 °C, forming Cr2O3 scales. In dry SO2 for 20 h, sulphur enrichment and scattered Cr-sulphides were observed at the scale-alloy interface, together with internal Cr-sulphide precipitates. After 100 h, sulphur disappeared from the interface, while more internal Cr-sulphides were produced. In wet SO2, the sulphur enrichment and Cr-sulphides were maintained in both times, but no internal sulphidation was seen. Atom probe analysis revealed sulphur enrichment on chromia grain boundaries in both gases, to a greater extent in wet SO2. These effects are discussed in terms of chromia grain boundary diffusion.

Effect of Compressed Natural Gas (CNG) on corrosion behaviour of brass valve of CNG cylinder

In this case study, failure root cause analysis of the Compressed Natural Gas (CNG) cylinder brass valve was investigated. Detailed metallurgical analysis of the cracked CNG valve was performed. Higher content of sulphur and carbon while depletion of zinc observed by Scanning Electron Microscope (SEM) - Energy Dispersive Spectroscopy (EDS) analysis at crack location and on black corrosion product. Microstructure analysis of the cross section near to fracture surface indicated dendritic structure of alpha and beta phase and depletion of zinc from beta phase at the inner diameter (ID) of valve and near to crack region by SEM-EDS analysis. The overall observation indicates that the failure of brass valve body of CNG cylinder was due to the dezincification. As per the IS 15958 standard, the CNG valves, which have failed, may be due to more than specified limit of the corrosive components (S and CO2) in the CNG. This resulted into diffusion of sulphur and carbon dioxide in beta phase at internal surface of valve. Adsorbed sulphur and CO2 from the CNG lead to the preferential dezincification from beta phase throughout the inner diameter (ID) of the valve. Electrochemical reaction during dezincification lead to weak spongy copper layer, which subsequently initiated and propagated crack to the outer diameter (OD) and resulted into leakage and failure.

Multiple Effects of High Surface Area Hollow Nanospheres Assembled by Nickel Cobaltate Nanosheets on Soluble Lithium Polysulfides

Inhibiting the shuttle effect of soluble polysulfides and improving slow reaction kinetics are key factors for the future development of Li-S batteries. Herein, edelweiss shaped NiCo2O4 hollow nanospheres with a high surface area were prepared by a simple template method to modify the separator to realize multiple physical constraints and strong chemical anchoring on the polysulfides. On one hand, the good electrolyte wettability of NiCo2O4 promoted the migration of Li-ions and greatly improved the dynamics. On the other hand, mesoporous NiCo2O4 nanomaterials provided many strong chemical binding sites for loading sulfur species. The hollow structure also provided a physical barrier to mitigate the sulfur species diffusion. Therefore, the modified separator realized multiple physical constraints and strong chemical anchoring on sulfur species. As a result, the sulfur cathode based on this composite separator showed significantly enhanced electrochemical performance. Even at 4 C, a high capacity of 505 mAh g-1 was obtained, and about 80.6% could be retained after 300 cycles.

Understanding the growth mechanism of BaZrS3 chalcogenide perovskite thin films from sulfurized oxide precursors

Barium zirconium sulfide (BaZrS3) is an earth-abundant and environmentally friendly chalcogenide perovskite with promising properties for various energy conversion applications. Recently, sulfurization of oxide precursors has been suggested as a viable solution for effective synthesis, especially from the perspective of circumventing the difficulty of handling alkali earth metals. In this work, we explore in detail the synthesis of BaZrS3 from Ba-Zr-O oxide precursor films sulfurized at temperatures ranging from 700 °C to 1000 °C. We propose a formation mechanism of BaZrS3 based on a two-step reaction involving an intermediate amorphization step of the BaZrO3 crystalline phase. We show how the diffusion of sulfur (S) species in the film is the rate-limiting step of this reaction. The processing temperature plays a key role in determining the total fraction of conversion from oxide to sulfide phase at a constant flow rate of the sulfur-containing H2S gas used as a reactant. Finally, we observe the formation of stoichiometric BaZrS3 (1:1:3), even under Zr-rich precursor conditions, with the formation of ZrO2 as a secondary phase. This marks BaZrS3 quite unique among the other types of chalcogenides, such as chalcopyrites and kesterites, which can instead accommodate quite a large range of non-stoichiometric compositions. This work opens up a pathway for further optimization of the BaZrS3 synthesis process, straightening the route towards future applications of this material.

Development of a Novel, Impurity-Scavenging, Corrosion-Resistant Coating for Ni-Based Superalloy CMSX-4

Sulfur, a common impurity arising from atmospheric and environmental contamination, is highly corrosive and detrimental to the lifespan of nickel superalloys in jet engines. However, sulfur-scavenging coatings have yet to be explored. Our study presents the successful development of a stable, uniform, impurity-scavenging Ni-Mn coating on Ni-based superalloy CMSX-4, through electroplating. The coating was characterised via combined scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. An optimal coating thickness of > 600 nm was deposited. The coated alloy was exposed to corrosive salt mixture 98% Na2SO4–2% NaCl at 550 °C for 100 h, mimicking engine exposure conditions, thereby proving that the coating successfully trapped sulfur and prevented its diffusion into an underlying alloy. This work presents a promising development for the prevention of sulfur-induced corrosion in industrial setting such as gas turbine engine, where the effects of sulfur diffusion into the bulk alloy could lead to premature failure.Graphical

Effect of temperature on hot corrosion of nickel-based alloys for 700 °C A-USC power plants

Nickel-based alloys were exposed to a synthetic flue gas at varying temperatures from 700 °C to 800 °C. Two main damage mechanisms were revealed, including general surface oxidation caused by eutectic melting of sulfates and internal cracking caused by sulfur diffusion. The damage level of the alloys did not monotonically increase with temperature. Significant weight losses due to molten sulfate corrosion were found at 700–760 °C, and the minimum damage was at 780 °C. Nimonic 263 with the highest cobalt, titanium contents and the lowest aluminum content exhibited the best resistance to both molten sulfate corrosion and sulfur invasion.

Space Weathering Effects in Troilite by Simulated Solar-Wind Hydrogen and Helium Ion Irradiation.

Space weathering is a key process in the interpretation of airless planetary surfaces. As we engage new missions to planetary objects with potentially novel surfaces such as 16 Psyche, there is renewed interest in expanding our knowledge of space weathering effects to a wider variety of analog materials, including the physical/chemical effects of solar‐wind ions on planetary regoliths. We have experimentally simulated the effects of solar ions on two polished thick sections of meteoritic troilite (FeS) via irradiation with 1 keV hydrogen (H+) and 4 keV helium (He+), to investigate effects resulting from different ion species. We detected depletion of sulfur over the course of each irradiation using in situ X‐ray photoelectron spectroscopy. Sulfur depletion rates were surprisingly similar for H+ and He+, interpreted as a function of subsurface ion‐activated diffusion. By comparing XPS‐derived elemental abundances with SDTrimSP computer simulations, we further quantified sulfur diffusion, sputtering yield, and altered‐layer composition with respect to incident‐ion fluence, and accounted for the influence of surface oxidation due to atmospheric sample storage. Using scanning electron microscopy, we detected an increase in nanoscale surface roughness resulting from the irradiation, which we quantified using atomic force microscopy. Based on these results, we estimate that an exposure time of order 103 Earth‐years is required for troilite on Psyche to reach equilibrium sulfur depletion within the first atomic layer.