Bulk Sulfur Content Research Articles

Anomalous texture developments, new two-dimensional primary growth modeling, and fully [formula omitted]-textured electrical steels

Various anomalous texture developments have been investigated in C-free and AlN-free electrical sheets, and new two-dimensional (2D) primary growth modeling has been carried out to understand them. In one-stage cold-rolled sheets, the primary (001) texture pole intensity (TPI) increases with decreasing bulk sulfur content and sheet thickness. The high-index hkl and (001) TPIs increase concurrently with increasing annealing time. In other case, the (001) TPI increases to a maximum after which it rather decreases. In two-stage cold-rolled sheets showing the primary 001+(110) texture, the (001) TPI increases with decreasing sheet thickness and second-stage cold-rolling ratio (CRR). The final (001) grain size is determined by the combination between sheet thickness, bulk sulfur content, CRR, heating rate, and MnS precipitation reaction. New 2D primary growth modeling supports strongly that the higher surface energy grains as well as the lower surface energy ones can grow, although their growth is transient and peripheral. Several unique concepts implied in the 2D growth maps well explain the various anomalous texture developments. The (111) island grains in electrical sheets fully (001)-textured after final annealing are always consumed with further annealing, regardless of the grain size. However, the (110) island grains may grow or not, which depends on the grain size and the number of neighboring ones. Fully developed (110)[001] Goss or (001) texture can be obtained from electrical sheets of the same composition, depending on the processing variables. Fully (001)-textured electrical sheets of high magnetic properties were developed through the experimental results and the 2D growth modeling.

Evidence for Seawater Retreat With Advent of Meghalayan Era (∼4200 a BP) in a Coastal Harappan Settlement

AbstractThe transformation of mature (urbanized) phase of the ancient Indus civilisation between ∼4200 and 3800 years Before Present (yr BP) overlaps with the beginning of the Meghalayan Age (∼4200 ± 100 yr BP). Though exact cause(s) for decline of urbanized Indus phase are not yet clear, researchers continue to debate whether monsoonal dryness was the sole cause or several other regional factors manifested in a compounding manner. Here, we show a regional relative sea level fall in the downstream area of Indus habitation (south‐western Gujarat region) which initiated at 4150 ± 230 and continued up to 3625 ± 200 yr BP. We provide a multi‐proxy (chronological, sedimentological, mineralogical, isotopic and elemental abundance) data set from a well‐dated vertical sediment trench from Lothal (ancient dockyard area of Indus era) to support this inference. Chief proxies used for inferring the relative sea level fall were bulk sediment carbon and sulfur contents along with their stable isotopes (δ13C and δ34S) and foraminiferal assemblage. The conspicuous shifts in majority of proxies hint at a lowering of sea stand at the regional level that likely dried this ancient Harappan dockyard (used for sea trade). Findings of our study possess implications for Holocene climate changes and their plausible impact(s) on Harappan trade and culture. Additionally, it invites evidences for large scale geological changes at ∼4200 yr BP distinct to the Meghalayan era.

Production and Preservation of Sulfide Layering in Mercury's Mantle

AbstractA striking feature of Mercury's volcanic surface is its high S and low FeO contents, which is thought to be produced by very reducing conditions compared to other terrestrial bodies. Experiments show that S solubility in silicate melts increases to % wt levels for oxygen fugacities lower than three log units below the iron‐wustite (IW) buffer. During magma ocean solidification, large amounts of sulfide could potentially precipitate. This work investigates the effects of primordial sulfide layering on the first 750 Myr of Mercury's mantle dynamics. It is proposed that sulfide layering could have been produced by fractional solidification in the highly reduced Mercury magma ocean (MMO). Such chemical layering implies mantle sources with variable sulfur contents that might have played an important role in early Mercurian magmatism. Our models investigate the production of sulfide‐rich layers and their preservation during post‐MO solid‐state mantle dynamics. An intriguing question is the role of these sulfide‐rich layers on mantle dynamics as they are expected to incorporate a substantial amount of heat‐producing elements (U, Th, and K). We use experimentally determined sulfur solubility in silicate melts to predict the depth at which sulfides precipitate in the MMO. The model produces primordial sulfide layers whose thickness and locations depend upon the oxygen fugacity (fO2) and initial sulfur content (Sinit) of the MMO. Several geodynamic regimes have been identified in the fO2‐Sinit space. This study shows that oxygen fugacity, bulk sulfur content, and sulfide segregation are key for the early thermochemical evolution of Mercury.

Extracellular enzyme activities of estuarine mudflats in French Guiana in relation with environmental factors across spatial and seasonal scales

The main aim of this study was to investigate the dynamic of extracellular enzyme activities within estuarine intertidal mudflats and to explore their potential environmental driving factors. Estuarine slikkes of the main rivers of French Guiana were sampled during two annual contrasted hydro-climatic seasons (wet and dry) over a two-year period (n = 38). The spatio-temporal variability of four enzyme activities (alkaline phosphomonoesterase, arylsulfatase, β-glucosidase, urease) was assessed and physico-chemical analyses (dry bulk density, salinity, pH, carbon, nitrogen and sulfur content) of sediments were carried out. Results showed that the hydro-sedimentary specificities of each estuary, combined with the alternation of hydro-climatic seasons, had a strong influence on sediment physico-chemical characteristics. They revealed a gradient of mudflats under mainly continental versus marine influence. Mudflats under mainly continental influence were characterized by oligohaline pore-waters, more acidic pH and relatively high organic matter content, and conversely for slikkes under mainly marine influence. Crossing of physico-chemical and functional data showed that the main factor associated with enzyme activities was the total nitrogen content. To a lesser extent, pH and organic carbon content were also related to enzyme activities, but these relationships could not be generalized to all enzymes. Moreover, relationships between enzyme activities and physico-chemical variables were not dependent on the mudflat types, except for the β-glucosidase which showed higher activity under mainly marine influence. Finally, relationships between enzyme activities and physico-chemical variables were not dependent on the seasons, except for alkaline phosphomonoesterase and urease activity, which showed opposite patterns according to seasons.

Petrological characteristics and volatile content of magma of the 1979, 1989, and 2014 eruptions of Nakadake, Aso volcano, Japan

Petrological observations and chemical analyses of melt inclusions in scoria were used to investigate the magma ascent and eruption processes of the 1979, 1989, and 2014 eruptions of Nakadake, Aso volcano, Japan. Major elements and sulfur contents of the melt inclusions were determined using an electron probe microanalyzer, and their water and CO2 contents were determined using secondary ion mass spectrometry. Five scoria specimens from the 2014 eruptions had an andesite composition identical to the scoria from the 1979 and 1989 eruptions. Thermometry using the chemical composition of the groundmass and the rims of the phenocrysts indicated that the temperature of the 2014 magma was 1042–1092 °C. Melt inclusions in plagioclases, clinopyroxenes, and olivines in the 2014 scoria had an andesite composition similar to that of the groundmass. The volatile content of the melt inclusions was 0.6–0.8 wt% H2O, 0.003–0.017 wt% CO2, and 0.008–0.036 wt% S. The variation in CO2 and S content of the melt inclusions was not correlated with the K2O content, suggesting that the magma degassed as pressure decreased. Melt inclusions in plagioclases, clinopyroxenes, and olivines from the 1979 and 1989 scoria had similar major elements and volatile content to the 2014 eruption specimens. The similarity in chemical composition of both the whole-rock and melt inclusions among all samples suggests that the magmas of these eruptions were derived from the same magma chamber. The gas saturation pressure estimated from the H2O and CO2 contents of the 1979, 1989, and 2014 scoria ranged from 18 to 118 MPa, corresponding to depths of 1–4 km. Comparison of this depth with geophysical observations suggests that the inclusion entrapments occurred in the upper part of the magma chamber and/or a conduit. By combining the melt inclusion analysis with volcanic gas observations, we estimated the bulk volatile content of the magma. Based on the bulk sulfur content of the magma and the SO2 flux between January 2014 and December 2017, the amount of degassed magma over that period was estimated to be the equivalent of 1–3 km3 of dense rock. The estimated volume was more than 600 times larger than that of products erupted during the same period. This suggests that magma degassing occurred at several depths in the magma chamber due to magma convection in a conduit.

Cube + Goss Textured Electrical Steels

After final annealing, the cube + Goss texture is stronger at the higher final thickness reduction. The annealing texture becomes stronger with the decreasing bulk sulfur content. At a fixed bulk sulfur content, the cube + Goss texture is well developed under a pure hydrogen atmosphere compared with a mixed-gas atmosphere. The excellent magnetic properties are obtained from the strip containing the bulk sulfur content of 6 ppm.

Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf‐W Chronometry of Iron Meteorites

AbstractIron meteorites provide some of the most direct insights into the processes and timescales of core formation in planetesimals. Of these, group IVB irons stand out by having one of the youngest 182Hf‐182W model ages for metal segregation (2.9 ± 0.6 Ma after solar system formation), as well as the lowest bulk sulfur content and hence highest liquidus temperature. Here, using a new model for the internal evolution of the IVB parent body, we show that a single stage of metal‐silicate separation cannot account for the complete melting of pure Fe metal at the relatively late time given by the Hf‐W model age. Instead, a complex metal‐silicate separation scenario is required that includes migration of partial silicate melts, formation of a shallow magma ocean, and core formation in two distinct stages of metal segregation. In the first stage, a protocore formed at ≈1.5 Ma via settling of metal particles in a mantle magma ocean, followed by metal segregation from a shallow magma ocean at ≈5.4 Ma. As these stages of metal segregation occurred at different times, the two metal fractions had different 182W compositions. Consequently, the final 182W composition of the IVB core does not correspond to a single differentiation event, but represents the average composition of early‐ and late‐segregated core fractions. Our best fit model indicates an ≈100 km radius for the IVB parent body and provides an accretion age of ≈0.1–0.5 Ma after solar system formation. The computed solidification time is, furthermore, consistent with the Re‐Os age for crystallization of the IVB core.

Mass independent sulfur isotope signatures in CMs: Implications for sulfur chemistry in the early solar system

We have investigated the quadruple sulfur isotopic composition of inorganic sulfur-bearing phases from 13 carbonaceous chondrites of CM type. Our samples include 4 falls and 9 Antarctic finds. We extracted sulfur from sulfides, sulfates, and elemental sulfur (S0) from all samples. On average, we recover a bulk sulfur (S) content of 2.11±0.39wt.% S (1σ). The recovered sulfate, S0 and sulfide contents represent 25±12%, 10±7% and 65±15% of the bulk S, respectively (all 1σ). There is no evidence for differences in the bulk S content between falls and finds, and there is no correlation between the S speciation and the extent of aqueous alteration. We report ranges of Δ33S and Δ36S values in CMs that are significantly larger than previously observed. The largest variations are exhibited by S0, with Δ33S values ranging between −0.104±0.012‰ and +0.256±0.018‰ (2σ). The Δ36S/33S ratios of S0 are on average −3.1±1.0 (2σ). Two CMs show distinct Δ36S/33S ratios, of +1.3±0.1 and +0.9±0.1. We suggest that these mass independent S isotopic compositions record H2S photodissociation in the nebula. The varying Δ36S/Δ33S ratios are interpreted to reflect photodissociation that occurred at different UV wavelengths. The preservation of these isotopic features requires that the S-bearing phases were heterogeneously accreted to the CM parent body. Non-zero Δ33S values are also preserved in sulfide and sulfate, and are positively correlated with S0 values. This indicates a genetic relationship between the S-bearing phases: We argue that sulfates were produced by the direct oxidation of S0 (not sulfide) in the parent body. We describe two types of models that, although imperfect, can explain the major features of the CM S isotope compositions, and can be tested in future studies. Sulfide and S0 could both be condensates from the nebula, as the residue and product, respectively, of incomplete H2S photodissociation by UV light (wavelength <150nm). This idea requires that FeS formation and the S0 condensation co-occur. As an alternative, ice accretion to the CM parent body could allow the delivery of S-MIF in CMs. In that case, sulfides would have been the only S-bearing condensate in CM precursors, and S0 would have been derived from the oxidation of H2S trapped in ices, after its photodissociation at low temperature (<500K) in the nebula. In our models, the observations of H2S UV photodissociation is required to occur at the disk surface, and allowed in nebular environments with canonical C/O ratios. Vertical motions in the disk would redistribute phases that condensed at high altitude to the midplane, where they accreted in the phases that make up the chondritic matrix.

Dependence of Elevated Temperature Intergranular Cracking on Grain Size and Bulk Sulfur Content in TP347H Austenitic Stainless Steels

Dependence of Elevated Temperature Intergranular Cracking on Grain Size and Bulk Sulfur Content in TP347H Austenitic Stainless Steels

New bulk sulfur measurements of Martian meteorites and modeling the fate of sulfur during melting and crystallization – Implications for sulfur transfer from Martian mantle to crust–atmosphere system

Sulfur storage and transport between different reservoirs such as core, mantle, crust and atmosphere of Mars are tied to igneous processes. Martian meteorites carry a record of mantle melting and subsequent differentiation history of Martian magmas. Investigation of S geochemistry of Martian meteorites can thus provide an understanding of how S is transferred from the Martian interior to the exosphere. In this study we measured bulk S concentration of 7 Martian meteorites and modeled the behavior of S during both isobaric crystallization of primary Martian magmas and isentropic partial melting of Martian mantle. Comparisons between measured data and modeled results suggest that (1) sulfides may become exhausted at the source during decompression melting of the mantle and mantle-derived basalts may only become sulfide-saturated after cooling and crystallization at shallow depths and (2) in addition to degassing induced S loss, mixing between these differentiated sulfide-saturated basaltic melts and cumulus minerals with/without cumulate sulfides could also be responsible for the bulk sulfur contents in some Martian meteorites. In this case, a significant quantity of S could remain in Martian crust as cumulate sulfides or in trapped interstitial liquid varying from 2 to 95 percent by weight. Our modeling also suggests that generation of sulfide-undersaturated parental magmas requires that the mantle source of Martian meteorites contain <700–1000 ppm S if melting degree estimation of 2–17 wt.% based on compositions of shergottites is relevant.

Surface and bulk characterization of an ultrafine South African coal fly ash with reference to polymer applications

South African coal-fired power stations produce about 25 million tons of fly ash per annum, of which only approximately 5% is currently reused. A growing concern about pollution and increasing landfill costs stimulates research into new ways to utilize coal fly ash for economically beneficial applications. Fly ash particles may be used as inorganic filler in polymers, an application which generally requires the modification of their surface properties. In order to design experiments that will result in controlled changes in surface chemistry and morphology, a detailed knowledge of the bulk chemical and mineralogical compositions of untreated fly ash particles, as well as their morphology and surface properties, is needed. In this paper, a combination of complementary bulk and surface techniques was explored to assess the physicochemical properties of a classified, ultrafine coal fly ash sample, and the findings were discussed in the context of polymer application as fillers. The sample was categorized as a Class F fly ash (XRF). Sixty-two percent of the sample was an amorphous glass phase, with mullite and quartz being the main identified crystalline phases (XRD, FTIR). Quantitative carbon and sulfur analysis reported a total bulk carbon and sulfur content of 0.37% and 0.16% respectively. The spatial distribution of the phases was determined by 2D mapping of Raman spectra, while TGA showed a very low weight loss for temperatures ranging between 25 and 1000°C. Individual fly ash particles were characterized by a monomodal size distribution (PSD) of spherical particles with smooth surfaces (SEM, TEM, AFM), and a mean particle size of 4.6μm (PSD). The BET active surface area of this sample was 1.52m2/g and the chemical composition of the fly ash surface (AES, XPS) was significantly different from the bulk composition and varied considerably between spheres. Many properties of the sample (e.g. spherical morphology, small particle size, thermal stability) appeared to be suitable for its applicability as filler in polymers, although the wide variation in surface composition between individual particles may challenge the development of a suitable surface modification technique. The observation that the bulk and surface compositions of the particles were so intrinsically different, strongly suggested that surface characterization is important when considering compatibility between matrices when applying fly ash as filler in polymers.

Constraints from sulfur isotopes on the origin of gypsum at concrete/claystone interfaces

Two in situ concrete/claystone interfaces were sampled at the laboratory level in the Andra Meuse/Haute Marne (France) Underground Research Laboratory (URL) in order to study five years of interactions between Callovian–Oxfordian (COx) claystone and two cementitious materials (concrete bottom slab and shotcrete on the walls of the main gallery), with a specific focus on sulfur. Combined mineralogical, chemical and sulfur isotopic investigations were carried out to define the degree of the perturbation of the sulfur system in the claystone and in both the cementitious materials. At both interfaces, results show that the main perturbation on the claystone side is the formation of scarce μm-sized gypsum, the sulfur content of which is essentially derived from pyrite oxidation. The distribution of gypsum is highly correlated with the fissure network of the damaged zone due to excavation of the gallery. Its presence is also often associated with a loss of cohesion of the concrete/claystone interface. Due to the small amounts of gypsum and its μm-size, measurements were performed by ion microprobe. Adaptations were needed on account of the reactivity of gypsum and sulfates in general under the beam. The use of ion microprobe analysis provided evidence of high local isotopic heterogeneity that could be attributed to kinetic fractionation effects. Some analyses suggest a minor contribution of dissolved sulfates in pore water of claystone and possibly of concrete. The perturbation on the concrete side is marked by a significant increase in the bulk sulfur content within three millimeters of the interface with the claystone, showing a sulfur gradient from claystone to concrete. The main objective of this work was to define the extent of the chemical and mineralogical perturbations, taking into account in situ URL conditions, i.e. hydrodynamic conditions (shotcrete sprayed on the gallery walls and subjected to ventilation of the galleries), damaged zone of claystone induced by excavation and multi-scale heterogeneity. This identifies the relevant parameters to better constrain predictive reactive transport models of concrete/claystone interactions at a realistic scale.

Anomalous Sulfur Segregation Kinetics Governed by MnS Precipitation Reaction and {110} Annealing Texture Development in Al-free and 0.1% Mn–Added 3% Si–Fe Alloys

In 0.1% Mn–added 3% Si–Fe alloys, the total number of {110} grains increased with increasing bulk sulfur content and with decreasing heating rate. This is contrary to that in Mn-free alloys. During isothermal annealing, the segregation concentration of sulfur for the initial time range was lower in the alloy containing 95 ppm sulfur than that in the other alloy containing 25 ppm sulfur. Also the maximum segregation concentration of sulfur appeared at a later time in the former. Such an annealing texture development and a segregation behavior can be attributed to the MnS precipitation and the subsequent dissolution into the matrix.

Sulfur isotopic systematics of granitoids from southwestern New Brunswick, Canada: implications for magmatic-hydrothermal processes, redox conditions, and gold mineralization

Bulk δ 34Srock values, sulfur contents, and magnetic susceptibility were determined for 12 gold-related granitoid intrusions in southwestern New Brunswick, the Canadian Appalachians. The sulfur isotope compositions of sulfide minerals in some of the granitoid samples were also analyzed. This new dataset was used to characterize two distinctive groups of granitoids: (1) a Late Devonian granitic series (GS) and (2) a Late Silurian to Early Devonian granodioritic to monzogranitic series (GMS). The GS rocks have a large range in δ 34S values of −7.1‰ to +13‰ with an average of 2.2 ± 5.0‰ (1σ), low bulk-S contents (33 to 7,710 ppm) and low magnetic susceptibility values (<10−4 SI), consistent with reduced ilmenite-series granites. The GMS rocks have a relatively narrower variation in δ 34S values of −4.4‰ to +7.3‰ with an average 1.2 ± 2.9‰ but with larger ranges in bulk-S contents (45 to 11,100 ppm) and high magnetic susceptibility values (>10−3 SI), indicative of oxidized magnetite-series granites. The exceptions for the GMS rocks are the Lake George granodiorite and Tower Hill granite that display reduced characteristics, which may have resulted from interaction of the magmas forming these intrusions with graphite- or organic carbon-bearing sedimentary rocks. The bulk δ 34S values and S contents of the GMS rocks are interpreted in terms of selective assimilation–fractional crystallization (SAFC) processes. Degassing processes may account for the δ 34S values and S contents of some GS rocks. The characteristics of our sulfur isotope and abundance data suggest that mineralizing components S and Au in intrusion-related gold systems are dominantly derived from magmatic sources, although minor contaminants derived from country rocks are evident. In addition, the molar sulfate to sulfide ratio in a granitic rock sample can be calculated from the δ 34Srock value of the whole-rock sample and the δ 34Ssulfide (or δ 34Ssulfate) value of sulfide and/or sulfate mineral in the sample on the basis of S-isotope fractionation and mass balance under the condition of magmatic equilibrium. This may be used to predict the speciation of sulfur in granitic rocks, which can be a potential exploration tool for intrusion-related gold systems.

Segregation behavior at TGO/bondcoat interfaces

The segregation of sulfur and other elements at the interface between thermally grown alumina and a few coatings have been reviewed and compared with studies made at oxide/metal interfaces formed on model alloys. The coatings studied were NiPtAl on CMSX-4 or AM1 with two different bulk sulfur contents, and NiCoCrAlY on PWA 1484. The segregation behavior at the oxide/PWA1484 interface was also reported. Auger electron microscopy was used to study the chemistry at the oxide/coating interface after portions of the oxide were removed in ultra high vacuum (UHV) by scratches made on the oxidized sample surface. The extent of oxide spallation in relation to the scratch width was utilized to evaluate the interfacial strength, which was then correlated with the interface impurity level. Results showed strong relationship between sulfur segregation and the composition of the alloy substrates. In addition to substrate sulfur content, the degree of sulfur segregation was most significantly increased by Cr co-segregation or decreased by Y doping of the coating. Pt and Hf could stop segregation only when present together. P was found as a significant segregand in one case where sulfur segregation was prevented by Y. These behaviors are discussed in terms of various thermochemical interactions in the bulk and at the interface.

Sulfur partition coefficient between apatite and rhyolite: the role of bulk S content

Experimental studies have been performed to constrain sulfur behavior during apatite crystallization and to determine sulfur partition coefficient between apatite and melt (Kd S apatite/melt ) at oxidizing conditions. Crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk sulfur contents (0.15 to 2 wt.% S) at 900 and 1,000°C, 200 MPa and Δlog $$f_{{{\rm O}_{2} }} $$ =NNO+3.6. The sulfur content in the glass increases with increasing amount of added S. Anhydrite crystallizes for S added = 0.75 wt.% (0.10 and 0.13 wt.% SO3 in glass at 900 and 1,000°C, respectively). The amount of anhydrite increases and the amount of apatite decreases with increasing amount of added sulfur. The sulfur exchange reaction in apatite is influenced by the bulk composition of the melt (e.g., P content). However, changing melt composition has only little effect on Kd S apatite/melt for the investigated rhyolitic composition. The Kd S apatite/melt does not depend directly on temperature, decreases from 14.2 to 2.7 with increasing S content in glass from SO3=0.03 to 0.19 wt.%, respectively, and can be predicted from the following equation: ln Kd = −0.0025×S in melt (in ppm)+2.9178. The combination of experimental data obtained for rhyolitic and andesitic melts reveals that the sulfur partition coefficient tends toward a value of 2 for high-sulfur content in the glass (>0.2 wt.% SO3). Using S in apatite as proxy for determining S content in melt is promising but additional experimental data are needed to clarify the individual effects of T, $$f_{{{\rm S}_{2} }} $$ , and P and Ca content in the melt on S partitioning.

Solubility and speciation of sulfur in silicate melts: The Conjugated Toop-Samis-Flood-Grjotheim (CTSFG) model

A Conjugated Toop-Samis-Flood-Grjotheim (CTSFG) model is developed by combining the framework of the Toop-Samis polymeric approach with the Flood-Grjotheim theoretical treatment of silicate melts and slags. Electrically equivalent ion fractions are computed over the appropriate matrixes (anionic and cationic) in a Temkin notation for fused salts, and are used to weigh the contribution of the various disproportionation reactions of type: M 2/ ν O (melt) + ½ S 2(gas) ⇔ M 2/ ν S (melt) + ½ O 2(gas) M 2/ ν O (melt) + ½ S 2(gas) + 3 2 O 2,(gas) ⇔ M 2/ ν SO 4(melt) ν being the charge of the generic M ν+ cation. The extension of the anionic matrix is calculated in the framework of a previously developed polymeric model (Ottonello et al., 2001), based on a parameterization of Lux-Flood acid-base properties of melt components. Model activities follow the Raoultian behavior implicit in the Temkin notation, without the needs of introducing adjustable parameters. The CTSFG model is based on a large amount of data available in literature and exhibits a satisfactory heuristic capability, with virtually no compositional limits, as long as the structural role given to each oxide holds. The model may be employed to compute gas-melt equilibria involving sulfur and allows computing sulfide and sulfate contents of silicate melts whenever the fugacity of a gaseous sulfur species and oxygen are known. Alternatively, the model calculates the oxidation state of the system (i.e., oxygen fugacity), whenever an analytical determination of either sulfide/sulfate or ferrous/ferric ratios in the melt is provided. Calculated sulfide and sulfate capacities allow the estimates of sulfur abundance in various melts of geological interest, both under anhydrous and hydrous conditions or, alternatively, of fS 2, given fO 2 and the bulk sulfur content. In this case, fSO 2 and fH 2S may be eventually computed along the water-sulfur-melt boundary provided fH 2O is known.

Delayed alumina scale spallation on Rene'N5+Y: moisture effects and acoustic emission

The single crystal superalloy Rene'N5 (with or without Y-doping and hydrogen annealing) was cyclically oxidized at 1150 °C for 1000 h. After considerable scale growth (≥500 h), even the adherent alumina scales formed on Y-doped samples exhibited delayed interfacial spallation during subsequent water immersion tests, performed up to 1 year after oxidation. Spallation was characterized by weight loss, the amount of spalled area and acoustic emission response. Hydrogen annealing (prior to oxidation) reduced spallation both before and after immersion, but without measurably reducing the bulk sulfur content of the Y-doped alloys. The duration and frequency of sequential, co-located acoustic emission events implied an interfacial crack growth rate at least 10 −3 m s −1, but possibly higher than 10 2 m s −1. This is much greater than classic moisture-assisted slow crack growth rates in bulk alumina (10 −6 to 10 −3 m s −1), which may still have occurred undetected by acoustic emission. An alternative failure sequence is proposed: an incubation process for preferential moisture ingress leads to a local decrease in interfacial toughness, thus allowing fast fracture driven by stored strain energy.

Oxidative recession, sulfur release, and Al 2O 3 spallation for Y-doped alloys

Some spallation of alumina scales occurred after long-term oxidation of Rene'N5+Y and immersion in water. It is proposed that 0.15 monolayers of sulfur segregation is enabled as the surface is consumed by oxidation for every 1 mg/cm 2 weight gain and a bulk sulfur content of 5 ppmw S.

Alkyl and polynuclear aromatic thiophenes in Neogene sediments of the Shinjo basin, Japan.

Alkyl and polynuclear aromatic thiophenes were detected in sedimentary rocks of a stratigraphic sequence from Miocene to Pliocene in Shinjo basin, Japan. C25 Highly branched isoprenoid (HBI) thiophenes, dibenzothiophene, C1- and C2-alkyldibenzothiophenes, and benzo[b]naphto[1, 2-d]thiophene were rather predominantly present. The C25 HBI thiophenes consist of three isomers including a pair of diastereomers. They were present in sediments from the Nakawatari to the upper part of the Kusanagi Formations and absent at the middle and lower parts of the Formation. The depth profiles of their concentrations do not coincide with those of the C25 HBI alkane concentration and bulk sulfur content in the same sediment samples. It is postulated that the C25 HBI thiophenes and the C25 HBI alkane were produced by the reaction of C25 HBI alkadiene and C25 HBI polyene, respectively, with reduced sulfur during early diagenesis. The variation in composition of the C25 HBI thiophene isomers was observed in the sediments, suggesting that they were derived from different kinds of C25 HBI alkadienes. The concentrations of the polynuclear aromatic thiophenes showed an increasing trend downwards the upper to middle Kusanagi Formation. Among these thiophenes dibenzothiophene and benzo[b]naphto[1, 2-d]thiophene concentrations varied from 10 to 730 and 14 to 210 pmol g-1, respectively. The depth profiles of their concentrations were different from that of the C25 HBI thiophenes. It is likely that the polynuclear aromatic thiophene formation started from different precursors followed by different processes from those of the C25 HBI thiophenes.