Middle Carbon Research Articles

Enhanced middle Holocene organic carbon burial in tropical floodplain lakes of the Pantanal (South America)

Wetland carbon storage is an important and environmentally sensitive ecosystem service. Carbon burial in the floodplain lakes of the Pantanal (tropical South America) appears to have varied during the late Quaternary, but several paleolimnological studies have recorded unusually high sediment organic carbon content from ~ 7.3 to 6.0 cal kyr BP in lakes connected to the Upper Paraguay River. We conducted a multi-indicator (phytoliths, sponge spicules, and geochemistry) study of a sediment core from Lake Caceres (Bolivia), and found evidence for enhanced organic carbon burial during the middle Holocene that provides insights into the flooding history of the Upper Paraguay River. δ13Corg and C/N data suggest that organic matter deposited at that time in Lake Caceres was from macrophytes. Similar datasets from three other floodplain lakes are consistent with this finding. We suggest that enhanced carbon burial occurred when lake levels declined under relatively dry climate conditions, which increased the littoral area at the expense of open water and captured floating macrophyte islands. This study sheds new light on hydroclimate controls on carbon cycling in the Pantanal wetlands, and improves interpretations of geochemical measures on bulk organic matter in floodplain lake cores.

Tailoring strength/ductility combination in 2.5 wt% Si-alloyed middle carbon steel produced by the two-step Q-P treatment with a prolonged partitioning stage

The present work aimed at studying the effect of the two-step “Quenching-and-Partitioning” (Q-P) processing with a prolonged partitioning stage on the mechanical properties of middle carbon steel with the composition of 0.56 wt% С, 2.50 wt% Si, 1.70 wt% Mn, 0.50 wt% Cr, 0.21 wt % Mo, 0.12 wt% V, 0.05 wt% Nb. A total of 28 regimes with the quenching temperature of 160 °C and 200 °C, the partitioning temperatures of 200–300 °C and the partitioning time of 10–300 min were applied. Under Q-P treatment the UTS value ranged between 1535 and 2374 MPa, the total elongation ranged between 8 and 23% and the U-notched impact toughness ranged between 48 and 117 J/cm2, and TEL and KCU values were twice those of the “Quenching-Tempering” (Q-T) treatment. The Q-P-treated specimens possessed a multi-phase structure consisting of 38–61 vol% of tempered martensite (with transitional carbide precipitates), lower carbide-free bainite and 11–28 vol% of retained austenite enriched with 0.80–1.23 wt% carbon. The tensile strength gradually increased with the decrease in the partitioning temperature and partitioning time. In contrast, the ductility and the impact toughness tended to increase with the increasing partitioning temperature and partitioning time, and this phenomenon could be attributed to martensite tempering, bainite transformation and the increase in volume fraction of retained austenite. Q-P regimes were tailored for different strength/ductility combinations. The Q-P treatment with the regime of quenching at 160 °C, and partitioning at 270 °C for 50–120 min ensured the most advanced mechanical properties with the combination of 1743–1830 MPa UTS, 20–21% TEL, 36.6 GPa⋅% PSE, 75–79 J/cm2 KCU. The combination of the ultra-high tensile strength of 2374 MPa with 9% TEL and 61 J/cm2 KCU was obtained by quenching at 160 °C and partitioning at 200 °C for 90 min. The structural characteristics of the Q-P-treated steel were analyzed by SEM, TEM, XRD, nanoindentation, and dilatometric measurements.

Norwegian Sea area Permo-Triassic organic-carbon-rich deposits from seismic

Seismic surveys of the Permo-Triassic successions in Norwegian Sea sub-basins have been studied to determine the distribution of organic-carbon-rich intervals in the deeper basinal areas. Upper Permian to Lower Triassic organic-carbon-rich deposits had been described in cores from the margins of the basin, but their distribution in the deeper parts of the basin was unknown. The distribution of the organic-carbon-rich deposits in the deeper basin areas has been determined using a combination of amplitude versus angle/offset (AVA/AVO) analysis and an assessment of strata-bound deformation structures. AVA/AVO anomaly class IV, which has a negative normal incident reflection coefficient that decreases with angle/offset, has been used to predict the presence of organic-carbon-rich rocks in this work. The intercept (I) and gradient (G) plots (IG-crossplots) together with the Near-Far angle amplitude comparison of the seismic surveys have been used to complement the interpretation. The IG cross-plotting was done by selecting small windows (data probes) along the intervals speculated to be organic-carbon-rich. Any data probe which displayed AVO class IV elements on the IG crossplots and exhibited amplitude dimming with angle has been considered to indicate an organic-carbon-rich layer. The results of this work show the presence of both Upper Permian and Middle Triassic organic carbon rich sediments in the deeper parts of sub-basins within the Froan and Helgeland basins in the Norwegian Sea area. Two and one organic-rich intervals are indicated in the Froan and Helgeland basins respectively. The distribution of these organic-rich rocks was partly tectonically controlled, resulting in spatially limited deposits in the compartmentalized Froan Basin but more extensive deposits in the Helgeland Basin. None of the Lower Triassic sections examined in this study showed AVA/AVO characteristics indicative of organic-carbon-rich sediments on IG crossplots.

Darriwilian carbon isotope stratigraphy in the Taebaeksan Basin, Korea and its implications for Middle Ordovician paleoceanography

The middle Darriwilian carbon isotope excursion (MDICE) event is first documented from central eastern Korea (Taebaeksan Basin), the eastern part of the Sino-Korean Block, and is well correlated with global carbon isotope chemostratigraphy. The Korean MDICE record shows three broad positive peaks and complements records from the Middle Ordovician peri-Gondwanan epeiric seas showing incomplete records due to disconformity. This study reconstructed paleoceanographic conditions with nitrogen isotopic compositions and clay mineral compositions to understand the causes of carbon isotope excursions. The heavier excursion in nitrogen isotopic curve and abrupt increase of kaolinite in the early MDICE interval are interpreted as a result of epeiric sea denitrification associated with strong seawater stratification, and the main cause of those conditions was likely increased precipitation in the adjacent land. Subsequent sea-level rise caused an anti-estuarine circulation in the Taebaeksan sea and increased the organic carbon burial in the adjacent basin setting, which might have sustained the MDICE. The documentation of the MDICE event in this study supports the view that the MDICE occurred globally. This study provides not only information on the regional paleoceanographic conditions that occurred in the Middle Ordovician epeiric seas during the course of MDICE, but also reports that the MDICE event occurred as a response to seawater circulation associated with global sea-level rising in the Middle Ordovician.

Effects of grain refinement by HPT processing in carbon steel with various cementite morphology

This article reports on the effect of the initial phase composition (martensitic, patented, spheroidized) of the middle carbon steel C45 (0.45 wt.% C) on grain refinement during high-pressure torsion (HPT) at elevated temperature. It is established that the cementite dissolution and the final grain size after HPT strongly depend on the processing regime, as well as on the cementite morphology in the initial state of the steel. As result of this study, new approaches to obtain a very high-strength state in carbon steels have been proposed.

Middle Permian organic carbon isotope stratigraphy and the origin of the Kamura Event

Large carbon cycle perturbations associated with the Middle Permian (Capitanian) mass extinction have been widely reported, but their causes and timing are still in dispute. Low resolution carbon isotope records prior to this event also limit the construction of a Middle Permian chemostratigraphic framework and global or local stratigraphic correlation, and hence limit our understanding of carbon cycle and environmental changes. To investigate these issues, we analyzed the 13Corg values from the Middle Permian chert-mudstone sequence (Gufeng Formation) in the Lower Yangtze deep-water basin (South China) and compared them with published records to build a chemostratigraphic scheme and discuss the underlying environmental events. The records show increased δ13Corg values from late Kungurian to early Guadalupian, followed by a decrease to the late Wordian/early Capitanian. The early-mid Capitanian was characterized by elevated δ13Corg values suggesting the presence of the “Kamura Event”: an interval of heavy positive values seen in the δ13Ccarb record. We propose that these heavy Capitanian δ13C values may be a response to a marked decline in chemical weathering rates on Pangea and associated reduction in carbonate burial, which we show using a biogeochemical model. The subsequent negative δ13C excursion seen in some carbonate records, especially in shallower-water sections (and in a muted expression in organic carbon) coincide with the Capitanian mass extinction may be caused by the input of isotopically-light carbon sourced from the terrestrial decomposition of organic matter.

Numerical and experimental investigation on friction welding of austenite stainless steel and middle carbon steel

A numerical simulation with an axisymmetric coupled thermo-mechanical model has been performed for analyzing the heat transfer and plastic deformation in continuous drive friction welding (CDFW) of 1045 carbon steel and 304 stainless steel. The simulated results shows that higher temperature and lower stress distribute in the surrounding heat affected zone at the side of 304 stainless steel. The interfacial temperature shows an increasing trend from center to periphery, indicating the non-uniformity of temperature distribution along the interface. Larger deformation amount of carbon steel is attributed to the low high temperature strength. During process, a larger temperature gradient close to the interface initially appears at 304 stainless steel side and subsequently appears at 1045 carbon steel side, owing to more heat flowing out from interface with extrusion of softened metals. Comparisons of the numerical and experimental results suggest that the developed mode can be effectively used to predict the temperature and deformation in dissimilar steels CDFW. Based on the developed model, the influences of welding parameters on the temperature and deformation variables in dissimilar steels CDFW are investigated systemically. Finally, the microstructure of the actual welded joint is investigated experimentally.

Electromagnetic stirring in billet CCM molds and continuously casted billet quality

Electromagnetic stirring (EMS) is one of methods to improve the quality of continuously casted billet. Under EMS impact nonmetallic inclusions are removed out of the solidification area and move to the center of meniscus of liquid metal. Besides, high speeds of convection flows in the liquid metal avoid the remaining of gases at the crystallization border and decrease therefore the number of gas bubbles under metal shell. This mechanism of EMS action in a mold results in decreasing of gas bubbles under the metal shell and impurities in continuously casted billet. Operation of a billet CCM was studied at Moldavsky steel-works, where an EMS stator was imbedded into the mold. Influence of EMS on the quality of continuously casted billet was studied. The work was accomplished in several stages. First, the EMS system with a test mold with electromagnetic stirrer was studied for casting of 135×135 mm billets and 800 mm long, next 125×125 mm billet and 1000 mm long and then 125×125 mm billet and 800 mm long. Main comparative parameters of used EMS systems in the mold presented in the article. All the molds-EMS systems were designed based on existing regular molds so that they could be installed at the CCM without changing the existing oscillation frame and water input and output piping. As a result of templates metal science studies cut out of test and regular metal, influence of EMS in the mold on the billet macro structure was revealed, comparing with a standard strand. The following phenomena were studied: decrease of average degree of cracks and liquation strips along the billet section, of cracks in the billet axis zone, central pore volume and border point contaminations; increase of axis liquation degree (but liquation became more distributed), decrease of carbon axis liquation coefficient in high carbon steels. The average growth values of equiaxed crystal zone at the templates of test heats with EMS amounted for 55% at high carbon steels comparing with regular billet templates, at the middle carbon steels – 48%, at the low carbon steels – 92%. The elaborated EMS system in the mold allows improving considerably the quality of continuously casted billets.

Carbon pool in soil under organic and conventional farming systems

Changes in the agricultural management and climatic changes within the past 25 years have had a serious impact on soil organic matter content and contribute to different carbon storage in the soil. Prediction of soil carbon pool, validation, and quantification of different models is important for sustainable agriculture in the future and for this purpose a long-term monitoring data set is required. RothC-26.3 model was applied for carbon stock simulation within two different climatic scenarios (hot-dry with rapid temperature increasing and warm-dry with less rapid temperature increasing). Ten years experimental data set have been received from conventional and organic farming of experimental plots of Mendel University School Enterprise (locality Vatín, Czech-Moravian Highland). Average annual temperature in this area is 6.9°C, average annual precipitation 621 mm, and altitude 530 m above sea level. Soil was classified as Eutric Cambisol, sandy loam textured, with middle organic carbon content. Its cumulative potential was assessed as high. Results showed linear correlation between carbon stock and climatic scenario, and mostly temperature and type of soil management has influenced carbon stock. In spite of lower organic carbon inputs under organic farming this was less depending on climatic changes. Conventional farming showed higher carbon stock during decades 2000–2100 because of higher carbon input. Besides conventional farming was more affected by temperature.

Effect of Carbide Precipitation on Mechanical Properties of Si-added Middle Carbon Martensitic Steels

Effect of Carbide Precipitation on Mechanical Properties of Si-added Middle Carbon Martensitic Steels

MOF-derived hollow TiO2@C/FeTiO3 nanoparticles as photoanodes with enhanced full spectrum light PEC activities

In the current work, the ternary TiO2@C/FeTiO3 (TCF) hollow nanotubes are synthesized using MOF-Fe nanorods as a sacrificial template and precursor via the thermal carbonization under N2 atmospheres. Due to such delicate structure features that consist of hollow needle-like framework, middle conductive-layer carbon and monodisperse FeTiO3 nanoparticles embedded on carbon layer, the hollow TCF composites can effectively harvest full spectrum light energy, enhance the interfacial charge separation and suppressed the recombination of photogenerated electron-hole pairs, resulting in enhanced photoelectrocatalytic (PEC) activity. Among as-synthesized samples, TCF-20% photoanode exhibits the best performance towards the degradation of phenol under full spectrum light irradiation with an anodic bias of 1.5 V vs. SCE and the degradation rate constant is 0.586 h−1, which is 2.75 times larger than that of the corresponding sum of both EC and PC process. In addition, triple synergistic effects of the possible mechanism with the enhancement of PEC activity was proposed on the basis of PEC degradation results. This work also opens a new insight for synthesis of photocatalysts based on novel MOFs.

1,2,3-propanetriol radicals formed during oxidative stress.

The presented results attempt to approximate the proper structure of the radical formed as a result of the oxidation of 1,2,3-propanetriol. To fulfil the aim unstable radical originated in 1,2,3-propanetriol was trapped by PBN. Resulted spin adduct was measured using EPR spectroscopy and the isotropic hyperfine coupling constants aiso (14 N) and aiso (1 H) were obtained by simulation of the EPR spectrum. The next step consisted of conducting a comparative analysis of EPR parameters, based on the calculations conducted at the DFT and MP2 methods level in open-shell formalism including solvent effects. For comparison, calculations were also carried out at the level of combined methods (UB3LYP/QCISD and UMP2/QCISD) in terms of the ONIOM formalism. Comparison of the experimental EPR data of the isotropic hyperfine coupling constants aiso (14 N) and aiso (1 H) with the calculated parameters indicate that oxidation of 1,2,3-propanetriol leads to a carbon centred radical where unpaired electron is situated on the second (middle) carbon of 1,2,3-propanetriol. What is important, this conclusion could be made regardless of the chosen calculation method. However, it could be stated that for calculation of the isotropic hyperfine coupling constants aiso (14 N) and aiso (1 H) of PBN/gly• adducts, UMP2 polarisable conductor calculation model with two ethanol molecules is explicitly defined.

Thermo-mechanical Treatment of 0.4C-0.6Mn-2Si Steel with Various Soaking and Annealing Hold Temperatures

Middle carbon low alloyed steel 0.4C-0.6Mn-2Si was subjected to thermo-mechanical treatment typical for TRIP (transformation induced plasticity steels). The processing consisted from soaking at the temperatures of 850-1000 °C and cooling at 30 °C/s to various annealing holds in bainite transformation temperature interval of 350-500 °C. During the cooling from the soaking temperature, two compressive deformations were carried out, the second one always at 720 °C. Resulting microstructures were analysed using light and scanning electron microscopy. X-ray diffraction phase analysis was carried out to establish volume fraction of retained austenite and mechanical properties were measured by tensile test. Tensile strengths in the region of 847-963 MPa were obtained and very good total elongations of 30-40% were achieved at the same time. Multiphase microstructures were obtained with various amounts of ferrite, bainite, retained austenite and pearlite.

An astronomically forced cooling event during the Middle Ordovician

Abstract A cooling trend during the Middle Ordovician may have resulted in significant biotic, atmospheric and hydrologic changes, but the exact timing and forcing of this climate event still remain largely ambiguous. Here, we present astronomically calibrated magnetic susceptibility (MS) and gamma ray (GR) data from the shale and carbonate successions of the Kalpin area in the Tarim Basin, NW China to study the Middle Ordovician climate. The spectral analyses of the 405-kyr calibrated MS and GR time series reveal periodicities close to 405 (calibrated), 100, 31 and 19 kyr, supporting a Milankovitch forcing for the sedimentary cyclicity. The eccentricity and obliquity amplitude modulation cycles show main periodicities of ~2.4 and ~1.2 Myr, respectively. A cooling event along with the middle Darriwilian isotope carbon excursion (MDICE) appears to have been initiated by the alignment of the eccentricity and obliquity amplitude minima at 4.07 Myr prior to the Darriwilian/Sandbian (D/S) boundary. This climate event was in pace with high-amplitude obliquity oscillations during a period when the 1.2 Myr obliquity amplitude modulation cycles controlled the global third-order eustatic sequences. The termination of this cooling event corresponding to a global third-order highstand was initiated by an eccentricity oscillation maximum at 0.63 Myr prior to the D/S boundary. Subsequent climate alleviation was dominated by eccentricity forcing until the earliest Sandbian. We suggest that although the climate changes have been primarily associated with the CO2 level, a specific sequence of astronomical variations during the Middle Ordovician was responsible for the time when the critical threshold was crossed.

Synthesis of new triazole tethered derivatives of curcumin and their antibacterial and antifungal properties

New derivatives of curcumin connected to 1,2,3-triazole ring were synthesized by Knoevenagel reaction of the middle carbon with aromatic aldehydes, followed by alkyne-azide 1,3-dipolar cycloaddition. These new compounds were evaluated for their antimicrobial activity against Staphylococcus aureus, Escherichia coli, Bacillus cereus and Pseudomonas aeruginosa. Many of the synthesized compounds showed a better antibacterial and antifungal activity in comparison with the parent molecule, curcumin. Then quantitative structure–activity relationship (QSAR) modeling was performed to determine the structural descriptors which correlate to the antibacterial and antifungal activities with the synthesized curcumin derivatives. QSAR study showed a good agreement between the experimental results and the predicted values.

Lower–Middle Ordovician carbon and oxygen isotope chemostratigraphy at Hällekis, Sweden: implications for regional to global correlation and palaeoenvironmental development

A high-resolution chemostratigraphical (coupled δ13Ccarb and δ18Ocarb) study of the topmost Floian through the middle Darriwilian (Ordovician) succession at the Hällekis quarry, Kinnekulle, southern Sweden, shows relatively steady isotopic values with overall minor changes, although some notable short- and long-term shifts are discernible. A pronounced positive shift in δ13C in the uppermost part of the study succession is identified as the Middle Darriwilian Isotopic Carbon Excursion (MDICE), representing the only named global isotopic excursion in the data set. Regional and global comparisons suggest that few details in the different carbon and oxygen isotope curves can be confidently correlated, but longer-term patterns appear quite consistent. Trends in the isotope data are in agreement with palaeogeographical reconstructions. Differences in stratigraphical patterns of both carbon and oxygen isotopes between localities suggest strong secular development at several spatiotemporal scales; any global signal involving relatively minor isotopic shifts is often masked/subdued by local and regional overprinting and care should be taken not to overinterpret data sets. Collectively, the data suggest rising sea levels and cooling climates through the studied time interval, but detailed interpretations remain problematic.

N-doped carbon dots@layer facilitated heterostructure of TiO2 polymorphs for efficient photoelectrochemical water oxidation

Abstract A cocktail strategy was developed to fabricate sandwich nanostructure of hydrogenated C-doped anatase TiO2 nanocrystals/N-doped carbon dots@layer/rutile TiO2 nanorod array as an efficient photocatalyst for photoelectrochemical water oxidation. The one-dimensional, single crystalline nature of the innermost rutile TiO2 nanorod facilitates charge transport. The middle N-doped carbon dots@layer offers dual functionalities, with the N-doped carbon dots as the photosensitizer to harvest long wavelength lights and the N-doped carbon layer as the conductive layer for fast charge transport toward the current collector. The outermost hydrogenated C-doped anatase TiO2 nanocrystals serve to increase the visible light absorption and to form a type II heterostructure with the innermost rutile TiO2 nanorods to enahnce the charge separation. An enhancement of 86% in photocurrent density was achieved at 1.23 V (vs. RHE) under illumination of simulated sun light of 100 mW/cm2 by the sandwich nanostrcuture, as compared to that of the plain rutile TiO2 nanorod array. The enhancement was boosted to 228% under visible simulated sun light (λ > 400 nm) illumination. The photoconversion efficiency and photocurrent density retention rate were significantly improved from 0.23% and 60% for the plain rutile TiO2 nanorod array to 0.65% and 84% for the sandwich nanostructure, respectively.

A flexible 3D graphene@CNT@MoS2 hybrid foam anode for high-performance lithium-ion battery

A three-dimensional (3D) flexible hybrid foam composed of graphene foam@carbon nanotubes decorated with MoS2 nanoparticles is synthesized for flexible anode applications in lithium-ion battery. The inner layer of graphene foam (GF), serving as a 3D skeleton of the hybrid foam, enlarges the electrode/electrolyte contact, shortens the diffusion distance of Li+ ions and provides enough internal void space to accommodate the large volume change of MoS2 nanoparticles. The middle carbon nanotubes (CNT) layer wrapped on the graphene foam is more conductive to facilitate electron/ion transport within the hybrid foam and can further enhance the flexibility of the hybrid foam. The outer layer of active MoS2 nanoparticles can provide high specific capacity. Owing to these advantages, the flexible GF@CNT@MoS2 electrodes delivers a specific capacity of 935 mAh g−1 at a current density of 0.1 A g−1, high reversible capacity of 606 mAh g−1 after 200 cycles at 0.2 A g−1.

Darriwilian (Middle Ordovician) chemostratigraphy linked to graptolite, conodont and trilobite biostratigraphy in the Fågelsång-3 drill core, Scania, Sweden

A recent core drilling in the geologically classical Fågelsång area resulted in a 58.70-m-long drill core through the lowermost Sandbian Sularp Shale, the Darriwilian Almelund Shale and Komstad Limestone, and part of the late Tremadocian to earliest Darriwilian Tøyen Shale. The shales contain zone index graptolites that are used for an update of the standard Darriwilian graptolite zone succession in Baltoscandia in which six zones are now recognized. The Komstad Limestone interval and lowermost part of the Almelund Shale have been subdivided into four conodont zones. The δ13Corg chemostratigraphy, which has been established through the entire drill core based on 120 closely spaced samples, shows a somewhat subdued development of the middle Darriwilian Isotope Carbon Excursion (MDICE), which is dated in terms of graptolite biostratigraphy. The Fågelsång isotope curve is correlated with a closely similar δ13Ccarb curve from a coeval, apparently stratigraphically essentially continuous, succession at Kårgärde in south-central Sweden, which previously has been subdivided into 13 conodont zones and subzones. For the first time, these conodont zonal units can be calibrated with Fågelsång graptolite zones using δ13Corg chemostratigraphy. The several new results of this study are expected to be useful for assessing biostratigraphic relations between units in shale and carbonate facies in Baltoscandia and elsewhere in the world.

In situ promoting water dissociation kinetic of Co based electrocatalyst for unprecedentedly enhanced hydrogen evolution reaction in alkaline media

Carbon-encapsulated 3d-transition metal (TM) hybrid structure (denoted as M@C) have been considered as a promising candidate for HER. In recent years, the Co@C composites have exhibited effective HER catalytic performance in acidic media. However, the catalytic performance of Co@C in alkaline media is still unsatisfactory because of the sluggish water dissociation in Volmer step. In this work, by using carbon encapsulated metal Co nanoparticles hybrid structure (CoNP@C) as precatalyst, we firstly demonstrate that the HER activity of Co-based precatalysts could be unprecedentedly promoted through a simple in situ electrochemical activation process. Compared with initial CoNPs@C precatalyst, the activated catalyst realizes about 3.5-fold improved activity and the overpotential greatly decreases from 191 mV to 58 mV at 10 mA cm−2. Specially, the remarkable reduced Tafel slope (from 113 mV dec−1 to 51 mV dec−1) indicates that the sluggish kinetics of the water dissociation step (Volmer step) is effectively speeded up by in situ electrochemical activation. Such a highly enhanced catalytic performance is mainly due to the in situ introduction of cobalt hydroxides NPs as water dissociation promoter and the synergetic effects among core Co NPs, middle layered carbon structure and outer cobalt hydroxides NPs. Our study offers a generic strategy for development of high-performance 3d-transition metal hybrid based HER catalysts in alkaline media.