Higher Degree Of Oxidation Research Articles

Oxidation on the current-carrying rolling surface and its subsequent impact on the damage of Cu contact pairs in O2/N2 mixture

The oxidation of copper surface under current-carrying conditions were investigated by using a disc-disc rolling tribometer in different oxygen contents. Energy-dispersive X-ray spectrometry on rolling surface showed that the increase of oxygen content promoted surface oxidation. An interesting phenomenon was that the friction coefficient increased with the oxygen content. Contact angle tests indicated that the surface with a higher oxidation degree had a better hydrophilicity, which would cause a higher friction coefficient because of the additional meniscus force. Meanwhile, material damage styles changed from adhesive wear to lamellar fatigue wear due to the shear deformation induced by high friction coefficient, which has been demonstrated by electron back-scattered diffraction observation.

Zones of PGE–Chromite Mineralization in Relation to Crystallization of the Pados-Tundra Ultramafic Complex, Serpentinite Belt, Kola Peninsula, Russia

The lopolithic Pados-Tundra layered complex, the largest member of the Serpentinite belt–Tulppio belt (SB–TB) megastructure in the Fennoscandian Shield, is characterized by (1) highly magnesian compositions of comagmatic dunite–harzburgite–orthopyroxenite, with primitive levels of high-field-strength elements; (2) maximum values of Mg# in olivine (Ol, 93.3) and chromian spinel (Chr, 57.0) in the Dunite block (DB), which exceed those in Ol (91.7) and Chr (42.5) in the sills at Chapesvara, and (3) the presence of major contact-style chromite–IPGE-enriched zones hosted by the DB. A single batch of primitive, Al-undepleted komatiitic magma crystallized normally as dunite close to the outer contact, then toward the center. A similar magma gave rise to Chapesvara and other suites of the SB–TB megastructure. Crystallization proceeded from the early Ol + Chr cumulates to the later Ol–Opx and Opx cumulates with accessory Chr in the Orthopyroxenite zone. The accumulation of Chr resulted from efficient cooling along boundaries of the Dunite block. The inferred front of crystallization advanced along a path traced by vectors of Ol and Chr compositions. Grains and aggregates of Chr were mainly deposited early after the massive crystallization of olivine. Chromium, Al, Zn and H2O, all incompatible in Ol, accumulated to produce podiform segregations or veins of chromitites. This occurred episodically along the moving front of crystallization. Crystallization occurred rapidly owing to heat loss at the contact and to a shallow level of emplacement. The Chr layers are not continuous but rather heterogeneously distributed pods or veins of Chr–Ol–clinochlore segregations. Isolated portions of melt enriched in H2O and ore constituents accumulated during crystallization of Ol. Levels of fO2 in the melt and, consequently, the content of ferric iron in Chr, increased progressively, as in other intrusions of the SB–TB megastructure. The komatiitic magma vesiculated intensely, which led to a progressive loss of H2 and buildup in fO2. In turn, this led to the appearance of anomalous Chr–Ilm parageneses. Diffuse rims of Chr grains, abundant in the DB, contain elevated levels of Fe3+ and enrichments in Ni and Mn. In contrast, Zn is preferentially partitioned into the core, leading to a decoupling of Zn from Mn, also known at Chapesvara. The sulfide species display a pronounced Ni-(Co) enrichment in assemblages of cobaltiferous pentlandite, millerite (and heazlewoodite at Khanlauta), deposited at ≤630 °C. The oxidizing conditions have promoted the formation of sulfoselenide phases of Ru in the chromitites. The attainment of high degrees of oxidation during crystallization of a primitive parental komatiitic magma accounts for the key characteristics of Pados-Tundra and related suites of the SB–TB megastructure.

Geochemistry and Microthermometry of Fluid Inclusions of Cu and Fe Mineralization in North Khour Volcanic Rocks, Northwestern Birjand

The volcanic complex of North Khour is located in southern khorasan province, in 90 km of northwest of Birjand.The study volcanic igneous rocks are including Basaltic andesite, Andesite and trachyandesite, Latite, Dacite to Rhyodacite and pyroclastic rocks are including Tuff and breccia. The majority texture of these rocks is porphyry. Magmatic series of most samples are calc alkaline but some samples have inclination to tholleiitic serie. Furthermore in diagram of magmatic arc definition, the study rocks are situating in field of continental arc and seems which magmatism of area has been result of subduction of a oceanic crust under the continental crust. Because of the area is an upper part of a cu porphyry system, this paper is a very important research to know more about this system. Iron mineralization in area is as magnetite, hematite and as lower amount of goethite and with attention to the field observations, it seems this mineralization has magmatic origin. Burnite as alone Cu ore has been formed as primary and very little. The presence of bornite and pyrite as sulfide phases as very little and absence of other Cu primary sulfide ores in area together with secondary Cu mineralization phases in very high amounts, is showing a hydrothermal solution with high oxidation degree which has passed the latest magmatic differentiation and has caused to form surface Cu ores as calcosite in supergene zone. The thermobarrometry studies of fluid inclusions has specified degree of 10 weight percent of NaCl, 50 megapascal pressure and temperature range of 200-220 centigrade degrees for this mineralization.Therefore it seems that mineralization is related to upper parts of a Cu–porphyry system which is showing a lower temperature.

Detection of organosulfates and nitrooxy-organosulfates in Arctic and Antarctic atmospheric aerosols, using ultra-high resolution FT-ICR mass spectrometry

Organosulfates (OSs) are recognized as important secondary organic aerosols (SOAs) in recent years. Due to their amphipathy and light absorptive capacity, OSs may potentially impact climate. Moreover, OSs can serve as molecular tracers for precursors and multiple processes leading to the generation of SOA. However, studies on OSs are lacking in the polar regions which limits our understanding of both their formation pathways and impacts on the polar environment. Here we present the first investigation into OSs in both the Arctic and Antarctic. Organic compounds in aerosol samples collected from the polar regions during the 2013/2014 Chinese National Arctic/Antarctic Research Expedition (CHINARE) were analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) coupled with negative ion mode electrospray ionization (ESI(−)). Hundreds to thousands of OSs were detected at the polar sampling sites. The estimated total concentrations of OSs were in the range of 46–670 ng/m3 in the Arctic sampling area, and 47–260 ng/m3 in the Antarctic sampling area, accounting for 1–16% of total OM. OSs were found to have undergone a high degree of oxidation in the aerosol samples, which might be due to the combined effects of enhanced photo-oxidation in summertime or continuous oxidation during transport to the polar region. The potential appointment of OS precursors highlights the important role of long-range air-mass transport on the OSs derived from biogenic precursors and a notably large contribution from anthropogenic emissions, suggesting that human activities have significant impacts in remote polar environments. The results of this study provide important insights into the characteristics of OSs in the polar atmosphere. However, the need for further research focusing on the quantification, formation mechanisms and impacts of OSs on climate is emphasized.

Surface oxidation of transition metal sulfide and phosphide nanomaterials

Many transition metal sulfides and phosphides are susceptible to surface oxidation under ambient conditions. The formed surface oxidation layer, which is likely to further restructure under reaction conditions, alters the chemical properties of the pristine material but has not been well studied. In this work, we for the first time use X-ray photoelectron spectroscopy to quantify the natural surface oxidation of transition metal phosphide and sulfide nanoparticles and employ a simplified Deal-Grove model to analyze the kinetics. We show that CoS2 oxidizes faster than CoS whereas CoP2 is more difficult to oxidize compared to CoP, and there exists an inverse correlation between the surface oxidation rate and the Co-S/P distance in the pristine structure. More inclusive investigation unveils different types of surface oxidation behavior: CoS, NiS and FeS are limited by their reactivity with oxygen; CoS2 is the most reactive and its oxidation is governed by oxygen diffusion; CoP2 is influenced by both reactivity and diffusion; CoP, Ni2P, Cu3P and MoP exhibit high initial oxidation degrees and the kinetics are not well-defined; MoS2 is largely stable against oxidation.

Thermal oxidation of graphite as the first step for graphene preparation: effect of heating temperature and time

Oxidation of graphite is the first important step for the industrial scale preparation of graphene by top-down method using graphite as a starting material. In this study, graphite was oxidized by economically viable and environmentally friendly thermal oxidation method. Pristine graphite (PG) was heated in a furnace under atmospheric condition between 200 and 1000 °C for specific time (5–20 min) and the samples were characterized through thermogravimetry analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, atomic force microscopy (AFM) and finally crystal simulation and molecular dynamic (MD) simulation were performed. The results exhibited that significant oxidation of PG took place when it was heated between 200 and 600 °C for shorter time (≤ 5 min), but partial reduction in oxidized graphite happened when heated for longer time (≥ 10 min) at same temperature. However, reduction of PG took place when it was heated between 800 and 1000 °C. The extent of oxidation was the maximum (17%) when graphite was heated at 400 °C for 5 min. Van der walls energy for graphite and oxygen system determined from MD simulation also found to be the maximum at 400 °C causing higher degree of oxidation. Finally, plausible mechanism of oxidation and reduction of graphite at different temperature and time was discussed based on experimental and simulation results.

Characterization of polyaniline thin films prepared on polyethylene terephthalate substrate

The polyaniline thin films were prepared by in situ chemical polymerization of aniline on polyethylene terephthalate substrate in the aqueous solutions of citric acid with ammonium peroxydisulfate as oxidant. Using ultraviolet–visible and Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron with energy-dispersive X-ray microscopy, atomic force microscopy, and four-point probe resistivity measurements, pure polyethylene terephthalate and polyaniline thin films were thoroughly characterized. Chemical analysis confirmed the formation of polyaniline with a high degree of oxidation in the form of a smooth thin film (with a thickness of ~ 80 ± 10 nm) on polyethylene terephthalate surface. However, delocalized polyaniline macromolecule aggregates in the spherical shape (with the diameter of ~ 30–40 nm) as well as in the irregular shape (the maximum size of ~ 300 nm) were found on the substrate. The values of average arithmetic roughness, average square roughness, asymmetry, kurtosis, average maximal profile height as well as average maximal height, and depth of roughness were calculated based on the atomic force microscopy data for pure polyethylene terephthalate and polyaniline thin films.

Self-assembled perylenetetracarboxylic acid-reduced graphene oxide film for high-sensitive impedimetric determination of thrombin

Graphene-based thin film has been widely used as signal conductor and platform material in electrochemical sensors. For commonly used reduced graphene oxide (rGO), oxygen-containing functional groups can provide coupling sites to conjugate with bio-cognitive elements, but high degree of oxidation can harm its structural integrity and signal conductivity. In this work, a new strategy is developed to balance the conductivity and functionality of rGO. The PTCA-rGO composite film was prepared by self-assembly and used to fabricate electrochemical biosensor. To form reusable thrombin aptasensor, an in situ layer-by-layer self-assembling method was adopted to stepwise deposit reduced graphene oxide (rGO), 3, 4, 9, 10-perylenetetracarboxylic acid (PTCA), and thrombin aptamer (TBA) onto 3-aminopropyltriethoxy silane (APTES)-modified glassy carbon electrode (GCE). The as-prepared aptasensor was used to determine thrombin in response to impedimetric signal by electrochemical impedance spectroscopy (EIS). The as-prepared GCE/rGO/PTCA/TBA sensor provided outstanding performance for determination of thrombin concentration with wide linear range (1 pM-100 nM), low detection limit (0.2 pM), reusability, and good specificity to thrombin. The good performance of GCE/rGO/PTCA/TBA aptasensor can be attributed to the electrochemical property of rGO-PTCA composite film and the in situ layer-by-layer fabricated strategy. This PTCA-modification method is promising to be widely used in the fabrication of graphene-based electrochemical devices.

Using ESI FT-ICR MS to Characterize Dissolved Organic Matter in Salt Lakes with Different Salinity.

Dissolved organic matter (DOM) composition in salt lakes is critical for water quality and aquatic ecology, and the salinization of salt lakes affects the DOM composition. To the best of our knowledge, no study has explored the effects of salinity on salt lake DOM composition at the molecular level. In this work, we selected Qinghai Lake (QHL) and Daihai Lake (DHL) as typical saline lakes. The two lakes have similar geographical and climatic conditions, and the salinity of QHL is higher than that of DHL. Fourier transform ion cyclotron resonance mass spectrometry coupled with electrospray ionization was applied to compare the DOM molecular composition in the two lakes. At higher salinity, the DOM showed larger average molecular weight, higher oxidation degree, and lower aromaticity. Moreover, the proportion of DOM that is vulnerable to microbial degradation (e.g., lipids), photo-degradation (e.g., aromatic structures), or both processes (e.g., carbohydrates and unsaturated hydrocarbons) reduced at higher salinity. On the contrary, compounds that are refractory to microbial degradation (e.g., lignins/CRAM-like structures and tannins) or photo-degradation (e.g., aliphatic compounds) accumulated. Our study provides a useful and unique method to study DOM molecular composition in salt lakes with different salinity and is helpful to understand DOM transformation during the salinization of salt lakes.

Effect of graphene oxide particle size on the tensile strength and stability of natural rubber graphene composite

Graphene oxide (GO) is a great candidate to improve the strength and stability of natural rubber latex (NRL) composite. The size of GO plays a crucial role because smaller size tends to oxidise easily. The nano-size and micron-size of GO were synthesized and then compounded with NRL via in-situ reduction method. The NRL with nano size GO (GO-N) possess a high tensile strength of 22.03 ± 0.84 MPa at 700% elongation (M700) and good ageing stability. We discovered that the GO-N is not only exhibit high degree of oxidation but also the GO-N is fully embedded in the rubber film to furnish smooth surface. The high degree of oxidation of GO-N promotes better inter-particle crosslinking between rubber-filler that enhance the stability of NRL composite. This study provides understanding of GO-N which enable the production of thinner and stable NRL composite.

An experimental investigation on the sulfur and nitrogen co-doping and oxidation of prepared graphene by electrochemical exfoliation of pencil graphite rods

In this research, the electrochemical exfoliation of pencil rods was carried out for the synthesis of graphene sheets in different mixtures of H2SO4 and HNO3 solution. Influence of different volume ratios of H2SO4: HNO3 at a low concentration (0.6 M) on the morphology and structure of prepared graphene sheets was investigated by field emission electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Raman spectroscopy and atomic force microscopy (AFM) analyses. Results indicated that the mixtures of few-layered graphene, multi-layered graphene, and graphene oxide were achieved by applying an anodic voltage of +10 V. However, the number of layers, degree of oxidation and defect density of the synthesized powders were different. By increasing the volume ratio of HNO3 in electrolytes, the degree of exfoliation of graphite decreased. On the other hand, the highest degree of oxidation was achieved for the prepared graphene by electrochemical method in the mixture of H2SO4: HNO3 with 1:1 ratio. EDS results of the prepared powders demonstrated the occurrence of nitrogen and sulfur co-doping of graphene sheets.

Regulating the pore structure of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) oxidized cellulose membranes: impact of drying method and organic solvent processing

AbstractCellulose‐based membrane is a satisfactory candidate for the separator of lithium‐ion batteries due to its renewability, abundant pore structure and outstanding thermal–chemical stability. In this study, 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) oxidized cellulose fiber (TOCF) membranes with different oxidation degrees were prepared. Membranes with high oxidation degree are faced with a pore closure issue, resulting in low porosity. In order to improve the pore structure, the TOCF membranes were dried differently through air drying, vacuum drying and freeze drying. Furthermore, air‐dried membranes were processed by three organic solvents – n‐butyl alcohol, carbon tetrachloride and n‐heptane. The physical properties, pore structure characteristics, mechanical properties and the electrochemical performance of the membranes were measured and characterized. From the results, freeze drying is found to provide the highest porosity and mean pore diameter. Unfortunately, Young’s modulus of the freeze‐dried membranes is the smallest as well. However, membranes processed by n‐butyl alcohol have weak tensile properties. Compared to non‐processed membranes, membranes processed by organic solvents present better pore structure and significantly better electrochemical performance. With all properties considered, TOCF membranes processed by carbon tetrachloride or n‐heptane are qualified for serving as battery separators as they possess improved pore structure, enhanced Young’s modulus, considerable tensile strength and improved electrochemical properties. © 2020 Society of Chemical Industry

Thermal Conductivity of Graphene Oxide: A Molecular Dynamics Study

The thermal properties of graphene oxide containing hydroxyl and epoxy functional groups were studied using non-equilibrium molecular dynamics to understand the thermal transport phenomena involved and the structure factors limiting heat conduction. Estimates were given in terms of phonon mean free paths for the reduction in thermal conductivity by interior defects due to scattering. The mechanism of phonon transport in the graphene oxide was discussed. The results indicated that the degree of oxidation can significantly affect the thermal performance of graphene oxide. A low degree of oxidation is necessary to enhance the phonon transport properties of graphene oxide and reduce the probability of phonon-defect scattering. Phonon transport in graphene oxide with a high degree of oxidation is governed by the mean free path of phonons associated with scattering from interior defects. Oxygen-containing functional groups can adversely affect performance and reduce the efficiency of phonon transport in graphene oxide due to phonon mean free paths limited mainly by interior defects. The calculated intrinsic thermal conductivity of graphene oxide at room temperature is about 72 W/(m K) with an oxidation degree of 0.35 and about 670 W/(m K) with an oxidation degree of 0.05. The phonon mean free path decreases with increasing the degree of oxidation due to enhanced phonon-defect scattering, making the thermal conductivity very sensitive to the concentration of oxygen-containing functional groups.

Biodegraded bitumens dispersed in Vendian (Neoproterozoic) rocks of the Khatyspyt Formation, Northeastern Siberia

The organic matter of the Vendian (Neoproterozoic) Khatyspyt Formation was investigated. The new data obtained from the GS and GS-MS analyses include: high UCM humps andheightened peaks of steranes and terpanes against the backdrop of C27+ alkanes on chromatograms of saturated hydrocarbons fractions of five samples; predominance of С21-С26 in n-alkanes distribution; the presence of 12- and 13-monomethylalkanes on chromatograms and demethylatedterpanes on filtered chromatograms (m/z 191 and 177). Besides, dispersed bitumens with biodegraded hydrocarbons have been for the first time identified in carbonate and carbonate-siliceous rocks of the Khatyspyt Formation. Also 8,14-sekohopanes resistant to biodegradation and gammacerane were established. The revealed features of the composition and distribution of hydrocarbons showed that their source was the autochthonous (syngeneic) organic matter of the Khatyspyt Formation,one of the potential hydrocarbon source rock of Northeastern Siberia. The composition and content of bitumen are found to be controlled by the inputs of primary organisms (eukaryotes and prokaryotes)which lived in Vendian seas, by changing redox conditions of sediment deposition and transformation, as well as by relatively little effect of temperature and high degree of biological oxidation in hypergenesis. The patterns of bitumen distribution throughout the section show, that besides the overlying deposits,their accumulations canbe discoveredin the Khatyspyt Formation.

Synthesis of graphene oxides particle of high oxidation degree using a modified Hummers method

High-oxidation-degree graphene oxide particles were synthesized using a modified Hummers' method. Six different types of particles were synthesized by varying the operating conditions, including the temperature, the reactant ratios, and the oxidation time. The oxidation degree, represented by the oxygen content, and the atomic oxygen/carbon (O/C) ratio were determined using CHNSO elemental analysis, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy-universal attenuated total reflectance sensor (FTIR-UATR) and Raman spectroscopy. The structural morphology of graphene oxide was evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal stability of the particles was studied using thermogravimetric analysis (TGA). The SEM images showed that the prepared GO samples had different graphitic layer structures. The TEM images showed different stacking levels and transparency of GO flakes caused by the difference in oxidation level. The oxygen content and O/C ratios ranged between 34.7 and 50.0 wt% and 0.43 and 0.8, respectively. The highest oxygen content and O/C ratio were found to be 50 wt% and 0.8, respectively, for GO prepared at 95 °C with a 1-hr reaction time (GO2-a). A quantitative analysis on the FTIR-UATR spectra was performed and was in reasonable agreement with the CHNSO analysis results. The Raman spectra showed two characteristic bands (D and G) with different relative intensities, as characterized by the ID/IG ratio, suggesting that the prepared samples had different crystallite sizes and defects. The crystallite size (La) of the prepared GO particles was estimated using the Tuinstra-Koenig model and were ranging between 9 and 24 nm. The TGA results were correlated with the elemental analysis results and showed a clear dependence of the weight loss on the GO elemental compositions. GO2-a exhibited the lowest thermal stability because of a high oxygen content, whereas GO1-b exhibited the highest thermal stability.

Shedding light on the catalytic synergies between Fe(II) and PMS in vacuum UV (VUV/Fe/PMS) photoreactors for accelerated elimination of pharmaceuticals: The case of metformin

In this work, an efficient VUV/Fe/PMS process was developed to degrade pharmaceutical compounds in contaminated waters. The effect of addition of low Fe(II) and PMS amounts individually and simultaneously was scrutinized for treating metformin (MET) as a model contaminant. Co-addition of 0.05 mg/L Fe(II) and 20 mg/L PMS to the bench-scale VUV photoreactor emitting both UV254 and UV185 photons, respectively, produced both HO∙ and SO4•- which had a considerable synergistic effect (30%) for the degradation of MET. Furthermore, adding Fe(II) and PMS to the VUV photoreactor resulted to a decreased electrical energy consumption by 3.5 times. The optimum treatment pH was near neutral, while a high degree of MET oxidation was reached even in the presence of common water anions. The complete degradation and mineralization of 5 mg/L MET in tap water was achieved in a continuous-flow VUV/Fe(II)/PMS mode at a hydraulic retention time of 60 min. The findings suggest that the VUV/Fe(II)/PMS process could be an effective and efficient advanced process for oxidation of emerging water contaminants.

Understanding the Critical Role of Binders in Phosphorus/Carbon Anode for Sodium‐Ion Batteries through Unexpected Mechanism

AbstractPolymer binders that combine active materials with conductive agents have played a critical role in maintaining the structural integrity of phosphorus anodes with a huge volume change upon sodiation/desodiation. Herein, the role of binders on the structural/chemical stability of phosphorus/carbon anode is spectroscopically uncovered through unexpected mechanism. Surprisingly, the selection of different binders is found to determine the oxidation degree of active phosphorus in various electrodes, which correlate well with their electrochemical properties. At a high oxidation degree, the electrode applying a conventional poly(vinylidene difluoride) binder displays the worst electrochemical properties, while the electrode using a sodium alginate binder delivers the best electrochemical performance (a highly reversible capacity of 1064 mAh g−1 with a 90.1% capacity retention at 800 mA g−1 after 200 cycles and an outstanding rate capability of 401 mAh g−1 at 8000 mA g−1) for its negligible oxidation. Additionally, the emergence/decomposition of surface intermediates, including (PO2)3− and (PO4)3− species, are observed in the discharging/charging processes via the ex situ P K‐edge X‐ray absorption spectroscopies. This novel discovery of the unique role of binders in phosphorus anodes, not only provides an opportunity to ameliorate their electrochemical properties, but also enables their practical applications in high‐energy sodium‐ion batteries.

Geochemistry and paleoecology of shales from the Cenomanian-Turonian Afowo formation Dahomey Basin, Nigeria: Implication for provenance and paleoenvironments

Cenomanian – Turonian (CT) Afowo shales selected from offshore X, and coastline Orimedu-1 and Ise-2 exploratory wells in the Dahomey Basin, southwestern Nigeria, were analyzed for foraminifera, major oxide and trace elements to evaluate their provenance and paleoenvironments.The hydrocarbon rich calcareous CT shale is about 100m thick in the coastline area and 300m thick in offshore area with abundant of marine planktonic and benthonic foraminifera. Benthonic species were significantly present in the coastline wells suggesting a shallow marine condition probably a neritic to inner shelf environments while abundant deep water Rotaliporid sp. and shallow water fauna heterohelix sp. in X well suggest inner shelf to bathyal (ca. >350 m) depositional environments.SiO2 and Al2O3 are the most abundant oxides of CT shale with average value of 46.4% and 12.7% in X, 57.1% and 15.65% in Orimedu-1 and 55.3% and 13.1% in Ise-2 respectively suggesting high influx of terrigenous and argillaceous sediments at the coastal area. Average Al2O3/TiO2 of 19.2 in X, 17.8 in Orimedu-1 and 19.3 in Ise-2 indicates that the sediments were sourced from intermediate igneous rock. Favorable oxic conditions for chemical weathering is more pronounce in the manganese concentration of 658–937 ppm in Orimedu-1 and 829–838 ppm in Ise-2 than 364–604 ppm in the shales from X well. Their degree of weathering estimated from chemical index of alteration (CIA) averaging 97 in the coastline wells is higher than 61 in X well, thus indicating high degree of oxidation in the depositional environments. Vanadium to nickel ratio ranging from 2.88 to 5.0 in X well suggest mixed marine and terrigenous source under dysoxic to oxic conditions for the shales while 0.48–1.2 values in Orimedu-1 further indicates a prevailing oxidizing condition at the time of deposition.Dysoxic-oxic and moderate deep-water conditions were more favorable in the offshore area and probably a significant paleo-factor for organic matter preservation of CT shales in the basin.

Determination of the Formation Field of Artificial CRM and pTRM by the Thellier Method at Different Oxidation Stages of Natural Titanomagnetite

Artificial chemical remanent magnetization (CRM) created on a basalt rock from the Red Sea rift zone, originally containing titanomagnetite (TM) with a Curie temperature of 203–208°С, is studied at various oxidation stages. CRM was formed by annealing the samples at temperature T = 355°C during 4.5–350 h in the magnetic field with induction of 100 μT. The thermomagnetic analysis has shown that with the increase of the annealing time, a single-phase oxidation process takes place, the degree of the oxidation increases and reaches its maximum after annealing during 110 hours. It is established that the subsequent heating of the samples to 600°C in argon leads to the homogenization of the single-phase-oxidized titanomaghemite. When the annealing time increases to 350 h, oxi-exsolution of titanomaghemite begins. CRM as well as the sum of CRM and partial thermoremanent magnetization (pTRM) have been investigated by the Thellier–Coe procedure. The magnetic field Bcalc calculated in the temperature interval 355–475°C from chemical magnetization formed at the annealing times of 4.5, 16.5, and 40.5 h (CRM4.5, CRM16.5 and CRM40.5) proved to be underestimated by 55, 48–52, and 16–34%, respectively. The difference between the calculated and true field decreases with the growth in the degree of single-phase oxidation. The Bcalc values calculated in the temperature interval 475–580°С from CRM40.5 and CRM110 corresponding to the high degree of single-phase oxidation turned out to be underestimated by 69–72 and 62–63%. The last result is caused by the mineral transformations of titanomaghemite at heatings in the Thellier–Coe experiments. During paleointensity determination, it is proposed to control mineral transformations not only using the check-point procedure but also based on the difference in the removal of remanent magnetization in the Thellier experiments and by thermal demagnetization.

The magnetization of the ocean floor: stress and fracturing of titanomagnetite particles by low-temperature oxidation

SUMMARY The natural remanent magnetization (NRM) of the ocean floor is carried by titanomagnetite grains that undergo low-temperature oxidation after initial cooling. Progressing oxidation is known to generate shrinkage cracks in grains larger than approximately 5 μm, and is suspected to control the long wavelength variation of NRM-intensity across the ocean floor. Here we develop a quantitative theory of single-phase oxidation and crack formation by solving the vacancy-diffusion equation that describes the oxidation process for spherical titanomagnetite particles, where the diffusion coefficient strongly decreases with vacancy concentration. The latter dependence has been experimentally demonstrated and is essential to explain the peculiarities of the observed variations of oxidation-degree with ocean-floor age. The calculated diffusion profiles provide the exact stress distributions inside oxidized titanomagnetite spheres, and predict a size limit for shrinkage-crack formation that agrees with microscopic observations of crack appearance in ocean-floor basalt samples. The new diffusion model provides a unified explanation of long-known experimental facts that (1) temperatures for the onset of low-temperature oxidation during laboratory heating are theoretically estimated as 200–400 ○C, depending on grain size and (2) that heating to 400–500 ○C is required to obtain a sufficiently high degree of oxidation z ≈ 0.8 for the development of high-temperature exsolution lamellae. Calculations for ocean-floor conditions quantitatively suggest that a rapid decrease of NRM intensity during the first 40 ka results from a deflection of magnetization by strong stresses that emerge in titanomagnetite grains of subcritical sizes, and randomization of domain-state by crack formation in larger grains.