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1.
The E.S.R. g-values of a variety of bituminous materials have been plotted against a function of their heteroatom content ∑δκXκ, where δ is the splitting coefficient of the given heteroatom κ, and X is its atomic fraction. Three discrete series are evident: two coal series, one exhibiting direct variation of g with ∑δκXκ (Series I), the other exhibiting an inverse relationship (Series II). The petroleum asphaltenes, as well as most asphaltites and asphaltoids (Series III), lie above and roughly parallel to Series I. Sulfur-treated asphaltics approach Series I, whereas heated asphaltenes and resins are situated around the intersection of Series II and III.Bituminous deposits may transform through diagenesis to their mature forms, as evidenced by their increase in the delocalization (increased aromaticity) with a decrease in heteroatom content. The diagenesis of coal is reliant on oxygen whose elimination may result in aromatization (Series I), and further transformations may increase active peripheral oxygen function groups (Series II). The intersection of Series I and II contains the delocalization states. There exist major differences in the precursors and mode of transformation between members of the coal and asphaltene series.  相似文献   

2.
Paramagnetic centers in two- and three-component coal blends carbonized at 1000 °C were studied by X-band (9.3 GHz) electron paramagnetic resonance (EPR) technique. The blends were prepared from three different Polish coals with carbon contents [wt.%]: 88.66, 86.21, and 82.67, respectively. The aim of this work was to compare EPR parameters and concentrations of paramagnetic centers in the initial and carbonized coal samples. Furthermore the spin–spin and spin–lattice interactions were characterized.EPR spectra were measured with magnetic modulation 100 kHz and microwave power 0.7 mW. Amplitudes and linewidths of EPR spectra were obtained. g-Factors were calculated from resonance condition. Concentrations of paramagnetic centers in the samples were determined. Influence of microwave power in the range 0.7–70 mW on EPR spectra was analyzed.All the studied samples revealed paramagnetism. Unpaired electrons are localized in the same atoms, because similar g-values in the range 2.0035–2.0038 were obtained for all the original samples. The EPR parameters of coal blends were additive in comparison with the parent coals. EPR spectra strongly changed after carbonization of the coal samples. Narrower EPR lines were measured for the original coal samples than for carbonized ones. We detected lower concentrations of paramagnetic centers in carbonized three-component coal blends than in two-component carbonized blends. EPR lines of the studied carbonized blends were not saturated at the microwave power used, which suggests fast spin–lattice relaxation processes in the samples. EPR examination proved chemical interactions between coal constituents during carbonization of coal blends.  相似文献   

3.
Complexes formed by the addition of vanadyl salts to a peat humic acid have been studied by EPR spectroscopy. The spectra show that the vanadium is in an environment with approximately axial symmetry. The g-values and 51V hyperfine coupling constants indicate that the vanadium remains in the vanadyl state and is complexed possibly either by oxygen donor groups or by mixed oxygennitrogen donor groups in the humic acid. Identical spectra were obtained when the vanadium was added to the humic acid as the metavanadate ion, thus showing that reduction of vanadium from oxidation state (V) to (IV) occurs.  相似文献   

4.
A natural sample of clinochlore from the Longitudinal Valley area of northeastern Taiwan has been characterized by using the powder X-ray diffraction (XRD), differential thermal analysis and electron paramagnetic resonance (EPR) spectroscopic techniques. The lattice parameters of the monoclinic (IIb) clinochlore with the composition (Mg2.988 Al1.196 Fe1.6845 Mn0.026)5.8945 (Si2.559 Al1.441)4 O10 (OH)8 have been calculated from the powder XRD data and are found to be a = 5.347 Å, b = 9.223 Å, c = 14.250 Å, β = 97.2° and Z = 2. The thermal behaviour of the sample showed the typical behaviour of clinochlore with a hydroxyl content of 12.5 wt%. The EPR spectrum at room temperature exhibits two resonance signals centred at g ≈ 2.0 and g ≈ 8.0. The signal at g ≈ 2.0 shows a six-line hyperfine structure which is a characteristic of Mn2+ ions in octahedral symmetry. The resonance signal at g ≈ 8.0 is a characteristic of Fe3+ ions. The EPR spectra have also been recorded at different temperatures (123–295 K). The population of spin levels (N) has been calculated for g ≈ 2.0 and g ≈ 8.0 resonance signals. It is observed that N increases with decreasing temperature. From EPR spectra, the spin-Hamiltonian parameters have been evaluated. The zero-field splitting parameter (D) is found to be temperature dependent. The peak-to-peak width of the g ≈ 8.0 resonance signal is found to increase with decrease in temperature.  相似文献   

5.
Natural blue and colorless rare-gem mineral specimens of euclase from Brazil are investigated by electron paramagnetic resonance (EPR). Angular dependences of Fe3+ EPR spectra in three mutually perpendicular crystal planes are analyzed revealing g and D tensors with significant low-symmetry effects, as for example, the high asymmetry parameter E/D = 0.28. Fourth-order degree Stevens parameters are also included in analysis. The anisotropy of both g and D tensors is consistent with Fe3+ substituting for Al3+ ions in strongly distorted AlO5(OH) octahedra in which the oxygen distances range from 1.85 to 1.98 Å. Fe3+ is not responsible for the blue color because colorless and blue euclase show nearly the same Fe3+ concentration as measured by EPR. However, total iron content in blue sample is much higher than in the colorless one suggesting that the existing model that Fe2+–Fe3+ intervalence charge transfer transition may explain the blue color of euclase.  相似文献   

6.
The investigated Ni doped forsterite was grown with the floating zone technique. The EPR spectra were taken at room temperature using both 9.5 and 35 GHz. All specimens show EPR signals resulting from Mn2+ at M2 and Fe3+ at M1, M2, and Si positions. Ni2+ EPR signals are observed at 35 GHz but not at 9.5 GHz. The Ni2+ spectra are described by the spin Hamiltonian
  相似文献   

7.
Being the heaviest fraction of crude oils, asphaltenes are liable to aggregate, and other molecules in the oils can be steadily adsorbed onto, and even occluded inside the macromolecular structures of the asphaltenes. These occluded compounds inside the asphaltenes can survive over geological time in oil reservoirs owing to effective protection by the macromolecular structures of the asphaltenes. The asphaltenes of a crude oil (ZG31) from the central Tarim Basin, NW China, were hierarchically degraded by increasing the amount of H2O2/CH3COOH to release the occluded compounds. Besides the common components, series of even numbered n-alk-1-enes and 3-ethylalkanes were detected among the occluded compounds. Comparison of the biomarker distributions and the compound-specific C isotopic results between the compounds from the maltenes and those from the occluded fraction, the ZG31 reservoir was suggested to have been charged multiple times, with different charges being derived from different strata of source rocks.  相似文献   

8.
The isotopic compositions of S (δ34S) and C (δ13C) were determined for the coal utilized by a power plant and for the fly ash produced as a by-product of the coal combustion in a 220-MW utility boiler. The coal samples analyzed represent different lithologies within a single mine, the coal supplied to the power plant, the pulverized feed coal, and the coal rejected by the pulverizer. The ash was collected at various stages of the ash-collection system in the plant. There is a notable enrichment in 34S from the base to the top of the coal seam in the mine, with much of the variation due to an upwards enrichment in the δ34S values of the pyrite. Variations in δ34S and in the amount of pyritic S in the coal delivered to the plant show that there was a change of source of coal supplied to the plant, between week one and week two of monitoring, supporting a previous study based on metal and sulfide geochemistry for the same plant. The fly ash has a more enriched δ34S than the pulverized coal and, in general, the δ34S is more enriched in fly ashes collected at cooler points in the ash-collection system. This pattern of δ34S suggests an increased isotopic fractionation due to temperature, with the fly ash becoming progressively depleted in 34S and the flue gas S-containing components becoming progressively enriched in 34S with increasing temperatures. Substantially less variation is seen in the C isotopes compared to S isotopes. There is little vertical variation in δ13C in the coal bed, with δ13C becoming slightly heavier towards the top of the coal seam. An 83–93% loss of solid phase C occurs during coal combustion in the transition from coal to ash owing to loss of CO2. Despite the significant difference in total C content only a small enrichment of 0.44–0.67‰ in 13C in the ash relative to the coal is observed, demonstrating that redistribution of C isotopes in the boiler and convective passes prior to the arrival of the fly ash in the ash-collections system is minor.  相似文献   

9.
Sulfide sulfur in mid-oceanic ridge hydrothermal vents is derived from leaching of basaltic-sulfide and seawater-derived sulfate that is reduced during high temperature water rock interaction. Conventional sulfur isotope studies, however, are inconclusive about the mass-balance between the two sources because 34S/32S ratios of vent fluid H2S and chimney sulfide minerals may reflect not only the mixing ratio but also isotope exchange between sulfate and sulfide. Here, we show that high-precision analysis of S-33 can provide a unique constraint because isotope mixing and isotope exchange result in different Δ33S (≡δ33S-0.515 δ34S) values of up to 0.04‰ even if δ34S values are identical. Detection of such small Δ33S differences is technically feasible by using the SF6 dual-inlet mass-spectrometry protocol that has been improved to achieve a precision as good as 0.006‰ (2σ).Sulfide minerals (marcasite, pyrite, chalcopyrite, and sphalerite) and vent H2S collected from four active seafloor hydrothermal vent sites, East Pacific Rise (EPR) 9-10°N, 13°N, and 21°S and Mid-Atlantic Ridge (MAR) 37°N yield Δ33S values ranging from −0.002 to 0.033 and δ34S from −0.5‰ to 5.3‰. The combined δ34S and Δ33S systematics reveal that 73 to 89% of vent sulfides are derived from leaching from basaltic sulfide and only 11 to 27% from seawater-derived sulfate. Pyrite from EPR 13°N and marcasite from MAR 37°N are in isotope disequilibrium not only in δ34S but also in Δ33S with respect to associated sphalerite and chalcopyrite, suggesting non-equilibrium sulfur isotope exchange between seawater sulfate and sulfide during pyrite precipitation. Seafloor hydrothermal vent sulfides are characterized by low Δ33S values compared with biogenic sulfides, suggesting little or no contribution of sulfide from microbial sulfate reduction into hydrothermal sulfides at sediment-free mid-oceanic ridge systems. We conclude that 33S is an effective new tracer for interplay among seawater, oceanic crust and microbes in subseafloor hydrothermal sulfur cycles.  相似文献   

10.
Radiation-induced smoky color and associatedelectron paramagnetic resonance (EPR) signals develop only in potassium feldspar (KAlSi3O8) free of structurally bound molecular water. Fluid inclusion water does not influence coloration. The integrated intensity of each of the four bands (11,600, 16,200, 19,100, and 27,200 cm?1) in the optical absorption spectra are linearly correlated with the doubly-integrated intensity of a broad, asymmetric first derivative atg eff=2.027 in EPR spectra. In microcline, the EPR pattern is resolved into an asymmetric six-line pattern atg eff=2.024 and a single derivative atg eff=2.009 which, based on analogy to alkali-silicate glass, are due respectively to [SiO4/K+]2+ and a hole shared between two nonbonding oxygens on Si. We propose that structural water inhibits formation of smoky centers in feldspar by releasing atomic hydrogen during irradiation which destroys centers while diffusing towards a stable site.  相似文献   

11.
Measurements were made of sulphur and oxygen isotope ratios of sulphate in some Slovenian rivers, lakes and tap waters. δ34S ranged from −0.2 to + 13.3‰, δ18O ranged from +4.9 to + 13.6‰, and the sulphate content varied from 0.8 to 41.4 mg/L. Rivers flowing from the Julian Alps contain a very low amount of sulphate that is leached from a thin horizon of soil by rain. As confirmed by their low δ18O values, these sulphates do not enter the rivers directly in rain, but arise from biochemical cycling in the soil. The low δ34S of this sulphate indicates that it originates from the oxidation of sedimentary sulphides. The evolution of sulphates along the river course was investigated for the Sava and Ljubljanica rivers. The variations observed in sulphate from the waters studied result from variations in the contribution of sulphates of different origin. Downstream the Sava River sulphate is depleted in the heavy isotopes of both sulphur and oxygen, with δ-values gradually tending toward the δ-values of groundwater sulphates in the watershed. In contrast, the δ-values of sulphate in the Ljubljanica River are almost constant and similar to those of sulphate in local groundwater. Introduction of water from Italian and Slovenian mines was recorded in the Soča River, where the lowest δ34S value of sulphate sulphur (−0.2‰) was observed. In addition, the influence of sulphate from the oxidation of sedimentary sulphides was recorded in the Sotla River. No evidence was found for introduction of sulphate from factories.  相似文献   

12.
《Organic Geochemistry》1987,11(2):65-71
ESR measurements of stepwise-pyrolyzed melanoidins and humic substances (at various temperatures, mesh size, and pH values) furnished the following information: the melanoidin structure stabilizes the long-living free radicals in a manner similar to humic substances; the g and Ng values of melanoidins are similar to those of the humic substances, the cleavage of CC and CX (X = heteroatom) bonds increases the Ng value. Thermogravimetric curves, weight loss by stepwise pyrolysis, and 13C-CP/MAS NMR were found to be in good correlation with ESR data regarding the structural features of melanoidins and humic substances.  相似文献   

13.
《Applied Geochemistry》2000,15(6):777-784
In connection with the discovery of a new type of Pt deposit in low-rank brown coals and black shales, the interaction of Pt-bearing aqueous solutions with fractionated organic matter (asphaltenes and asphaltenic acids) was studied at 200–400°C and 1 kbar total pressure. It was found that chemical sorption onto the organic matter lowers Pt content in the aqueous solutions by about two orders of magnitude relative to organic-free systems. Thermal maturation of the asphaltenes leads to its aromatization and concomitant sorption of Pt from n×10−4 mPt (mol per kg of dry matter) at 200°C to n×10−2 mPt at 400°C. Thus, the Pt chemisorption on activated carbonized organic matter may be an effective mechanism of Pt accumulation in C-bearing rocks.  相似文献   

14.
Single-crystal electron paramagnetic resonance (EPR) spectra of a natural citrine quartz without any artificial irradiation, measured at W-band frequencies (∼94 GHz) and temperatures of 77, 110 and 298 K, allow better characterization of three previously-reported Centers (#6, #7 and B) and discovery of three new defects (B′, C′ and G′). The W-band EPR spectra reveal that Centers #6 and #7 do not reside on twofold symmetry axes, contrary to results from a previous X-band EPR study. The W-band spectra also show that the previously reported Center B is a mixture of two defects (B and B′) with similar g matrices but different-sized 27Al hyperfine structures. Center C′ has similar principal g values to the previously reported Center C but is distinct from the latter by a larger 27Al hyperfine structure with splittings from 0.10 to 0.22 mT. Also, Center G′ has a similar g matrix to the previously reported Center G but a different 27Al hyperfine structure with splittings from 0.41 to 0.53 mT. These spin-Hamiltonian parameters, together with observed thermal properties and microwave-power dependence, suggest that Centers #6 and #7 probably represent O23− type defects. Centers B and B′ are probably superoxide radicals (O2−) with the unpaired spin localized on the same pair of oxygen atoms around a missing Si atom but linked to a substitutional Al3+ ion each at different neighboring tetrahedral sites. Similarly, Centers G and G′ are most likely superoxide radicals with the unpaired spin localized on another pair of oxygen atoms around a missing Si atom and linked to a substitutional Al3+ ion each at different neighboring tetrahedral sites. Center C′ is probably an ozonide radical associated with a missing Si atom and linked to a substitutional Al3+ ion at the neighboring tetrahedral site. This study exemplifies the value of  high-frequency EPR for discrimination of  similar defect centers and determination of  small local structural distortions that are often difficult to resolve in conventional  X- and Q-band EPR studies.  相似文献   

15.
Moisture content is the main factor affecting the occurrence and flow of gas in bituminous coal and restricts the gas permeability of the coal seam, which affects the effectiveness of gas extraction from the coal seam directly. In order to study the influence of moisture content on the gas seepage characteristics of bituminous coal, this paper focused on bituminous coal from the Xutuan coal mine and used a bespoke laboratory unit called a Gas Flow and Displacement Testing Apparatus (GFDTA). The moisture content of bituminous coal was measured, and the axial and radial gas seepage experiments of bituminous coal under different moisture content conditions were carried out. The average original moisture content (1.3%) and the average saturated moisture content (2.4%) of the bituminous coal sample were obtained. It was observed that, with the increase of time, the original moisture content of the coal decreased with a negative exponential function and the wetting moisture content increased with an Exponential Association function. The gas axial seepage experimental results showed that when the moisture content was lower, the coal adsorbed CH4; when the moisture content was higher than Mad, the two fields of gas and liquid are coupled and affect the axial flow of the CH4, decreasing the moisture content. With higher moisture content, the interaction between the two is more readily evident and the diffusion behavior of the CH4 has a greater impact on the moisture content. Axial and radial gas seepage experiments, under the same gas pressure, axial pressure, and confining pressure, revealed that with the increase of moisture content, the axial and radial permeability of bituminous coal first increased and then decreased. This phenomenon is analyzed by the water lock effect, the effects of sorption on gas seepage and moisture content on gas adsorption effects. Among them, critical moisture content of approximately 1% exists when the axial and confining pressures are loaded or unloaded at the same time as well as the axial pressure loading or unloading alone. However, the critical moisture content is about 0.5% under confining pressure loading or unloading alone. In addition, in radial seepage experiments, it was observed that the volumetric strain of the coal decreased with the increase in the moisture content.  相似文献   

16.
Raman spectra of natural and synthetic samples of stishovite have been measured with a micro-optical spectrometer system. These spectra have a pattern that is characteristic of rutile-structured oxides. The spectrum of synthetic stishovite is characterized by well-resolved bands at 231, 589, 753, and 967 cm?1, which are assigned as theB 1g,E g,A 1g, andB 2g fundamentals, respectively, of the first-order Raman spectrum of the ideal, ordered structure. Natural stishovite obtained from Meteor Crater, Arizona has a first-order Raman spectrum that is fully consistent with that of the synthetic material. The observed spectrum of the natural sample, however, is weaker and has bands in addition to those identified as fundamentals in the spectrum of the synthetic material. A broad band at ～475 cm?1 may be indicative of glass or contaminants derived from the extraction procedure. Alternatively, this band may arise from multiphonon scattering that is enhanced by poor crystallinity or structural disorder in the natural shocked sample.  相似文献   

17.
Natural specimens of green gemological euclase (chemical formula BeAlSiO4(OH)) from Brazil were investigated by electron paramagnetic resonance (EPR) and optical absorption. In addition to iron-related EPR spectra, analyzed recently in blue and colorless euclase, chromium and vanadium-related EPR spectra were also detected in green euclase. Their role as color causing centers is discussed. The results indicate that Cr3+ ions substitute for Al3+ ions in the euclase structure. The EPR rotation patterns of Cr3+ with electron spin S = 3/2 were analyzed with monoclinic spin Hamiltonian leading to the parameters of g xx , g yy and g zz equal to 2.018, 2.001 and 1.956 and electronic fine structure parameters of D = −8.27 GHz and E = 1.11 GHz, respectively, with high asymmetry ratio E/D = 0.13. For the vanadium-related EPR spectra the situation is different. It is concluded that vanadium is incorporated as the vanadyl radical VO2+ with electron spin S = 1/2 with nearly axial spin Hamiltonian parameters gzz = 1.9447, g xx  = 1.9740 g yy  = 1.9669 and axial hyperfine interactions due to the nuclear spin I = 7/2 of the 51V isotope leading to A zz  = 502 MHz, A xx  = 150 MHz and A yy  = 163 MHz. The green color of euclase is caused by two strong broad absorption bands centered at 17,185 and 24,345 cm−1 which are attributed to the 4A2g → 4T2g, 4T1g transitions of Cr3+, respectively. Vanadyl radicals may introduce some absorption bands centered in the near infrared with tail extending into the visible spectral range.  相似文献   

18.
Data on the pulse structure and variations of the linear polarization angle at frequencies near 1 GHz have been used to estimate the angles β between the rotational axis and magnetic moment of the neutron stars assocaited with 80 pulsars. The calculations applied several methods. The minimum values of β were estimated from the observed pulse width W 10 at the 10% level for the entire sample. Maximum estimates of β were obtained for six sources with small polarization position angle derivatives. Equations for the angle β were derived for various forms of the observed profile, and solutions obtained for 34 pulsars. The β values calculated using different methods are compared. For three pulsars with known interpulses, the obtained values of β demonstrate that two (PSR B1055-52 and PSR 1822-09) are aligned rotators, whereas the other (PSR B1702-19) is an orthogonal rotator. A search for interpulses and interpulse emission in PSRB1641-45, PSR1642-03, and PSR 1944+17 is necessary, and a search for an interpulse at 180° from the main pulse is required in PSR B2321-61.  相似文献   

19.
The spin Hamiltonian parameters (zero-field splittings D, g factors g // and g ⊥) for V3+ in the alum compounds are theoretically studied using the perturbation formulas for these parameters for a 3d2 ion in the trigonally distorted octahedra. The contributions from the dynamical Jahn–Teller effect, the configuration interactions and the ligand orbital and spin–orbit coupling interactions are considered from the cluster approach in a uniform way. The angles in the deformed octahedra around V3+ ions are increased by 1.1°–2.7°, as compared with those ones for the host. The theoretical spin Hamiltonian parameters based on the above angular variations and the related effects show good agreement with the experimental data, which reveal that these effects (especially the Jahn–Teller effect) can bring forward significant influences on the spin Hamiltonian parameters, and should be taken into account in electron paramagnetic resonance (EPR) analysis. The contributions from the configuration interactions and the ligand orbital and spin–orbit coupling interactions are quantitatively involved from the cluster approach in a uniform way. The results are discussed.  相似文献   

20.
Previous studies of both ore and non-ore-bearing intrusives in the Permo-Triassic flood basalts of the Siberian platform in the Noril’sk area have shown that high-grade Ni-Cu-platinum group elements (PGE) mineralization is associated with anomalously high δ34S values of ∼8 to 12‰. In addition, several researchers have proposed that observed depletions in the Cu, Ni, and PGE content of basaltic lavas of the Nadezhdinsky (Nd) Formation are related to diffusional exchange with, and upgrading in metal tenor of, sulfides in the volcanic conduit system. Sulfur isotopic studies of the lavas at Noril’sk were initiated to determine if interaction with crustally derived sulfur in the conduit system was evident, and if the Nd lavas in particular were characterized by an anomalous isotopic signature. δ34S values of the lavas range from −4.5 to 8.7‰ Vienna Cañon Diablo Troilite (VCDT), with S concentrations from <40 to 1373 ppm. The majority of δ34S values range from 0 to 4‰, and are similar to those from S-poor intrusions in the Noril’sk area. Although textural data are not supportive of early sulfide saturation and the presence of immiscible sulfide droplets in the lavas, recrystallization may have erased expected mineralogical and textural evidence. Mineralogical data indicate that hydrothermal alteration of the lavas has occurred, but S redistribution has been restricted to localized areas and δ34S values have not been affected. The relatively low S concentrations of the lavas are thought to be due in large part to degassing of the lavas in the shallow conduit system and during eruption. Our calculations are consistent with the premise that degassing of basaltic magmas at temperatures in excess of ∼900°C at QFM leads to only minor 34S-depletion of sulfur remaining in the melt, and decreases in δ34S values of less than 2‰ at 90% degassing. For this reason all lavas with δ34S values in excess of ∼ 2‰ require a contribution of 34S-enriched country rock sulfur. Because of the high S content and δ34S value (∼ 16-20‰) of evaporites in the country rocks at Noril’sk, contamination of less than 0.5% is required to explain the most 34S-enriched lavas. The Nd lavas have an average δ34S of 2.9‰, but show no difference in S isotopic composition relative to the other lavas, suggesting that metal depletion involved only limited S transfer, or that exchange between mantle-derived S and S of crustal origin buffered δ34S values to less than ∼5‰. Anomalously positive δ34S values, similar to those of the ore-bearing intrusives in the Noril’sk region, are not consistently found in low-S rocks, either lavas or intrusives. Although the mechanism for the derivation of sulfide in the ore-bearing intrusions remain speculative, it is clear that the formation of sulfide ores characterized by high metal tenors proceeded only in the presence of sulfur of crustal origin.  相似文献   

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