首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The solubilities of PbCO3(s), 2PbCO2·Pb(OH)2(s), and of 3PbCO3 2Pb(OH)2(s) have been studied at 25°C ± 0.1°C in solutions of the constant ionic strength I = 0.3 mol/dm3, consisting primarily of sodium perchlorate. A few experiments with hydrocerussite were performed in solutions of 0.1 M KNO3. The concentrations of lead and hydrogen ions have been determined in solution in contact with the solid phase. From experimental data the following values for equilibrium constants are obtained: log [Pb2+]·pCO2·[H+]?2 = 5.20log [Pb2+]·pCO0.672·[H+]?2 = 6.80log [Pb2+]3·[CO2?3]2·[OH?]2 = ?44.08 (and ?44.8 forI = 0.1 M)log [PbCO03]·[Pb2+]?1·[CO2?3]?1 = 5.40log [Pb(CO3)2?2]·[Pb2+]?1·[CO2?3]?2 = 8.86 The data indicate that hydrocerussite is the most stable solid phase in natural waters. Comparison with the literature and needs for further research are also presented.  相似文献   

2.
Solution calorimetric measurements compared with solubility determinations from the literature for the same samples of gibbsite have provided a direct thermochemical cycle through which the Gibbs free energy of formation of [Al(OH)4 aq?] can be determined. The Gibbs free energy of formation of [Al(OH)4 aq?] at 298.15 K is ?1305 ± 1 kJ/mol. These heat-of-solution results show no significant difference in the thermodynamic properties of gibbsite particles in the range from 50 to 0.05 μm.The Gibbs free energies of formation at 298.15 K and 1 bar pressure of diaspore, boehmite and bayerite are ?9210 ± 5.0, ?918.4 ± 2.1 and ?1153 ± 2 kJ/mol based upon the Gibbs free energy of [A1(OH)4 aq?] calculated in this paper and the acceptance of ?1582.2 ± 1.3 and ?1154.9 ± 1.2 kJ/mol for the Gibbs free energy of formation of corundum and gibbsite, respectively.Values for the Gibbs free energy formation of [Al(OH)2 aq+] and [AlO2 aq?] were also calculated as ?914.2 ± 2.1 and ?830.9 ± 2.1 kJ/mol, respectively. The use of [AlC2 aq?] as a chemical species is discouraged.A revised Gibbs free energy of formation for [H4SiO4aq0] was recalculated from calorimetric data yielding a value of ?1307.5 ± 1.7 kJ/mol which is in good agreement with the results obtained from several solubility studies.Smoothed values for the thermodynamic functions CP0, (HT0 - H2980)T, (GT0 - H2980)T, ST0 - S00, ΔH?,2980 kaolinite are listed at integral temperatures between 298.15 and 800 K. The heat capacity of kaolinite at temperatures between 250 and 800 K may be calculated from the following equation: CP0 = 1430.26 ? 0.78850 T + 3.0340 × 10?4T2 ?1.85158 × 10?4T212 + 8.3341 × 106 T?2.The thermodynamic properties of most of the geologically important Al-bearing phases have been referenced to the same reference state for Al, namely gibbsite.  相似文献   

3.
The thermodynamic properties of monohydrocalcite, CaCO3 · H2O, have been obtained using a well-characterized natural specimen. Equilibration of the solid with water at 25°C under 0.97 atm CO2 led to an activity product [Ca2+][CO32?] = 10?7.60±0.03 and a free energy of formation ΔGfo = ?325,430 ± 270 calmol?. The enthalpy of solution of monohydrocalcite in 0.1 N HCl at 25°C led to a standard enthalpy of formation ΔHfo = ?358,100 ± 280 cal mol?1. Estimates of the variation of ΔGf with temperature and pressure showed monohydrocalcite to be metastable with respect to calcite and aragonite.  相似文献   

4.
The heat capacity of natural chamosite (XFe=0.889) and clinochlore (XFe=0.116) were measured by differential scanning calorimetry (DSC). The samples were characterised by X-ray diffraction, microprobe analysis and Mössbauer spectroscopy. DSC measurements between 143 and 623?K were made following the procedure of Bosenick et?al. (1996). The fitted data for natural chamosite (CA) in J?mol?1?K?1 give: C p,CA = 1224.3–10.685?×?103?×?T ??0.5???6.4389?× 106?×T ??2?+?8.0279?×?108?×?T ??3 and for the natural clinochlore (CE): C p,CE = 1200.5–10.908?×?103?×T ??0.5?? 5.6941?×?106?×?T ??2?+?7.1166?×?108?×?T ??3. The corrected C p-polynomial for pure end-member chamosite (Fe5Al)[Si3AlO10](OH)8 is C p,CAcor = 1248.3–11.116?× 103?×?T ??0.5???5.1623?×?106?×?T ??2?+?7.1867?×?108×T ??3 and the corrected C p-polynomial for pure end-member clinochlore (Mg5Al)[Si3AlO10](OH)8 is C p,CEcor = 1191.3–10.665?×?103?×?T ??0.5???6.5136?×?106?×?T ??2?+ 7.7206?×?108?×?T ??3. The corrected C p-polynomial for clinochlore is in excellent agreement with that in the internally consistent data sets of Berman (1988) and Holland and Powell (1998). The derived C p-polynomial for chamosite (C p,CAcor) leads to a 4.4% higher heat capacity, at 300?K, compared to that estimated by Holland and Powell (1998) based on a summation method. The corrected C p-polynomial (C p,CAcor) is, however, in excellent agreement with the computed C p-polynomial given by Saccocia and Seyfried (1993), thus supporting the reliability of Berman and Brown's (1985) estimation method of heat capacities.  相似文献   

5.

Coal mining has serious impacts on local environment, including damage to the land and soil by subsidence, damage to ground-water systems through the fracturing and subsiding of overlying rocks, contamination of surface waters with acid mine drainage, and pollution of the atmosphere by release of toxic gases. The damage to ground water and its consequent impacts on the regional environment is the core of research of the coal mining from the perspective of environment protection. The present paper focuses on the changes of surface vegetation coverage, the pollutants released from pit coal power plants, and the damages to the ground aquifers induced by mining activities in arid Eastern Junggar coalfield of China. At first, the authors investigated the changes of surface vegetation coverage, since mining began in the 2000s using Landsat data. Results show that the low surface vegetation coverage (grade 1 plus grade 2) in the southern part of the region decreased from 11.62?×?108 m2 in 2003 to 9.57?×?108 m2 in 2017 (?17.6%), while it increased from 11.58?×?108 m2 in 2003 to 12.70?×?108 m2 in 2017 (+?9.7%) in the eastern part. The high surface vegetation coverage (grade 3 plus grade 4) in the southern part increased from 1.94?×?108 m2 in 2003 to 4.00?×?108 m2 in 2017 (+?106.2%), while it decreased from 4.39?×?108 m2 in 2003 to 3.26?×?108 m2 in 2017 (?25.74%) in the eastern part. The data of annual precipitation during the same period in this area show that the changes of surface vegetation coverage have less relationship with the annual precipitation, which indicates that the mining activities is probably the major factor for that. Second, a statistic of air pollutants generated from pit coal power plants was made based on data of references. Results show that the estimated gaseous pollutant emissions increased as 865.23 tons of smoke particles, 5940.73 tons of SO2, and 7584.48 tons of NO2 in 2013, which increased rapidly with 9.73 times the smoke particle, 21.69 times the SO2, and 9.24 times the NO2 than that of 2007. And then, the physical and numerical simulation of the damage of mining activities to aquifers was made to show the permeability of the reference points of overlying aquifers varies associated with mining activities. Results show that the porous rock matrix permeability has a negative relationship with fluctuation during mining, while the fracture permeability shows a positive one. Finally, a case investigation in southern area surrounding this coalfield was illustrated. Result shows that the local ground-water level decreased by 16 m difference from the altitude level of?+?774 m in 2003 to?+?758 m in 2013. Data and results from this study presented the already and the potential pollutions and damages to local environment induced by the mining activities in this region.

  相似文献   

6.
The high-pressure response of the cell parameters of calcite, CaCO3, has been investigated by single crystal X-ray diffraction. The unit cell parameters have been refined from 0 to 1.435?GPa, and the linear and volume compressibilities have been measured as β a =2.62(2)?×?10?3?GPa?1,β c =7.94(7)?×?10?3?GPa?1, β v =13.12?×?10?3?GPa?1. The bulk modulus has been obtained from a fit to the Birch-Murnaghan equation of state, giving K 0=73.46?±?0.27?GPa and V 0=367.789 ±?0.004?Å3 with K′=4. Combined with earlier data for magnesite, ankerite and dolomite, these data suggest that K 0 V 0 is a constant for the Ca-Mg rhombohedral carbonates.  相似文献   

7.
A workflow is described to estimate specific storage (S s) and hydraulic conductivity (K) from a profile of vibrating wire piezometers embedded into a regional aquitard in Australia. The loading efficiency, compressibility and S s were estimated from pore pressure response to atmospheric pressure changes, and K was estimated from the earliest part of the measurement record following grouting. Results indicate that S s and K were, respectively, 8.8?×?10?6 to 1.2?×?10?5 m?1 and 2?×?10?12 m s?1 for a claystone/siltstone, and 4.3?×?10?6 to 9.6?×?10?6 m?1 and 1?×?10?12 to 5?×?10?12 m s?1 for a thick mudstone. K estimates from the pore pressure response are within one order of magnitude when compared to direct measurement in a laboratory and inverse modelled flux rates determined from natural tracer profiles. Further analysis of the evolution and longevity of the properties of borehole grout (e.g. thermal and chemical effects) may help refine the estimation of formation hydraulic properties using this workflow. However, the convergence of K values illustrates the benefit of multiple lines of evidence to support aquitard characterization. An additional benefit of in situ pore pressure measurement is the generation of long-term data to constrain groundwater flow models, which provides a link between laboratory scale data and the formation scale.  相似文献   

8.
The heat capacities of lawsonite, margante, prehnite and zoisite have been measured from 5 to 350 K with an adiabatic-shield calorimeter and from 320 to 999.9 K with a differential-scanning calorimeter. At 298.15 K, their heat capacities, corrected to end-member compositions, are 66.35, 77.30, 79.13 and 83.84 cal K?1 mol?1; their entropies are 54.98, 63.01, 69.97 and 70.71 cal K?1 mol?1, respectively. Their high-temperature heat capacities are described by the following equations (in calories, K, mol): Lawsonite (298–600 K): Cp° = 66.28 + 55.95 × 10?3T ? 15.27 × 105T?2 Margarite (298–1000 K): Cp° = 101.83 + 24.17 × 10?3T ? 30.24 × 105T?2 Prehnite (298–800 K): Cp° = 97.04 + 29.99 × 10?3T ? 25.02 × 105T?2 Zoisite (298–730 K): Cp° = 98.92 + 36.36 × 10?3T ? 24.08 × 105T?2 Calculated Clapeyron slopes for univariant equilibria in the CaO-Al2O3-SiO2-H2O system compare well with experimental results in most cases. However, the reaction zoisite + quartz = anorthite + grossular + H2O and some reactions involving prehnite or margarite show disagreements between the experimentally determined and the calculated slopes which may possibly be due to disorder in experimental run products. A phase diagram, calculated from the measured thermodynamic values in conjunction with selected experimental results places strict limits on the stabilities of prehnite and assemblages such as prehnite + aragonite, grossular + lawsonite, grossular + quartz, zoisite + quartz, and zoisite + kyanite + quartz. The presence of this last assemblage in eclogites indicates that they were formed at moderate to high water pressure.  相似文献   

9.
In order to examine the fluxes of methane (CH4) from the Indian estuaries, measurements were carried out by collecting samples from 26 estuaries along the Indian coast during high discharge (wet) and low water discharge (dry) periods. The CH4 concentrations in the estuaries located along the west coast of India were significantly higher (113?±?40 nM) compared to the east coast of India (27?±?6 nM) during wet and dry periods (88?±?15 and 63?±?12 nM, respectively). Supersaturation of CH4 was observed in the Indian estuaries during both periods ((0.18 to 22.3?×?103 %). The concentrations of CH4 showed inverse relation with salinity indicating that freshwater is a significant source. Spatial variations in CH4 saturation were associated with the organic matter load suggesting that its decomposition may be another source in the Indian estuaries. Fluxes of CH4 ranged from 0.01 to 298 μmol m?2 day?1 (mean 13.4?±?5 μmol m?2 day?1) which is ~30 times lower compared to European estuaries (414 μmol m?2 day?1). The annual emission from Indian estuaries, including Pulicat and Adyar, amounted to 0.39?×?1010 g CH4?year?1 with the surface area of 0.027?×?106 km2 which is significantly lower than that in European estuaries (2.7?±?6.8?×?1010 g CH4?year?1 with the surface area of 0.03?×?106 km2). This study suggests that Indian estuaries are a weak source for atmospheric CH4 than European estuaries and such low fluxes were attributed to low residence time of water and low decomposition of organic matter within the estuary. The CH4 fluxes from the Indian estuaries are higher than those from Indian mangroves (0.01?×?1010 g CH4?year?1) but lower than those from Indian inland waters (210?×?1010 g CH4?year?1).  相似文献   

10.
The solubility and dissolution kinetics of apatite in felsic melts at 850°–1500°C have been examined experimentally by allowing apatite crystals to partially dissolve into apatite-undersaturated melts containing 0–10 wt% water. Analysis of P and Ca gradients in the crystal/melt interfacial region enables determination of both the diffusivities and the saturation levels of these components in the melt. Phosphorus diffusion was identified as the rate-limiting factor in apatite dissolution. Results of four experiments at 8 kbar run in the virtual absence of water yield an activation energy (E) for P diffusion of 143.6 ± 2.8 kcal-mol?1 and frequency factor (D0) of 2.23+2.88?1.26 × 109cm2-sec?1. The addition of water causes dramatic and systematic reduction of both E and D0 such that at 6 wt% H2O the values are ~25 kcal-mol?1 and 10?5 cm2-sec?1, respectively. At 1300°C, the diffusivity of P increases by a factor of 50 over the first 2% of water added to the melt, but rises by a factor of only two between 2 and 6%, perhaps reflecting the effect of a concentration-dependent mechanism of H2O solution. Calcium diffusion gradients do not conform well to simple diffusion theory because the release of calcium at the dissolving crystal surface is linked to the transport rate of phosphorus in the melt, which is typically two orders of magnitude slower than Ca. Calcium chemical diffusion rates calculated from the observed gradients are about 50 times slower than calcium tracer diffusion.Apatite solubilities obtained from these experiments, together with previous results, can be described as a function of absolute temperature (T) and melt composition by the expression: In Dapatite/meltP = [(8400 + ((SiO2 ? 0.5)2.64 × 104))/T] ? [3.1 + (12.4(SiO2 ? 0.5))] where SiO2 is the weight fraction of silica in the melt. This model appears to be valid between 45% and 75% SiO2, 0 and 10% water, and for the range of pressures expected in the crust.The diffusivity information extracted from the experiments can be directly applied to several problems of geochemical interest, including I) dissolution times for apatite during crustal anatexis, and 2) pileup of P, and consequent local saturation in apatite, at the surfaces of growing major-mineral phases.  相似文献   

11.
{M[UO2¦AsO4]2 · nH2O} with M=Cu2+, Co2+, Ni2+ has been synthesized from reagent grade chemicals and by ion exchange of trögerite {HUO2AsO4 · 4 H2O}. Synthetic meta-zeunerite (M=Cu2+), meta-kirchheimerite (M=Co2+) and nickel-uranylarsenate are all tetragonal. The cell parameters determined from Guinier-Hägg diffraction data for {Cu[UO2¦AsO4]2 · 8 H2O} are a=b=7.10 Å and c=17.42 Å, with Z=2 and the measured density 3.70 g cm?3. The cell parameters for {Co[UO2¦AsO4]2 · 7 H2O} and {Ni[UO2¦AsO4]2 · 7 H2O} are a=b=20.25 Å and c=17.20 Å, with Z=16 and the measured density 3.82 and 3.74 g cm?3, respectively. The solubility products for synthetic Cu-, Co- and Ni-uranylarsenate at 25° C are 10?49.20, 10?45.34 and 10?45.10, respectively. The zeta-potential remains negative between pH=2 and pH=9 and is strongly affected by the presence of different cations.  相似文献   

12.
Thermal expansion data, determined by powder X-ray diffraction methods are presented for 11 members of the (Li,Na,K,Rb)8(Al6Si6O24)Cl2 solid solution series, 3 members of the (Na,K)8(Al6Si6O24)Br2 solid solution series and Na8(Al6Si6O24)I2. Only the latter showed a discontinuity in its expansion curve at 810° C wigh a mean linear expansion coefficient of 22.0×10?6 °C?1 below and 7.7×10?6 °C?1 above the discontinuity. The mean expansion coefficients from 0° to 500° C decrease gradually over the range of room temperature cell edges from 8.4 to 8.89 Å, then increase up to a cell edge of 9.01 Å above which they decrease sharply and extrapolate to a zero coefficient at 9.4 Å. These variations may be related to the expansion characteristics of the bonds between the cavity cations and cavity anions in different sodalites. The aluminosilicate-sodalites which show a discontinuity in their thermal expansion curves are those with large cavity anions, I? or SO 4 2? ; the discontinuity is believed to occur at the point when the x-coordinate of the cavity cation becomes 0.25.  相似文献   

13.
Distribution coefficients were obtained for yttrium and the rare earth elements (YREEs) in aqueous solutions containing freshly precipitated hydroxides of trivalent cations (Fe3+, Al3+, Ga3+, and In3+). Observed patterns of log i K S–, where i K S = [MS i ][M3+]?1[S i ]?1, [MS i ] is the concentration of a sorbed YREE, [M3+] is the concentration of a free hydrated YREE ion, and [S i] is the concentration of a sorptive solid substrate (Fe(III), Al, Ga, In)– exhibited similarities to patterns of YREE solution complexation constants with hydroxide (OH β 1) and fluoride (F β 1), but also distinct differences. The log i K S pattern for YREE sorption on Al hydroxide precipitates is very similar to the pattern of YREE hydroxide stability constants (logOH β 1) in solution. Linear free-energy relationships between log i K S and logOH β 1 showed excellent correlation for YREE sorption on Al hydroxide precipitates, good correlation for YREE sorption on Ga or In hydroxide precipitates, yet poor correlation for YREE sorption on Fe(III) hydroxide precipitates. Whereas the correlation between log i K S and logF β 1 was generally poor, patterns of log( i K S/F β 1) displayed substantially increased smoothness compared to patterns of log i K S. This indicates that the conspicuous sequence of inflections along the YREE series in the patterns of log i K S and logF β 1 is very similar, particularly for In and Fe(III) hydroxide precipitates. While the log i K S patterns obtained with Fe(III) hydroxide precipitates in this work are quite distinct from those obtained with Al, Ga, and In hydroxide precipitates, they are in good agreement with patterns of YREE sorption on ferric oxyhydroxide precipitates reported by others. Furthermore, our log i K S patterns for Fe(III) hydroxide precipitates bear a striking resemblance to predicted log i K S patterns for natural surfaces that are based on YREE solution chemistry and shale-normalized YREE concentrations in seawater. Yttrium exhibits an itinerant behavior among the REEs: sorption of Y on Fe(III) hydroxide precipitates is intermediate to that of La and Ce, while for Al hydroxide precipitates Y sorption is similar to that of Eu. This behavior of Y can be rationalized from the propensities of different YREEs for covalent vs. ionic interactions. The relatively high shale-normalized concentration of Y in seawater can be explained in terms of primarily covalent YREE interactions with scavenging particulate matter, whereby Y behaves as a light REE, and primarily ionic interactions with solution ligands, whereby Y behaves as a heavy REE.  相似文献   

14.
Ab initio, molecular orbital calculations at the 3–21G* level were carried out on H6Si3O9, [H6Si2AlO2]1?, [H6SiAl2O9]2?, and [H6A13O9]3? cyclic molecules in order to determine their structures and vibrational frequencies. These three-membered rings were found to have minima in their potential energy surfaces indicating stability of the species. The H6Si3O9 ring was found to be slightly non-planar, but the [H6SiAl2O9]2? and [H6Al33O9]3? configurations are more planar. Vibrational frequencies of the Raman-active, bridging oxygen “breathing” modes increase with Si4+ content. Galeener's (1982a, b) assignment of the D2 peak (606 cm?1) in the Raman spectrum of vitreous silica to an oxygen breathing mode in rings of three SiO4 tetrahedra is reconfirmed. Correlation of the ring breathing mode frequencies as a function of (AI/AI + Si) with Raman peaks in the SiO2-NaAlSiO4 system is high. Three-membered aluminosilicate rings are likely to exist and give rise to Raman peaks between 540 and 600 cm?1 in fully-polymerized aluminosilicate glasses.  相似文献   

15.
The solubility of quartz has been determined in borax buffer solutions having total boron concentrations of 0.10, 0.20, 0.40 and 0.60 mol kg?1 and over the temperature range 130–350°C at the saturated vapour pressure of the system. The first ionization constant of silicic acid was calculated from the solubility data and varied from ?logK1 = 8.88 (± 0.15) at 130°C to ?logK1 = 10.06 (± 0.20) at 350°C. The solubility of quartz in these solutions was due to the presence of the three species, H4SiO4, H3SiO4? and NaH3SiO4°. The equilibrium constant for the reaction, Na+ + H3SiO4? = NaH3SiO4° extended from log Kas = 1.18?1.40 (± 0.20) over the temperature interval 135–301°C. The formation of NaH3SiO4° ion pairs was concluded to contribute significantly to the solubility of quartz in alkaline hydrothermal solutions when pH > 8 and sodium concentration exceeds 0.10 mol kg?1.  相似文献   

16.
We estimated CO2 and CH4 emissions from mangrove-associated waters of the Andaman Islands by sampling hourly over 24 h in two tidal mangrove creeks (Wright Myo; Kalighat) and during transects in contiguous shallow inshore waters, immediately following the northeast monsoons (dry season) and during the peak of the southwest monsoons (wet season) of 2005 and 2006. Tidal height correlated positively with dissolved O2 and negatively with pCO2, CH4, total alkalinity (TAlk) and dissolved inorganic carbon (DIC), and pCO2 and CH4 were always highly supersaturated (330–1,627 % CO2; 339–26,930 % CH4). These data are consistent with a tidal pumping response to hydrostatic pressure change. There were no seasonal trends in dissolved CH4 but pCO2 was around twice as high during the 2005 wet season than at other times, in both the tidal surveys and the inshore transects. Fourfold higher turbidity during the wet season is consistent with elevated net benthic and/or water column heterotrophy via enhanced organic matter inputs from adjacent mangrove forest and/or the flushing of CO2-enriched soil waters, which may explain these CO2 data. TAlk/DIC relationships in the tidally pumped waters were most consistent with a diagenetic origin of CO2 primarily via sulphate reduction, with additional inputs via aerobic respiration. A decrease with salinity for pCO2, CH4, TAlk and DIC during the inshore transects reflected offshore transport of tidally pumped waters. Estimated mean tidal creek emissions were ～23–173 mmol m?2 day?1 CO2 and ～0.11–0.47 mmol m?2 day?1 CH4. The CO2 emissions are typical of mangrove-associated waters globally, while the CH4 emissions fall at the low end of the published range. Scaling to the creek open water area (2,700 km2) gave total annual creek water emissions ～3.6–9.2?×?1010 mol CO2 and 3.7–34?×?107 mol CH4. We estimated emissions from contiguous inshore waters at ～1.5?×?1011 mol CO2?year?1 and 2.6?×?108 mol CH4?year?1, giving total emissions of ～1.9?×?1011 mol CO2?year?1 and ～3.0?×?108 mol CH4?year?1 from a total area of mangrove-influenced water of ～3?×?104 km2. Evaluating such emissions in a range of mangrove environments is important to resolving the greenhouse gas balance of mangrove ecosystems globally. Future such studies should be integral to wider quantitative process studies of the mangrove carbon balance.  相似文献   

17.
Nitrogen oxides (NO x ) are involved in acid rain and ozone formation, as well as destruction. NO x are climate-relevant trace gases in the atmosphere. Atmospheric NO x originate from anthropogenic emissions (mainly combustion processes). NO from natural processes derives from thunderstorms and soil microbial processes. They may play a crucial role in soil?Catmosphere feedback processes. This study aims to investigate NO x -emissions from soils under different land use, geographical and meteorological conditions. NO x -emissions were quantified in both field and laboratory experiments with a closed static chamber. Disturbed soil samples have been used for laboratory experiments. A climate chamber was used to regulate soil temperature of the samples. Field experiments showed that NO-soil emissions strongly depend on soil temperature. NO-emissions from a soil under meadow showed significant daily variations, unlike soil below spruce forest. Peak emission values were 18???g NO?CN?m?2?h?1 above meadow and 1.3???g NO?CN?m?2?h?1 under forest canopy. In addition, NO-emissions of meadow and forest soil were studied in a climate chamber, enhanced by an additional experiment with agricultural soil. These experiments revealed strong exponential correlations of NO-emissions and soil temperature. Maximum values reached above 400???g NO?CN?m?2?h?1 from agricultural soils at soil temperatures above 50°C. This study shows that soil NO-emissions strongly depend on temperature, vegetation type and geographical position. Consequently, NO-emissions may have a positive feedback effect on climate change.  相似文献   

18.
It is generally accepted that carbonates can be subducted to the mantle depths, where they are reduced with iron metal to produce a diamond. In this work, we found that this is not always the case. The mantle carbonates from inclusions in diamonds show a wide range of cation compositions (Mg, Fe, Ca, Na, and K). Here we studied the reaction kinetics of these carbonates with iron metal at 6–6.5 GPa and 1000–1500 °C. We found that the reduction of carbonate with Fe produces C-bearing species (Fe, Fe-C melt, Fe3C, Fe7C3, C) and wüstite containing Na2O, CaO, and MgO. The reaction rate constants (k = Δx2/2t) are log-linear relative to 1/T and their temperature dependences are determined to bekMgCO3 (m2/s) = 4.37 × 10?3 exp [?251 (kJ/mol)/RT]kCaMg(CO3)2 (m2/s) = 1.48 × 10?3 exp [?264 (kJ/mol)/RT]kCaCO3 (m2/s) = 3.06 × 10?5 exp [?245 (kJ/mol)/RT] andkNa2CO3 (m2/s) = 1.88 × 10?10 exp [?155 (kJ/mol)/RT].According to obtained results at least, 45–70 vol% of carbonates preserve during subduction down to the 660-km discontinuity if no melting occurs. The slab stagnation and warming, subsequent carbonate melting, and infiltration into the mantle saturated with iron metal are accompanied by a reduction of carbonate melt with Fe. The established sequence of reactivity of carbonates: FeCO3 ≥ MgCO3 > CaMg(CO3)2 > CaCO3 ? Na2CO3, where K2CO3 does not react at all with iron metal, implies that during reduction carbonate melt with Fe evolves toward alkali-rich. The above conclusions are consistent with the findings of carbonates in inclusions in diamonds from the lower mantle and high concentrations of alkalis, particularly K, in mantle carbonatite melts entrapped by diamonds from kimberlites and placers worldwide.  相似文献   

19.
The possibilities of exoelectron spectroscopy to investigate defects in dielectrics are demonstrated for phenakite Be2SiO4, its structural analogs Zn2 SiO4, Be2GeO4, solid solutions Be2Si1?x Ge x O4 (x=0÷1) and α-quartz. Emission maxima at 330 and 670 K in phenakite have been found to be due to [GeO4]5? andE' centers, respectively. Structural disturbances in the silicon and oxygen positions have been shown to control the exoemission activity of the crystals. Radiation induced decrease of exoemission activity connected with generation ofE' centers by neutron irradiation has been discovered. The energy level scheme of active centers in the subsurface region of Be2SiO4 has been established.  相似文献   

20.
Synthetic, flux-grown uvarovite, Ca3Cr2 [SiO4]3, was investigated by optical methods, electron microprobe analysis, UV-VIS-IR microspectrometry, and luminescence spectroscopy. The crystal structure was refined using single-crystal X-ray CCD diffraction data. Synthetic uvarovite is optically isotropic and crystallizes in the “usual” cubic garnet space group Ia3¯d [a=11.9973 Å, Z=8; 21524 reflections, R1=2.31% for 454 unique data and 18 variables; Cr–O=1.9942(6), Si–O=1.6447(6), Ca–Oa=2.3504(6), Ca–Ob= 2.4971(6) Å]. The structure of Ca3Cr2[SiO4]3 complies with crystal-chemical expectations for ugrandite group garnets in general as well as with predictions drawn from “cubically averaged” data of non-cubic uvarovite–grossular solid solutions (Wildner and Andrut 2001). The electronic absorption spectra of Cr3+ in trigonally distorted octahedra of synthetic uvarovite were analyzed in terms of the superposition model (SM) of crystal fields. The resulting SM and interelectronic repulsion parameters are =9532 cm?1, =4650 cm?1, power law exponent t 4=6.7, Racah B35=703 cm?1 at 290 K (reference distance R 0=1.995 Å; fixed power law exponent t 2=3 and spin-orbit parameter ζ=135 cm?1). The interelectronic repulsion parameters Racah B 55=714 cm?1 and C=3165 cm?1 were extracted from spin-forbidden transitions. This set of SM parameters was subsequently applied to previously well-characterized natural uvarovite–grossular solid solutions (Andrut and Wildner 2001a; Wildner and Andrut 2001) using their extrapolated Cr–O bond lengths to calculate the energies of the spin-allowed bands. These results are in very good agreement with the experimentally determined band positions and indicate the applicability of the superposition model to natural 3d N prevailing systems in geosciences. Single-crystal IR absorption spectra of synthetic uvarovite in the region of the OH-stretching vibration exhibit one isotropic absorption band at 3508 cm?1 at ambient conditions, which shifts to 3510 cm?1 at 77 K. This band is caused by structurally incorporated hydroxyl groups via the (O4H4)-hydrogarnet substitution. The water content, calculated using an integral extinction coefficient ?=60417 cm?2 l mol?1, is c H2O=33 ppm.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号