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1.
Two pumpellyites with the general formula W
8
X
4
Y
8
Z
12O 56-n
(OH)
n
were studied using 57Fe Mössbauer spectroscopic and X-ray Rietveld methods to investigate the relationship between the crystal chemical behavior of iron and structural change. The samples are ferrian pumpellyite-(Al) collected from Mitsu and Kouragahana, Shimane Peninsula, Japan. Rietveld refinements gave Fe( X):Fe( Y) ratios (%) of 41.5(4):58.5(4) for the Mitsu pumpellyite and 46(1):54(1) for the Kouragahana pumpellyite, where Fe( X) and Fe( Y) represent Fe content at the X and Y sites, respectively. The Mössbauer spectra consisted of two Fe 2+ and two Fe 3+ doublets for the Mitsu pumpellyite, and one Fe 2+ and two Fe 3+ doublets for the Kouragahana pumpellyite. In terms of the area ratios of the Mössbauer doublets and the Fe( X):Fe( Y) ratios determined by the Rietveld refinements, Fe 2+( X):Fe 3+( X):Fe 3+( Y) ratios are determined to be 22:14:64 for the Mitsu pumpellyite and 27:8:65 for the Kouragahana pumpellyite. By applying the Fe 2+:Fe 3+-ratio determined by the Mössbauer analysis and the site occupancies of Fe at the X and Y sites given by the Rietveld method together with chemical analysis, the resulting formula of the Mitsu and Kouragahana pumpellyites are established as Ca 8(Fe
0.88
2+
Mg 0.68Fe
0.77
3+
Al 1.66) Σ3.99(Al 5.67Fe
2.34
3+
) Σ8.01Si 12O 42.41(OH) 13.59 and Ca 8(Mg 1.24Fe
0.65
2+
Fe
0.46
3+
Al 1.66) Σ4.01(Al 6.71Fe
1.29
3+
) Σ8.00Si 12O 42.14(OH) 13.86, respectively. Mean Y–O distances and volumes of the YO 6 octahedra increase with increasing mean ionic radii, i.e., the Fe 3+→Al substitution at the Y site. However, change of the sizes of XO 6 octahedra against the mean ionic radii at the X site is not distinct, and tends to depend on the volume change of the YO 6 octahedra. Thus, the geometrical change of the YO 6 octahedra with Fe 3+→Al substitution at the Y site is essential for the structural changes of pumpellyite. The expansion of the YO 6 octahedra by the ionic substitution of Fe 3+ for Al causes gradual change of the octahedra to more symmetrical and regular forms. 相似文献
2.
Tourmaline with the general formula XY3Z6(BO 3) 3Si 6O 18(OH,O) 3(OH,F) and the trigonal space group R3 m ( C3v5) is known as a gemstone with great variety of colors. Some color centers are related to transition metal ions, and others to electron or hole traps. In this paper we report on a combined study using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and the optical detection of EPR (ODEPR) on a yellow color center produced by -irradiation in colorless Li-bearing elbaite tourmaline from Brazil. The color center is an O – hole trap center, which is stabilized within the plane spanned by three Y sites, and is located in the structural channels formed by Si 6O 18. We suggest that two of the Y sites are substituted by 27Al and the other by 6,7Li. During the irradiation process atomic hydrogen H 0 is also produced, which shows the same thermal stability as the hole center (250 °C). Therefore, we assign H 0 to be the local charge compensator for the hole trap. From the ODEPR measurements we conclude that the yellow color is caused by the O – hole center. The large negative isotropic Al superhyperfine interaction of the O – hole trap center is consistent with a calculation of the transferred hyperfine interactions by exchange polarization supporting the proposed defect model of an O – at the O 1 sites, whereby the O – is relaxed into the plane formed by three Y ions. 相似文献
3.
The technique of nebular-gas diagnostics was used to find electronic temperatures T e , concentrations n e , relative ion concentrations n(A +i )/ n(H +), and chemical abundances A/H for planetary nebulae in the Large and Small Magellanic Clouds. This analysis took into account inhomogeneities of the nebular-gas density in the nebulae. We determined the pre-galactic helium abundance Y p and its rate of enrichment dY/dZ for the envelopes of nine nebulae in the Large Magellanic Cloud. Taken together with the Galaxy’s planetary nebulae and HII regions in blue compact dwarf galaxies, Y p = 0.248 ± 0.002, dY/dZ = 2.31 ± 0.48 and Y p = 0.247 ± 0.002, dY/dZ = 3.03 ± 0.56, respectively, when macroinhomogeneities and macro/microinhomogeneities of the gas density in galactic nebulae are taken into account. 相似文献
4.
We present a systematic density-functional study of phase relations in three 4 d-transition-metal sesquioxides: Y 2O 3, Rh 2O 3, and In 2O 3. Y 2O 3 and In 2O 3 undergo pressure-induced transitions to phases with larger cation coordination number (from 6 to 7) at low pressures. However,
this does not occur in Rh 2O 3 at least up to ~300 GPa. This cannot be explained by usual arguments based on ionic-radii ratios often used successfully
to explain phase relations in simple-metal and rare-earth sesquioxides and sesquisulfides. Inspection of their electronic
structures shows that, in Rh 2O 3, the electronic occupancy of 4 d orbitals, 4 d
6, plays a fundamental role in the extraordinary stability of the Rh 2O 3(II)-type phase with respect to coordination increase. We point out that d-orbital occupancy is a fundamental factor in explaining phase relations in transition-metal sesquioxides and sesquisulfides. 相似文献
5.
Pumpellyite of the general formula W 8X 4Y 8-Z 12O 56-n(OH) n contains Fe, Al and Mg in two crystallographically different octahedral sites. Three different pumpellyite samples covering the known compositional field from Al- to Fe-rich have been studied to determine the valence state and intracrystalline partitioning of the Fe cations between the two independent octahedral sites. Fe +2 and Fe +3 cation partitioning is interpreted on the basis of results obtained by 57Fe Mössbauer spectroscopy at 293 and 77 K and from Rietveld structure analysis performed on powder X-ray diffraction data. Pumpellyite from low-grade metamorphic rocks typically contains a majority of iron in the Fe +3 oxidation state, which is found in the smaller and less symmetrical octahedral Y-site. Fe +2 was also present in all pumpellyite samples studied and it is located in the larger and more symmetrical octahedral X-site. 相似文献
6.
A new method for accurate determination of oxygen isotopes in uranium oxides encountered in the nuclear fuel cycle was developed using the conventional BrF 5 fluorination technique. Laser‐assisted fluorination was tested for comparison. We focused on fine powders of triuranium octoxide (U 3O 8), uranium dioxide (UO 2±x with 0 ≤ x ≤ 0.25), uranium trioxide (UO 3. nH 2O, with 0.8 ≤ n ≤ 2) and diuranates (M 2U 2O 7. nH 2O, with M = NH 4, Na or Mg 0.5 and 0 ≤ n ≤ 6). Fluorination at room temperature and heating under vacuum at 150 °C are shown to eliminate both adsorbed and structural water from the powder samples. Precision fit for purpose of δ 18O values (± 0.3‰, 1 s) and oxygen yields (close to 100%) were obtained for U 3O 8 and UO 2 where oxygen is only bound to uranium. A lower precision was observed for UO 3. nH 2O and M 2U 2O 7. nH 2O where oxygen is both present in the structural H 2O and bonded to uranium and where the extracted O 2(g) can be contaminated by NF 3 and NO x compounds. Laser‐assisted fluorination gave shifted δ 18O values between +0.8 and +1.4‰ for U 3O 8, around ?0.8‰ for UO 3. nH 2O and between ?3.9 and ?4.5‰ for M 2U 2O 7. nH 2O (± 0.3‰, 1 s) compared with the conventional method. 相似文献
7.
Summary
The first natural tourmaline (because tourmaline with [4]B has also been synthesized, we distinguish here between natural and synthetic tourmaline) that has been unequivocally demonstrated
to contain B as a substituent at the T sites was described from Koralpe, Styria, Austria. This colourless B-rich olenite occurs as rims overgrowing schorl (black
crystals up to a few cm) that has not yet been structurally characterized. A crystal structure refinement ( R = 0.019) of this Al-rich schorl shows that [4]B occurs in the overgrown schorl; the optimized occupants of the atomic positions yield
X
(Na 0.64Ca 0.10K 0.06□ 0.20)
Y
(Fe 2+
1.72Al 1.08Ti 0.11Zn 0.03□ 0.06)
Z
(Al 5.70Mg 0.20Fe 0.08
2+Mn 0.02) ( [3]BO 3) 3.00
T
(Si 5.76
[4]B 0.24)O 18 [F 0.11(OH) 3.31O 0.58]. This is the first known (Al-rich) schorl where a structure refinement has detected [4]B. Comparing the structure refinements and the chemical composition of the Koralpe schorl and other [4]B-bearing tourmalines with tourmalines which contain no [4]B, it is of interest that only structure refinements of tourmalines which are low in magnesium and with a higher component
of olenite show substantial amounts of [4]B; the role of Mg in controlling the amount of [4]B is not known, but it seems that an Al-component on the Y site (olenite-component), a boron-enriched environment and special P-T-t conditions are necessary to get tourmaline with
substantial amounts of [4]B.
Received July 7, 2000; revised version accepted June 6, 2001 相似文献
8.
CNDO/2 MO calculations on H12Si5O16 clusters modeling silicate tetrahedral linkage in the silica polymorphs show total energy minima at bent SiOSi angles and a correlation between the Si-O bond lengths, d(Si-O), used in the calculation and the minimum energy value of the SiOSi angle. Calculations on hydrogen saturated Si5O16 clusters isolated from the structures of low quartz, low cristobalite and coesite which were adjusted by DLS methods so that all d(Si-O) equal 1.61 Å and all
L
OSiO equal 109.47° yield Mulliken bond overlap populations, n(Si-O), and Si-O two-center energies, E(Si-O), which correlate with observed bond lengths; shorter bonds involve larger n(Si-O) values and more negative E(Si-O) values. 相似文献
10.
The concept of a random function and, consequently, the application of kriging cells for the implicit assumption that the data locations are embedded within an infinite domain. An implication of this assumption is that, all else being equal, outlying data locations will receive greater weight because they are seen as less redundant, hence, more informative of the infinite domain. A two- step kriging procedure is proposed for correcting this siring effect. The first step is to establish the total kriging weight attributable to each string. The distribution of that total weight to the samples in the string is accomplished by a second stage of kriging. In the second stage, a spatial redundancy measure r (n)
is used in place of the covariance measure in the data-data kriging matrix. This measure is constructed such that each datum has the same redundancy with the (n) data of the string to which it belongs. This paper documents the problem of kriging with strings of data, develops the redundancy measure r (n), and presents a number of examples. 相似文献
11.
A new mineral fivegite has been identified in a high-potassium hyperalkaline pegmatite at Mt. Rasvumchorr in the Khibiny alkaline
complex of the Kola Peninsula in Russia. This mineral is a product of the hydrothermal alteration of delhayelite (homoaxial
pseudomorphs after its crystals up to 2 × 3 × 10 cm in size). Hydrodelhayelite, pectolite, and kalborsite are products of
fivegite alteration. The associated minerals are aegirine, potassic feldspar, nepheline, sodalite, magnesiumastrophyllite,
lamprophyllite, lomonosovite, shcherbakovite, natisite, lovozerite, tisinalite, ershovite, megacyclite, shlykovite, cryptophyllite,
etc. Areas of pure unaltered fivegite are up to 2 mm in width. The mineral is transparent and colorless; its luster is vitreous
to pearly. Its Cleavage is perfect (100) and distinct (010). Its Mohs hardness is 4, D(meas) = 2.42(2), and D(calc) = 2.449 g/cm 3. Fivegite is optically biaxial positive: α 1.540(1), β 1.542(2), γ 1.544(2), and 2 V(meas) 60(10)°. Its orientation is X = a, y = c, and Z = b. Its IR spectrum is given. Its chemical composition (wt %; electron microprobe, H 2O determined by selective sorption) is as follows: 1.44 Na 2O, 19.56 K 2O, 14.01 CaO, 0.13 SrO, 0.03 MnO, 0.14 Fe 2O 3, 6.12 Al 2O 3, 50.68 SiO 2, 0.15 SO 3, 0.14 F, 3.52 Cl, 4.59 H 2O; −O = −0.85(Cl,F)2; total 99.66. The empirical formula based on (Si + Al + Fe) = 8 is H 4.22K 3.44Na 0.39Ca 2.07Sr 0.01Fe 0.01Al 1.00Si 6.99O 21.15F 0.06Cl 0.82(SO 4) 0.02. The simplified formula is K 4Ca 2[AlSi 7O 17(O 2 − x
OH
x
][(H 2O) 2 − x
OH
x
]Cl ( X = 0−2). Fivegite is orthorhombic: Pm2 1
n, a = 24.335(2), b = 7.0375(5), c = 6.5400(6) ?, V = 1120.0(2) ? 3, and Z = 2. The strongest reflections of the X-ray powder pattern are as follows ( d, ?, ( I, %), [ hkl]): 3.517(38) [020], 3.239(28) [102], 3.072(100) [121, 701], 3.040(46) [420, 800, 302], 2.943 (47) [112], 2.983(53) [121],
2.880 (24) [212, 402], 1.759(30) [040, 12.2.0]. The crystal structure was studied using a single crystal: R
hkl
= 0.0585. The base of fivegite structure is delhayelite-like two-layer terahedral blocks [(Al,Si) 4Si 12O 34(O 4 − x
OH
x
)] linked by Ca octahedral chains. K + and Cl − are localized in zeolite-like channels within the terahedral blocks, whereas H 2O and OH occur between the blocks. The mineral is named in memory of the Russian geological and mining engineer Mikhail Pavlovich
Fiveg (1899–1986), the pioneering explorer of the Khibiny apatite deposits. The type specimen is deposited at the Fersman
Mineralogical Museum of the Russian Academy of Sciences in Moscow. The series of transformations is discussed: delhayelite
K 4Na 2Ca 2[AlSi 7O 19]F 2Cl—fivegite K 4Ca 2[AlSi 7O 17(O 2 − x
OH
x
]Cl—hydrodelhayelite KCa 2[AlSi 7O 17(OH) 2](H 2O) 6 − x
. 相似文献
12.
The crystal structure of a new compound, [(H 5O 2)(H 3O)(H 2O)][(UO 2)(SeO 4) 2] (monoclinic, P2 1/ n a = 8.3105(15), b = 11.0799(14), c = 13.227(2) Å, β = 103.880(13)°, V = 1182.4(3) Å 3), has been solved by direct methods and refined to R 1 = 0.036. The structure is based on [(UO 2)(SeO 4) 2] 2? sheet complexes formed by corner-shared UO 7 pentagonal bipyramids and SeO 4 tetrahedrons. The sheets are parallel to the ( $ \bar 1 The crystal structure of a new compound, [(H5O2)(H3O)(H2O)][(UO2)(SeO4)2] (monoclinic, P21/n a = 8.3105(15), b = 11.0799(14), c = 13.227(2) ?, β = 103.880(13)°, V = 1182.4(3) ?3), has been solved by direct methods and refined to R
1 = 0.036. The structure is based on [(UO2)(SeO4)2]2− sheet complexes formed by corner-shared UO7 pentagonal bipyramids and SeO4 tetrahedrons. The sheets are parallel to the (01) plane. Oxonium ions and water molecules forming [(H3O)·(H2O)·(H5O2)]2+ complexes are interlayer. Among minerals, the existence of (H5O2)+ has been unambiguously confirmed only in rhomboclase, (H5O2)+[Fe2(SO4)2(H2O)2].
Original Russian Text ? S.V. Krivovichev, 2008, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2008, No.
2, pp. 123–130. 相似文献
13.
The equilibrium water content of cordierite has been measured for 31 samples synthesized at pressures of 1000 and 2000 bars
and temperatures from 600 to 750° C using the cold-seal hydrothermal technique. Ten data points are presented for pure magnesian
cordierite, 11 data points for intermediate iron/magnesium ratios from 0.25 to 0.65 and 10 data points for pure iron cordierite.
By representing the contribution of H 2O to the heat capacity of cordierite as steam at the same temperature and pressure, it is possible to calculate a standard
enthalpy and entropy of reaction at 298.18° K and 1 bar for,
(Mg,Fe) 2Al 4Si 5O 18+H 2O ⇄ (Fe,Mg) 2Al 4Si 5O 18.H 2O
Combining the 31 new data points with 89 previously published experimental measurements gives: Δ H
°
r
=–37141±3520 J and Δ S
°
r
=–99.2±4 J/degree. This enthalpy of reaction is within experimental uncertainty of calorimetric data. The enthalpy and entropy
of hydration derived separately for magnesian cordierite (–34400±3016 J, –96.5±3.4 J/degree) and iron cordierite (–39613±2475,
–99.5±2.5 J/degree) cannot be distinguished within the present experimental uncertainty. The water content as a function of
temperature, T(K), and water fugacity, f(bars), is given by n
H2O=1/[1+1/( K ⋅ f
H2O)] where the equilibrium constant for the hydration reaction as written above is, ln K=4466.4/ T–11.906 with the standard state for H 2O as the gas at 1 bar and T, and for cordierite components, the hydrous and anhydrous endmembers at P and T.
Received: 2 August 1994/Accepted: 7 February 1996 相似文献
14.
Based on a new mixing model of two end-members, the water column remineralization ratios of P/N/C org - O 2 = 1/13 ± 1/135 ± 18/170 ± 9 are obtained for the Hawaii Ocean Time-series (HOT) data set at station ALOHA. The traditional Redfield ratios of P/N/C org/–O 2 = 1/16/106/138 have standard deviations of more than 50%, when they are based on the average composition of phytoplankton. Apparently, the remineralization processes in the water column have smoothed out the observed large variability of plankton compositions. A new molar formula for the remineralized plankton may be written as 135H 280O 105N 13P or C 25(CH 2O) 101(CH 4) 9(NH 3) 13(H 3PO 4). Oxidation of this formula results inC 25(CH 2O) 101(CH 4) 9(NH 3) 13(H 3PO 4) + 170O 2 135CO 2 + 132H 2O + 13NO 3
- + H 2PO 4
- + 14H +.For comparison, remineralization using Redfield's formula gives:(CH 2O) 106(NH 3) 16(H 3PO 4) + 138O 2 106CO 2 + 122H 2O + 16NO 3
-+ H 2PO 4
- + 17H + 相似文献
15.
The melting reaction: albite (solid)+ H 2O (fluid) =albite-H 2O (melt) has been determined in the presence of H 2O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H 2O–CO 2 fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant
pressure is principally determined by water activity. At 5 kbar, the temperature ( T)- mole fraction ( X
(H2O) ) melting relations in the two systems are almost coincident. By contrast, H 2O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 °C higher in H 2O–NaCl brines than in H 2O–CO 2 fluids for X
(H2O) =0.8 and ∼100 °C higher for X
(H2O) =0.5. The melting temperature of albite in H 2O–NaCl fluids of X
(H2O)=0.8 is ∼100 °C higher than in pure water. The P– T curves for albite melting at constant H 2O–NaCl show a temperature minimum at about 5 kbar. Water activities in H 2O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H 2O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure
at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids
provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral
assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity
in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but
may be due to the presence of low a
(H2O) brines.
Received: 17 March 1995/Accepted: 9 April 1996 相似文献
16.
The heat capacity of paranatrolite and tetranatrolite with a disordered distribution of Al and Si atoms has been measured
in the temperature range of 6–309 K using the adiabatic calorimetry technique. The composition of the samples is represented
with the formula (Na 1.90K 0.22Ca 0.06)[Al 2.24Si 2.76O 10]· nH 2O, where n=3.10 for paranatrolite and n=2.31 for tetranatrolite. For both zeolites, thermodynamic functions (vibrational entropy, enthalpy, and free energy function)
have been calculated. At T=298.15 K, the values of the heat capacity and entropy are 425.1 ± 0.8 and 419.1 ±0.8 J K −1 mol −1 for paranatrolite and 381.0 ± 0.7 and 383.2 ± 0.7 J K −1 mol −1 for tetranatrolite.
Thermodynamic functions for tetranatrolite and paranatrolite with compositions corrected for the amount of extraframework
cations and water molecules have also been calculated. The calculation for tetranatrolite with two water molecules and two
extraframework cations per formula yields: C
p
(298.15)=359.1 J K −1 mol −1, S(298.15) − S(0)=362.8 J K −1 mol −1. Comparing these values with the literature data for the (Al,Si)-ordered natrolite, we can conclude that the order in tetrahedral
atoms does not affect the heat capacity. The analysis of derivatives d C/d T for natrolite, paranatrolite, and tetranatrolite has indicated that the water- cations subsystem within the highly hydrated
zeolite may become unstable at temperatures above 200 K.
Received: 30 July 2001 / Accepted: 15 November 2001 相似文献
17.
In order to gain insight into the correlations between 29Si, 17O and 1H NMR properties (chemical shift and quadrupolar coupling parameters) and local structures in silicates, ab initio self-consistent
field Hartree-Fock molecular orbital calculations have been carried out on silicate clusters of various polymerizations and
intertetrahedral (Si-O-Si) angles. These include Si(OH) 4 monomers (isolated as well as interacting), Si 2O(OH) 6 dimers (C 2 symmetry) with the Si-O-Si angle fixed at 5° intervals from 120° to 180°, Si 3O 2(OH) 8 linear trimers (C 2 symmetry) with varying Si-O-Si angles, Si 3O 3(OH) 6 three-membered rings (D 3 and C 1 symmetries), Si 4O 4(OH) 8 four-membered ring (C 4 symmetry) and Si 8O 12(OH) 8 octamer (D 4 symmetry). The calculated 29Si, 17O and 1H isotropic chemical shifts (δ i
Si, δ i
O and δ i
H) for these clusters are all close to experimental NMR data for similar local structures in crystalline silicates. The calculated
17O quadrupolar coupling constants ( QCC) of the bridging oxygens (Si-O-Si) are also in good agreement with experimental data. The calculated 17O QCC of silanols (Si-O-H) are much larger than those of the bridging oxygens, but unfortunately there are no experimental data
for similar groups in well-characterized crystalline phases for comparison. There is a good correlation between δ i
Si and the mean Si-O-Si angle for both Q
1 and Q
2, where Q
n
denotes Si with n other tetrahedral Si next-nearest neighbors. Both the δ
i
O and the 17O electric field gradient asymmetry parameter, η of the bridging oxygens have been found to depend strongly on the O site
symmetry, in addition to the Si-O-Si angle. On the other hand, the 17O QCC seems to be influenced little by structural parameters other than the Si-O-Si angle, and is thus expected to be the most
reliable 17O NMR parameter that can be used to decipher Si-O-Si angle distribution information. Both the 17O QCC and the 2H QCC of silanols decrease with decreasing length of hydrogen bond to a second O atom (Si-O-H···O), and the δ
i
H increase with the same parameter.
Received: 18 July 1997 / Revised, accepted: 23 February 1998 相似文献
18.
Here, I describe a theoretical approach to the structure and chemical composition of minerals based on their bond topology. This approach allows consideration of many aspects of minerals and mineral behaviour that cannot be addressed by current theoretical methods. It consists of combining the bond topology of the structure with aspects of graph theory and bond-valence theory (both long range and short range), and using the moments approach to the electronic energy density-of-states to interpret topological aspects of crystal structures. The structure hierarchy hypothesis states that higher bond-valence polyhedra polymerize to form the (usually anionic) structural unit, the excess charge of which is balanced by the interstitial complex (usually consisting of large low-valence cations and (H 2O) groups). This hypothesis may be justified within the framework of bond topology and bond-valence theory, and may be used to hierarchically classify oxysalt minerals. It is the weak interaction between the structural unit and the interstitial complex that controls the stability of the structural arrangement. The principle of correspondence of Lewis acidity–basicity states that stable structures will form when the Lewis-acid strength of the interstitial complex closely matches the Lewis-base strength of the structural unit, and allows us to examine the factors that control the chemical composition and aspects of the structural arrangements of minerals. It also provides a connection between a structure, the speciation of its constituents in aqueous solution and its mechanism of crystallization. The moments approach to the electronic energy density-of-states provides a link between the bond topology of a structure and its thermodynamic properties, as indicated by correlations between average anion coordination number and reduced enthalpy of formation from the oxides for [6]Mg m [4] Si n O (m+2n) and MgSO 4(H 2O) n . 相似文献
19.
We measured the adsorption of Cu(II) onto goethite (α-FeOOH), hematite (α-Fe 2O 3) and lepidocrocite (γ-FeOOH) from pH 2-7. EXAFS spectra show that Cu(II) adsorbs as (CuO 4H n) n−6 and binuclear (Cu 2O 6H n) n−8 complexes. These form inner-sphere complexes with the iron (hydr)oxide surfaces by corner-sharing with two or three edge-sharing Fe(O,OH) 6 polyhedra. Our interpretation of the EXAFS data is supported by ab initio (density functional theory) geometries of analogue Fe 2(OH) 2(H 2O) 8Cu(OH) 4and Fe 3(OH) 4(H 2O) 10Cu 2(OH) 6 clusters. We find no evidence for surface complexes resulting from either monodentate corner-sharing or bidentate edge-sharing between (CuO 4H n) n−6 and Fe(O,OH) 6 polyhedra. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed even though we are supersaturated with respect to CuO and Cu(OH) 2. Having identified the bidentate (FeOH) 2Cu(OH) 20 and tridentate (Fe 3O(OH) 2)Cu 2(OH) 30 surface complexes, we are able to fit the experimental copper(II) adsorption data to the reactions
20.
The results of the study of optical properties of 13 anthracites from different parts of the world are presented in this paper. Measurements of reflectance values were made on non-oriented vitrinite grains for a minimum of 300 points per sample. The reconstruction of Reflectance Indicating Surfaces (RIS) were made by Kilby's method [Kilby, W.E., 1988. Recognition of vitrinite with non-uniaxial negative reflectance characteristics. Int. J. Coal Geol. 9, 267–285; Kilby, W.E., 1991. Vitrinite reflectance measurement — some technique enhancements and relationships. Int. J. Coal Geol. 19, 201–218]. It was found that the use of Kilby's method for strongly anisotropic materials like anthracites did not give unambiguous results. Some improvement in Kilby's method, consisting of the division of the cumulative cross-plot into several elemental components, is suggested. Each elemental cross-plot corresponds to a textural class of anthracite, which is characterized by the values of RIS main axes RMAX(k), RINT(k) and RMIN(k) ( k=1,2,… n; n — number of classes). The global texture of anthracite is characterized as a RIS with main axes calculated as the weighted means of
,
and
for each class of this anthracite.The division of cumulative Kilby's cross-plot on elemental components makes possible the calculation of new coefficients Ht and H10 characterizing the heterogeneity of the structure and texture of anthracites. The results of our study show that all anthracites have biaxial negative textures, but their heterogeneity varies in a wide range of Ht and H10 coefficients depending upon the individual coal basin. 相似文献
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