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1.
Natural samples of typical cyclosilicates beryl and cordierite include water and carbon dioxide molecules in channels formed
by the open cavities. Water molecules in the channels have two forms that are distinguished by whether they coordinate to
extra-framework cations (type II) or not (type I). We measured polarized infrared (IR) spectra for thin sections of the (100)
plane of beryl or the (100) and (010) planes (cb and ca planes) of cordierite under various temperature conditions. The spectral features of major bands clearly showed the distinguishable
behavior of types I and II water molecules under high temperature as follows. Over the temperature range from room temperature
to 800°C where rapid dehydration did not occur, the decrease in band heights for type II water molecules were smaller than
those for type I, and band shifts were more predominant for type II water molecules. The decrease in band heights and band
shifts of type I/II bands differed also for beryl and cordierite, which arises from the different ways in which water molecules
are fixed in the channels. Dehydration was enhanced at 850°C. The IR spectra at room temperature quenched from 850°C both
for beryl and cordierite showed that the vibrational bands related to type II water molecules were stable after those related
to type I water molecules disappeared. In addition, frequency changes of type II bands were observed, possibly because of
changes of coordination states of type II water molecules to extra-framework cations in the channels. 相似文献
2.
Spectroscopic and bond-topological investigation of interstitial volatiles in beryl from Slovakia 总被引:1,自引:0,他引:1
Jana Fridrichová Peter Bačík Valéria Bizovská Eugen Libowitzky Radek Škoda Pavel Uher Daniel Ozdín Martin Števko 《Physics and Chemistry of Minerals》2016,43(6):419-437
Nine beryl samples from Western Carpathians, Slovakia, were investigated by infrared and Raman spectroscopy and differential thermal analysis. Two types of water H2O I and H2O II were detected. Infrared spectroscopy proved the presence of water type I and II in the presence of alkali cations with several bands: (1) symmetric stretching vibration—ν1; (2) antisymmetric stretching mode—ν3; (3) bending vibration—ν2. The presence of singly and doubly coordinated type II water (IIs and IId) was confirmed by single-crystal IR spectroscopy. From Raman spectra a band at 3606 cm?1 was assigned to ν1 of water type I and the range of 3597–3600 cm?1 to water type II. The presence of doubly coordinating water indicates a relatively highly hydrated environment with the presence of alkali ions including Na as the dominant cation coordinated by H2O II. CO2 bands were detected only by single-crystal IR spectroscopy. Thermal analysis proved total water loss in the range of 1.4–2.0 wt% and three main dehydration events. Based on the study of bond-topological arrangements two molecules of H2O IId are each bound with two H···O1 bonds and one Na–OW bond with an angular distortion, and by releasing one H2O molecule more stable H2O IIs is produced. The H2O I molecule is bound only by two equivalent hydrogen bonds. The H2O IIs molecule with a Na–OW bond strength of 0.28 vu and two H···O1 bonds of 0.14 vu without any forced angular distortion is the most stable of all. 相似文献
3.
Giancarlo Della Ventura Fabio Bellatreccia Paolo Rossi 《Physics and Chemistry of Minerals》2007,34(10):727-731
We report here a single-crystal polarized-light study of stoppaniite, ideally (Fe,Al,Mg)4(Be6Si12O36)(H2O)2(Na,□), from Capranica (Viterbo). Polarized-light FTIR spectra were collected on an oriented (hk0) section, doubly polished
to 15 μm. The spectrum shows two main bands at 3,660 and 3,595 cm−1; the former is strongly polarized for E ⊥c, while the latter is polarized for E //c. A sharp and very intense band at 1,620 cm−1, plus minor features at 4,000 and 3,228 cm−1 are also polarized for E //c. On the basis of literature data and considering the pleochroic behavior of the absorptions, the 3,660 cm−1 band is assigned to the ν3 stretching mode and the 1,620 cm−1 (associated with an overtone 2*ν2 at 3,230 cm−1) band to the ν2 bending mode of “type II” water molecules within the structural channels of the studied beryl. The sharp band at 3,595 cm−1 is not associated with a corresponding ν2 bending mode; thus it is assigned to the stretching vibration of O–H groups in the sample. The minor 4,000 cm−1 feature can be assigned to the combination of the O–H bond parallel to c with a low-frequency metal-oxygen mode such as the Na–O stretching mode. The present results suggest that the interpretation
of the FTIR spectrum of Na-rich beryl needs to be carefully reconsidered. 相似文献
4.
The polarized single-crystal Raman spectra of synthetic H2O-containing alkali-free beryl were recorded at room and low temperatures, and the polarized single-crystal IR spectra at
room temperature. The H2O molecule in the channel cavities is characterized by a Raman-active symmetric stretching vibration (ν1) at 3607 cm−1 and an IR-active asymmetric stretch (ν3) at 3700 cm−1 at room temperature. At low temperatures this ν3 mode is observed in the Raman. Weak ν1 and ν3 modes of a second type of H2O are also observed in the Raman spectra but only at 5 K. The H⋯·H vector of the most abundant type of H2O is parallel to the channel axis of beryl along [0 0 0 1]. The components of the polarizability tensor of the ν1 mode of H2O are similar to, but not exactly the same as, those of a free H2O molecule. The Raman measurements indicate that the H2O molecule is rotationally disordered around [0 0 0 1]. External translation and librational modes of H2O could be observed as overtones with the internal H2O-stretching modes. In the case of the librational motions, normal modes could also be observed directly in the Raman spectra
at ∼200 cm−1. The energies of the translational modes can be determined from an analysis of the overtones and are about 9 cm−1 in energy (i.e., Tz). The energies of the librational modes are about 210 cm−1 for Rx and 190 cm−1 for Ry.
Received: 8 April 1999 / Accepted: 5 April 2000 相似文献
5.
The incorporation of hydrogen (deuterium) into the coesite structure was investigated at pressures from 3.1 to 7.5 GPa and
temperatures of 700, 800, and 1100 °C. Hydrogen could only be incorporated into the coesite structure at pressures greater
5.0 GPa and 1100 °C . No correlation between the concentration of trace elements such as Al and B and the hydrogen content
was observed based on ion probe analysis (1335 ± 16 H ppm and 17 ± 1 Al ppm at 7.5 GPa, 1100 °C). The FTIR spectra show three
relatively intense bands at 3575, 3516, and 3459 cm−1 (ν1 to ν3, respectively) and two very weak bands at 3296 and 3210 cm−1 (ν4 and ν5, respectively). The band at 3516 cm−1 is strongly asymmetric and can be resolved into two bands, 3528 (ν2a) and 3508 (ν2b) cm−1, with nearly identical areas. Polarized infrared absorption spectra of coesite single-crystal slabs, cut parallel to (0 1
0) and (1 0 0), were collected to locate the OH dipoles in the structure and to calibrate the IR spectroscopy for quantitative
analysis of OH in coesite (ɛ
i
,tot=190 000 ± 30 000 l mol−1
H2O cm−2). The polarized spectra revealed a strong pleochroism of the OH bands. High-pressure FTIR spectra at pressures up to 8 GPa
were performed in a diamond-anvil cell to gain further insight into incorporation mechanism of OH in coesite. The peak positions
of the ν1, ν2, and ν3 bands decrease linearly with pressure. The mode Grüneisen parameters for ν1, ν2, and ν3 are −0.074, −0.144 and −0.398, respectively. There is a linear increase of the pressure derivatives with band position which
follows the trend proposed by Hofmeister et al. (1999). The full widths at half maximum (FWHM) of the ν1, ν2, and ν3 bands increase from 35, 21, and 28 cm−1 in the spectra at ambient conditions to 71, 68, and 105 in the 8 GPa spectra, respectively. On the basis of these results,
a model for the incorporation of hydrogen in coesite was developed: the OH defects are introduced into the structure by the
substitution Si4+(Si2)+4O2−= [4]□(Si2) + 4OH−, which gives rise to four vibrations, ν1, ν2a, ν2b, and ν3. Because the OH(D)-bearing samples do contain traces of Al and B, the bands ν4 and ν5 may be coupled to Al and/or B substitution.
Received: 19 December 2000 / Accepted: 23 April 2001 相似文献
6.
Polarized absorption spectra, σ and π, in the spectral range 30000–400 cm−1 (3.71–0.05 eV) were obtained on crystal slabs // [001] of deep blue rutile at various temperatures from 88 to 773 K. The
rutile crystals were grown in Pt-capsules from carefully dried 99.999% TiO2 rutile powder at 50 kbar/1500 °C using graphite heating cells in a belt-type apparatus. Impurities were below the detection
limits of the electron microprobe (about 0.005 wt% for elements with Z≥13). The spectra are characterized by an unpolarized
absorption edge at 24300 cm−1, two weak and relatively narrow (Δν1/2≈3500–4000 cm−1), slightly σ-polarized bands ν1 at 23500 cm−1 and ν2 at 18500 cm−1, and a complex, strong band system in the NIR (near infra red) with sharp weak peaks in the region of the OH stretching fundamentals
superimposed on the NIR system in the σ-spectra. The NIR band system and the UV edge produce an absorption minimum in both
spectra, σ and π, at 21000 cm−1, i.e. in the blue, which explains the colour of the crystals. Bands ν1 and ν2 are assigned to dd transitions to the Jahn-Teller split upper Eg state of octahedral Ti3+. The NIR band system can be fitted as a sum of three components. Two of them are partly π-polarized, nearly Gaussian bands,
both with large half widths 6000–7000 cm−1, ν3 at 12000 cm–1 and the most intense ν4 at 6500 cm−1. The third NIR band ν5 of a mixed Lorentz-Gaussian shape with a maximum at 3000 cm−1 forms a shoulder on the low-energy wing of ν4. Energy positions, half band widths and temperature behaviour of these bands are consistent with a small polaron type of
Ti3+Ti4+ charge transfer (CT). Polarization dependence of CT bands can be explained on the basis of the structural model of defect
rutile by Bursill and Blanchin (1983) involving interstitial titanium. Two OH bands at 3322 and 3279 cm−1 in σ-spectra show different stability during annealing, indicating two different positions of proton in the rutile structure,
one of them probably connected with Ti3+ impurity. Total water concentration in blue rutile determined by IR spectroscopy is 0.10 wt-% OH. The EPR spectra measured
in the temperature interval 20–295 K show the presence of an electron centre at temperatures above 100 K and Ti3+ ions in more than one structural position, but predominantly in compressed interstitial octahedral sites, at lower temperatures.
These results are in good agreement with the conclusions based on the electronic absorption data.
Received: 24 March 1997 / Revised, accepted: 14 October 1997 相似文献
7.
A. Yu. Likhacheva E. A. Paukshtis Yu. V. Seryotkin S. G. Shulgenko 《Physics and Chemistry of Minerals》2002,29(9):617-623
The IR spectrum of ammonium-exchanged natural analcime (basalt, Nidym River, Siberian platform) exhibits several features
that suggest a lowered symmetry for the NH4
+ ion and that this is influenced by hydrogen bonding within the framework. These features are: the pronounced splitting into
three components and high-frequency shift of the ν4-bending mode; appearance of the ν1-stretching mode which is predicted to become IR-active when the ideal T
d
symmetry of NH4
+ ion is violated, and the low-frequency shift of the ν1- and ν3-stretching modes. The absence of absorption lines in the 1800–2400-cm−1 region indicates that hydrogen bonding between the framework and the NH+
4 ion is very weak. The three-component splitting of the ν4-bending mode indicates that the symmetry of NH+
4 ion is lower than C3v. This implies that at least two N–H bonds of the NH+
4 ion are disturbed by hydrogen bonding. Computer analysis of the normal vibrations of the NH+
4 molecule for different symmetry types (using harmonic approximation) indicates that the best fit to the observed ν4 triplet frequencies for C1 symmetry implies a deviation of the valent angle ∠H–N–H from ideal T
d
symmetry of around ±2.5°. The factors governing the behaviour of the NH+
4 ion in the analcime structure are discussed. The geometry of the nearest environment of the NH+
4 ion in the analcime structure is analyzed with respect to the present IR data.
Received: 2 January 2002 / Accepted: 26 June 2002
Acknowledgements We thank Dr. D. Harlov and an anonymous reviewer for their helpful comments, as well as Dr. I.A. Belitsky and Dr. S.V. Goryainov
for discussion of the material. This work is supported by RFBR grants 01-05-65414, 00-05-65305 and 02-05-65313. 相似文献
8.
P. Comodi A. Kurnosov S. Nazzareni L. Dubrovinsky 《Physics and Chemistry of Minerals》2012,39(1):65-71
The effects of pressure on the dehydration of gypsum materials were investigated up to 633 K and 25 GPa by using Raman spectroscopy
and synchrotron X-ray diffraction with an externally heated diamond anvil cell. At 2.5 GPa, gypsum starts to dehydrate around
428 K, by forming bassanite, CaSO4 hemihydrate, which completely dehydrates to γ-anhydrite at 488 K. All the sulphate modes decrease linearly between 293 and
427 K with temperature coefficients ranging from −0.119 to −0.021 cm−1 K−1, where an abrupt change in the ν3 mode and in the OH-stretching region indicates the beginning of dehydration. Increasing the temperature to 488 K, the OH-stretching
modes completely disappear, marking the complete dehydration and formation of γ-anhydrite. Moreover, the sample changes from
transparent to opaque to transparent again during the dehydration sequence gypsum-bassanite-γ-anhydrite, which irreversibly
transforms to β-anhydrite form at 593 K. These data compared with the dehydration temperature at room pressure indicate that
the dehydration temperature increases with pressure with a ΔP/ΔT slope equal to 230 bar/K. Synchrotron X-ray diffraction experiments show similar values of temperature and pressure for the
first appearance of bassanite. Evidence of phase transition from β-anhydrite structure to the monazite type was observed at
about 2 GPa under cold compression. On the other hand at the same pressure (2 GPa and 633 K), β-anhydrite was found, indicating
a positive Clausis-Clayperon slope of the transition. This transformation is completely reversible as showed by the Raman
spectra on the sample recovered after phase transition. 相似文献
9.
Boris Kolesov 《Physics and Chemistry of Minerals》2008,35(5):271-278
Single-crystal polarized Raman spectra (3,000–4,000 cm−1 at 3 ≤ T ≤ 300 K) were measured for synthetic alkali-free and natural beryl, Be2Al3Si6O18·xH2O, to determine the behavior of H2O molecules of both Type I and Type II in the cavities. At low temperature, the H2O molecules of Type I displace from the center of cavity and give rise to very weak hydrogen bonding with the host lattice.
The H2O Type I translational motion is characterized by substantial anharmonicity and looks like a motion of “a particle in the
box” with a frequency of 6.3 cm−1. Water Type II is characterized by a free rotation with respect to the C
2 molecule axis, and it makes possible the water nuclear isomers (i.e. ortho- and para-) to be observed at low temperature.
相似文献
Boris KolesovEmail: |
10.
Anton Beran Dominik Talla Zdenek Losos Jiri Pinkas 《Physics and Chemistry of Minerals》2010,37(3):159-166
The infrared (IR) spectra of gem-quality baryte crystals from different occurrences are characterized by relatively weak but
strongly pleochroic absorption bands at 3,280, 3,220, 3,155, and 3,115 cm−1. These bands are assigned to anti-symmetric and symmetric OH stretching vibrations of two types of H2O molecules localized on vacant Ba sites. The H–H axis of the H2O I molecule is slightly tilted from the a-axis direction, its twofold axis being nearly parallel to the b-axis, thus defining the plane of the H2O molecule practically parallel to (001). The H2O II molecule has its H–H axis parallel to the b-axis direction, with its plane lying approximately parallel to (101). The values of the total water contents of the baryte
crystals, calculated on the basis of IR spectroscopic data, are ranging from about 1.7–3.8 wt.ppm. The possible presence of
H3O+ ions is also discussed. 相似文献
11.
High-pressure Raman investigations were carried out on a synthetic fluorapatite up to about 7 GPa to analyse the behaviour
of the phosphate group's internal modes and of its lattice modes. The Raman frequencies of all modes increased with pressure
and a trend toward reduced splitting was observed for the PO4-stretching modes [(ν3a(Ag) and ν3b(Ag); ν3a(E2g) and ν3b(E2g)] and the PO4 out-of-plane bending modes [ν4a(Ag) and ν4b(Ag)]. The pressure coefficients of phosphate modes ranged from 0.0047 to 0.0052 GPa−1 for ν3, from 0.0025 to 0.0044 GPa−1 for ν4, from 0.0056 to 0.0086 GPa−1 for ν2 and 0.0046 for ν1 GPa−1, while the pressure coefficients of lattice modes ranged from 0.0106 to 0.0278 GPa−1. The corresponding Grüneisen parameters varied from 0.437 to 0.474, 0.428, 0.232 to 0.409 and 0.521 to 0.800 for phosphate
modes ν3, ν1, ν4, ν2, respectively, and from 0.99 to 2.59 for lattice modes. The vibrational behaviour was interpreted in view of the high-pressure
structural refinement performed on the same crystal under the same experimental conditions. The reduced splitting may thus
be linked to the reduced distortion of the environment around the phosphate tetrahedron rather than to the decrease of the
tetrahedral distortion itself. Moreover, the amount of calcium polyhedral compression, which is about three times the compression
of phosphate tetrahedra, may explain the different Grüneisen parameters.
Received: 25 April 2000 / Accepted: 20 December 2000 相似文献
12.
Xiaozhi Yang Leonid Dubrovinsky M. A. G. M. Manthilake Qingguo Wei 《Physics and Chemistry of Minerals》2012,39(1):57-64
In situ Raman spectra of hydrous wadsleyite (β-Mg2SiO4) with ~1.5 wt% H2O, synthesized at 18 GPa and 1,400°C, have been measured in an externally heated diamond anvil cell up to 15.5 GPa and 673 K.
With increasing pressure (at room temperature), the three most intense bands at ~549, 720 and 917 cm−1 shift continuously to higher frequencies, while with increasing temperature at 14.5 GPa, these bands generally shift to lower
frequencies. The temperature-induced frequency shifts at 14.5 GPa are significantly different from those at ambient pressure.
Moreover, two new bands at ~714 and ~550 cm−1 become progressively significant above 333 and 553 K, respectively, and disappear upon cooling to room temperature. No corresponding
Raman modes of these two new bands were reported for wadsleyite at ambient conditions, and they are thus probably related
to thermally activated processes (vibration modes) at high-pressure and temperature conditions. 相似文献
13.
A series of in-situ high temperature infrared (IR) measurements of water in an agate sample and in a milky quartz has been conducted in order to understand the nature of water in silica at high temperatures (50–700?°C) and the dehydration behavior. IR absorption bands of water molecules trapped in the milky quartz showed a systematic decrease in intensities and a shift from 3425?cm?1 at 50?°C toward 3590?cm?1 at 700?°C without any loss of water. This indicates a change in IR absorption coefficients corresponding to different polymeric states of water at different temperatures. The broad 3430?cm?1 band in the agate sample also showed a systematic decrease in IR intensity and a band shift toward higher frequency with increasing temperature (~700?°C). This indicates that the agate sample also contains fluid inclusion-like water. For this agate sample, a dehydration of loosely hydrogen-bonded molecular water occurred at lower temperatures (<200?°C). At higher temperatures (>400?°C), sharp bands around 3660 and 3725?cm?1 (3740?cm?1 at 50?°C) due to surface silanols, appeared. This indicates dehydration of H2O molecules that are hydrogen bonded to surface silanols. SiOH species in the agate are divided into three groups, namely SiOH group located at structural defects, surface silanols hydrogen bonded to each other and free surface silanols. Former two dehydrate below 700?°C and the dehydration rate of the SiOH at structural defects is faster than the other. IR spectra show that SiOH species decrease continuously even after the dehydration of most of H2O molecules. All these results provide realistic bases for the change in physicochemical states of different OH species in silica at high temperatures. 相似文献
14.
Relative humidity (
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} , partial pressure of water)-dependent dehydration and accompanying phase transitions in NAT-topology zeolites (natrolite,
scolecite, and mesolite) were studied under controlled temperature and known
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} conditions by in situ diffuse-reflectance infrared Fourier transform spectroscopy and parallel X-ray powder diffraction.
Dehydration was characterized by the disappearance of internal H2O vibrational modes. The loss of H2O molecules caused a sequence of structural transitions in which the host framework transformation path was coupled primarily
via the thermal motion of guest Na+/Ca2+ cations and H2O molecules. The observation of different interactions of H2O molecules and Na+/Ca2+ cations with host aluminosilicate frameworks under high- and low-
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} conditions indicated the development of different local strain fields, arising from cation–H2O interactions in NAT-type channels. These strain fields influence the Si–O/Al–O bond strength and tilting angles within and
between tetrahedra as the dehydration temperature is approached. The newly observed infrared bands (at 2,139 cm−1 in natrolite, 2,276 cm−1 in scolecite, and 2,176 and 2,259 cm−1 in mesolite) result from strong cation–H2O–Al–Si framework interactions in NAT-type channels, and these bands can be used to evaluate the energetic evolution of Na+/Ca2+ cations before and after phase transitions, especially for scolecite and mesolite. The 2,176 and 2,259 cm−1 absorption bands in mesolite also appear to be related to Na+/Ca2+ order–disorder that occur when mesolite loses its Ow4 H2O molecules. 相似文献
15.
Monika Koch-Müller Stanislav S. Matsyuk Dieter Rhede Richard Wirth Natasha Khisina 《Physics and Chemistry of Minerals》2006,33(4):276-287
The incorporation of hydrogen in mantle olivine xenocrysts from the Udachnaya kimberlite pipe was investigated by Fourier-transform infrared spectroscopy and secondary ion mass spectrometry (SIMS). IR spectra were collected in the OH stretching region on oriented single crystals using a conventional IR source at ambient conditions and in situ at temperatures down to −180°C as well as with IR synchrotron radiation. The IR spectra of the samples are complex containing more than 20 strongly polarized OH bands in the range 3,730–3,330 cm−1. Bands at high energies (3,730–3,670 cm−1) were assigned to inclusions of serpentine, talc and the 10 Å phase. All other bands are believed to be intrinsic to olivine. The corresponding point defects are (a) associated with vacant Si sites (3,607 cm−1 E || a, 3,597 E || a, 3,571 cm−1 E || c, 3,567 E || c, and 3,556 E || b), and (b) with vacant M1 sites (most of the bands polarized parallel to a). From the pleochroic behavior and position of the OH bands associated with the vacant M1 sites, we propose two types of hydrogen—one bonded to O1 and another to O2, so that both OH vectors are strongly aligned parallel to a. The O2–H groups may be responsible for the OH bands at higher wavenumbers than those for the O1–H groups. The multiplicity of the corresponding OH bands in the spectra can be explained by different chemical environments and by slightly different distortions of the M1 sites in these high-pressure olivines. Four samples were investigated by SIMS. The calculated integral molar absorption coefficient using the IR and SIMS results of 37,500±5,000 L mol H2O cm−2 is within the uncertainties slightly higher than the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003) (28,450±1,830 L mol H2O cm−2). The reason for the difference is the different distributions of the absorption intensity of the spectra of both studies (mean wavenumber 3,548 vs. 3,570 cm−1). Olivine samples with a mean wavenumber of about 3,548 cm−1 should be quantified with the absorption coefficient as determined in this study; those containing more bands at higher wavenumber (mean wavenumber 3,570 cm−1) should be quantified using the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003).
相似文献
Monika Koch-MüllerEmail: Phone: +49-331-2881492 |
16.
Etienne Balan Simon Delattre Damien Roche Loïc Segalen Guillaume Morin Maxime Guillaumet Marc Blanchard Michele Lazzeri Christian Brouder Ekhard K. H. Salje 《Physics and Chemistry of Minerals》2011,38(2):111-122
The crystallinity of natural and synthetic apatite samples is often determined from the broadening of ν
4 PO4 infrared absorption bands. However, various physical mechanisms contribute to the observed linewidth. In the present study,
the factors determining the linewidth in the powder spectrum of synthetic fluorapatite and hydroxyapatite samples are investigated.
The temperature dependence of the infrared spectrum (10–270 K) is used to assess the respective contributions of homogeneous
broadening, related to the decay of phonons through anharmonic coupling, and heterogeneous broadening related to elastic strain
and macroscopic electrostatic effects. This latter contribution is dominant in the investigated samples and depends on the
shape of powder particles. It is discussed under the light of the theoretical modeling of the low-frequency dielectric properties
of apatite based on first-principles density functional theory calculations. The linewidth of the weak ν
1 PO4 absorption band provides a reliable information on microscopic sources of broadening, i.e., apatite crystallinity. In comparison,
the other more intense PO4 bands are more sensitive to long-range electrostatic effects. 相似文献
17.
Tae Hyun Yoon Stephen B. Johnson Gordon E. Brown Jr. 《Geochimica et cosmochimica acta》2004,68(22):4505-4518
The types and structures of adsorption complexes formed by oxalate at boehmite (γ-AlOOH)/water and corundum (α-Al2O3)/water interfaces were determined using in situ attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy and quantum chemical simulation methods. At pH 5.1, at least four different oxalate species were found at or near the boehmite/water interface for oxalate surface coverages (Γox) ranging from 0.25 to 16.44 μmol/m2. At relatively low coverages (Γox < 2.47), strongly adsorbed inner-sphere oxalate species (IR peaks at 1286, 1418, 1700, and 1720 cm−1) replace weakly adsorbed carbonate species, and a small proportion of oxalate anions are adsorbed in an outer-sphere mode (IR peaks at 1314 and 1591 cm−1). IR peaks indicative of inner-sphere adsorbed oxalate are also observed for oxalate at the corundum/water interface at Γox = 1.4 μmol/m2. With increasing oxalate concentration (Γox > 2.47 μmol/m2), the boehmite surface binding sites for inner-sphere adsorbed oxalate become saturated, and excess oxalate ions are present dominantly as aqueous species (IR peaks at 1309 and 1571 cm−1). In addition to these adsorption processes, oxalate-promoted dissolution of boehmite following inner-sphere oxalate adsorption becomes increasingly pronounced with increasing Γox and results in an aqueous Al(III)-oxalate species, as indicated by shifted IR peaks (1286 → 1297 cm−1 and 1418 → 1408 cm−1). At pH 2.5, no outer-sphere adsorbed oxalate or aqueous oxalate species were observed. The similarity of adsorbed oxalate spectral features at pH 2.5 and 5.1 implies that the adsorption mechanism of aqueous HOx− species involves loss of protons from this species during the ligand-exchange reaction. As a consequence, adsorbed inner-sphere oxalate and aqueous Al(III)-oxalate complexes formed at pH 2.5 have coordination geometries very similar to those formed at pH 5.1.The coordination geometry of inner-sphere adsorbed oxalate species was also predicted using quantum chemical geometry optimization and IR vibrational frequency calculations. Geometry-optimized Al8O12 and Al14O22 clusters with the reactive surface Al site coordinated by three oxygens were used as model substrates for corundum and boehmite surfaces. Among the models considered, calculated IR frequencies based on a bidentate side-on structure with a 5-membered ring agree best with the observed frequencies for boehmite/oxalate/water samples at Γox = 0.25 to 16.44 μmol/m2 and pH 2.5 and 5.1, and for a corundum/oxalate/water sample at Γox = 1.4 μmol/m2 and pH 5.1. Based on these results, we suggest that oxalate bonding on boehmite and corundum surfaces results in 5-coordinated rather than 4- or 6-coordinated Al surface sites. 相似文献
18.
Isothermal thermogravimetric experiments have been carried out to determine the reaction kinetics of the dehydration processes
in fuller's earth, a natural Ca-montmorillonite. Dehydration in swelling clays is a complex reaction, and analysis of the
thermogravimetric data using empirical rate equations and time-transformation analysis reveals that the nature of the rate
controlling mechanism is dependent upon both the temperature regime of the sample as well as the extent of reaction. For fuller's
earth, we find that the dehydration kinetics are dominated by a nucleation and growth mechanism at low temperatures and fractions
transformed (stage I), but above 90 °C the last stages of the reaction are diffusion controlled (stage II). The activation
energy for dehydration during stage I is around 35 kJ · mol−1, whereas the removal of water during stage II requires an activation energy of around 50 kJ · mol−1. These two stages of dehydration are associated with primary collapse of the interlayer (stage I) and movement of water that
is hydrated to cations within the interlayer (stage II).
Received: 28 August 1998 / Revised, accepted: 27 January 1999 相似文献
19.
Marek Kwaśniewski 《Rock Mechanics and Rock Engineering》2011,44(1):103-111
Based on the hypothesis that shearing stresses and normal tensile stresses both play a decisive role in fracturing and brittle
failure of rock material, a novel strength criterion was developed in one of the earlier works of the author. In the criterion,
a certain parameter ν′ occurs which depends on the structure of the material. Originally, the parameter was treated as a constant, which resulted
in a linear form of the strength function F
σ
1 = f(σ
3), where σ
3 = σ
2. Although the linear strength criterion is sometimes found to be applicable to various particular rock materials, it is not,
in general, of a universal character. Analysis of the triaxial test results for 75 different sandstones revealed that parameter
ν′ usually increases in an exponential or linear manner as confining pressure increases, and only in isolated cases does it
seem to be independent of the confining pressure. For these three types of function ν′ = f(p) appropriate strength criteria F
σ
1 = f(σ
3) are given in the present paper. These criteria were used to fit all of the collected empirical data sets. In general, a
very good fit to the data was obtained. 相似文献
20.
In situ unpolarized and polarized Fourier transform infrared spectra of a natural orthopyroxene at varying temperatures were
obtained using a heating stage attached on an Infrared microscope. The three main bands (3,595, 3,520 and 3,410 cm−1) at room temperature are ascribed to OH fundamental stretching bands. With increasing temperature from room temperature to
500 °C, the 3,595 cm−1 band shifts 20 cm−1 to lower frequency. The total integral absorbance decreases with increasing temperature. These changes are reversible. Excluding
the influences of dehydration, proton migration, thermal expansion, and changes in OH dipole direction, the change of integral
absorbance with temperature reflects the temperature dependence of absorption coefficient due to the anharmonicity of OH vibration.
Based on the integral absorption coefficient at room temperature (14.84 ppm−1 cm−2) from Bell et al. (Am Mineral 80:463–474, 1995), the integral absorption coefficients at other temperatures are calculated. The variation of integral absorption coefficient
between room temperature and 500 °C obtained in this study is about 18.5 % and may be greater at higher temperature according
to the proposed linear relationship. 相似文献