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1.
Julien Gasc Fabrice Brunet Nikolai Bagdassarov Victor Morales-Flórez 《Physics and Chemistry of Minerals》2011,38(7):543-556
The effect of intergranular water on the conductivity of polycrystalline brucite, Mg(OH)2, was investigated using impedance spectroscopy at 2 GPa, during consecutive heating–cooling cycles in the 298–980 K range.
The grain boundary hydration levels tested here span water activities from around unity (wet conditions) down to 10−4 (dry conditions) depending on temperature. Four orders of magnitude in water activity result in electrical conductivity variations
for about 6–7 orders of magnitude at 2 GPa and room temperature. Wet brucite samples containing, initially, about 18 wt% of
evaporable water (i.e. totally removed at temperatures below 393 K in air), display electrical conductivity values above 10−2–10−3 S/m. A.C. electrical conductivity as a function of temperature follows an Arrhenius behaviour with an activation energy of
0.11 eV. The electrical conductivity of the same polycrystalline brucite material dried beforehand at 393 K (dry conditions)
is lower by about 5–6 orders of magnitude at room temperature and possesses an activation energy of 0.8–0.9 eV which is close
to that of protonic diffusion in (001) brucitic planes. Above ca. 873 K, a non-reversible conductivity jump is observed which
is interpreted as a water transfer from mineral bulk to grain boundaries (i.e. partial dehydration). Cooling of such partially
dehydrated sample shows electrical conductivities much higher than those of the initially dry sample by 4 orders of magnitude
at 500 K. Furthermore, the corresponding activation energy is decreased by a factor of about four (i.e. 0.21 eV). Buffering
of the sample at low water activity has been achieved by adding CaO or MgO, two hygroscopic compounds, to the starting material.
Then, sample conductivities reached the lowest values encountered in this study with the activation energy of 1.1 eV. The
strong dependency of the electrical conductivity with water activity highlights the importance of the latter parameter as
a controlling factor of diffusion rates in natural processes where water availability and activity may vary grandly. Water
exchange between mineral bulk and mineral boundary suggests that grain boundary can be treated as an independent phase in
dehydroxylation reactions. 相似文献
2.
Dehydration behavior of muscovite flake was investigated at 760–860°C by using in situ high-temperature IR microspectroscopy
for the OH absorption band around 3,620 cm−1. Isothermal kinetic heating experiments at each temperature gave detailed decrease curves of the OH band area with time.
These curves have been simulated by the first and second order reactions or mono- and two-dimensional diffusion processes.
The mono-dimensional diffusion was found to give the best fit to the experimental data and apparent diffusion coefficients
D were determined at 760–860°C with the activation energy of 290 ± 20 kJ/mol. The apparent diffusion coefficients D varied with the sample thickness L. This variation can be explained by an m layers model with a unit length of L′ with a constant diffusion coefficient D′. Therefore, the dehydration process might be rate-limited by mono-dimensional diffusion through tetrahedral silicate sheet
perpendicular to (001) planes of muscovite with a unit length of L′. 相似文献
3.
The high-pressure behavior of Keokuk kaolinite has been studied to 9.5 GPa by infrared spectroscopy using synchrotron radiation.
The kaolinite-I → kaolinite-II and kaolinite-II → kaolinite-III transformations have clear spectroscopic expression, with
discontinuities coinciding with the transformation pressures bracketed by X-ray diffraction (Welch and Crichton in Am Mineral
95:651–654, 2010). The experimental spectra have been interpreted from band assignments derived from density functional theory for the structures
of kaolinite-II and kaolinite-III, using as starting models the ab initio structures reported by Mercier and Le Page (Acta
Crystallogr A B64:131–143, 2008, Mater Sci Technol 25:437–442, 2009) and unit-cell parameters from Welch and Crichton (Am Mineral 95:651–654, 2010). The relaxed theoretical structures are very similar to those reported by Mercier and Le Page (Acta Crystallogr A B64:131–143,
2008, Mater Sci Technol 25:437–442, 2009) in their theoretical investigation of kaolinite polytypes at high pressure. The vibrational spectra calculated from the
quantum-mechanical analysis allow band assignments of the IR spectra to be made and provide insights into the behavior of
different OH environments in the two high-pressure polytypes. The single perpendicular-interlayer OH group of kaolinite-III
has a distinctive spectroscopic signature that is diagnostic of this polytype (ν = 3,595 cm−1 at 9.5 GPa) and is sensitive to the compression/expansion of the interlayer space. This OH group also has a distinctive signature
in the calculated spectra. The spectra collected on decompression are those of kaolinite-III and persist largely unchanged
to 4.6 GPa, except for a continuous blue shift of the 3,595 cm−1 band to 3,613 cm−1. Finally, kaolinite-I is recovered at 0.6 GPa, confirming the kaolinite-III → kaolinite-I transformation previously observed
by X-ray diffraction, and the irreversibility of the kaolinite-II → kaolinite-III transformation. The ambient spectra collected
at the start and finish of the experiment are those of kaolinite-I, and start/finish band frequencies agree to within 6 cm−1. 相似文献
4.
The oxidation of dihydroxyaromatics to benzoquinones by FeIII (hydr)oxides is important in respiratory electron shuttling by microorganisms and has been extensively studied. Prior publications
have noted that the Gibbs Free Energy (ΔG) for the forward reaction is sensitive to dihydroxyaromatic structure, pH, and concentrations of reactants and products.
Here, we address the back reaction, benzoquinone reduction by FeII. Rates markedly increase with increasing pH, in accord with increases in ΔG. Ring substituents that raise the potential of the p-benzoquinone/hydroquinone half reaction raise reaction rates: –OCH3 < –CH3 < –C6H5 < –H < –Cl. p-Naphthoquinone, with a reduction potential lower than the five substituted p-benzoquinones just listed, yields the lowest reaction rates. The complexity of the reaction is reflected in lag periods and
less-pronounced S-shaped time course curves. Benzoquinone reduction by FeII may be an important link in networks of electron transport taking place in suboxic and anoxic environments. 相似文献
5.
Using a combination of dielectric spectroscopy and atomistic computer simulation techniques, the dynamical behaviour of the
loosely bound (Na+ and K+) channel ions in nepheline has been investigated. The low-frequency dielectric properties of a natural Bancroft nepheline
have been studied from room temperature to 1100 K. At each temperature, the dielectric constant, conductivity and dielectric
loss were determined over a range of frequencies from 100 Hz to 10 MHz. At high temperatures a distinct Debye-type relaxation
in the dielectric loss spectrum was observed; the activation energy for this process was determined to be 1.38 ± 0.02 eV.
Atomistic simulation techniques were used to elucidate the mechanism and energetics of cation migration. A mechanism involving
the hopping of Na+ ions between oval sites and partially occupied hexagonal (K+) sites, via a bottleneck consisting of a distorted sixfold ring of (Al,Si)O4 tetrahedra, was found to give a calculated energy barrier in very good agreement with the experimentally determined activation
energy. These results confirm the nature of the process responsible for the observed dielectric behaviour. Overall, this study
demonstrates the intrinsic, microscopic control of cation diffusion processes in rock-forming minerals. Identifying specific
energy barriers and preferred diffusion pathways is fundamental to the prediction of diffusion energetics.
Received: 8 May 2000 / Accepted: 21 July 2000 相似文献
6.
7.
Tomoo Katsura Sho Yokoshi Kazuyuki Kawabe Anton Shatskiy Maki Okube Hiroshi Fukui Eiji Ito Akifumi Nozawa Ken-ichi Funakoshi 《Physics and Chemistry of Minerals》2007,34(4):249-255
The electrical conductivity of (Mg0.93Fe0.07)SiO3 ilmenite was measured at temperatures of 500–1,200 K and pressures of 25–35 GPa in a Kawai-type multi-anvil apparatus equipped
with sintered diamond anvils. In order to verify the reliability of this study, the electrical conductivity of (Mg0.93Fe0.07)SiO3 perovskite was also measured at temperatures of 500–1,400 K and pressures of 30–35 GPa. The pressure calibration was carried
out using in situ X-ray diffraction of MgO as pressure marker. The oxidation conditions of the samples were controlled by
the Fe disk. The activation energy at zero pressure and activation volume for ilmenite are 0.82(6) eV and −1.5(2) cm3/mol, respectively. Those for perovskite were 0.5(1) eV and −0.4(4) cm3/mol, respectively, which are in agreement with the experimental results reported previously. It is concluded that ilmenite
conductivity has a large pressure dependence in the investigated P–T range. 相似文献
8.
Summary The temperature dependence of photoluminescence emission of a natural fluorite has been studied in the wavelength region of
380–500 nm and in the temperature range of 17.5–300 K. The emission spectra of the sample show a broad emission band between
380 and 500 nm for temperatures above 100 K. At 100 K and below, vibronic lines appear on the emission band at approximately
413.3, 418.1, 419.3, 420.2, 423.9 and 427.1 nm. This broad emission band and the vibronic lines in fluorite are usually associated
with phonon-coupled electronic transitions from 4f65d to 4f7 in the Eu2+ ion. Temperature dependences of the peak energy, intensity and full-width at half-maximum of the broad emission band are
discussed, and the behaviour explained in terms of a configurational coordinate model. The excited state vibrational energy
was obtained to be 0.023 ± 0.001 eV and this is lower than the LO phonon energy of 0.062 eV in pure fluorite. The activation
energy of thermal quenching of the photoluminescence intensity was found to be 0.022 ± 0.002 eV. 相似文献
9.
Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary,New Brunswick,Canada 总被引:1,自引:0,他引:1
Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment.
A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study
on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada,
with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel
originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88
species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m−2 (ranged from 4,371 to 19,930 ind. m−2), 23.4 species grab−1 and 3.29 grab−1, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution
in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well
as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth
(1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting
(σI). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay
fraction, σI and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction
as the single best-correlated variable. 相似文献
10.
D. Vielzeuf A. Baronnet A. L. Perchuk D. Laporte M. B. Baker 《Contributions to Mineralogy and Petrology》2007,154(2):153-170
Concentration gradients in calcium are common in metamorphic or magmatic garnets and can be used to determine the timescales
of geological processes. However, the kinetics of Ca diffusion in garnet is poorly constrained and experimental studies have
to date yielded widely varying diffusion coefficients. In this paper, we describe a new method for generating diffusion profiles
in garnet. We incorporated polished and compositionally homogeneous garnet seeds in a finely ground powder of clinopyroxene
and garnet. During the experiments (1.3 GPa, 1,050–1,250°C, and ƒO2 ≤ the graphite-O2 buffer), the mineral powder partially melted, recrystallized, and formed a 10–50 μm wide overgrowth zone of compositionally
distinct garnet around the seeds. Long duration experiments generated measurable relaxation profiles at these seed/overgrowth
interfaces. We performed analytical transmission electron microscope traverses across the interfaces in each experiment. Thirteen
usable compositional profiles were obtained with characteristic distances of diffusion ranging from 300 to 1,000 nm. From
these profiles, Ca–(Fe, Mg) interdiffusion coefficients were retrieved using an analytical solution for the diffusion equation
and the data were cast in an Arrhenius relation. Linear regression of the data yields an activation energy Q
Ca–(Fe, Mg) equal to 188 ± 48 kJ mol−1 and a frequency factor D
0 equal to 6.6 × 10−14 m2 s−1. Within the compositional range studied, the composition of garnet has no major effect on the Ca–(Fe, Mg) interdiffusion
coefficient. The very slow diffusion rate of Ca is in agreement with natural observations indicating that Ca diffuses more
slowly than Fe and Mg. The Ca diffusion coefficients derived from this study are not model-dependent and can be used to determine
the durations of geological events from Ca relaxation profiles in natural garnets.
相似文献
D. VielzeufEmail: |
11.
R. Wirth 《Physics and Chemistry of Minerals》1997,24(8):561-568
Electron energy-loss spectroscopy EELS of the oxygen K edge of OH– containing minerals and minerals with molecular water reveals a peak at about 528 eV prior to the onset of the O-K edge at 532 eV. This peak is never observed in minerals without water or OH– groups. The intensity of the signal at 528 eV increases with increasing water content of the minerals. The peak at 528 eV
is attributed to OH groups or water molecules. From the observations it is concluded that EELS provides a new method to determine
the OH– or water content of minerals with a spatial resolution far beyond that of optical spectroscopy.
Received: 28 April 1997 / Revised, accepted: 25 July 1997 相似文献
12.
Ľubomír Smrčok Daniel Tunega Anibal Javier Ramirez-Cuesta Eva Scholtzová 《Physics and Chemistry of Minerals》2010,37(8):571-579
The dynamics of the hydrogen atoms in the highly ordered kaolinite was studied by vibrational spectroscopy based on inelastic
neutron scattering method with the focus on the spectral region of 100–1,250 cm−1. The experimental spectrum was interpreted by means of the solid state density functional theory calculations covering both
normal mode analysis and molecular dynamics going beyond the harmonic approximation. The Al–O–H bending modes were found to
be spread over the large interval of 100–1,100 cm−1, with the dominant contributions located between 800 and 1,100 cm-1. The shapes of the individual hydrogen spectra depend on the strengths of the individual interlayer O–H···O hydrogen bonds
involving the inner surface hydroxyl groups. The modes assigned to the in-plane movements of the respective hydrogen atoms
are well-defined and always appear on the top of the intervals of energy transfer. In contrast, the modes generated by the
out-of-plane movements are spread over large intervals of energies spanning down to the region of external (lattice) modes. 相似文献
13.
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
14.
Yves Noel Raffaella Demichelis Fabien Pascale Piero Ugliengo Roberto Orlando Roberto Dovesi 《Physics and Chemistry of Minerals》2009,36(1):47-59
The structure and vibrational spectrum of boehmite have been investigated at the quantum-mechanical level with the CRYSTAL
code, using a Gaussian-type basis set and the B3LYP Hamiltonian. Three space groups are considered in this study: Cmcm, Cmc21, P21/c. Cmcm turns out to correspond to a transition state, whereas Cmc21 and P21/c are minimum energy structures. The difference among them is the position of H atoms only, the Al-O frame being essentially
the same. Harmonic frequencies at the Γ point have been computed. The comparison between calculated and experimental frequencies
shows a good agreement for the Al-O part of the spectrum (under 790 cm−1). For the Al-OH bending modes (800–1,300 cm−1) an absolute differences of 50–100 cm−1 is observed; for the OH stretching modes (3,200–3,500 cm−1) it increases to 120–200 cm−1: anharmonicity is large because OH groups are involved in strong hydrogen bonds. 相似文献
15.
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
16.
Single-crystal electron paramagnetic resonance (EPR) spectra of a gem-quality jeremejevite, Al6B5O15(F, OH)3, from Cape Cross, Namibia, reveal an S = 1/2 hole center characterized by an 27Al hyperfine structure arising from interaction with two equivalent Al nuclei. Spin-Hamiltonian parameters obtained from single-crystal
EPR spectra at 295 K are as follows: g
1 = 2.02899(1), g
2 = 2.02011(2), g
3 = 2.00595(1); A
1/g
e
β
e
= −0.881(1) mT, A
2/g
e
β
e
= −0.951(1) mT, and A
3/g
e
β
e
= −0.972(2) mT, with the orientations of the g
3- and A
3-axes almost coaxial and perpendicular to the Al–O–Al plane; and those of the g
1- and A
1-axes approximately along the Al–Al and Al–OH directions, respectively. These results suggest that this aluminum-associated
hole center represents hole trapping on a hydroxyl oxygen atom linked to two equivalent octahedral Al3+ ions, after the removal of the proton (i.e., a VIAl–O−–VIAl center). Periodic ab initio UHF and DFT calculations confirmed the experimental 27Al hyperfine coupling constants and directions, supporting the proposed structural model. The VIAl–O−–VIAl center in jeremejevite undergoes the onset of thermal decay at 300 °C and is completely bleached at 525 °C. These data
obtained from the VIAl–O−–VIAl center in jeremejevite provide new insights into analogous centers that have been documented in several other minerals. 相似文献
17.
Riko Iizuka Hiroyuki Kagi Kazuki Komatsu Daichi Ushijima Satoshi Nakano Asami Sano-Furukawa Takaya Nagai Takehiko Yagi 《Physics and Chemistry of Minerals》2011,38(10):777-785
The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature
from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic
conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening (partial amorphization)
observed from the Raman and IR spectra of Ca(OH)2 occurred at lower pressures than those of Ca(OD)2. In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns.
X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization
in a helium pressure medium within the examined pressure region. These results suggest that the H–D isotope effect is engendered
in the local environment surrounding H(D) atoms. Moreover, the ratio of sample-to-methanol–ethanol pressure medium (i.e.,
packing density) in the sample chamber had a significant effect on the increase in the half widths of the diffraction lines,
even at pressures below the hydrostatic limit of the pressure medium. 相似文献
18.
The kinetics of hydrogen diffusion in enstatite was studied by hydrogen–deuterium exchange experiments in the range of 1–5,000 bar and 700–850°C using synthetic single crystals of pure and Cr-doped enstatites. The OH- and OD-content in the samples was quantified after each thermal treatment with Fourier transformed infrared spectroscopy. H–D-exchange rates were measured parallel to the three crystallographic axes. In addition, in order to visualize diffusion profiles, OH and OD were mapped for some samples, utilizing synchrotron IR micro-spectroscopy. Hydrogen self-diffusivities derived from D/H exchange experiments at one atmosphere are very similar to the chemical diffusivity of hydrogen in natural Fe-bearing orthopyroxene, which was reported previously (Stalder and Skogby 2003) to exhibit a small, but significant anisotropy (D[001] > D[100] > D[010]). Activation energies are estimated to be 211 (±31) kJ/mol for diffusion parallel [100] and 185 (±28) kJ/mol for diffusion parallel [010]. Lattice diffusion of hydrogen is decelerated by more than one order of magnitude when Cr is dissolved in enstatite. In comparison to the chemical composition, pressure seems to have only a minor influence on hydrogen diffusion. Compared to other minerals in the Earth’s upper mantle, enstatite exhibits the highest activation energy for hydrogen diffusion, suggesting faster diffusion than in other mafic minerals at mantle temperatures, but slower diffusion at crustal conditions. Thus under upper mantle conditions, physical properties that are expected to be influenced by hydrogen mobility, such as electrical conductivity, may in enstatite be more intensely affected by the presence of hydrogen than in other upper mantle minerals. 相似文献
19.
A.Yu. Likhacheva S. A. Veniaminov E. A. Paukshtis 《Physics and Chemistry of Minerals》2004,31(5):306-312
The thermal decomposition of ammonium-exchanged natural analcime is characterized by gas chromatography, IR spectroscopy and X-ray diffraction. The de-ammoniation and dehydroxylation proceed in parallel throughout the decomposition, which evidences the instability of the protonated analcime framework. The mechanism of degassing of NH4-analcime changes throughout its decomposition. At the initial step, the mechanism of de-ammoniation consists in thermal dissociation of NH4+ molecule onto NH3 and proton (framework OH group) and diffusion of NH3 out of the structure. Subsequent decomposition and removal of the OH groups lead to a progressive loss of crystallinity. At this step, an apparent activation energy for NH3 desorption is estimated to be 145(±13) kJ mol–1. This value is within the upper limit of the activation energy characteristic for the NH3 desorption from proton centres in large-pore zeolites. At the final step, the adsorption of NH3 and protons onto the defect centres in the amorphosed aluminosilicate framework results in a significant increase of an apparent activation energy for the de-ammoniation and dehydroxylation up to 270(±20) kJ mol–1. 相似文献
20.
Bijaya B. Karki Dipesh Bhattarai Mainak Mookherjee Lars Stixrude 《Physics and Chemistry of Minerals》2010,37(2):103-117
We have explored first-principles molecular dynamics simulation data for hydrous MgSiO3 liquid (with 10 wt% water) to gain insight into its structural and dynamical behavior as a function of pressure (0–150 GPa)
and temperature (2,000–6,000 K). By visualizing/analyzing a number of parameters associated with short- and mid-range orders,
we have shown that the melt structure changes substantially on compression. The speciation of the water component at low pressures
is dominated by the isolated structures (with over 90% hydrogen participated) consisting of hydroxyls, water molecules, O–H–O
bridging and four-atom (O–H–O–H and H–O–H–O) groups, where every oxygen atom may be a part of polyhedron or free (i.e., bound
to only magnesium atom). Hydroxyls favor polyhedral sites over magnesium sites whereas molecular water is almost entirely
bound to magnesium sites, and also interpolyhedral bridging (Si–O–H–O–Si) dominates other types of bridging. Water content
is shown to enhance and suppress, respectively, the proportions of hydroxyls and molecular water. As compression increases,
these isolated structures increasingly combine with each other to form extended structures involving a total of five or more
O and H atoms and also containing threefold coordination species, which together consume over 80% hydrogen at the highest
compression studied. Our results show that water lowers the mean coordination numbers of different types including all cation–anion
environments. The hydrous melt tends to be more tetrahedrally coordinated but with the Si–Si network being more disrupted
compared to the anhydrous melt. Protons increase the content of non-bridging oxygen and decrease the contents of bridging
oxygen as well as oxygen triclusters (present at pressures above 10 GPa). The calculated self-diffusion coefficients of all
atomic species are enhanced in the presence of water compared to those of the anhydrous melt. This is consistent with the
prediction that water depolymerizes the melt structure at all pressures. Our analysis also suggests that proton diffusion
involves two processes—the transfer of H atoms (requiring the rupture and formation of O–H bonds) and the motion of hydroxyls
as hydrogen carriers (requiring the rupture and formation of Si–O and/or Mg–O bonds). Both the processes are operative at
low compression whereas only the first process is operative at high compression. 相似文献