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1.
Iron tracer diffusion experiments in diopside have been performed using natural and synthetic single crystals of diopside,
and stable iron tracers enriched in 54Fe, at temperatures in the range 950–1100 °C, total pressure 1 atm, for times up to 29 days. Iron isotope diffusion profiles
were determined with an ion microprobe. For experiments performed at log pO2 = −13, in directions parallel to the c axis and the b axis of two natural, low iron (Fe ∼ 1.8 at %) diopsides, the data obey
a single Arrhenius relationship of the form D = 6.22−5.9
+49.6×10−15 exp(−161.5 ± 35.0 kJ mol−1/RT) m2 s−1. A single datum for iron diffusion in iron-free, single-crystal diopside at 1050 °C, is approximately 1 order of magnitude
slower than in the natural crystals. The pO2 dependence of iron diffusion in natural crystals at 1050 °C (power exponent = 0.229 ± 0.036) indicates a vacancy mechanism;
this is consistent with the results of unpublished atomistic simulation studies. There is no evidence of anisotropy for iron
diffusion in diopside.
Received: 16 March 1999 / Accepted: 10 April 2000 相似文献
2.
地球外核液态铁的不断流动造成了地球磁场 ,决定这一流动的基本性质之一是剪切粘滞度。研究外核液态铁的剪切粘滞度对认识地球磁场的运转机制具有非常重要的意义。地震波和大地测量研究表明地球内部除了剪切衰减外 ,还具有体积衰减。研究外核液态铁的体粘滞度对认识地球内部非弹性性质具有重要意义。由于外核所处的温度和压力状态 ,目前还无法从实验的角度对外核的粘滞度进行测量 ,因此必须采用实际观测和理论模拟计算相结合的方法。在考察了地球外核的主要成分和所处的温压状态后 ,简要介绍了研究外核的一种有效的理论方法———分子动力学。在此基础上 ,重点评述了国际上对外核液态铁剪切粘滞度和体粘滞度的研究现状。在剪切粘滞度方面 ,理论计算值位于实际地球观测值区间的下限。在体粘滞度方面 ,理论计算与实际地球观测之间均存在巨大的差别。这一巨大差异的解决将加深人们对地球内部非弹性性质的认识。 相似文献
3.
J. Zhang 《Physics and Chemistry of Minerals》2000,27(3):145-148
Isobaric volume measurements for MgO were carried out at 2.6, 5.4, and 8.2 GPa in the temperature range 300–1073 K using
a DIA-type, large-volume apparatus in conjunction with synchrotron X-ray powder diffraction. Linear fit of the thermal expansion
data over the experimental pressure range yields the pressure derivative, (∂α/∂P)
T
, of −1.04(8) × 10−6 GPa−1 K−1 and the mean zero-pressure thermal expansion α0,
T
= 4.09(6) × 10−5 K−1. The α0,
T
value is in good agreement with results of Suzuki (1975) and Utsumi et al. (1998) over the same temperature range, whereas
(∂α/∂P)
T
is determined for the first time on MgO by direct measurements. The cross-derivative (∂α2/∂P∂T) cannot be resolved because of large uncertainties associated with the temperature derivative of α at all pressures. The
temperature derivative of the bulk modulus, (∂K
T/∂T)
P
, of −0.025(3) GPa K−1, obtained from the measured (∂α/∂P)
T
value, is in accord with previous findings.
Received: 2 April 1999 / Revised, accepted: 22 June 1999 相似文献
4.
Assessment of heavy-metal contamination of floodplain soils due to mining and mineral processing in the Harz Mountains, Germany 总被引：9，自引：2，他引：7
2 study area was assessed with respect to its heavy-metal load on the basis of the current guideline values. The heavy-metal
loads of the soils in the study area have ranges of <0.2–200 mg kg−1 for Cd, <10–30,000 mg kg−1 for Pb, 7–10,000 mg kg−1 for Cu and 50–55,000 mg kg−1 for Zn. Mobility of the heavy metals was determined by extraction at different pH values. The acid neutralisation capacity
(ANCx) at these pH values was also determined to estimate the probability that the pH can drop to pH=x. The ANC values in the study area ranged from 6 to 3000 mmol H+ kg−1, from −33 to 800 mmol H+ kg−1 and from −74 to 160 mmol H+ kg−1 for ANC3.5, ANC5.0 and ANC6.2, respectively. Together with pedological data, the extraction experiments permit differentiation between soil units that
have been placed in the same environmental hazard class on the basis of total heavy-metal loads.
Received: 10 August 1998 · Accepted: 14 August 1999 相似文献
5.
N. S. Bagdassarov 《Physics and Chemistry of Minerals》1999,26(6):513-520
The present study deals with the small strain torsion deformation of MACOR glass-ceramic samples at high temperatures (450–850 °C)
and over a range of low frequencies (20 Hz–5 mHz). The samples of MACOR ceramic consist of 55 vol% randomly oriented, sheet-like
fluorophlogopite mica crystals (∼100–20 μm in planar size, 1–2 μm in thickness) and 45 vol% of isotropic alumino-borosilicate
glass matrix. Measurements of the complex shear modulus show that the sample does not possess the relaxed shear viscosity
even at temperatures above the glass transition temperature of the glass matrix. The maximum of the imaginary component G
′′() of the shear modulus is ∼0.15 of the unrelaxed value G
∞, the relaxation strength Δ≈0.9. The activation energy of the peak of G
′′() is ∼245 kJ mol−1. Using this value of E
a
, the data obtained at various frequencies and temperatures have been reduced to a master curve using the dimensionless variable
ωτ, where ∼0 exp(−E
a
/RT). The internal friction Q−1(ωτ) is ∝1/()0.35−0.4 in the low-temperature high-frequency range (1); passes through a maximum at ∼1 and trends asymptotically to a value Q−1∼0.25–0.30 at ≪1. The behaviour of Q
−1(ωτ) differs from that of a Caputo body by the presence of the resolved peak which may be attributed to the slow mechanical
relaxation of mica crystals due to rotation as well as flexing and bending modes of crystal deformation.
Received: 26 June 1998 / Revised, accepted: 13 January 1999 相似文献
6.
The expansivity of supercooled diopside liquid has been determined using techniques of container-based dilatometry. Two thermal
strategies have been employed, one in which the sample is brought to volumetric equilibrium by long-duration dwells at low
temperatures (817 °C) and one in which scanning dilatometry of the sample has been performed at somewhat higher temperatures
(890–913 °C). The results of both experiments yield a supercooled liquid expansivity for diopside liquid in the temperature
range of 817–913 °C of 84.4 ± 2.8 × 10−4 cm3/mol K. The expansivity is 65% higher than that obtained for diopside melt obtained at superliquidus temperatures using the
double bob Archimedean method. Combined fitting of the new low temperature, volume–temperature data from the present study
and the superliquidus data from the literature has been performed. The combined fit yields the following equations for the
volume–temperature relationship of diopside liquid (T=temperature in °C):
The standard error of the fit using both equations reproduces the volume–temperature data for diopside liquid within experimental
error. This result reconciles the disparate values of expansivity measured at low temperatures in the supercooled state and
at superliquidus temperatures and confirms the temperature-dependence of the expansivity of diopside liquid. Comparison with
previous low temperature estimates of melt volume and expansivity are discussed in light of these new results.
Received: 18 November 1999 / Accepted: 24 January 2000 相似文献
7.
Thermodynamic properties of high-pressure minerals that are not recoverable from synthesis experiments by conventional quenching
methods (“unquenchable” phases) usually are calculated from equation of state data and phase diagram topologies. The present
study shows that, with cryogenic methods of recovery and sample treatment, phases with a suitable decomposition rate can be
made accessible to direct thermodynamic measurements. A set of samples of Ca(OH)2-II has been synthesized in a multianvil device and subsequently recovered by cooling the high-pressure assembly with liquid
nitrogen. Upon heating from liquid nitrogen to room temperature, the material transformed back to Ca(OH)2-I. The heat effect of this backtransformation was measured by differential scanning calorimetry. A commercial differential
scanning calorimeter (Netzsch DSC 404), modified to allow sample loading at liquid nitrogen temperature was used to heat the
material from −150 to +200 °C at rates varying between 5 and 15 °C min−1. The transformation started around −50 °C very gradually, and peaked at about 0 °C. To obtain a baseline correction, each
sample was scanned under exactly the same conditions after the backtransformation was complete. Because of the relative sluggishness,
onset and offset temperatures were not well defined as compared to fast (e.g., melting) reactions. To aid in integration,
the resulting signals were successfully fitted using a generic asymmetric peak model. The enthalpy of backtransformation was
determined to be ΔH =−10.37 ± 0.50 kJ mol−1. From previous in situ X-ray diffraction experiments, the location of the direct transformation in P-T space has been constrained to 5.7 ± 0.4 GPa at 500 °C (Kunz et al. 1996). With the reaction volume known from the same study,
and assuming that ΔC
p
of the transformation remains negligible between the conditions of our measurements and 500 °C, our result gives an estimate
of the entropy of transition and the P-T slope of the reaction curve. To a first approximation, the values ΔS = −16.00 ± 0.65 J(mol · K)−1 and dP/dT = 0.0040 ± 0.0002 GPa/K have been determined. These results need to be refined by equation of state data for Ca(OH)2-II.
Received: 30 December 1999 / Accepted: 10 April 2000 相似文献
8.
The dissolved fluoride (F−) in the Lower Ganges-Brahmaputra-Meghna (GBM) river system, Bengal basin, Bangladesh, was studied during 1991–1993 to determine
its distribution and source in the basin, and its annual flux to the Bay of Bengal. The concentration of dissolved F− varied between 2 and 11 μmol l−1 with statistically significant variations both spatially and temporally in the basin. Such variations are attributable to
the geology of the individual subbasins (Ganges, Brahmaputra and Meghna), dilution by rainwater during monsoon and groundwater
contribution to the river systems during dry season. Correlation coefficients among F− and major cations and anions suggest diverse inorganic processes responsible for regulating the concentration of F− in these river systems. However, fluorite seems to be one of the major sources of dissolved F−. The concentration of F− in the Lower GBM river system is low compared to the rivers draining Deccan Plateau and arid regions of the subcontinent,
for example, Yamuna and its tributaries. However, it is within the range of most of the other Peninsular and Himalayan rivers.
The GBM system contributes about 115×103 tonnes year−1 of dissolved F− into the Bay of Bengal, and thus accounts for about 3% of the global F− flux to the oceans annually.
Received: 19 May 1999 · Accepted: 11 October 1999 相似文献
9.
Water from the Kombat mine was delivered to the Omatako dam via the 263-km-long Grootfontein-Omatako canal during test runs
in 1997. It is intended to supply water from Kombat and other underground mines in the Otavi Mountain Land to the capital
Windhoek. The Cu-Pb-Zn orebodies are hosted by carbonate rocks and the mine waters are supersaturated with respect to calcite
and CO2. Along the length of the canal, the CO2 partial pressure drops from 10−2.1 atm at the inlet of the Kombat mine to 10−3.5 atm at the end of the canal. This is accompanied by a drop in Ca concentration from about 60 to about 20 mg/l. The heavy
metal concentrations (Cd, Cu, Mn, Pb and Zn) drop along the course of the canal to values far below the national drinking-water
standard. Scavenging by calcium carbonate precipitation is the major depletion mechanism.
Received: 21 June 1999 · Accepted: 29 August 1999 相似文献
10.
Unit-cell dimensions of a natural phlogopite from Pargas, Finland, have been determined in the temperature interval of 27–1050 °C
by X-ray powder diffraction technique. Expansion rates vary discontinuously with temperature with a break at 412 °C. Below
this temperature, the linear expansions (α) for a, b and c axis lengths are 3.74 × 10−5 K−1, 1.09 × 10−5 K−1, and 1.19 × 10−5 K−1, respectively, and above that they are 0.86 × 10−5 K−1, 0.80 × 10−5 K−1, and 1.93 × 10−5 K−1. The volume thermal expansion coefficients are 6.26 × 10−5 K−1 and 3.71 × 10−5 K−1 for low-temperature and high-temperature intervals, respectively. The observed kink in the rate of thermal expansions with
temperature could be due to the different mode of structural changes. Thermogravimetric analysis of the sample indicates the
oxidation of iron in the temperature range of 500–600 °C and dehydroxylation as well as decomposition of phlogopite in the
temperature range of 900–1200 °C.
Received: 8 September 1998 / Accepted: 28 February 2000 相似文献
11.
Surface tension (σ) profoundly influences the ability of gas bubbles to nucleate in silicate melts. To determine how temperature impacts σ, experiments were carried out in which high-silica rhyolite melts with 5 wt% dissolved water were decompressed at temperatures
that ranged from 775 to 1,085°C. Decompressions were also carried out using dacite melts with 4.3 wt% dissolved water at 1,150°C.
Water bubbles nucleated in rhyolite only when decompressions exceeded 95 MPa at all temperatures. Bubbles nucleated in number
densities that increased as decompression increased and at hotter temperatures at a given amount of decompression. After correcting
decompression amounts for temperature differences, values for σ were estimated from nucleation rates and found to vary between 0.081 and 0.093 N m−1. Surface tension decreases as temperature increases from 775 to 875°C, but then increases as temperature increases to 1,085°C.
Those values overlap previous results, but only when melt viscosity is less than 104 Pa s. For low-viscosity rhyolite, there is a strong correlation of σ with temperature, in which σ increases by 6.9 × 10−5 N m−1 C−1. That variation is robust for 5–9 wt% dissolved water, as long as melt viscosity is ≤104 Pa s. More viscous rhyolite deviates from that correlation probably because nucleation is retarded in stiffer melts. Bubbles
nucleated in dacite when decompressions exceeded 87 MPa, and occured in one or more events as decompression increased. Surface
tension is estimated to be 0.083 (±0.001) N m−1 and when adjusted for temperature agrees well with previous results for colder and wetter dacite melts. At a given water
content, dacite melts have lower surface tensions than rhyolite melts, when corrected to a fixed temperature. 相似文献
12.
Haruka Ozawa Kei Hirose Masanori Mitome Yoshio Bando Nagayoshi Sata Yasuo Ohishi 《Physics and Chemistry of Minerals》2009,36(6):355-363
Partitioning of oxygen and silicon between molten iron and (Mg,Fe)SiO3 perovskite was investigated by a combination of laser-heated diamond-anvil cell (LHDAC) and analytical transmission electron
microscope (TEM) to 146 GPa and 3,500 K. The chemical compositions of co-existing quenched molten iron and perovskite were
determined quantitatively with energy-dispersive X-ray spectrometry (EDS) and electron energy loss spectroscopy (EELS). The
results demonstrate that the quenched liquid iron in contact with perovskite contained substantial amounts of oxygen and silicon
at such high pressure and temperature (P–T). The chemical equilibrium between perovskite, ferropericlase, and molten iron at the P–T conditions of the core–mantle boundary (CMB) was calculated in Mg–Fe–Si–O system from these experimental results and previous
data on partitioning of oxygen between molten iron and ferropericlase. We found that molten iron should include oxygen and
silicon more than required to account for the core density deficit (<10%) when co-existing with both perovskite and ferropericlase
at the CMB. This suggests that the very bottom of the mantle may consist of either one of perovskite or ferropericlase. Alternatively,
it is also possible that the bulk outer core liquid is not in direct contact with the mantle. Seismological observations of
a small P-wave velocity reduction in the topmost core suggest the presence of chemically-distinct buoyant liquid layer. Such
layer physically separates the mantle from the bulk outer core liquid, hindering the chemical reaction between them. 相似文献
13.
Pb diffusion in rutile 总被引：16，自引：0，他引：16
D. J. Cherniak 《Contributions to Mineralogy and Petrology》2000,139(2):198-207
Diffusion of Pb was measured in natural and synthetic rutile under dry, 1 atmosphere conditions, using mixtures of Pb titanate
or Pb sulfide and TiO2 as the sources of diffusant. Pb depth profiles were then measured with Rutherford Backscattering Spectrometry (RBS). Over
the temperature range 700–1100 °C, the following Arrhenius relation was obtained for the synthetic rutile: D=3.9 × 10−10exp(−250 ± 12 kJ mol−1/RT) m2s−1. Results for diffusion in natural and synthetic rutile were quite similar, despite significant differences in trace element
compositions. Mean closure temperatures calculated from the diffusion parameters are around 600 °C for rutile grains of ∼100 μm
size. This is about 100 °C higher than rutile closure temperature determinations from past field-based studies, suggesting
that rutile is more resistant to Pb loss through volume diffusion than previously thought.
Received: 28 June 1999 / Accepted: 29 December 1999 相似文献
14.
High-pressure and high-temperature Raman spectra of CaGeO3 tetragonal garnet have been collected to 11.5 GPa and 1225 K, respectively, in order to investigate possible intrinsic anharmonic
behaviour in this phase. The Raman peak positions were observed to vary linearly with pressure and temperature within the
ranges studied, with the higher-energy peaks showing larger P- and T-induced shifts than the low energy modes. The observed T-induced shifts are similar to those reported for grossular and andradite, while the observed P-induced shifts are generally larger than those of aluminosilicate and MgSiO3 majorite garnets (Gillet et al. 1992; Rauch et al. 1996) due to the larger bulk modulus of CaGeO3 garnet. The observed mode shifts of CaGeO3 garnet were used to determine the isothermal and isobaric mode Grüneisen parameters for this phase. These parameters are
similar in value to those reported previously for grossular and andradite (Gillet et al. 1992). The calculated intrinsic anharmonic
parameters, a
i
, for CaGeO3 garnet were determined to be nonzero, indicating significant anharmonic behaviour for this phase. These values, which range
from −3.8 × 10−5 K−1 to −1.3 × 10−5 K−1, are also similar to those reported for andradite and grossular, but smaller than those determined for pyrope (Gillet et al.
1992). Hence, we expect MgSiO3 majorite to show greater anharmonicity than the germanate analogue studied by us. The anharmonic parameters determined for
CaGeO3 tetragonal garnet may now be introduced into quasiharmonic vibrational heat capacity models to account for the observed anharmonic
behaviour.
Received: 21 April 1999 / Revised, accepted: 11 September 1999 相似文献
15.
The uranium deposits in the basin of Franceville (Gabon) host the only natural fission reactors known in the world. Unique
geological conditions favoured a natural fission reaction 2 Ga ago. This was detected by anomalous isotopic compositions of
uranium and rare earth elements (REE), which are produced by the fission reaction. In total, 16 reactor zones were found.
Most of them are mined out. The reactor zone of Bangombé, is only 10–11 m below the surface. This site has been influenced
by surface weathering processes. Six drill cores have been sampled at the site of the reactor zone of Bangombé during the
course of the study and only one drill core (BAX 08) hit the core of the reactor. From these data and previous drilling campaigns,
the reactor size is estimated to be 10 cm thick, 2–3 m wide and 4–6 m long. The migration of fission products can be traced
by the anomalous isotope ratios of REE because of the fission process. The 149Sm/147Sm ratio close to the reactor zone is only 0.28 (normal: 0.92) because of the intense neutron capture of 149Sm and subsequent transmutation, whereas 147Sm is enriched by the fission reaction. Similar changes in isotopic patterns are detectable on other REE. The isotope ratios
of Sm and Nd of whole rock and fracture samples surrounding the reactor indicate that fission-genic REE migrated only a few
decimetres above and mainly below the reactor zone. Organic matter (bitumen) seems to act as a trap for fission-genic REE.
Additional REE-patterns show less intense weathering with increasing depth in the log profile and support a simple weathering
model.
Received: 26 November 1999 · Accepted: 2 May 2000 相似文献
16.
Taras Nahnybida Sarah A. Gleeson Brian G. Rusk Len I. Wassenaar 《Mineralium Deposita》2009,44(8):837-848
A bulk geochemical study has been carried out on fluid inclusion leachates extracted from quartz veins from porphyry Cu deposits
in Butte, Montana, USA and Bingham Canyon, Utah, USA. The leachates mostly represent low-salinity magmatic–hydrothermal fluid
inclusions. Their halogen ratios (Br/Cl) of fluid inclusion leachates were determined by ion chromatography, and δ37Cl values of the leachates were measured by continuous-flow isotope ratio mass spectrometry. Br/Cl ratios from early pre-Main
stage and later Main stage veins at Butte range from 0.60 to 1.88 × 10−3 M. Ratios are similar in pre-Main stage veins with sericite bearing selvages and Main stage samples ranging from 0.81 to
1.08 × 10−3 and from 0.92 to 1.88 × 10−3 M, respectively, clustering below seawater (1.54 × 10−3 M) and overlapping mantle values (~1–2 × 10−3 M). Two samples associated with early pre-Main stage potassic alteration yield distinctly lower Br/Cl ratios of 0.60 and
0.64 × 10−3 M. Butte δ37Cl values range from −0.8‰ to −2.3‰ with no significant difference between pre-Main stage and Main stage samples. Br/Cl ratios
for quartz veins from Bingham Canyon range from 0.18 to 3.68 × 10−3 M. Br/Cl ratios from Bingham range above and below previously reported for porphyry copper deposits. In contrast to Butte,
δ37Cl values for Bingham are lower, ranging from −0.9‰ to −4.1‰. In the absence of any processes which can significantly fractionate
chlorine isotopes at high temperatures, we suggest that the porphyry system at Bingham, and to a lesser extent at Butte, have
inherited negative chlorine isotopic signatures from the subducting slab generated at low temperatures. 相似文献
17.
Alison Pawley 《Contributions to Mineralogy and Petrology》2000,138(3):284-291
The low-pressure stability of clinohumite has been investigated in phase-equilibrium experiments on the reaction forsterite + brucite = clinohumite.
The reaction was bracketed between 2.45 and 2.84 GPa at 650 °C, extending to between 1.37 and 1.57 GPa at 850 °C. At temperatures
above the reaction brucite = periclase + vapour, the reaction clinohumite = forsterite + vapour was bracketed between 1.27
and 1.52 GPa at 900 °C, rising to between 1.90 and 2.00 GPa at 1000 °C. The position of the reaction forsterite + brucite = clinohumite
is ∼0.5 GPa below the position determined in previous work, the difference arising either from pressure uncertainties in both
studies, from enhanced reaction to clinohumite in this study due to the presence of excess brucite in the starting material,
or from different concentrations of defects in the two samples. The brackets on the reaction were combined with other measured
and estimated thermodynamic data for clinohumite to determine its enthalpy of formation and entropy, in a revised version
of the thermodynamic dataset of Holland and Powell (1998). The values obtained were ΔH
f
=−9607.29±3.05 kJ mol−1, S=445 J mol−1 K−1. These data were used to calculate positions of other reactions involving clinohumite. The calculations suggest a larger
stability field for clinohumite than implied by the results of previous experimental studies, indicating a need for more high-pressure
phase-equilibrium studies to provide better thermodynamic data.
Received: 30 April 1999 / Accepted: 8 November 1999 相似文献
18.
The hydroelectric reservoir of Petit Saut, French Guiana, was created in 1994–1995 by flooding 350 km2 of tropical forest. When sampled in 1999, the lake exhibited a permanent stratification separating the 3–5 m thick, oxygenated
epilimnion from the anoxic hypolimnion. The rate of anaerobic organic carbon mineralization below the oxycline was on the
order of 1 μmol C m−2 s−1 and did not show a pronounced difference between wet and dry seasons. Methanogenesis accounted for 76–83% of anaerobic carbon
mineralization, with lesser contributions of sulfate reduction and dissimilatory iron reduction. Upward mixing of reduced
inorganic solutes explained 90% of the water column O
2 demand during the dry season, while most O
2 consumption during the wet season was coupled to aerobic respiration of organic matter synthesized in the surface waters.
Inorganic mercury species represented 10–40% of total dissolved mercury in the epilimnion, but were of relatively minor importance
(≤10%) in the anoxic portion of the water column. Net production of soluble organic mercury compounds in the flooded soils
and anoxic water column did not vary significantly between wet and dry seasons. Methylmercury accounted for about 15% of total
dissolved mercury below the oxycline. Its estimated net production rate, 0.04 mg m−2 yr−1, is of the same order of magnitude as values reported for contaminated lakes and flooded terrestrial ecosystems. 相似文献
19.
S. Ono E. Ito T. Katsura A. Yoneda M. J. Walter S. Urakawa W. Utsumi K. Funakoshi 《Physics and Chemistry of Minerals》2000,27(9):618-622
In situ synchrotron X-ray experiments in the system SnO2 were made at pressures of 4–29 GPa and temperatures of 300–1400 K using sintered diamond anvils in a 6–8 type high-pressure
apparatus. Orthorhombic phase (α-PbO2 structure) underwent a transition to a cubic phase (Pa3ˉ structure) at 18 GPa. This transition was observed at significantly lower pressures in DAC experiments. We obtained the
isothermal bulk modulus of cubic phase K
0 = 252(28) GPa and its pressure derivative K
′=3.5(2.2). The thermal expansion coefficient of cubic phase at 25 GPa up to 1300 K was determined from interpolation of the
P-V-T data obtained, and is 1.7(±0.7) × 10−5 K−1 at 25 GPa.
Received: 7 December 1999 / Accepted: 27 April 2000 相似文献
20.
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