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1.
A single crystal of scolecite, CaAl2Si3O10· 3H2O, was studied by X-ray diffraction methods at room temperature. The intensities were measured with MoKα radiation (λ=0.71069?Å) in a complete sphere of reflection up to sinθ/λ=0.9?Å?1. The structure was refined in the pseudo-orthorhombic setting of space group F1d1 instead of the conventional setting Cc for better comparison with natrolite (Fdd2). The cell parameters are: a=18.502(1)?Å, b=18.974(2)?Å, c=6.525(1)?Å, β=90.615(7)°, V=2290.6(3)?Å3, Z=8. A refinement of high-order diffraction data yielded residuals of R(F)=0.9%, R w (F)=0.9%, GoF=1.73 for 1831 high-angle reflections (0.7≤sinθ/λ≤0.9?Å?1) and R(F)=1.2%, R w (F)=1.4%, GoF=3.22 for all 3478 independent reflections. In comparison with natrolite, the replacement of 2 Na+ by 1 Ca2+ and 1 H2O leads to a reduction of symmetry from Fdd2 to F1d1. Each general atomic position in natrolite (except of Na) splits into two crystallographically independent positions in scolecite. The T?O distances and T?O?T angles of these two sites differ distinctly from each other due to the influence of the calcium ions on the framework. An unexpected result of our detailed analysis of the data is that the additional water molecule (O7) disturbs the symmetry of the framework to a greater extent than the replacement of Na+ by Ca2+. As a comparison of the displacement parameters indicates, the bonds within the tetrahedral framework and to the extraframework cations are stronger in scolecite than in natrolite. The isotropic U(equ) values of the framework atoms and extraframework cations are about 10% smaller in scolecite compared to natrolite. The same tendency is shown by the analysis of the internal vibrational amplitudes ΔU. The corresponding force constants are in the range of F=358 to 3367?Nm?1 for the T?O bonds in scolecite (in natrolite: F=354 to 824?Nm?1). The values of the force constants which determine the vibrations of the Ca ions and water molecules against the framework oxygen atoms lie in the range of F=33 to 1757?Nm?1 (in natrolite: F=57 to 293?Nm?1).  相似文献   

2.
Part I: Chemical and structural effects of cation-exchange Attempts were made to prepare, by appropriate exchange methods, homoionic samples of phillipsite, gismondite, harmotome, chabazite and gmelinite containing Ba, Ca, K, Na or Li-ions. Powdered natural samples were used as starting material. All samples were analysed chemically before and after the cation exchange. The results of the analyses demonstrated clearly that the „exchange capacity“ depends on the method used, the structure of the zeolite and the nature of the cation involved in the exchange. The analyses also disclosed the important fact that the ratio in Mole % of the sum of exchangeable cations: Al2O3 of the natural and of the exchanged samples is generally <1, and can be as low as 0.74. Examples are presented where cation exchange results in a substantial change in the framework structure. Part II: Dehydration behavior and structural changes at elevated temperatures Samples of the natural zeolites mentioned above, and of some of their cation exchange products were dehydrated in air of controlled humidity up to 600° C. The slopes of the weight loss curves of chabazite and gmelinite are continuous, whereas those of phillipsite, gismondite, and harmotome show a discontinuity between 90–190° C, indicating the existence of two discrete hydrated phases for each of these zeolites. High temperature x-ray studies of powdered samples confirmed this result. The high temperature hydrates of phillipsite, gismondite, and harmotome persist reversibly up to approximately 230° C. At higher temperatures, new probably anhydrous phases form. Gmelinite, at 240° C, transforms irreversibly to anhydrous gmelinite which is stable up to >700° C. The transition was studied by single crystal techniques. The chabazite structure remains intact up to >700° C. The absolute water content and the dehydration behavoir of the zeolites investigated are primarily dependent on the nature of the exchange cation. The structural changes at elevated temperatures are determined by the silica alumina framework. Part III: Hydrothermal stability* and interconversions The stability of phillipsite, gismondite, harmotome, chabazite, gmelinite, their exchange products, and of the synthetic Linde zeolites Faujasite and Type A was studied in the temperature range between 150° and 350° C at a constant pressure of 1000 atm of H2O. Between 180° and 260° C all examined Sodium and Calcium zeolites were metastable with respect to analcite (wairakite**). Phillipsite and sodium-rich zeolites generally converted to analcite (wairakite) directly. Caex-chabazite and Caex-gmelinite formed phillipsite, whereas Ca-gismondite and Ca-Type A formed natrolite as intermediate phases. Li-gmelinite converted to bikitaite***. (This represents the first successful preparation of natrolite and bikitaite. Attempts starting from gels or glasses have been unsuccessful so far.) Ba-gmelinite converted to harmotome at 250° C. This transformation was studied microscopically and by single crystal x-ray techniques. The transformations that take place on hydrothermal treatment as well as on low temperature cation exchange of zeolites (see Part I) indicate that, unlike the conditions prevailing in clays, the type of cation and the ratio of cations in the exchange positions have an important influence on the structure of the silicaalumina-oxygen framework. This explains two phenomena: The lack of solid solution between two potential end members of a solid solution series (for instance phillipsite-gismondite), and the large number of different zeolites in nature, where a great variety in the ratios of available alkali and alkaline earths ions must be expected. Any classification of zeolites becomes still more difficult in view of the fact that conversions among different groups (chabazite → phillipsite) and different structures (three-dimensional framework → fibre) take place relatively easily. Contribution No. 59–92, College of Mineral Industries, The Pennsylvania State University, University Park, Pennsylvania.  相似文献   

3.
The incorporation of the molecular species of C-H-N fluid (ammonium, methane, and propane) into the structural cavities of natrolite and scolecite was experimentally studied at t = 200°C, P = 20 MPa, and an experiment duration of 192 h. The zeolites were modified without ion exchange by the exposure of a preliminarily dehydrated mineral to the appropriate gas. The presence of ammonium and light hydrocarbons in the crystal matrix of zeolites was confirmed by IR and Raman spectroscopy and gas chromatography. The data of differential thermogravimetry revealed differences in the behavior of CH4- and NH3-zeolites during heating. The X-ray diffraction patterns and IR and Raman spectra of zeolites in the region of framework vibration indicate deformations in the matrix structure after the experiments. The interaction of dehydrated scolecite with “dry” propane resulted in amorphization under the experimental parameters. The maximum methane contents in the freshly synthesized zeolites determined by gas chromatography are 4.12 wt % for CH4-scolecite and 8.96 wt % for CH4-natrolite. The synthetic C3H8-natrolite contains 4.45 wt % C3H8. In the zeolites saturated with respect to dry ammonium, the highest NH3 contents were observed in the 0.4–0.25 mm scolecite fraction (12.86 wt %), 0.25–0.05 mm scolecite fraction (11.43 wt %), and NH3-natrolite (9.28 wt %).  相似文献   

4.
Experimente zur Zeolithbildung durch hydrothermale Umwandlung   总被引：1，自引：0，他引：1  
The formation of zeolites by hydrothermal alteration has been investigated by taking trass from the Laach volcanic area as a sample. Zeolites to be found are chabazite, phillipsite and analcime, all of which originated from the same phonolitic glass. This paper aims at explaining the formation of zeolites by means of experimental alteration of the pumice with various solutions. NaOH and KOH solutions were used in the experiments, these limited the formation conditions of chabazite, phillipsite, analcime in alkaline environments. Moreover, experiments were carried out with H2O dist and with solutions that formed during the alteration of pumice by reacting with H2O. These experiments were conducted to supply clues concerning the formation of zeolites in the Laach volcanic area. With NaOH solutions zeolites were formed from pumice within a temperature range of 70 to 250° C and a concentration range of 0.001 to 1.0 n; with KOH solutions they were formed in the same concentration range within a temperature range of 100 to 250° C. The formation of zeolites proved to depend much on temperature and concentration: At low temperatures high concentrations are necessary, higher temperatures need lower concentrations. With NaOH solutions the zeolites are formed in the succession, chabazite, phillipsite, analcime at increasing temperatures and increasing concentrations. With KOH solutions the same succession is to be found with rising temperature. With rising concentration, however, this succession is changed at higher temperatures: Phillipsite appears in place of analcime at high temperatures and concentrations. By the alteration of pumice with H2O, zeolites are formed from 200° C onward. With solutions that had been formed during the alteration of pumice by reacting with H2O, the minimum temperature for the formation of zeolites was 180° C. Concerning the genesis of zeolites in the Laach volcanic area, the experiments showed that the temperature for the formation of analcime was about 250° C; for the formation of chabazite and phillipsite it was between 150 and 190° C. The pH of the reacting solutions may have been between 7 and 8. Thus the experiments proved that from the same material different zeolites, chabazite, phillipsite, analcime may be formed by temperature change of the reacting solutions (H2O to slightly alkaline solutions).  相似文献   

5.
We present an ultrasonic and neutron powder diffraction study of crystalline MgSO4·7H2O (synthetic epsomite) and MgSO4·7D2O under pressure up to ~3 GPa near room temperature and up to ~2 GPa at lower temperatures. Both methods provide complementary data on the phase transitions and elasticity of magnesium sulphate heptahydrate, where protonated and deuterated counterparts exhibit very similar behaviour and properties. Under compression in the declared pressure intervals, we observed three different sequences of phase transitions: between 280 and 295 K, phase transitions occurred at approximately 1.4, 1.6, and 2.5 GPa; between 240 and 280 K, only a single phase transition occurred; below 240 K, there were no phase transformations. Overall, we have identified four new phase fields at high pressure, in addition to that of the room-pressure orthorhombic structure. Of these, we present neutron powder diffraction data obtained in situ in the three phase fields observed near room temperature. We present evidence that these high-pressure phase fields correspond to regions where MgSO4·7H2O decomposes to a lower hydrate by exsolving water. Upon cooling to liquid nitrogen temperatures, the ratio of shear modulus G to bulk modulus B increases and we observe elastic softening of both moduli with pressure, which may be a precursor to pressure-induced amorphization. These observations may have important consequences for modelling the interiors of icy planetary bodies in which hydrated sulphates are important rock-forming minerals, such as the large icy moons of Jupiter, influencing their internal structure, dynamics, and potential for supporting life.  相似文献   

6.
Natural γ-CrOOH was first found and studied in rischorrite of the Khibina Massif, in which this mineral is associated with gonardite, natrolite, phillipsite, and saponite and usually forms microcrystallites in a matrix of amorphous CrOOH hydrogel or, more rarely, occurs as fine-crystalline, thin acicular, and lumpy aggregates of a green and emerald-green color. X-ray powder diffraction data indicate that crystalline blocks consist of a mineral with a rhombohedral unit cell, Cmcm, a = 3.86 Å, b = 12.78 Å, and c = 3.04 Å. Chromium oxyhydroxide from the Khibina Massif is isostructural with γ-CrOOH from the Iksinskoe deposit, but significantly differs from it in bearing low Al concentrations. The empirical formula of the Khibina γ-CrOOH is (Cr0.94Mg0.03Al0.02Ti0.01Fe0.01)1.01O(OH) · nH2O. The Cr oxyhydroxide and associated zeolites crystallized from low-temperature hydrothermal solutions rich in Na. The most probable source of Cr for the γ-CrOOH in the Khibina Massif was titanomagnetite in xenoliths of ultrabasic rocks in the rischorrites affected by postmagmatic alterations.  相似文献   

7.
《Chemical Geology》2006,225(3-4):373-387
Rock-forming zeolites often exhibit complex solid solutions reflecting isomorphous substitutions between Si and Al in tetrahedral framework sites, between charge-balancing extraframework cations, and between water molecules and vacancies. Although the number of moles of charge on extraframework cations in a zeolite must equal the moles of Al in order to maintain charge balance, the relationships between Si–Al and extraframework substitutions vary considerably across this mineral group. Review of available compositional data suggests that there are three main modes of Si–Al substitution in zeolites: 1) coupled CaAl–NaSi substitution; 2) coupled substitution of a single extraframework cation plus Al for Si; and 3) completely uncoupled substitution among extraframework cations and Si and Al on tetrahedral sites. Among zeolites that exhibit the latter two modes of solid solution, Si–Al substitution can be described by an SiO2 (± H2O) compositional exchange vector from a hypothetical, pure-silica endmember composition. Recent calorimetric, structural, and theoretical investigations suggest that Si–Al substitution follows a non-ideal, athermal solution model characterized by no excess enthalpies of mixing and negative excess entropies of mixing. Because Si–Al exchange in these minerals can be explicitly or implicitly described by exchange of an SiO2 component, the Si/Al ratio in their framework can be predicted solely as a function of temperature, pressure, and the chemical potential of SiO2. Application of this model leads to calculated Si/Al ratios in stilbite (coexisting with albite), analcime, and chabazite consistent with observed mineral compositions and parageneses in very low-grade metamorphic environments. Coexistence of silica polymorphs with zeolites containing SiO2·nH2O exchange vectors potentially provides a means of performing thermobarometric calculations in very low-grade metamorphic and diagenetic environments.  相似文献   

8.
A single crystal of natrolite, Na2Al2Si3O10 ·2H2O (space group Fdd2), was studied by X-ray diffraction methods at room temperature. The intensities were measured in a complete sphere of reflection up to sinΘ/ λ=0.903 Å?1. A refinement of high-order diffraction data yielded residuals of R/(F)=0.9%, Rw(F)=0.8%, GoF=1.40 for 1856 high-angle reflections (0.7≤sinΘ/ λ≤0.903 Å?1) and R(F)=1.0%, Rw(F)=1.2%, GoF=3.07 for all 3471 independent reflections in the complete sphere of reflection. The X-X method was used to calculate deformation electron densities (DED) in natrolite. Within all tetrahedra, residual electron density-was found in the T-O bond directions indicating a considerable covalent contribution to the chemical bond. The range of the interatomic peak heights was from 0.19 to 0.34 e/Å3 in the SiO4 tetrahedra and from 0.11 to 0.23 e/Å3 in the AlO4 tetrahedron. The ionic contribution to the chemical bond manifests itself in the displacement of the peaks towards the oxygen atoms. Charge displacement due to interaction of nonframework cations with framework oxygen atoms as well as electron densities attributable to the lone pair orbitals in the water molecule have been observed.  相似文献   

9.
 For the fibrous zeolites natrolite, Na2[Al2Si3O10]·2H2O, mesolite, Na2Ca2[Al2Si3O10]3·8H2O, and scolecite, Ca[Al2Si3O10]·3H2O, with topologically identical aluminosilicate framework structures, accurate single-crystal X-ray diffraction data have been analyzed by least-squares refinements using generalized scattering factor (GSF) models. The final agreement indices were R(F ) = 0.0061, 0.0165, and 0.0073, respectively. Ensuing calculations of static deformation [Δρ(r)], and total, [ρ(r)], model electron density distributions served to study chemical bonding, in particular by topological electron density analyses yielding bond critical point (bcp) properties and in situ cation electronegativities. The results for 32 SiO, 24 AlO, 14 CaO, and 12 NaO unique bonds are compiled and analyzed in terms of both mean values and correlations between bond lengths, bonded oxygen radii, bcp densities, curvatures at the bcps, and electronegativities. Comparison with recent literature data obtained from both experimental electron density studies on minerals and model calculations for geometry-optimized molecules shows that the majority of the present findings conforms well with chemical expectation and with the trends observed from molecular modeling. For the SiO bond, the shared interaction is indicated to increase with decreasing bond length, whereas the AlO bond is of distinctly more polar nature, as is the NaO bond compared to CaO. Also, the observed ranges of the Si and Al in situ electronegativities and their mean electronegativities agree well with both Pauling's values and model calculation results, and statistically significant correlations are obtained which are consistent with trends described for oxide and nitride molecules. Received: 10 May 1999 / Revised, accepted: 14 September 1999  相似文献   

10.
In the formation of zeolites by hydrothermal alteration volcanic glasses are the starting material in most cases. The experiments aimed at demonstrating in what way the chemistry of the volcanic glass influences:
  1. the alteration rate of the volcanic glass to zeolites,
  2. the kind of zeolites being formed and their formation conditions.
Three volcanic glasses were used, a basaltic, a phonolitic, and a rhyolitic one. The experimental conditions were as similar as possible to the natural alteration conditions. Solutions being used: H2O dist (pH ～5.5), 0.01 n NaOH (pH ～10.5), and solutions of similar chemistry to the natural ones. The temperatures were 180 °, 200 °, 250 ° C. The experiments were carried out both in closed and in open systems. The experimental results show a difference in the alteration rate and in the zeolites being formed between the basaltic and the phonolitic glasses on the one hand and the rhyolitic one on the other. In case of the closed system the SiO2-poor volcanic glasses react more rapidly than the SiO2-rich one. The zeolites being formed are chabazite, phillipsite, analcime respectively mordenite, analcime. In case of the open system the influence of the chemistry of the volcanic glass on the alteration rate and the zeolite being formed is less significant. Which zeolite is formed at a given temperature depends on: the chemistry of the starting material, the chemistry of the reacting solution and wether there is a closed or an open system.  相似文献   

11.
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   

12.
Based on the experiments on dehydration-melting of solid samples of Al-rich gneiss (H029) and biotite granulitite (H013), the fugacities of O2, H2O and H2 have been calculated. It is recognized that the fugacities of O2, H2O and H2 vary regularly, but the fugacity of H2O shows a tendency of abrupt increasing at about 700°C and 800°C. According to the above fact, the melting mechanism of biotite can be well documented. Under relatively low temperatures (< 750°C), part of the water can be liberated and induce plagioclase to melt, which may mark the beginning of migmatization. At high temperatures (> 800°C), biotite can be dissociated and a larger amount of water can be released, which would result in a bigger degree of melting, hence leading to the formation of granitic magma.  相似文献   

13.
High temperature infrared spectra of hydrous microcrystalline quartz   总被引：1，自引：0，他引：1  
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.
Cymrite, BaAl2Si2O8 · nH2O, is a rare mineral formed during low-grade dynamothermal metamorphism (T = 250–300°C, P = 1–3 kbar). Cymrite has been described from many metasedimentary ores and hydrothermal rocks. In carbonatites, it has been found for the first time. Cymrite has been identified in the Kovdor and Seblyavr massifs, Kola Peninsula. In Kovdor, this mineral has been described from one of the hydrothermal veins cutting the pyroxenite-melilitite-ijolite complex at the Phlogopite deposit; cymrite is associated with thomsonite, calcite, and stivensite. In the Seblyavr pluton, cymrite occurs in thin veins of calcite carbonatite that cut pyroxenite contacting with ijolite. Cymrite from the Seblyavr pluton is associated with calcite, natrolite, pyrite, and chalcopyrite. The mineral is optically negative and uniaxial, with extinction parallel to elongation; ω ～ 1.607(1). According to X-ray diffraction data, cymrite from Seblyavr is monoclinic, space group P1m1; unit-cell dimensions are: a = 5.33, b = 36.96, c = 7.66 Å, β = 90°, V = 1510.55 Å3. According to the results of IR spectroscopy, in the series of samples from different massifs (in the running order Kovdor-Voishor-Seblyavr), the double-layer deformation is enhanced and accompanied by a decrease in the Si-O-Si angle and weakening of hydrogen bonds of interlayer water. The empirical formulas of cymrite calculated from electron microprobe analyses are Ba0.93–0.95Ca0.01–0.02K0.00–0.05Na0.02–0.04Al1.97–2.01Si1.99–2.03O8(H2O) and Ba1.00–1.02Ca0.00–0.01Sr0.00–0.01Fe0.00–0.01Al1.94–2.00Si1.98–2.03O8(H2O) at Seblyavr and Kovdor, respectively. Cymrite from the carbonatite massifs of the Kola Peninsula was formed under hydrothermal conditions at low temperature (200–300°C), high activity of Ba and Si, and high water pressure. At Kovdor, the mineral crystallized directly from the residual solution enriched in Ba. The sequence of mineral deposition is as follows: thomsonite-cymrite-calcite-stevensite. Cymrite from the Seblyavr pluton is a product of hydrothermal alteration of primary Na-K-Ba silicates of ijolite: nepheline, feldspar, and probably celsian. Natrolite replaces cymrite indicating high alkalinity of late hydrothermal fluids.  相似文献   

15.
Fluid inclusion analyses leave little doubt that solutions containing large concentrations of H2O, CO2, and electrolytes are involved in a wide range of geologic processes. Although the miscibility gap in the system H2O-CO2 occurs only at low temperatures, experimental data reported by Takenouchi and Kennedy (1965) and Gehrig (1980) indicate that the addition of 6 weight percent NaCl relative to H2O + Nacl extends the region of immiscibility in the system H2O-CO2-NaC] to ≥700°C at 500 bars and mole fractions of CO2 (XCO2) ? 0.1. In contrast, addition of 20 weight percent NaCl relative to H2O + NaCl at 700°C and 500 bars expands the miscibility gap to XCO2 ? 0.2. At 2000 bars, addition of 20 and 35 weight percent NaCl relative to H2O + NaCl causes the miscibility gap to extend to ~500° and ~700°C, respectively, at XCO2 ? 0.3. The existence of the immiscible region in this high-pressure/temperature environment has a profound effect on temperatures of equilibration for metamorphic mineral assemblages (Bowers and Helgeson, 1983). To determine the extent to which nonideality in the ternary system affects these equilibria, the modified Redlich-Kwong (MRK.) equation of state was fit to pressure-volume-temperature data taken from Gehrig (1980) along pseudobinaries for which XNaClXH2O is constant. Fugacity coefficients of the components were then generated from the fugacity coefficient analog of the MRK equation of state and these coefficients were used together with solubility data to determine the compositions of the coexisting immiscible phases. The tie lines connecting the coexisting phases shift in orientation from nearly parallel to the H2O-CO2 binary at low temperatures to almost perpendicular to this binary at high temperatures.  相似文献   

16.
《Applied Geochemistry》1997,12(5):693-703
Natural zeolitic material composed of natrolite and thomsonite intergrowths (NAT/THO) was treated in solutions of different initial pH values at 25°C under N2 atmosphere and in 1M KCl as ionic modulator, until pH equilibration. The solid experimental products were studied by means of powder X-ray diffraction (XRD), scanning electron microscopy-energy dispersive system (SEM-EDS), Fourier-transformed infra-red (FTIR) and thermogravimetric analysis/differential thermal analysis (TGA/DTA). The liquid experimental products were analysed using atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES). The NAT/THO material exhibited an amphoteric character with a tendency to neutralise the reacting solutions. The pH equilibration was faster for the acidic region than for the basic one. The H+ ions are chemisorbed on the bulk material, whereas the OH− ions promote a proton detachment from the exchangable cation-water complexes. No Brœnsted acidity, possibly responsible for the neutralisation in the basic region, was found by temperature-programmed desorption (TPD) measurements. Reaction mechanisms involving hydrolysis and degradation-dissolution are proposed. Zeolite crystals remaining at the end of the experiments showed no loss of crystallinity, phase transformation nor even framework dealumination. The insertion of K+ into the zeolites is suggested here as the reason as to why no collapse of their crystal structure occurred in the most acidic solutions causing the zeolites to be more resistant to chemical weathering.  相似文献   

17.
An increasing number of occurrences of margarite have been reported in the last years. However, previous experimental investigations in the system CaO-Al2O3-SiO2-H2O are limited to the synthesis of margarite and to the upper stability limit according to the reaction (1) 1 margarite?1 anorthite +1 corundum +1 H2O (Chatterjee, 1971; Velde, 1971). Since margarite often occurs together with quartz, the upper stability limit of margarite in the presence of quartz is of special interest. Therefore, the reactions (5) 1 margarite +1 quartz ?1anorthite +1 kyanite/andalusite +1 H2O and (6) 4 margarite+3 quartz ? 2 zoisite+5 kyanite+3 H2O were investigated experimentally using mixtures of natural margarite (from Chester, Mass., USA), quartz, kyanite, andalusite, zoisite, and synthetic anorthite. The indicated equilibrium temperatures at water pressures equal to total pressure are: 515± 25°C at 4 kb, 545 ±15°C at 5 kb, 590±10°C at 7 kb, and 650±10°C at 9 kb for reaction (5), and 651±11°C at 10 kb, 648 ± 8°C at 12.5kb, and 643±13°C at 15kb for reaction (6), respectively. Besides this, additional brackets for equilibrium temperatures were determined for the above cited reaction (1): 520±10°C at 3 kb, 580±10°C at 5 kb, and 640± 20°C at 7 kb. On the basis of these experimentally determined reactions (1), (5), and (6) and of the reactions (3) 2 zoisite +1 kyanite? 4 anorthite +1 corundum +1 H2O (7) 2 zoisite +1 kyanite +1 quartz ? 4 anorthite +1 H2O and (10) 1 pyrophyllite ? 1 andalusite/kyanite+3 quartz+1 H2O for which experimental or, in the case of reaction (3), calculated data were already available, a pressure-temperature diagram with 3 invariant points and 11 univariant reactions was developed using the method of Schreinemakers. This diagram, summarizing both experimental and phase relation studies, allows conclusions about the conditions under which margarite has been formed in nature. Margarite is limited to low grade metamorphism at water pressures up to approximately 3.5 kb; in the presence of quartz, margarite is even limited to low grade metamorphism at water pressures up to 5.5 kb. Only at water pressures higher than the values stated before margarite, and margarite+quartz, respectively, can occur in medium grade metamorphism (as defined by Winkler, 1970 and 1973). For the combined occurrence of margarite+quartz and staurolite as reported by Harder (1956) and Frey (personal communication, 1973) it may be estimated that water pressure has been greater than approximately 5.5 kb, wheras temperature has been in the range from 550 to 650°C. Furthermore, the present study shows that the assemblage zoisite+kyanite (+ H2O) is an indicator of both pressure [P H 2 O> approximately 9kb]and temperature [T> approximately 640 to 650° Cat water Pressures up to 15 kb].  相似文献   

18.
 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 (Na1.90K0.22Ca0.06)[Al2.24Si2.76O10]·nH2O, 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 dC/dT 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   

19.
Thermodynamic simulation of the system living matter (algae, zooplankton, or green plants) + mineral matter (25% carbonates + 75% clay minerals) + standard seawater at temperatures and pressure corresponding to diagenesis indicates that kerogen can be synthesized, together with hydrocarbons and carbon dioxide, in the reaction mix. The removal of CO2(g) and N2(g) from the system is favorable for the reaction Δ1C292H288O12 (s; H/C = 0.99, O/C = 0.041) → Δ2C128H68O7 (s; H/C = 0.53, O/C = 0.055) + xСH4(aq) + yCO2(aq) + zH2O, whose constant and stoichiometric coefficients were calculated based on the simulation results. It is demonstrated that a pressure increase is favorable, while a temperature increase is not, for the procedure of this reaction at P-T parameters of diagenesis: log K =–567 (20°C, 35 bar), 1170 (20°C, 200 bar),–1530 (20°C, 60 bar), and +1030 (20°C, 600 bar).  相似文献   

20.
The melting of phlogopite-quartz and sanidine-quartz under vapor-absent conditions and in the presence of H2O-CO2 vapor have been determined from 5–20 kbar. In the lower crust (P=6–10 kbar), phlogopite + quartz melts incongruently to enstatite + liquid at temperatures as low as 710° C in the presence of H2O. When the activity of water is sufficiently reduced by addition of CO2, phlogopite + quartz undergoes a dehydration reaction to enstatite + sanidine + vapor, for example at 790±10° C, 5 kbar, with \(X_{H_2 O}^V\) =0.35. In the absence of vapor, phlogopite + quartz is stable up to a maximum temperature of 900° C in the crust; at higher temperatures this assemblage melts incongruently to enstatite + sanidine + liquid. The melting of sanidine-quartz in the presence of H2O-CO2 vapor shows marked topological differences from melting in the system albite-H2O-CO2, and as a result, apparent activity coefficients for water calculated from sanidine-quartz H2O-CO2 are less than those calculated from albite-H2O-CO2 by up to a factor of five. These data shed light on anatexis in the lower crust, but uncertainties related to ordering of Al and Si in natural and synthetic micas forestall a more rigorous analysis. Nevertheless, maximum temperatures for some granulite terranes can be established.  相似文献   

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