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1.
H. Gailhanou J. Rogez A.C.G. van Genderen C. Gilles N. Michau P. Blanc 《Geochimica et cosmochimica acta》2009,73(16):4738-4749
The heat capacities of the international reference clay mineral chlorite CCa-2 from Flagstaff Hill, California, were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 5 to 520 K (at 1 bar). The studied chlorite is a Fe-bearing trioctahedral chlorite with an intermediary composition between ideal clinochlore (Si3Al)(Mg5Al)O10(OH)8 and chamosite (Si3Al)(Fe5Al)O10(OH)8. Only few TiO2 impurities were detected in the natural chlorite sample CCa-2. Its structural formula, obtained after subtracting the remaining TiO2 impurities, is (Si2.633Al1.367)(Al1.116Mg2.952Mn0.012Ca0.011)O10(OH)8. From the heat capacity results, the entropy, standard entropy of formation and heat content of the chlorite were deduced. At 298.15 K, the heat capacity of the chlorite is 547.02 (±0.27) J mol−1 K−1 and the molar entropy is 469.4 (±2.9) J mol−1 K−1. The standard molar entropy of formation of the clay mineral from the elements is −2169.4 (±4.0) J mol−1 K−1. 相似文献
2.
Michele Zema Mark D. Welch Roberta Oberti 《Contributions to Mineralogy and Petrology》2012,163(5):923-937
The thermoelastic behaviour of a natural gedrite having the crystal-chemical formula ANa0.47
B(Na0.03 Mg1.05 Fe0.862+ Mn0.02 Ca0.04) C(Mg3.44 Fe0.362+ Al1.15 Ti0.054+) T(Si6.31 Al1.69)O22
W(OH)2 has been studied by single-crystal X-ray diffraction to 973 K (Stage 1). After data collection at 973 K, the crystal was heated to 1,173 K to induce dehydrogenation, which was registered by significant
changes in unit-cell parameters, M1–O3 and M3–O3 bond lengths and refined site-scattering values of M1 and M4 sites. These changes and the crystal-chemical formula calculated from structure refinement show that all Fe2+ originally at M4 migrates into the ribbon of octahedrally coordinated sites, where most of it oxidises to Fe3+, and there is a corresponding exchange of Mg from the ribbon into M4. The resulting composition is that of an oxo-gedrite with an inferred crystal-chemical formula ANa0.47
B(Na0.03 Mg1.93 Ca0.04) C(Mg2.56 Mn0.022+ Fe0.102+ Fe1.223+ Al1.15 Ti0.054+) T(Si6.31 Al1.69) O22
W[O1.122− (OH)0.88]. This marked redistribution of Mg and Fe is interpreted as being driven by rapid dehydrogenation at the H3A and H3B sites, such that all available Fe in the structure orders at M1 and M3 sites and is oxidised to Fe3+. Thermoelastic data are reported for gedrite and oxo-gedrite; the latter was measured during cooling from 1,173 to 298 K
(Stage 2) and checked after further heating to 1,273 K (Stage 3). The thermoelastic properties of gedrite and oxo-gedrite are compared with each other and those of anthophyllite. 相似文献
3.
A mica whose structural formula: (K1.76Na0.31)(Fe2.22Mn1.29Mg0.99Ti0.28Al0.240.98) ·(Si7.33Al0.67)O20.26(F2.16OH1.58) closely approximates that of tetrasilicic potassium mica K2(M
5
2+
)Si8O20(OH,F)4 where M2+ represents Mg2+, Fe2+, Mn2+, ..., has been discovered in the matrix of a peralkaline rhyolite (comendite) of the Mont-Dore massif (France). These micas had been obtained previously by synthesis only. In the groundmass of the rock, the micaceous phase is accompanied by a manganoan arfvedsonite, pyrophanite, magnetite, apatite, sphene, zircon and fluorite. The crystallographic properties of the mica are typically that of a tetrasilicic mica, with d
060 = 1.533Å and space group C2/m. There is a regular decrease of d
060 (parameter b) with the ionic radius of the octahedral cation in synthetic micas containing Fe2+, Co2+, Mg2+, Ni2+. The purely Mn2+ end-member could not be synthesised; its instability is discussed on the basis of structural considerations. The conditions of crystallization of the micaceous phase are estimated to be 760 ° C, 800 bars with a f
o
2=10–14.7 bar. This mica has crystallized from a residual liquid, with high activity of silica and low activity of alumina, whose origin is discussed. The name MONT-DORITE is proposed for this natural tetrasilicic mica having Fe/Fe+Mg >1/2 and Fe/Fe+Mn >1/2. This name is from the stratovolcano Mont-Dore. 相似文献
4.
《Geochimica et cosmochimica acta》1986,50(7):1475-1484
The heat capacity of a natural monticellite (Ca1.00Mg.09Fe.91Mn.01Si0.99O3.99) measured between 9.6 and 343 K using intermittent-heating, adiabatic calorimetry yields Cp0(298) and S2980 of 123.64 ± 0.18 and 109.44 ± 0.16 J · mol−1K−1 respectively. Extrapolation of this entropy value to end-member monticellite results in an S0298 = 108.1 ± 0.2 J · mol−1K−1. High-temperature heat-capacity data were measured between 340–1000 K with a differential scanning calorimeter. The high-temperature data were combined with the 290–350 K adiabatic values, extrapolated to 1700 K, and integrated to yield the following entropy equation for end-member monticellite (298–1700 K): ST0(J · mol−1K−1) = S2980 + 164.79 In T + 15.337 · 10−3T + 22.791 · 105T−2 − 968.94. Phase equilibria in the CaO-MgO-SiO2 system were calculated from 973 to 1673 K and 0 to 12 kbar with these new data combined with existing data for akermanite (Ak), diopside (Di), forsterite (Fo), merwinite (Me) and wollastonite (Wo). The location of the calculated reactions involving the phases Mo and Fo is affected by their mutual solid solution. A best fit of the thermodynamically generated curves to all experiments is made when the S0298 of Me is 250.2 J · mol−1 K−1 less than the measured value of 253.2 J · mol−1 K−1.A best fit to the reversals for the solid-solid and decarbonation reactions in the CaO-MgO-SiO2-CO2 system was obtained with the ΔG0298 (kJ · mole−1) for the phases Ak(−3667), Di(−3025), Fo(−2051), Me(−4317) and Mo(−2133). The two invariant points − Wo and −Fo for the solid-solid reactions are located at 1008 ± 5 K and 6.3 ± 0.1 kbar, and 1361 ± 10 K and 10.2 ± 0.2 kbar respectively. The location of the thermodynamically generated curves is in excellent agreement with most experimental data on decarbonation equilibria involving these phases. 相似文献
5.
K.-D. Grevel A. Navrotsky W. A. Kahl D. W. Fasshauer J. Majzlan 《Physics and Chemistry of Minerals》2001,28(7):475-487
Calorimetric and P–V–T data for the high-pressure phase Mg5Al5Si6O21(OH)7 (Mg-sursassite) have been obtained. The enthalpy of drop solution of three different samples was measured by high-temperature
oxide melt calorimetry in two laboratories (UC Davis, California, and Ruhr University Bochum, Germany) using lead borate (2PbO·B2O3) at T=700 ∘C as solvent. The resulting values were used to calculate the enthalpy of formation from different thermodynamic datasets;
they range from −221.1 to −259.4 kJ mol−1 (formation from the oxides) respectively −13892.2 to −13927.9 kJ mol−1 (formation from the elements). The heat capacity of Mg5Al5Si6O21(OH)7 has been measured from T=50 ∘C to T=500 ∘C by differential scanning calorimetry in step-scanning mode. A Berman and Brown (1985)-type four-term equation represents
the heat capacity over the entire temperature range to within the experimental uncertainty: C
P
(Mg-sursassite) =(1571.104 −10560.89×T
−0.5−26217890.0 ×T
−2+1798861000.0×T
−3) J K−1 mol−1 (T in K). The P
V
T behaviour of Mg-sursassite has been determined under high pressures and high temperatures up to 8 GPa and 800 ∘C using a MAX 80 cubic anvil high-pressure apparatus. The samples were mixed with Vaseline to ensure hydrostatic pressure-transmitting
conditions, NaCl served as an internal standard for pressure calibration. By fitting a Birch-Murnaghan EOS to the data, the
bulk modulus was determined as 116.0±1.3 GPa, (K
′=4), V
T,0
=446.49 3 exp[∫(0.33±0.05) × 10−4 + (0.65±0.85)×10−8
T dT], (K
T/T)
P
= −0.011± 0.004 GPa K−1. The thermodynamic data obtained for Mg-sursassite are consistent with phase equilibrium data reported recently (Fockenberg
1998); the best agreement was obtained with Δf
H
0
298 (Mg-sursassite) = −13901.33 kJ mol−1, and S
0
298 (Mg-sursassite) = 614.61 J K−1 mol−1.
Received: 21 September 2000 / Accepted: 26 February 2001 相似文献
6.
H. Gailhanou J.C. van Miltenburg J. Olives E.C. Gaucher 《Geochimica et cosmochimica acta》2007,71(22):5463-5473
The heat capacities of the anhydrous international reference clay minerals, smectite MX-80, illite IMt-2 and mixed-layer illite-smectite ISCz-1, were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 6 to 520 K (at 1 bar). The samples were chemically purified and Na-saturated. Dehydrated clay fractions <2 μm were studied. The structural formulae of the corresponding clay minerals, obtained after subtracting the remaining impurities, are K0.026Na0.435Ca0.010(Si3.612Al0.388) (Al1.593Mg0.228Ti0.011)O10(OH)2 for smectite MX-80, K0.762Na0.044(Si3.387Al0.613) (Al1.427Mg0.241O10(OH)2 for illite IMt-2 and K0.530Na0.135(Si3.565Al0.435)(Al1.709Mg0.218Ti0.005)O10(OH)2for mixed-layer ISCz-1. From the heat capacity values, we determined the molar entropies, standard entropies of formation and heat contents of these minerals. The following values were obtained at 298.15 K and 1 bar:
(J mol−1 K−1) S0 (J mol−1 K−1) Smectite MX-80 326.13 ± 0.10 280.56 ± 0.16 Illite IMt-2 328.21 ± 0.10 295.05 ± 0.17 Mixed-layer ISCz-1 320.79 ± 0.10 281.62 ± 0.15 - Full-size table
7.
L. P. Ogorodova I. A. Kiseleva M. F. Vigasina L. V. Mel’chakova I. A. Bryzgalov D. A. Ksenofontov 《Geochemistry International》2017,55(9):814-821
The paper reports original thermochemical data on six natural amphibole samples of different composition. The data were obtained by high-temperature melt solution calorimetry in a Tian–Calvet microcalorometer and include the enthalpies of formation from elements for actinolite Ca1.95(Mg4.4Fe 0.5 2+ Al01)[Si8.0O22](OH)2(–12024 ± 13 kJ/mol) and Ca2.0(Mg2.9Fe 1.9 2+ Fe 0.2 3+ )[Si7.8Al0.2O22](OH)2, (–11462 ± 18 kJ/mol), and Na0.1Ca2.0(Mg3.2Fe 1.6 2+ Fe 0.2 3+ )[Si7.7Al0.3O22](OH)2 (–11588 ± 14 kJ/mol); for pargasite Na0.5K0.5Ca2.0-(Mg3.4Fe 1.8 2+ Al0.8)[Si6.2Al1.8O22](OH)2 (–12316 ± 10 kJ/mol) and Na0.8K0.2Ca2.0(Mg2.8Fe 1.3 3+ Al0.9) [Si6.1Al1.9O22](OH)2 (–12 223 ± 9 kJ/mol); and for hastingsite Na0.3K0.2Ca2.0(Mg0.4Fe 1.3 2+ Fe 0.9 3+ Al0.2) [Si6.4Al1.6O22](OH)2 (?10909 ± 11 kJ/mol). The standard entropy, enthalpy, and Gibbs free energy of formation are estimated for amphiboles of theoretical composition: end members and intermediate members of the isomorphic series tremolite–ferroactinolite, edenite–ferroedenite, pargasite–ferropargasite, and hastingsite. 相似文献
8.
9.
Geometrical changes induced by cation substitutions {Si4+/Al3+}[Mg2+/Al3+], {2Si4+/2Al3+} [2Mg2+/2Al3+], {Si4+/Fe3+} [Mg2+/Al3+] or [Mg2+/Fe3+], where {} and [] indicate tetrahedral and octahedral sheet in lizardite 1T, are studied by ab-initio quantum chemistry calculations. The majority of the models are based on the chemical compositions
reported for various lizardite polytypes with the amount of Al in the tetrahedral sheets reported to vary from 3.5% to 8%
in the 1T and 2H
1, up to ~30% in the 2H
2 polytype. Si4+ by Fe3+ substitution in the tetrahedral sheet with an Al3+ (Fe3+) in the role of a charge compensating cation in the octahedral sheet is also examined. The cation substitutions result in
the geometrical changes in the tetrahedral sheets, while the octahedral sheets remain almost untouched. Substituted tetrahedra
are tilted and their basal oxygens pushed down from the plane of basal oxygens. Ditrigonal deformation of tetrahedral sheets
depends on the substituting cation and the degree of substitution. 相似文献
10.
Low-temperature heat capacity measurements for MgCr2O4 have only been performed down to 52 K, and the commonly quoted third-law entropy at 298 K (106 J K−1 mol−1) was obtained by empirical extrapolation of these measurements to 0 K without considering the magnetic or electronic ordering
contributions to the entropy. Subsequent magnetic measurements at low temperature reveal that the Néel temperature, at which
magnetic ordering of the Cr3+ ions in MgCr2O4 occurs, is at ∼15 K. Hence a substantial contribution to the entropy of MgCr2O4 has been missed. We have determined the position of the near-univariant reaction MgCr2O4+SiO2=MgSiO3+Cr2O3. The reaction, which has a small positive slope in P-T space, has been bracketed at 100 K intervals between 1273 and 1773 K by reversal experiments. The reaction is extremely sluggish,
and lengthy run times with a flux (H2O, BaO-B2O3 or K2O-B2O3) are needed to produce tight reversal brackets. The results, combined with assessed thermodynamic data for Cr2O3, MgSiO3 and SiO2, give the entropy and enthalpy of formation of MgCr2O4 spinel. As expected, our experimental results are not in good agreement with the presently available thermodynamic data.
We obtain Δ
f
H
∘
298=−1759.2±1.5 kJ mol−1 and S
∘
298=122.1±1.0 J K−1 mol−1 for MgCr2O4. This entropy is some 16 J K−1 mol−1 more than the calorimetrically determined value, and implies a value for the magnetic entropy of MgCr2O4 consistent with an effective spin quantum number (S') for Cr3+ of 1/2 rather than the theoretical 3/2, indicating, as in other spinels, spin quenching.
Received: 9 May 1997 / Accepted: 28 July 1997 相似文献
11.
The molar volume of glaucophane [Na2Mg3Al2Si8O22(OH)2] has been determined in this study by correcting synthetic glaucophane-rich amphiboles made in the system Na2O–MgO–Al2O3–SiO2–H2O for very small deviations from ideal glaucophane composition using recent volume data on key amphibole components. The derived unit-cell volume for end-member glaucophane is 862.7±1.6 Å3, which gives a molar volume of 259.8±0.5 cm3/mol and a calculated density of 3.016±0.006 g/cm3. This value has been corroborated through an essentially independent method by correcting the volumes of natural sodic amphiboles reported in the literature for non-glaucophane components, particularly including calcium-rich components, to yield a value of 861.2±1.9 Å3. The unit-cell volume derived from the synthetic amphiboles, which is considered here to be more reliable, is somewhat smaller than that reported previously in the literature. A thermal expansion (αV) at 298 K of 1.88±0.06×10?5/K was derived from unit-cell volumes measured in the range of 25–500°C for a synthetic glaucophane sample, which is noticeably smaller than previously reported. 相似文献
12.
Charles A. Geiger Edgar Dachs Gilberto Artioli 《Geochimica et cosmochimica acta》2010,74(18):5202-5215
Armenite, ideal formula BaCa2Al6Si9O30·2H2O, and its dehydrated analog BaCa2Al6Si9O30 and epididymite, ideal formula Na2Be2Si6O15·H2O, and its dehydrated analog Na2Be2Si6O15 were studied by low-temperature relaxation calorimetry between 5 and 300 K to determine the heat capacity, Cp, behavior of their confined H2O. Differential thermal analysis and thermogravimetry measurements, FTIR spectroscopy, electron microprobe analysis and powder Rietveld refinements were undertaken to characterize the phases and the local environment around the H2O molecule.The determined structural formula for armenite is Ba0.88(0.01)Ca1.99(0.02)Na0.04(0.01)Al5.89(0.03)Si9.12(0.02)O30·2H2O and for epididymite Na1.88(0.03)K0.05(0.004)Na0.01(0.004)Be2.02(0.008)Si6.00(0.01)O15·H2O. The infrared (IR) spectra give information on the nature of the H2O molecules in the natural phases via their H2O stretching and bending vibrations, which in the case of epididymite only could be assigned. The powder X-ray diffraction data show that armenite and its dehydrated analog have similar structures, whereas in the case of epididymite there are structural differences between the natural and dehydrated phases. This is also reflected in the lattice IR mode behavior, as observed for the natural phases and the H2O-free phases. The standard entropy at 298 K for armenite is S° = 795.7 ± 6.2 J/mol K and its dehydrated analog is S° = 737.0 ± 6.2 J/mol K. For epididymite S° = 425.7 ± 4.1 J/mol K was obtained and its dehydrated analog has S° = 372.5 ± 5.0 J/mol K. The heat capacity and entropy of dehydration at 298 K are Δ = 3.4 J/mol K and ΔSrxn = 319.1 J/mol K and Δ = −14.3 J/mol K and ΔSrxn = 135.7 J/mol K for armenite and epididymite, respectively. The H2O molecules in both phases appear to be ordered. They are held in place via an ion-dipole interaction between the H2O molecule and a Ca cation in the case of armenite and a Na cation in epididymite and through hydrogen-bonding between the H2O molecule and oxygen atoms of the respective silicate frameworks. Of the three different H2O phases ice, liquid water and steam, the Cp behavior of confined H2O in both armenite and epididymite is most similar to that of ice, but there are differences between the two silicates and from the Cp behavior of ice. Hydrogen-bonding behavior and its relation to the entropy of confined H2O at 298 K is analyzed for various microporous silicates.The entropy of confined H2O at 298 K in various silicates increases approximately linearly with increasing average wavenumber of the OH-stretching vibrations. The interpretation is that decreased hydrogen-bonding strength between a H2O molecule and the silicate framework, as well as weak ion-dipole interactions, results in increased entropy of H2O. This results in increased amplitudes of external H2O vibrations, especially translations of the molecule, and they contribute strongly to the entropy of confined H2O at T < 298 K. 相似文献
13.
The heat capacity of synthetic ferrosilite, Fe2Si2O6, was measured between 2 and 820 K. The physical properties measurement system (PPMS, Quantum Design®) was used in the low-temperature region between 2 and 303 K. In the temperature region between 340 and 820 K measurements were performed using differential scanning calorimetry (DSC). The C p data show two transitions, a sharp λ-type at 38.7 K and a small shoulder near 9 K. The λ-type transition can be related to collinear antiferromagnetic ordering of the Fe2+ spin moments and the shoulder at 10 K to a change from a collinear to a canted-spin structure or to a Schottky anomaly related to an electronic transition. The C p data in the temperature region between 145 and 830 K are described by the polynomial $C_{p} {\left[ {\hbox{J\,mol}^{{ - 1}}\,{\hbox{K}}^{{ - 1}} } \right]} = 371.75 - 3219.2T^{{ - 1/2}} - 15.199 \times 10^{5} T^{{ - 2}} + 2.070 \times 10^{7} T^{{ - 3}} $ The heat content [H 298 – H 0] and the standard molar entropy [S 298 – S 0] are 28.6 ± 0.1 kJ mol?1 and 186.5 ± 0.5 J mol?1 K?1, respectively. The vibrational part of the heat capacitiy was calculated using an elastic Debye temperature of 541 K. The results of the calculations are in good agreement with the maximum theoretical magnetic entropy of 26.8 J mol?1 K?1 as calculated from the relationship 2*Rln5. 相似文献
14.
L. P. Ogorodova I. A. Kiseleva L. V. Melchakova M. F. Vigasina V. V. Krupskaya 《Geochemistry International》2013,51(6):484-494
The paper reports results of an experimental thermochemical study (in a heat-flux Tian-Calvet microcalorimeter) of montmorillonite from (I) the Taganskoe and (II) Askanskoe deposits and (III) from the caldera of Uzon volcano, Kamchatka. The enthalpy of formation Δ f H el 0 (298.15 K) of dehydrated hydroxyl-bearing montmorillonite was determined by melt solution calorimetry: ?5677.6 ± 7.6 kJ/mol for Na0.3Ca0.1(Mg0.4Al1.6)[Si3.9Al0.1O10](OH)2 (I), ?5614.3 ± 7.0 kJ/mol for Na0.4K0.1(Ca0.1Mg0.3Al1.5Fe 0.1 3+ )[Si3.9Al0.1O10](OH)2 (II), ?5719 ± 11 kJ/mol for K0.1Ca0.2Mg0.2(Mg0.6Al1.3Fe 0.1 3+ ) [Si3.7Al0.3O10](OH)2 (III), and ?6454 ± 11 kJ/mol for water-bearing montmorillonite (I) Na0.3Ca0.1(Mg0.4Al1.6)[Si3.9Al0.1O10](OH)2 · 2.6H2O. The paper reports estimated enthalpy of formation for the smectite end members of the theoretical composition of K-, Na-, Mg-, and Ca-montmorillonite and experimental data on the enthalpy of dehydration (14 ± 2 kJ per mole of H2O) and dehydroxylation (166 ± 10 kJ per mole of H2O) for Na-montmorillonite. 相似文献
15.
The heat capacities of synthetic pyrope (Mg3Al2Si2O12), grossular (Ca3Al2Si3O12) and a solid solution pyrope60grossular40 (Mg1.8Ca1.2Al2Si3O12) have been measured by adiabatic calorimetry in the temperature range 10–350 K. The samples were crystallized from glasses in a conventional piston-cylinder apparatus.The molar thermophysical properties at 298.15 K (J mol?1 K?1) are:
Cop | So298?So0 | Ho298?Ho0/T | |
Pyrope | 325.31 | 266.27 | 47852 |
Grossular | 333.17 | 260.12 | 47660 |
Py60Gr40 | 328.32 | 268.32 | 47990 |