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1.
The enthalpy of Mg-Fe ordering in En50Fs50 orthopyroxene was measured using the transposed temperature drop calorimetric method. Heat effects associated with two consecutive drops were recorded. In the first drop, synthetic orthopyroxene samples equilibrated at 823?K, 0.1?MPa and a f?O2 of the WI buffer were dropped from 823?K into the calorimeter, which was held at 1173?K. The measured heat effect corresponds to the enthalpy change due to the heat capacity of the sample from 823 to 1173?K and to the enthalpy associated with the (dis)ordering of Mg and Fe2+. In the second drop, the samples, with an Fe-Mg order corresponding to 1173?K, were dropped again from 823 to 1173?K. From the difference of the heat effects measured in the two experiments, the enthalpy of disordering associated with the temperature change from 823 to 1173?K was calculated to be ?1.73±0.04 J mol?1. The observed enthalpy corresponds to a change in the mole fraction of iron on the M2 site, ΔX Fe,M2=?0.096 ± 0.001, which leads to of ΔH 0 exch of 18.0 ± 0.4 kJ mol?1 for the exchange reaction: The degree of Fe-Mg order was characterized by 57Fe Mössbauer resonance spectroscopy. In order to minimize the error due to the thickness of the absorber, the iron concentration of the absorber was reduced step by step from 5 to 1 mg?Fe?cm?2. The iron distribution extrapolated to zero thickness was used for the calculations of the enthalpy of exchange reaction.  相似文献   

2.
Calcium-free carbonate cancrinite with formula unit Na8.28[Al5.93Si6.07O24](CO3)0.93(OH)0.49·3.64H2O (CAN) has been synthesized under hydrothermal conditions. The product has been characterized by the methods of scanning electronic microscopy and energy dispersive X-ray analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis with FTIR of evolved gases (TGA–FTIR), and X-ray powder diffraction. The heat capacity of CAN has been measured from 6 to 259 K via low-temperature adiabatic calorimetry. A linear combination of Einstein functions has been used to approximate the obtained data on the heat capacity. The thermal contributions to the entropy and enthalpy of CAN in the temperature range 0–300 K have been calculated from these data. The heat capacity and third-law absolute entropy of CAN at 298.15 K are 1,047 ± 30 and 1,057 ± 35 J mol?1 K?1, respectively. High-temperature oxide-melt solution calorimetry has been used to determine the enthalpy of formation from elements of CAN at 298.15 K; the value equals ?14,684 ± 50 kJ mol?1. The Gibbs energy of formation from elements at 298.15 K has been calculated and totaled ?13,690 ± 51 kJ mol?1.  相似文献   

3.
The thermodynamic properties of the copper carbonates malachite and azurite have been studied by adiabatic calorimetry, by heat-flux Calvet Calorimetry, by differential thermal analysis (DTA) and by thermogravimetrie (TGA) analysis. The heat capacities, C p 0 of natural malachite and azurite have been measured between 3.8 and 300 K by low-temperature adiabatic calorimetry. The heat capacity of azurite exhibits anomalous behavior at low temperatures. At 298.15 K the molar heat capacities C p 0 and the third law entropies S 298.15 0 are 228.5±1.4 and 254.4±3.8 J mol?1 K?1 for azurite and 154.3±0.93 and 166.3±2.5 J mol?1 K?1 for malachite. Enthalpies of solution at 973 K in lead borate 2PbO·B2O3 have been measured for heat treated malachite and azurite. The enthalpies of decomposition are 105.1±5.8 for azurite and 66.1±5.0 kJ mol? for malachite. The enthalpies of formation from oxides of azurite and malachite determined by oxide melt solution calorimetry, are ?84.7±7.4 and ?52.5±5.9 kJ mol?1, respectively. On the basis of the thermodynamic data obtained, phase relations of azurite and malachite in the system Cu2+-H2O-CO2 at 25 and 75 °C have been studied.  相似文献   

4.
We have performed experiments to determine the effects of pressure, temperature and oxygen fugacity on the CO2 contents in nominally anhydrous andesitic melts at graphite saturation. The andesite composition was specifically chosen to match a low-degree partial melt composition that is generated from MORB-like eclogite in the convective, oceanic upper mantle. Experiments were performed at 1–3 GPa, 1375–1550?°C, and fO2 of FMQ ?3.2 to FMQ ?2.3 and the resulting experimental glasses were analyzed for CO2 and H2O contents using FTIR and SIMS. Experimental results were used to develop a thermodynamic model to predict CO2 content of nominally anhydrous andesitic melts at graphite saturation. Fitting of experimental data returned thermodynamic parameters for dissolution of CO2 as molecular CO2: ln(K 0) = ?21.79?±?0.04, ΔV 0?=?32.91?±?0.65 cm3mol?1, ΔH 0?=?107?±?21 kJ mol?1, and dissolution of CO2 as CO3 2?: ln(K 0 ) = ?21.38?±?0.08, ΔV 0?=?30.66?±?1.33 cm3 mol?1, ΔH 0?=?42?±?37 kJ mol?1, where K 0 is the equilibrium constant at some reference pressure and temperature, ΔV 0 is the volume change of reaction, and ΔH 0 is the enthalpy change of reaction. The thermodynamic model was used along with trace element partition coefficients to calculate the CO2 contents and CO2/Nb ratios resulting from the mixing of a depleted MORB and the partial melt of a graphite-saturated eclogite. Comparison with natural MORB and OIB data suggests that the CO2 contents and CO2/Nb ratios of CO2-enriched oceanic basalts cannot be produced by mixing with partial melts of graphite-saturated eclogite. Instead, they must be produced by melting of a source containing carbonate. This result places a lower bound on the oxygen fugacity for the source region of these CO2-enriched basalts, and suggests that fO2 measurements made on cratonic xenoliths may not be applicable to the convecting upper mantle. CO2-depleted basalts, on the other hand, are consistent with mixing between depleted MORB and partial melts of a graphite-saturated eclogite. Furthermore, calculations suggest that eclogite can remain saturated in graphite in the convecting upper mantle, acting as a reservoir for C.  相似文献   

5.
Enthalpies of solution in 2PbO · B2O3 at 974 K have been measured for glasses along the joins Ca2Si2O6 (Wo)-Mg2Si2O6 (En) and Mg2Si2O6-MgAl2SiO6 (MgTs). Heats of mixing are symmetric and negative for Wo-En with WH = ?31.0 ± 3.6 kJ mol?. Negative heats of mixing were also found for the En-MgTs glasses (WH = ?33.4 ± 3.7 kJ mol?).Enthalpies of vitrification of pyroxenes and pyroxenoids generally increase with decreasing alumina content and with decreasing basicity of the divalent cation.Heats of mixing along several glassy joins show systematic trends. When only non-tetrahedral cations mix (outside the aluminosilicate framework), small exothermic heats of mixing are seen. When both nontetrahedral and framework cations mix (on separate sublattices, presumably), the enthalpies of mixing are substantially more negative. Maximum enthalpy stabilization near compositions with Al/Si ≈ 1 is suggested.  相似文献   

6.
High-temperature oxide-melt calorimetry and Rietveld refinement of powder X-ray diffraction patterns were used to investigate the energetics and structure of the hematite–corundum solid solution and ternary phase FeAlO3 (with FeGaO3 structure). The mixing enthalpies in the solid solution can be described by a polynomial ΔHmix=WX hem(1?X hem) with W=116 ± 10 kJ mol?1. The excess mixing enthalpies are too positive to reproduce the experimental phase diagram, and excess entropies in the solid solution should be considered. The hematite–corundum solvus can be approximately reproduced by a symmetric, regular-like solution model with ΔG excess=(W H ?TW S )X hem X cor, where W H= 116 ± 10 kJ mol?1 and W S =32 ± 4 J mol?1 K?1. In this model, short-range order (SRO) of Fe/Al is neglected because SRO probably becomes important only at intermediate compositions close to Fe:Al=1:1 but these compositions cannot be synthesized. The volume of mixing is positive for Al-hematite but almost ideal for Fe-corundum. Moreover, the degree of deviation from Vegard's law for Al-hematite depends on the history of the samples. Introduction of Al into the hematite structure causes varying distortion of the hexagonal network of oxygen ions while the position of the metal ions remains intact. Distortion of the hexagonal network of oxygen ions attains a minimum at the composition (Fe0.95Al0.05)2O3. The enthalpy of formation of FeAlO3 from oxides at 298 K is 27.9 ± 1.8 kJ mol?1. Its estimated standard entropy (including configurational entropy due to disorder of Fe/Al) is 98.9 J mol?1 K?1, giving the standard free energy of formation at 298 K from oxides and elements as +19.1 ± 1.8 and ?1144.2 ± 2.0 kJ mol?1, respectively. The heat capacity of FeAlO3 is approximated as C p (T in K)= 175.8 ? 0.002472T ? (1.958 × 106)/T 2? 917.3/T 0.5+(7.546 × 10?6) T 2 between 298 and 1550 K, based on differential scanning calorimetric measurements. No ferrous iron was detected in FeAlO3 by Mössbauer spectroscopy. The ternary phase is entropy stabilized and is predicted to be stable above about 1730 ± 70 K, in good agreement with the experiment. Static lattice calculations show that the LiNbO3-, FeGaO3-, FeTiO3-, and disordered corundum-like FeAlO3 structures are less stable (in the order in which they are listed) than a mechanical mixture of corundum and hematite. At high temperatures, the FeGaO3-like structure is favored by its entropy, and its stability field appears on the phase diagram.  相似文献   

7.
The thermochemical study of a natural basic copper phosphate, pseudomalachite Cu5(PO4)2(OH)4 (Virneberg deposit, Germany), was carried out using high-temperature melt solution calorimetry method with a Tian–Calvet microcalorimeter. The enthalpy of formation of the mineral from elements was obtained to be Δ f Hel(298.15 K) =–3214 ± 13 kJ/mol. The value of the Gibbs energy of pseudomalachite formation calculated using literature data on its standard entropy is Δ f Hel°(298.15 K) =–2812 ± 13 kJ/mol.  相似文献   

8.
The heat capacity of synthetic pretulite ScPO4(c) was measured by adiabatic calorimetry within a temperature range of 12.13–345.31 K, and the temperature dependence of the pretulite heat capacity at 0–1600 K was derived from experimental and literature data on H 0(T)-H 0(298.15 K) for Sc orthophosphate. This dependence was used to calculate the values of the following thermodynamic functions: entropy, enthalpy change, and reduced Gibbs energy. They have the following values at 298.15 K: C p 0 (298.15 K) = 97.45 ± 0.06 J K−1 mol−1, S 0(298.15 K) = 84.82 ± 0.18 J K−1 mol−1, H 0(298.15 K)-H 0(0) = 14.934 ± 0.016 kJ mol−1, and Φ 0(298.15 K) = 34.73 ± 0.19 J K−1mol−1. The enthalpy of formation Δ f H 0(ScPO4, 298.15 K) = − 1893.6 ± 8.4 kJ mol−1.  相似文献   

9.
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   

10.
The paper reports pioneering data on the calorimetrically determined enthalpy of formation from elements of cuspidine, Ca fluordiorthosilicate Ca4Si2O7F2, from the Tyrny-Auz Mo–W deposit in Kabardino- Balkaria, Russia. The data were obtained by high-temperature melt solution calorimetry. The determined value is ΔfHel° (298.15 K) =–5190 ± 13 kJ/mol. The paper reports estimated S°(298.15 K) and ΔfGel° (298.15 K) of cuspidine.  相似文献   

11.
Based on the expert review of literature data on the thermodynamic properties of species in the Cl-Pd system, stepwise and overall stability constants are recommended for species of the composition [PdCl n ]2 ? n , and the standard electrode potential of the half-cell PdCl 4 2? /Pd(c) is evaluated at E 298,15° = 0.646 ± 0.007 V, which corresponds to Δ f G 298.15° = ?400.4 ± 1.4 kJ/mol for the ion PdCl 4 2? (aq). Derived from calorimetric data, Δ f H 298.15° PdCl 4 2? (aq) = ?524.6 ± 1.6 kJ/mol and Δ f H 298.15° Pd2+(aq) = 189.7 ± 2.6 kJ/mol. The assumed values of the overall stability constant of the PdCl 4 2? ion and the standard electrode potential of the PdCl 4 2? /Pd(c) half-cell correspond to Δ f G 298.15° = 190.1 ± 1.4 kJ/mol and S 298.15° = ?94.2 ± 10 J/(mol K) for the Pd2+(aq) ion.  相似文献   

12.
《Geochimica et cosmochimica acta》1999,63(13-14):1969-1980
The solubility of ettringite (Ca6[Al(OH)6]2(SO4)3 · 26H2O) was measured in a series of dissolution and precipitation experiments at 5–75°C and at pH between 10.5 and 13.0 using synthesized material. Equilibrium was established within 4 to 6 days, with samples collected between 10 and 36 days. The log KSP for the reaction Ca6[Al(OH)6]2(SO4)3 · 26H2O ⇌ 6Ca2+ + 2Al(OH)4− + 3SO42− + 4OH− + 26H2O at 25°C calculated for dissolution experiments (−45.0 ± 0.2) is not significantly different from the log KSP calculated for precipitation experiments (−44.8 ± 0.4) at the 95% confidence level. There is no apparent trend in log KSP with pH and the mean log KSP,298 is −44.9 ± 0.3. The solubility product decreased linearly with the inverse of temperature indicating a constant enthalpy of reaction from 5 to 75°C. The enthalpy and entropy of reaction ΔH°r and ΔS°r, were determined from the linear regression to be 204.6 ± 0.6 kJ mol−1 and 170 ± 38 J mol−1 K−1. Using our values for log KSP, ΔH°r, and ΔS°r and published partial molal quantities for the constituent ions, we calculated the free energy of formation ΔG°f,298, the enthalpy of formation ΔH°f,298, and the entropy of formation ΔS°f,298 to be −15211 ± 20, −17550 ± 16 kJ mol−1, and 1867 ± 59 J mol−1 K−1. Assuming ΔCP,r is zero, the heat capacity of ettringite is 590 ± 140 J mol−1 K−1.  相似文献   

13.
The heat capacity of eskolaite Cr2O3(c) was determined by adiabatic vacuum calorimetry at 11.99–355.83 K and by differential calorimetry at 320–480 K. Experimental data of the authors and data compiled from the literature were applied to calculate the heat capacity, entropy, and the enthalpy change of Cr2O3 within the temperature range of 0–1800 K. These functions have the following values at 298.15 K: C p 0 (298.15) = 121.5 ± 0.2 J K−1mol−1, S 0(298.15) = 80.95 ± 0.14 J K−1mol−1, and H 0(298.15)-H 0(0) = 15.30±0.02 kJ mol−1. Data were obtained on the transitions from the antiferromagnetic to paramagnetic states at 228–457 K; it was determined that this transition has the following parameters: Neel temperature T N = 307 K, Δ tr S = 6.11 ± 0.12 J K−1mol−1 and δ tr H = 1.87 ± 0.04 kJ mol−1.  相似文献   

14.
Thermodynamic properties of several TeO2 polymorphs and metal tellurites were measured by a combination of calorimetric techniques. The most stable TeO2 polymorph is α-TeO2, with its enthalpy of formation (ΔfHo) selected from literature data as ?322.0 ± 1.3 kJ·mol?1. β-TeO2 is metastable (in enthalpy) with respect to α-TeO2 by +1.40 ± 0.07 kJ·mol?1, TeO2 glass by a larger amount of +14.09 ± 0.11 kJ·mol?1. >200 experimental runs and post-synthesis treatments were performed in order to produce phase-pure samples of Co, Cu, Mg, Mn, Ni, Zn tellurites. The results of the hydrothermal and solid-state syntheses are described in detail and the products were characterized by powder X-ray diffraction. The standard thermodynamic data for the Te(IV) phases are (standard enthalpy of formation from the elements, ΔfHo in kJ·mol?1, standard third-law entropy So in J·mol?1·K?1): Co2Te3O8: ΔfHo = ?1514.2 ± 6.0, So = 319.2 ± 2.2; CoTe6O13: ΔfHo = ?2212.5 ± 8.1, So = 471.7 ± 3.3; MgTe6O13: ΔfHo = ?2525.8 ± 7.9, So = 509.2 ± 3.6; Ni2Te3O8: ΔfHo not measured, So = 293.3 ± 2.1; NiTe6O13: ΔfHo = ?2198.7 ± 8.2, So = 466.5 (estimated); CuTe2O5: ΔfHo = ?820.2 ± 3.3, So = 187.2 ± 1.3; Zn2Te3O8: ΔfHo = ?1722.5 ± 4.0, So = 299.3 ± 2.1. The solubility calculations show that the Te(IV) concentration in an aqueous phase, needed to produce such phases, must be at least 3–5 orders of magnitude higher than the natural Te background concentrations. The occurrence of these minerals, as expected, are restricted to hotspots of Te concentrations. In order to produce more reliable phase diagrams, more work needs to be done on the thermodynamics of potential competing phases in these systems, including Te(VI) phases.  相似文献   

15.
Enthalpies of solution of synthetic pentlandite Fe4.5Ni4.5S8, natural violarite (Fe0.2941Ni0.7059)3S4 from Vermillion mine, Sudbury, Ontario, synthetic pyrrhotite, FeS, synthetic high temperature NiS, synthetic vaesite, NiS2, synthetic pyrite, FeS2, Ni and Fe have been measured in a Ni0.6S0.4 melt at 1,100 K. Using these data and the standard enthalpies of formation of binary sulfides, given in literature, standard enthalpies of formation of pentlandite and violarite were calculated. The following values are reported: ΔH f o, Pent =?837.37±14.59 kJ mol?1 and ΔH f o, Viol =?378.02±11.81 kJ mol?1. While there are no thermo-chemical data for pentlandite with which our new value can be compared, an equilibrium investigation of stoichiometric violarite by Craig (1971) gives a significantly less negative enthalpy of formation. It is suggested that the difference may be due to the higher degree of order in the natural sample.  相似文献   

16.
The results of thermochemical studies are reported for nontronite samples from the Pinares-de-Majari (Eastern Cuba) (Sample I) and Kempirsai serpentine massif (South Urals, Kazakhstan) (Sample II). The enthalpies of formation of dehydrated hydroxyl-bearing nontronites from elements were determined by melt dissolution calorimetry using high-temperature heat-flux Tiana-Calvet microcalorimeter: Δ f H el o (298.15 K): ?4958 ± 13 kJ/mol for Mg0.4(Fe 1.5 3+ Mg0.4Ni0.1)[Si3.7Al0.3O10](OH)2 (I) and ?5003.6 ± 8.0 kJ/mol for Mg0.3Na0.1Ca0.1(Fe 1.4 3+ Mg0.5Ni0.1)[Si3.7Al0.3O10](OH)2 (II). It was determined experimentally that the enthalpy of dehydration (removal of molecular adsorption and interlayer water) of the studied nontronites is 6 ± 2 kJ per 1 mole H2O. The enthalpy of formation of nontronite of theoretical composition Mg0.15Fe 2 3+ [Si3.7Al0.3]O10(OH)2 was estimated at ?4750 kJ/mol. The Gibbs free energies of formation of the nontronites were calculated.  相似文献   

17.
The thermodynamic properties of monohydrocalcite, CaCO3 · H2O, have been obtained using a well-characterized natural specimen. Equilibration of the solid with water at 25°C under 0.97 atm CO2 led to an activity product [Ca2+][CO32?] = 10?7.60±0.03 and a free energy of formation ΔGfo = ?325,430 ± 270 calmol?. The enthalpy of solution of monohydrocalcite in 0.1 N HCl at 25°C led to a standard enthalpy of formation ΔHfo = ?358,100 ± 280 cal mol?1. Estimates of the variation of ΔGf with temperature and pressure showed monohydrocalcite to be metastable with respect to calcite and aragonite.  相似文献   

18.
Using the method of direct synthesis calorimetry, we determined the standard enthalpy of formation of PtSb (stumpflite), Δ f H°298.15 (PtSb, cr) =–105.16 ± 0.84 kJ/mol and PdSb2 (geversite), Δ f H°298.15 (PtSb2,cr) =–160.92 ± 0.84 kJ/mol. Isothermal (298.15 K, p = 1 bar) phase diagrams were computed for the Pt–Sb–S and Pt–Sb–O ternary systems in the coordinates composition of the Pt–Sb binary system versus fugacity of a gaseous volatile component (O2, S2).  相似文献   

19.
The heat capacity of xenotime YPO4(c) was measured by adiabatic calorimetry at 4.78–348.07 K. Our experimental and literature data on H 0(T)-H 0(298.15 K) of Y orthophosphate were utilized to derive the C p 0(T) function of xenotime at 0–1600 K, which was then used to calculate the values of thermodynamic functions: entropy, enthalpy change, and reduced Gibbs energy. These functions assume the following values at 298.15 K: C p 0 (298.15 K) = 99.27 ± 0.02 J K−1 mol−1, S 0(298.15 K) = 93.86 ± 0.08 J K−1 mol−1, H 0(298.15 K) − H 0(0) = 15.944 ± 0.005 kJ mol−1, Φ0(298.15 K) = 40.38 ± 0.08 J K−1 mol−1. The value of the free energy of formation Δ f G 0(YPO4, 298.15 K) is −1867.9 ± 1.7 kJ mol−1.  相似文献   

20.
The low-temperature heat capacity of knorringite garnet (Mg3Cr2Si3O12) was measured between 2 and 300 K, and thermochemical functions were derived from the results. The measured heat capacity curves show a sharp lambda-shaped anomaly peaking at around 5.1 K. Magnetic susceptibility data show that the transition is caused by antiferromagnetic ordering. From the C p data, we suggest a standard entropy (298.15 K) of 301 ± 2.5 J mol?1 K?1 for Mg3Cr2Si3O12. The new data are also used in conjunction with previous experimental results to constrain ?H f ° for knorringite.  相似文献   

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