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1.
The thermodynamic properties of carnegieite and NaAlSiO4 glass and liquid have been investigated through C p determinations from 10 to 1800 K and solution-calorimetry measurements. The relative entropies S 298-S0 of carnegieite and NaAlSiO4 glass are 118.7 and 124.8 J/mol K, respectively. The low-high carnegieite transition has been observed at 966 K with an enthalpy of transition of 8.1±0.3 kJ/mol, and the enthalpy of fusion of carnegieite at the congruent melting point of 1799 K is 21.7±3 kJ/mol. These results are consistent with the reported temperature of the nepheline-carnegieite transition and available thermodynamic data for nepheline. The entropy of quenched NaAlSiO4 glass at 0 K is 9.7±2 J/mol K and indicates considerable ordering among AlO4 and SiO4 tetrahedra. In the liquid state, progressive, temperature-induced Si, Al disordering could account for the high configurational heat capacity. Finally, the differences between the entropies and heat capacities of nepheline and carnegieite do not seem to conform to current polyhedral modeling of these properties  相似文献   

2.
The standard enthalpy of formation of thorite and huttonite and the enthalpy of the phase transition between these polymorphs were determined using high-temperature oxide melt solution calorimetry and transposed temperature drop calorimetry. Standard enthalpies of formation of thorite and huttonite are reported for the first time and are −2117.6 ± 4.2 kJ/mol and −2110.9 ± 4.7 kJ/mol, respectively. Based on our measurements, thorite and huttonite are metastable relative to SiO2 (quartz) and ThO2 (thorianite) at standard conditions, but are presumably stabilized at high temperature by the entropy contribution. Based on the measured enthalpy of the thorite-huttonite phase transition of 6.7 ± 2.5 kJ/mol, a dP/dT slope for the transformation was calculated as −1.21 ± 0.45 MPa/K.  相似文献   

3.
The enthalpies of drop solution of calcite, magnesite, dolomite, wollastonite and diopside have been measured in a lead borate solvent at 977 K in a Calvettype microcalorimeter. The carbonate calorimetry was done under flowing gas atmosphere. Both natural and synthetic samples were used. From these calorimetric data, the enthalpies of several reactions of carbonate with quartz were calculated. The enthalpies of these reactions (kJ/mol) at 298 K are: calcite+quartzwollastonite+CO2, 92.3±1.0; magnesite+quartzenstatite+CO2, 82.9±2.8; dolomite+quartzdiopside+CO2, 163.0±1.9. These values generally are in agreement with those calculated from Robie et al., Helgeson et al., Berman and Holland and Powell. The enthalpy of dolomite-quartz reaction overlaps marginally with those from Berman and Holland and Powell. The enthalpy of formation of dolomite from magnesite and calcite (-11.1±2.5 kJ/mol) was also derived from the measured enthalpies, and this value is consistent with that from acid solution calorimetric measurements as shown by Navrotsky and Capobianco, but different from values in the earlier literature. These results support the premise that drop-solution of carbonates into molten lead borate results in a well-defined final state consisting of dissolved oxide and evolved CO2. This was also confirmed by weight change experiments. Thus, oxide melt calorimetry is applicable to carbonates.  相似文献   

4.
We report on the thermochemistry of proton hydration by water in the gas phase both experimentally using high-pressure mass spectrometry (HPMS) and theoretically using multilevel G3, G3B3, CBS-Q, CBS-QB3, CBS/QCI-APNO as well as density functional theory (DFT) calculations. Gas phase hydration enthalpies and entropies for protonated water cluster equilibria with up to 7 waters (i.e., n ? 7H3O+·(H2O)n) were observed and exhibited non-monotonic behavior for successive hydration steps as well as enthalpy and entropy anomalies at higher cluster rank numbers. In particular, there is a significant jump in the stepwise enthalpies and entropies of cluster formation for n varying from 6 to 8. This behavior can be successfully interpreted using cluster geometries obtained from quantum chemical calculations by considering the number of additional hydrogen bonds formed at each hydration step and simultaneous weakening of ion-solvent interaction with increasing cluster size. The measured total hydration energy for the attachment of the first six water molecules around the hydronium ion was found to account for more than 60% of total bulk hydration free energy.  相似文献   

5.
A series of synthetic and biogenicmagnesian calcites was dissolved in weak acetic acidsolutions to measure the enthalpies of dissolution at25°C. For the synthetic phases, heat releasedwas 33.5 kJ/mol for calcite, decreasing to 33 kJ/molfor a phase of 2 mol % MgCO3, and increasing to35 kJ/mol for a phase of 15 mol %. Values of excessenthalpies, ΔHxs, calculated using calciteand magnesite end-members, average about -1 kJ/mol forthe synthetic phases. Total entropies of solidsolution formation, ΔSSS, also werecalculated using available data on Gibbs free energiesof formation and these excess enthalpies. Values ofΔSSS range from -2 J/(mol-K) at 2 mol % to-5 J/(mol-K) at 15 mol % MgCO3. These negativevalues of ΔHxs and ΔSSSsuggest that some form of ordering (cation?) isobtained in the synthetic phases, and that vibrationalentropies of the solid solution are diminished incomparison to the end-members. In contrast, biogenic samples generally have positivevalues of ΔHxs, increasing from +1 kJ/molat 5 mol % to +3 kJ/mol at 20 mol % MgCO3. Mostvalues of ΔSSS are equal (within errors)to values expected from configurational enthalpyalone. Thus, in most biogenic materials cationordering probably is not obtained, and most phases aremore typical of equivalent-site solid solutions.  相似文献   

6.
An internally consistent thermodynamic dataset has been derived for 148 endmember phases (145 solids and 3 fluids) comprising the elements Li, Na, K, Be, Mg, Ca, Ti, Cr, Mn, Fe, Zn, Al, Si, C, H, and O. This has been achieved by simultaneous treatment of phase property (like standard enthalpy of formation, standard entropy, molar heat capacity, molar volume, thermal expansivity, bulk modulus etc.) and reaction reversal data by the Bayesian method. The theory underlying the approach, and the computational methods involved, are briefly outlined. (For the benefit of readers unfamiliar with inference statistics, the basic concepts of the Bayes method are also presented in such a way that they can be grasped intuitively.) Although not yet addressed, this method can be extended to refine the thermodynamic mixing properties of crystalline solutions. The sources of the input data, culled from the literature, are summarized in the Appendix. The resulting database is succinctly documented in this paper. It includes the enthalpies of formation and entropies, their uncertainties, and the correlation among them. The database allows calculation of P-T, T-X CO2, P-X CO2, and T-f O2 sections, with error propagation into the computed phase diagrams on a routine basis. A user-friendly computer program has been written to generate such phase diagrams. It is public domain software. The software and the thermodynamic database (which includes a complete documentation of the thermodynamic data above and beyond those listed (Table 2, here) may be downloaded from the web site http://homepage.ruhr-uni-bochum.de/niranjan.chatterjee/Index.htm. Examples of computed phase diagrams are given to illustrate the quality of the data and the capabilities of the software. Received: 11 March 1998 / Accepted: 11 June 1998  相似文献   

7.
Solution enthalpies of synthetic olivine solid solutions in the system Mg2SiO4-Fe2SiO4 have been measured in molten 2PbO·B2O3 at 979 K. The enthalpy data show that olivine solid solutions have a positive enthalpy of mixing and the deviation from ideality is approximated as symmetric with respect to composition, in contrast to the previous study. Applying the symmetric regular solution model to the present enthalpy data, the interaction parameter of ethalpy (WH) is estimated to be 5.3±1.7 kJ/mol (one cation site basis). Using this Wh and the published data on excess free energy of mixing, the nonideal parameter of entropy (Ws) of olivine solid solutions is estimated as 0.6±1.5 J/mol·K.  相似文献   

8.
We report relative enthalpy measurements on quartz, cristobalite and amorphous SiO2 between 1000 and 1800 K. We have observed a glass transition around 1480 K for amorphous SiO2. From our results and available Cp, relative enthalpy, and enthalpy of solution data we have derived a consistent set of thermodynamic data for these phases. Our calculated enthalpies of fusion are 8.9 ± 1.0 kJ mole?1 for cristobalite at 1999 K and 9.4 ± 1.0 kJ mole?1 at 1700 K for quartz.  相似文献   

9.
Calorimetric measurements of fusion enthalpies for Ni2SiO4 and Co2SiO4 olivines were carried out using a high-temperature calorimeter, and Ni and Co partitioning between olivine and silicate liquid was analyzed using the measured heats of fusion. The fusion enthalpy of Co2SiO4 olivine measured by transposed-temperature drop calorimetry was 103 ± 15 kJ/mol at melting point (1688 K). The fusion enthalpy of Ni2SiO4 olivine was calculated based on the enthalpies of liquids in the system An50Di50-Ni2SiO4 measured by transposed-temperature drop calorimetry at 1773 K, and was 221 ± 26 kJ/mol at its metastable melting point (1923 K). The fusion enthalpy of Ni2SiO4 is the largest among those of olivine group, this is caused by the large crystal field stabilization energy of six-coordinated Ni2+ in olivine. The larger fusion enthalpy of Ni2SiO4 can account for the large and variable partition coefficient of Ni between olivine and silicate liquid. Based on the comparison between partition coefficients calculated from thermodynamic data and those observed in partition experiments, it is considered that the magnitude of partition coefficients is primarily dependent on the heats of fusion of the components. Furthermore, the activity coefficients for Ni-, Co- and Mn-bearing components in magmatic liquid are nearly of the same magnitude.  相似文献   

10.
Equilibrium in the chabazite-H2O system was investigated by isothermal thermogravimetric analysis over a large range of temperatures (from 23 to 315°C) and H2O-vapor pressures (from 0.03 to 28 mbar). Thermodynamic analysis of the phase-equilibrium data revealed the existence of three energetically distinct types of H2O, referred to as S-1, S-2, and S-3. At 23°C and 26 mbar of H2O-vapor pressure, chabazite has maximum H2O occupancies of 8.2, 11.1, and 3.1 wt.% for S-1, S-2, and S-3, respectively. During dehydration, S-1 H2O is lost first, followed by S-2 H2O and then S-3 H2O, with significant overlap for S-1 and S-2 as well as S-2 and S-3. The thermodynamics of chabazite-H2O were modeled using three independent equilibrium formulations for S-1, S-2, and S-3. These formulations yielded standard-state molar Gibbs free energy of hydration of −21.8 ± 0.6, −52.1 ± 1.8, and −111.7 ± 6.7 kJ/mol for S-1, S-2, and S-3. Standard-state molar enthalpies of hydration for each type of H2O are −65.6 ± 0.5, −100.1 ± 1.6, and −156.9 ± 6.2 kJ/mol, respectively. Integral molar values for the Gibbs free energy of hydration for each type of H2O are −19.0 ± 0.7, −40.1 ± 2.1, and −76.9 ± 9.6 kJ/mol, respectively. Integral molar values for the enthalpy of hydration for each type of H2O are −62.8 ± 0.6, −88.1 ± 1.9, and −122.2 ± 9.3 kJ/mol, respectively. Integration of the predicted total partial molar enthalpy of hydration for all three types of H2O over the full H2O content of chabazite gave an integral molar enthalpy of −39.65 ± 9.3 kJ/mol relative to liquid water. The thermodynamic data obtained for the hydration of natural chabazite were used to predict the hydration state of chemically similar chabazites under various temperatures and PH2O, ranging from 25 to 400°C and from 10−5 to 104 bars.  相似文献   

11.
Thermochemistry and melting properties of basalt   总被引：1，自引：0，他引：1  
The heat capacities of the liquid, glassy and crystalline phases of an alkali basalt have been determined from relative enthalpies measured between 400 and 1,800 K. Values given by available models of calculation generally agree to within 2% of these results. As derived from the new data and the enthalpy of vitrification measured at 973 K by oxide-melt drop solution calorimetry for the same sample, the enthalpy of fusion of this basalt increases from 15.4 kJ/mol at 1,000 K to 33.6 kJ/mol at 1,800 K. Comparisons between the enthalpies of fusion of basalt and model compositions confirm the small magnitude of the enthalpy of mixing between the molten mineral components of the liquids. Minor variations in the chemical composition have only a small effect in the heat capacity and the enthalpy of melting of basalt. The enthalpies of formation at 298 K from the oxides of the crystallized and glass phases of this alkali basalt are −112.2 and −98.5 kJ/mol, respectively, for a gram formula weight based on one mole of oxide components.  相似文献   

12.
The thermochemical study of two natural trioctahedral Mg–Fe chlorites—clinochlores was carried out using high-temperature melt solution calorimetry with a Tian–Calvet microcalorimeter. The enthalpies of formation of clinochlores of compositions (Mg4.9Fe 0.3 2+ Al0.8)[Si3.2Al0.8O10](OH)8 (–8811 ± 12 kJ/mol) and (Mg4.3Fe 0.7 2+ Al1.0)[Si3.0Al1.0O10](OH)8 (–8696 ± 13 kJ/mol) from elements were determined. The values of the standard entropies and the Gibbs energies of formation of the studied natural minerals as well as thermodynamic properties of Mg–Fe chlorites of theoretical composition were estimated.  相似文献   

13.
坡缕石粘土对有机染料的吸附热力学研究   总被引：1，自引：0，他引：1  
将甘肃靖远坡缕石粘土分离提纯,通过静态吸附实验,研究了坡缕石对水中有机染料亚甲基蓝、结晶紫和苯胺蓝的吸附等温线,探讨了吸附热力学特征.实验结果显示,在实验温度范围内3种染料在坡缕石上的吸附在30 min可达平衡,吸附等温线均能较好符合Langmuir模型,饱和吸附量大小顺序为:结晶紫＞亚甲基蓝＞苯胺蓝;吸附均为吸热过程,亚甲基蓝、结晶紫和苯胺蓝的吸附焓分别为15.52、9.26和2.59 kJ/mol;吸附Gibbs函数约为-35～-30 kJ/mol,吸附熵均大于零,吸附是自发过程.  相似文献   

14.
The accepted standard state entropy of titanite (sphene) has been questioned in several recent studies, which suggested a revision from the literature value 129.3 ± 0.8 J/mol K to values in the range of 110–120 J/mol K. The heat capacity of titanite was therefore re-measured with a PPMS in the range 5 to 300 K and the standard entropy of titanite was calculated as 127.2 ± 0.2 J/mol K, much closer to the original data than the suggested revisions. Volume parameters for a modified Murgnahan equation of state: V P,T  = V 298° × [1 + a°(T − 298) − 20a°(T − 298)] × [1 – 4P/(K 298 × (1 – 1.5 × 10−4 [T − 298]) + 4P)]1/4 were fit to recent unit cell determinations at elevated pressures and temperatures, yielding the constants V 298° = 5.568 J/bar, a° = 3.1 × 10−5 K−1, and K = 1,100 kbar. The standard Gibbs free energy of formation of titanite, −2456.2 kJ/mol (∆H°f = −2598.4 kJ/mol) was calculated from the new entropy and volume data combined with data from experimental reversals on the reaction, titanite + kyanite = anorthite + rutile. This value is 4–11 kJ/mol less negative than that obtained from experimental determinations of the enthalpy of formation, and it is slightly more negative than values given in internally consistent databases. The displacement of most calculated phase equilibria involving titanite is not large except for reactions with small ∆S. Re-calculated baric estimates for several metamorphic suites yield pressure differences on the order of 2 kbar in eclogites and 10 kbar for ultra-high pressure titanite-bearing assemblages.  相似文献   

15.
This study investigated the sorption behaviour of two endocrine disrupting chemicals; 17β-estradiol (E2) and 17β-ethinylestradiol and their thermodynamic properties in an activated sludge biomass. The partition coefficient values measured for E2 and EE2 at varying temperatures range from 245–604 L/kg ( log Kd 2.39–2.78) and 267–631 L/kg (Log Kd 2.43–2.80), respectively. The Kd values were inversely related to temperature. The average percentages of E2 and EE2 adsorbed to the solid phase at 4.3 % dry solid were 87.2 % and 92.5 %, respectively. Sorption of E2 and EE2 to the activated sludge biomass was found to be spontaneous and entropy retarded with ΔG values in the range of ?13 to ?16 KJ/mol and ΔS value of?105.2J/mol/K and 96.7 J/mol/k for E2 and EE2, respectively. The enthalpy changes for E2 and EE2 were ?45.7KJ/mol and ?43.4KJ/mol respectively, demonstrating that the sorption process is exothermic. The values of the enthalpy changes also show that the mechanism of sorption is physisorption with some element of chemisorption.  相似文献   

16.
We used titration calorimetry to measure the bulk heats of proton and Cd adsorption onto a common Gram positive soil bacterium Bacillus subtilis at 25.0 °C. Using the 4-site non-electrostatic model of Fein et al. [Fein, J.B., Boily, J.-F., Yee, N., Gorman-Lewis, D., Turner, B.F., 2005. Potentiometric titrations of Bacillus subtilis cells to low pH and a comparison of modeling approaches. Geochim. Cosmochim. Acta69 (5), 1123-1132.] to describe the bacterial surface reactivity to protons, our bulk enthalpy measurements can be used to determine the following site-specific enthalpies of proton adsorption for Sites 1-4, respectively: −3.5 ± 0.2, −4.2 ± 0.2, −15.4 ± 0.9, and −35 ± 2 kJ/mol, and these values yield the following third law entropies of proton adsorption onto Sites 1-4, respectively: +51 ± 4, +78 ± 4, +79 ± 5, and +60 ± 20 J/mol K. An alternative data analysis using a 2-site Langmuir-Freundlich model to describe proton binding to the bacterial surface (Fein et al., 2005) resulted in the following site-specific enthalpies of proton adsorption for Sites 1 and 2, respectively: −3.6 ± 0.2 and −35.1 ± 0.3 kJ/mol. The thermodynamic values for Sites 1-3 for the non-electrostatic model and Site 1 of the Langmuir-Freundlich model of proton adsorption onto the bacterial surface are similar to those associated with multifunctional organic acid anions, such as citrate, suggesting that the protonation state of a bacterial surface site can influence the energetics of protonation of neighboring sites. Our bulk Cd enthalpy data, interpreted using the 2-site non-electrostatic Cd adsorption model of Borrok et al. [Borrok, D., Fein, J.B., Tischler, M., O’Loughlin, E., Meyer, H., Liss, M., Kemner, K.M., 2004b. The effect of acidic solutions and growth conditions on the adsorptive properties of bacterial surfaces. Chem. Geol.209 (1-2), 107-119.] to account for Cd adsorption onto B. subtilis, yield the following site-specific enthalpies of Cd adsorption onto bacterial surface Sites 2 and 3, respectively: −0.2 ± 0.4 and +14.4 ± 0.9 kJ/mol, and the following third law entropies of Cd adsorption onto Sites 2 and 3, respectively: +57 ± 4 and +128 ± 5 J/mol K. The calculated enthalpies of Cd adsorption are typical of those associated with Cd complexation with anionic oxygen ligands, and the entropies are indicative of inner sphere complexation by multiple ligands. The experimental approach described in this study not only yields constraints on the molecular-scale mechanisms involved in proton and Cd adsorption reactions, but also provides new thermodynamic data that enable quantitative estimates of the temperature dependence of proton and Cd adsorption reactions.  相似文献   

17.
At high pressures, CdGeO3 pyroxenoid transforms to garnet, then to ilmenite, and finally to perovskite. Enthalpies of transition among the four phases were measured by high temperature calorimetry. The entropies of transition and slopes of the boundaries were calculated using the measured enthalpies and free energies calculated from the phase equilibrium data. Pyroxenoid and garnet are very similar energetically. However garnet is a high pressure phase because of its lower entropy and smaller volume. The pyroxenoid-garnet transition has a small positiveP-T slope. Ilmenite is intermediate in enthalpy between garnet and perovskite, but is lower in entropy than both phases. Therefore the garnet-ilmenite transition has a positivedP/dT, while a negativedP/dT is calculated for the ilmenite-perovskite transition. The thermochemical data for the CdGeO3 phases are generally consistent with the observed high pressure phase relations. The high entropy of perovskite relative to ilmenite, observed in several ABO3 comounds including CdGeO3, is related to the structural features of perovskite, in which relatively small divalent cations occupy the large sites of 8–12 fold coordination. The thermochemistry of the CdGeO3 polymorphs shows several similarities to that of the CaGeO3 system.  相似文献   

18.
A study of Ca self-diffusion along the b axis in synthetic (iron free) diopside single crystal was performed at temperatures ranging from 1273 K to 1653 K. Diffusion profiles of 44Ca were measured using α-particles Rutherford Backscattering (α-RBS) micro analysis. We unambiguously find two distinct diffusional regimes, characterized by activation enthalpies H = 280 ± 26 kJ/mol and H = 951 ± 87 kJ/mol at temperatures lower and upper than 1515 K, respectively. This change of diffusion regime takes place near the onset of premelting as detected in calorimetric measurements and can be interpreted in terms of enhanced formation of Frenkel point defects with an activation enthalpy of formation of 1524 ± 266 kJ/mol (H f/2 = 762 kJ/mol), in accordance with our high-temperature diffusion data. If premelting of diopside is actually related to Ca-Frenkel point defect concentration, this concentration could reach up to few mole percents close to the melting temperature.  相似文献   

19.
The heat of mixing for the binary solid solution diopside–Ca-Tschermak was investigated at T = 980 K by lead borate solution calorimetry. A new statistical technique was applied to overcome the problem of using experimental data of various precisions. A two-parameter Margules model was fitted to the calorimetric data leading to W CaTs–DiH = 31.3 ± 3.4 kJ mol−1 and W H Di–CaTs = 2.4 ± 4.3 kJ mol−1. The results are in good agreement with calorimetric data given in the literature. They agree also with enthalpy data that were extracted from phase equilibrium experiments. With configurational entropy values taken from the literature, the volume and the vibrational entropy, presented in Part I of this work, and the enthalpy data of this study, the activity–composition relationships of the diopside–Ca-Tschermak binary were calculated.  相似文献   

20.
Abstract This, the second of two papers, represents the application of a least squares approach, discussed in the previous paper, to the generation of an internally consistent thermodynamic dataset involving 60 reactions among 43 phases, in the system K2O–Na2O–CaO–MgO–Al2O3–SiO2–H2O–CO2. We make the assumption that all the thermodynamic data, with the exception of enthalpies of formation of the phases, are well known, and solve for an internally consistent set of enthalpies which reproduces the 60, experimentally determined, phase equilibrium reactions. An important difference between our dataset and that of previous alternatives in the literature is that we are able to determine the uncertainties on, and correlations between, the enthalpies of formation for all phases in the set, and hence are able to apply simple error propagation techniques to determine the uncertainties in any phase equilibrium calculations performed using this dataset. Selection of reactions, for geothermometry and geobarometry, may be more readily made by choosing equilibria with small uncertainties in their thermodynamics. Our data are in reasonably close agreement with the high temperature molten oxide calorimetry results on silicate minerals where available, a fact which lends a degree of confidence to the results.  相似文献   

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