理想完全互溶双液系相图的数学解析

理想完全互溶双液系是两个组分都严格遵守Raoult定律的体系，从数学角度看，其平面相图有着确定的函数关系。本文以Clausius-Clapeyron方程为基础，推导了该类理想体系的p-x、T-x及p-T相图的函数解析式。     

The phase diagram of ammonium nitrate

The pressure-temperature (P-T) phase diagram of ammonium nitrate (AN) [NH(4)NO(3)] has been determined using synchrotron x-ray diffraction (XRD) and Raman spectroscopy measurements. Phase boundaries were established by characterizing phase transitions to the high temperature polymorphs during multiple P-T measurements using both XRD and Raman spectroscopy measurements. At room temperature, the ambient pressure orthorhombic (Pmmn) AN-IV phase was stable up to 45 GPa and no phase transitions were observed. AN-IV phase was also observed to be stable in a large P-T phase space. The phase boundaries are steep with a small phase stability regime for high temperature phases. A P-V-T equation of state based on a high temperature Birch-Murnaghan formalism was obtained by simultaneously fitting the P-V isotherms at 298, 325, 446, and 467 K, thermal expansion data at 1 bar, and volumes from P-T ramping experiments. Anomalous thermal expansion behavior of AN was observed at high pressure with a modest negative thermal expansion in the 3-11 GPa range for temperatures up to 467 K. The role of vibrational anharmonicity in this anomalous thermal expansion behavior has been established using high P-T Raman spectroscopy.     

Solid-solute phase equilibria in aqueous solution. IV. Calculation of Phase Diagrams

The thermodynamic principles of conventional (T-x, P-T) phase diagrams and solubility (log ΣK-x) diagrams depicting solid-solute phase equilibria in aqueous solution are derived from a unifying point of view. It is shown that thermodynamic quantities necessary for the construction of conventional phase diagrams can be obtained from solubility measurements. The unary system calcite-aragonite and the binary system aragonite-strontianite, where solubility data are available over the whole compositional range, have been selected as examples. In the latter case, the constraint of constant composition of the solid phase leading to a metastable equilibrium with the respective solute species is an essential point in the thermodynamic derivation and was observed experimentally as well.     

Predicting mixture phase equilibria and critical behavior using the SAFT-VRX approach

The SAFT-VRX equation of state combines the SAFT-VR equation with a crossover function that smoothly transforms the classical equation into a nonanalytical form close to the critical point. By a combinination of the accuracy of the SAFT-VR approach away from the critical region with the asymptotic scaling behavior seen at the critical point of real fluids, the SAFT-VRX equation can accurately describe the global fluid phase diagram. In previous work, we demonstrated that the SAFT-VRX equation very accurately describes the pvT and phase behavior of both nonassociating and associating pure fluids, with a minimum of fitting to experimental data. Here, we present a generalized SAFT-VRX equation of state for binary mixtures that is found to accurately predict the vapor-liquid equilibrium and pvT behavior of the systems studied. In particular, we examine binary mixtures of n-alkanes and carbon dioxide + n-alkanes. The SAFT-VRX equation accurately describes not only the gas-liquid critical locus for these systems but also the vapor-liquid equilibrium phase diagrams and thermal properties in single-phase regions.     

THE STABILITY OF LAIHUNITE——A THERMODYNAMIC RE-ANALYSIS

A topological analysis on the ternary 7-phase multisystem involving laihunite (FeO-Fe_2O_3-SiO_2; Q-H-M-W-L-Fa-fs) in P-T plane has resulted in an n+4 phase closed-net-diagram. The most possible straightline-net-diagram was derived by using the thermodynamic properties of the phases concerned. From the straight-line-net-diagram it is apparent that laihunite is not a phase stable only at high pressures. P-T-fo_2, analysis suggests that the formation and stabilization of laihunite are closely related to oxygen fugacity. However, laihunite shows different ways of formation at different pressures. At low pressures, it is formed via the oxidation of fayalite; with increasing pressures the contribution of ferrosilite to the formation of laihunite increases; at very high pressures laihunite can be formed only by the oxidation of ferrosilite.     

Two-component system CCl4 + (CH3)3CBr: extrema in equilibria involving orientationally disordered phases

Phase equilibria involving orientationally disordered (OD) and liquid phases of the two-component system between carbon tetrachloride (CCl4) and 2-methyl-2-bromomethane ((CH3)3CBr) have been determined by means of X-ray powder diffraction and thermal analysis techniques from 210 K up to the liquid state. The isomorphism relation between the OD stable face-centered cubic (FCC) phase of (CH3)3CBr and the metastable FCC phase of CCl4 has been demonstrated throughout the continuous evolution of the lattice parameters and the existence of the two-phase equilibrium [FCC + L] for the whole range of composition, despite the monotropy of the FCC phase for the CCl4 component with respect to its OD rhombohedral (R) stable phase. A continuous series of OD R mixed crystals is found, which confirms the R lattice symmetry of the OD phase II of (CH3)3CBr, for which the crystallographic results have been long-time misinterpreted. X-ray patterns of such a phase were indexed according to the recent single-crystal results obtained by Rudman (Rudman, R. J. Mol. Struct. 2001, 569, 157). In addition, some experimental evidences are given to confirm the number of molecules per unit cell (Z = 21). The thermodynamic assessment reproduces coherently the phase diagram for the stable [R + L] and [R + FCC] two-phase equilibria as well as for the partially metastable [FCC + L] two-phase equilibrium and provides a set of data for the thermodynamic properties of nonexperimentally available phase transitions of pure components. Surprisingly, the phase equilibrium involving R and FCC OD phases appears as one of the very few showing a solid-solid equilibrium with two extremes.     

Fluid phase stability and equilibrium calculations in binary mixtures: Part II: Application to single-point calculations and the construction of phase diagrams

The methodology presented in Part I of this work is applied to a large number of pressure–temperature flash calculations, and to the automated construction of constant temperature pressure–composition phase diagrams, and constant pressure temperature–composition phase diagrams for binary mixtures modeled with an augmented van der Waals equation of state. An automated prototype implementation of the algorithm is developed for this purpose. We follow the classification of Scott and van Konynenburg [R.L. Scott, P.H. van Konynenburg, Discuss. Faraday Soc. 49 (1970) 87] and present phase diagrams corresponding to non-azeotropic mixtures of the five main types of fluid phase behavior (I–V), studying in detail representative diagrams at constant pressure and constant temperature. Special attention is given to the solution of numerically problematic equilibrium regions, such as those close to three-phase equilibria where metastable and unstable critical points can also be found. Of the order of 10⁴ flash calculations at varying temperatures and pressures, and for different intermolecular parameters of the components in the mixture, have been carried out. The algorithm provides the correct stable equilibrium state for all of the points considered. Despite the fact that our implementation is not optimised for performance, we find that the algorithm identifies the stable solution in difficult regions of the phase space without any penalty in terms of computational time, when compared to simpler regions.     

The effect of carboxylate anions on the formation of clathrate hydrates of tetrabutylammcnium carboxylates

The solid-liquid phase diagrams of binary mixtures of water with tetrabutylammonium carboxylate having an unsaturated alkyl group in the carboxylate anion ((n-C₄H₉)₄NOOCR; R=C₂H₃–C₉H₁₇) were examined in order to confirm the formation of clathrate-like hydrates. The results are summarized as follows: (1) the formation of a clathrate-like hydrate is newly confirmed for all the 13 carboxylates examined; (2) these hydrates are classified into three groups I, II, and III on the basis of the hydration numbers; (3) the group I hydrates, which are formed by the carboxylates with R=C₂ and R=C₃, have hydration numbers around 30 and are the most stable hydrates among those examined in this study; (4) the group II hydrates, with hydration numbers around 39, are formed by all the carboxylates with R=C₄ and C₅ including sorbate and are less stable than the group I hydrates; (5) the group III hydrates, with hydration numbers around 30 like the group I hydrates, are formed by carboxylates with long alkyl chains such as 2-octenoate and 2-decenoate and are generally unstable.     

Raman investigation of the n(2)-o(2) binary system as a function of pressure and temperature

We produced mixtures of N2-O2 with different concentrations and performed low-temperature Raman studies at ambient and high pressures. From spectra in vibron and phonon regions, we determined band frequency, bandwidth, and band intensity as a function of temperature, pressure, and concentration. We determined the vibron Raman cross-sections and deduced the true concentrations of mixtures from vibron Raman band intensities. These concentrations were different from those determined from partial gas pressure of the initial gaseous mixtures. From fingerprints in Raman spectra, such as jumps in band frequencies or additional band splitting, we were able to prove phase transitions and propose a preliminary T-x phase diagram. We compared this diagram with two reported in the literature from structural analysis. Comparing all three variants of the T-x phase diagrams we found several discrepancies and inconsistencies, which we associate with different solid sample production techniques. Since we could prove that our samples were in thermodynamic equilibrium, we are convinced that we improved the known phase diagram substantially. From Raman band intensities of the O2 vibrations in different phases of N2 and O2, we were able to determine quantitatively the solubility of O2 in N2. Preliminary Raman studies of 2% and 7% O2 in N2 at high pressure and low temperatures showed that a larger amount of O2 can be dissolved in N2 than at ambient pressure. At the critical pressure (p approximately 15 GPa) we found from Raman spectra that O2 is demixed from 7% O2 in N2 to form epsilon-O2. This was previously called a "new phase" in the literature and not understood up to now. Finally, from band frequencies we determined the environmental shift of oxygen molecules in the mixture which is related to the intermolecular potential U(N2-O2) between different types of molecules.     

Crystal structure prediction using ab initio evolutionary techniques: principles and applications

We have developed an efficient and reliable methodology for crystal structure prediction, merging ab initio total-energy calculations and a specifically devised evolutionary algorithm. This method allows one to predict the most stable crystal structure and a number of low-energy metastable structures for a given compound at any P-T conditions without requiring any experimental input. Extremely high (nearly 100%) success rate has been observed in a few tens of tests done so far, including ionic, covalent, metallic, and molecular structures with up to 40 atoms in the unit cell. We have been able to resolve some important problems in high-pressure crystallography and report a number of new high-pressure crystal structures (stable phases: epsilon-oxygen, new phase of sulphur, new metastable phases of carbon, sulphur and nitrogen, stable and metastable phases of CaCO3). Physical reasons for the success of this methodology are discussed.     

低共熔混合锂盐相图的绘制及应用

采用热分析法对不同组成的混合锂盐二元体系进行研究, 绘制了混合锂盐体系的步冷曲线和T-x相图, 结果表明体系均为具有最低共熔点的二元体系. LiOH-LiNO3、LiOH-LiCl、LiOH-Li2CO3及LiNO3-LiCl体系的最低共熔点分别为175.7、294.5、418.2及221.6 ℃. 利用低共熔混合物LiNO3-LiOH为锂盐与不同前驱体反应, 制备出了层状结构良好的锂离子电池正极材料LiNiO2、LiNi0.8Co0.2O2及LiNi1/3Co1/3Mn1/3O2. X射线衍射分析表明, 合成的材料具有规整的层状NaFeO2结构, 且XRD衍射峰强度之比I(003)/I(104)>2.0, 电性能测试表明, 在2.7-4.3 V(vs Li/Li+)的电压范围内进行0.1C倍率充放电, LiNiO2、LiNi0.8Co0.2O2、LiNi1/3Co1/3Mn1/3O2首次充电比容量分别达168.0、225.4、194.0 mAh·g-1, 放电比容量分别为138.4、165.8、157.7 mAh·g-1.     

Melting curve and fluid equation of state of carbon dioxide at high pressure and high temperature

The melting curve and fluid equation of state of carbon dioxide have been determined under high pressure in a resistively heated diamond anvil cell. The melting line was determined from room temperature up to 11.1+/-0.1 GPa and 800+/-5 K by visual observation of the solid-fluid equilibrium and in situ measurements of pressure and temperature. Raman spectroscopy was used to identify the solid phase in equilibrium with the melt, showing that solid I is the stable phase along the melting curve in the probed range. Interferometric and Brillouin scattering experiments were conducted to determine the refractive index and sound velocity of the fluid phase. A dispersion of the sound velocity between ultrasonic and Brillouin frequencies is evidenced and could be reproduced by postulating the presence of a thermal relaxation process. The Brillouin sound velocities were then transformed to thermodynamic values in order to calculate the equation of state of fluid CO2. An analytic formulation of the density with respect to pressure and temperature is proposed, suitable in the P-T range of 0.1-8 GPa and 300-700 K and accurate within 2%. Our results show that the fluid above 500 K is less compressible than predicted from various phenomenological models.     

High-resolution NMR spectra of n-alkanes penetrating into carbon fibers and of protons in carbon fibers

We present a simple NMR method for microscopically exploring the local environment in carbon fibers. The method utilizes n-alkanes as probe molecules, where the n-alkanes penetrate carbon fibers of interest. The high-resolution (1)H NMR spectra for a mixture of a carbon fiber and n-alkanes acquired by this method show a shift of the resonance line, which is due to the local structure of the fiber. The utility of this method is discussed on the basis of the (1)H NMR spectra obtained. In addition, the (1)H distribution and the local motion in the structure of the carbon fiber are revealed in view of the (1)H NMR spectra.     

Fast separation and quantification of C60 and C70 fullerenes using thermostated micro thin-layer chromatography.

Thermostated micro planar chromatography was applied for systematic separation studies of C60 and C70 fullerenes using n-alkanes as mobile phases on TLC and HPTLC plates coated with polyamide, silica gel, aluminum oxide as well as two types of octadecylsilica (C18) sorbents. Retention data were collected at constant temperature at 20 degrees C (+/-0.05 degrees C) using an unsaturated chamber mode with an eluent, such as n-pentane, n-hexane and n-heptane. The separation results under both saturated and unsaturated chamber modes for selected mobile/stationary phases were also examined, and several parameters, including separation factor (alpha) and resolution (R(S)), were compared with data obtained with high-performance liquid chromatography conditions. Interestingly, C60/C70 fullerenes separation performed on HPTLC plates with a developing distance of 45 mm was better for those observed on a 25 cm length analytical HPLC column under similar conditions to that on carbon coverage of the stationary phase, n-hexane as the mobile phase and separation temperature (R(S) = 1.84 and 1.68 for HPTLC, and HPLC, respectively). Moreover the advantage of the planar chromatographic separation of fullerenes studied is a short elution time of less than 6 min. Furthermore, the reported separation protocol shows a capability for the evaluation of fullerenes quantity in commercial samples.     

High-pressure vibrational properties of polyethylene

The pressure evolution of the vibrational spectrum of polyethylene was investigated up to 50 GPa along different isotherms by Fourier-transform infrared and Raman spectroscopy and at 0 K by density-functional theory calculations. The infrared data allow for the detection of the orthorhombic Pnam to monoclinic P2(1)∕m phase transition which is characterized by a strong hysteresis both on compression and decompression experiments. However, an upper and lower boundary for the transition pressure are identified. An even more pronounced hysteresis is observed for the higher-pressure transition to the monoclinic A2/m phase. The hysteresis does not allow in this case the determination of a well defined P-T transition line. The ambient structural properties of polyethylene are fully recovered after compression/decompression cycles indicating that the polymer is structurally and chemically stable up to 50 GPa. A phase diagram of polyethylene up to 50 GPa and 650 K is proposed. Analysis of the pressure evolution of the Davydov splittings and of the anomalous intensification with pressure of the IR active wagging mode provides insight about the nature of the intermolecular interactions in crystalline polyethylene.     

Hydropyrolysis as a preparative method for the compound-specific carbon isotope analysis of fatty acids

Compound-specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry is an effective and risk-free means of investigating fatty acid metabolism. Straightforward analysis, however, leads to poor chromatographic resolution, while derivatization adds carbon thereby corrupting the starting stable isotopic composition. Hydropyrolysis is a new approach which defunctionalizes fatty acids to yield the corresponding n-alkanes thus retaining the carbon skeleton intact and improving chromatography, allowing the faithful measurement of carbon isotope ratios.     

Solvation enthalpies and heat capacities of n-alkanes in four polymer phases by capillary gas chromatography

Molar solvation enthalpy (deltasol H(o)298) and molar heat capacity changes (deltasol C(o)p) were determined by gas chromatography for the C6-C12 n-alkanes on four preferred stationary phases (100% polydimethyl siloxane, 50% diphenyl-50% dimethyl polysiloxane, 50% trifluoropropyl methylsiloxane, and polyethylene glycol) in commercial FSOT. Statistical evaluation indicated the temperature independence of deltasol C(o)p in the range 303-393 K. Deltasol H(o)298 depends linearly on the number of carbon atoms in the n-alkanes, but no linearity could be established for deltasol C(o)p of higher homologues on polar columns, which may be due to a more ordered state on the liquid phase. The homologues for which a linear temperature dependence exists demonstrated that deltasol C(o)p is related linearly to the van der Waals volume and the temperature derivative of the density of the stationary phase. The results are consistent with a simple physical explanation at the molecular level.     

Molecular simulation and macroscopic modeling of the diffusion of hydrogen, carbon monoxide and water in heavy n-alkane mixtures

The self-diffusion coefficient of hydrogen (H(2)), carbon monoxide (CO) and water (H(2)O) in n-alkanes was studied by molecular dynamics simulation. Diffusion in a few pure n-alkanes (namely n-C(8), n-C(20), n-C(64) and n-C(96)) was examined. In addition, binary n-C(12)-n-C(96) mixtures with various compositions as well as more realistic five- and six-n-alkane component mixtures were simulated. In all cases, the TraPPE united atom force field was used for the n-alkane molecules. The force field for the mixture of n-alkanes was initially validated against experimental density values and was shown to be accurate. Moreover, macroscopic correlations for predicting diffusion coefficient of H(2), CO and H(2)O in n-alkanes and mixtures of n-alkanes were developed. The functional form of the correlation was based on the rough hard sphere theory (RHS). The correlation was applied to simulation data and an absolute average deviation (AAD) of 5.8% for pure n-alkanes and 3.4% for n-alkane mixtures was obtained. Correlation parameters vary in a systematic way with carbon number and so they can be used to provide predictions in the absence of any experimental or molecular simulation data. Finally, in order to reduce the number of adjustable parameters, for the n-alkane mixtures the "pseudo-carbon number" approach was used. This approach resulted in relatively higher deviation from MD simulation data (AAD of 18.2%); however, it provides a convenient and fast method to predict diffusion coefficients. The correlations developed here are expected to be useful for engineering calculations related to the design of the Gas-to-Liquid process.     

On the irrelevance of electrostatics for the crystal structures and polymorphism of long even n-alkanes

It is known that the experimental triclinic crystal structures of even n-alkanes are not well reproduced upon energy minimization with current force fields. The inclusion of electrostatics does not solve this, and, moreover, some charge schemes show unphysical features such as positively charged carbon atoms or charge alternation. The effect of the electrostatics on the energies of the crystal structures of the even n-alkanes, and thereby on their polymorphism, has never been established. A new charge scheme is introduced that yields physically sensible charges without constraints. It will also be shown, however, that electrostatics are relevant neither for the structures of the crystals, nor for their energies.     

Phase behaviour of three homologues of the discotic hexa-n-alkoxyanthraquinones under pressure

The phase transition behaviour of three homologous discotic mesogens, the hexa-n-alkoxyanthraquinones HOAQ(n), n indicating the number of carbon atoms in the alkoxy group, was investigated under hydrostatic pressures up to 500 MPa using a high pressure differential thermal analyser. The T vs. P phase diagrams of HOAQ(6), HOAQ(8) and HOAQ(9) were constructed for solution- (Cr₀) and melt-crystallized (Cr₁) samples of the compounds. HOAQ(6) shows the reversible Cr₀-rectangular columnar phase (Col_r)-hexagonal columnar phase (Col_h)-isotropic liquid (I) phase sequence at atmospheric pressure. The stable Col_r phase of HOAQ(6) has a decreased temperature range with increasing pressure and then the Col_r phase disappears under pressures above about 350 MPa; instead the Cr₀-Col_h-I phase sequence is exhibited. For HOAQ(8), the solution-grown sample exhibits the stable Cr₀-Col_h-I phase sequence at atmospheric pressure. Applying pressure to the solution-grown sample induces the formation of the stable Col_r phase in the pressure region between 10 and 350 MPa, leading to the Cr₀-Col_r-Col_h-I phase sequence. The pressure-induced Col_r phase disappears under higher pressures. The melt-cooled sample of HOAQ(8) shows the formation of the metastable crystal (Cr₁), unknown mesophase (X) and Col_r phases at lower temperatures under atmospheric pressure, and exhibits the reversible Cr₁-X-Col_r-Col_h-I phase sequence on subsequent thermal cycles. The metastable phase sequence was observed under pressures up to 100 MPa, but the phase transitions were too small to be detected under higher pressures. In HOAQ(9) the stable Cr₀-Col_h-I phase sequence is observed at all pressures, while the melt-cooled sample shows the metastable Cr₁-Col_r-Col_h-I phase sequence under pressures up to 300 MPa. The metastable Col_r phase disappears under higher pressures.