Temperature-pressure phase diagram of a D2O-D2 system at pressures to 1.8 kbar

Using a volumetric technique, the deuterium solubility, X, in heavy water (L), low-pressure hexagonal ice (I h), and high-pressure cubic clathrate ice (sII) is studied at deuterium pressures up to 1.8 kbar and temperatures from -40 to +5 degrees C. The triple point of the L + I(h) + sII equilibrium is located at P = 1.07(3) kbar and T = -4.5(8) degrees C. The molar ratios D2/D2O of phases at the triple point are X(L) = 0.020(5), X(Ih) = 0.012(5), and X(sII) = 0.207(5).     

Contribution to the phase diagram of the system PbCl2-AgCI

The side parts of the phase diagram of the binary system PbCl₂-AgCl were studied by using DTA. The only miscibility was found on the silver chloride side up to a concentration of 1.5±0.5 mole% PbCl₂. No solid solution of AgCl in PbCl₂ was observed on the lead chloride side.

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Zusammenfassung Mittels DTA wurden die Randzonen des Phasendiagrammes des binären Systemes PbCl₂-AgCl untersucht. Mischbarkeit konnte lediglich auf der Silberchloridseite bis zu einer Konzentration von 1.5±0.5 mol% mol% PbCl₂ festgestellt werden. Auf der Bleichloridseite konnten keinerlei Mischkristalle zwischen AgCl und PbCl₂ beobachtet werden.

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PbCl₂-AgCl. 1,5±0,5 %. .

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We are very grateful to our colleagues Dr E. Krová and Dr Z. Pokorná for the preparation of the single-crystals and for the chemical analysis.     

Experimental determination of the H2SO4/(NH4)2SO4/H2O phase diagram

We have experimentally investigated the water and sulfuric acid-rich regions of the H2SO4/(NH4)2SO4/H2O ternary liquid/solid phase diagram using differential scanning calorimetry (DSC) and infrared spectroscopy of thin films. We present the liquid/solid ternary phase diagram for temperatures below 373 K and H2SO4 concentrations below 60 wt %. We have determined two ternary eutectics and two tributary reaction points for this system in the regions studied. It is also seen that sulfuric acid tetrahydrate (SAT) forms as a metastable solid over a large concentration range. Two true binary systems have been identified: ice/letovicite and SAT/ammonium bisulfate. Finally, we have compared our results to the predictions of the aerosol inorganics model and have found significant differences both in the final melting points and in the location of some of the phase boundaries including a significant discrepancy in the invariant points predicted versus those observed.     

Activity coefficients of water and sulfolane from the solid + liquid phase diagram

The solid + liquid phase diagram drawn from thermal analysis is presented. It exhibits a eutectic at x₂ = 0.303 and T = 262.2 K and precludes the existence of definite compounds between the two components. Mixed crystals are observed in the sulfolane-rich region. The activity coefficients of water, f_{x, 1}, and of sulfolane, f_{x, 2}, are calculated from the initial freezing points of water. Log f_{x, 1} and log f_{x, 2} show a steady dependence on volume composition, providing evidence for the supposition that strongly self-associated water and monomer sulfolane scarcely interact with one another, and that the thermodynamic properties of the mixtures should rather be related to steric factors.     

The phase diagram and supercooling conditions for the Ca(NO3)2−CaCl2−H2O system

The liquidus temperature and induction periods were measured for crystallization in a system of calcium nitrate, calcium chloride, and water over a concentration range of 5–20 mole% Ca(II), i.e., R=4–18 [R=moles H₂O/moles Ca(II)] and y_cl=0–1 [y_cl=moles Cl^–/moles (NO ₃ ^– +Cl^–)]. A ternary phase diagram was constructed, and qualitative dependences of the supercooling at which the solution began to crystallize on the system composition were found. A wide range of stability toward crystallization was found for solutions withR=4–10 and y_cl=0–0.7 The relationships between the system stability toward crystallization and the viscosity, glass-transition temperature, and the liquidus temperature are discussed.     

Electron spin resonance study on H6+, H5D+, H4D2+, and H2D4+ in solid parahydrogen

We carried out an electron spin resonance (ESR) study on hydrogen ion radicals produced by radiolysis of solid para-H(2). In addition to quartet ESR lines proposed to be H(2) (+)-core H(6) (+) (D(2d)) ions in solid para-H(2) [T. Kumada et al., Phys. Chem. Chem. Phys. 7, 776 (2005)], we newly observed totally more than 50 resolved lines in gamma-ray irradiated solid para-H(2)-ortho-D(2) (1 mol %) and para-H(2)-HD (1 mol %) mixtures. We assigned these lines to be isotope substituents of H(2) (+)-core H(6) (+) ions such as H(5)D(+), H(4)D(2) (+), and H(2)D(4) (+) throughout the comparison of their ESR parameters with theoretical results. These results provide a conclusive evidence that H(2) (+)-core H(6) (+) ions are generated in irradiated solid hydrogens. Analysis of the EPR spectrum and ab initio calculations predicts D(2d) symmetry of the H(6) (+) ions, whereas a lowering symmetry (D(2d)-->C(2v)) induced by asymmetric nuclear wave function is observed in H(5)D(+) and H(4)D(2) (+). We also observed isotope-substitution reactions such as H(6) (+)+D(2)-->H(4)D(2) (+)+H(2) and H(6) (+)+HD-->H(5)D(+)+H(2), which are analogous to the well-known isotope-condensation reactions of H(3) (+) in dark nebula, H(3) (+)+HD-->HD(2) (+)+H(2) and HD(2) (+)+HD-->D(3) (+)+H(2).     

3-D phase diagram of HPC/H2O/H3PO4 tertiary system

A 3-D phase diagram of the HPC/H₂O/H₃PO₄ tertiary system against various temperatures was established. Four distinct phases—the completely separated phase (S), the cloudy suspension phase (CS), the liquid crystalline miscible phase (LC), and the isotropically miscible phase (I)—were identified. The S phase shrank as the temperature increased, revealing that the HPC solubility increased with temperature, regardless of the LCST (lower critical solution temperature) characteristic. The addition of H₃PO₄ suppressed the formation of LC phase. However, as the temperature was raised sharply from 50 to 70?°C, the LC phase could only be maintained at high H₃PO₄ concentration region; it was a triangular shape, and the top apex of the triangle was the temperature-invariant L* point (HPC/H₂O/H₃PO₄ 38/9/53?wt%). The CS phase expanded considerably into the H₂O-rich but H₃PO₄-poor region when the temperature continued to increase over 48?°C. The LCST points of the CS phase that contained 0 and 15?wt% of H₃PO₄ were 34 and 38?°C, respectively. These CS results demonstrate that H₃PO₄ suppresses the occurrence of LCST behavior. Additionally, the binodal curve exhibits a weak or even zero dependence of binodal temperature on the HPC concentration at HPC concentrations of less than 30?wt% in a pure water system. A hypothesis concerning the sequential desorption of water molecules was proposed to explain such behavior.     

Formation of continuous solid solutions near the minimum point of a phase diagram

A model of structure ordering in alloys of the compositions corresponding to the minimum points of phase diagrams with continuous series of solid solutions was proposed based on calculating the concentration dependence of the energy of mixing and the results of X-ray powder diffraction study of solid solutions in the systems Sb-As, Sb₂Se₃-Bi₂S₃, and Cu-Mn.     

T-x diagram and transport properties of the GeSe-GeI2 solid electrolyte

The T-x diagram for the GeSe-GeI₂ system was plotted based on DTA, XRD, and conductivity data. The diagram features a simple eutectic and a limited region of solid solutions with prevalent GeSe content. It was established that, in the region of solid solutions, the properties of the GeSe-GeI₂ solid electrolyte are substantially dependent on the concentration of the GeI₂ dopant. The highest conductivity (10^?3?10^?4 S/cm at 150°C), lowest activation energy of electric conduction (0.3–0.4 eV), and lowest electronic (hole) transport numbers (10^?5?10^?7 at 150°C) at high ionic (～1.0) and cationic (0.9–1.0) transport numbers were observed at a GeI₂ concentration of 3–6 mol %. In the two-phase region, the transport properties (conductivity and activation energy of conduction) only slightly depend on the dopant concentration.     

Phase diagram of the B-B2O3 system at 5 GPa: experimental and theoretical studies

X-ray diffraction with synchrotron radiation has been used to study in situ the chemical interaction of beta-rhombohedral boron with boron (III) oxide and phase relations in the B-B2O3 system at pressures up to 6 GPa in the temperature range from 300 to 2800 K. The B-B2O3 system has been thermodynamically analyzed, and its equilibrium phase diagram at 5 GPa has been constructed. Only one thermodynamically stable boron suboxide, B6O, exists in the system. It forms eutectic equilibria with boron and B2O3.     

Tunneling chemical reactions D + H2 --> DH + H and D + DH --> D2 + H in solid D2-H2 and HD-H2 mixtures: an electron-spin-resonance study

Tunneling chemical reactions D + H2 --> DH + H and D + DH --> D2 + H in solid HD-H2 and D2-H2 mixtures were studied in the temperature range between 4 and 8 K. These reactions were initiated by UV photolysis of DI molecules doped in these solids for 30 s and followed by measuring the time course of electron-spin-resonance (ESR) intensities of D and H atoms. ESR intensity of D atoms produced by the photolysis decreases but that of H atoms increases with time. Time course of the D and H intensities has the fast and slow processes. The fast process, which finishes within approximately 300 s after the photolysis, is assigned to the reaction of D atom with one of its nearest-neighboring H2 molecules, D(H2)n(HD)(12-n) --> H(H2)(n-1)(HD)(13-n) or D(H2)n(D2)(12-n) --> H(HD)(H2)(n-1)(D2)(12-n) for 12 > or = n > or = 1. Rate constant for the D + H2 reaction between neighboring D atom-H2 molecule pair is determined to be (7.5 +/- 0.7) x 10(-3) s(-1) in solid HD-H2 and (1.3+/-0.3) x 10(-2) s(-1) in D2-H2 at 4.1 K, which is very close to that calculated based on the theory of chemical reaction in gas phase by Hancock et al. [J. Chem. Phys. 91, 3492 (1989)] and Takayanagi and Sato [J. Chem. Phys. 92, 2862 (1990)]. This rate constant was found to be independent of temperature up to 7 K within experimental error of +/-30%. The slow process is assigned to the reaction of D atom produced in a cage fully surrounded by HD or D2 molecules, D(HD)12 or D(D2)12. This D atom undergoes the D + DH reaction with one of its nearest-neighboring HD molecules in solid HD-H2 or diffuses to the neighbor of H2 molecules to allow the D + H2 reaction in solid HD-H2 and D2-H2. The former is the main channel in solid HD-H2 below 6 K where D atoms diffuse very slowly, whereas the latter dominates over the former above 6 K. Rate for the reactions in the slow process is independent of temperature below 6 K but increases with the increase in temperature above 6 K. We found that the increase is due to the increase in hopping rate of D atoms to the neighbor of H2 molecules. Rate constant for the D + DH reaction was found to be independent of temperature up to 7 K as well.     

Contribution to the study of the Al-Zn phase diagram

Calorimetric measurements in the AI-Zn system rule out the existence of anα″-phase and of a second monotectoid reaction at 340?.     

Application of DTA and TG to studies of the CaCO3-CaF2 phase diagram

A new method (based on DTA and TG) for the determination of the eutectic composition is proposed for systems in which one of the components is unstable in the vicinity of the eutectic melting temperature. The eutectic composition established by means of this method for the CaCO₃-CaF₂ system is in very good agreement with the results obtained in a classical way.

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Zusammenfassung Eine neue Methode zur Bestimmung der eutektischen Zusammensetzung von Systemen, deren eine Komponente in der Nähe der eutektischen Temperatur instabil ist, beruht auf der simultanen TG-Messung. Mit der vorgeschlagenen Methode wird die eutektische Zusammensetzung des Systems CaF₂-CaCO₃ in sehr guter Übereinstimmung mit den Ergebnissen klassischer Untersuchungen gefunden.

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, . , CaCO₃-CaF₂, , .

     

High pressure-temperature Raman measurements of H2O melting to 22 GPa and 900 K

The melting curve of H(2)O has been measured by in situ Raman spectroscopy in an externally heated diamond anvil cell up to 22 GPa and 900 K. The Raman-active OH-stretching bands and the translational modes of H(2)O as well as optical observations are used to directly and reliably detect melting in ice VII. The observed melting temperatures are higher than previously reported x-ray measurements and significantly lower than recent laser-heating determinations. However, our results are in accord with earlier optical determinations. The frequencies and intensities of the OH-stretching peaks change significantly across the melting line while the translational mode disappears altogether in the liquid phase. The observed OH-stretching bands of liquid water at high pressure are very similar to those obtained in shock-wave Raman measurements.     

Calculation of the brillouin frequencies close to phase transitions in NaNO2.

We calculate here the Brillouin frequencies of the L-mode [010], [001] and [100] of NaNO2 for the phase transitions from the paraelectric phase to the sinusoidal anti-ferroelectric phase near the Neel temperature (TN = 437.7 K) and to the ferroelectric phase near the critical temperature (TC = 436.3 K) in this crystalline system. For calculating the frequencies. we use the thermal expansivity data for the phase regions considered, under the assumption that the mode Gruneisen parameter determined for each mode remains constant across the phase transitions. Our calculated frequencies agree well with the observed frequencies for the modes studied in NaNO2.     

Ab initio thermodynamics and phase diagram of solid magnesium: a comparison of the LDA and GGA

The finite temperature density functional theory and quasiharmonic lattice dynamics have been used to compute numerous thermodynamic properties of hexagonal close packed magnesium using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation potential. Generally, it is found that there exist only minor differences between the LDA and GGA computed properties, with both giving good agreement with experiment. The hcp-bcc phase boundary has also been computed and is found to be in agreement with experimental observation. Again, only slight differences are found between the LDA and GGA.     

Subsolidus phase diagram of the binary system (n-C n H2n+1NH3)2CoCl4

The perovskite-type layered compounds decylammonium tetrachlorocobaltate (n-C₁₀H₂₁NH₃)₂CoCl₄ and dodecylammonium tetrachlorocobaltate (n-C₁₂H₂₅NH₃)₂CoCl₄ exist the solid–solid phase transition in the temperatures range 330–380 K. These laminar materials contain bilayers sandwiched between metal halide layers. The experimental subsolidus binary phase diagram of (n-C₁₀H₂₁NH₃)₂CoCl₄–(n-C₁₂H₂₅NH₃)₂CoCl₄ has been established over the whole composition range by differential thermal analysis and X-ray diffraction. In the phase diagram, one intermediate compound (n-C₁₀H₂₁NH₃) (n-C₁₂H₂₅NH₃)CoCl₄ at $ W_{{{\text{C}}_{ 1 0} {\text{Co}}}} \% = 50. 9 2 $ and two eutectoid invariants points at $ W_{{{\text{C}}_{ 10} {\text{Co}}}} \% = 2 9. 8 3 $ and $ W_{{{\text{C}}_{ 10} {\text{Co}}}} \% = 7 7. 9 8 $ were observed, two eutectoids temperatures are about 343 ± 1 and 340 ± 1 K. There are three noticeable solid solution ranges (α, β, γ) at the left and right boundary and middle of the phase diagram.     

The spin-orbit transition of atomic chlorine in solid H2, HD, and D2

Essential to understanding the reaction dynamics of spin-orbit (SO) excited atomic chlorine (2P1/2) with molecular hydrogen is experimental measurements of the SO splitting of Cl in the van der Waals region of the entrance channel to reaction. Here we report high-resolution direct absorption studies of the SO transition (2P1/2<--2P3/2) of atomic chlorine isolated in solid molecular hydrogen (H2, HD, and D2).     

Experimental determination of the NH4NO3/(NH4)2SO4/H2O phase diagram

We have studied the thermodynamic properties of the ammonium nitrate/ammonium sulfate/water system using differential scanning calorimetry and infrared spectroscopy of thin films at low temperatures. This is the first study focused on low temperatures, as previous experimental work on this system has been at 273 K and above. We have combined our experimental results with melting point data from the literature at high temperatures to create a solid/liquid phase diagram of the ammonium nitrate/ammonium sulfate/water system for temperatures below 343 K. Using phase diagram theory and Alkemade lines, we predict which solids are stable at equilibrium for all concentrations within the studied region. We also observed the decomposition of a solid at low temperatures which has not previously been reported. Finally, we have compared our predicted solids and final melting temperatures to the Aerosol Inorganics Model (AIM).     

Phase diagram of the tetramethylammonium heptadecafluorononanoate (TMAHFN)/D2O system as determined by 2H and 14N NMR

The high resolution phase diagram of the tetramethylammonium heptadecafluorononanoate (TMAHFN)/D₂O system has been mapped out using ²H and ¹⁴NNMR spectroscopy. The ¹⁴N quadruple splittings are more than an order of magnitude larger than corresponding ²H splittings, while the line widths are only two to three times larger. Thus, ¹⁴NNMR offers an order of magnitude improvement over ²H NMR in the resolution of the spectra from coexisting phases. The ²H spectra of samples in biphasic regions are often complicated by chemical exchange of D₂O molecules between coexisting phases, particularly at low TMAHFN concentrations. Analysis of the ²H line shapes of a TMAHFN/D₂O sample with a weight fraction of TMAHFN of 0.230 obtained at various times following cooling of the sample into the isotropic/nematic biphasic region shows that the mean diameter for the dispersed nematic droplet grows from about 7 to about 26 μm over a period of 2 h. At a mean droplet size of 7 μm the exchange of TMA⁺ ions between the coexisting phases is slow on the NMR time-scale and exchange effects are not observed in ¹⁴N spectra. The TMAHFN/D₂O phase diagram exhibits the generic form of those of the CsPFO/water and APFO/D₂O systems, which are the only other systems composed of stable discotic micelles for which high resolution phase diagrams are currently available, but the nematic phase is displaced to smaller TMAHFN concentrations. Specifically, a discotic nematic phase N_D⁺, intermediate between an isotropic micellar phase I and a lamellar phase L, exists for weight fractions of TMAHFN between 0.149 (φ = 0.105) and 0.420 (φa = 0.325) and temperatures between 277.3 and 327.6 K.