The thermodynamic characteristics of vaporization in the NaI-PrI<Subscript>3</Subscript> system

The vaporization of the NaI-PrI₃ quasi-binary system was studied by high-temperature mass spectrometry over the whole concentration range. At 623–994 K, saturated vapor contained not only (NaI) _n and (PrI₃) _n molecules (n = 1, 2) and Na⁺(NaI) _n (n = 0–4) and I^?(PrI₃) _n (n = 1–2) ions but also mixed molecular and ionic associates recorded for the first time (NaPrI₄, Na₂PrI₅, NaPrI ₃ ⁺ , Na₂PrI ₄ ⁺ , Na₃PrI ₅ ⁺ , Na₄PrI ₆ ⁺ , NaPrI ₅ ^? , and NaPr₂I ₈ ^? ). The partial vapor pressures of molecules were calculated, and the equilibrium constants of the dissociation of neutral and charged associates were measured. The enthalpies of molecular and ion-molecular reactions were determined, and the enthalpies of formation of gaseous molecules and ions were obtained.     

The thermodynamic characteristics of diethylzinc-diethylsulfur solutions

The p-T-x dependences for diethylsulfur and diethylzinc-diethylsulfur solutions were studied. The enthalpies and entropies of vaporization were determined, and the composition of the vapor phase calculated. It was shown that S(C₂H₅)₂ existed as monomers in the vapor phase. The component activity coefficients and excess Gibbs energies were obtained. The structures formed in solution were shown to be solvato complexes; specific intermolecular interactions in them involved the essentially lone 2s ²(c) electron pair of five-coordinate carbon. The energies of specific intermolecular interactions in the structures of solvato complexes decreased in the series \(D_{Zn \to S} (11.50) > D_{Zn - C_2 H_5 \to Zn} (9.70) > D_{S - C_2 H_5 \to S} (8.72) > D_{Zn - C_2 H_5 \to C_2 H_5 \to S} \)(4.5 kJ/mol).     

The thermodynamic characteristics of natural iron-lithium micas

A thermochemical study of natural lithium micas, iron-containing polylithionite and lepidolite, was performed on a high-temperature heat-flux Calvet microcalorimeter (Setaram, France). Melt solution calorimetry was used to measure the enthalpies of mineral formation from the elements Δ_f H°_el (298.15 K), ?5989.3 ± 9.6 and ?5981.3 ± 6.3 kJ/mol, respectively. The drop method was used to determine the enthalpy increments heating of the micas over the temperature interval 444–973 K. The equations for the temperature dependences of the heat capacities and enthalpies of Fe-polylithionite and Fe-lepidolite were obtained. The S° (298.15 K) and Δ_f G°_el (298.15 K) values were estimated. The thermodynamic functions of the micas were calculated over the temperature range 298.15–1000 K.     

The thermodynamic characteristics of aggregation of fine-dispersed palladium

The size-dependent effects of the heterogeneous reaction PdCl₄²⁻ + 2e = Pd⁰ + 4Cl⁻ were studied in hydrochloric acid solutions of H₂PdCl₄ at 40–70°C. Changes in the structural characteristics of palladium black were analyzed by transmission electron microscopy and X-ray diffraction. The temperature dependence of the redox potential of the PdCl₄²⁻/Pd⁰ pair was used to determine the thermodynamic characteristics of aggregation of fine-dispersed palladium. The heat effect of the reaction was in satisfactory agreement with direct differential scanning calorimetry measurements.     

The thermodynamic characteristics of sublimation of chromium trichloride

The sublimation of stoichiometric chromium trichloride was experimentally studied by the static method of vapor pressure measurements. The main reaction was found to be CrCl₃(cr) = CrCl₃(g). The enthalpy and entropy of this reaction were calculated. Sublimation was also performed in the presence of excess chlorine. The thermodynamic characteristics of the reaction 2CrCl₃(g) + Cl₂ = 2CrCl₄(g) were estimated.     

The thermochemical characteristics of vaporization and formation of organic three-coordinate arsenic derivatives

The experimental data on the enthalpies of vaporization and formation of more than 30 three-coordinate arsenic derivatives of various structures were collected and analyzed. The group contributions of arsenic-containing fragments to the enthalpies of vaporization and formation were calculated. This opens up the possibility of calculating the fundamental thermochemical characteristics of a wide range of As(III) derivatives by the additive scheme.     

The thermodynamic characteristics of sublimation of fenamate molecular crystals

The temperature dependences of vapor pressure were determined by the transpiration method and the thermodynamic functions of sublimation were calculated for six molecular crystals from the group of nonsteroidal antiinflammatory drugs, for niflumic, flufenamic, tolfenamic, mefenamic, and N-phenylanthranylic acids and diphenylamine. The influence of substituents on the enthalpies of sublimation of compounds of this class was studied. A correlation was observed between the enthalpies of sublimation under standard conditions and the temperatures of fusion.     

The thermodynamic characteristics of 15-pentadecanolide and 16-hexadecanolide

Combustion calorimetry was used to determine the enthalpies of formation of 15-pentadecanolide (I) and 16-hexadecanolide (II). The temperature dependences of vapor pressure of lactones and the enthalpies of vaporization were determined by the transpiration method. Differential scanning calorimetry measurements were performed to find the temperatures and enthalpies of fusion of lactones. Conformational analysis and quantum-chemical calculations of the structural, vibrational, and energy characteristics of stable conformers of I were performed. The molecular and spectral data were used to calculate the thermodynamic properties of I in the ideal gas state. An explanation was suggested of the special features of changes in the enthalpies of vaporization in the series of unsubstituted lactones as the size of their rings increased.     

The thermodynamic characteristics of ferrocene alkyl and acyl derivatives

The heat capacity of iso-butylferrocene C₅H₅FeC₅H₄-C₄H₉-i was measured over the temperature range 7–372 K in an adiabatic vacuum calorimeter. Substance purity and the thermodynamic characteristics of fusion (temperature, enthalpy, and entropy) were determined. Saturated vapor pressures and the enthalpies of vaporization of n-propylferrocene C₅H₅FeC₅H₄-C₃H₇-n, propionylferrocene C₅H₅FeC₅H₄-COC₂H₅, and iso-butylferrocene were measured by the dynamic method of substance transfer in an inert gas flow. The entropy, enthalpy, and Gibbs energy of the substances in the ideal gas state at 298.15 K were calculated. The thermodynamic values obtained in this work and reported in the literature for ferrocene alkyl and acyl derivatives were critically analyzed. The mutual consistency of the data on both homologous series was checked.     

The thermodynamic characteristics of formation of nanoparticles from supercritical solvents

A thermodynamic model for calculating equilibria and the phase states of fluid-solid systems over wide temperature, pressure, and composition ranges was suggested. Calculations were performed to determine the parameter regions where a substance was isolated in the form of a solid depending on the chemical composition of the initial mixture and the amounts of and ratio between the solvent and antisolvent in it. The calculations were performed for a model system containing ethanol, carbon dioxide, and phenanthrene. The rapid expansion of this supercritical fluid was simulated to model the conditions of the formation of a solid (phenanthrene) and nanoparticles based on it. It was shown that the selection of the state parameters of the supercritical mixture determined the optimum conditions of solid state formation as the fluid expanded.     

Etching characteristics of GaN by plasma chemical vaporization machining

A high‐quality bulk gallium nitride (GaN) substrate, which is suitable for high‐quality homoepitaxial growth, is indispensable for realizing high‐performance GaN devices. With improvement in the quality of the bulk GaN substrate, the removal of subsurface damage induced during surface polishing has become increasingly necessary. To remove the subsurface damage from the bulk GaN substrate, a chemical finishing method that does not produce further damage is required. We applied plasma chemical vaporization machining (CVM) to remove the subsurface damage from the bulk GaN substrate. In this study, we investigated the etching characteristics of GaN by plasma CVM applying atmospheric pressure Cl₂/He plasma. The maximum removal rate in the depth direction by plasma CVM was 9100 nm/min, which is seven times greater than that of reactive ion etching (RIE). The activation energy in plasma CVM was estimated to be 2.1 kcal/mol, which is 1.75 times greater than that in RIE. It is supposed that some of the energy required for the removal reaction in RIE is supplied by ion bombardment, but plasma CVM depends on only a chemical reaction without high‐energy ion collision. This result suggests that plasma CVM is a finishing method that causes less subsurface damage than RIE. Copyright © 2008 John Wiley & Sons, Ltd.     

Solubility products,thermodynamic functions and stability constants for the praseodymium and ytterbium fluoride — Water systems

The solubility products and thermodynamic functions for the praseodymium and ytterbium fluoride-water systems have been measured using different analytical techniques for comparison among the measured values as well as with values reported in literature. Although there is not much difference among our values obtained by potentiometric, conductometric and radiometric methods, the values for PrF₃ disagree with at least two of the reported values. The effects of precipitant, aging of the precipitate and pH of the saturated solutions on the solubility product were studied and found to be significant. The standard enthalpy and free energy changes for the dissolution of both fluorides were found to be positive although the enthalpy for YbF₃ is about twice as high as that for PrF₃. The standard entropy change for PrF₃ is negative, but that for YbF₃ is positive. The overall stability constants for the mono- and difluoride complexes of both Pr and Yb have also been measured potentiometrically using a simplified approach.     

Structural and thermodynamic characteristics of amide solvents

The structural and thermodynamic characteristics of amide solvents are calculated with different types of molecular self-assembly through hydrogen bonding. Under a model-based approach, the specific and nonspecific components of the total energy of intermolecular interactions are identified for primary, secondary, and tertiary amides of carboxylic acids. It is found that similarly to water, primary amides have a network of hydrogen bonds and belong to the class of liquids characterized by an increase in nonspecific interactions with temperature. In secondary amides with the chain self-assembly, the contribution of these interactions is practically independent of temperature, and in tertiary amides it decreases with an increase in temperature. The molar values of the specific and nonspecific components are used to analyze the intermolecular interactions and the structural properties of amides with different degrees of N-substitution.     

The thermodynamic characteristics of formation of vacancies in carbon subgroup element crystals

A method for calculating the parameters of formation of vacancies in crystals formed by spherically symmetrical atoms was developed. Both quantum effects at low temperatures and the possibility of the delocalization of atoms at high temperatures were studied. The parameters of formation of vacancies in carbon subgroup element crystals C-diam, Si, Ge, α-Sn, and Pb were calculated. The inclusion of the delocalization of atoms was shown to increase the enthalpy, entropy, and volume of vacancy formation. At low temperatures, the parameters of vacancy formation were found to depend strongly on the temperature, and the entropy of vacancy formation became negative. At high temperatures, close agreement with experimental data and theoretical estimates reported by other authors was obtained. The temperature dependence of vacancy parameters was studied for diamond heated isobarically from 100 to 4500 K. The applicability scope of the Arrhenius equation with a temperature-independent activation energy is discussed. The validity of the “compensation rule” (correlation between the entropy and enthalpy of vacancy formation) was demonstrated. It was also shown that the volume and entropy of vacancy formation were correlated over the whole temperature range studied.

     

Thermal decomposition of praseodymium acetate as a precursor of praseodymium oxide catalyst

Thermal events encountered throughout the heat treatment of praseodymium acetate, Pr(CH₃COO)₃·H₂O, were studied in nitrogen and air atmospheres. The samples calcined at the 300–700 °C temperature range were characterized using XRD, IR and N₂ adsorption. Moreover, in situ electrical conductivity was employed to follow up the formation of the different decomposition intermediates. The results indicated that the anhydrous salt decomposes to the final product, PrO_1.833, through the formation of the following intermediates: Pr(OH)(CH₃COO)₂, PrO(CH₃COO) and Pr₂O₂(CO₃). PrO_1.833 formed at 500, 600, and 700 °C possesses a surface area of 17, 16 and 10 m²/g and crystallites size of 14, 17 and 30 nm, respectively.     

The connection between the optical and thermodynamic characteristics of transition metal compounds

The energy of stabilization of the crystal field (ESCF) for the MX₆ group may be calculated from thermodynamic and from optical data. Values of ESCF obtained from thermodynamic data are always greater than the corresponding values calculated from optical data. The reason for these deviations lies in the inaccuracy of the existing equation for evaluating ESCF from thermodynamic data. The two means arrived at for evaluating ESCF are in agreement with each other if a correction is introduced into the equation for the nonlinear character of the change in the ionic radii of the transition elements by using the correlation radii suggested in this paper. Correlation radii have been found for the bivalent ions of manganese, iron, cobalt, nickel, and copper. An equation has been proposed for evaluating the coulomb integrals and the effective charges on the metal atoms in MX₆ groups, based upon spectroscopic data (using the parameters D_q). The coulomb integrals and the effective charges on the metal atoms have been calculated in the complexes M(H₂O) ₆ ²⁺ (where M=Fe, Co, Ni), M (NH₃) ₆ ²⁺ (where M=Co, Ni), and NiF ₆ ⁴ . On the basis of these data the effective bondings characterizing the difference in the thermodynamic stability of the complexes considered have been calculated.Communication to the Symposium on Quantum Chemistry, Palanga, June 1965.     

Correlation of the thermodynamic characteristics of polymorphic crystals

Analytical expressions for the correlation of volume and entropy, isobaric heat capacity, volume thermal expansion, and the compressibility of crystalline phases are obtained. The pair correlations of the above values and their correlation with the geometrical characteristics of the solid-phase equilibrium line (including the neighborhood of a triple point) are described using the obtained expressions. An analytical form for the correlation of the characteristics of polymorphic crystal polar modification is found.     

Calculation of the crystal field parameters of praseodymium ethyl sulfate and praseodymium trichloride

A method of applying the extended Hückel molecular orbital method for the evaluation of crystal field parameters in the rare earth compounds is presented. The charge distribution in the crystal field and the effect of the outer coordinated sphere on the calculation of the crystal field parameters is discussed. From the calculated charge distribution, the crystal field parameters A₂₀r², A₄₀r⁴, A₆₀r⁶, and A₆₆r⁶ of praseodymium ethyl sulfate crystal and praseodymium trichloride crystal have been obtained. The calculated results are in agreement with the experimental data. Some possible sources of the error in the calculation are discussed.