Literature Thermodynamic Data Research Articles

Why alloying with noble metals does not decrease the oxidation of platinum: a DFT-based ab initio thermo-dynamics study.

Despite its well-known nobility, even platinum is subject to corrosion under the harsh conditions that many technical applications require. Based on the assumption that the platinum loss is mainly caused by the formation of volatile PtO2, alloying is a promising strategy to reduce it. This investigation explores the bulk stability of Pt-Au, Pt-Ir, Pt-Re, Pt-W, Pt-Ag, Pt-Rh, Pt-Cu, Pt-Ni and Pt-Co, as well as their oxides, utilizing density functional theory, as well as ab initio and literature thermodynamic data. The alloy model combines special-quasi random structures with thermodynamic properties interpolated from the constituting metals, which are complemented by the configuration entropy. The results suggest that reducing platinum oxidation by alloying decreases the overall nobility of the alloy, since platinum- and oxygen affinity of the alloying metal are related to each other. Despite this limitation, copper was identified as a promising candidate for stabilizing the platinum catalyst in the Ostwald process.

Temperature Effect in the Babassu (Orbignya speciosa) Oil: A Physico-Chemical Study

Babassu (Orbignya speciosa) is a Brazilian palm with extraordinary importance in socioeconomic and ecologic terms. It is found in humid tropical areas, especially in degraded landscapes. There are several uses for babassu coconut and babassu oil. However, their immense potential for large-scale providing other industrial products still needs to be explored due to the necessity for modern scale planning and deep knowledge of vast spectrum thermodynamic properties. This paper gathers a new experimental physico-chemical study of the temperature effect on two critical properties, density and ultrasonic velocity for babassu oil, due to its rising economic significance and a high potential for intensive farming in regions with low economic resources. We consider how accurately different theoretical prediction methods work due to modern processes, design, and algorithm simulations being strongly computer-oriented. The Agrawal-Thodos equation for density and Collision Factor Theory for ultrasonic velocity was selected, mainly attending to ease of use and range of application. We observed a good response at the studied conditions, despite geometrical simplifications into triglyceride molecules and using estimated critical magnitudes by molecular group contribution approach. A broad comparison was made with disposable open literature thermodynamic data, showing an essential dispersion of data, and highlighting the quality of the experimental data presented in this work.

Dual-capillary dilatometer for density measurements of supercooled water

An apparatus tailored to accurate density measurements of supercooled water, i.e. liquid water in a metastable state below the freezing point temperature, was recently developed at the Institute of Thermomechanics of the Czech Academy of Sciences. The apparatus, dual-capillary dilatometer, is described, together with the measurement procedure and the evaluation methodology. The primary result of the dual-capillary method are relative densities with respect to the density at a reference temperature and given pressure. In order to calculate absolute densities, densities at the reference temperature as a function of pressure are needed. For calculation of such pressure dependence of density, so called thermodynamic integration involving literature thermodynamic data and our experimental results is used. The dual-capillary dilatometer was successfully employed in density measurements of ordinary water, heavy water and seawater. The data in the temperature range from 238.15 to 303.15 K at pressures from atmospheric up to 200 MPa are presented and compared with respective IAPWS formulations of thermodynamic properties. The data for ordinary water are also compared with an accurate equation of state for supercooled water of Holten et al. (2014) revealing good mutual agreement. The expanded uncertainty of relative densities acquired by means of the dual-capillary method is estimated to be lower than 50 ppm.

Thermodynamic properties of liquid Ag-Li alloys

The electrochemical concentration cell method was used in the measurements of the activities of Li in the Ag-Li liquid and solid alloys. Activity measurements were performed with the use of electrochemical cells with liquid LiCl-LiF and LiCl-KCl electrolytes for 9 alloys in the xLi concentration range from 0.1 to 0.9 and at temperatures between 643K and 916K. The linear temperature dependencies of EMF of the Ag-Li alloys were observed and described by the equation EMF(T)=a+bT. The calculated partial thermodynamic functions of Li showed negative deviations from the ideal behaviour. With the application of all the available literature thermodynamic data, the interaction parameters of the Redlich-Kister equation for the liquid Ag-Li phase were worked out with the use of the least square method. The partial and integral Gibbs energies, entropies and enthalpies were calculated and presented in tables and figures. Additionally, the concentration-concentration partial structure factors for the ideal and real Ag-Li solutions were calculated and graphically presented.

Thermochemistry of Ruthenium Oxyhydroxide Species and Their Impact on Volatile Speciations in Severe Nuclear Accident Conditions

Literature thermodynamic data of ruthenium oxyhydroxides reveal large uncertainties in some of the standard enthalpies of formation, motivating the use of high-level relativistic correlated quantum chemical methods to reduce the level of discrepancies. Reaction energies leading to the formation of all possible oxyhydroxide species RuOx(OH)y(H2O)z have been calculated for a series of reactions combining DFT (TPSSh-5%HF) geometries and partition functions, CCSD(T) energies extrapolated to the complete basis set limits. The highly accurate ab initio thermodynamic data were used as input data of thermodynamic equilibrium computations to derive the speciation of gaseous ruthenium species in the temperature, pressure and concentration conditions of severe nuclear accidents occurring in pressurized water reactors. At temperatures lower than 1000 K, gaseous ruthenium tetraoxide is the dominating species, between 1000 and 2000 K ruthenium trioxide becomes preponderant, whereas at higher temperatures gaseous ruthenium oxide, dioxide and even Ru in gaseous phase are formed. Although earlier studies predicted the formation of oxyhydroxides in significant quantities, the use of highly accurate ab initio thermodynamic data for ruthenium gaseous species leads to a more reliable inventory of gaseous ruthenium species in which gaseous oxyhydroxide ruthenium molecules are formed only in negligible amounts.

Thermodynamic properties of compounds in the PdO-H2O system at 25°C

Literature thermodynamic data on species and particles existing in the heterogeneous PdO-H2O system were checked for consistency, and the equilibrium constants for dissolution of palladium oxide and hydroxide in water and for Pd2+ (aq) hydrolysis were recommended. Δ f G 298.15 ° obtained in this work for Pd2+(aq) sharply differs (no less than by 6 kJ/mol) from values that are reported in fundamental thermodynamic reference books and based on experimentally measured palladium electrode potential at 25°C. Detailed examination of literature data on the thermodynamic properties of compounds in the Cl-Pd(aq) system is required to account for revealed inconsistency.

Spectroscopic investigations of Np(V/VI) redox speciation in hyperalkaline TMA-(OH, Cl) solutions

Abstract The redox chemistry of Np(V/VI) was investigated in ∼0.6 M tetramethylammonium hydroxide/chloride (TMA-(OH, Cl)) solutions with 9 ≤ −log [H+] ≤ 13.5. Redox conditions were defined by the absence or presence of ClO− as oxidizing agent (Na-salt, 5 × 10−3 M and 5 × 10−2 M). The high total Np concentration ([Np]tot ∼ 2 × 10−3 M) led to the precipitation of solid phases in some of the samples. The carbonate concentration (as impurity of TMA-OH) was 2–3 × 10−3 M. UV-vis/NIR spectra obtained from the supernatant in TMA-(OH, Cl) solutions and absence of ClO− showed clear Np(V) features, identified as NpO2 +, NpO2CO3 − and (NpO2) x (CO3) y (OH) z x−2y−z . No NIR features were observed within 800 nm ≤ λ ≤ 1300 nm for samples with ClO−. XANES edge energies and features of these samples confirmed the predominance of Np(V) in the absence of ClO− and Np(VI) in the presence of ClO−, by comparison to XANES reference spectra of Np(III/IV/V/VI) prepared within the present work by in-situ electrolysis. A similar Np redox distribution was observed for the solid phases based on XANES and EXAFS measurements. EXAFS spectra indicative of NpVO2OH(s) and NpVIO3· xH2O(s) were obtained for samples in absence and presence of ClO−, respectively. The formation of a Na-Np(VI) phase in 5 × 10−2 M ClO− and −log [H+] ∼ 12 was also indicated from the EXAFS, chemical analysis and SEM-EDS. These results indicate that Np(VI) aqueous species and solid compounds prevail far below the oxidation border of water in alkaline solutions and also far below the E H border calculated with the current NEA data selection [1]. These observations are further supported by correlations of literature thermodynamic data for actinides (U, Np, Pu and Am), which predict the formation of NpO2(OH)3 − and NpO2(OH)4 2− aqueous species with stability constants (log * βº1,3 and log * βº1,4) similar to those available for U(VI).

Experimental investigation and thermodynamic calculation of the Ga–Sb–Zn phase diagram

Phase equilibrium of ternary Ga–Sb–Zn system was investigated by applying CALPHAD method and using literature thermodynamic data for constitutive binary systems. The liquidus surface and isothermal section at 673 K were calculated. Calculated results were verified experimentally on the alloys samples with the compositions corresponding to the characteristic vertical sections: SbZn (1:1)–Ga; GaZn(1:1)–Sb; and GaSb(1:1)–Zn. Phase transitions temperatures were determined by differential thermal analysis and differential scanning calorimetry. Microstructure and phase composition investigation were investigated by using scanning electronic microscopy with energy dispersive spectrometry. The experimental and analytical results showed good agreement, concerning the temperatures of phase transitions and phase compositions of alloys concerned.

Phase relations of nahcolite and trona at high P-T conditions

Using cold-seal hydrothermal bomb and piston-cylinder apparatus, we have carried out both forward and reversal experiments to investigate the phase boundary between nahcolite (NaHCO3) and trona (NaHCO3·Na2CO3·2H2O). We found that the temperature of this phase boundary remains low at least up to 10 kbar, so that this phase transformation maintains its univariant nature in our investigated P-T space. The locus of this phase boundary in a log(pCO2)-T space is defined as log(pCO2) = 0.0240(±0.0001)T − 9.80(±0.06) (with pCO2 in bar and T in K), in excellent agreement with earlier 1 atm experiments at different partial pressures of CO2 (pCO2) and theoretical calculation. Using this equation and literature thermodynamic data, the entropy of trona at 298.15 K is constrained to be 303.8 J mol−1 K−1, essentially identical to earlier estimates from different methods. Our experimental results have also been used to constrain the genesis of nahcolite in some fluid inclusions of diverse origins, and it is suggested that nahcolite in these occurrences is most likely a daughter mineral which crystallized from the fluids as temperature decreased, rather than an accidentally trapped phase.

On the superhydrophobicity of tetrafluoromethane

Tetrafluoromethane, CF 4, is markedly less soluble in water than methane and neopentane around room temperature: it is a superhydrophobic solute. An analysis of the physical origin of this superhydrophobicity is performed, exploiting literature thermodynamic data covering the 5–55 °C temperature range. It results that the CF 4–water dispersion interactions are markedly weaker in magnitude than those of a ‘hypothetical’ hydrocarbon having the same size of tetrafluoromethane, providing a smaller counterbalancing effect of the work spent to create the cavity in water. The weakness of the CF 4–water dispersion interactions is due to the very small polarizability of CF 4, which, in turn, is caused by the strong electronegativity of fluorine atoms.

Application of the simple salt lattice energy approximation to the solubility of minerals

The simple salt approximation for the lattice energy of double salts is used to provide an estimate of their molar solubilities. These calculations are compared with solubilities obtained from literature thermodynamic data and are within an order of magnitude for about 75% of the 81 minerals and other double salts examined. The solubilities of about two-thirds of the double salts are similar to the solubilities of the less soluble simple salt .constituents,. and the solubilities of the other one-third lie between the solubilities of the .constituents.. In general, the solubilities of a series of salts with different stoichiometries containing the same ions are dependent on both the stoichiometry of the salt and the proportion of the less soluble constituent. This generalization is rationalized with the simple salt approximation and is used to explain the observed stoichiometries of a variety of minerals.

Repair of oxidative guanine damage in plasmid DNA by indoles involves proton transfer between complementary bases.

We have used the single electron oxidizing agent (SCN)(2)(*)(-) (generated by gamma-irradiation of aqueous thiocyanate) to produce guanyl radicals in plasmid DNA. The stable product(s) formed from these radicals can be detected after conversion with a base excision repair endonuclease to single strand breaks. The yield of enzyme-induced breaks is decreased by the presence during irradiation of indole compounds. Rate constants for the reduction of DNA guanyl radicals by these indoles can be calculated from the concentration dependence of the attenuation in the yield of enzyme sensitive sites. Indoles bearing electron-donating groups (methoxy or methyl) appear to react at the diffusion-controlled rate, but those bearing electron-withdrawing groups (cyano or nitro) are significantly less reactive. At physiological pH values, the reduction of a DNA guanyl radical involves the transfer of a proton as well as an electron. Comparison of the kinetic results with literature thermodynamic data suggests that the source of this proton is the complementary base-paired cytosine.

Potential‐pH Diagrams for Sulfur and Oxygen Adsorbed on Chromium in Water

The concept of equilibrium potential‐pH diagrams (E‐pH) for two‐dimensional species adsorbed on metals is applied to the case of sulfur and oxygen adsorbed on chromium in water. Standard Gibbs energies of formation for sulfur and oxygen adsorbed on chromium are calculated from literature thermodynamic data for chemisorption from the gas phase. The E‐pH relations associated with the equilibria between water, the dissolved sulfur species, and adsorbed sulfur and oxygen are given at 25 and 300°C. The corresponding E‐pH diagrams are calculated for a sulfur activity of and are superimposed on the usual Pourbaix diagrams for the system. Formation of adsorbed sulfur monolayers on the metal surface is predicted in E‐pH domains where the usual diagrams do not predict the stability of a chromium sulfide. Predictions of the corrosion risk for chromium in sulfur‐containing aqueous environments can be done using the reported E‐pH diagrams.

Phase equilibria in phospholipid-water systems

This work is a critical account of phase studies of phospholipid-water mixtures. The Phase Rule and equations of thermodynamics of heterogeneous systems are applied in the analysis of calorimetric and dilatometric results for these systems. It is inferred that the approach in which a lipid-water mixture of low lipid content is regarded as a one-component system is misleading and unhelpful. A mixture containing water and a pure synthetic phospholipid is a binary system, and the Phase Rule can be applied to it in a straightforward manner. Non-isothermal transitions and invariant three-phase reactions of the eutectic, peritectic and polytectic type can be encountered in lipid-water systems, like in other binary mixtures. The concentration dependence of the enthalpy of the isothermal three-phase transition yields a well-known Tammann triangle. For the volume change at such transition an analog of the Tammann triangle can be drafted which can be useful in interpretation of dilatometric and densitometric data for heterogeneous binary systems. The literature thermodynamic data for the aqueous lipids are analyzed on the basis of the phase diagram of the DPPC-water system. The measured values of the transition enthalpy and volume change at the pre- and main transitions refer to invariant phase reactions. The measured heat capacities and thermal coefficients of expansion actually characterize the biphasic lipid-water mixtures and may reflect phenomena specific for heterogeneous binary systems only. A reinterpretation of the literature DSC data for the DPPC-water system at temperatures below zero is suggested. Experience gained in the study of equilibrium phase diagram, kinetic and colloidal aspects of phase behaviour of dioctadecyldimethylammonium chloride-water system indicates that the common procedures of the sample preparation of lipid-water mixtures may lead to the states which are non-equilibrium in two respects: the system contains a metastable phase, and the phase is dispersed to such an extent that an irreversible colloidal structure is formed. Definitive phase studies of the phase behaviour of phospholipid-water systems in the whole concentration range are urgently needed.

Potential pH Diagrams for Sulfur and Oxygen Adsorbed on Nickel in Water at 25 and 300°C

The principle of equilibrium potential‐pH diagrams for two‐dimensional species adsorbed on metals3 is applied to the case of sulfur and oxygen adsorbed on nickel in water. Standard Gibbs energies of formation for sulfur and oxygen adsorbed on nickel are calculated from literature thermodynamic data for chemisorption from the gas phase. The E‐pH relations associated with the equilibria between water, the dissolved sulfur species, and adsorbed sulfur and oxygen are given at 25 and 300°C. The corresponding E‐pH diagrams are drawn for two sulfur activities (10−4 and 10−6) and superimposed on the usual Pourbaix diagrams for the system. Formation of adsorbed sulfur monolayers on the metal surface is predicted in E‐pH domains where the usual diagrams do not predict the stability of a nickel sulfide. The E‐pH diagrams for species adsorbed on metals allow one to make new predictions of the corrosion risk for metals in sulfur‐containing aqueous environments.

The effect of H 2O gas on volatilities of planet-forming major elements: I. Experimental determination of thermodynamic properties of Ca-, Al-, and Si-hydroxide gas molecules and its application to the solar nebula

Vapor pressures of Ca(OH) 2(g) and Al(OH) 3(g) were measured using the transpiration technique, employing the reactions CaO(s) + H 2O(g) ⇌ Ca(OH) 2(g); 2CaAl 2O 4(s) + H 2O(g) ⇌ CaAL 4O 7(s) + Ca(OH) 2(g); and CaAl 4O 7(s) +3H 2O(g) ⇌ CaAl 2O 4(s) + 2Al(OH) 3(g). From these vapor pressures, enthalpy and entropy changes in the above reactions were determined for the average experimental temperature (1650 K). This, combined with literature thermodynamic data, gives the heats of formation and entropies of the hydroxide gas species at the standard state (1 atm and 298.15 K): ΔH 0 = −615.0 ± 7.1 (2 σ) kJ/ mol and S 0 = 284.5 ± 7.9 (2 σ) J/ mol · K for Ca( OH) 2( g), and ΔAH 0 = −1004.2 ± 15.0 (2 σ) kJ/ mol and S 0 = 313.8 ± 7.9 (2 σ) J/ mol · K for Al( OH) 3( g). The Si-tetrahydroxide molecule, Si(OH) 4, was produced in the reaction SiO 2(s) + 2H 2O(g) ⇌ Si(OH) 4(g) by application of the same technique. This is the first report of a stable Si-hydroxide gas species. Its heat of formation and entropy at 1600 K and 1 atm was determined to be −1342.7 ± 2.7 (2 σ) kJ/ mol and 592.5 ± 1.0 (2 σ) J/ mol · K, respectively. Using these values for the gas species investigated and literature thermodynamic data for other gas species, “volatilities” (the total of vapor pressures of gas species containing the element in question, over the pure condensed oxide ofthat element) of the five major planet-forming elements Fe, Mg, Si, Ca, and Al were calculated for a range of physical and chemical conditions ( P, T, bulk system composition) appropriate to the solar nebula. The results indicate 1. (1) volatilities of all the elements investigated are significantly enhanced if the formation of hydroxide species by reaction with H 2O(g) is taken into account, compared with previous calculations which neglected these species; 2. (2) generally, hydroxide gas species predominate at relatively low temperatures and/or in an oxidizing atmosphere, while monatomic and undersaturated-oxidized gas species are most abundant at high temperatures and/or in a reducing atmosphere; 3. (3) hydroxide species of Ca and Al are relatively stable even at high temperatures compared to those of Si, Mg, and Fe; 4. (4) these effects explain how Ca and Al could have evaporated from Ca,Alrich inclusions in carbonaceous chondrites while Si, Mg, and Fe condensed onto them during the preaccretion alteration of CAIs.

The thermochemistry of ammonium compounds and the energy barrier opposing ammonium ion reorientation

There is a good linear correlation between the energy barrier opposing cation reorientation in a compound (NH4)nX and the quantity Δ(Xn–)=1//n{ΔH⊖f[(NH4)nX, s]–ΔH⊖f(RbnX, s)}. At zero barrier height, Δ(Xn–)= 143 ± 3 kJ mol–1. There is a sense in which depressions below this threshold are a measure of cation–anion hydrogen bonding but this sense is an unconventional one. The estimated value of ΔH⊖f(NH4+, g) derived from the threshold is 638 ± 9 kJ mol–1. The correlation is also used to improve literature thermodynamic data on ammonium and alkali-metal perrhenates, e.g., ΔH⊖f(NH4ReO4, s)=–965 ± 5 kJ mol–1. Unknown enthalpies of formation of some ammonium and rubidium salts are also predicted, and the procedure is used to explore the thermodynamic stability of non-existent solid ammonium compounds. Both metallic ammonium and ammonium hydroxide are unstable at normal pressures. The former is most unlikely to be stabilized at high pressure, but it may be possible to synthesize the hydroxide in this way. The problem of the ionic radius of NH4+ is also discussed.

Thermoelectric Power of the Molten Systems (Cu, Ag) X (X=Cl, Br, I)

Initial thermoelectric power determinations were carried out on the molten systems (Cu, Ag)X, (X=Cl, Br, I) at 1000 K. As for the employing of either cooper or silver electrodes thermocells, the choice was based on literature thermodynamic data. Comparison between ideal and actual behaviour allowed to discover negative excess partial ionic entropies.

The phosphorus-phosphorus bond energy in diphosphorus tetra-iodide

The enthalpies of sublimation at 298·15 K of phosphorus tri-iodide and diphosphorus tetra-iodide (15·2 ± 0·9 and 16·7 ± 0·5 kcal.mole −1 respectively) have been determined using an effusion manometer. Combination of these enthalpies with literature thermodynamic data gives an estimate of 62 kcal for the phosphorus-phosphorus bond energy in P 2I 4.

A thermochemical study of boron triiodide

The properties of baron triiodide are discussed from the viewpoint of their importance in heterogeneous nucleation studies by vapor deposition. Known properties are reviewed and others calculated or determined experimentally. From the literature thermodynamic data the solid vapor pressure of boron triiodide was calculated to follow logP = −3610 T −2.52 logT+17.9. The surface tension of Bl 3 under its own vapor was determined to be σ 1− v = −0.0926 T+66.5 by capillary rise in vacuo. Time-of-flight mass spectrometry showed that no dimers or polymers of Bl 3 exist in the vapor phase. The contact angle of Bl 3 on tungsten was found to approach zero by the sessile-drop technique in vacuo. Evidence for thermal nonacommodation of Bl 3 on Pyrex is presented, however, the thermal accomodation coefficient of Bl 3 on tungsten was calculated to be essentially unity from critical supersaturation temperature dependence data.