Enthalpies Of Sublimation Research Articles

Thermodynamic Characteristics of Alkali Metal Pivalates (CH3)3CCOOM (M = Li, Na, K, Rb, Cs)

The thermodynamic properties of alkali metal pivalates (CH3)3CCOOM, where M = Li, Na, K, Rb, Cs, were studied by mass spectrometry, thermogravimetric analysis, and differential scanning calorimetry. The sublimation of the compounds was determined to be congruent. The saturated vapor contains oligomeric forms MnPivn (n = 1–6), which are dominated by dimeric and tetrameric molecules in the case of Na and K pivalates and by monomeric and dimeric molecules in the case of Rb and Cs pivalates. The partial pressures of the main components of the gas phase, their temperature dependence, and their standard enthalpies of sublimation were calculated. The enthalpies of dissociation of dimeric and tetrameric molecules were found. The standard enthalpies of formation MPiv(solid) and MPiv(gas) were estimated.

Enthalpy of Sublimation of Organic and Metal-Organic Compounds: Influence of the Polarization Effect

Enthalpy of Sublimation of Organic and Metal-Organic Compounds: Influence of the Polarization Effect

Theoretical Prediction of the Sublimation Behavior by Combining Ab Initio Calculations with Statistical Mechanics

We develop a theoretical model to predict the sublimation vapor pressure of pure substances. Moreover, we present a simple monoatomic molecule approximation, which reduces the complexity of the vapor pressure expression for polyatomic gaseous molecules at a convincing level of accuracy, with deviations of the Arrhenius prefactor for NaCl and NaF being 5.02% and 7.08%, respectively. The physical model is based on ab initio calculations, statistical mechanics, and thermodynamics. We illustrate the approach for Ni, Cr, Cu (metallic bond), NaCl, NaF, ZrO2 (ionic bond) and SiO2 (covalent bond). The results are compared against thermodynamic databases, which show high accuracy of our theoretical predictions, and the deviations of the predicted sublimation enthalpy are typically below 10%, for Cu even only 0.1%. Furthermore, the partial pressures caused by gas phase reactions are also explored, showing good agreement with experimental results.

Thermodynamics of Evaporation from the Ocean Surface

Adopted by the Intergovernmental Oceanographic Commission (IOC) of UNESCO in 2010 and the International Union of Geodesy and Geophysics (IUGG) in 2011, the Thermodynamic Equation of Seawater 2010 (TEOS-10) is the current geophysical standard for the thermodynamic properties of humid air, seawater and ice. TEOS-10 equations for evaporation and sublimation enthalpies are derived mathematically from the thermodynamic potential of a »sea air« model, denoting a multi-phase equilibrium composite of the geophysical aqueous mixtures. To estimating evaporation rates from the ocean, Dalton equations in various versions are implemented in numerical climate models. Some of those equations appear to be biased on climatic time scales if compared with proper thermodynamic driving forces. Such equations may lead to a spurious amplification of the hydrological cycle and an implied effect of cooling oceans. As an unbiased alternative, Dalton equations are proposed in terms of TEOS-10 relative fugacity (RF) or its conventional relative humidity (RH) approximations. With respect to RH uncertainties or trends, the substantial sensitivity of the evaporation flux may be estimated to be as much as 5 W m−2 per 1 %rh. Within a maximum error of only 0.04 %rh, sea-surface RF may be approximated in terms of dew-point or frost-point temperatures using a simple formula.

Standard molar enthalpy of sublimation of form I nicotinamide

The standard (p° = 0.1 MPa) molar enthalpy of sublimation of form I nicotinamide (NIC, cr I), at 298.15 K, was determined by drop-sublimation Calvet microcalorimetry. Experiments carried out under isothermal and non-isothermal conditions led to ΔsubHmo(NIC, cr I) = 108.0 ± 0.5 kJ·mol−1. The present study allowed to resolve to a significant extent the large discrepancy observed between published ΔsubHmo(NIC) results obtained by calorimetry and by vapor-pressure measurements, using samples of unspecified crystal form.

Thermochemistry, Tautomerism, and Thermal Stability of 5,7-Dinitrobenzotriazoles

Nitro derivatives of benzotriazoles are safe energetic materials with remarkable thermal stability. In the present study, we report on the kinetics and mechanism of thermal decomposition for 5,7-dinitrobenzotriazole (DBT) and 4-amino-5,7-dinitrobenzotriazole (ADBT). The pressure differential scanning calorimetry was employed to study the decomposition kinetics of DBT experimentally because the measurements under atmospheric pressure are disturbed by competing evaporation. The thermolysis of DBT in the melt is described by a kinetic scheme with two global reactions. The first stage is a strong autocatalytic process that includes the first-order reaction (Ea1I = 173.9 ± 0.9 kJ mol-1, log(A1I/s-1) = 12.82 ± 0.09) and the catalytic reaction of the second order with Ea2I = 136.5 ± 0.8 kJ mol-1, log(A2I/s-1) = 11.04 ± 0.07. The experimental study was complemented by predictive quantum chemical calculations (DLPNO-CCSD(T)). The calculations reveal that the 1H tautomer is the most energetically preferable form for both DBT and ADBT. Theory suggests the same decomposition mechanisms for DBT and ADBT, with the most favorable channels being nitro-nitrite isomerization and C-NO2 bond cleavage. The former channel has lower activation barriers (267 and 276 kJ mol-1 for DBT and ADBT, respectively) and dominates at lower temperatures. At the same time, due to the higher preexponential factor, the radical bond cleavage, with reaction enthalpies of 298 and 320 kJ mol-1, dominates in the experimental temperature range for both DBT and ADBT. In line with the theoretical predictions of C-NO2 bond energies, ADBT is more thermally stable than DBT. We also determined a reliable and mutually consistent set of thermochemical values for DBT and ADBT by combining the theoretically calculated (W1-F12 multilevel procedure) gas-phase enthalpies of formation and experimentally measured sublimation enthalpies.

Metal-Organic Chemical Vapor Deposition Precursors: Diagnostic Check for Volatilization Thermodynamics of Scandium(III) β-Diketonates

Scandium complexes with β-diketonate ligands are valuable precursors for the metal–organic chemical vapor deposition (MOCVD) of scandia based materials, but data on their volatilization thermodynamics crucial to MOCVD technology are in a huge disarray. We have addressed this issue with a diagnostic tool based on the principles of group additivity and structure–property relationships, which had been developed by us specifically for metal–organic objects. For this purpose, a mass of experimental data on the vapor pressures and enthalpies of sublimation, vaporization and fusion available in the literature for scandium(III) β-diketonates has been compiled and analyzed. Additionally, saturated vapor pressures and thermodynamic sublimation characteristics have been obtained for scandium(III) complexes with acetylacetone, hexafluoroacetylacetone, and 3-methyl-2,4-pentanedione by transpiration and thermogravimetric methods. New data have allowed us to arbitrate the conflict of literature data. As a result, a consistent set of enthalpies of the three discussed processes has been obtained for eight scandium complexes. Dispersion interactions and non-additive effects have been shown to be typical for metal tris-β-diketonates. They have been taken into account to improve the diagnostic check. It is now possible to quite easily assess the thermodynamics of tris-β-diketonate complexes with different metals which are in demand as precursors in gas-phase technology.

Cosmic-ray sputtering of interstellar ices in the electronic regime

Aims. With this article, we aim to provide the sputtering yields for molecular species of potential astrophysical interest and in the electronic regime of interaction characteristic of cosmic rays. We specifically target molecules that are constitutive of interstellar ice mantles.Methods. We used a compendium of existing data on electronic sputtering to calculate the prefactors leading to the generalisation of the stopping-power-dependent sputtering yield for many species condensing at low temperature. In addition, we present new experimental results to constrain the yield for solid CH4, C6, and CH3CN.Results. Electronic sputtering is constrained using literature data for H2, HD, D2, Ne, N2, CO, Ar, O2, Kr, Xe, CO2, SO2, NH3, S, H2O, D2O, CH3OH, Leucine, C20H12, C24H12, and C60. A first-order relation with the sublimation enthalpy is derived, which allows us to predict the sputtering yield within an order of magnitude for most species. The fluctuations around the mean are partly assignable to the differences in resilience towards radiolysis for individual species, and partly to the micro-physics details of the energy transfer to the lattice.

Is everything correct? The formation enthalpy estimation and data revision of nitrate and perchlorate salts

In modern searches for the structure of high-energy-density compounds with high operational,detonation, and physicochemical characteristics, a special place belongs to salts, which have anumber of significant advantages over neutral compounds. The development of this area ofHEDM is hampered by the lack of effective calculation schemes for estimating the enthalpy offormation DHf0 of salts, as a key parameter in assessing the prospects for their use. Based on theauthor's method (MICCM), which is superior in accuracy to currently available calculationmethods, the enthalpies of formation of various salts of nitrates and perchlorates for a promisingclass of high-energy amino-1,2,4-triazoles are calculated and the accuracy of calculations isestimated by other methods. Relationships between the thermochemical characteristics of saltsdepending on various cations are considered. Among the considered compounds, calculations ofthe enthalpies of salts of three amino-1,2,4-triazoles showed a significant discrepancy with theexperimental data. Calculations DHf0of salts were performed using three methods: volume-base thermodynamic(Jenkins/Bartlett method), the method of adding of ions contributions (MAIC, Matyushin'smethod), and the method of ions and cocrystals contribution mixing (MICCM, Khakimov'smethod). Calculations by the MICCM method were carried out on the basis of quantumchemistry methods (when estimating the enthalpies of formation in the gas phase) and themethod of atom-atom potentials (AAP) when calculating the enthalpy of sublimation of salts. Wehave optimized all the structures in the gas phase using the Becke three hybrid exchange andLee-Yang-Parr correlation functional with Grimme's dispersion correction, B3LYP-D2, and aug-cc-pVDZ basis set using the Gaussian16 software. The AAP calculations were performed usingthe FitMEP software packages (for adjusting the charges of the molecular electrostatic potential)and PMC (for the procedure for constructing crystal packings and searching for optimal ones).

Phase Transitions Equilibria of Five Dichlorinated Substituted Benzenes.

This work reports an experimental study aiming to determine the thermodynamic properties of five chlorinated compounds with environmental impact. The vapor pressures of the crystalline phases of three isomers of dichlorobenzoic acid (2,4-, 2,5-, and 2,6-) and 2,6-dichlorobenzonitrile were measured at several temperatures using the Knudsen effusion technique. Another technique (a static method based on capacitance diaphragm manometers) allowed the measurement of the vapor pressures of both the crystalline and liquid phases of 2,4-dichlorobenzonitrile between 303.0 and 380.0 K. This latter technique also enabled the measurement of sublimation vapor pressures of 2,6-dichlorobenzonitrile over a larger range interval of temperatures, T = 328.7 and 391.8 K. The standard molar enthalpy, entropy, and Gibbs energy of sublimation (for all the compounds studied) and vaporization (for 2,4-dichlorobenzonitrile) were derived, at reference temperatures, from the experimental vapor pressure results. The temperatures and enthalpies of fusion and the isobaric heat capacities of the five crystalline-substituted benzenes were determined using differential scanning calorimetry. The contributions of the three substituents (-COOH, -CN, and -Cl) to the sublimation thermodynamic properties of the compounds studied were discussed.

Vaporization enthalpies of self-associated aromatic compounds at 298.15 K: A review of existing data and the features of heat capacity correction. Part I. Phenols

Vaporization, sublimation and fusion enthalpies of 39 phenol derivatives were thoroughly analyzed using Kirchhoff's and Hess's laws of Thermochemistry to derive the reliable ΔlgH°(298.15 K) values. During the analysis, the correction for non-ideality for the high-temperature vaporization enthalpies was performed. The crystal, liquid and gas heat capacities available from the literature were complemented with the additional experimental measurements of the condensed phases and the computations of the ideal gas properties. Analyzing the available information, we proposed a simple approach for the estimation of the temperature dependence of the vaporization enthalpy of phenol derivatives that showed high accuracy for compounds of various structure.

Thermochemical study of the antioxidant activity of some hydroxycoumarins

This work reports a combined thermochemical experimental and computational study on 6-hydroxycoumarin. The standard (p° = 0.1 MPa) molar enthalpy of formation in the condensed state of this compound was derived from the standard molar energy of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. Calvet microcalorimetry was used to derive the standard molar enthalpy of sublimation. By combining these values, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, −(339.8 ± 2.4) kJ⋅mol−1 was derived.Accurate quantum chemical calculations at the composite G3 and at the DLPNO-CCSD(T) levels of theory have also been conducted in order to characterize the energetics of all the hydroxycoumarins studied and their radicalar related species, allowing us to further support our experimental measurements and to adequately quantify and rationalize the antioxidant activity of these systems.

Sublimation of Drugs from the Site of Application of Topical Products.

The objective of the project was to investigate the plausibility of active pharmaceutical ingredients (APIs) to undergo sublimation from topical application following evaporation of solvent. Topical formulations with different APIs were subjected to a sublimation screening test. The APIs in the selected topical products were found to undergo sublimation to a different extent. The salicylic acid topical product was found to undergo a significant loss due to sublimation. The extent of sublimation of salicylic acid was significantly greater at skin temperature compared to room temperature. When the APIs were subjected to the sublimation screening test in their neat form at 32 ± 1 °C, the natural log of the rate of sublimation decreased linearly with the standard enthalpy of sublimation of compound (R2 = 0.89). The formulation composition was found to have a significant impact on the extent of sublimation of the representative API, salicylic acid. The sublimation of APIs from the topical product was found to affect the mass balance studies in the case of the salicylic acid ointment. Furthermore, the results of the human studies agreed with the in vitro experimental results demonstrating the plausibility of loss of API due to sublimation from the site of application.

Investigation of through micropatterns fabrication on C194 copper foil by ultraviolet nanosecond pulsed laser microdrilling

While the lead frames of C194 copper alloy widely used in IC packages contain high density of through micropatterns, the method for realizing high precision manufacturing of the micropatterns on copper foil with thickness down to a few hundred micrometers is highly demanded. In the present work, we demonstrate the feasibility of manufacturing high density through micropatterns on C194 copper foil with high precision and high uniformity by using ultraviolet nanosecond pulsed laser microdrilling. Specifically, the absorption coefficient of C194 copper foil for 355 nm wavelength is experimentally derived, based on which the sublimation enthalpy of the material is calibrated by iteratively comparing predicted crater morphology by finite element simulations with experimental data. Then the multi-pulse laser ablation mechanisms of C194 copper foil are investigated jointly by finite element simulations and experiments, which derive the quantitative correlation of ablation crater depth with laser ablation parameters. Finally, high density arrays of through micropatterns with high dimensional accuracy and high uniformity are fabricated on C194 copper foil with a thickness of 100 μm by the proposed ultraviolet nanosecond pulsed laser microdrilling with theoretically predicted repeat scanning number. Furthermore, the effect of pickling on surface quality and resistance of the manufactured copper lead frame is addressed. This work provides a feasible method for manufacturing copper alloy lead frames with high precision through micropatterns in an environmentally friendly manner.

Enthalpy of formation of 6-phenyl-1,5-diazabicyclo[3.1.0]hexane by combustion calorimetry and theoretical approach for efficient prediction of thermochemistry of diaziridines.

The combustion energy and standard molar enthalpy of formation of crystalline 6-phenyl-1,5-diazabicyclo[3.1.0]hexane (PDABH) were determined using an isoperibolic calorimeter with a static bomb. PDABH is the first diaziridine for which the experimental value of the enthalpy of formation was obtained. This value was validated by the theoretical values of gas phase enthalpy of formation and enthalpy of sublimation. The gas phase enthalpy of formation was calculated using the DLPNO-CCSD(T1)/CBS method in conjunction with isodesmic-type reactions. This method was chosen in comparison to another high quality evaluative method (G4), which has been shown to provide unreliable results for cyclic nitrogen containing compounds. The descriptors of the molecular electrostatic potential (MEP) were used to estimate the enthalpy of sublimation of PDABH. The proposed MEP model is based on experimental enthalpies of sublimation for 75 compounds structurally similar to PDABH. The high-level ab initio calculations of gas phase enthalpies of formation combined with enthalpies of sublimations estimated using descriptors of MEP allow predicting the enthalpies of formation of diaziridines in the solid phase.

The cohesive properties and pyrolysis mechanism of an aprotic ionic liquid tetrabutylammonium bis(trifluoromethanesulfonyl)imide.

As the cohesive properties (such as the enthalpy of sublimation) of solid organic salts (or ionic liquids, ILs) are unmeasurable, a method of their indirect determination is proposed in this paper. For this purpose, the thermogravimetric analysis (TGA) and differential scanning calorimetric analysis (DSC) were carried out over a wide range of temperatures. In this study, the mathematical relationship of the thermodynamic properties between the liquid and solid phases of ILs is established using the Born-Fajans-Haber cycle, in which the sum of the vaporization enthalpy of ILs, melting enthalpy and the enthalpy of solid-solid phase transition is regarded as the sublimation enthalpy of solid organic salts. With this method, the cohesive properties of tetrabutylammonium bis(trifluoromethanesulfonyl)imide ([N4444][NTf2]), which is an aprotic IL, were successfully obtained. Additionally, the difference between the lattice energy and the cohesive energy was employed to quantitatively calculate the charge separation distance of single ion pair (r12) in the gas phase of ionic liquids for the first time, which can serve as a standard methodology to measure the closeness in distance between the anion and the cation in a gas phase ion pair. The pyrolysis mechanism of [N4444][NTf2] was also explored.

Состав пара и термодинамические характеристики газообразных молекул вольфраматов щелочноземельных металлов

Calculated and experimental mass spectra (at temperatures region of 1600 – 2000 K) of gaseous alkaline earth metals tungstates: MgWO4(g), CaWO4(g), SrWO4(g), BaWO4(g) are given. The partial vapor pressures are determined and the equations for the temperature dependences of the partial pressures of gaseous molecules of alkaline earth metals tungstates were derived for liquid in the form (Р, atm): lgP(MgWO4(L)) = –28737/Т + 7,95 for the area 1600 – 1900 K; lgP(CaWO4(L)) = – 25265/Т + 6,913 for the area 1850 – 2000 K; lgP(SrWO4(L)) = – 25052/Т + 7,13 for the area 1800 – 1900 K; lgP(BaWO4(L)) = –20570/Т + 4,58 for the area 1770 – 1900 K. Based on experimental data on vapor pressure, the enthalpies of evaporation (DН0s,0), formation (–DН0f,0) and atomization (DН0at,0) of gaseous alkaline earth metals tungstates were calculated, which respectively amounted to (DН0, kJ/mol): MgWO4 — 652, 890, 2855; CaWO4 — 644, 974, 2968; SrWO4 — 615, 1045, 3056; BaWO4 — 548, 1045, 3095. The enthalpy of sublimation of alkaline earth metals tungstates decreases from magnesium to barium.

A combined experimental and computational thermodynamic study of fluoronitrophenol isomers

Combustion energies of the 5-fluoro-2-nitrophenol, 4-fluoro-2-nitrophenol, 3-fluoro-4-nitrophenol and 2-fluoro-4-nitrophenol isomers were obtained by means of a rotating-bomb combustion calorimeter. From these determinations, standard molar combustion enthalpies and standard molar formation enthalpies, at T = 298.15 K, in the crystalline state, were derived. The Knudsen mass-loss effusion technique was used to determine the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the studied compounds. The standard molar enthalpies of sublimation of the four isomers were also measured by Calvet microcalorimetry. The gas-phase standard molar enthalpies of formation were derived from the experimental measurements, at T = 298.15 K, for the fluoronitrophenols studied.Additionally, the standard molar enthalpies of formation were estimated by means of computational methodology at the G3(MP2)//B3LYP level. The estimated values are in very good agreement with experimental data, giving us support to estimate the gas-phase enthalpies of formation of the remaining isomers whose values have not been determined experimentally.A simple group additivity scheme was successfully applied for prediction of molar enthalpies of formation.The computational study was also extended to the determination of OH bond dissociation enthalpies for all the isomers.

Effects of metal redeposition in plasma sputtering

Ion sputtering, whereby atoms on target surfaces are bombarded by energetic ions, is a key process in the film-coating industry. However, its detailed mechanism has not yet been clarified and remains an empirical operation. This article demonstrates that the redeposition of metal on the target surface significantly enhances the sputtering rate. Although the effect differs depending on the metal species, significant enhancement in the sputtering rate occurs in glow-discharge plasma sputtering––a maximum increase of approximately 2.4 times was observed under experimental conditions. The experimental data agree well with the model equation, which superimposes two processes: sputtering by the desorbed redeposited metal and reduction of the enthalpy of sublimation by the adsorbed redeposited metal. The results of this study demonstrate that the metal redeposition effect is a key mechanism missing in the plasma sputtering process and that taking redeposition into account frees us from its empirical use. These findings are expected to address several of the existing questions related to sputtering, enabling the development of a wide variety of applications.

Standard enthalpies of formation of 3-hydroxyphthalic anhydride

In this investigation thermochemical properties of 3-hydroxyphthalic anhydride were determined. Fusion enthalpy, fusion temperature and molar heat capacity in solid phase were obtained by differential scanning calorimetry. By the Knudsen effusion method, the molar enthalpy of sublimation at 298.15 K was obtained. By thermogravimetric data, it was possible to determine the molar enthalpy of sublimation and the molar enthalpy of vaporization. On the other hand, the molar enthalpy of formation in solid phase at 298.15 K was determined by combustion calorimetry. The molar enthalpy of formation in gas phase at 298.15 K was calculated from molar enthalpy of sublimation at 298.15 K and molar enthalpy of formation in solid phase at 298.15 K. This experimental value was compared both theoretical enthalpy of formation in gas phase by using Gaussian methods at the G3 and G4 levels and with an estimated value in relation to phthalic anhydride.