Search Results (34)

In this study, the sublimation and vapor pressure characteristics of RuO₄ were systematically investigated using ab initio thermodynamic calculations. Structural optimizations and vibrational frequency analyses were performed for gaseous RuO₄ and four candidate solid phases (monoclinic Cm, P2₁/c, C2/c, and cubic P-43n) within the density functional theory (DFT) framework. Gibbs free energies were evaluated by incorporating electronic energies, zero-point corrections, and entropic contributions from translational, rotational, and vibrational modes. The results identify monoclinic C2/c and cubic P-43n as the most stable solid phases across the studied temperature range. Calculated sublimation temperatures of 322 K at 1 atm and 240 K at 1 × 10⁻³ atm were obtained in good agreement with experimental melting and boiling points. Calculated vapor pressures show reasonable agreement with experimental measurements below the triple point, with deviations at higher temperatures attributable to approximating liquid-gas behavior using solid-gas sublimation data. These findings provide the first theoretical description of RuO₄ vapor pressure and offer a computational framework extendable to other transition-metal ALD precursors. Full article

This study prepared an adsorption-based water-containing lunar regolith simulant under low-temperature conditions to investigate H₂O behavior in simulated lunar environments. Experiments established that water binds to regolith particles via adsorption rather than existing in liquid/solid states, with critical initial pressure thresholds identified at various temperatures to ensure pure adsorption conditions. Crucially, coexisting substances extend H₂O preservation to −100 °C, suggesting substantial water retention in lunar polar regolith even under extreme cold. Sublimation modeling further revealed phase transition boundaries, indicating water ice likely persists in both permanently shadowed regions and illuminated polar areas. These findings provide fundamental insights into: adsorption-driven enrichment/preservation mechanisms of lunar water, thermodynamic stability thresholds at ultralow temperatures, and water ice distribution patterns across lunar polar terrains. The data advance understanding of lunar water’s stability and extractability, offering critical scientific support for future in situ resource utilization and sustained lunar exploration. Full article

Classical thermodynamics omits rigidity, which property distinguishes solids from gases and liquids. By accounting for rigidity (i.e., Young’s elastic modulus, ϒ), we recently amended historical formulae and moreover linked heat capacity, thermal expansivity, and ϒ. Further exploration is motivation by the importance of classical thermodynamics to various applied sciences. Based on heat performing work, we show here, theoretically, that density times sublimation enthalpy divided by the molar mass (ρΔH_sub/M, energy per volume), depends linearly on ϒ (1 GPa = 10⁹ J m⁻³). Data on diverse metals, non-metallic elements, chalcogenides, simple oxides, alkali halides, and fluorides with cubic structures validate this relationship at ambient conditions. Furthermore, data on hcp metals and molecular solids show that ρΔH_sub/M is proportional to ϒ for anisotropic materials. Proportionality constants vary only from 0.1 to 0.7 among these different material types (>100 substances), which shows that the elastic energy reservoir of solids is large. Proportionality constants depend on whether molecules or atoms are sublimated and are somewhat affected by structure. We show that ductility of refractory, high-ϒ metals affect high-temperature determinations of their ΔH_sub. Our results provide information on sublimation processes and subsequent gas phase reactions, while showing that elasticity of solids is the key parameter needed to assessing their energetics. Implications are highlighted. Full article

In this work, detailed information on the phase-transition thermodynamics of the analgesic and antipyretic drug phenazone, also known as antipyrine, is reported. It was found that the compound forms two polymorphs. Fusion thermodynamics of both forms was studied between 298.15 K and T_m using the combination of differential scanning calorimetry and solution calorimetry. The vapor pressures above crystalline and liquid phenazone were measured for the first time using thermogravimetry—fast scanning calorimetry technique. These studies were complemented by computation of the ideal gas entropy and heat capacity and by measurements of the condensed phase heat capacities. On the basis of experiments performed, we derived sublimation and vaporization enthalpies and vapor pressure above liquid and both crystalline modifications of phenazone in a wide range of temperatures. Full article

In this work, the influences of the Ar flow-rate and sublimation temperature on the phase composition and morphological structure of the sublimation products of analytical reagent MoO₃ are investigated. The results show that the sublimation products are always composed of thermodynamically stable orthorhombic molybdenum trioxide (α-MoO₃) and metastable monoclinic molybdenum trioxide (β-MoO₃) under different reaction conditions, among which the proportion of β-MoO₃ gradually increases with the increase in Ar flow-rate and the decrease in sublimation temperature. The formation temperature of α-MoO₃ is mainly between 780 K and 847 K, with the particles exhibiting an obvious sheet-like morphology. This work also finds that β-MoO₃ is mainly generated below 500 K; however, due to the co-actions of the deposition of gaseous MoO₃ molecules, the adsorption of Ar molecules, and the collision effect between the different particles, the newly formed β-MoO₃ is more inclined to take a spherical-shaped morphology in order to maintain its lowest energy state. Full article

Halogenated benzaldehydes possess unique chemical properties that render them valuable in pharmaceutical synthesis, pesticide formulation, and dye production. However, thorough thermodynamic data for these compounds remain scarce. This study aims to fill this knowledge gap by investigating key physical properties of several halogenated benzaldehydes, namely 4-chlorobenzaldehyde, 4-bromobenzaldehyde, 2,3-dichlorobenzaldehyde, 2,4-dichlorobenzaldehyde, and 2,6-dichlorobenzaldehyde. The physical properties determined in this study include volatility, phase transitions, and water solubility, all of which are crucial for predicting the environmental fate of these compounds. The vapor pressures of both crystalline and liquid phases were measured using a reliable static method, allowing for the determination of standard molar enthalpies, entropies, and Gibbs energies of sublimation and vaporization, as well as their triple points. The melting temperature and molar enthalpy, along with the isobaric molar heat capacity of the crystalline phase, were assessed using differential scanning calorimetry. Water solubility was evaluated at 25 °C through the saturation shake-flask method, complemented by ultra-violet visible spectroscopy. By combining sublimation and solubility data, additional properties such as Gibbs energies of hydration and Henry’s law constants were derived. The experimental results were integrated into existing databases, enhancing the predictive models for properties including melting temperature, vapor pressure, solubility, Gibbs energy of hydration, and Henry’s constant. These findings significantly improve the environmental modeling capabilities, providing valuable insights into the mobility and fate of halogenated benzaldehydes in various environmental contexts. Full article

This article presents the results of thermodynamic and experimental studies on the joint processing of a mixture of Shalkiya deposit zinc–lead sulfide ore and its concentration tailings in the presence of coke and magnetite. Using the HSC-6.0 software package, it was established by thermodynamic modeling that the silicon-containing products of the SiO₂ reduction in the system under consideration are FeSi, Si, Fe₃Si, Fe₅Si₃, FeSi₂, FeSi_2.33, and SiOg, which, based on the starting reduction temperature, form an increasing series: Fe₃Si (1200 °C); Fe₅Si₃, Si (1400 °C); and SiOg, FeSi₂, FeSi_2.33 (1500 °C). The smelting of the zinc–lead sulfide ore and concentration tailings mixture in the case of replacing 55% of the iron contained in the magnetite concentrate with steel shavings iron allowed us to produce FeSi45 ferrosilicon (41.9%–42.1% Si), with the extraction of 85% of the silicon in it, and sublimates containing 26.03% zinc and 13.47% lead, with the extraction of 97% of the zinc and 99% of the lead in them. In comparison with the initial ore-tailings mixture, the resulting sublimates are 11.83 times richer in zinc. Full article

Liquid organic hydrogen carriers (LOHCs) are aromatic molecules that are being considered for the safe storage and release of hydrogen. The thermodynamic properties of a range of aromatic ethers were investigated using various experimental and theoretical methods to assess their suitability as LOHC materials. The absolute vapour pressures were measured for benzyl phenyl ether, dibenzyl ether and 2-methoxynaphthalene using the transpiration method. The standard molar enthalpies and entropies of vaporisation/sublimation were derived from the temperature dependence of the vapour pressures. The combustion energies of benzyl phenyl ether and dibenzyl ether were measured using high-precision combustion calorimetry, and their standard molar enthalpies of formation were derived from these data. High-level quantum chemical calculations were used to calculate the standard molar enthalpies of formation in the gas phase for benzyl phenyl ether, dibenzyl ether and 2-methoxynaphthalene. The latter values agreed very well with the experimental results obtained in this work. The thermodynamic properties of the hydrogenation/dehydrogenation reactions in liquid phase in LOHC systems based on methoxy–benzene, diphenyl ether, benzyl phenyl ether, dibenzyl ether and 2-methoxynaphthalene were derived and compared with the data for similarly structured hydrogen carriers based on benzene, diphenylmethane, 1,2-diphenylethane, 1,3-diphenylpropane and naphthalene. The influence of the oxygen functionality on the thermodynamic properties of the hydrogenation/dehydrogenation reactions was evaluated. Full article

Thermodynamic theory was employed in this study to investigate the feasibility of separating antimony (Sb) from crude arsenic (As) using vacuum sublimation. Ab initio molecular dynamics simulations are used to calculate the structure, stability, and diffusion properties of AsmSbn (m + n ≤ 6) clusters. As₄, As₃Sb, As₂Sb₂, and AsSb₃ are the possible clusters in this thermodynamic calculation, and the molecular dynamics results confirmed their structural stability and stabilization in the gas phase. As₄ had the largest diffusion coefficients, which is the reason it separates from the Sb-containing clusters (As₃Sb, As₂Sb₂, and AsSb₃) during gas-phase diffusion and condensation processes. The experimental results show that As vapor was transformed from crystalline to amorphous with increasing subcooling, and the Sb-containing clusters that enter the gas phase were mainly condensed and deposited at the proximal end of the heating zone. Not considering the volatilization rate, the removal rate of Sb in products can reach 99.35% by increasing the condensation disk and expanding the condensation zone; thus, experiments confirmed that industrial crude arsenic can realize deep Sb removal after vacuum sublimation. Full article

UAV rotors are at a high risk of ice accumulation during their operations in icing conditions. Thermal ice protection systems (IPSs) are being employed as a means of protecting rotor blades from ice, yet designing the appropriate IPS with the required heating density remains a challenge. In this work, a reduced-order modeling technique based on the Unsteady Vortex Lattice Method (UVLM) is proposed as a way to predicting rotor icing and to calculate the required anti-icing heat loads. The UVLM is gaining recent popularity for aircraft and rotor modeling. This method is flexible enough to model difficult aerodynamic problems, computationally efficient compared to higher-order CFD methods and accurate enough for conceptual design problems. A previously developed implementation of the UVLM for 3D rotor aerodynamic modeling is extended to incorporate a simplified steady-state icing thermodynamic model on the stagnation line of the blade. A viscous coupling algorithm based on a modified α-method incorporates viscous data into the originally inviscid calculations of the UVLM. The algorithm also predicts the effective angle of attack at each blade radial station (r/R), which is, in turn, used to calculate the convective heat transfer for each r/R using a CFD-based correlation for airfoils. The droplet collection efficiency at the stagnation line is calculated using a popular correlation from the literature. The icing mass and heat transfer balance includes terms for evaporation, sublimation, radiation, convection, water impingement, kinetic heating, and aerodynamic heating, as well as an anti-icing heat flux. The proposed UVLM-icing coupling technique is tested by replicating the experimental results for ice accretion and anti-icing of the 4-blade rotor of the APT70 drone. Aerodynamic predictions of the UVLM for the Figure of Merit, thrust, and torque coefficients agree within 10% of the experimental measurements. For icing conditions at −5 °C, the proposed approach overestimates the required anti-icing flux by around 50%, although it sufficiently predicts the effect of aerodynamic heating on the lack of ice formation near the blade tips. At −12 °C, visualizations of ice formation at different anti-icing heating powers agree well with UVLM predictions. However, a large discrepancy was found when predicting the required anti-icing heat load. Discrepancies between the numerical and experimental data are largely owed to the unaccounted transient and 3D effects related to the icing process on the rotating blades, which have been planned for in future work. Full article

Some amino acid systems are known to exhibit solid solution and/or co-crystal behavior upon crystallization, which significantly affects their phase diagrams and complicates the design of their purification processes. Such behaviors are observed in the l-valine/l-leucine system. In this work, the formation and stability of a 3:1 co-crystal of the two amino acids (designated as V₃L) is further investigated. To accomplish the formation, liquid-assisted grinding, slurry equilibration, and sublimation experiments were performed and analyzed via HPLC and PXRD. Additionally, periodic DFT calculations were used to calculate lattice energies and determine the thermodynamics of possible solid phases. Experimental results show a clear metastability of the investigated V₃L co-crystals when compared to its stable solid solution. The calculations underline the metastability and the possible formation of continuous solid solutions between l-valine and l-leucine since lattice energy differences between pure amino acids and mixed compositions are negligible. This previously unknown phase behavior can be used to assess the influence of V₃L on the amino acid purification process and provides a basis for investigating similar systems with small energy differences between pure and mixed compositions in future studies. In addition, it demonstrates the particular variability of solid phases and their relationships in such simple but biologically important amino acid systems. Full article

The reversible hydrogenation/dehydrogenation of aromatic molecules, known as liquid organic hydrogen carriers, is considered as an attractive option for the safe storage and release of elemental hydrogen. The recently reported efficient synthetic routes to obtain methoxy-biphenyls in high yield make them promising candidates for hydrogen storage. In this work, a series of methoxy-substituted biphenyls and their structural parent compounds were studied. The absolute vapour pressures were measured using the transpiration method and the enthalpies of vaporisation/sublimation were determined. We applied a step-by-step procedure including structure–property correlations and quantum chemical calculations to evaluate the quality of thermochemical data on the enthalpies of phase transitions and enthalpies of formation of the studied methoxy compounds. The data sets on thermodynamic properties were evaluated and recommended for calculations in chemical engineering. A thermodynamic analysis of chemical reactions based on methoxy-biphenyls in the context of hydrogen storage was carried out and the energetics of these reactions were compared with the energetics of reactions of common LOHCs. The influence of the position of the methoxy groups in the rings on the enthalpies of the reactions relevant for hydrogen storage was discussed. Full article

Metal acetylacetonates belong to the β-diketonate family and are considered as classics among precursors for metal–organic chemical vapor deposition (MOCVD). The success of film preparation is crucially dependent on the volatilization thermodynamics of the precursors used. Data on the volatilization thermodynamics of metal acetylacetonates are in huge disarray. We amassed and analyzed experimental data on the vapor pressures and on the enthalpies and entropies of fusion, vaporization, and sublimation of acetylacetonate tris-complexes of metals(III) (Al, Sc, Cr, Mn, Fe, Co, Ru, Rh, In, and Ir) available in the literary sources. In addition, saturated vapor pressures over crystalline Al(III), Cr(III), and In(III) acetylacetonates and corresponding thermodynamic sublimation properties were determined. New findings enabled us to arbitrate the conflict among literature data. The enthalpies and entropies of sublimation, vaporization, and fusion were adjusted to the reference temperature for a correct comparison using the empirically estimated differences in heat capacities. The heat capacity of the crystalline phase was shown to depend weakly on the metal atom. As a result, a reliable set of enthalpies and entropies of the mentioned processes of fundamental importance was derived for ten metal complexes. Relationships between volatility and structure were established depending on the central metal. The suggested algorithm can be fairly easily transferred to the acetylacetonate or other β-diketonate isoligand complexes with metals of different valence. Full article

The processes of the sublimation and thermal decomposition of the 1-ethyl-3-methylimidazolium hexafluorophosphate ionic liquid (EMImPF₆) were studied by a complex approach including Knudsen effusion mass spectrometry, IR and NMR spectroscopy, and quantum chemical calculations. It was established that the vapor over the liquid phase primarily consists of decomposition products under equilibrium conditions. Otherwise, the neutral ion pairs are the only vapor components under Langmuir conditions. To identify the nature of the decomposition products, an experiment on the distillation of the ionic liquid was performed and the collected distillate was analyzed. It was revealed by the IR and NMR spectroscopy that EMImPF₆ decomposes to substituted imidazole-2-ylidene (C₆N₂H₁₀PF₅) and HF. The measured vapor pressure of C₆N₂H₁₀PF₅ reveals a very low activity of the decomposition products (<10⁻⁴) in the liquid phase. The absence of a significant accumulation of decomposition products in the condensed phase makes it possible to determine the enthalpy of sublimation of the ionic liquid assuming its unchanged activity. The thermodynamics of the EMImPF₆ sublimation was studied by Knudsen effusion mass spectrometry. The formation enthalpy of EMImPF₆ in the ideal gas state was found from a combination of the sublimation enthalpy and formation enthalpy of the ionic liquid in the condensed state. The obtained value is in good agreement with those calculated by quantum chemical methods. Full article

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 $\mathrm{NaCl}$ and $\mathrm{NaF}$ 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 $\mathrm{Ni}$, $\mathrm{Cr}$, Cu (metallic bond), $\mathrm{NaCl}$, $\mathrm{NaF}$, ${\mathrm{ZrO}}_2$ (ionic bond) and ${\mathrm{SiO}}_2$ (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 $\mathrm{Cu}$ even only 0.1%. Furthermore, the partial pressures caused by gas phase reactions are also explored, showing good agreement with experimental results. Full article