Thermodynamic Predictions Research Articles

Urban aerosol chemistry at a land–water transition site during summer – Part 2: Aerosol pH and liquid water content

Abstract. Particle acidity (aerosol pH) is an important driver of atmospheric chemical processes and the resulting effects on human and environmental health. Understanding the factors that control aerosol pH is critical when enacting control strategies targeting specific outcomes. This study characterizes aerosol pH at a land–water transition site near Baltimore, MD, during summer 2018 as part of the second Ozone Water-Land Environmental Transition Study (OWLETS-2) field campaign. Inorganic fine-mode aerosol composition, gas-phase NH3 measurements, and all relevant meteorological parameters were used to characterize the effects of temperature, aerosol liquid water (ALW), and composition on predictions of aerosol pH. Temperature, the factor linked to the control of NH3 partitioning, was found to have the most significant effect on aerosol pH during OWLETS-2. Overall, pH varied with temperature at a rate of −0.047 K−1 across all observations, though the sensitivity was −0.085 K−1 for temperatures > 293 K. ALW had a minor effect on pH, except at the lowest ALW levels (< 1 µg m−3), which caused a significant increase in aerosol acidity (decrease in pH). Aerosol pH was generally insensitive to composition (SO42-, SO42-:NH4+, total NH3 (Tot-NH3) = NH3 + NH4+), consistent with recent studies in other locations. In a companion paper, the sources of episodic NH3 events (95th percentile concentrations, NH3 > 7.96 µg m−3) during the study are analyzed; aerosol pH was higher by only ∼ 0.1–0.2 pH units during these events compared to the study mean. A case study was analyzed to characterize the response of aerosol pH to nonvolatile cations (NVCs) during a period strongly influenced by primary Chesapeake Bay emissions. Depending on the method used, aerosol pH was estimated to be either weakly (∼ 0.1 pH unit change based on NH3 partitioning calculation) or strongly (∼ 1.4 pH unit change based on ISORROPIA thermodynamic model predictions) affected by NVCs. The case study suggests a strong pH gradient with size during the event and underscores the need to evaluate assumptions of aerosol mixing state applied to pH calculations. Unique features of this study, including the urban land–water transition site and the strong influence of NH3 emissions from both agricultural and industrial sources, add to the understanding of aerosol pH and its controlling factors in diverse environments.

Thermodynamic performance and emission prediction of CI engine fueled with diesel and Vachellia nilotica (Babul) biomass-based producer gas and optimization using RSM

Currently, the requirement of alternate fuel has become significant for the mitigation of petroleum fuel and to reduce exhaust emission. To effectively use alternate fuel with diesel, the present investigation presents a simulation-based prediction of engine performance and emission of a CI engine fueled by Diesel and producer gas derived from Vachellia nilotica (Babul) biomass, and optimization by response surface methodology (RSM). The peculiarity of this study is that it focuses on optimizing the operational parameters of diesel engines that run on babul-based PG combined with diesel fuel to achieve optimal performance and emissions. The data to be used for RSM optimization were obtained by using comprehensive thermodynamic quasi-dimension combustion modeling at different blending ratios (BR), Compression ratio (CR), and Injection timing (IT). Simulation result validation with experimental one was attained with a good agreement. The RSM-based optimization has been employed to optimize the input variables to obtain the best response of dual fueled engine performance (BP, ITE, BSFC) and emission (CO, NO). The RSM study showed that the optimal values of BP, ITE, BSFC, CO, and NO are equals to 3.72 kW, 36%, 0.37 kg/kWh, 0.0091 (vol%), and 245.68 ppm respectively corresponding to BR 65%, CR 18.19, and IT 31.11 bTDC. To check model capability, the regression coefficient obtained was 0.80. According to the ANOVA-based regression modeling, it was found that the results lie lower prediction error R2 values for BP, ITE, BSFC, CO, and NO are 96.66%, 97.37%, 97.85%, 97.67%, and 99.79% respectively Thus, RSM is one of the effective tool to predict optimized inputs with the best response of engine performance.

The influence of the Nb:Ta ratio on the microstructural evolution in refractory metal superalloy systems

Refractory metal superalloys have the potential to facilitate a significant increase in gas turbine operating temperatures that would enhance efficiency and reduce emissions. However, fulfilling this potential requires a much more detailed understanding of the underlying metallurgy and how it is influenced by alloying additions. Here, the influence of systematically varying the Nb:Ta ratio in a series of Ti–Zr–Nb–Ta alloys has been studied and compared to thermodynamic predictions. The experimental results show that higher Nb:Ta ratios suppress phase separation but lower the inter-phase misfit. As such, optimizing these alloys for specific applications will require careful balancing of these effects.

Additive single atom values for thermodynamics I: Volumes, entropies, heat capacities of ionic solids

In an earlier simple “group contribution” method, molar volumes of organic and inorganic materials were predicted by summing optimised single atom values weighted according to the molecular formula. We here first revisit this procedure for volumes and then apply the method to entropies and heat capacities, providing updated predictive methods. The atom sum method has the unique advantage of working with an essentially complete parameter set because of the finite number of chemical elements but at the expense of omitting the nuance of special interactions as in other more sophisticated and complex group contribution methods. Thus, it does not distinguish among materials with the same chemical formula (that is, among phases or isomers).We here analyse data for nearly 3 500 inorganic materials, both anhydrous and hydrated. On analysing this wealth of data, we note that the optimised atom sum volume data follow the atomic sequence pattern of element volume data quite closely, but with relatively reduced values for the alkali metals and alkaline earths. The entropy atom sum values are similarly dispersed across the atomic sequence. Heat capacity atom sum values have a much reduced range, corresponding to the relatively small range of the ambient heat capacities of inorganic solids as implied by the Dulong-Petit upper limit of 3R per atom. We provide estimates of linear temperature effects for each of the three properties: volume, entropy and heat capacity.The properties of water in hydrates versus pure liquid water are compared for each thermodynamic property yielding information on the effects of incorporation of water into the solid.In summary, summations encompassing inorganic anhydrate and hydrate volumes, entropies and heat capacities over temperature ranges are available from this work, enabling simple first-order thermodynamic predictions and checks.

Reducing detrimental sulfate-based phase formation in concrete exposed to sodium chloride using supplementary cementitious materials

The sodium chloride (NaCl) can chemically interact with the monosulfate (AFm) within the concrete matrix, leading to a detrimental sulfate-based phase formation during thermal cycling. This paper studies the potential of reducing the sulfate-based phase in the cementitious pastes made using different types of supplementary cementitious materials (SCMs) used as a partial replacement of ordinary portland cement (OPC). A low-temperature differential scanning calorimetry was used to quantify the amount of the sulfate-based phase. The results indicated that the addition of SCMs as a partial replacement of OPC revealed different effects on forming the sulfate-based phase through pozzolanic activities and/or dilution effects. The addition of slag or class F fly ash can lower the formation of the sulfate-based phase through the dilution effect, while the addition of silica fume can substantially lower the formation of the sulfate-based phase by both dilution and pozzolanic activities. The use of class C fly ash, however, showed negative effects through increasing the formation of the sulfate-based phase. Thermodynamic modeling was used to predict the phase equilibrium of hydrated cementitious systems. Results from thermodynamic predictions were in agreement with the experimental results, indicating that the formation of the sulfate-based phase was associated with the amount of AFm present in the cementitious systems.

Thermodynamically study of phase formation of Ni-Ti-Si nanocomposites produced by self-propagating high-temperature synthesis method

Understanding the phase formation mechanisms in self-propagating high-temperature synthesis from the thermodynamical aspect of view is important. In this study, the phase formation of the ternary system of nickel-titanium-silicon was studied by using the HSC software V6.0, and phase formation is predicted by calculating the adiabatic temperature of exothermic reaction between reagents. Then, by using X-ray diffractometer analysis, the results of the simulation were evaluated by experimental achievements. Results showed a good correlation between thermodynamical calculation and prediction with experimental. It could be concluded that the equilibrium mechanism is the dominant mechanism in phase formation in the SHS synthesis method. NiTiSi solid solution phase is obtained from the reaction between Ti5Si3 and Ni2Si and Ni.

Fundamental study on the thermodynamic non-equilibrium freezing probability prediction model taking into account the super cooling phenomena in porous material

It is commonly considered that frost damage is caused by sudden freezing of supercooled water, which is a random phenomenon. Therefore, the aims of this study are to establish a prediction model for the probability of freezing until any lowest reached temperature, and to obtain the probability distribution function of the freezing point for the proposed analytical prediction model. First, theoretical prediction model for the probability of the instantaneous increment of ice content when lowest achieving temperature was known was derived based on these assumptions that building structure is an aggregation of small elements. Next, the freezing point measurement was carried out by using saturated mortar samples as the small element. As the results, it could be found that the first freezing due to supercooling occurred from -4 to -11 deg. C and the maximum probability was appeared at -7.5 deg. C. The average increment of ice content at every temperature closed to the 40 % volume of pore water until the thermodynamically-based freezing point. Moreover, the proposed method that can calculate the probability distributions of the instantaneous increment of ice content for any lowest achieving temperature from pore size distribution had good agreements with the measurement results.

Thermodynamic predictions of CANDU fuel volatilization and fission product behaviour under severe accident conditions

A comprehensive thermodynamic investigation has been performed on irradiated uranium dioxide CANDU fuel under representative severe accident conditions. Two cases have been explored in this work: Case I) the fuel is in contact with varying combinations of hydrogen and steam (i.e., mainly reducing), and Case II) the fuel is in contact with varying combinations of air and steam (i.e., oxidizing). The system thermochemistry has been computed for a wide range of gas mixtures for both cases, fuel to gas ratios, temperatures, and hydrostatic pressures. The calculations predict fission gas speciation and fuel volatilization based on equilibrium thermodynamics, including the formation of several secondary phases, changes in UO2±x stoichiometry, fission product solubility in various phases, melting, and vaporization. The overall objective of this work was to inform source term analyses in the industry standard toolset SOURCE under severe accident conditions of a CANDU station.

The hindered rotor theory: A review

AbstractHindered rotations are common in nature and can greatly affect thermodynamic properties. Typically, the standard rigid‐rotor harmonic‐oscillator approximation is used to compute thermodynamic properties; however, it often leads to serious errors, particularly for molecules with hindered rotations. Hence, to reach accurate thermodynamic predictions for such cases, the hindered rotor approximation must be applied. Different methods to compute thermodynamic properties for molecules with hindered rotations are available. Herein, we review the theoretical basis of different methods, their accuracy, and applicability. We also present the different algorithms to identify hindered rotors and obtain the input parameters for the hindered rotor model, and the software available to compute thermodynamic properties under this scheme.This article is categorized under: Structure and Mechanism > Molecular Structures Theoretical and Physical Chemistry > Reaction Dynamics and Kinetics

Thermodynamic Prediction and Synthesis of a Titanium Diboride Powder by Reduction of Titanium Dioxide with Boron Carbide in Argon Atmosphere

Thermodynamic Prediction and Synthesis of a Titanium Diboride Powder by Reduction of Titanium Dioxide with Boron Carbide in Argon Atmosphere

Synthesis of high-entropy alloy thin films via grain boundary diffusion–assisted solid-state alloying

Herein, CoCrFeNi high-entropy alloy thin films were successfully synthesized via solid-state alloying from Al6(CoCrFeNi)94 multilayer films, forming a CoCrFeNi-based solid solution phase with a face-centered cubic structure by optimizing Al content to prevent any oxide reaction. The microstructural and phase evolutions in the multilayer films were systematically investigated to understand the alloying behavior. Interestingly, it can be evaluated that the alloying elements could be diffused into layers, even those with nonconnected interfaces, through the grain boundaries owing to the presence of nanostructured columnar grains. Thus, these grain boundaries act as a network of diffusion paths for alloying elemental atoms to be homogenized throughout multilayer films and form the reactive phase regardless of the thermodynamic and kinetic prediction. Consequently, grain boundary diffusion–assisted solid-state alloying can be used to synthesize high-entropy alloy thin films for various multicomponent alloy systems by only controlling the layer thickness in multilayer films.

Estimation of e-NRTL binary interaction parameters and its impact on the prediction of thermodynamic properties of multicomponent electrolyte systems

The main objective of the current work is to obtain and validate the binary interaction parameters of the e-NRTL model for different salts in water, using the data of mean ionic activity coefficients vs. molality compiled by Robinson and Stokes (Electrolyte Solutions, Dover Publications, 2012). This way, the interaction parameters τsalt,water and τwater,salt of the e-NRTL thermodynamic model for 171 binary (salt + water) electrolyte systems have been calculated by non-linear regression of the data available in the literature. The fitting was performed by the Marquardt-Levenberg algorithm which was computationally implemented in an Excel VBA homemade program. The e-NRTL equation was solved by using two different procedures: (i) included in the Excel VBA code or, (ii) implemented in Aspen Plus by linking the process simulator and the Excel VBA code via automation as the third-party software. The interaction parameters obtained by both approaches were able to adequately fit the experimental results. They were successfully validated by the thermodynamic prediction of multicomponent systems reported by other authors. Additionally, the current predictions were compared with those obtained with the parameters contained in the Aspen Properties database showing a significant improvement for several systems. Finally, this work demonstrates that it is possible enhancing the quality of the prediction of multicomponent systems with proper values of the binary electrolyte interaction parameters, without considering electrolyte-electrolyte interactions foreseen in the original e-NRTL model, which makes possible the simulation of processes containing a variety of chemical species regardless their nature.

Solubility and speciation of iron in cementitious systems

Aqueous iron hydrolysis products and chloride complexes influence steel corrosion kinetics and dictate the amount and type of corrosion products formed. Here, we compile a thermodynamic database devoted to aqueous iron species and solid oxides as well as chloride complexes, aiming to describe their speciation and solubility within the prevailing chemical environment of interest for cementitious systems. We compare thermodynamic calculations to empirical data on the elemental composition of pore solutions from cementitious systems.It is found that dissolved iron concentrations in cement pore solutions can differ considerably from thermodynamic predictions. In particular, measured Fe(II) concentrations can exceed the thermodynamic limit by 2–5 orders of magnitude. Additionally, experimentally obtained iron solubility in the presence of chloride exceed thermodynamic predictions. We discuss that these differences may be explained by so far unknown iron complexes, stabilisation of intermediate phases such as chloride green rust, or due to (kinetic) hindrance of precipitation.

Hybrid thermochemical sorption seasonal storage for ultra-low temperature solar energy utilization

The effective upgrading and utilization of low or ultra-low temperature heat (below 50 °C) could meet a significant fraction of space and water heating loads. To fulfill this goal, hybrid sorption thermal energy storage (TES) to recover ultra-low grade solar heat below 50 °C is investigated, aiming to address the issue of winter heating in severe cold regions. A water-based solar photovoltaic-thermal (PVT) system is integrated to provide heat and electricity for a sorption TES system. Composite ammonium chloride is used for thermodynamic prediction in terms of weather conditions in different places. It is demonstrated that when water temperatures increase from 31.4 °C to 51.2 °C, energy efficiencies of hybrid sorption TES system under theoretical and selected working conditions in Hangzhou increase from 0.52 to 0.57 and from 0.33 to 0.38, respectively. The overall exergy efficiencies of hybrid TES with the PVT system under theoretical and selected working conditions increase from 0.059 to 0.062 and from 0.046 to 0.057, respectively. The overall exergy efficiency of the hybrid system in Helsinki is 0.55, which is 4.3% higher than those in Hangzhou. One remarkable fact is that hybrid sorption TES integrated with the PVT system is quite promising especially for severe cold regions.

Solid-State Transformation of an Additive Manufactured Inconel 625 Alloy at 700 °C.

Inconel 625, a nickel-based superalloy, has drawn much attention in the emerging field of additive manufacturing (AM) because of its excellent weldability and resistance to hot cracking. The extreme processing condition of AM often introduces enormous residual stress (hundreds of MPa to GPa) in the as-fabricated parts, which requires stress-relief heat treatment to remove or reduce the internal stresses. Typical residual stress heat treatment for AM Inconel 625, conducted at 800 °C or 870 °C, introduces a substantial precipitation of the δ phase, a deleterious intermetallic phase. In this work, we used synchrotron-based in situ scattering and diffraction methods and ex situ electron microscopy to investigate the solid-state transformation of an AM Inconel 625 at 700 °C. Our results show that while the δ phase still precipitates from the matrix at this temperature, its precipitation rate and size at a given time are both smaller when compared with their counterparts during typical heat treatment temperatures of 800 °C and 870 °C. A comparison with thermodynamic modeling predictions elucidates these experimental findings. Our work provides the rigorous microstructural kinetics data required to explore the feasibility of a promising lower-temperature stress-relief heat treatment for AM Inconel 625. The combined methodology is readily extendable to investigate the solid-state transformation of other AM alloys.

Iron-Speciation Control of Chalcopyrite Dissolution from a Carbonatite Derived Concentrate with Acidic Ferric Sulphate Media

The mechanisms involved in the dissolution of chalcopyrite from a carbonatite concentrate in a ferric sulphate solution at pH 1.0, 1.5 and 1.8, and temperatures 25 °C and 50 °C were investigated. Contrary to expectations and thermodynamic predictions according to which low pH would favour high Cu dissolution, the opposite was observed. The dissolution was also highly correlated to the temperature. CuFeS2 phase dissolution produced intermediate Cu rich phases: CuS, Cu2S and Cu5FeS4, which appeared to envelop CuFeS2. Thermodynamic prediction revealed CuS to be refractory and could hinder dissolution. CuFeS2 phase solid-state dissolution process was further discussed. Free Fe3+ and its complexes (Fe(HSO4)2+, Fe(SO4)2– and FeSO4+ were responsible for Cu dissolution, which increased with increasing pH and temperature. The dissolution improved at pH 1.8 rather than 1.0 due to the increase of (Fe(HSO4)2+, Fe(SO4)2– and FeSO4+, which were also the predominating species at a higher temperature. The fast and linear first dissolution stage was attributed to the combined effect of Fe3+ and its complex (Fe(HSO4)2+, while Fe(SO4)2– was the main species for the second Cu dissolution stage characterised by a slow rate.

Methane hydrate thermodynamic phase stability predictions in the presence of salt inhibitors and their mixture for offshore operations

A thermodynamic model is developed and used in this study to predict the phase equilibrium conditions of a methane -aqueous salt inhibitor -water hydrate system. The modified van der Waals-Platteeuw (vdWP) model is used to calculate the equilibrium condition of the hydrate phase. To compute the fugacities of gas and liquid phases, the Peng-Robinson equation of state (PR-EoS) and a previously developed Pitzer-Mayorga-Zavitsas-hydration model are used. The model predictions are compared to experimental results on methane hydrate phase equilibrium in the presence of an aqueous salt inhibitor. The absolute average relative deviation in predicted methane -aqueous salt inhibitor -water hydrate equilibrium pressure (AARD-P%) with the developed Pitzer-Mayorga-Zavitsas-Hydration model is 3.59% for CH4+NaCl, 1.52% for CH4+KCl, and 2.70% for CH4+ CaCl2. Finally, the hydrate suppression temperature caused by aqueous salt inhibitors and their mixtures on methane hydrate phase stability is calculated, and it is CaCl2>KCl>NaCl in that order. This work's phase equilibrium model demonstrates the potential application of determining methane hydrate equilibrium conditions in the presence of aqueous salt inhibitors and their mixtures used in offshore oil field applications.

Hydrogen Generation from Ammonia-Borane over Ni–B Amorphous Alloys Prepared from Aqueous Solution Based on Thermodynamic Prediction of Hidden Metastable of State

Hydrogen Generation from Ammonia-Borane over Ni–B Amorphous Alloys Prepared from Aqueous Solution Based on Thermodynamic Prediction of Hidden Metastable of State

Thermodynamic behavior and spectroscopic properties of CO and C3H8 mixed gas hydrates: Implications for hydrate-based gas separation

Gas mixtures containing carbon monoxide (CO) and propane (C3H8) are encountered in a variety of chemical processes such as the incomplete combustion of fossil fuels, syngas production, and steel plants. Here we investigate the thermodynamic stability and spectroscopic properties of CO-C3H8 mixed gas hydrates for potential applications related to hydrate-based gas separation (HBGS). The CO-C3H8 mixed gas hydrates were formed from CO/C3H8 gas mixtures at pressures of 0.5–1.4 MPa and 274 K. Three-phase (H–Lw–V) equilibrium conditions of the CO-C3H8 mixed gas hydrates were shifted to higher pressure and lower temperature regions with increasing CO concentration in the vapor phase. X-ray diffraction patterns of the CO-C3H8 mixed gas hydrates suggest the formation of cubic Fd3m structures (sII hydrate). Sold-state 13C cross polarization/magic angle spinning NMR and Raman spectroscopy demonstrated the preferential occupation behavior of CO and C3H8 molecules in the hydrate cages. Thermodynamic predictions using the predictive Soave–Redlich–Kwong model with the UNIFAC group contribution method were in excellent agreement with the experimental phase equilibria and the cage occupancy analysis by 13C NMR and Raman spectroscopy. The compositions of the CO-C3H8 mixed gas hydrates were examined by gas measurements after hydrate dissociations, which were very close to the 13C NMR analysis results and theoretical predictions. The recovery ratio of C3H8 was always higher than 1 and gradually increased with decreasing C3H8 concentration in the vapor phases. These results indicate that the HBGS process can effectively be used for selectively separating CO and C3H8 from CO/C3H8 gas mixtures.

Synthesis of Ti(C, N, O) ceramic from rutile at low temperature by CH4-H2-N2 gas mixture

Titanium carbides, oxides, nitrides, and carbonitrides possess many special and excellent properties. But the high production cost caused by the traditional carbothermic reduction process severely limits the wide applications. In this study, a novel synthesis process has been proposed by reducing and carbonitriding TiO2 with a CH4-H2-N2 gas mixture at low temperatures. The synthesis of Ti(C, N, O), reaction mechanism, and the composition of the product have been investigated. Thermodynamic analysis indicated that TiO2 could be ultimately reduced and carbonitrided to Ti(C, N, O) by CH4-H2-N2 gas mixture. Based on the predictions of thermodynamics, the effects of reduction time, temperature, and gas composition have been studied experimentally. The obtained results indicated that increasing reduction temperature and introduction of N2 are beneficial to the synthesis of Ti(C, N, O). Finally, the optimum reaction conditions have been obtained. The density functional theory (DFT) results further demonstrated the reaction mechanism. This work provides a new approach to prepare metallic carbonitrides from their oxides.