Abstract Accurate prediction of corrosion behavior in chemically diverse environments is critical for material selection, process reliability, and asset longevity. To address this need, this study presents the application of the Mixed-Solvent Electrolyte (MSE) thermodynamic framework, integrated with an electrochemical corrosion model, to predict the general corrosion behavior of three corrosion-resistant alloys: UNS S31600 (316 stainless steel), UNS N06625 (alloy 625), and commercially pure titanium. The MSE Corrosion model can predict the anodic and cathodic half reactions, passive film formation, and the active-passive transition across a wide range of conditions, including variations in pH, temperature, and electrolyte concentration. The model was calibrated using experimental data from a diverse set of chemical systems, including single acids, acid mixtures, neutral and alkaline solutions, systems containing dissolved oxygen, acid gases etc. Each environment was used to parametrize specific aspects of the corrosion model, ensuring accurate representation under both oxidizing and reducing conditions, while capturing the influence of aggressive and inhibitive species. The mechanistic basis of the model allows it to extrapolate to complex systems and conditions where experimental data may be sparse or unavailable.

Geothermal systems experience a wide range of environments and temperatures and are susceptible to localized corrosion. Due to the potentially highly corrosive conditions, CRAs are used for the equipment. As part of a broader study, various CRA, including Titanium Grade 2, were tested to help develop and validate the Mixed Solvent Electrolyte corrosion model for predicting localized corrosion susceptibility at higher temperatures representative of geothermal systems. Grade 2, a commercially pure titanium alloy, forms a protective oxide film which aids in resistance to harsh environments. Unlike stainless steels where crevice corrosion grows with increasingly positive potentials relative to the repassivation potential, Grade 2 becomes more passive. This requires an alternative test method from the standard cyclic potentiodynamic polarization or potentiodynamic-galvanostatic-potentiostatic techniques used to evaluate localized corrosion susceptibility of CRA. Although several studies are reported in literature on localized corrosion testing of Ti alloys, detailed experimental procedures are lacking. Experimental work was performed to study the localized corrosion susceptibility of Grade 2 in geothermal environments and develop a reproducible electrochemical test method to measure crevice repassivation potentials of Ti alloys. Results were compared with literature for creviced Grade 2 in high chloride environments at high temperatures. This paper discusses the lessons learned and the details of the test method.

Localized corrosion poses a critical challenge for geothermal systems due to the presence of high temperatures and corrosive species such as chlorides, acid gases, and dissolved oxygen. Models that can accurately predict the risk of localized corrosion are thus essential for effective asset management. This study extends the Mixed-Solvent Electrolyte (MSE) corrosion model to predict the risk of localized corrosion to conditions relevant for geothermal systems. The model incorporates two key electrochemical potentials, i.e., the corrosion potential (Ecorr) and repassivation potential (Erp), predicting localized corrosion risk when Ecorr exceeds Erp. The focus of this study is improving predictions for Erp. The previously developed MSE Erp model is extended to account for the effect of reduced sulfur species, such as H2S and S2O32-, which are present in some geothermal systems and can either promote or inhibit localized corrosion depending on the environmental conditions. To improve Erp predictions, high temperature electrochemical data, which are scarce in the literature, were obtained for alloys frequently used in geothermal systems. This data was then used to develop parameters and to validate the model’s accuracy under geothermal conditions.

Alternative sourcing of critical metals from lithium-ion batteries (LIBs) is necessary to secure the future supplies of Li, Ni, and Co. Most recovery processes of LIBs utilize pyrometallurgical and hydrometallurgical methodologies; however, these processes to recycle LIB cathode/anode materials can require several steps to isolate the desired metals. We have developed a facile isolation of the valued metals, where Ni and Co will co-crystallize as a sulfate double salt, called Tutton's salt [(NH4)(2)Ni/Co(SO4)(2)6H(2)O]. Thermodynamic modelling of these Ni(II)/Co(II) sulfate double salts shows that Ni is less soluble than Co which could enhance the separation of Ni and Co from electrochemical (EC) leachates. This calculated difference between Ni and Co can be controlled further by temperature and ammonium sulfate concentration. Here, Ni-rich sulfate double salts were achieved at 30-45 degrees C while Co-rich sulfate double salts were formed at 2-9 degrees C, where 99% Ni and 89% Co were recovered from the EC-leach solution. Further tests with the leachate solution show that crystallization occurs above pH 2 which allows for higher pulp density leachates. Chemical analyses and single crystal X-ray characterization confirm that the Ni-rich sulfate double salts contain Ni and Co. However, the Co-rich sulfate double salts have similar to 30% Mn(II) in the crystal lattice with similar to 37% of Ni. As a result, this process reduces the total number of steps to isolate the desired metals while also reducing chemical waste generation and without employing organic solvents.

Crude unit overhead systems contain complex mixtures of hydrocarbon, water, and various ionic species, which under the right set of conditions, can cause aggressive corrosion. Understanding the corrosion characteristics of the system is further complicated because the composition and phase behavior of the overhead stream is also changing rapidly as it is being condensed. Ionic modeling has been used to better understand the rapidly changing phase behavior in this system and to shed light on some factors which may influence corrosion. Ionic modeling of a crude unit overhead system predicts the formation of a concentrated "salty water" phase that precedes the formation of a bulk water phase. The formation of this concentrated solution may help explain the aggressive corrosion characteristics of some amine hydrochloride salts in crude unit overhead systems. Additionally the presence of small quantities of tramp amines may influence the salt formation characteristics and phase behavior of the system.

The influence of the hydrodynamic effects of fluid flow on the hydrothermal deposition of (001) oriented epitaxial Pb(Zr0.7Ti0.3)O-3 (PZT) thin films onto single-crystal SrTiO3 (100) substrates was investigated. The films were grown at 150 degrees C from lead acetate, zirconyl chloride, and titanium dioxide precursors and potassium hydroxide mineralizer under batch quiescent conditions and at varying stirring rates in the range of 200-1700 rpm. To ensure that the hydrodynamic effects of the stirring rate were not unique to a specific set of thermodynamic variables, two sets of reaction conditions were chosen corresponding to a precursor concentration of 0.3 m (Zr + Ti) and mineralizer concentrations of 6 and 10 in KOH. Thermodynamic computations predicted that the perovskite phase was stable at > 99% yield under both sets of conditions. Characterization of the films by field-emission scanning electron microscopy, Rutherford backscattering, and X-ray diffraction showed that fluid flow derived from stirring significantly altered the microstructure, compositional homogeneity, phase purity, and crystal quality of the films. It was found that films deposited at higher stirring rates were thinner but also exhibited a higher degree of stoichiometry, phase purity, and epitaxy with the substrate. The study of the PZT film and particles growing simultaneously in the hydrothermal reactor provided useful insight into the crystallization mechanism. The mechanistic implications of these observations for the nucleation and growth of epitaxial films under hydrothermal conditions at low temperatures are discussed and related to mass transport effects, such as particle motion and chemical diffusion. A new crystallization mechanism is proposed based on particle encounters with a crystallizing surface and overlap of electrical double layers.

Thermodynamic modeling of hydrothermal solutions was used to examine the influence of ethylenediamine tetra-acetic acid (EDTA) on the synthesis of lead-based perovskites, PbTiO3 and PbZr0.52Ti0.48O3. Temperature, pH, input reagent concentrations, and Pb/(Ti + (Zr)) and Pb/EDTA ratios were examined. Thermodynamic calculations from 25 to 100 degreesC indicated that, when the Pb/EDTA and Pb/(Ti + (Zr)) molar ratios were 2.0 and Pb input concentration was 0.1 m, phase-pure perovskites formed across the greatest pH range (7-14+). Precipitation of unwanted unary lead phases such as PbO was suppressed in all cases. In the absence of EDTA and solutions containing a molar excess of lead ions, the formation of phase-pure perovskites was limited to narrow pH ranges (5-8 and above 14) because of PbO precipitation. Theoretical predictions were experimentally validated with use of X-ray diffraction, transmission electron microscopy, energy dispersive spectrometry, and atomic absorption spectroscopy. Experimental results validated the theoretical predictions at temperatures above a minimum reaction temperature. Relative to comparable hydrothermal systems free of EDTA, the addition of EDTA was found to lower the minimum reaction temperature by 70 degreesC for PbTiO3 (70 degreesC) and 25 degreesC for PbZr0.52Ti0.48O3 (125 degreesC).

Thin and thick films of lead zirconate titanate (PZT) with Zr/Ti molar ratio of 70130 were hydrothermally grown on polished (100) oriented strontium titanate (ST) substrates using conventional and microwave reactors in the 120-180 degreesC temperature range. In 2.5 m KOH or tetramethylammonium hydroxide (TMAH) the growth results in island growth of isolated PZT platelets whereas in 10 m KOH a continuousa nd smooth PZT film is obtained (1 mum thick). However, in 2.5 m KOH or TMAH, PZT nucleation can be promoted by proper surface modification to achieve full coverage of the substrate. After nucleation, thick layers of PZT can be grown with an apparent activation energy of 12 kcal/mol. XRD investigations showed that the thin and thick PZT films (17 mum) are epitaxial and have a single crystal nature (normal and in-plane orientation).

A study was conducted to compare the minimum reaction temperatures for the hydrothermal synthesis of pure lead titanate crystallites with precursors I and II. The synthesis conditions (i.e., temperature, pH, and input reagent concentrations) were calculated using a thermodynamic model. A comparison between the theoretically modeled and experimental conditions was made. Although the models predicted reactions as low as 25/spl deg/C, the minimum temperatures for a 72 h reaction time with precursors I and II were 120 and 140/spl deg/C, respectively. Furthermore, by increasing the Pb/Ti molar stoichiometric ratio from 1.0 to 2.0 (with precursor LT) the reaction temperature for phase-pure lead titanate could further be reduced below 90/spl deg/C; while with precursor I phase-pure lead titanate was difficult to obtain and was not obtained below 140/spl deg/C. It can be concluded that precursor composition and stoichiometry influence the reaction temperature.

Vapour pressures of organic nitrogen-containing compounds have been analysed using an equation of state allowing for association which was developed by Wenzel, Moorwood and Baumgartner, (Fluid Phase Equilibria, 9 (1982) 225). Besides vapour pressures, the equation accurately reproduces liquid and vapour densities at room temperature and critical coordinates of polar compounds. The equation is also able to predict vapour pressures in a wide temperature range from limited experimental input information.

The Świȩtosławski ebulliometer has been modified so as to extend its range of applicability to lower pressures. The device has been shown to yield accurate results from 0.1 kPa to atmospheric pressure. Vapour pressures have been measured using the apparatus for pyridine, 2-methylpyridine, 2,4-dimethylpyridine, 2,6-dimethylpyridine, and 2,4,6-trimethylpyridine. The results have been correlated using the Antoine equation.

Vapour pressures of 2,6-, 2,4-, and 3,5-dimethylpyridine have been measured using a static method in the range of temperatures from 267 to 360 K. A correlation equation representing vapour pressure of methyl- and dimethyl-pyridines, the low-pressure region included, is developed and its application discussed.

Molar enthalpies of vaporization for five di- and two tri-methylpyridines were determined with an accuracy of 0.25 per cent, using an adiabatic vaporization calorimeter. The measurements were performed over the temperature range from 313 to 368 K for four dimethylpyridines and from 328 to 368 K for the other compounds. The results were correlated as a function of temperature, and molar enthalpies of vaporization at 298.15 K and the normal boiling temperatures were obtained by extrapolation. Molar cohesive energies were calculated from experimental values for Δ1gHm and correlated as a function of temperature.

Molar enthalpies of vaporization of pyridine and three isomers of methylpyridine were measured over the temperature range from 298 to 368 K with an accuracy of 0.25 per cent, using an adiabatic vaporization calorimeter. The results combined with literature values relating to higher temperatures were fitted to a functional expression enabling Δ1gHm to be calculated with an uncertainty of less than 0.3 per cent within the following temperature ranges: pyridine, 298 to 388 K; 2-methylpyridine, 298 to 403 K; 3-methylpyridine, 298 to 417 K; 4-methylpyridine, 298 to 434 K. Molar cohesive energies were evaluated from Δ1gHm and correlated with temperature.