Dissolution Reaction Rate Research Articles

Study on a new molten salt for electrolytic preparation of Ti: dissolution mechanism and kinetic analysis of TiO2 in NaCl-KCl-K2TiF6

Understanding the dissolution behavior and reaction rate of TiO2 in the NaCl-KCl-K2TiF6 electrolyte system is paramount for the advancement of a novel titanium metal production process. Initially, the liquidus temperature of the electrolyte system decreases with an increase in K2TiF6 content or the addition of a small amount of TiO2. Kinetic analysis reveals that the dissolution of TiO2 in the electrolyte follows a zero-order reaction for the first 30 min, with an activation energy of 2.46 × 105 (J/mol). The saturation concentration of TiO2 is reached at 300 min, and higher reaction temperatures or increased K2TiF6 content enhance the solubility of TiO2 in the electrolyte. In addition, the regression equation Y = − 25.02096 + 1.06412x1 + 0.0362x2 among the solubility of TiO2 (Y), the ratio of fluoride to chloride in electrolyte (x1) and experimental temperature (x2) was established by multivariate regression model. The analysis indicates that TiO2 dissolves in the electrolyte system as a complex K2NaTiOF5, releasing TiOF2 gas during the reaction. Finally, characterization studies on the elemental composition, chemical state, molecular structure, and material morphology of K2NaTiOF5 complex and TiOF2 gas reveal even distribution of elements. The K2NaTiOF5 complex molecules exhibit irregularly polygonal dispersion, while TiOF2 exists as agglomerated particles.

Azoles as corrosion inhibitors in alkaline medium for ruthenium chemical mechanical planarization applications:Electrochemical and theoretical analysis

The adsorption performance and inhibition mechanism of azoles; Imidazole (IMD), 1, 2, 4-Triazole (TAZ), and 1, 2, 3-Benzotriazole (BTAH) inhibitors on ruthenium (Ru) at 9 pH, were investigated in this study using electrochemical techniques and density functional theory (DFT) simulations. The electrochemical data demonstrate that the three azole compounds being investigated are mixed type corrosion inhibitors with anodic predominance, and the order of corrosion inhibition efficiency for Ru is BTAH > TAZ > IMD. The azole compounds suppress the metal dissolution reaction rate by adhering on to the Ru surface and nature of adsorption (combined physisorption and chemisorption) is explained via Langmuir adsorption isotherm model. The increase in contact angle on the Ru surface verified the successful adsorption of the three organic inhibitors on the Ru surface. Furthermore, the suppression of corrosion reaction kinetics is validated with field emission scanning electron microscopy (FESEM) images. The results of quantum chemistry calculations indicate that the corrosion inhibition effect of BTAH is superior to that of IMD and TAZ. Further, using molecular dynamics modelling, the reliable configuration of the organic inhibitor molecules on the Ru (001) surface in aqueous medium was investigated and the total adsorption energy was computed.

Revealing of rich living radicals in oxide melts via weak magnetic effect on alumina dissolution reaction

Oxide melts are basic media in materials preparation, high-temperature processing and hot corrosion. The melt structure is essential to understand oxide melt properties and plays a fundamental role in ceramic preparation and tailoring. In this work, the rich living radicals in oxide melts were discovered and verified by the variation in the dissolution reaction rate of alumina ceramic in oxide melts with the magnetic flux density, as well as the ESR test results. The radical-rich coexistence structure and forming path of radicals were proposed beyond the traditional inorganic melt structure theory; the weak magnetic effect and associated controlling threshold on free radical reaction in high-temperature inorganic chemical process was revealed. It provides new thoughts on smelting and purification of metals, preparation of ceramic materials, corrosion resistance of refractories and high temperature inorganic reaction-related research.

Kinetics of Reductive Dissolution of a Magnetite Specimen Using Oxalic Acid

The removal of radionuclides from the primary coolant system of nuclear power plants occurs with the dissolution of corrosion metal oxide layers deposited with the radionuclides. Kinetic dissolution experiments were conducted with a synthetic magnetite specimen in the form of a thin plate using an aqueous solution of oxalic acid as a reducing agent. The effects of acid concentration and temperature were investigated on the kinetics of the reductive dissolution of a magnetite specimen. In particular, the kinetic experiments were performed in a wide temperature range from low (57 °C) to high (120 °C), above the normal boiling point of water. The dissolution of magnetite increased with increasing acid concentration and temperature. The acid concentration dependence of the dissolution reaction rate of Fe at a given temperature was correlated with the nth power of the oxalic acid concentration. Additionally, the temperature dependence of the dissolution reaction rate of Fe at a fixed oxalic acid concentration was studied with an Arrhenius-type equation.

Electrolyte Based Modeling of Corrosion Processes in Sulfuric Acid Mixtures, Part 1: Nonoxidizing Conditions

The corrosion behavior of stainless steels and Ni-based alloys in nonoxidizing sulfuric acid mixtures at concentrations below approximately 30 mol/kg H2O is modeled. The redox potential in sulfuric acid across a broad concentration range, from 0 to 80 mol% (0 to 95.6 wt%), is determined by the proton reduction reaction. Thus, in the absence of other oxidizing species, sulfuric acid behaves as a nonoxidizing (reducing) acid. The calculated corrosion rates, using an electrochemical model up to about 30 mol/kg H2O (about 75 wt%), are in agreement with experimental values. The predicted polarization curves of anodic and cathodic processes show that the alloys in these environments are in active dissolution regime, consistent with experimental data. The model predictions of corrosion rates in H2SO4+HCl, H2SO4+HF, and H2SO4+HCl+HF mixtures are in agreement with weight-loss corrosion data. The corrosion rate of alloys in the nonoxidizing sulfuric acid mixtures correlated to an equivalent alloy composition given by (Ni0.7-Cr0.1+Mo+0.5 W). The effect of alloying elements under these conditions may be related to their beneficial effect on active dissolution and proton reduction reaction rates.

A revision of mechanistic modeling of mild steel corrosion in H2S environments

In this study, a predictive model for the corrosion rate and the polarization response of bare steel in aqueous hydrogen sulfide (H2S) environments based on H2S dissociation and its buffering effect was developed. In this model, the hydrogen ion reduction is the only cathodic reaction. The results confirmed that the increased limiting cathodic current densities and the characteristic “double wave” behavior in the cathodic current of this system could be explained by hydrogen sulfide dissociation in the vicinity of the metal surface. The effect of hydrogen sulfide on the rate of iron dissolution reaction was also taken into account by introducing a reaction sequence involving sulfide intermediates into the calculations, parallel to the acidic iron dissolution reaction. The developed model was shown to be able to reasonably represent the characteristic electrochemical behavior of this system. Furthermore, the predicted corrosion rates are shown to be in good agreement with the available experimental data in the literature over a wide range of conditions.

Pore-scale investigation on reactive flow in porous media considering dissolution and precipitation by LBM

The reactive transport process in oil gas reservoirs is complicated due to the coupling between dissolution and precipitation. In the present study, based on lattice Boltzmann method, the coupled dissolution and precipitation process in randomly generated porous media by quartet structure generation is investigated at the scale of geological pores. The fluid velocity, temperature and concentration in porous media are solved by multicomponent flow lattice Boltzmann model, multicomponent thermal lattice Boltzmann model and mass transport lattice Boltzmann model, respectively. The solid phase is updated by volume of pixel method. The results show that the dissolution reaction rate has a positive impact on the consumption of reactants. For different precipitation reaction rates, there exists an optimal value resulting in abundant precipitate and sparse solid distribution. Reaction equilibrium constant affects reaction rates slightly but influence the solid morphology heavily. The coupled dissolution and precipitation process accelerates with the increase of Peclet number, but the precipitate produced increases with the decrease of Peclet number.

Synthesis of KAlSiO4 by Hydrothermal Processing on Biotite Syenite and Dissolution Reaction Kinetics

To make potassium from K-bearing rocks accessible to agriculture, processing on biotite syenite powder under mild alkaline hydrothermal conditions was carried out, in which two types of KAlSiO4 were obtained successfully. The dissolution-precipitation process of silicate rocks is a significant process in lithospheric evolution. Its effective utilization will be of importance for realizing the comprehensiveness of aluminosilicate minerals in nature. Two kinds of KAlSiO4 were precipitated in sequence during the dissolution process of biotite syenite. The crystal structures of two kinds of KAlSiO4 were compared by Rietveld structure refinements. The kinetics model derived from geochemical research was adopted to describe the dissolution behavior. The reaction order and apparent activation energy at the temperature range of 240–300 °C were 2.992 and 97.41 kJ/mol, respectively. The higher dissolution reaction rate of K-feldspar mainly relies on the alkaline solution, which gives rise to higher reaction order. During the dissolution-precipitation process of K-feldspar, two types of KAlSiO4 with different crystal structure were precipitated. This study provides novel green chemical routes for the comprehensive utilization of potassium-rich silicates.

Experimental simulation on mineral and hydrochemical evolution in response to water–coal–gas interaction of closed gassy coal mines

One ubiquitous environmental issue with the abandoned gassy coal mine is the potential of changes in water quality due to water–rock–gas action caused by high residual gas content. Therefore, a better understanding of how to accurately characterize the new multiphase system in the closed gassy coal mine is required. The gas in closed coal mine mainly includes CH $$_{4}$$ , CO $$_{2,}$$ N $$_{2}$$ , H $$_{2}$$ S, CO, etc., existing in the adsorbed, dissolved and free phases, which also leads to complex gas–water–rock interactions in the underground flooded pool. The recovery of the water level caused by the closure of the coal mine varied dramatically in hydrogeochemical conditions as well as gas flow performance in the flooded mine. Based on the nationwide investigation and case studies of high residual coal mine gas in abandoned coal mines in China, some sealed gassy coal mines have been experiencing the CO $$_{2}$$ inrush problems. Modeling experiments of mine water–rock (coal)–gas(CO $$_{2}$$ /N $$_{2}$$ ) reaction were conducted in closed coal mines. The results show that with the increasing reaction time, pH value increases gradually, and the relationship between Eh and pH is negative, by taking CO $$_{2}$$ /N $$_{2}$$ as gas phases in the water–rock reaction. The concentration of HCO $$_{3}^{-}$$ , SO $$_{4}^{2-}$$ , Ca $$^{2+}$$ , Mg $$^{2+, }$$ and SiO $$_{2}$$ increases with a different magnitude, and the level of total Fe decreases gradually, while the TDS of the solution increases. The reaction between typical minerals in coal and high SO $$_{4}^{2-}$$ and Fe $$^{3+}$$ mine water is simulated. The chemical composition of mine water and coal mineral compositions are modified in order to obtain the influence of particular reactions. The results show that in the mine water–rock–gas reaction with CO $$_{2}$$ as gas phase, the pH value of the solution increases, and the Eh decreases. The dissolution of mineral phases leads to an increasing trend in the content of HCO $$_{3}^{-}$$ , SO $$_{4}^{2-}$$ , Ca $$^{2+}$$ , Mg $$^{2+}$$ , and soluble SiO $$_{2}$$ in the water. The concentration of the total Fe in the solution gradually decreases, and the mineralization of the solution gradually increases. Each mineral has individual distinct dissolution reaction rate. The dissolution of kaolinite promotes the dissolution of quartz, while calcite dissolves along with the regeneration of new carbonate minerals. Pyrite dissolves accompanied by chlorite formation. For the N $$_{2}$$ gas phase, changes in hydrochemistry and mineral phases are mainly controlled by water–rock interaction.

Mesoscopic modeling of transport resistances in a polymer-electrolyte fuel-cell catalyst layer: Analysis of hydrogen limiting currents

Understanding transport resistances in a polymer-electrolyte fuel cell (PEFC) catalyst layer (CL) is essential to mitigate the unexpected voltage loss when using low loadings of precious metals. In this paper, we explore through mesoscopic modeling the quantification analyses of the transport resistances in CL as derived using hydrogen-pump limiting current. Numerical treatments on the conjugated interfacial conditions at interfaces of ionomer/pore and Pt/ionomer are proposed to describe the mesoscopic transport processes of hydrogen and proton. Characterizations of the reconstructed microstructure of CL are performed. Parameter analyses on the influences of the critical transport properties such as the permeation coefficient and the dissolution and adsorption reaction rates at the surfaces of ionomer/pore and Pt/ionomer on the local transport resistance are presented. It is found that the local transport resistance is mainly originated from the diffusion resistance of the ionomer thin-film, which is more resistive than its bulk analogue with its permeation coefficient fitted to be 5.9% of the bulk one. The interfacial transport resistances and the diffusion resistance are coupled. The local transport resistance increases with I/C ratio due to thicker ionomer coated on the particles. Higher Pt/C ratio and bare carbon fraction lead to higher local transport resistance since the ionomer loading relative to Pt roughness factor decreases. The local transport resistance decreases with the porosity. The contribution of pores to the CL resistance, which decreases with the porosity, is comparatively small at low loadings.

Studying ilmenite dissolution using mechanical activation method

In this work, the effects of temperature, acid concentration, and mechanical activation on dissolution of ilmenite were studied using the statistical design of experiment technique. Mechanical activation was carried out using a planetary ball mill in dry mode, and the resulting structural changes were characterized by the particle size analysis, specific surface area measurements, and X-ray diffraction method. The results obtained indicated that intensive milling led to a significant decrease in the ilmenite particle size and that after 20 minutes, particles tended to agglomerate. However, after 90 minutes, the BET specific surface area increased to 9.36 m2/g. In addition to surface changes, mechanical activation led to intense changes and disorders in the crystal structure of ilmenite as amorphization degree increased to 94.30% and the volume weighted crystallite size and lattice strain changed from 346 nm and 0.13% to 14 nm and 1.44%, respectively. The results of the dissolution tests in the form of experimental design indicated that a suitable model could fit the experimental data in 95% confidence level. The coefficient factors for acid concentration, mechanical activation, and temperature were 3.75%, 33.04%, and 9%, respectively. Mechanical activation had the highest effect on titanium extraction in comparison to the other factors involved. Also in addition to its dominant effect on ilmenite dissolution, it also weakened the temperature effect. However, the results of the kinetic tests proved that mechanical activation led to promotion of the temperature effect on increasing the dissolution reaction rate in the initial stages. Finally, a dissolution yield of more than 98% was achieved through 90 minutes of activation at 95° C and 55 wt.% acid concentration.

A review of geochemical–mechanical impacts in geological carbon storage reservoirs

AbstractGeological carbon storage (GCS) refers to the technology of capturing man‐made carbon dioxide (CO2) emissions, typically from stationary power sources, and storing such emissions in deep underground reservoirs. GCS is an approach being explored globally as a defense mechanism against climate change projections, although it is not without its critics. An important focus has been recently placed on understanding the coupling between rock–fluid geochemical alterations and mechanical changes for CO2 storage schemes in saline aquifers. This article presents a review of the current state of knowledge regarding CO2‐induced geochemical reactions in subsurface reservoirs, and their potential impact on mechanical properties and microseismic events at CO2 storage sites. This review focuses, in particular, on the current state of the art in fluid–rock interactions within the GCS context. Key issues to be addressed include geochemical reactions and the alteration of transport and mechanical properties. Specific review topics include the swelling of clays, the prediction of dissolution and precipitation reaction rates, CO2‐induced changes in porosity and permeability, constitutive models of chemo–mechanical interactions in rock, and correlations between geochemical reactions and induced seismicity. The open questions in the field are emphasized, and new research needs are highlighted. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Features affecting the cupric chloride leaching of gold

The current study investigated gold dissolution in cupric chloride solution, which is one of the most promising alternatives to replace cyanide, although not yet in operation on industrial scale. In this paper, the gold dissolution reaction rate and mechanism were studied by varying the process variables of temperature (28–95 °C), cupric concentration (0.02–1.0 M), chloride concentration (1–5 M), rotational speed (100–2500 RPM), and pH (0.5–2.0). The parameters affecting either the anodic or cathodic reaction, or both, were identified for the first time to the best of the authors’ knowledge in this wide range and with these parameter intervals. Tafel and linear polarization methods as well as cyclic voltammetry were used for pure gold with both rotating disk and stationary gold electrodes. An increase in the gold dissolution rate was observed with an increase in temperature, chloride concentration, and rotational speed. Additionally, an increase in cupric concentration ([Cu2+] = 0.02–0.75 M) promoted the gold dissolution rate, whereas the gold dissolution rate decreased with [Cu2+] from 0.75 to 1.0 M. The conditions for maximizing the gold dissolution rate in cupric chloride solution were concluded to be T > 55 °C, [Cu2+] = 0.5–0.75 M, [Cl−] = 5 M, and pH = 1.0 and the highest gold dissolution rate (2.9 · 10−4 mol m−2 s−1) was achieved at 95 °C with [Cu2+] = 0.5 M, [Cl−] = 5 M, pH = 1.0, and ωcyc = 2500 RPM. The pH was shown not to affect the gold dissolution rate at all, but only to affect the solubility of the oxidant. It was suggested that gold dissolved as aurous species in the conditions of this study, although the increase in chloride concentration promoted the dissolution of gold as both, auric and aurous, species.The reaction mechanism was interpreted using mixed potential theory. An increase in temperature was shown to promote only the cathodic reduction of cupric ion to cuprous at lower temperatures (28–55 °C); however, both the anodic gold dissolution reaction and cathodic cupric reduction reaction were enhanced at higher temperatures (65–95 °C). The cathodic reaction was also enhanced with an increase in cupric concentration (0.02–0.5 M), whereas the anodic reaction was promoted when the cupric concentration was increased from 0.5 to 0.75 M. When the cupric concentration was increased from 0.75 to 1.0 M, the cathodic reaction rate decreased. However, the reason for the decrease in the cathodic reaction rate was not clear. An increase in chloride concentration enhanced the cathodic reaction in the investigated range (1–5 M), whereas an increase in rotational speed (i.e., improved mass transfer) increased the anodic gold dissolution rate, specifically at low rotational speeds.

Pore-scale study of reactive transport processes in catalyst layer agglomerates of proton exchange membrane fuel cells

Porous structures of agglomerates in cathode catalyst layers (CLs) of proton exchange membrane fuel cells are reconstructed, in which all the four phases are resolved including Platinum, carbon, ionomer and pore. A pore-scale reactive transport model based on the lattice Boltzmann method is developed, in which oxygen dissolution reaction at pore-ionomer interface, oxygen diffusion inside ionomer, and electrochemical reaction at ionomer-Pt interface are considered. Emphasis is put on structural parameters, especially Pt/C mass ratio, on the reactive transport process and the volumetric reaction rate (or current density). Pore-scale results show that while under high Pt loading oxygen is depleted quite close to the surface of the spherical agglomerate, it has to penetrate deep into the porous agglomerate before it is completely consumed under low Pt loading which is not captured by classical agglomerate model based on homogeneous mixture assumption. Pore-scale results also found that effects of transport inside the agglomerate decreases as reaction rate, porosity or ionomer thickness increases. Finally, local transport resistance inside the agglomerate is evaluated, and it increases as the agglomerate size increases or the dissolution reaction rate decreases.

Open circuit potential and leaching rate of pyrite in cupric chloride solution

ABSTRACTAs a refractory gold mineral, pyrite needs to be oxidised prior to gold leaching. In this study, the effect of [Cl−] concentration (40.6–149.8 g/L), [Cu2+] concentration (0.8–31.6 g/L), pH (1.5–2.5) and temperature (25–90 –C) on the pyrite leaching rate was investigated. In addition, the open circuit potential (OCP) values of pyrite in cupric chloride solution were investigated. A linear regression model was constructed to predict pyrite dissolution rate i.e. corrosion current density. It was shown that the temperature had a significant positive effect on pyrite dissolution, while increased cupric ion concentration was also shown to provide some dissolution enhancement. According to the regression analysis, pH had no effect on the corrosion current density at OCP. Dissolution rates of pyrite varied between 0.05 and 2.9 µm/h. The activation energy values varied from 20 to 90 kJ/mol, indicated that the pyrite dissolution reaction rate was controlled by the chemical reaction or mixed mechanism rather than diffusion alone. The simultaneous increase in corrosion potential and corrosion current density indicated that the anodic pyrite dissolution reaction was rate determining at OCP.

Dissolution kinetics of solid fuels used in COREX gasifier and its influence factors

Carbon dissolution from solid fuels used in a COREX gasifier was investigated in a high-temperature furnace to investigate the influences of temperature, carbon structure and ash properties of solid fuels into molten iron on carbon dissolution behavior. The results showed that the final carbon content of molten iron and dissolution reaction rate of carbon increased as the temperature increased. However, the dissolution behavior of different solid fuels varied with their properties. At the same temperature, the dissolution reaction rate of solid fuel from high to low was coke, semi-coke and lump coal. The apparent reaction rate constants of solid fuel were calculated using the piecewise fitting method based on the experimental data. The analyzed results showed that the dissolution rates of solid fuels had a good correlation with their microcrystalline structures. Moreover, the carbon crystallite structures of solid fuels used in COREX had greater influence on dissolution behavior than their ash properties.

Research into effect of electrochemical etching conditions on the morphology of porous gallium arsenide

The method for the formation of porous gallium arsenide in a solution of hydrochloric acid was improved. The goal of present research was to establish correlation between conditions of electrochemical etching of gallium arsenide crystals and morphology of low-dimensional structures. Porous layers were formed by the method of electrochemical etching in a solution of hydrochloric acid. The mode of electrolyte agitation was applied. This makes it possible to avoid the formation of bubbles on the surface of the crystal during etching and leads to the formation of regular porous space. Basic regularities in the formation of porous spaces were studied. It was shown that morphological properties of por-GaAs depend on etching conditions. The effect was explored of current density on the thickness of a porous layer and diameter of pores. It was established that the composition and concentration of electrolyte correlate with surface porosity and affect the rate of crystal dissolution reaction. Etching time determines thickness of a porous layer and surface porosity. Chemical composition of por-GaAs was explored. An oxide layer was not formed on the surface of the examined samples; oxygen was present only in small concentrations. Stoichiometry of the samples was disrupted towards an excess of gallium atoms

Connection between Atomic Scale Characterization and Electrochemical Behavior during Passivation of Polycrystalline and Single Crystal Ni-Cr and Ni-Cr-Mo Alloys

Ni-Cr and Ni-Cr-Mo alloys owe their superior corrosion resistance to the surface enrichment of passivating Cr-rich oxides or hydroxides and the synergistic effect of Mo in the film1–3. However, the specific role of alloying elements such as Mo are not well-understood, especially with respect to their position relative to the oxide/metal interface and atomistic influence on film growth, localized breakdown, and repassivation processes. The composition, structure, and thickness of the passivating oxide films are additionally challenging to characterize in-situ due to their nanoscale dimensions and the high electric field imposed by aqueous growth. The key processes which take place in oxide films and regulate their behavior in aqueous environments are atomic, ionic, and electronic in nature and currently poorly understood, often requiring study at the resolution and detection limits of characterization methods4. The main goal of this work is to integrate bulk polycrystalline and single crystal electrochemical measurements with nanoscale characterization to advance the fundamental understanding of the structure, molecular, and electronic properties of oxides formed during aqueous passivation and uncover the role of Mo on surface stability in corrosive environments. The alloys under study are Ni-11Cr, Ni-11Cr-6Mo, Ni-22Cr, and Ni-22Cr-6Mo, wt%, polycrystalline solid solutions with additional focus on individual grain orientations in isolation from grain or twin boundaries. DC and AC electrochemical techniques were utilized for exploring the controlled growth of passive oxide films on these materials in aqueous chloride and chloride-free solutions of various acidity. The repassivation kinetics of polycrystalline and single grain crystal surfaces were determined potentiostatically and galvanostatically after previously formed air oxides were reduced. A major challenge to analysis of the oxidation rate from electrochemical data is that film thickening rate must be assessed independently from the total oxidation rate. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) results indicate that a significant portion of the applied anodic charge during oxidation is associated with direct cation ejection and/or dissolution rather than film thickening. Single frequency electrochemical impedance spectroscopy (SF-EIS) and ICP-MS were thus applied as novel characterization methods to model the electrochemically grown oxides and measure in-situ changes in oxide thickness and elementary dissolution reaction rates during passivation and film dissolution and/or cation emission. The oxide thicknesses calculated using these methods were related to the charge that goes toward oxide film growth and the related oxidation current density. Atomic force microscopy (AFM) topography images and profiles across single grain surfaces at intermediate stages of potentiostatically and galvanostatically controlled oxide growth were obtained to give insight on the nucleation and morphology of oxides formed. The surface roughness was derived from these images in order to quantify the influence of the minor alloying elements, and chloride presence on the morphology and degree of film breakdown during the stages of passivation. 3D atom probe tomography and X-ray photoelectron spectroscopy analysis of the oxides following potentiostatic and galvanostatic growth provided additional information regarding the location and chemical identity of elements across the films. This pairing of operando mesoscale electrochemical techniques with ex-situ microscopy describes the competitive oxidation and dissolution processes in aqueous environments and achieves an atomic-scale understanding of the oxide surface morphology along with the influence of minor alloying elements. The fate of all elements during fast repassivation was tracked operando for analysis of the significant impact of dissolution and cation ejection during passivation using ICP-MS, SF-EIS, and AFM measurements. The role of kinetics on passivation was found to play a crucial role over thermodynamics, resulting in non-conformal and unexpected oxide growth dictated by the minimization of interfacial energy and stresses. Finally, Mo was found to serve a number of roles during passivation and collects at the film/solution interface as well as throughout oxides. ACKNOWLEDGEMENTS This work was funded by the U.S. Office of Naval Research Multi-University Research Initiative under a subcontract from Northwestern University SP0028970-PROJ0007990 with Dr. David A. Shifler. REFERENCES 1. F. Bocher, R. Huang, and J. R. Scully, Corrosion, 66, 1–15 (2010). 2. A. C. Lloyd, J. J. Noël, S. McIntyre, and D. W. Shoesmith, Electrochim. Acta, 49, 3015–3027 (2004). 3. A. C. Lloyd, J. J. Noël, N. S. McIntyre, and D. W. Shoesmith, JOM, 57, 31–35 (2005). 4. P. Jakupi, D. Zagidulin, J. J. Noël, and D. W. Shoesmith, Electrochim. Acta, 56, 6251–6259 (2011).

Stimulation of high temperature carbonate gas reservoirs using seawater and chelating agents: Reaction kinetics

The use of hydrochloric acid (HCl) in gas well stimulation of high temperature reservoirs is currently facing different challenges. These challenges include rapid corrosion of the well tubulars, face dissolution, very high and uncontrolled reaction rate, and formation damage in high clay content and iron-rich reservoirs. In this study, water-soluble diethylene triamine penta acetic acid (DTPA) chelating agent is introduced as alternative to eliminate the risk associated with HCl at high temperatures. In addition, the potential of using seawater to replace fresh water in the stimulation process is explored to save the cost of fresh water transportation to deep offshore oil and gas wells. The effect of seawater on the reaction kinetics of DTPA with carbonate rocks under high pressure and high temperature conditions is investigated using the rotating disk apparatus. The reactions of DTPA solution diluted with fresh water (DTPA/DI) and seawater (DTPA/SW) with carbonate rocks were carried out at the same conditions. In the case of fresh water, the reaction is controlled by the surface reaction regime. Adding HCl to adjust DTPA pH did not turn the reaction into a mass transfer controlled reaction like the case of using HCl alone. The heavy matrix of seawater increased the resistance of ions diffusion, which resulted in a low reaction rate and transformed the reaction into a mass transfer limited regime. Corrosion tests were carried out on production and coiled tubing coupons obtained from the gas wells and the results of the new DTPA/SW formulation is compared to the standard HCl formulation. DTPA showed very low corrosion rate of 0.0034 g/cm2 without adding corrosion inhibitors compared to 0.205 g/cm2 of 15 wt% HCl with 3% corrosion inhibitors while the industry limit is 0.0244 g/cm2 in 6 h. The reaction regime of DTPA chelating agent with calcite is identified to be mass transfer limited in seawater and surface reaction limited in fresh water. The rate expression for the dissolution of Ca2+ in DTPA/SW solution is obtained. Coreflooding experiments were performed to determine the optimum injection rate using low permeability Indiana limestone core samples. The optimum injection rate required to stimulate a very deep carbonate gas well was found to be 1.4 bbl/min after scaling up the coreflooding results to field scale. The application of the new DTPA/SW formulation in treating deep gas wells is expected to save the cost of fresh water and eliminate the cost of corrosion inhibitors.

A new alternative approach for investigating acidization dissolution front propagation in fluid-saturated carbonate rocks

The natural phenomenon associated with the chemical dissolution of dissolvable minerals of rocks can be employed to develop innovative technology in mining and oil extracting engineering. This paper presents a new alternative approach for theoretically dealing with chemical dissolution front (CDF) propagation in fluid-saturated carbonate rocks. Note that the CDF is represented by the porosity front in this study. In this new approach, the porosity, pore-fluid velocity and acid concentration are directly used as independent variables. To illustrate how to use the present new approach, an acidization dissolution system (ADS) consisting of carbonate rocks, which belongs to one of the many general chemical dissolution systems (CDSs), is taken as an application example. When the acid dissolution capacity (ADC) number (that is defined as the ratio of the volume of the carbonate rock dissolved by an acid to that of the acid) approaches zero, the present new approach can be used to obtain analytical solutions for the stable ADS. However, if the ADC number is a nonzero finite number, then numerical solutions can be only obtained for the ADS, especially when the ADS is in an unstable state. The related theoretical results have demonstrated that: (1) When the ADS is in a stable state and in the case of the ADC number approaching zero, the present new approach is mathematically equivalent to the previous approach, in which the porosity, pore-fluid pressure and acid concentration are used as independent variables. However, when the ADS is in an unstable state, the use of the present new approach leads to a free parameter that needs to be determined by some other ways. (2) The existence of a non-step-type dissolution front within a transient region should at least satisfy that none of the ADC number, injected acid velocity and reciprocal of the dissolution reaction rate is equal to zero in the stable ADS.