Dissolution Rate Constants Research Articles

Rates of Fe(II)-Oxidation and Solubility of Bacteriogenic Iron Oxides

ABSTRACTThe oxidation of Fe(II) at circumneutral pH by natural bacterial consortia capable of oxidizing Fe(II) in flocculent mats of bacteriogenic iron oxides (BIOS) was investigated in a series of microcosm experiments under constant pH and pO2 conditions. The oxidation of Fe(II) was faster in the presence BIOS compared to chemical oxidation in solution with pseudo–first-order rate constants ranging from 0.036 to 0.248 min−1 for BIOS compared to 0.004 min−1 for the chemical control. The Fe(II)-oxidation rates exhibited a kinetic dependency on BIOS concentrations, measured in terms of a pseudo–second-order rate constant at 0.066 Lg−1min−1. From the asymptotic decline in Fe(total) in the microcosms, apparent rate constants for HFO dissolution (zero-order values 0.001 to 0.046 mgL−1min−1) and precipitation (second-order values 0.007 to .297 min−1) were obtained from the BIOS and control microcosms, which yield an apparent equilibrium BIOS solubility of 0.157 mgL−1 (i.e., 2.8 μM). These results reflect the complex interplay of Fe(II) oxidation reactions associated with BIOS including homogenous chemical oxidation in solution, chemical oxidation on HFO surfaces, and bacterially mediated oxidation. Furthermore, BIOS precipitated in response to Fe(II) oxidation exhibit a greater apparent solubility than more stable varieties of HFO. The implication is that the competitive advantage of Fe(II)-oxidizing bacteria over autocatalytic surface chemical Fe(II) oxidation on HFO might be enhanced by a reduction in the total amount of BIOS that is precipitated.

Encapsulation of light hydrophobic liquids with fine quartz sand: Property based characterization and stability in aqueous media with different salinities

A novel method for capturing oil slicks in aquatic environments with granular solids was investigated. Experiments were conducted with pure hydrophobic liquids (HL) (decane, tetradecane, hexadecane, benzene, toluene, ethylbenzene, and m-xylene) representing the main groups in crude oil (alkanes and aromatics), and fine quartz sand (passing sieve no. 40 with 0.425mm openings). The amounts of HL captured in the HL/sand globules were correlated with the properties of HLs. Positive correlations between the aggregated HL volume with density and surface tension were observed. Aggregation number (AN) is introduced to estimate the amount of HL aggregated with fine quartz sand (using 0.5mL HL and 1.0g sand; floating HL layer thickness to particle diameter ratio >4:1). Change in the aggregated HL volume over time was examined and dissolution rate constants were obtained. Benzene and toluene completely dissolved from the aggregated globules within 3–4 days after the aggregation, while the other HLs exhibited relatively small change in the globule size over time. Salinity of water did not affect the aggregation rates of HLs but slightly decreased the dissolution rate constants for some HLs.

Two-phase model of hydrogen transport to optimize nanoparticle catalyst loading for hydrogen evolution reaction

With electrocatalysts it is important to be able to distinguish between the effects of mass transport and reaction kinetics on the performance of the catalyst. When the hydrogen evolution reaction (HER) is considered, an additional and often neglected detail of mass transport in liquid is the evolution and transport of gaseous H2, since HER leads to the continuous formation of H2 bubbles near the electrode. We present a numerical model that includes the transport of both gaseous and dissolved H2, as well as mass exchange between them, and combine it with a kinetic model of HER at platinum (Pt) nanoparticle electrodes. We study the effect of the diffusion layer thickness and H2 dissolution rate constant on the importance of gaseous transport, and the effect of equilibrium hydrogen coverage and Pt loading on the kinetic and mass transport overpotentials. Gaseous transport becomes significant when the gas volume fraction is sufficiently high to facilitate H2 transfer to bubbles within a distance shorter than the diffusion layer thickness. At current densities below about 40 mA/cm2 the model reduces to an analytical approximation that has characteristics similar to the diffusion of H2. At higher current densities the increase in the gas volume fraction makes the H2 surface concentration nonlinear with respect to the current density. Compared to the typical diffusion layer model, our model is an extension that allows more detailed studies of reaction kinetics and mass transport in the electrolyte and the effects of gas bubbles on them.

Dissolution and Persistence of Copper-Based Nanomaterials in Undersaturated Solutions with Respect to Cupric Solid Phases.

Dissolution of copper-based nanoparticles (NPs) can control their environmental persistence and toxicity. Previous research has generally reported limited dissolution of Cu-based NPs at circumneutral pH, but the environmentally important case of dissolution in solutions that are undersaturated with respect to copper mineral phases has not been investigated thoroughly. In this study, immobilized Cu-based NPs were fabricated on solid supports. Metallic copper (Cu), cupric oxide/hydroxide (Cuox), and copper sulfide (CuxS) NPs were investigated. Dissolution rate constants were measured in situ by an atomic force microscope equipped with a flow-through cell. A mass-balance model indicated that the flowing solution was consistently undersaturated with respect to cupric solid phases. Based on the measured rate constants, Cuox NPs are expected to dissolve completely in these undersaturated conditions within a matter of hours, even at neutral to basic pH. The expected persistence of metallic Cu NPs ranges from a few hours to days, whereas CuxS NPs showed no significant dissolution over the time scales studied. Field deployment of Cu-based NP samples in a freshwater stream confirmed these conclusions for a natural aquatic system. These results suggest that Cu and Cuox NPs will be short-lived in the environment unless dissolution is hindered by a competing process, such as sulfidation.

Multiscale modeling of aspirin dissolution: from molecular resolution to experimental scales of time and size

Predicted absolute and face-specific rate constants of aspirin dissolution are incorporated in a simulation based on the equations of classical mass transfer to reproduce kinetic dissolution in experiment using a Jamin-type interferometer.

Oxidative dissolution of silver nanoparticles: A new theoretical approach

A general model of an oxidative dissolution of silver particle suspensions was developed that rigorously considers the bulk and surface solute transport. A two-step surface reaction scheme was proposed that comprises the formation of the silver oxide phase by direct oxidation and the acidic dissolution of this phase leading to silver ion release. By considering this, a complete set of equations is formulated describing oxygen and silver ion transport to and from particles’ surfaces. These equations are solved in some limiting cases of nanoparticle dissolution in dilute suspensions. The obtained kinetic equations were used for the interpretation of experimental data pertinent to the dissolution kinetics of citrate-stabilized silver nanoparticles. In these kinetic measurements the role of pH and bulk suspension concentration was quantitatively evaluated by using the atomic absorption spectrometry (AAS). It was shown that the theoretical model adequately reflects the main features of the experimental results, especially the significant increase in the dissolution rate for lower pH. Also the presence of two kinetic regimes was quantitatively explained in terms of the decrease in the coverage of the fast dissolving oxide layer. The overall silver dissolution rate constants characterizing these two regimes were determined.

Deconvolution and IVIVC: Exploring the Role of Rate-Limiting Conditions.

In vitro-in vivo correlations (IVIVCs) play an important role in formulation development and drug approval. At the heart of IVIVC is deconvolution, the method of deriving an in vivo “dissolution profile” for comparison with in vitro dissolution data. IVIVCs are generally believed to be possible for highly permeable and highly soluble compounds with release/dissolution as the rate-limiting step. In this manuscript, we apply the traditional deconvolution methods, Wagner-Nelson and numerical deconvolution, to profiles simulated using a simplified small intestine absorption and transit model. Small intestinal transit, dissolution, and absorption rate constants are varied across a range of values approximately covering those observed in the literature. IVIVC plots and their corresponding correlation coefficients are analyzed for each combination of parameters to determine the applicability of the deconvolution methods under a range of rate-limiting conditions. For highly absorbed formulations, the correlation coefficients obtained during IVIVC are comparable for both methods and steadily decline with decreasing dissolution rate and increasing transit rate. The applicability of numerical deconvolution to IVIVC is not greatly affected by absorption rate, whereas the applicability of Wagner-Nelson falls when dissolution rate overcomes absorption rate and absorption becomes the rate-limiting step. The discrepancy between the expected and deconvolved input arises from the violation of a key assumption of deconvolution that the unknown input and unit impulse enter the system in the same location.

Hydrogen production from the dissolution of nano zero valent iron and its effect on anaerobic digestion

Nano zero valent iron (NZVI) has shown inhibition on methanogenesis in anaerobic digestion due to its reductive decomposition of cell membrane. The inhibition was accompanied by the accumulation of hydrogen gas due to rapid NZVI dissolution. It is not clear whether and how rapid hydrogen release from NZVI dissolution directly affects anaerobic digestion. In this study, the hydrogen release kinetics from NZVI (average size = 55 ± 11 nm) dissolution in deionized water under anaerobic conditions was first evaluated. The first-order NZVI dissolution rate constant was 2.62 ± 0.26 h−1 with its half-life of 0.26 ± 0.03 h. Two sets of anaerobic digestion experiments (i.e., in the presence of glucose or without any substrate but at different anaerobic sludge concentrations) were performed to study the impact of H2 release from rapid NZVI dissolution, in which H2 was generated in a separate water bottle containing NZVI (i.e., ex situ H2 or externally supplied from NZVI dissolution) before hydrogen gas was introduced to anaerobic digestion. The results showed that the H2 partial pressure in the headspace of the digestion bottle reached as high as 0.27 atm due to rapid NZVI dissolution, resulting in temporary inhibition of methane production. Nevertheless, the 5-d cumulative methane volume in the group with ex situ H2 production due to NZVI dissolution was actually higher than that of control, suggesting NZVI inhibition on methanogenesis is solely due to the reductive decomposition of cell membrane after direct contact with NZVI.

Packed-bed microreactors for understanding of the dissolution kinetics and mechanisms of asphaltenes in xylenes

Insightful information concerning the dissolution of asphaltenes in quartz porous media was acquired through the use of transparent packed-bed microreactors (μPBRs), inline UV–vis spectroscopy and pressure transducers. Experimental results showed that longer shut-in time (16h) facilitated the removal of asphaltenes, but the dissolution rate constants decreased gradually. At larger ReP values of 5.52×10-2, less time was allowed to dissolve asphaltenes and as a result less asphaltenes were removed. At a higher n-heptane volume composition of 80vol%, more low molecular weight asphaltenes were deposited in μPBRs but were easier to dissolve. At temperature range of 25–90°C, more asphaltenes were removed as increasing temperature. Estimation of permeability–porosity relationships indicated that even when ~70–90wt% asphaltenes were removed from the damaged packed-bed microreactors (DμPBRs), the permeability impairments were still much lower than expected. The remaining asphaltenes in the DμPBRs plugged the pore throat of porous media, and as a result resisted the flow of fluids. Understanding the dissolution kinetics and mechanisms of asphaltenes in porous media can be useful in designing remediation treatments that minimize production losses and the resultant economic losses.

Effects of Natural Organic Matter Properties on the Dissolution Kinetics of Zinc Oxide Nanoparticles.

The dissolution of zinc oxide (ZnO) nanoparticles (NPs) is a key step of controlling their environmental fate, bioavailability, and toxicity. Rates of dissolution often depend upon factors such as interactions of NPs with natural organic matter (NOM). We examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution using anodic stripping voltammetry to directly measure dissolved zinc concentrations. The observed dissolution rate constants (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg C L(-1)) for Suwannee River humic and fulvic acids and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, kobs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. The findings of this study facilitate a better understanding of the fate of ZnO NPs in organic-rich aquatic environments and highlight SUVA as a facile and useful indicator of NOM interactions with metal-based nanoparticles.

Modeling of Reactive Diffusion in Glass‐Ceramics

A model of reactive ion‐exchange diffusion in glassy materials (glasses and glass‐ceramics) has been developed. The model can be used to simulate the processes of ion‐exchange‐induced decrystallization of glass‐ceramics and ion‐exchange‐induced glass crystallization. Analysis of the model in dimensionless form resulted in determining a set of dimensionless complexes comprising dimensional parameters of the ion exchange system (diffusivity, rate constant of grain dissolution, initial size and composition of the crystalline grains, etc.). Numerical values of the complexes enable one, not solving the problem, to predict the composition and structure of glass‐ceramic subsurface layers produced in a certain glassy material and under given ion‐exchange conditions. It was shown that the developed model correctly describes experimental data on ion‐exchange‐induced glass‐ceramics decrystallization. It appears that the model can be used in developing a new technology of optical glass‐ceramics for photonic applications.

Mcb (Mass and Charge Balance) Model Simulation of Corrosion of Co-Cr Alloy Stellite-6

Understanding of oxide formation and growth on an alloy is very important in predicting its corrosion behaviour. Several models for oxide growth as well as metal dissolution kinetics in the presence of an oxide layer have been developed. These models focus on describing the transport of charged species through the oxide film and the electrochemical reactions at the metal/oxide and oxide/solution interfaces, although the detailed description and formulation of these processes vary. However, these models do not consider the type of oxide that can form. Consequently, the models have limited capability of predicting changes in the corrosion rate with time as corrosion progresses, or the dependence of corrosion kinetics on the solution redox conditions. Recently, we have developed a corrosion model that can predict the rates of metal oxidation, oxide growth and dissolution simultaneously as a function of time. The model imposes reaction thermodynamics constraints, and mass and charge balance (MCB) requirements on corrosion reaction rates and hence is labelled the MCB model [1]. The mass and charge balance requirements dictate that the flux of metal cations created by oxidation of metal atoms at the m|ox interface (the oxidation flux) must be equal to the sum of the fluxes of the metal cations forming an oxide at the oxide/solution interface (the oxide formation flux) and the flux of metal cations dissolving into solution (the dissolution flux). The oxidation flux is calculated by using a modified Butler-Volmer equation with an effective overpotential that is defined as a function of the equilibrium potential of the metal oxidation and the potential drop across the oxide layer that is growing. Both the oxide formation dissolution fluxes have a first-order dependence on the oxidation flux. The first-order rate constant for the oxide formation follows an Arrhenius dependence with an activation energy that increases linearly with oxide thickness. The dissolution rate constant depends on surface hydration and the solution environment (pH and temperature), but is independent of the oxide thickness. Consequently, under constant solution conditions the rate constant for the oxide formation, kMO(t), changes with time as the oxide grows but the rate constant of dissolution, kdiss, is constant with time. Due to a mass balance constraint and competition between the two processes for the metal ions, the oxide formation and dissolution fluxes cannot vary independently. The fraction of the oxidation flux that leads to oxide formation or dissolution depends on their rate constants; fk-MO(t) = kMO(t)/(kMO(t) + kdiss) and fk-diss(t) = 1 - fk-MO(t), respectively. In this paper, we present MCB model simulation results of potentiostatic polarization experiments performed on Co-Cr alloy Stellite-6 [2]. The simulations results are compared with the experimental measurements of the corrosion current as a function of time and the final composition and structure of the oxide(s) that formed. In these simulations, the parameters such as rate constants, exchange current density and field strength (or specific potential drop) across an oxide layer were kept constant for a specific pH and temperature. The main rate parameter that varies with pH and temperature was . This rate constant ratio is higher under conditions which promote oxide formation over dissolution, such as high pHs where the solubility of metal cations is low. The MCB model with the same model parameters was then applied to different sets of experimental data which include measurements of corrosion potential as a function of time and determination of the amounts of dissolved metals in coupon corrosion tests conducted in sealed quartz vials. The excellent agreement between the model results and experimental data over a range of polarization potential, pH and temperature indicates that the MCB model is a valuable method for simulating time-dependent corrosion behaviour while an oxide film is changing.

Controlled Release of Antipyrine from Tablets Using Synthesized Copolymers as Matrices in Gastric Medium

Abstract: Introduction: In order to control and modify the drug release, several types of devices were used to obtain a controlled release of the organic drug. A drug delivery system can be a matrix of polymer incorporating the active agent. New solid dosage forms (tablets) composed from the active agent (Antipyrine) and copolymers synthesized: Poly (vinyl acetate-co-methyl methacrylate) and Poly (vinyl pyrrolidone-co-methyl methacrylate) able to control drug release have been prepared and investigated in this paper. Methods: These copolymers synthesized were characterized (FTIR, 13C RMN, Tg and Mv), solid dosage forms (tablets): T(VAc1), T(Vac2) and T(VP) composed from the active agent (AP) and copolymers synthesized: poly (VAc-co-MMA) and poly (VP-co-MMA) as matrices were elaborated. The drug release from these formulations are performed in a cylindrical double-wall glass reactor (100 mL), kept at a temperature of (37 ± 0.5)°C and was followed using UV-Vis spectrophotometer in acidic medium at pH 1.2. The effect of the matrix on the drug release was studied. Results: The drug dissolution from matrix tablets is significantly influenced by the nature of matrix. The results showed that after 2 h (the time corresponding to the drug retention in the human stomach), the percentages of the drug released from T(VAc1), T(Vac2) and T(VP) are 1.04 %, 0.37 %, and 36.89% respectively. The release is even greater when the matrix is hydrophilic. Swellable matrix tablets, such as poly (vinyl acetate-co-methyl methacrylate) tablets, are activated by water, and drug release is controlled by the interaction between water, polymer and drug. Theoretical analyses of the kinetics of controlled release of AP have been established and Antipyrine dissolution rate constants were calculated from Higuchi’srelease model and the n exponents from Korsmeyer–Peppas model were determinate. Conclusion: The suitable kinetics model for describing the release of AP from the matrix tablets was the Higuchi model. The coefficients of correlation r2 in this model are above 0.99. The results of the Korsmeyer–Peppas equation, the values of n are in agreement with the experimental results already reported. Key words: Antipirine, Drug release, Poly (vinylacetate-co-methyl methacrylate), Poly(vinylpyrrolidone-co-methylmethacrylate), Tablets.

Effect of Fly Ash as an Additive on the Limestone Dissolution Rate Constant

Limestone dissolution is a very important factor in flue gas desulfurization systems because it determines its reactivity toward SO2. Fly ash, a siliceous material, has been reported to improve sorbent reactivity. This study investigates the effect of adding fly ash to limestone on its dissolution rate constant. The experiments were carried out using a pH stat apparatus where the effects of the reaction variables, fly ash/limestone ratio, slurry pH, reaction temperature, and concentration of acid, used were investigated. The central composite design (CCD) of the experiment was used to develop a model that correlates the dissolution rate constant and the reaction variables. It was found that fly ash had a positive effect on the dissolution rate constant of limestone, with the pH having the most significant effect. The dissolution rate constant was found to increase with an increase in the temperature and acid concentration. X-ray diffraction (XRD) analysis showed products of hydration formed, which are mainly calcium silicate hydrates, on the samples. This led to an increase in the specific surface area, as observed in the Brunauer–Emmett–Teller (BET) analysis.

Dissolution and biodurability: Important parameters needed for risk assessment of nanomaterials.

Biopersistence and biodurability have the potential to influence the long-term toxicity and hence pathogenicity of particles that deposit in the body. Therefore, biopersistence and biodurability are considered to be important parameters needed for the risk assessment of particles and fibres. Dissolution, as a measure of biodurability, is dependent on the chemical and physical properties (size, surface area, etc.) of particles and fibres and also of the suspension medium including its ionic strength, pH, and temperature. In vitro dissolution tests can provide useful insights as to how particles and fibres may react in biological environments; particles and fibres that release ions at a higher rate when suspended in vitro in a specific simulated biological fluid will be expected to do so when they exist in a similar biological environment in vivo. Dissolution of particles and fibres can follow different reaction kinetics. For example, the majority of micro-sized particles and fibres follow zero-order reaction kinetics. In this case, although it is possible to calculate the half-time of a particle or fibre, such calculation will be dependent on the initial concentration of the investigated particle or fibre. Such dependence was eliminated in the shrinking sphere and fibre models where it was possible to estimate the lifetimes of particles and fibres as a measure of their biodurability. The latter models can be adapted for the dissolution studies of nanomaterials. However, the models may apply only to nanomaterials where their dissolution follows zero-order kinetics. The dissolution of most nanomaterials follows first-order kinetics where dependence on their initial concentration of the investigated nanomaterials is not required and therefore it is possible to estimate their half-times as a measure of their biodurability. In dissolution kinetics for micro-sized and nano-sized particles and fibres, knowledge of dissolution rate constants is necessary to understand biodurability. Unfortunately, many studies on dissolution of nanoparticles and nanofibres do not determine the dissolution rates and dissolution rate constants. The recommendation is that these parameters should be considered as part of the important descriptors of particle and fibre physicochemical properties, which in turn, will enable the determination of their biodurability.

Semi-physiologic model validation and bioequivalence trials simulation to select the best analyte for acetylsalicylic acid

The objective of this paper is to apply a previously developed semi-physiologic pharmacokinetic model implemented in NONMEM to simulate bioequivalence trials (BE) of acetyl salicylic acid (ASA) in order to validate the model performance against ASA human experimental data. ASA is a drug with first-pass hepatic and intestinal metabolism following Michaelis–Menten kinetics that leads to the formation of two main metabolites in two generations (first and second generation metabolites). The first aim was to adapt the semi-physiological model for ASA in NOMMEN using ASA pharmacokinetic parameters from literature, showing its sequential metabolism. The second aim was to validate this model by comparing the results obtained in NONMEM simulations with published experimental data at a dose of 1000mg. The validated model was used to simulate bioequivalence trials at 3 dose schemes (100, 1000 and 3000mg) and with 6 test formulations with decreasing in vivo dissolution rate constants versus the reference formulation (kD 8–0.25h−1). Finally, the third aim was to determine which analyte (parent drug, first generation or second generation metabolite) was more sensitive to changes in formulation performance.The validation results showed that the concentration–time curves obtained with the simulations reproduced closely the published experimental data, confirming model performance. The parent drug (ASA) was the analyte that showed to be more sensitive to the decrease in pharmaceutical quality, with the highest decrease in Cmax and AUC ratio between test and reference formulations.

Dilute nitric or nitrous acid solution containing halide ions as effective media for pure gold dissolution.

The greatly enhanced oxidation ability of dilute aqueous nitric acid (0.10-2.0 mol L(-1)) containing bromide and iodide salts as well as chloride salts has been examined based on the dissolution kinetics of pure gold at 30-60 °C. It has been found that bromide salts are more effective than chloride salts in gaining the ability of dissolving gold in dilute aqueous nitric acid solution. At 60 °C, a piece of gold-wire (ca. 20 mg) is dissolved in 20 mL of as low as 0.10 mol L(-1) HNO3 solution containing 1.0-5.0 mol L(-1) NaBr and the dissolution rate constant, log(k/s(-1)), increases linearly (from -5.78 to -4.52) with the increasing NaBr concentration. The addition of organic solvents, such as acetonitrile and acetic acid, causes acceleration of gold dissolution in LiBr and NaBr solutions. With increasing MeCN contents, for instance, the log(k/s(-1)) value of 0.10 mol L(-1) HNO3 solution containing 2.0 mol L(-1) NaBr increases linearly from -5.30 to -4.61 at 30% (v/v) MeCN. The bromide salts affect the gold dissolution rate constant in the order of KBr < NaBr < LiBr < CaBr2. With increasing NaI concentration (0.20-3.0 mol L(-1)), some acceleration in log(k/s(-1)) of 0.50 or 1.0 mol L(-1) HNO3 solution has been observed; however, the slope of acceleration as the function of NaI concentration is much smaller than that of NaCl or NaBr. The gold dissolution ability has been examined also for nitrous acid containing chloride and bromide ions at 35 °C. The NaNO2 solution containing twice or more amounts of HX (X = Cl, Br) gives the maximum efficiency for gold dissolution, according to the log(k/s(-1)) values of the mixed solutions of NaNO2 (0.10-2.0 mol L(-1)) and HX of various concentrations. The influence of oxidation by dilute nitric and nitrous acids on the gold dissolution is discussed from the standpoint of the redox potentials in "modified" aqueous solutions and not of the changes in the activity coefficients of ions.

A Mathematical Model to Study Capacity Fading in Lithium Ion Batteries: Formation and Dissolution Reactions

A mathematical model based on formation and dissolution kinetics is formulated for the formation of the Solid Electrolyte Interphase layer on the anode and cathode in a lithium ion battery. The model assumes that the formation of the Solid Electrolyte interphase (SEI) at the anode and cathode involves formation and dissolution of the SEI layer. The model evaluates capacity fading as a function of temperature for various values of formation and dissolution rate constants. Model results also predict capacity fade results when there is no dissolution of the SEI layer. Model results show that at higher temperatures dissolution of the SEI layer plays a major role in the capacity loss in a lithium ion battery.

Hopping intermittent contact-scanning electrochemical microscopy (HIC-SECM) as a new local dissolution kinetic probe: application to salicylic acid dissolution in aqueous solution.

Dissolution kinetics of the (110) face of salicylic acid in aqueous solution is determined by hopping intermittent contact-scanning electrochemical microscopy (HIC-SECM) using a 2.5 μm diameter platinum ultramicroelectrode (UME). The method operates by translating the probe UME towards the surface at a series of positions across the crystal and inducing dissolution via the reduction of protons to hydrogen, which titrates the weak acid and promotes the dissolution reaction, but only when the UME is close to the crystal. Most importantly, as dissolution is only briefly and transiently induced at each location, the initial dissolution kinetics of an as-grown single crystal surface can be measured, rather than a surface which has undergone significant dissolution (pitting), as in other techniques. Mass transport and kinetics in the system are modelled using finite element method simulations which allows dissolution rate constants to be evaluated. It is found that the kinetics of an 'as-grown' crystal are much slower than for a surface that has undergone partial bulk dissolution (mimicking conventional techniques), which can be attributed to a dramatic change in surface morphology as identified by atomic force microscopy (AFM). The 'as-grown' (110) surface presents extended terrace structures to the solution which evidently dissolve slowly, whereas a partially dissolved surface has extensive etch features and step sites which greatly enhance dissolution kinetics. This means that crystals such as salicylic acid will show time-dependent dissolution kinetics (fluxes) that are strongly dependent on crystal history, and this needs to be taken into account to fully understand dissolution.

Stability and dissolution kinetics of Pd/MCM-41

The stability of Pd impregnated MCM-41 (Pd/MCM-41) at mass per cent loadings of Pd of 0.12 and 1.2% was investigated over 50 days. Results showed that the silica in Pd/MCM-41 dissolves at a lower rate than in pure MCM-41 and is likely metastable with respect to amorphous silica. Dissolution rates were lower at a higher mass per cent loading of Pd. Simulations of Pd/MCM-41 dissolution kinetics made using Phreeqci indicated log dissolution rate constants of −12.7 and −12.9 for 0.12 and 1.2% Pd/MCM-41, respectively.