Dissolution Model Research Articles

Optimization of Hydroxy Propyl Methyl Cellulose and Carbomer In Diltiazem Hydrochloride Mucoadhesive Buccal Film

Diltiazem hydrochloride (HCl) is a category of calcium channel blocker used as an antihypertensive agent. Diltiazem HCl is a low bioavailable drug due to high first-pass metabolism and a short half-life (3-5 hours); hence mucoadhesive buccal film was made to overcome this weakness. Bioavailability of Diltiazem HCl increase if the buccal preparations can contact the mucosa for a sufficient time. Therefore, in this study, two polymers are combined to obtain good film characteristics, especially residence time and mucoadhesive strength. This study was aimed to optimize Hydroxy Propyl Methyl Cellulose (HPMC) and Carbomer's amount in Diltiazem HCl mucoadhesive buccal film. The formulas were prepared by the solvent casting method and optimized with design expert software. The release kinetics and mechanism were evaluated using DDSolver program. The optimum amount of polymer obtained from optimization was 40 mg of HPMC and 10 mg of Carbomer. The optimum formula's swelling index was 4.18. The mucoadhesive strength was 53.07 gF, and the mucoadhesive residence time was 529.33 min. The FTIR spectra showed there was no interaction between Diltiazem HCl and other excipients. Thus it did not disturb the therapeutic effect. Based on the DDSolver statistical parameters and curve-fitting, the dissolution model of Diltiazem HCl from buccal mucoadhesive film follows Korsmeyer-Peppas. The release exponent (n) is 0.55, which shows a non-fickian/anomalous diffusion release mechanism. These mechanisms represent drug release controlled by a combination of diffusion and erosion.

Modeling of carbon dioxide dissolution in an injection well for geologic sequestration in aquifers

Carbon dioxide (CO2) sequestration is considered to be one of the most effective technologies of mitigating greenhouse gas emissions. In this technology, single phase supercritical CO2 is injected into an underground geological formation such as a deep saline aquifer. Existing sequestration projects demonstrate that successful implementations are possible; however, significant uncertainties associated with the risks of leakage remain an obstacle for broader use of this technology. The security of underground disposal could be considerably increased by dissolving the CO2 in a brine produced from the aquifer, then re-injecting the mixture underground. The dissolution process occurs before the mixture reaches the aquifer; this significantly reduces or completely eliminates the risks of CO2 leakage. This technique can drastically extend the amount of worldwide aquifers available for carbon sequestration. As was previously shown, complete dissolution could be achieved in a surface pipeline operating under the pressure of a target aquifer, where CO2 is injected. In this paper, a comprehensive model of CO2 droplet dissolution in a vertical injection well is presented. The model accounts for droplet breakup, coalescence, and dissolution processes as well as temperature and pressure variations over well depth. Feasibility and results are discussed and compared with surface dissolution options.

Thermal Stability of Type II Modifications Inscribed by Femtosecond Laser in a Fiber Drawn from a 3D Printed Preform

Fiber drawing from a 3D printed perform was recently discussed to go beyond the limitations of conventional optical fiber manufacturing in terms of structure and materials. In this work, the photosensitivity of silica optical fibers to femtosecond laser light, and fabricated by 3D printing a preform, is investigated. The writing kinetics and the thermal performance of Type II modifications are studied by varying the laser pulse energy and investigating the birefringence response of the femtosecond (fs)-laser written structures. Compared with a conventional telecom single mode fiber (SMF28), the fiber made by 3D printing is found to have similar writing kinetics and thermal performance. Additionally, the thermal stability of the imprinted fs-laser induced nanostructures is investigated based on the Rayleigh–Plesset equation, describing a model of nanopores dissolution underpinning Type II modifications with thermal annealing.

A two-scale iterative scheme for a phase-field model for precipitation and dissolution in porous media

Mineral precipitation and dissolution processes in a porous medium can alter the structure of the medium at the scale of pores. Such changes make numerical simulations a challenging task as the geometry of the pores changes in time in an apriori unknown manner. To deal with such aspects, we here adopt a two-scale phase-field model, and propose a robust scheme for the numerical approximation of the solution. The scheme takes into account both the scale separation in the model, as well as the non-linear character of the model. After proving the convergence of the scheme, an adaptive two-scale strategy is incorporated, which improves the efficiency of the simulations. Numerical tests are presented, showing the efficiency and accuracy of the scheme in the presence of anisotropies and heterogeneities.

A continuous time random walk method to predict dissolution in porous media based on validation of experimental NMR data

We develop a reactive transport model for dissolution of porous materials using a Continuous Time Random Walk (CTRW) formulation with first-order kinetics. Our model is validated with a dataset for a Ketton carbonate rock sample undergoing dissolution on injection of an acid, monitored using Nuclear Magnetic Resonance (NMR). The experimental data includes the 3D porosity distribution at the beginning and end of the experiment, 1D porosity profiles along the direction of flow during dissolution, as well as the molecular fluid displacement probability distributions (propagators). With the calibration of only a single parameter, we successfully predict the porosity changes and the propagators as a signature of flow heterogeneity evolution in the dissolution experiment.We also demonstrate that heterogeneity in the flow field leads to an effective reaction rate, limited by transport of reactants, that is almost three orders of magnitude lower than measured under batch reaction conditions. The effective reaction rate predicted by the model is in good agreement with the experimentally measured rate. Furthermore, as dissolution proceeds, the formation of channels in the rock focused the flow in a few fast-flowing regions. The predicted dissolution patterns are similar to those observed experimentally. This study establishes a workflow to calibrate and validate the CTRW reactive transport model with NMR experiments.

Geochemical Modeling of Water-Rock Interaction Processes in the Pollino National Park

This work is aimed at reconstructing the water-rock interaction processes controlling the geochemical characteristics of the shallow or relatively shallow groundwaters of the Pollino National Park, based on the data acquired for 105 water samples from local springs. Reaction path modeling of rock dissolution was carried out in a purely stoichiometric mode for the main lithotypes cropping out in the study area, that is, limestone, Mg-limestone, dolomite, serpentinite, Al-silicate fraction of calcschist, and carbonate fraction of calcschist. Reaction path modeling was carried out in a purely stoichiometric mode, considering the rocks of interest as materials of known stoichiometry and unknown thermodynamic properties. Calculations were carried out assuming a closed system for secondary solid phases whereas an open system was assumed for gases, O2(g) and CO2(g). Comparison of the results of geochemical modeling and the analytical data acquired for the groundwaters of the Pollino National Park shows that concentrations of major solutes, SiO2, Li, Al, and Fe of the different chemical types of waters, are explained by the dissolution of pertinent lithotypes. Moreover, the detected concentrations of Al, Cl, F, NO3, and SO4 are within the threshold values recommended by WHO.

Underground Rock Dissolution and Geomechanical Issues

Many soluble rocks will dissolve when in contact with fluid such as water. This transformation of rock solid into flowing fluid may trigger the creation of cavities which may further lead to either smooth subsidence or sudden collapse of land surface. Dissolution phenomenon can be of natural or human origin. This paper deals with the problem of the dissolution of underground soluble rocks and the geomechanical consequences such as subsidence, sinkholes and underground collapse. In this paper, rock dissolution and the induced underground cavities are computed using a Diffuse Interface Model, which does not require to follow interfaces explicitly. We describe briefly the mathematical and physical framework for the dissolution model. We first explain the transition (upscaling) of a multiphysics problem formulated at the microscopic (pore-) scale level to the macroscopic (Darcy-) scale level. Rock material considered in this paper is gypsum, despite that the developed method is also suitable for over soluble rocks (e.g., limestone, Halite). The second part of this paper is devoted to a set of problems dealing with mechanical response of the rock mass in connection with the dissolution process. We discuss the subsidence induced by the dissolution of one or more gypsum lenses, the stability of the covering, and finally the failure of a gypsum pillar in an abandoned quarry. These examples, while they may involve rather theoretical hypotheses, have the virtue of showing the relevance of the method as well as the very diverse issues that it can treat.

Comment on "On the thermodynamic stability of bubbles, immiscible droplets, and cavities" by G. S. Manning, Phys. Chem. Chem. Phys., 2020, 22, 17523.

In this comment, the thermodynamic analysis of the stability of nanobubbles is discussed in reference to the recent paper by Manning (G. S. Manning, On the Thermodynamic Stability of Bubbles,Immiscible Droplets, and Cavities, Phys. Chem. Chem. Phys., 2020, 22, 17523-17531). It is argued that Manning's critcism on the classical Epstein-Plesset model of bubble stability is unwarranted, and that the Young-Laplace-equation must be understood as a fundamental law of the pressure difference across a curved interface regardless of the reaction of the gas in the bubble. Consequently, the internal pressure and the radius of a bubble are inherently linked, so that the net force considered in Manning's stability analysis does not exist.

Corrosion fatigue crack growth mechanisms in welded joints of marine steel structures

This paper presents a model of fatigue crack growth in a welded joint and a two-dimensional model of anodic dissolution based on Donahue model and anodic dissolution mechanism, respectively. In addition, a model for predicting the corrosion fatigue crack growth rate in welded joints of steel marine structures is established and crack growth mechanisms are analyzed. The results show that during early stages of crack growth, corrosion fatigue crack growth rate in welded joints is mainly controlled by corrosion action, whereas cyclic loading becomes more influential during the later stage of crack propagation. Loading frequency and effective stress ratio can affect rupture period of protective film at the corrosion fatigue crack tip and the length of corrosion crack increment, respectively, which changes the influence of corrosion action on crack growth rate. However, the impact of stress amplitude on crack growth rate is only significant when crack propagation is caused by cyclic loading. Welding residual stress not only improves the effective stress ratio of cyclic loading, but also promotes crack closure and increases corrosion fatigue crack growth rate in welded joints. Compared to corrosion action, welding residual stress has a more significant influence on crack growth caused by cyclic loading.

Enhanced saturation of liquid-saturated porous medium with atmosphere gases due to surface temperature oscillations

We study the non-isothermal diffusion transport of a poorly soluble substance in a porous liquid-saturated medium being in contact with the reservoir of this substance. The surface temperature of a half-space porous medium oscillates in time, which creates a decaying temperature wave propagating deep into sediments. Since the solubility exponentially strongly depends on temperature, a decaying running solubility wave forms in the porous medium. In such a system, the zones of saturated solution and non-dissolved phase coexist with the zones of undersaturated solution. The effect is considered for the case of annual oscillation of the surface temperature of water-saturated ground being in contact with atmosphere. We reveal the phenomenon of formation of a near-surface bubbly horizon due to the temperature oscillation for one- and two-component solutes. In the case of a two-component solute, the solubility depends on the composition of the nondissolved phase, which necessitates the construction of a corresponding mathematical model of dissolution of multicomponent mixtures. We develop an analytical theory of the phenomenon of formation of the bubbly horizon. In both analytical theory and numerical simulations, the temperature dependence of the molecular diffusion coefficient is taken into account. In the presence of a propagating temperature wave, the nonlinear interaction between this dependence and the temperature dependence of the solubility creates an additional nonzero contribution to the mean-over-period mass flux. For multicomponent solutions, we report the formation of a diffusive boundary layer, which is not possible for single-component solutions. We construct an analytical theory for this boundary layer and derive effective boundary conditions for the problem of the diffusive transport beyond this layer. Theoretical results are in fair agreement with the results of numerical simulation.

A Selective Dissolution Process Featuring a Classification Device for the Removal of Fines in Crystallization

The presence of fine crystals is a common condition that may hinder the downstream processing of a powder obtained through a crystallization process. This study investigates through simulations a process featuring a hydrocyclone for their removal. Hydrocyclones, solid–liquid separation devices widely applied in several fields of chemical engineering, enable the classification of suspended solids based on their size. The classification step allows for a selective dissolution of the fine crystals, thus leading to a more efficient process when compared to a simpler temperature cycle, where partial dissolution of larger crystals is deliberately though reluctantly accepted. A pathway for the selection of a suitable hydrocyclone design is outlined, and a novel graphical tool useful to describe the performance of the device for the fines separation task is presented. The selection of the operating variables and their operating window is discussed, and their effect on the overall process is elucidated. The design space and the performance of the selective fines removal process is investigated by coupling for the first time the detailed modeling of fines dissolution by heating and crystallization by cooling, both based on population balance equations, and the hydrocyclone behavior, for which an established model due to Braun is used. Simulation runs are presented for different scenarios and allow assessing the process performance in terms of reductions of fines, processing time, and energy demand, thus providing a valuable insight into its applicability.

Biorelevant dissolution models to assess precipitation of weak base drug

The impact of precipitation can affect the amount of drug absorbed, thereby affecting the amount of drug in the systemic body. The precipitation process is preceded by a supersaturation phase, caused by decreased drug solubility in the gastrointestinal tract. This precipitation occurs for weak base drugs with low solubility. When the drug entering the small intestine, the solubility of weak base drugs decrease, then occurs supersaturation, which leads to precipitation, so that drug precipitation is one of a challenge for the pharmaceutical industry in drug development. Precipitation testing of water-soluble weak base drugs can be carried out by the pH shift method to describe the gastrointestinal pH gradient from gastric to small intestine. This pH change can cause supersaturation and then trigger precipitation, especially for weak base drugs. The methods that can used to assess precipitation drug is modification of the USP dissolution which are two compartment and multi compartment model. The choice of dissolution medium play an important role in the test results. The use of bio relevant medium can produce closer in vitro and in vivo correlations than the use of buffers. Generally, the medium used to simulate the weakly condition in the small intestine is FaSSIF (Fasted State Simulated Intestinal Fluid) or FeSSIF (Fed State Stimulate Intestinal Fluid) medium. The medium used to simulate the acidic condition in the stomach is FaSSGF (Fasted state simulated gastric fluid) or FeSSGF (Fed state simulated gastric fluid) medium.

Development of a Physiologically Based Pharmacokinetic Model for Prediction of Ethanol Concentration-Time Profile in Different Organs.

A physiologically based pharmacokinetic (PBPK) modeling approach was used to simulate the concentration-time profile of ethanol (EtOH) in stomach, duodenum, plasma and other tissues upon consumption of beer and whiskey under fasted and fed conditions. A full PBPK model was developed for EtOH using the advanced dissolution, absorption and metabolism (ADAM) model fully integrated into the Simcyp Simulator® 15 (Simcyp Ltd., Sheffield, UK). The prediction performance of the developed model was verified and the EtOH concentration-time profile in different organs was predicted. Simcyp simulation showed ≤ 2-fold difference in values of EtOH area under the concentration-time curve (AUC) in stomach and duodenum as compared to the observed values. Moreover, the simulated EtOH maximum concentration (Cmax), time to reach Cmax (Tmax) and AUC in plasma were comparable to the observed values. We showed that liver is exposed to the highest EtOH concentration, faster than other organs (Cmax=839.50mg/L and Tmax=0.53h), while brain exposure of EtOH (AUC=1139.43mg·h/L) is the highest among all other organs. Sensitivity analyses (SAs) showed direct proportion of EtOH rate and extent of absorption with administered EtOH dose and inverse relationship with gastric emptying time (GE) and steady-state volume of distribution (Vss). The current PBPK model approach might help with designing in vitro experiments in the area of alcohol organ damage or alcohol-drug interaction studies.

Selective laser sintering (SLS) technique for pharmaceutical applications—Development of high dose controlled release printlets

The paper presents the unique approach to 3D printing by Selective Laser Sintering of high dose controlled release pharmaceutical dosage form, which contains almost exclusively drug substance - just crystalline paracetamol as a model drug substance and small amount of dye were used. Comprehensive printlet characterization, that included pore space analysis, drug release and subsequent dissolution modeling as well as exploratory analysis, revealed various degrees of freedom for tuning its functional properties i.e. dissolution performance. Two degrees of freedom were found substantial for the proposed approach: (1) the macro structure shaping in terms of active surface to volume ratio; (2) microstructure shaping in terms of pore space structure. The latter was found to have a great potential and can be modified by the manufacturing parameters, e.g. hatch spacing. The simplicity of the preparation and flexibility to control the dissolution performance of the pharmaceutical dosage are the advantages of the proposed approach. • Pharmaceutical high dose oral administration. • Highly drug-loaded controlled release formulations by selective laser sintering • Macro and micro structure shaping for drug dissolution tuning. • Flexible dosage form design for personalized medicine. • Simple manufacturing and simple dissolution mechanism.

Modeling of Limestone Dissolution for Flue Gas Desulfurization with Novel Implications

Solid-liquid dissolution is a central step in many industrial applications such as pharmaceutical, process engineering, and pollution control. Accurate mathematical models are proposed to improve reactor design and process operations. Analytical methods are significantly beneficial in the case of iterative methods used within experimental investigations. In the present study, a detailed analytical solution for the general case of solid particles dissolving in multiphase chemical reaction systems is presented. In this model, the authors consider a formulation that considers the particles’ shape factor. The general case presented could be utilized within different problems of multiphase flows. These methods could be extended to different cases within the chemical engineering area. Examples are illustrated here in relation to limestone dissolution taking place within the Wet Flue Gas Desulfurization process, where calcium carbonate is dissolving in an acidic environment. The method is the most common used technology to abate SO2 released by fuel combustion. Limestone dissolution plays a major role in the process. Nevertheless, there is a need for improvements in the optimization of the WFGD process for scale-up purposes. The mathematical model has been tested by comparison with experimental data from several mild acidic dissolution assays of sedimentary and metamorphic limestone. We have found that R2 ⊂ 0.92 ± 0.06 from dozens of experiments. This fact verifies the model qualifications in capturing the main drivers of the system.

(Invited) Multiscale Modelling of Titanium Oxide Growth and Dissolution in Fluoride-Containing Electrolytes

Nanostructured valve metal oxides have been extensively investigated due to the variety of applications related to their valuable chemical and physical properties, including mechanical and thermal resistance, catalytic and photocatalytic activity, and biocompatibility. The technology to form well defined porous anodic oxides on titanium will strongly benefit from an optimization of the process parameters based on deterministic modelling. The relatively large number of adjustable parameters often precludes the unambiguous interpretation of steady-state and transient electrochemical data in terms of a unique kinetic model.An approach to overcome this ambiguity by parameterization of the models of barrier film growth [1, 2] on Ti and its alloys (Figure 1) using a combination of in-situ EIS in a large frequency range, dynamic high-frequency impedance and photocurrent measurements, combined with ex-situ characterization of the oxides by X-ray photoelectron spectroscopy (XPS) is presented. Additional estimates of kinetic parameters are derived from density functional theory (DFT) modelling of adsorption of water and fluoride on Ti and TiO2 [3, 4]. Ways to extract information on the rate-limiting steps of the process of passive film formation, growth and restructuring are described and the significance of the obtained parameters for the kinetics of barrier film growth and dissolution is outlined. Stancheva, M. Bojinov, Electrochim. Acta 78, 65 (2012).Bojinov, I. Betova, V. Karastoyanov, Electrochim. Acta 344, 136137 (2020).Stancheva, B. Diawara, F. Lebreau, M. Bojinov, J. Electrochem. Soc. 161, E3188 (2014).Betova, M. Bojinov, V. Karastoyanov, M. Stancheva, Computational Mater. Sci.171, 109260 (2020). Acknowledgments: The financial support of the National Science Fund of Bulgaria under contract ДН19/3-2017 „Modeling, optimization and modification of nanoporous anodic oxide films as catalysts for water photoelectrolysis“is gratefully acknowledged. Figure 1

PtCo Catalyst Dissolution and Oxidation Modeling for Durability Improvement of Automotive Fuel Cell

Polymer electrolyte fuel cell (PEFC) is one of the candidates to replace automotive power sources using fossil fuels. For this purpose, we need to overcome three major criteria: cost, performance, and durability. One of the important topics of PEFC durability is how to keep its catalyst activity for oxygen reduction reaction (ORR). The catalyst activity is product of the electrochemical surface area (ECSA) and activity per surface area. A central issue of catalyst durability is the loss of ECSA over time. This ECSA is approximately the same as the effective surface area of the catalyst. To maximize the ECSA, the radius of catalyst particles is in the order of nano meters.In this study we focus on the ECSA loss of PtCo alloy catalysts on carbon support. These alloy catalysts have much higher activity for ORR than traditionally used Pt1. Our model of ECSA loss combines the following two mechanism:(i) Co dissolution from the surface of the alloy catalyst,(ii) Pt dissolution from small particles and precipitation onto large (Ostwald ripening).The mechanism (i) changes the distribution of the alloy ratio in particle. Because of the standard dissolution potential of Co is -0.28 V vs NHE at 25◦C, Co is easy to dissolve in the aqueous media especially under low pH condition such as PEFC, and the Co ratio near surface is smaller than that of the center 2. In the case of dissolution under high potential, the amount of its depends on the Co ratio.In the mechanism (ii), the balance between Pt and its oxides on particle surface has an important role to simulate ECSA change. While Pt is known to form stable oxide species as well as hydroxide intermediates, the mechanism and specification still remain the subject of research 1. In the previous papers, this oxidation step is described by the nonlinear reaction rate coefficient called Temkin term1, 3, 4. Though this nonlinear term is able to describe the generation of the higher oxidation such as multi-layer of PtO and PtOx (x ≥2) by only one equation3. This term is one of the reasons for extended computing time, and we cannot derive the term consistently from (non-equilibrium) thermodynamics. Here we consider the kinetics of PtCo catalyst dissolution under 0.9V/cell, which is a typical condition in vehicle usage for improving the durability5. Under this condition we need not to consider the higher oxidation process, the following simple two independent fundamental reactions1 is considered:Pt + H2O = PtOH + H+ + e−, (1)PtOH = PtO + H+ + e−. (2)These consecutive reactions are based on spectroscopic results by Ishiguro et al .6 The reaction rates are determined by the ordinary Butler-Volmer equations with some parameters which depend on the temperature and the humidity, without Temkin term. Using the above model, we can calculate the evolution of ECSA loss for the long period and the results are in good agreement with experimental data [Fig. 1].Another application of our model is to predict the necessary conditions in order to achieve both initial performance and durability. For example, if the mean radius of the catalyst is 4 nm, the deviation of this size distribution function must have about 0.7 nm or than less. The results are very severe conditions but needed to overcome for widely spread of PEFC vehicles.Figure 1.Experiment (symbols) and modeled (solid line) ECSA change as function of square-wave potential cycle (0.1 V (3 sec) <-> 0.80, 0.85, and 0.90 V (3 sec))1. R. K. Ahluwalia, X. Wang, J.-K. Peng, N. N. Kariuki, D. J. Myers, S. Rasouli, P. J. Ferreira, Z. Yang, A. Martinez-Bonastre, D. Fongalland and J. Sharman, J. Electrochem. Soc. , 165, 6, p. F3316 (2018).2. M. Watanabe, H. Yano, D. A. Tryk and H. Uchida, J. Electrochem. Soc. , 163 , 6, p. F455 (2016).3. R. M. Darling and J. P. Meyers, J Electrochem. Soc. , 150 , 11, p. A1523 (2003).4. P. Schneider, C. Sadeler, A.-C. Scherzer, N. Zamel and D. Gerteisen, J. Electrochem. Soc. , 166 , 4, p. F322 (2019).5. S. Stariha, N. Macauley, B. T. Sneed, D. Langlois, K. L. More, R. Mukundan and R. L. Borup, J. Electrochem. Soc. , 165 , 7, p. F492 (2018).6. N. Ishiguro, S. Kityakarn, O. Sekizawa, T. Uruga, H. Matsui, M. Taguchi, K. Nagasawa, T. Yokoyama and M. Tada, J. Phys. Chem. C , 120 , 35, p. 19642 (2016). Figure 1

Probing Sensitivity of Discharge Characteristics to Model Selection Using Uncertainty Quantification in an Aprotic Li-Oxygen Battery

Currently, there are several models in the literature, such as kinetic, microstructural, and mass transport, that describe a Li-oxygen battery’s discharge behavior. Many of these models are calibrated and tested at low current densities and are not easily transferable to higher current densities (local current density exceeding 1μA/cm2). Even at low current densities, there is no quantitative method for a researcher to choose a reaction kinetic model such as classical Butler-Volmer and its derivatives, or modified Marcus-Hush-Chidsey, a resistance model for lithium peroxide such as electron transport via tunneling or linear resistivity, a surface coverage model (lithium peroxide growth) such as partial coverage or full coverage, and mass transport model (a review of these models is discussed in Ref. [1]). Also, it is time-consuming to test different models at high current density (≥1C) due to a lack of well-tested models and well-calibrated model parameters. For this presentation, we will develop an analytical model, which acts as a surrogate model for a full finite element model to predict discharge time and discharge voltage. Next, we use an uncertainty quantifying technique called reduced-order stochastic optimization [2, 3] to determine the uncertainty in model parameters for rate kinetics, lithium peroxide resistivity, and parasitic resistance. Finally, a finite element simulation is performed to determine the error introduced by the surrogate model (from various assumptions and simplifications) and its influence on the uncertainty in the model parameters.Our preliminary polarization analysis (overvoltage vs. current density) shows that the resistance models, coupled with Butler-Volmer kinetics, cannot describe the voltage polarization observed in the experiments at high current densities. In order to quantify and rank models describing the lithium peroxide deposition, first, an analytical model is developed to account for discharge product distribution, concentration polarization, and voltage polarization as a function of time, based on the previous work on aqueous electrolytes, presented in Ref. [4]. The analytical model considers reaction kinetics, oxygen mass transport, voltage polarization from lithium peroxide deposition as a conformal coating, and the change in porosity, lithium peroxide thickness, and the active surface is assumed to be uniform throughout the cathode.In order to rank the kinetic and resistance models, the uncertainty in the model parameters is assumed using a probability distribution function, and the resulting statistics are gathered using the Stochastic Reduced Order Model (SROM) approach. SROM is a computationally lite approach that uses significantly less number of samples compared to Monte Carlo to represent the input distribution. Since the number of samples required for Monte Carlo increases with model complexity, which significantly increases the computational time and resources required for full finite element simulations. The SROM approach can reduce the computational requirement by at least ten times without introducing algorithm-based error into the analysis.Although the analytical model incorporates the important aspects to simulate a battery, it neglects the complexity of spatial distribution and temporal variation of the discharge product and the complicated relationship between microstructure and mass transport of oxygen and lithium ions. These neglected interactions introduce a model error in the final parameter estimation and need to be accounted for in order to rank various models. The finite element model (FEM) is used to quantify the error in the surrogate model because of its low fidelity. The FEM model is implemented in COMSOL and considers porous electrode theory for the cathode, concentrated theory for the electrolyte, a resistance model for the discharge products, a kinetic model, Fickian diffusion for the oxygen transport, and an oxygen dissolution model [5].

Volumetric reduction and dissolution prediction of monosodium urate crystal during urate-lowering therapy – a study using dual-energy computed tomography

Objective : Dissolution velocity of monosodium urate (MSU) crystal during urate-lowering therapy (ULT) had been inadequately studied. By using dual-energy computed tomography (DECT), which allows accurate assessment of MSU load, we analyze relationship between serum urate (SU) and volumetric reduction rate of MSU and develop a model that predicts dissolution time. Methods Baseline and follow-up DECTs were performed under a standard ULT protocol. Monthly dissolution rates were calculated by simple and compound methods. Correlations with average SU were compared and analyzed. Best-fit regression model was identified. MSU dissolution times were plotted against SU at different endpoints. Results In 29 tophaceous gout patients, MSU volume reduced from baseline 10.94 ± 10.59 cm3 to 2.87 ± 5.27 cm3 on follow-up (p = .00). Dissolution rate had a stronger correlation with SU if calculated by compound method (Pearson’s correlation coefficient r= −0.77, p = .00) and was independent of baseline MSU load. The ensuing dissolution model was logarithmic and explained real-life scenarios. When SU > 0.43 mmol/l, dissolution time approached infinity. It improved to 10–19 months at SU = 0.24 mmol/l. When SU approximated zero (as with pegloticase), dissolution flattened and still took 4–8 months. Conclusion MSU dissolution is better described as a logarithmic function of SU, which explains, predicts, and facilitates understanding of the dissolution process.

Effect of heat treatment on the microstructure, microhardness and impact toughness of TC11 and TC17 linear friction welded joint

The service life of whole blisks for the aero-engine compressor is sharply decreased due to the dissimilar linear friction welded (LFWed) joint of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) and Ti–4Mo–4Cr–5Al–2Sn–2Zr (TC17) alloys, which have the different microstructure and mechanical properties. To optimize the microstructure and performance of the joint, and improve service life of the whole blisks, the post-weld heat treatment (PWHT) with annealing, solution plus aging were adopted for the welded joint. The results show that the nucleation rate of primary αP phase increases obviously, which are spheres, rods and strips, and orthorhombic martensite αs phases transform into hexagonal martensite αs phases interlaced evenly on the β phase matrix on the WZ of TC17 side; meanwhile, acicular hexagonal martensite αs phases transform into lamellar αs phases on the WZ of TC11 side after solid solution and dual aging. The difference of the microhardness on both sides of the joint is narrowed significantly. The impact toughness of the joint is improved sharply from 9.3 J/cm2 after welding to 27.6 J/cm2 with an increase of 200%. In addition, the dissolution and growth model of primary αp phases were established, which can reasonably predict the nucleation and grow process of α phase. Furthermore, the narrowed discrepancy of the microhardness and increased impact toughness can be attributed to the decreased slice thickness of martensite αs phase, based on the dislocation slip mechanism and distorted discordant model.