Flow Curves Research Articles

Optimizing the Performance of NMC 622 Battery Half Coin Cells by Using Amphiphilic Aqueous Binders to Modulate the Percolation of Carbon Black

N-methyl-2-pyrrolidone (NMP) is the conventional solvent for processing high-nickel cathodes as it dissolves the polymer binder polyvinylidene fluoride (PVDF) and does not leach nickel from the cathode material. NMP is restricted under REACH1 regulations as a ‘substance of very high concern’. Aqueous processing with hydrophilic polymer binders is an emerging alternative to the NMP/PVDF solvent/binder system. Aqueous processed cathodes offer advantages over conventional processing with NMP, namely nontoxic, unrestricted use and cost-effectiveness being 100 times less expensive than NMP/PVDF. However, carbon black is hydrophobic so it does not disperse in water. One way around this problem is to substitute the binder for one that is water-soluble so it can bind to and disperse the carbon black.Aqueous binders have generally yielded unimpressive battery performance, therefore a novel binder system has been studied. In this work, an amphiphilic polymer (pluronic F68) was used to control the dispersion of carbon black in the slurry, and a high molecular weight polyethylene oxide (PEO) was used as a viscosity modifier. Measuring steady-state viscosity flow curves and oscillatory strain measurements, a narrow viscosity range in which carbon black percolates in the cathode slurry was identified, and validated by conductivity data. Working within this range of viscosities, a series of formulations were developed that maximize the mass fraction of active material whilst ensuring enough binder is present to disperse the carbon black in water. The PEO to pluronic ratio was varied for each formulation. Slurries are optically opaque and difficult to characterize, so zeta potential measurements were taken to assess the degree of carbon-black dispersion in the slurry and QCMD to quantify the density. The ratio of active material (NMC 622) to carbon black to polymer was 95:3:2 respectively. Ultimately, the formulations presented were of a constant viscosity, attained by controlling the solids loading of the slurries. Half-coin cells were cycled at charge and discharge rates of 1C, using a voltage range of 3.0 to 4.3 V.An optimal ratio of 25% PEO to 75% pluronic-F68 was identified; these half-coin cells achieved a mean 1st specific discharge capacity of 147 mAhg-1 with capacity retention averaging 86%. Through adsorption measurements, it was found that the affinity between the binder and carbon black seems to correlate with the size of carbon black flocs that form, enabling the tuning of the percolation of carbon black in the slurry. By carefully controlling the viscosity, it was shown that electrochemical cell performance correlates very strongly with both the PEO to pluronic ratio and the slurry conductivity for this system, as seen in Fig.1. This data, along with adsorption and zeta-potential measurements indicate that the affinity of the polymer binder to carbon black can affect the electrochemical performance of the cell.References Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) 2019, Article 57. Figure 1

Characterization of Electrolyte Reduction Reactions on Freshly Plated Lithium Using Electrochemical Heat Flow Calorimetry

Electrochemical heat flow calorimetry can be used to measure the evolved heat during the operation of a lithium-ion battery cell. The data obtained are useful for the optimization of thermal management systems on the cell and system level, but they can also be used to detect and characterize parasitic reactions, such as unwanted reactions of the electrolyte. The heat evolved from a reversibly operated lithium-ion cell can be described as the sum of irreversible heat, resulting from cell polarization, and reversible heat, related to entropy changes.1 In order to quantitatively measure the contribution of a parasitic heat flow, which is usually small in comparison, the irreversible and reversible heat flow must be known to a high accuracy. Two main approaches have been reported in the literature to obtain such defined measurement conditions.2, 3 The first method requires the integration of the heat flow over a full charge/discharge cycle.2 This cancels the reversible heat flow contributions and enables an estimation of the total irreversible heat from the difference of the charge and discharge energies. The second method analyzes the heat flow during a voltage hold after the cell has reached a steady-state condition and exclusively exhibits parasitic processes.3 Both of these approaches allow for an estimation of the mean reaction enthalpies per mole of electrons when the parasitic heat is correlated to the irreversible capacity or to the parasitic current, respectively.In the present work, we introduce an approach to characterize the heat of the electrolyte reduction reactions on freshly plated lithium. For this, we measure the heat flow during overlithiation of an artificial graphite electrode in a half-cell, using our previously reported setup.4 Figure 1 shows the voltage profile and the measured heat flow for an exemplary experiment, where the graphite electrode is first fully lithiated and then overlithiated to induce significant lithium plating before the electrode is fully delithiated again. Both the voltage and heat flow curves show characteristic features indicating lithium plating (LP) and lithium stripping (LS).5 During continuous lithium plating we expect a significant contribution of a parasitic heat flow from the electrolyte reduction reactions on the newly exposed lithium surface. The here analyzed conditions enable a straightforward separation of this parasitic heat flow from the reversible and irreversible heat flow contributions from lithium plating: since lithium is being plated on already deposited lithium on the graphite electrode surfaces and simultaneously being stripped from the lithium metal counter electrode, the system can be considered a quasi-symmetrical cell. This means that the reversible heat flow contributions cancel out and that the irreversible heat flow from cell polarization can be calculated from the offset of the measured cell voltage from 0 V. In the present study, we analyzed the parasitic heat flow during lithium plating, changing different measurement parameters (e.g., degree of overlithiation, plating current, electrolyte) to gain insights into the interplay of lithium plating and electrolyte reactions. By a correlation to the irreversible capacity losses, the mean reaction enthalpy per mole of electrons can be estimated. Finally, the results were correlated to electrolyte reduction reactions postulated by gassing analysis from online electrochemical mass spectrometry (OEMS) measurements. The gas analysis allows for comparing electrolyte reduction pathways at larger potentials (~0.8 V vs. Li+/Li) during the formation of a pristine graphite surface as compared to electrolyte decomposition onto plated lithium at potentials around 0 V vs. Li+/Li. Acknowledgements We gratefully acknowledge the German Federal Ministry of Education and Research (BMBF) for its financial support within the AQua HysKaDi project (03XP0321B).

The quermassintegral-preserving mean curvature flow in the sphere

The quermassintegral-preserving mean curvature flow in the sphere

Fuzzy logic as a method of analysis of hot forging process of 80MnSi8-6 steel

A novel approach was proposed, based on the application of the fuzzy logic (FL) method for the fast analysis of the hot deformation process of 80MnSi8-6 steel. In the first stage, the curves developed from plastometric tests and the results of studies of the microstructure of the deformed samples were used as input data for the analysis. Input and output variables were adopted and a set of rules based on cause-and-effect relationships was defined, defining the interactions between the variables. A fast FL-controller was designed, and the correctness of its operation was verified by comparison with experimental results and the results of finite element method (FEM) analysis, carried out taking into account the evolution of the microstructure. The process of hot compression under isothermal conditions of 80MnSi8-6 steel specimens was simulated on the Warmumformsimulator (WUMSI), assuming such parameters and other conditions as were used in real tests. It was confirmed that the proposed method, based on the analysis of flow curves and prior austenite grain size using a fuzzy controller, gave satisfactory results. Subsequently, a novel FL-controller was developed to analyze the kinetics of dynamic recrystallization (DRX), using data obtained from the author’s model of this phenomenon for its construction and calibration. The correctness of the controller was confirmed by comparing the results of its DRX volume fraction calculations with the distributions of this value determined by the model and the model-based FEM analysis method, respectively. It was shown that FL is applicable also when a model of the analyzed phenomenon is available. Unlike model-based calculations, a properly designed controller allows the indication of deviations from general trends that can be pointed out and interpreted by a human expert, but significantly faster. It can also serve as a component of a system analyzing complex processes, such as hot multi-stage forging. Fuzzy controller can be used in parallel with modeling or replace models in calculations.

On the inverse mean curvature flow by parallel hypersurfaces in space forms

We consider the inverse mean curvature flow by parallel hypersurfaces in space forms. We show that such a flow exists if and only if the initial hypersurface is isoparametric. The flow is characterized by an algebraic equation satisfied by the distance function of the parallel hypersurfaces. The solutions to the flow are obtained explicitly when the distinct principal curvatures have the same multiplicity. This is an additional assumption only for isoparametric hypersurfaces of the hyperbolic space or of the sphere with two or four distinct principal curvatures. The boundaries of the maximal interval of definition, when finite, are determined in terms of the number g g of distinct principal curvatures, their multiplicities m m and the mean curvature H H of the initial hypersurface. We describe the collapsing submanifolds of the flow at the boundaries of the interval. In particular, we show in the Euclidean space the solutions are eternal, while in the hyperbolic space there are eternal and immortal solutions. Starting with a connected isoparametric submanifold of the sphere, we show that the flow is an ancient solution, that collapses into a minimal hypersurface whose square length of its second fundamental form and its scalar curvature are constants given in terms of g g and n n . The minimal hypersurface is totally geodesic when g = 1 g=1 , it is a Clifford minimal hypersurface of the sphere when g = 2 g=2 and it is a Cartan type minimal submanifold when g ∈ { 3 , 4 , 6 } g\in \{3,4,6\} .

Mean curvature flows of graphs sliding off to infinity in warped product manifolds

We study mean curvature flows in a warped product manifold defined by a closed Riemannian manifold and R. In such a warped product manifold, we can define the notion of a graph, called a geodesic graph. We prove that the curve shortening flow preserves a geodesic graph for any warping function, and the mean curvature flow of hypersurfaces preserves a geodesic graph for some monotone convex warping functions. In particular, we consider some warping functions that go to zero at infinity, which means that the curves or hypersurfaces go to a point at infinity along the flow. In such a case, we prove the long-time existence of the flow and that the curvature and its higher-order derivatives go to zero along the flow.

Dynamics of area-preserving curvature flow of convex plane curves with small area in an inhomogeneous medium

AbstractIn 1986, Gage studied area-preserving curvature flows in a two-dimensional homogeneous medium and proved that an initially convex closed curve remains convex and converges to a circle as time approaches infinity. However, a medium may not be homogeneous in many applications such as cell motility and motions of active matters. Therefore, this work introduces an area-preserving curvature flow in an inhomogeneous medium, which is a natural extension of an inhomogeneous medium. Through this extension, a closed curve numerically moves towards the higher medium by the flow. To show this fact, the case is considered in which the area enclosed by the closed curve is small. In this situation, it is shown that the dynamics of its center is approximated by a gradient flow determined by the distribution of the inhomogeneous medium and that its center moves toward the critical point of the inhomogeneous medium.

REDUCING THE VISCOSITY OF THE OIL MIXTURE BY A ROTARY PULSE APPARATUS IN UKHTA — YAROSLAVL OIL PIPELINE

Physical methods of exposure can be used to improve the rheological characteristics of viscous, resinous oils, the transportation of which through main pipelines requires additional operating costs. The authors of this article evaluated the effectiveness of the method for improving oil rheology due to multifactorial effects (shear loads, high–amplitude pressure pulses, developed turbulence) on a sample of a mixture of oils of the Ukhta - Yaroslavl oil pipeline in a rotary pulse apparatus (RIA). The specific power consumption for processing an oil sample was 2.84 kWh/m3. The initial rheological and physico-chemical parameters of the studied oil are described, according to which it is characterized as heavy, viscous, highly resinous oil. The analysis of the flow curves showed that, by the nature of the flow, the sample of a mixture of oils from the Ukhta — Yaroslavl main oil pipeline belongs to Newtonian liquids. The evaluation of the effectiveness of the multifactorial effect on the oil sample implemented in RIA was carried out using dimensionless coefficients showing the ratio of dynamic viscosity, the specific power required to maintain the flow of oil in a rotary viscometer before and after physical exposure to oil, as well as the ratio of the change in the energy of thixotropy of oil to the energy spent on the processing process. The samples were processed in an RIA-based installation, in which pressure pulsations, developed turbulence, and large shear loads are generated in the liquid flow. When comparing the viscosity values of untreated and treated mixed oil in a rotary pulse apparatus, the dynamic viscosity measured at 20 °C decreased by 8 %. The component composition of the oil after processing in RIA has practically not changed. Measuring the viscosity of oil before processing and immediately after processing in RIA shows a decrease in viscosity by more than two times, since the temperature of the oil flow increases after passing through RIA by more than 10 °C. The increase in oil temperature during processing is due to large shear stresses during its flow in slit channels and in the gap between the rotor and stator due to the large amplitude of pressure pulsations and flow velocity.The relaxation time of the rheological parameters of the treated oil was seven days.

Hot Deformation Behavior and Microstructure Evolution of the Maraging Stainless Steel

Hot deformation behavior of the maraging stainless steel is studied in temperature range from 900 to 1150 °C and strain rate from 0.1 to 10 s−1. When the deformation temperature is 900−950 °C, the abnormal stress increase is observed at the end of the flow curves. Transmission electron micrographs reveal that the Laves phase at the interface between prior austenitic (γ) and high‐temperature ferrite (δ) impedes hot deformation. The microstructure analysis shows that the dynamic recrystallization (DRX) mechanism of γ and δ is discontinuous DRX and continuous DRX, respectively. When the specimens are deformed at 950 °C, the extent of DRX at a strain rate of 5 s−1 is higher than at 0.1 s−1. This anomaly is due to adiabatic heating causing the actual deformation temperature at high strain rate () to be higher than at low , indicating that DRX is more influenced by temperature compared to . The influences of adiabatic heating and friction are corrected. Strain‐dependent constitutive equation is developed based on the revised flow curves, yielding an average absolute relative error of 4.69% and a correlation coefficient of 0.99; the prediction accuracy exceeds 90% when the relative error is within 10%.

Mean curvature flow from conical singularities

We prove Ilmanen’s resolution of point singularities conjecture by establishing short-time smoothness of the level set flow of a smooth hypersurface with isolated conical singularities. This shows how the mean curvature flow evolves through asymptotically conical singularities. Precisely, we prove that the level set flow of a smooth hypersurface Mn⊂Rn+1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$M^{n}\\subset \\mathbb{R}^{n+1}$\\end{document}, 2≤n≤6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$2\\leq n\\leq 6$\\end{document}, with an isolated conical singularity is modeled on the level set flow of the cone. In particular, the flow fattens (instantaneously) if and only if the level set flow of the cone fattens.

Hypersurfaces with capillary boundary evolving by volume preserving power mean curvature flow

Hypersurfaces with capillary boundary evolving by volume preserving power mean curvature flow

Ruled surfaces as self-similar solutions to the harmonic mean curvature flow in Minkowski 3-space

Ruled surfaces as self-similar solutions to the harmonic mean curvature flow in Minkowski 3-space

Quantitative convergence of the nonlocal Allen–Cahn equation to volume-preserving mean curvature flow

AbstractWe prove a quantitative convergence result of the nonlocal Allen–Cahn equation to volume-preserving mean curvature flow. The proof uses gradient flow calibrations and the relative entropy method, which has been used in the recent literature to prove weak–strong uniqueness results for mean curvature flow and convergence of the Allen–Cahn equation. A crucial difference in this work is a new notion of gradient flow calibrations. We add a tangential component to the velocity field in order to prove the Gronwall estimate for the relative energy. This allows us to derive the optimal convergence rate without having to show the closeness of the Lagrange-multipliers.

A mean curvature flow arising in adversarial training

We connect adversarial training for binary classification to a geometric evolution equation for the decision boundary. Relying on a perspective that recasts adversarial training as a regularization problem, we introduce a modified training scheme that constitutes a minimizing movements scheme for a nonlocal perimeter functional. We prove that the scheme is monotone and consistent as the adversarial budget vanishes and the perimeter localizes, and as a consequence we rigorously show that the scheme approximates a weighted mean curvature flow. This highlights that the efficacy of adversarial training may be due to locally minimizing the length of the decision boundary. In our analysis, we introduce a variety of tools for working with the subdifferential of a supremal-type nonlocal total variation and its regularity properties.

Rheological properties of phosphorus-containing oligoester(meth)acrylate for processing by vacuum infusion

Objectives. To obtain polymer composite materials (PCM) with enhanced physicomechanical properties using the vacuum assisted resin transfer molding (VaRTM) method, binders must have a viscosity of up to 500 mPa∙s. In some cases, this leads to restrictions on the use of certain materials or requires the use of temporary diluents. This is closely related to the deterioration of other required composite characteristics, such as increased flammability. Three phosphorus-containing oligoester(meth)acrylates PhOEM-1, PhOEM-2, and PhOEM-3 were synthesized with significant differences in viscosity characteristics in the series PhOEM-1 << PhOEM-2 << PhOEM-3. The polymer based on PhOEM-1 exhibits inferior physicomechanical properties despite having lower viscosity. Hence, the aim of the study was to investigate the viscosity characteristics of mixtures of methacrylate binders of the same nature but different structures and functionalities. This was done by studying the rheological properties of the original oligoester(meth)acrylates and their mixtures taken in various ratios. The method used was to optimize compositions via a simplex lattice (Scheffe’s plan), in order to obtain PCM using the VaRTM technology.Methods. The study of rheological properties of phosphorus-containing oligoester(meth)acrylates and their mixtures was conducted using the method of rotational viscometry on a Brookfield LVDV-II + Pro viscometer with a spindle 27 at different shear rates ranging from 0 to 70 s−1 and temperatures from 30 to 70°C. Rheological studies were also conducted on a Lamy Rheology GT300 PLUS (GEL TIMER) viscometer in the same range of shear rates and temperatures.Results. It was established that the objects under investigation can be characterized by viscosity values ranging from 96 to 2137 mPa∙s depending on the temperature. The nature of the viscous flow of phosphorus-containing oligoester(meth)acrylates and their mixtures is similar to that of Newtonian liquids only at certain shear rates. The effective activation energies of the viscous flow of binders and their mixtures were calculated, and the influence of temperature on the viscosity of binders was determined.Conclusions. The study identified the features and nature of the flow curves of phosphorus-containing oligoester(meth)acrylate binders of the same nature but different structures and functionalities, as well as of their mixtures. The optimal composition ranges of threecomponent mixtures of phosphorus-containing oligoester(meth)acrylates for use in the VaRTM technological process in producing polymer composite materials within the temperature range of 30 to 70°C were defined. The optimal compositions and temperature conditions for obtaining polymer composite materials using the VaRTM technology were also identified. This enables the production of polymer products with complex geometric shapes and varying sizes.

The potential of uroflowmetry to predict and detect hemorrhagic cystitis following hematopoietic stem cell transplantation

Hemorrhagic cystitis (HC) is a serious complication following hematopoietic stem cell transplantation (HSCT) associated with significant morbidity and mortality. Early identification of at-risk patients and prompt diagnosis are crucial for effective management. This prospective cohort study evaluated the potential of uroflowmetry as a predictive tool for detecting HC in pediatric HSCT patients. Thirty-one children who underwent allogeneic HSCT were enrolled. Uroflowmetry was performed on admission (Day 0), post-HSCT Day 1 and Day 15, and at HC onset. Uroflowmetric parameters, including maximum flow rate (Qmax), average flow rate (Qavg), voided volume (VV), and flow curve shape, were compared between HC and non-HC patients. The incidence of HC within 100 days post-HSCT was 58%, with a mean onset time of 35 days. At baseline (Day 0), HC patients had significantly lower Qmax (12.5 vs. 17.8mL/s), Qavg (6.8 vs. 9.5mL/s), and VV (185 vs. 245mL) compared to non-HC patients (all p<0.05). Age-stratified analysis revealed the observation of these differences across all age groups. At HC onset, compared to Day 0, patients experienced a significant decrease in Qmax (8.7 vs. 12.5mL/s) and Qavg (4.2 vs. 6.8mL/s) (both p<0.05). Flow curve analysis demonstrated a shift from bell-shaped to interrupted curves in HC patients over time. Uroflowmetry can potentially predict and detect HC in pediatric HSCT patients. Lower baseline uroflowmetric parameters may identify patients at higher risk for HC, while a significant decrease in these parameters from baseline may indicate HC onset. Uroflowmetry is a simple, non-invasive tool that can be performed at home and monitored remotely, facilitating early detection and intervention for HC in this population.

Effect of flow direction on circumferential velocity, radial velocity, and flow resistance characteristics of rotating gap structures

A rotating gap structure is a type of viscous flow resistance using two disks where the rotation of one disk drives the fluid within the gap, generating rotational inertia. This inertia, combined with viscous friction, determines the flow resistance characteristic curve (pressure drop vs flow rate, or Δp-Q curve). By adjusting the disk's rotational speed, the rotational inertia and the Δp-Q curve can be modified. This paper examines how the radial flow direction (positive and negative) affects the circumferential velocity, radial velocity, and the Δp-Q curve of the rotating gap structure through theoretical modeling and experiments. Results show that radial flow direction and rate influence the symmetric distribution of radial velocity and the linear distribution of circumferential velocity, altering the main components of the Δp-Q curve: the viscous flow resistance curve (Δpvis-Q) and the rotational inertia flow resistance curve (Δprot-Q). The study found that the slope of the Δpvis-Q curve is smaller for positive flow than for negative flow due to differences in radial velocity distribution. Additionally, the circumferential velocity is weakened in positive flow and enhanced in negative flow, resulting in a smaller slope of the Δprot-Q curve for positive flow. These factors cause the Δp-Q curve to deviate from linearity, with greater deviation at higher rotational speeds. Finally, experimental verification was conducted, and the measured Δp-Q curve closely matched the theoretical calculations.

Mean curvature flows of two-convex Lagrangians

Mean curvature flows of two-convex Lagrangians

A Variational Discretization Method for Mean Curvature Flows by the Onsager Principle

A Variational Discretization Method for Mean Curvature Flows by the Onsager Principle

Heterogeneous dynamic restoration of Ti–15Mo alloy during hot compression

Near-β titanium alloys have shown low Young's modulus and good strength, making them excellent implant candidates. However, their processing using thermomechanical routes in single phase β region results in heterogeneous microstructures due to high content alloying elements and consequent slow diffusion-controlled processes such as dynamic recovery. This study investigates the deformation behaviour of a Ti–15Mo alloy through hot compression experiments using a Gleeble ® 3800 device in the single β domain at strain rates from 0.01 s−1 to 10 s−1, reaching final strains of 0.50 and 0.85 followed by immediate water quench. The findings show that the material presents a low strain rate sensitivity. The flow curves show significant strain hardening before reaching a steady-state regime, particularly at high strain rates. The strain hardening exponent calculations support the effect of molybdenum on retarding softening mechanisms such as dynamic recovery. Electron backscatter diffraction (EBSD) measurements of deformed samples revealed that dynamic recovery is the primary restoration mechanism, with continuous and geometric dynamic recrystallisation evidence. Due to the slow restoration process, we observe the subgrain formation for different deformation parameters. Therefore, we introduced an EBSD-based method to quantify dynamic recovery and subgrain size. We concluded that for a given deformation, the areas of dynamically recovered and recrystallised regions decrease with increasing strain rate and decreasing temperature, exhibiting negligible variation at higher strain rates.