Chemomechanical Effects Research Articles

Chemo-mechanical strain effects on band engineering of the TiO2 photocatalyst for increasing the water splitting activity

Tensile strain induced by dispersion of Au particles is effective for stabilizing the anatase phase of TiO2 at high temperature and also increasing the photocatalytic activity by an increase in the charge separation with band engineering.

Stress-resilient electrode materials for lithium-ion batteries: strategies and mechanisms.

Next-generation high-performance lithium-ion batteries (LIBs) with high energy and power density, long cycle life and uncompromising safety standards require new electrode materials beyond conventional intercalation compounds. However, these materials face a tradeoff between the high capacity and stable cycling because more Li stored in the materials also brings instability to the electrode. Stress-resilient electrode materials are the solution to balance this issue, where the decoupling of strong chemomechanical effects on battery cycling is a prerequisite. This review covers the (de)lithiation behaviors of the alloy and conversion-type anodes and their stress mitigation strategies. We highlight the reaction and degradation mechanisms down to the atomic scale revealed by in situ methods. We also discuss the implications of these mechanistic studies and comment on the effectiveness of the electrode structural and chemical designs that could potentially enable the commercialization of the next generation LIBs based on high-capacity anodes.

Elasto – plastic modelling of the behaviour of non - active clays under chemo – mechanical actions

Environmental variables such as temperature, matric suction and pore fluid composition are well known to influence the hydro-mechanical behavior of clays and shales. The type and the relevance of this influence depends on the mineralogical composition and on the fabric of the material. Soil activity is an engineering proxy for mineralogical composition which can be used for a preliminary characterization of the expected type of behaviour under chemical actions, if those do not imply very significant cation exchange or pH variations. Very large chemo-mechanical effects occur in highly active soils used in engineering works such as barriers for nuclear waste or landfills, however concentration changes also impact on the mechanical behavior of non – active soils and rocks, such as illitic or natural blends of clays. Such materials are widely distributed in nature and their mechanical response upon chemical changes can be problematic in many cases. Examples of engineering relevance include vast slope instabilities promoted by fabric changes due to desalinization in Scandinavian quick clays, and instability or convergence issues for boreholes drilled in shales exposed to muds with a different chemical composition from the one of the pore fluid. An elastoplastic model is formulated to simulate the volumetric behaviour of such materials along chemical and mechanical loads. In addition to the parameters of the Modified Cam Clay, it requires defining the dependency of the elasto-plastic compliance and reference void ratio on pore fluid salinity. The model performs well against experiments from literature where complex chemo-mechanical histories were imposed.

The softening effect during electrochemical drawing of AISI 1070 steel wire

Drawing deformation behaviors of AISI 1070 steel in conventional lubrication and electrochemical environments were compared. The anodic polarization in the electrochemical drawing not only decreases much the deformation resistance but also eliminates the work hardening. This can only be attributed to the reaction on the surface of the wire before it passes through the die. This chemomechanical effect, which is governed by surface dissolution rate, facilitates dislocation slip and permits a much smooth high speed drawing. It was a promising technology for the forming of brittle hard metal materials.

Perturbation solutions of the diffusive chemo-mechanical coupling problem without a failure of local Fick’s law

Silicon electrodes of lithium-ion batteries have a remarkable diffusive chemo-mechanical coupling effect during lithiation and delithiation. In order to study the variation of stresses and concentration distribution in the electrode, a nonlinear partial differential equation for the concentration is usually derived using the thermal analogy method and Fick’s laws, in the case without a failure of local Fick’s law. However, due to the nonlinearity of the equation and the boundary conditions, it is generally difficult to get the analytic solution. In this paper, by using the dimensionless quantities, the perturbation solutions are obtained for two fundamental problems, that is, the semi-infinite and the cylinder, which appears to be semi-analytic and easy for the numerical calculation. The results match with the numerical solutions very well, when the charge current density is controlled in a relatively appropriate range. The semi-analytic solutions show that the compressive stress promotes the diffusion of lithium in the electrode during lithiation, which cannot be neglected, compared with the condition without considering the coupling effect.

Seepage dissolution effect prediction on aging deformation of concrete dams by coupled chemo-mechanical model

Concrete dams undergo a seepage dissolution process because of huge reservoir water pressure and concrete permeability, and such dissolution weakens the mechanical properties of concrete and produces a certain amount of irreversible aging deformation. This study proposes a coupled chemo-mechanical model to predict the seepage dissolution effect on aging deformation of concrete dams. The interactions between elastic–plastic, chemical damage and mechanical damage are jointly explored combining with on-site inspection of long-term service performance of a concrete gravity dam firstly. Then an aging model of the seepage dissolution damage is digitized, and a novel model on chemo-mechanical coupled effect is put forward by introducing an overall chemo-mechanical damage scalar. The validity of the model is proved by a case study on the gravity dam through finite element simulation on its seepage dissolution and comparison with monitoring data. Finally, these methods are applied into an ultra-high arch dam to quantitatively calculate the irreversible aging deformation with the increase of the seepage dissolution degree. And the annual maximum aging deformation of the arch dam increases 0.65 mm after 100 years. The results indicate that the proposed model can effectively predict the aging deformation caused by the seepage dissolution during long-term operation of concrete dams.

Synergetics of geological mediums and its impact on the effectiveness of the exploitation and exploration for mineral deposits

The mechanisms of joint influence of mountain and reservoir pressures, saturating fluid, structure elements of rocks and external dynamic effects on their behavior in natural conditions, in particular near of the well, are investigated. With specific examples, it is shown that the behavior of rocks with such a set of influencing factors is determined by the laws of synergetics and the combined action of external influences, uneven stress-strain state of the rocks, the pore pressure and chemo mechanical effects. Examples are the results of gas-flow and gas-metric studies of closed wells, as well as the results of explosive perforation and intensification of producing wellbores at different depths. Defects occurrence in minerals with a high modulus of elasticity is initiated by an external dynamic effect and independently under the action of the saturating fluid. Then, under volumetric non-uniform compression and reservoir pressure, gradual fracturing of terrigenous rocks occurs at the micro and macro level. The result of these processes is the formation of areas of the improved permeability near the wells during drilling, production and suspending. When drilling on traditional technology they will impair formation reservoir properties via infiltration of water and solid phase. In oil and gas wells and in closed wells - improve these properties. Analysis of the behavior of rocks from the synergetic position shows that the best mode of loading on the reservoir during wells drilling, wells completion and oil and gas production is depression (reduced pressure) on the reservoir. The known and new promising technologies for the intensification of oil and gas production are determined.

CHEMOMECHANICAL ANALYSIS OF A FUNCTIONALLY GRADED SPHERICAL HYDROGEL

As a kind of new smart materials, hydrogel has a special chemomechanical coupling effect. By using the functionally graded material, the adaptability and controllability of the hydrogel can be improved distinctly. In this analysis, the crosslink density of the hydrogel is assumed to be a power-law function of the radial position. By employing the general multi-field coupling large deformation theory and the Flory-Huggins free energy function, the governing equations of the functionally graded spherical hydrogel (FGSH) undergoing the spherically symmetric deformation are developed. The theoretical analysis of the swelling behavior accompanying the inhomogeneous large deformation is presented for the FGSH when subjected to the internal pressure and the prescribed chemical potential. Numerical results show that both the internal pressure-internal radius curve and the internal pressure-radial stretch curve exhibit a stable region and an unstable region, which means that if the internal pressure exceeds a certain critical value, the instability will occur and the hydrogel will finally be damaged. The critical value of the internal pressure increases with the increasing of gradient index. It is shown that the material parameters, such as gradient index, the interaction parameter between the polymer network and the solvent, the cross-link density and the volume of the solvent molecular, and the environmental chemical potential have a significant effect on the swelling behavior of the FGSH. If the internal pressure is fixed, the radial displacement of FGSH at the internal surface is nearly linear with respect to the gradient index, while it appears obvious nonlinear to other parameters. The investigation is helpful to realize the precise control of the hydrogel-based smart structures and devices under the complex environments.

Chemo-mechanical coupling effect on high temperature oxidation: A review

The rapid development in the field of chemo-mechanical coupling has drawn increasing attention in recent years. Chemo-mechanical coupling phenomena exist in many research areas, ranging from development of advanced batteries, biomechanical engineering, hydrogen embrittlement, and high temperature oxidation, etc. In this review, we attempt to provide an overview of the recent advances in chemo-mechanical coupling study on high temperature oxidation. The theoretical frameworks, computational modeling, and experimental studies on this subject are summarized and discussed. The stress-diffusion coupling effect in diffusion-controlled oxidation process, stress-induced evolution of oxide morphology in microscale experiment, and stress-oxidation interaction at crack front for intergranular fracture are highlighted. In addition, potential applications and possible methods via surface engineering for improving oxidation-resistance of high temperature structural materials are briefly discussed.

Chemo-mechanical coupling effect in the high-temperature oxidation of metal materials: A review

The metal materials are susceptible to be oxidized when they are exposed to the complex and harsh environments, especially at the elevated temperature. The development of corresponding chemo-mechanical coupling theory is indispensable in theoretically and numerically predicting the material properties reduction and failures due to the oxidation. In this paper, we review the historical sketch of the coupling theory of chemical reactions and mechanics in the high-temperature oxidation of metal materials. The oxidation results in the stress generation while the generated stress in turn affects the chemical reaction rate and the diffusion process of the reactants. It is therefore a complex chemo-mechanical coupling problem. This review begins with the discussion of the diffusion-controlled oxidation, and then discusses the stress-dependent diffussion during the oxidation and the oxide growth induced stress, and ends with the discussion of interaction between chemical reactions and stress. This review of chemo-mechanical coupling literature is not exhaustive; we review much of the fundamental literature and draw comparisons of coupling theory development in the filed of metal oxidation.

Chemo-mechanical effects on the tribocorrosion behavior of titanium/ceramic dental implant pairs in artificial saliva

In this paper, the degradation mechanisms of the ceramic and the metal in Titanium/Zirconia pairs for biomedical applications were analyzed. To do that, an experimental set-up with well-controlled mechanical and chemical conditions was used based on a unidirectional ball-on-disk tribometer coupled to a potentiostat. Tribocorrosion tests were carried out in artificial saliva at different applied potentials, this is, different chemical conditions of the surface. Wear damage of the titanium/zirconia pair was influenced by the properties and the behavior of wear debris in the contact. Under passive conditions metallic and oxidized titanium particles (formed by the cyclic removal of the passive film and subsequent repassivation) were smeared and mechanically mixed within the contact forming compacted wear debris through which the loading was carried out. Properties and amount of oxidized titanium lead to low wear at low passive conditions (OCP) and higher wear at high passive conditions. Zirconia did not suffer any damage under all the studied conditions and oxidized titanium was transferred to the ball at anodic applied potentials.

First Evidence for Mechanism of Inverse Ripening from In-situ TEM and Phase-Field Study of \u03b4\u2032 Precipitation in an Al-Li Alloy

In-situ TEM investigation of aging response in an Al–7.8 at.% Li was performed at 200 °C up to 13 hours. Semi-spherical δ′ precipitates growing up to an average radius of 7.5 nm were observed. The size and number of individual precipitates were recorded over time and compared to large-scale phase-field simulations without and with a chemo-mechanical coupling effect, that is, concentration dependence of the elastic constants of the matrix solid solution phase. This type of coupling was recently reported in theoretical studies leading to an inverse ripening process where smaller precipitates grew at the expense of larger ones. Considering this chemo-mechanical coupling effect, the temporal evolution of number density, average radius, and size distribution of the precipitates observed in the in-situ experiment were explained. The results indicate that the mechanism of inverse ripening can be active in this case. Formation of dislocations and precipitate-free zones are discussed as possible disturbances to the chemo-mechanical coupling effect and consequent inverse ripening process.

Stress corrosion cracking of pipeline steels in near-neutral pH solutions: the role of mechanochemical and chemomechanical effects

The review presents brief theoretical foundations of the mechanochemical and chemomechanical surface effects (MCE and CME) associated with corrosion-mechanical destruction of metals, considers the results of various scientific publications that studied the mechanochemical behavior of steels in near-neutral pH media, and analyzes the application of the results of such studies with the purpose of their practical use in the stress corrosion cracking (SCC) prevention. The article attempts to summarize the results of modern experimental studies and numerical modeling of mechanochemical and chemomechanical processes occurring on the surface of pipe steels and at the tip of the crack under the simultaneous effects of stresses/strains and corrosion media. The influence of these processes on the mechanism and kinetics of corrosion cracking of pipe steels in near-neutral aqueous solutions is discussed. The criteria for the quantitative assessment of the influence of MCE and CME on the SCC of pipeline steels are considered. The analysis of research methods for the study of MCE and CME, was carried out with the aim of further developing a unified methodological approach to assessment and quantification in predicting SCC in neutral media.

Chemo-mechanical modeling of artificially and naturally bonded soils

Chemo-mechanical effects are known to be significant in a number of applications in modern geomechanics, ranging from slope stability assessment to soil improvement and CO2 sequestration. This work focuses on coupled chemo-mechanical modeling of bonded geomaterials undergoing either mechanical strengthening, due to increased cementation, or weakening, due to cement dissolution. A constitutive model is developed that accounts for the multi-scale nature of the chemo-mechanical problem, introducing some cross-scale functions establishing a relationship between the evolution of microscopic variables and the macroscopic material behavior, realistically following the evolution of the reactive surface area, cross-sectional area and the number of bonds along with dissolution/deposition. The model presented here builds up on a previously introduced framework. However, at variance with existing works, it is specialized on materials with only reactive bonds, such as carbonate cemented sandstone or microbially cemented silica sand. Model validation is provided upon reproducing different types of chemo-mechanical experimental datasets, on different naturally and artificially cemented materials, to establish the reliability of the proposed framework.

Numerical Benchmark of Phase-Field Simulations with Elastic Strains: Precipitation in the Presence of Chemo-Mechanical Coupling

Phase-field studies of solid-state precipitation under strong chemo-mechanical coupling are performed and benchmarked against the existing analytical solutions. The open source software packages OpenPhase and DAMASK are used for the numerical studies. Solutions for chemical diffusion and static mechanical equilibrium are investigated individually followed by a chemo-mechanical coupling effect arising due to composition dependence of the elastic constants. The accuracy of the numerical solutions versus the analytical solutions is quantitatively discussed. For the chemical diffusion benchmark, an excellent match, with a deviation <0.1%, was obtained. For the static mechanical equilibrium benchmark Eshelby problem was considered where a deviation of 5% was observed in the normal component of the stress, while the results from the diffuse interface (OpenPhase) and sharp interface (DAMASK) models were slightly different. In the presence of the chemo-mechanical coupling, the concentration field around a static precipitate was benchmarked for different coupling coefficients. In this case, it is found that the deviation increases proportional to the coupling coefficient that represents the strength of coupling concentration and elastic constants. Finally, the interface kinetics in the presence of the considered chemo-mechanical coupling were studied using OpenPhase and a hybrid OpenPhase–DAMASK implementation, replacing the mechanical solver of OpenPhase with DAMASK’s. The observed deviations in the benchmark studies are discussed to provide guidance for the use of these results in studying further phase transformation models and implementations involving diffusion, elasticity and chemo-mechanical coupling effect.

Controlling Surface Oxides in Si/C Nanocomposite Anodes for High‐Performance Li‐Ion Batteries

AbstractSi/C composites represent one promising class of anode materials for next‐generation lithium‐ion batteries. To achieve high performances of Si‐based anodes, it is critical to control the surface oxide of Si particles, so as to harness the chemomechanical confinement effect of surface oxide on the large volume changes of Si particles during lithiation/delithiation. Here a systematic study of Si@SiOx/C nanocomposite electrodes consisting of Si nanoparticles covered by a thin layer of surface oxide with a tunable thickness in the range of 1–10 nm is reported. It is shown that the oxidation temperature and time not only control the thickness of the surface oxide, but also change the structure and valence state of Si in the surface oxide. These factors can have a strong influence on the lithiation/delithiation behavior of Si nanoparticles, leading to different electrochemical performances. By combining experimental and modeling studies, an optimal thickness of about 5 nm for the surface oxide layer of Si nanoparticles is identified, which enables a combination of high capacity and long cycle stability of the Si@SiOx/C nanocomposite anodes. This work provides an in‐depth understanding of the effects of surface oxide on the Si/C nanocomposite electrodes. Insights gained are important for the design of high‐performance Si/C composite electrodes.

Discovery of a Voltage-Stimulated Heartbeat Effect in Droplets of Liquid Gallium.

Chemomechanical effects are known to initiate fluid oscillations in certain liquid metals; however, they typically produce an irregular motion that is difficult to deactivate or control. Here we show that stimulating liquid gallium with electrochemistry can cause a metal drop to exhibit a heart beating effect by shape shifting at a telltale frequency. Unlike the effects reported in the past for mercury, the symmetry-breaking forces generated by using gallium propel the drop several millimeters with velocities of the order of 1cm per second. We demonstrate pulsating dynamics between 0 and 610 beats per minute for 50-150 μL droplets in a NaOH electrolyte at 34 °C. The underlying mechanism is a self-regulating cycle initiated by fast electrochemical oxidation that adjusts the drop's surface tension and causes a transformation from spherical to pancake form, followed by detachment from the circular electrode. As the beat frequency can be activated and controlled using a dc voltage, the electrochemical mechanism opens the way for fluid-based timers and actuators.

Chemomechanical Effects in Electrocatalysis

We report on electrochemical materials and processes with strong chemomechanical effects during electrocatalysis. We are particularly focused on anode and cathode processes for electrochemical water splitting. A combination of solid state, gas phase and thin film synthetic methods are used to prepare well-defined electrode materials. An optical laser method is used to perform in-situ surface stress measurements. We also employ Raman spectroscopy and imaging to map strain fields and inhomogeneity on surfaces. Combination of these responses provide unique insight into chemomechanics of hydrogen and oxygen evolution reactions. We will discuss the results of surface stress and strain measurements during H+ adsorption and early stages of hydrogen evolution on model Pt-M (M = Cu and Ni) surface alloys and bilayers. We will also report on the catalytic properties of perovskite-based transition metal oxides toward oxygen evolution reaction. We focus on perovskites and brownmillerites of the Sr2-xCaxFe2O6-δ system, where δ = 0-1. This system exhibits varying oxygen deficiency, vacancy ordering and volumetric strain. Our results suggest that vacancy content, ordering, and lattice oxygens control the oxygen evolution activity. Particularly, we will explain the role of lattice oxygens in the Sr2-xCaxFe2O6-δ system using in-situ surface stress results.

Efficiency of Carbon Dioxide Storage and Enhanced Methane Recovery in a High Rank Coal

The high affinity and adsorption capacity of coal to carbon dioxide provides an alternative approach for the enhanced recovery of methane from unminable coalfields (CO2-ECBM) by which a potential solution for long-term CO2 sequestration in deep geological formations can also be achieved. However, due to chemomechanical effects induced by the interactions between CO2 and coal, the effective methane production and carbon dioxide storage can be degraded which has caused uncertainties about the techno-economic feasibility of the CO2-ECBM process. This study presents an experimental investigation that aims to address key knowledge gaps related to the efficiency of CO2 storage and CH4 recovery in high rank coals for which a comprehensive experimental data set and analysis are largely missing. Competitive displacements of CH4 with N2 or CO2 in an anthracite coal sample from a South Wales coalfield have been studies, based on a series of core flooding experiments. The results show that the N2 breakthrough time (t...

Electrochemical investigation of corrosion and repassivation of structural aluminum alloys under permanent load in bending

AbstractThis work reports an electrochemical investigation of corrosion and repassivation in NaCl solutions of structural Al 7075-T6 and Al 2024-T3 as a function of permanent load in bending by means of single-cycle anodic polarization. Experimental variables other than the load level were the extent of corrosion, chloride ion concentration and initial pH of the test solution, in addition to the pre-exposure in the aggressive environment and of the viscosity of the test solution for Al 7075-T6. The susceptibility to local stress during corrosion and repassivation depends on the alloy microstructure and corrosion mechanisms. In the case of Al 2024-T3, the mechanical activation is driven by cathodically controlled dissolution of this alloy at open circuit in concentrated NaCl, being indicative of a chemomechanical effect. Conversely, for Al 7075-T6, the effect of applied load is better discerned from the repassivation response. Film rupture/formation sequence and related interfacial (electro)chemical processes determine the stress-enhanced metastable repassivation of this alloy.