Evolution Of Interface Research Articles

An analytical review on interfacial reactions in high-temperature die-attach: The insights into the effect of surface metallization and filler materials

This review aims for a comprehensive insight into the interfacial reactions and the effects of surface metallization in high temperature die-attach, which is critical in governing the reliability of resultant interconnects of power electronic modules. With the emerging high-temperature filler materials, the interfacial interactions and microstructural evolutions exhibit various distinctive features, which demands detailed examination in order to identify suitable surface finishes. The metallization is not always beneficial to improving the quality and reliability of the interconnects, and consideration should also be given to the cost-effectiveness and manufacturability. The intermetallic compounds (IMCs) formed during interfacial reactions are of prime concerns for an extended discussion, together with the formation of solid solution at interfaces which can also be an important topic to explore. In this work, five commonly-encountered high temperature solder fillers are examined, including high-Pb, Au-based, Bi-Ag, Zn-Al solders and nano Ag paste, the emphasises are put on the interactions with different metallized surfaces in die-attach. The effects of metallization on interfacial reactions and formation of interfaces are discussed. Finally, the recommendations of suitable metallization are outlined to enable cost-effective and reliable interconnects for the related applications.

Flow pattern maps of double emulsions transporting through bifurcation microchannels.

The transportation behaviors of compound droplets in confined channels are widespread phenomena while the physical mechanisms are far from being completely unraveled. In this work, behaviors of double emulsions flowing through bifurcation microchannels are experimentally studied with the aim of building universal flow pattern maps. Three flow patterns are categorized according to different features of daughter droplets in terms of size, uniformity, and shell thickness. A detailed analysis of the dynamics of interfacial evolutions in different patterns is carried out and the coupling interaction between interfaces is found to affect the minimum tail distance during transportation. It is feasible to obtain the threshold of the occurrence of the coupling interaction, due to the different variation tendencies in the two states, which relies on three dimensionless parameters, i.e. droplet length, length ratio, and capillary number. Furthermore, a novel physical model is proposed to build the flow pattern map, with the two transition boundaries being expressed as different relationships in terms of the three identified parameters. The physical mechanisms are summarized with the aid of force analysis. An excellent agreement is shown between the model and experimental results in different liquid systems and bifurcation structures, indicating the generality of the proposed model.

Exploring Cr and molten salt interfacial interactions for molten salt applications.

Molten salts play an important role in various energy-related applications such as high-temperature heat transfer fluids and reaction media. However, the extreme molten salt environment causes the degradation of materials, raising safety and sustainability challenges. A fundamental understanding of material-molten salt interfacial evolution is needed. This work studies the transformation of metallic Cr in molten 50/50 mol% KCl-MgCl2via multi-modal in situ synchrotron X-ray nano-tomography, diffraction and spectroscopy combined with density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Notably, in addition to the dissolution of Cr in the molten salt to form porous structures, a δ-A15 Cr phase was found to gradually form as a result of the metal-salt interaction. This phase change of Cr is associated with a change in the coordination environment of Cr at the interface. DFT and AIMD simulations provide a basis for understanding the enhanced stability of δ-A15 Cr vs. bcc Cr, by revealing their competitive phase thermodynamics at elevated temperatures and probing the interfacial behavior of the molten salt at relevant facets. This study provides critical insights into the morphological and chemical evolution of metal-molten salt interfaces. The combination of multimodal synchrotron analysis and atomic simulation also offers an opportunity to explore a broader range of systems critical to energy applications.

Solvent-free preparation and thermocompression self-assembly: an exploration of performance improvement strategies for perovskite solar cells.

Perovskite solar cells (PSCs) exhibit sufficient technological efficiency and economic competitiveness. However, their poor stability and scalability are crucial factors limiting their rapid development. Therefore, achieving both high efficiency and good stability is an urgent challenge. In addition, the preparation methods for PSCs are currently limited to laboratory-scale methods, so their commercialization requires further research. Effective packaging technology is essential to protect the PSCs from degradation by external environmental factors and ensure their long-term stability. The industrialization of PSCs is also inseparable from the preparation technology of perovskite thin films. This review discusses the solvent-free preparation of PSCs, shedding light on the factors that affect PSC performance and strategies for performance enhancement. Furthermore, this review analyzes the existing simulation techniques that have contributed to a better understanding of the interfacial evolution of PSCs during the packaging process. Finally, the current challenges and possible solutions are highlighted, providing insights to facilitate the development of highly efficient and stable PSC modules to promote their widespread application.

Analysis of Thermal Expansion Behavior and Interface Evolution of TSV Under Thermal Cycle Loading Based on Crystal Plastic Finite Element Method

Analysis of Thermal Expansion Behavior and Interface Evolution of TSV Under Thermal Cycle Loading Based on Crystal Plastic Finite Element Method

DIRECT NUMERICAL SIMULATIONS OF TWO-PHASE FLUIDS INTERFACE IN 2D ROTATING DRUMS USING A COUPLED VOF–IBM NUMERICAL APPROACH

Rotating drums play important roles in numerous industrial applications, such as mineral processing. This work is focused on the numerical study of the interface evolution in liquid-liquid and liquid-gas phase rotating drums. A new coupling strategy between volume of fluid (VOF) and immersed boundary method (IBM) approaches is developed. Relevant dimensionless numbers, including Reynolds, Froude, and Bond numbers, alongside viscosity and density ratios, are considered for the flow pattern characterization. Direct numerical simulations are performed in order to explore flow regimes within the rotating drum, addressing a gap in the literature concerning less-explored flow patterns, particularly in the rotating drum containing liquid-liquid phases. The flow pattern families characterizing rotating drums carrying liquid-liquid phases found in this study are (i) gravity stratified, (ii) mixing, (iii) annular, and (iv) rotation stratified flows. Additionally, the characteristic flow pattern families, (i) gravity stratified, (ii) pool, (iii) annular with pool, and (iv) annular flows, are identified in rotating drums carrying liquid-gas phases. The difference in the transitory responses between the rotating drum featuring liquid-liquid and liquid-gas phases is also shown and discussed. The main results highlight significant contributions for understanding the dynamics of rotating drums, particularly concerning the transitional interface development. By identifying new flow patterns and exploring transitional phenomena, this study enriches the understanding of complex fluid behavior within rotating drum configurations.

Formation characteristics and acoustic regulation of liquid metal droplets in low-aspect-ratio channels

The uniformity in size of liquid metal droplets is crucial in determining the accuracy of flexible circuit printing as well as the stability in signal transmission. In this study, the numerical simulation and the experiment method are combined to analyze the droplet preparation process of liquid metal. Furthermore, the mechanism of the surface acoustic wave as an external force dominating the breakup of the liquid metal interface is investigated. The results show that the squeezing pressure and the capillary force are the dominant forces of the interface evolution in the low-aspect-ratio (height/width) channel. When the dispersed phase flow rate is low, the interface will retract upstream of the channel under the influence of large interfacial tension after breakup, resulting in fluctuations in flow rate, and therefore, the stability of droplet size is weak. When the dispersed phase flow rate is high, the interface randomly breaks up under the influence of the Rayleigh–Plateau instability, which also leads to uneven droplet size. As the acoustic intensity increases, the acoustic radiation pressure gradually becomes the dominant force responsible for the squeezing and breakup of the interface. It increases the radial contraction rate of the interface, shortens the droplet generation period, and ultimately reduces the droplet size. Additionally, the size deviation value is significantly reduced from 10.13% to 1.05%. This study is useful in elucidating the evolution mechanism of liquid metal interfaces in low-aspect-ratio channels, improving the fundamental theory of interface breakup caused by acoustic radiation pressure, and providing theoretical guidance for the controlled and stable production of liquid metal droplets.

Revealing the plating/stripping processes on Zn anodes in Zn metal batteries via in situ AFM

Mechanistic insights into the interfacial evolution are essential for advancing rechargeable zinc metal batteries (RZMBs). Employing in situ atomic force microscopy (AFM), we observed the Zn plating and stripping processes on the Zn metal anode and investigated the effect of initial stripping over the interfacial evolution. During the initial stripping process, the interfacial evolution is uneven, and by-products form at the Zn anode, which contributes to the heterogeneous nucleation and quick dendrite growth during the subsequent plating, causing performance fading. In contrast, uniform Zn deposition and reversible dissolution can be achieved during the initial plating and following stripping processes. The Zn substrate remains flat without evident cracks or pits, which ensures the interfacial stability of the Zn metal anode during cycling. This work provides direct insights into the morphological evolution and interfacial mechanism of Zn metal anode, promoting the optimal design of advanced RZMBs.

A Hard-Constraint Wide-Body Physics-Informed Neural Network Model for Solving Multiple Cases in Forward Problems for Partial Differential Equations

In the fields of physics and engineering, it is crucial to understand phase transition dynamics. This field involves fundamental partial differential equations (PDEs) such as the Allen–Cahn, Burgers, and two-dimensional (2D) wave equations. In alloys, the evolution of the phase transition interface is described by the Allen–Cahn equation. Vibrational and wave phenomena during phase transitions are modeled using the Burgers and 2D wave equations. The combination of these equations gives comprehensive information about the dynamic behavior during a phase transition. Numerical modeling methods such as finite difference method (FDM), finite volume method (FVM) and finite element method (FEM) are often applied to solve phase transition problems that involve many partial differential equations (PDEs). However, physical problems can lead to computational complexity, increasing computational costs dramatically. Physics-informed neural networks (PINNs), as new neural network algorithms, can integrate physical law constraints with neural network algorithms to solve partial differential equations (PDEs), providing a new way to solve PDEs in addition to the traditional numerical modeling methods. In this paper, a hard-constraint wide-body PINN (HWPINN) model based on PINN is proposed. This model improves the effectiveness of the approximation by adding a wide-body structure to the approximation neural network part of the PINN architecture. A hard constraint is used in the physically driven part instead of the traditional practice of PINN constituting a residual network with boundary or initial conditions. The high accuracy of HWPINN for solving PDEs is verified through numerical experiments. One-dimensional (1D) Allen–Cahn, one-dimensional Burgers, and two-dimensional wave equation cases are set up for numerical experiments. The properties of the HWPINN model are inferred from the experimental data. The solution predicted by the model is compared with the FDM solution for evaluating the experimental error in the numerical experiments. HWPINN shows great potential for solving the PDE forward problem and provides a new approach for solving PDEs.

Investigation of Ionomer/Catalyst Interfacial Degradation in PEMFC Using Pt Nanoparticle Array Electrode

Interface between catalyst and ionomer in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) has been a subject of keen interest, but its effect to the durability has not been fully understood due to the complexity of catalyst layer structure. Herein, we suggest Pt nanoparticle (NP) array electrode fabricated using block copolymers as a platform for a focused investigation of Nafion/Pt interface. The interfacial evolution between Pt NP and Nafion thin layer during holding with various fixed potentials were investigated using the Nafion thin layer-coated Pt NP array electrode. A set of analysis for the electrodes with various fixed potentials reveals that the Nafion thin layer becomes densely packed and the interaction between the end group of Nafion side chain and Pt surface is facilitated at the intermediate operating potential (0.4~0.7 V). The rearrangement leads to an increase of oxygen transport resistance, negatively impacting the power performance of PEMFC. The Pt NP array electrode provides a versatile tool to analyze Nafion/Pt interface and fresh insight on the degradation mechanism of PEMFC.

In-Situ Reflectance Absorption Infra-Red Spectroscopy (RAIRS) Study on ALD of HfO2 on TiN and Pt Electrodes

Ferroelectricity in hafnia fluoride analogues has been widely investigated for nonvolatile memory applications. Although ALD of HfO2 technology is enough mature for CMOS technology, hafnia-based ferroelectrics still suffer from major reliability issues such as relaxation, imprint, fatigue, and breakdown.1 These reliability characteristics are thought to be related to the interface conditions between the ferroelectric film and the electrode. Thus, many reports suggested routes to enhance reliability and ferroelectric characteristics by modifying the interface states of the metal-ferroelectric-metal (MFM) capacitors. Unfortunately, only few reports disclose direct observation on evolution of interface formation and its mechanism. Recently, it is reported that scaling down the ferroelectric hafnia-based films to a few nm range dramatically improves the MFM capacitors’ reliability where the series capacitance and surface effect dominate, making it crucial to understand the interface properties carefully.2 In this presentation, we perform In-situ characterization using reflectance absorption infrared spectroscopy (RAIRS) to monitor the surface reaction and interface formation while HfOx ALD using TDMA-Hf with various oxidation reactants, such as H2O, O3, and anhydrous H2O2. TiN and Pt bottom electrodes are investigated at 250 °C. The RAIRS results show that the initial exposure of the oxidant generates the most amount of oxidation on the TiN surface by showing Ti-O and TiN-O peaks which were not observed for the Pt substrate. Moreover, the Ti-O and TiN-O peak area increase versus the dosing time of oxidant was minimum for H2O, and O3 showed continuous peak increase even after 12 s exposure. Interestingly, for the H2O2 case, there was almost no peak increase in the Ti-O bond region like H2O, but the TiN-O and TiO-O peaks appeared after the first 3 s and saturated after 6 s exposure. Also, not only on the TiN substrate, the peak for O-O stretching was observed for the Pt substrate as well, indicating that the H2O2 generates self-limiting peroxide bonds on the surface with a minimum interface formation. This suppressed interface formation with superior film properties using H2O2 might be the reason behind the robust reliability of the H2O2-based HZO capacitor. We are going to report reliability characteristics in conjunction with interface evolution.Acknowledements: We thank to YEST and KEIT for supporting the project through ISTD Program (No.20010806). This work is also supported by GRC-LMD program (task#3001.001) through SRC. The BRUTE hydrogen peroxide was provided by RASIRC. Ozone generator for TMEICReferences 1 J. Mohan et al., ACS AELM, 4, 4 (2022). 2 K. Toprasertpong et al., ACS AMI, 14 (2022).

In-Situ Probing the Origin of Interfacial Instability of Na Metal Anode

The chemical-mechanical stability of solid–electrolyte interphase (SEI) is probably the most critical factor determining the performance of alkali metal anode (Li, Na, etc.) in secondary batteries. Although extensive advanced characterization methods have been carried out to study SEI layers of Na metal anode, including solid state nuclear magnetic resonance1, 2, cryogenic transmission electron microscopy3, etc., the structural/componential evolution of SEI is still an uncharted territory due to its transient formation process and complicated components. In this work, we systematically analyze the SEI formation and dissolution processes via jointly combining multiple in-situ characterization technologies. By revealing spatial-temporal resolved information of SEI evolution, the buried origin of chemical-mechanical instability of SEI in Na anode is further clarified, which provides valuable guidelines for SEI engineering. A dynamic SEI formation/dissolution model of Na metal anode is demonstrated as follow:Quantitative evaluation methods for the chemical instability (i.e., solubility) and mechanical instability (i.e., modulus) are designed. According to the mass variation in EQCM and the modulus measurement in in-situ AFM, we firstly quantitatively observe the chemical and mechanical stability evolution during SEI formation process.The dynamic evolution picture of SEI formation has been explicitly established. We discover the instantaneous electrochemical formation process of SEI is obviously divided into two stages based on the potential. It is revealed that the formation of efficient passivation layer anchored on Na surface during the 1st (passivating) stage (2.3 – 1 V vs Na/Na+) (Scheme 1 a-b) is the critical factor to construct stable SEI. In absence of passivation layer, the Na mental surface will trigger unrestricted electrolyte decomposition and homogenous components distribution during the subsequent (growing) stage.The dissolution model of SEI was revealed related to its spatial distribution of organics and inorganics. SEI with layered structure evolved from a compact passivation layer is found to have higher stability than that with homogenously distributed components. The inorganic species in the latter structure tend to detach from the SEI with the dissolution of organics, resulting in poor SEI chemical stability (Scheme 1 c and e). By contrast, SEIs with hierarchical structure growing based on the top of a passivation layer exhibits lower dissolution tendency (Scheme 1 d and f).The dynamic analysis of SEI evolution of Na anode presented in this work not only sheds light on how to construct a stable SEI, but also provides guiding significance in unveiling the seemingly complicated interfacial chemistry in batteries via a concerted characterization approach.References Gao, L.N., Chen, J.E., Chen, Q.L. et al. The chemical evolution of solid electrolyte interface in sodium metal batteries. Science Advances 8, 4606 (2022).Xiang, Y., Zheng, G., Liang, Z. et al. Visualizing the growth process of sodium microstructures in sodium batteries by in-situ 23Na MRI and NMR spectroscopy. Nat. Nanotechnol. 15, 883–890 (2020). Han, B., Zou, Y., Zhang, Z. et al. Probing the Na metal solid electrolyte interphase via cryo-transmission electron microscopy. Nat Commun 12, 3066 (2021). Figure 1

X-Ray Photoelectron Spectroscopy Investigation of Catalyst-Ionomer Interactions for PEMFC Electrodes

Proton exchange membrane fuel cells (PEMFCs) are an increasingly attractive clean energy technology to meet stationary and transportation energy demands without contributing to greenhouse gases. Further developments to PEMFCs are primarily focused on improving the cathode catalyst layer which uses expensive platinum catalysts to compensate for the sluggish oxygen reduction reaction and a thin film of proton conductive ionomer to aid in mass transport. It is understood that the Pt-based carbon supported catalyst may experience heterogeneity in ionomer coverage motivating further studies of catalyst layers with focus on catalyst-ionomer interface. Specifically, it is important to improve understanding of how support morphology, Pt catalyst loading, amount of ionomer, and method of catalyst layer coating affect the catalyst-ionomer interface to identify potential pathways to further to improve catalyst utilization as the technology increases in scalability.This study focuses on investigating the catalyst-ionomer interface using x-ray photoelectron spectroscopy (XPS) as it is highly surface sensitive (top ~3-10 nm) and can capture subtle differences in the chemistry of the catalyst, ionomer, and support at the catalyst-ionomer interface. Due to the ionomer’s inherent susceptibility to x-ray induced damage, XPS analysis was conducted with a recently developed protocol to mitigate instrumental artefacts. In this work, elemental ratio quantification metrics derived from XPS are used to track surface ionomer content relative to amount of Pt nanoparticles and the amount of carbon support producing two parameters. These parameters are used to show how variations in carbon support graphitization, Pt loading, ionomer chemistry, and ionomer loading affect the catalyst-ionomer interface in unique ways. Additionally, changes to the catalyst-ionomer interface after degradation were also assessed, comparing beginning of life and end of life samples. Further, this presentation will also discuss the evolution of the catalyst-ionomer interface under humidified conditions which was assessed with in situ XPS. This talk highlights the potential of XPS to improve our understanding of relationships between surface properties, processing, performance, and durability and motivates future work in understanding catalyst layer fabrication, performance, and degradation.

(Keynote) Thermo-Electrochemical Interactions in Solid-State Batteries

Solid-state batteries (SSBs) with a lithium metal anode hold tremendous promise to enable long-range electric vehicles and electric aviation. However, the successful realization of practical SSBs necessitates gaining a fundamental understanding of the complex nature of solid-solid interface evolution including the origin of various failure/degradation mechanisms such as lithium filament penetration, void growth and interphase formation. While the influence of chemo-mechanics at such interfaces has received significant research attention, the underpinnings of thermo-electrochemical coupling and the thermal stability of solid-solid interfaces still require critical investigation. In this presentation, we mechanistically delineate the spatio-temporal attributes and implications of thermal interactions in SSBs, including their critical role on interface stability of the anode, electrochemical-transport response in the cathode and crosstalk between the cathode/solid-electrolyte/anode interfaces. The effect of architectural asymmetry in a solid-state cell, consisting of a heat-generating cathode and a lithium-metal anode, on the occurrence of an intrinsic thermal gradient and associated degradation modes have been highlighted. A comprehensive description of mechanisms underlying the thermo-electrochemical stability of solid-solid interfaces in SSBs is presented.

Three-dimensional effects during thermocapillary-driven melting of PCMs in cuboidal containers in microgravity

The melting of a phase change material (PCM) in a cuboidal domain under microgravity conditions is investigated numerically. The upper surface of the PCM is free (in contact with air, for example) and variations in its surface tension drive thermocapillary convection in the liquid phase, which significantly enhances heat transfer and accelerates melting. Furthermore, the change in liquid fraction during melting is associated with transitions among various modes of thermocapillary dynamics, including an oscillatory instability to hydrothermal waves. While the characteristics of PCM melting and thermocapillary dynamics have previously been investigated in this system using a two-dimensional model, the current work examines the important question of transverse dynamics and their effect on the melting process. Careful quantitative comparisons are made between the three- and two-dimensional models in terms of melting times, solid/liquid interface evolution, thermal fields, and spectrograms. The results show that transverse modes are often, but not always, reflection symmetric about the midplane and that their influence on melting and PCM performance is relatively minor in most cases. Thus, two-dimensional models may be used to reduce computational costs while still providing a reasonable approximation of the melting process for high Prandtl number materials, especially when compared to the midplane of the full cuboidal domain.

CO2-brine interface evolution and corresponding overpressure in high-gravity CO2 storage complex

Technical and economic feasibility of large-scale CO2 geological storage projects (GCS) requires storing the maximum possible amounts of CO2 within a given pore space. However, one limitation is attributed to the overpressure that accompanies CO2 injection. Specifically, reliable estimation of the bottom-hole pressure during CO2 injection is essential to optimize the storage potential of the formation while ensuring the integrity of the rock. Several studies presented analytical/semi-analytical solutions to predict the overpressure accompanying CO2 injection. Nevertheless, they neglect the effects of gravity override on the temporal evolution of the plume and/or the bottom-hole pressure. Effects of gravity can be quantified by the dimensionless group “gravity number” which measures the relative importance of the gravitational-to-viscous forces within system. A lower gravity number expresses a more uniform/cylindrical displacement of CO2. Conversely, biasness of CO2 flow towards the top of the injection zone translates to a larger gravity number. The main objective of this work is to develop an analytical model able to predict the bottom-hole pressure during CO2 injection through a vertical well centered in the middle of a high-gravity thick saline aquifer. While accounting for the effects of gravity, the proposed solution will be developed assuming vertical equilibrium of pressure with a sharp interface separating the injected CO2 and the in-situ brine. First, we develop a closed-form analytical solution to estimate the evolution of CO2/brine interface considering strong gravity effects. The closed-form solution is based on extending the semi-analytical and/or the iterative expressions previously derived in the literature to predict the evolution of the plume during the injection period. Then, the interface model will be coupled with the assumption of the vertical equilibrium to obtain an analytical solution for the pressure field during injection. Next, the proposed solution for the evolution of pressure will be validated against numerical simulations for cases covering wide and practical ranges of gravity numbers and mobility ratios. The solution will be also validated against real field data to determine its robustness. Predictions of the overpressure from our analytical solution indicate a reasonable agreement with the simulations performed using a more complicated multi-phase flow simulator.

Mechanism of crack evolution and strength failure in chemo-mechanical induced fracture

Chemo-mechanical coupled fracture is ubiquitous among various application fields. Understanding the mechanism of crack propagation is critical to the prediction and control of fracture behavior. In this paper, mechanical damage and chemical erosion have been investigated by a combination of experiments and theoretical analysis. We developed a theoretical model to analyze the interface evolution and the mechanical state of the crack tip in chemically active environments based on the transition-state theory. This model enables us to predict mechanical failure and chemical corrosion of materials exposed to external acid attack. Theoretical predictions of the corrosion rate and fracture strength have been validated by fracture experiments performed in different concentrations of corrosive solutions. In particular, we discovered a non-monotonic and non-linear relationship between the degree of corrosion and fracture strength, which demonstrates that corrosion-induced crack tip blunting and mass loss of materials together affect the cracking critical state. We further conducted the thermodynamic analysis of a quasi-static cracked body to investigate the effect of corrosion on energy stored in the crack tip. Our theory-experiment-combined study reveals the mechanism of coupling chemical and mechanical damage and provides significant insight into corrosion-induced fracture behavior in aggressive environments.

Research on the monitoring friction hysteresis for the bolted interface by electromechanical impedance

Friction hysteresis manifests at the bolted interface when subjected to external excitation, leading to nonlinear structural responses. But the interface evolution is rarely considered in the health monitoring. In this paper, we introduce the pioneering concept of effective mechanical impedance of the contact interface (EMICI) and formulate a coupled structural impedance model that comprehensively incorporates both tangential loading and contact impedance considerations. EMICI was deemed to encapsulate intricate information pertaining to contact nonlinearity, and the theoretical equation was derived using principles of contact mechanics. Tangential loading experiments, time domain impedance analysis and impact hammer tests were conducted to confirm the close relationship between EMICI and the structural properties. The coupled structural impedance model is proved to be effective, in which EMICI can be identified by changing the tangential force and torque. Subsequent analysis revealed that the proposed model could additionally serve in the identification of system-related parameters. The loading coefficient in the model is linearly related to the tangential force, and the calculated EMICI corresponds to the slip characteristics of the bolted interface. The introduced concept of EMICI could be considered as a metric for assessing interface properties, offering dependable insights into contact evolution, and facilitating a deeper understanding of interface dynamics.

Study on the interfacial microstructure evolution of aluminum and CFRTP on FSLW joints: influence of pin length

Polymer/metal hybrid lightweight structures are increasingly employed in automotive, aerospace and electronics industries. Friction stir welding (FSW) is applied for the effective welding of metals and thermoplastic materials. For the welding of dissimilar materials, due to the significant property differences, it is hard to achieve high strength welded joints with smooth appearance. In this article, the influence of pin length is studied by experiments for the friction stir lap welding (FSLW) of Al alloy and carbon-fiber-reinforced thermoplastic (CFRTP). Tensile tests, OM, SEM and EBSD are carried out to evaluate the welding performance. Results indicate that the joint with smooth surface topography is obtained at the pin length of 2.5 mm with a peak temperature of 250.3 °C and the CFRTP matrix PEI thermal decomposition temperature residence time of 47.6 s. From OM and SEM micro analysis, the width of the bonding area is 3.02 mm and a thin uniform interaction layer is formed in the joint. EBSD confirms that the Al alloy in the stirring zone is refined after recrystallization. It is difficult to form a stacked layered structure in the bottom of joint, so the property of the joint is improved. The tensile strength is 32.9 MPa, which is 63.1% of CFRTP.

In situ dynamic re-structuring and interfacial evolution of SnS2 for high-performance electrochemical CO2 reduction to formate

The conversion of CO2 to value-added fuels and chemicals through electrochemical reduction has garnered substantial traction as an environmentally friendly approach toward a carbon-neutral society. Surface re-structuring of catalysts stands as one of the dynamic behaviors exhibited by electrocatalytic systems, exerting a significant influence on the catalysts' chemical, electronic, and physical characteristics, and thereby impacting their catalytic capabilities. Herein, we have discovered that the re-structured SnS2 nanoflowers with in situ formed Sn nanoclusters exhibit an enhanced Faradic efficiency of up to 93% with long-term stability for selective electroreduction of CO2 to formate with dynamic surface re-structuring. The in situ generated Sn nanoclusters on SnS2 nanoflowers at negative potential were found to play a vital role in facilitating over 90% CO2 electroreduction efficiency to formate. The presence of key intermediate OCHO* was proved through in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. It was also guided by first-principal calculations that the interfacial region between Sn nanoclusters and SnS2 nanosheet acts as the most favorable catalytic site for the formation of OCHO*. This work unveils the significance of surface re-structuring behaviors of electrocatalysts under in situ environment for the pathway and mechanism of CO2 electroreduction, demonstrating the promise of structure-modulated SnS2 as a candidate for formate production.