Thickness Of Surface Layer Research Articles

Quantifying Degradation Parameters of Single-Crystalline Ni-Rich Cathodes in Lithium-Ion Batteries.

Single-crystal LiNix Coy Mnz O2 (SC-NCM, x+y+z=1) cathodes are renowned for their high structural stability and reduced accumulation of adverse side products during long-term cycling. While advances have been made using SC-NCM cathode materials, careful studies of cathode degradation mechanisms are scarce. Herein, we employed quasi single-crystalline LiNi0.65 Co0.15 Mn0.20 O2 (SC-NCM65) to test the relationship between cycling performance and material degradation for different charge cutoff potentials. The Li/SC-NCM65 cells showed >77 % capacity retention below 4.6 V vs. Li+ /Li after 400 cycles and revealed a significant decay to 56 % for 4.7 V cutoff. We demonstrate that the SC-NCM65 degradation is due to accumulation of rock-salt (NiO) species at the particle surface rather than intragranular cracking or side reactions with the electrolyte. The NiO-type layer formation is also responsible for the strongly increased impedance and transition-metal dissolution. Notably, the capacity loss is found to have a linear relationship with the thickness of the rock-salt surface layer. Density functional theory and COMSOL Multiphysics modeling analysis further indicate that the charge-transfer kinetics is decisive, as the lower lithium diffusivity of the NiO phase hinders charge transport from the surface to the bulk.

Addition of silica in the adhesive primer layer of composite systems used to repair leak defects in metallic pipelines

Fibre reinforced polymer composites are often used to repair through-thickness corrosion damage in metal pipes. Usually, a primer adhesive layer is initially applied to the surface of the pipe and then the composite reinforcement is applied in concentric layers. This paper investigates the possibility of adding silica as a low-cost thixotropic thickener to a commercial epoxy resin to facilitate the application of the prime layer while maintaining the strength and effectiveness of the repair after curing. The study of the influence of the silica concentration on the rheological behaviour of the adhesive before fully cured was performed using a rheometer. A preliminary study about the influence of different fractions of silica on the rupture force of metal-composite hybrid bonded joints after full cure showed a good result with the concentration of 1% by weight of epoxy resin. Then, hydrostatic burst tests were carried out on specimens with through-thickness defects, repaired using the same composite, but with two different initial adhesive layers (same surface finish and layer thickness, but with silica and without silica). The study shows that introducing a low fraction of silica facilitates the application of the primer and does not significantly affect the strength of the repair.

Electric fields and local heating in additively manufactured nanocomposite parts

Conventional methods of thermoplastic manufacture suffer from high capital costs, while fused deposition modeling (FDM) faces the challenge of poor adhesion between printed layers. We have previously shown that carbon nanotubes can be used as electric field susceptors to locally heat the interfaces between printed layers. We also showed that dielectric barrier discharge (DBD) plasma applicators mounted on FDM nozzles can pass current to printed parts for welding. Little is known, however, about the interaction between the electric field and the printed part. In this work, we simulate the internal heating behavior of printed parts with local variations in conductivity. These studies show that thermal penetration scales with conductive surface layer thickness; the results also indicate that conductive inclusions within parts can create hotspots. These findings explain the heating behavior of FDM printed parts when coupled to a DBD applicator and show that inclusions within the parts could create mechanical defects.

Physical interpretations of diffusion-controlled intercalation and surface-redox charge storage behaviors

Pseudocapacitance shows emerging properties to achieve both high capacity and high-rate performance simultaneously, including lithium ion and sodium ion storage systems. Herein, this work investigated the insightful mechanisms of pseudocapacitive lithium ion and sodium ion storage of anatase titanium dioxide anode. A transient two-dimensional continuum electrochemical modeling was performed for electrodes consisting of a single TiO2 nanoparticle immersed in the electrolyte. The process of intrinsic surface-redox pseudocapacitance showed a uniform ion concentration across the electrochemical-active amorphous layer without hysteresis. By contrast, typical hysteresis and concentration gradients in the electrode were observed in the process of extrinsic intercalation pseudocapacitance, which enlarged with the increase in nanoparticle size or scan rate. The results indicated that sodium ion storage in TiO2 was a surface-redox pseudocapacitive reaction. Design guidelines for sodium ion storage in TiO2 electrodes was proposed by dimensional analysis. The dimensionless capacity for sodium ion storage remained nearly constant when the dimensionless scan rate was less than a critical value. This provided the guidance for the design and synthesis of the TiO electrode to enhance sodium ion storage by balancing nanoparticle size, thickness of NaxTiO2 surface layer, and effective diffusion coefficient of the electrode. Furthermore, such surface-redox pseudocapacitive sodium ion storage model could be extended to analyze other electrode materials.

Specimen size effect on dynamic modulus measurement of Cold recycled and full depth reclamation mixtures

Dynamic modulus was measured using large-scale (LS) and small-scale (SS) specimens of four cold recycled (CR) and one full depth reclamation mixtures. The study found emulsified mixtures showed similar and repeatable dynamic modulus (E*) results with both specimen geometries (<15% difference) and foamed mixtures showed poor agreement between specimens (>24% difference), likely due to the differences in the mix matrices. The mechanistic-empirical pavement design analysis showed that E* differences in LS and SS of CR mixtures with foam resulted in error in asphalt concrete (AC) rutting predictions for sections with a thin surface layer (25 mm [1 in.]) and did not affect rutting predictions once the surface layer thickness was above 76 mm (3.0 in.). An empirical SS to LS shift factor method is presented.

A new load bearing capacity assessment method of the road pavement based on surface strain and the spectrum of the acceleration

Based on the coupling res model of vehicular and road, the influences of surface layer modulus, surface layer thickness and equivalent modulus of elasticity on the spectrum of the acceleration, surface deflection under wheels, and surface strain at the distance of 0.4 m to 0.8 m away from wheels are analyzed. Results show that the fundamental frequency of the road pavement increases with the growth of surface layer modulus and equivalent modulus of elasticity, and decreases with the increase of surface layer thickness. Both surface deflections and surface strains decrease with the increase of equivalent modulus of elasticity as well as surface layer modulus and thickness. Moreover, when the equivalent modulus of elasticity is more than 2500 MPa and surface layer modulus is more than 4000 MPa, surface deflections and surface strains have a little variation with the enhance of the surface layer modulus and equivalent modulus of elasticity. The solution method of the spectrum of the acceleration and equivalent modulus of elasticity, surface deflection under wheels, surface strain at the distance of 0.4 m to 0.8 m away from wheels, and surface deflection based on surface strain are established. The load bearing capacity assessment method of the road pavement based on surface strain and the spectrum of the acceleration is provided. Finally, the feasibility and accuracy of this method is verified by comparing measured values in field testing. The method in this paper provides a theoretical support for the design, construction and maintenance of road engineering.

Quantitative strong motion simulations at three locations in downtown Mashiki during the 2016 Kumamoto Earthquake (Mw 7.0) based on the nonlinear ground response analyses with soil liquefaction

The mainshock of the 2016 Kumamoto Earthquake (Mw 7.0) caused extensive damage to buildings in downtown Mashiki, Kumamoto Prefecture, Japan. The heavy building damage in the area was associated with both strong ground motion and building response characteristics. Fortunately, there were two strong motion stations in the area and the observed records during the mainshock were distributed, showing peak ground velocities exceeding 100 cm/s on the surface. The level of shaking would be sufficient to make soft surface sediments nonlinear. To reproduce observed ground motions quantitatively, one-dimensional nonlinear effective-stress time-history analyses were conducted at three locations in downtown Mashiki. The input wave was employed as either the observed underground wave or simulated outcrop input motion based on the diffuse field theory. The main purpose of the study was twofold: to investigate the proper soil constitutive relationship and its nonlinear parameters based on the limited amount of in situ information, and to validate the method of input motion evaluation at the seismological bedrock level based on diffuse field theory. The nonlinear time history analyses using the on-site boring survey and the outcrop wave based on diffuse field theory showed that the waveform of the mainshock observed on the ground surface was explained with sufficient accuracy. In addition, the results of the effective stress analysis indicated that soil liquefaction might have occurred in the area with thick surface layers along the Akitsu River where the water table was considered to be quite shallow.Graphical

Microstructure, thermal stability and corrosion behavior of ultrasonic shot peened AA7034

Microstructure, thermal stability at room temperature and corrosion behavior of ultrasonic shot peened AA7034 were investigated in this work. Microstructure modification induced by ultrasonic shot peening was obtained by using OM, SEM, EBSD and XRD, and it was found that a ∼200 μm thick gradient surface layer with nano-scale grains on the topmost layer was induced on the peened sample. XRD peaks of the pre-existing aging-induced precipitates, i.e., η′ and η phases, disappeared after peening and did not show up during 52 months-long natural aging treatment, showing good thermal stability at room temperature. After peening, a significant improvement in intergranular corrosion resistance is evident. Electrochemical characterizations like open circuit potential and electrochemical impedance spectroscopy were conducted on various depths of the peened sample and the results indicated that uniform corrosion rate was largely accelerated by the presence of foreign Fe-rich contamination, implying that modifications should be made to reduce/avoid the foreign contamination. Additionally, mechanisms of corrosion improvement and good thermal stability of the nanocrystalline surface layer of AA7304 are also discussed.

Calculating the Surface Layer Thickness and Surface Energy of Aircraft Materials

The surface layer determines the physical properties of aviation materials and, based on these properties, the calculation of surface energy anisotropy can be implemented. Moreover, the value of the surface energy determines the service time and the destruction of aircraft structures surface layer, while the surface layer thickness determines the distance at which this process usually takes place. In this work, a new atomically smooth crystal empirical model is built without considering the surface roughness. This model can be used to theoretically predict the surface energy anisotropy and surface layer thickness of metals and other compounds, in particular the aviation materials. The work shows that the surface layer of an atomically smooth metal, like other compounds, consists of two nanostructured layers: d(I) and d(II). Having sufficient accuracy, the proposed model would allow the prediction of aviation materials performance properties without the need for ultrahigh vacuum or other complicated theoretical methods to analyze the surfaces of nanosystem atomic structures.

Influence of input motion and surface layer properties on seismic site response: A stochastic simulation method–based MLR model

AbstractSeismic site response analyses are simulations in which the effects of geological conditions on seismic waves are examined. The uncertainties that make these analyses crucial are defined as the source of motion, the travel path of seismic waves, and geological conditions. In this study, a series of non‐linear seismic response analyses were performed using data from site investigation studies. The results of non‐linear analyses performed under earthquakes with different characteristics based on real soil data were investigated in terms of acceleration time histories and response spectra. The relationship between site response with the surface layer properties and input motion properties used in the simulations was examined in a parametrical manner. Based on the results obtained, Monte Carlo simulation, which is a stochastic data simulation method, was performed. Additionally, multiple regression and variance analysis (ANOVA) was performed on the dataset created by both site response analysis and stochastic simulations. The MLR model displayed highly accurate results with a coefficient of determination, R2 of 0.9763, and a standard error of 0.109. The efficiency level of the independent variables used as input parameters in the simulations on the dependent variable, AF was examined. It was revealed that the coefficient of lateral earth pressure at rest (Ko), earthquake motion (i.e., PGA of input motion) and surface layer thickness (dsurface) from the soil properties had the highest effect on the amplification factor.

High-speed milling of hardened steel under minimal quantity lubrication with liquid nitrogen

Minimal quantity lubrication (MQL) can effectively reduce tool wear and improve surface quality in the high-speed milling of hardened steel, but MQL still suffers from poor cooling effect and oil-film failure at high cutting temperature. Compared with MQL, the cryogenic liquid nitrogen (LN2) or LN2 + MQL method with a highly strong cooling ability can further improve the processing conditions of the high-speed milling of hardened steel. However, the knowledge about the characteristics and mechanisms of the high-speed milling of hardened steel under the cryogenic LN2 and LN2 + MQL cooling is scarce. Thus, high-speed milling of hardened steel under cryogenic LN2 and LN2 + MQL cooling was studied in this paper. The machining characteristics were analyzed, and the machining mechanisms of cooling lubrication, tool wear, and surface deterioration layer formation were discussed. The experimental results show that the tool life of LN2 + MQL is remarkably longer than that of MQL, and high surface quality can be maintained at a long cutting distance. In the high-speed milling of hardened steel under the LN2 and LN2 + MQL modes, adhesion has little effect on tool wear, abrasion and chipping/flaking are the main tool wear mechanisms, and chipping/flaking is the main mechanism of tool breakage. MQL reduces the cutting interface friction using oil-film boundary lubrication, LN2 quickly removes the cutting interface heat using a strong cooling and heat transferability, and LN2 + MQL combines the advantages of both cooling and lubrication. Compared with MQL, the surface hardness of the plastic deformation layer of the LN2 and LN2 + MQL modes is considerably increased, whereas the thickness is smaller, and the strong low-temperature cooling is the main reason for this difference. The increase in tool wear will promote the cutting temperature and material slip deformation, increase the depth of high stress and strain zone and eventually increase the thickness of the plastic deformation surface layer in the LN2 and LN2 + MQL modes. In the two modes of LN2 and LN2 + MQL, there are no oxidation, nitridation, secondary quench hardening, and phase transformation in the surface layer. Severe dislocation strengthening caused by severe plastic deformation of the surface layer is the main hardening mechanism of the workpiece surface layer.

SILVER-INTEGRATED EDM PROCESSING OF TIAL6V4 IMPLANT MATERIAL HAS ANTIBACTERIAL CAPACITY WHILE OPTIMIZING OSSEOINTEGRATION

Periprosthetic joint infections (PJI) are one of the most common reasons for orthopedic revision surgeries. In previous studies, it has been shown that silver modification of titanium (Ti-6Al-4V) surfaces by PMEDM (powder mixed electrical discharge machining) has an antibacterial effect on Staphylococcus aureus adhesion. Whether this method also influences the proliferation of bacteria has not been investigated so far. Furthermore, the effect is only limitedly investigated on the ossification processes. Therefore, the aim of this work is to investigate the antibacterial effect as well as the in vitro ossification process of PMEDM machined surfaces modified by integration of silver.In this study, we analyzed adhesion and proliferation of S. aureus in comparison to of surface roughness, silver content and layer thickness of the silver-integrated-PMEDM surfaces (N = 5). To test the in vitro ossification, human osteoblasts (SaOs-2) and osteoclasts (differentiated from murine-bone-marrow-macrophages) were cultured on the silver surfaces (N = 3).We showed that the attachment of S. aureus on the surfaces was significantly lower than on the comparative control surfaces of pure Ti-6Al-4V without incorporated silver, independently of the measured surface properties. Bacterial proliferation, however, was not affected by the silver content. No influence on the in vitro ossification was observed, whereas osteoclast formation was drastically reduced on the silver-modified surfaces.We showed that 1 to 3% of silver in the surface layer significantly reduced the adhesion of S. aureus, but not the proliferation of already attached bacteria. At the same time, no influence on the in vitro ossification was observed, while no osteoclasts were formed on the surface. Therefore, we state that PMEDM with simultaneous silver modification of the machined surfaces represents a promising technology for endoprostheses manufacturing to reduce infections while at the same time optimizing bone ingrowth.

Exploring the Effects of Wetting and Free Fatty Acid Deposition on an Atomistic Hair Fiber Surface Model Incorporating Keratin-Associated Protein 5-1.

The complex development of cosmetic and medical formulations relies on an ever-growing accuracy of predictive models of hair surfaces. Hitherto, modeling efforts have focused on the description of 18-methyl eicosanoic acid (18-MEA), the primary fatty acid covalently attached to the hair surface, without explicit modeling of the protein layer. Herein, the molecular details of the outermost surface of the human hair fiber surface, also called the F-layer, were studied using molecular dynamics (MD) simulations. The F-layer is composed primarily of keratin-associated proteins KAP5 and KAP10, which are decorated with 18-MEA on the outer surface of a hair fiber. In our molecular model, we incorporated KAP5-1 and evaluated the surface properties of 18-MEA through MD simulations, resulting in 18-MEA surface density, layer thickness, and tilt angles in agreement with previous experimental and computational studies. Subsequent models with reduced 18-MEA surface density were also generated to mimic damaged hair surfaces. Response to wetting of virgin and damaged hair showed rearrangement of 18-MEA on the surface, allowing for water penetration into the protein layer. To demonstrate a potential use case for these atomistic models, we deposited naturally occurring fatty acids and measured 18-MEA's response in both dry and wet conditions. As fatty acids are often incorporated in shampoo formulations, this work demonstrates the ability to model the adsorption of ingredients on hair surfaces. This study illustrates, for the first time, the complex behavior of a realistic F-layer at the molecular level and opens up the possibility of studying the adsorption behavior of larger, more complex molecules and formulations.

Oblique wave trapping by a permeable wall breakwater connected with thick surface porous layer

ABSTRACT The reflection of surface gravity waves by a vertical wall breakwater connected with a thick surface porous layer is analysed under the framework of potential flow theory. The thick surface porous layer is placed within the confined space available between the vertical permeable wall and the impermeable seawall. The analytical investigation is progressed by creating the hidden water chamber beneath the surface porous layer. The Matched Eigenfunction Expansion Method (MEEM) is used based on the continuity of velocity and pressure along with orthogonal mode-coupling relation. The hidden water chamber will be helpful to enhance the trapping of incident wave energy and also to reduce the quantity of construction material. The present study results are well agreed with the results available in the literature when a hidden water chamber is absent. The effect of permeable wall porosity, thick surface layer porosity, angle of wave contact, depth of the surface porous layer, thickness of the permeable wall, and hidden chamber spacing on wave reflection against incident wave properties and breakwater physical properties are studied. A comparative study is performed between three different types of porous breakwaters to investigate the integrity of the proposed breakwater. The minor value of wave reflection and gradual reduction of fluid force experienced by the rigid wall is achieved due to the presence of a surface layer, which maximises the incident wave damping, as most of the wave energy propagates near the free surface.

Technologies for Asphalt Pavement Surface Testing in Road and Bridge Construction

Asphalt pavement is currently one of the main components in the construction of roads and bridges. However, from a practical point of view, various quality problems are prone to occur in the surface layer of asphalt pavement, which will lead to the poor overall quality of road and bridge projects. Therefore, it should be applied reasonably. Advanced testing technologies are used to test the mixture quality, compaction, segregation, thickness, and other aspects of the asphalt pavement surface layer, so as to improve the quality of the asphalt pavement surface layer, and then improve the overall quality of road and bridge construction. Therefore, this paper mainly analyzes the technologies for asphalt pavement surface layer testing in road and bridge engineering construction.

Electrochemical partial reduction of Ni(OH)2 to Ni(OH)2/Ni via coupled oxidation of an interfacing NiAl intermetallic compound for robust hydrogen evolution

Ni-based porous electrocatalysts have been widely used in the hydrogen evolution reaction (HER) in alkaline water electrolysis, and the catalysts are produced by selective leaching of Al from Ni-Al alloys. It is well known that chemical leaching of Ni-Al intermetallic compound (IMC) generates a high surface area in Ni(OH)2. However, the Ni(OH)2 produced by leaching the Ni-Al intermetallic compound retards the hydrogen evolution reaction, which is attributed to its weak hydrogen adsorption energy. In this study, we controlled the chemical state of Ni using plasma vapor deposition (PVD) followed by heat treatment, selective Al leaching, and electrochemical reduction. X-ray diffraction (XRD), scanning microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) were used to confirm the phase evolution of the electrocatalysts during fabrication. We reveal that the heat-treated Ni-Al alloy with a thick Ni2Al3 surface layer underwent selective Al leaching and produced biphasic interfaces comprising Ni(OH)2 and NiAl IMCs at the edges of the grains in the outermost surface layer. Coupled oxidation of the interfacing NiAl IMCs facilitated the partial reduction of Ni(OH)2 to Ni(OH)2/Ni in the grains during electrochemical reduction, as confirmed by X-ray photoelectron spectroscopy (XPS). An electrocatalyst containing partially reduced Ni(OH)2/Ni exhibited an overpotential of 54 mV at 10 mA/cm2 in a half-cell measurement, and a cell voltage of 1.675 V at 0.4 A/cm2 for single-cell operation. A combined experimental and theoretical study (density functional theory calculations) revealed that the superior HER activity was attributed to the presence of partially reduced metallic Ni with various defects and residual Al, which facilitated water adsorption, dissociation, and finally hydrogen evolution.

Sensitivity analysis of pavement response to subgrade moisture variations

Moisture has detrimental effects pavement structures. Moisture effects on different structures will vary depending on their dimensions and properties. In this study, sensitivity analysis of pavement response to moisture was conducted using multilayered elastic theory, based on arbitrarily assumed subgrade moduli and the moduli from literature sources, respectively. The selected simulation variables included elastic modulus and thickness of asphalt surface, base and subbase layers as well as axle load. The fatigue and rutting life as well as their sensitivity indexes were obtained for each scenario. The results show that the soil with a relatively higher plasticity generally resulted in a higher sensitivity, whilst this trend was not monotonic with the soil plasticity. Drainage implications were summarized to provide a reference for the pavement drainage design. A drainage design process was proposed by incorporating sensitivity analysis. This study will facilitate the understanding of pavement response under different subgrade moisture conditions and pavement drainage design.

8Li Spin Relaxation as a Probe of the Modification of Molecular Dynamics by Inelastic Deformation of Glassy Polystyrene

The molecular dynamics of inelastic strain in glasses remains poorly understood, in contrast to the plasticity of crystalline materials that is well-characterized by measurements of dislocation activity. We report initial results on a 300 nm thick atactic polystyrene film undergoing plastic strain in its glassy state. This physical modification was applied by nanoimprint stamping with a 1 mm ultra-smooth spherical die to induce a stress exceeding mechanical yield (0.8% residual strain). Using 8Li implanted-ion βNMR, we monitor the spin-lattice relaxation to infer depth-resolved rates of molecular dynamics. We find a significant change in the bulk molecular dynamics of the imprinted film (away from the surface) compared to an identically prepared control film. The relaxation is ∼ 20% slower in the film left densified by imprinting. We expect this relaxation to be coupled to the motion of the phenyl side rings; wherein slower dynamics due to densification is reasonable, as tighter packing should increase the energy barrier to molecular motion. In addition, we see an increase in the apparent thickness of a nanometric mobile surface layer, but this may be an artefact of surface roughening caused by imprinting.

Inertial Oscillations and Frontal Processes in an Alboran Sea Jet: Effects on Divergence and Vertical Transport

AbstractVertical transport pathways in the ocean are still only partially understood despite their importance for biogeochemical, pollutant, and climate applications. Detailed measurements of a submesoscale frontal jet in the Alboran Sea (Mediterranean Sea) during a period of highly variable winds were made using cross‐frontal velocity, density sections and dense arrays of surface drifters deployed across the front. The measurements show divergences as large as ±f implying vertical velocities of order 100 m/day for a ≈ 20 m thick surface layer. Over the 20 hr of measurement, the divergences made nearly one complete oscillation, suggesting an important role for near‐inertial oscillations. A wind‐forced slab model modified by the observed background frontal structure and with initial conditions matched to the data produces divergence oscillations and pattern compatible with that observed. Significant differences, though, are found in terms of mean divergence, with the data showing a prevalence of negative, convergent values. Despite the limitations in data sampling and model uncertainties, this suggests the contribution of other dynamical processes. Turbulent boundary layer processes are discussed, as a contributor to enhance the observed convergent phase. Water mass properties suggest that symmetric instabilities might also be present but do not play a crucial role, while downward stirring along displaced isopycnals is observed.

Effect of Zn Addition on the Microstructural Heterogeneity and Mechanical Properties of Vacuum‐Assisted High‐Pressure Die Casting Al–Si–Mg–Cu alloys

Herein, Al–8Si–0.5Mn–0.5 Mg–0.2Cu–xZn alloys (x = 0, 1, 2, and 3 wt%) are produced by a vacuum‐assisted high‐pressure die casting process. The effects of Zn addition on the surface layer thickness and segregation band, the number density of externally solidified crystals (ESCs), and mechanical properties of the alloys are systemically investigated. As the Zn content increases, the size and number density of the ESCs increase. The morphology and size of the eutectic Si phase could be modified by the addition of Zn. In addition, the microstructural heterogeneity indicates that the thickness of the surface layer and segregation band zone increase with increasing Zn content. Proper Zn addition can effectively promote the improvement of strength and elongation in the as‐cast state. When the Zn content is 2 wt%, the yield strength, ultimate tensile strength, and elongation of the alloy are 167, 311 MPa, and 10.8%, respectively.