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Effects of Adsorbed OH on Pt(100)/Water Interfacial Structures and Potential
No full textAdsorbates at the electrode change the structure of the electrode/electrolyte interface. Despite the important influence of the interfacial structure on electrochemical processes, computational investigations targeting this influence are still lacking. Even the impact of one of the most common adsorbates, namely, adsorbed OH, is so far largely unknown. In this study, we choose the Pt(100)/water interface as a model system to investigate the interfacial water structure at various OH coverages with ab initio molecular dynamics. We find that the interfacial water structure is highly sensitive to the adsorption site of OH (namely, top or bridge site) and that the preference of adsorption sites of OH is, in turn, strongly influenced by the solvation caused by interfacial water. This indicates that the structure of water is correlated with that of OH. Based on a detailed analysis, we attribute these observations to a strong hydrogen-bonding network between OH and the interfacial water. This hydrogen-bonding network also results in a complicated dependence of the interfacial potential on the OH coverage, which is governed not only by the dipole induced by OH but also by the influence the OH species have on the interfacial water structure
Study of Heavy Gas Pollutants' Dispersion in Street Canyon Terrain
No full textThis study focused on heavy gas dispersion under the terrain conditions of street canyons. The effects of street aspect ratio and height ratio were investigated, and the influence of environmental wind speed in the typical ideal street canyon terrain was explored. The results indicated that the surrounding flow field distributions in street terrains were dominated by higher buildings. In addition, when the building height was held constant, the flow field was affected by the joint influence of the two isolated buildings. The interception effect of the street canyon on upstream pollutants declined with the decrease in the street canyon's aspect ratio. In addition, when the height ratios were different, a large quantity of upstream pollutants accumulated on the windward side of higher buildings. The relative concentration per unit area inside the canyon was affected by the air circulation inside and outside the canyon and the size of the dispersion space. The increase in the environmental wind speed promotes the entry of pollutants into the street while aggravating the overall dispersion of the pollutants. Therefore, the emergence of the most unsafe wind speeds caused most of the pollutants to gather in the street canyons.</p
Corrosion and protection of galvanized steel in vegetation-growing concrete in marine environment (I): Corrosion performance
No full textGalvanized steel has excellent corrosion resistance in atmospheric and soil corrosive environments, because a dense and passive zinc oxide film, formed on the surface could effectively inhibit the corrosion of the Fe substrate. The galvanized steel wire has been widely embedded in vegetation-growing concrete for reinforcement and showed good corrosion resistance and strengthening performance. However, in the marine area, the corrosion rate of galvanized steel is accelerated, and the galvanized steel wire will be failed in vegetation-growing concrete in a short time. This study has been carried out with a view to analyze the corrosion performance and corrosion mechanism of galvanized steel wire embedded in vegetation-growing concrete in the marine environment. EIS and Tafel curves were employed to study the corrosion performance of galvanized steel under different chloride concentrations and temperatures in vegetation-growing concrete lixivium. Results showed that the corrosion rate of galvanized steel increased with the increase of chloride concentration and the temperature in vegetation-growing concrete lixivium
Understanding wear mechanisms of TiSiCN/Zr(C)N coatings at elevated temperatures
No full textTiSiCN/ZrN coating and TiSiCN/ZrCN coating were prepared using multi-arc ion plating technology. In this work, the composition, mechanical properties and wear properties at elevated temperatures of both coatings were investigated. XRD results show that both coatings are composed of Ti, Zr (C, N) phases. At elevated temperatures, TiSiCN/ZrCN coating exhibits a lower friction coefficient and slightly higher wear rate compared to TiSiCN/ZrN coating. The result is that the introduction of C plays the role of lubrication and friction reduction effect, but the more content carbon leads to increased brittleness of the coating, and cracks are prone to occur and propagate under the effect of thermal and mechanical coupling, thereby causing the wear rate of the coating increased. The increased brittleness of TiSiCN/ZrCN coating is confirmed via mechanical properties. Under high temperature wear, a thin oxide layer formed on both coatings surface acts as a glaze to impede wear and it would break down to form a transfer layer under period force. At 500 degrees C, TiSiCN/ZrN coating and TiSiCN/ZrCN coating display the mechanisms of adhesive wear and abrasive wear, respectively
Black phosphorene-cellulose nanofiber hybrid paper as flexible heat spreader
No full textIn this work, black phosphorene (BP) was exfoliated by solvent exfoliation of black phosphorus powders in N-methyl pyrrolidone. The BP-cellulose nanofiber (CNF) paper was prepared from the solution containing BP and CNF by vacuum filtrating. The as-prepared BP-CNF paper has a 'brick-and-mortar' structure. The BP-CNF paper has a high in-plane thermal conductivity of 22.3 W m(-1) K-1 at room temperature, benefiting from the thermal transition pathways constructed by the 'brick-and-mortar' structure. In addition, the BP-CNF possesses an excellent flexibility. Our results in this work demonstrate that BP has a great potential in the application of thermal management material
Fast Reprocessing of Acetal Covalent Adaptable Networks with High Performance Enabled by Neighboring Group Participation
No full textCovalent adaptable networks (CANS) represent a transition material combining favorable features of thermosets and thermoplastics. However, it is still a huge challenge to simultaneously achieve fast reprocessability and high performance for CANs. Here, we designed catechol-based acetal CANs to achieve continuous reprocessing without sacrificing thermal and mechanical properties. A small-molecule model study demonstrated the significantly accelerated acetal exchange by neighboring group participation (NGP) of phenolic hydroxyl. Using this internally catalyzed acetal chemistry, a series of CANs with a broad range of properties were simply prepared from bio-based epigallocatechin gallate (EGCG) and tri(ethylene glycol) divinyl ether (TEGVE) via one-step click cross-linking without using catalysts or releasing small-molecule byproducts. The dynamic nature of the CANs was confirmed via stress relaxation and multiple recycling methods including extrusion. While the dense cross-link density and high rigidity of the network provided high solvent resistance and mechanical properties. This work provides a promising and practical method to produce fast-reprocessing dynamic covalent polymer networks with dense cross-link density and superior performance
Influence of nitrogen partial pressure on structure, mechanical and tribological properties of TaCN coatings
No full textThe TaCN coatings were fabricated on Ti-6Al-4V by reactive magnetron sputtering with different nitrogen partial pressures. The results show that the TaCN coatings have a columnar crystal structure of TaC, TaN nano-crystal and amorphous phases (amorphous carbon and CNx). The crystallinity of TaCN coatings decreases with the increase of N-2 flow rate. It is found that hardness and adhesive strength have a downward trend and friction coefficient of TaCN coatings increases with the increase of N-2 flow rate. In particular, the TaCN coating with lowest N-2 flow rate of 30 sccm has the highest hardness (16.3 GPa), the biggest adhesive strength (74.8 N) and the lowest friction coefficient (similar to 0.19). The TaCN coating exhibits an excellent tribological performances even at high temperature. The lowest friction coefficient at 400 degrees C could reach below 0.1 thanks to the transfer layer containing graphitic clusters which generated during friction
An anti-stress relaxation, anti-fatigue, mildew proof and self-healing poly (thiourethane-urethane) for durably stretchable electronics
No full textConsidering the complicated environment in daily use of stretchable devices, the capabilities of anti-stress relaxation, anti-fatigue, anti-fungal and self-healing are very much appreciated, and the above four functionalities largely depend on the elastic matrix. Here, these demands are fulfilled by a poly(thiourethane-urethane) elastomer CBPU-3. In detail, a large amount of cyclohexane rings, with completely reversible boat-chair conformational transition, are introduced into the backbone of poly(thiourethane-urethane), and such nonplanar ring imparts molecular elasticity and modulus into the elastomer, resulting in remarkable anti-stress relaxation and anti-fatigue abilities. Even after 20 h fixation at 300% strain and 1000 times cyclic tensile (50% strain), the recovery ratio could still be higher than 98%, and its stable microstructure is proved by SAXS scattering patterns. In addition, the thioether bond ensures the effective mildew proof ability, and the mechanical properties and transmittance change little even after a severe mildew pollution for 30 days. Simultaneously, the relatively lower bond energy of C-S (62.0 Kcal/mol) in thiourethane bonds endowes the poly(thiourethane-urethane) with self-healing capability (highest: 40 mu m/min at 80 degrees C). Finally, the durability and usability of the deformable resistive sensor array based on this elastomer as the matrix are drastically enhanced due to the above integrated functionalities
Latest Advances in Development of Smart Phase Change Material for Soft Actuators
No full textInspired from the nature, soft actuators have been attracting the incremental attention on account of the benefits in terms of high flexibility and safety for human operators, but material selection and manufacturing process remain challenging. Compared with the conventional actuators in solid state, smart phase change materials (PCMs) are superior for the soft actuation applications because of the capability to change their shapes or properties in response to a wide range of stimulants, such as heat, light, pH, or electrical field. This review provides a comprehensive analysis of smart PCM applications on soft actuators, including metal alloys and their polymer counterparts, shape memory materials and liquid crystalline polymers. Such materials generally exhibit large deformation degrees, high complexity in movement and diverse versatility, which are compliant and well suited for soft actuators in the vast applications of soft mechatronics and robots. Since stiffness variable plays a significant role on actuator transformation, this review focuses on smart materials with an emphasis on the different forms of phase transformation among solid, liquid, and gas phase. This review enables a better understanding of phase transformation, performances, and limitations of smart PCMs, and provides insights into the potential applications for soft actuators
A damage-effect-involved phenomenological crystal plasticity model and computational methods for mechanical responses of FeCrAl alloys
No full textIn this study, a new damage-effect-involved phenomenological crystal plasticity model is proposed to capture macroscale straining hardening and strain softening behaviors of iron chromium aluminum (FeCrAl) alloys. The constitutive model is described with co-rotational tensors. Damage factor evolves with the effective plastic work calculated by the resolved shear stress and shear strain rate on all slip systems. A stress update algorithm is specially established, and the corresponding self-defined subroutines are incorporated into the finite element analysis via VUMAT in ABAQUS/Explicit. Fast convergence can be achieved with the maximum value of damage factor set very close to 1. The simulated macroscale stress-strain curves can agree well with the experimental ones for various FeCrAl alloys. The yield strengths and ultimate tensile strengths of these alloys can be well captured. The dependence of damage model parameters on the processing conditions, alloy compositions are discussed and analyzed. This work provides a basis for the multiscale simulation research on the mechanical performances of polycrystal alloys