Two-dimensional transition metal carbides and nitrides (MXenes) are widely applied in the fields of electrochemistry, energy storage, electromagnetism, etc., due to their extremely excellent properties, including mechanical performance, thermal stability, photothermal conversion and abundant surface properties. Usually, the surfaces of the MXenes are terminated by -OH, -F, -O or other functional groups and these functional groups of MXenes are related surface properties and reported to affect the mechanical properties of MXenes. Thus, understanding the effects of surface terminal groups on the properties of MXenes is crucial for device fabrication as well as composite synthesis using MXenes. In this paper, using molecular dynamics (MD) simulation, we study the adhesion and friction properties of Ti2C and Ti2CO2, including the indentation strength, adhesion energy and dynamics of friction. Our indentation fracture simulation reveals that there are many unbroken bonds and large residual stresses due to the oxidation of oxygen atoms on the surface of Ti2CO2. By contrast, the cracks of Ti2C keep clean at all temperatures. In addition, we calculate the elastic constants of Ti2C and Ti2CO2 by the fitting force-displacement curves with elastic plate theory and demonstrate that the elastic module of Ti2CO2 is higher. Although the temperature had a significant effect on the indentation fracture process, it hardly influences maximum adhesion. The adhesion energies of Ti2C and Ti2CO2 were calculated to be 0.3 J/m2 and 0.5 J/m2 according to Maugis-Dugdale theory. In the friction simulation, the stick-slip atomic scale phenomenon is clearly observed. The friction force and roughness (Ra) of Ti2C and Ti2CO2 at different temperatures are analyzed. Our study provides a comprehensive insight into the mechanical behavior of nanoindentation and the surface properties of oxygen functionalized MXenes, and the results are beneficial for the further design of nanodevices and composites.
Novel silicone-modified biochar adsorbents (BPS-MBCs) were prepared by utilizing waste black peanut shell (BPS) as a raw biochar and gamma-amino-propyl triethoxysilane (silicone) as an inorganic modifier. The novelty of this work is that the incorporation of silicone into BPS can rise the specific surface area and porosity of BPS-MBCs and elevate their adsorptions for copper (II). Sorption kinetics data for copper (II) were molded using five kinetic equations [i.e. Lagergren 1st-order and 2nd-order, intraparticle diffusion (IN-D), Elovich, and Diffusion-chemisorption]. The equilibrium adsorption data for copper (II) were analyzed using two-parameter isotherm equations [i.e. Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin] and three-parameter Sips, Redlich-Peterson and Toth isotherm models. It was validated that copper (II) sorption on BPS-MBCs matched better with pseudo-2nd-order kinetic, Diffusion-chemisorption and Langmuir isotherm models. The maximal q
Incoherent-twin boundaries (ITBs) can significantly affect the mechanical properties exhibited by metals. Although numerous studies have been conducted to date, the atomic structures of such ITBs remain unclear, owing to difficulties in imaging their structure. In this study, high-angle annular dark-field imaging was used to reveal the atomic structure of the ITBs present in Pt. We discovered that both the twin thickness and the dislocation-ITB interaction can affect the ITB phase structure. In thin twins, the {111} planes between the ITB remain flat without any obvious displacement along the <111> direction, whereas in thicker twins, the {111} planes between the ITB exhibit clear displacement along the <111> direction, with this displacement increasing as the twin thickness increases. The ITBs frequently absorb full dislocations, which leads to the formation of dislocation-misaligned ITBs. This twin-thickness effect and dislocation-ITB interaction, which resulted ITB-phase variation, has rarely been reported.
Abstract Non-exponential relaxation is pervasive in glassy systems and intimately related to unique thermodynamic features, such as glass transition and aging; however, the underlying mechanisms remain unclear. The time scale of non-exponential relaxation goes beyond the time limit (nanosecond) of classic molecular dynamics simulation. Thus, the advanced time scaling atomistic approach is necessary to interpret the relaxation mechanisms at the experimental timescale. Here, we adopted autonomous basin climbing (ABC) to evaluate the long-time stress relaxation. At the same time, based on the energy minimization principle, we carried out simulations at continuum levels on the long-time stress relaxation kinetics of Cu–Zr metallic glass over timescales greater than 100 s. Combined with atomistic and continuum models, we demonstrate that a strain-dependent transition from compressed to stretched exponentials would happen, consistent with recent experimental observations on metallic glasses. Further examination of the spatial and temporal correlations of stress and plastic strain reveals two predominant driving forces: the thermal energy gradient governs in the compressed regime and leads to a release of the local internal stress; in the stretched regime, the strain energy gradient rules and causes long-range structural rearrangements. The discovery of the competition between two driving forces advances our understanding of the nature of aging dynamics in disordered solids.
This paper analyzes the longitudinal surface crack on 2Cr13 steel slab produced with the 1280mm vertical caster of Taiyuan Steel and put forward the measures to improve the process.The better effect has been obtained.
Molecular-level liquid bridges at contact interfaces have a much more important impact on micro-/nanosystems and flexible wearable sensors. However, their dynamic behavior and mechanical properties are still vague due to the limitations of current characterization methods. Here, under the support of molecular dynamic simulations on smooth, pillared, and concave pillared plates, the heterogeneous anisotropic pressure distribution of layered liquids is found to be distinct from the isotropic pressure distribution in the macroscale liquid bridge. Oscillating interfacial contact forces appear in the period of layered liquid compression due to the oscillating system free energy, in which the peak forces greatly increase as the number of layers decreases. The layered liquids with impressively remarkable solid-like pressure-bearing capacity at the gigapascal level and exceptional fluidity along confined atomic layers can spontaneously strengthen adhesion vertically and facilitate pressure transport horizontally, respectively. The significance of layered liquids in contact systems can improve our understanding of liquid bridges at the molecular level, which is beneficial for interfacial mechanical regulation.
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