Robust natural nanocomposites realizing unprecedented ultrafast precise molecular separations

Synthetic polymer membranes can potentially reduce the large energy and carbon footprints that are typically associated with traditional chemical separation technologies. Unfortunately, current production protocols negate the green benefits of membrane separation. To address this bottleneck, here we report the use of natural materials monosaccharide – glucose and polydopamine and Zr-based metal organic frameworks (MOFs) to fabricate ultrathin nanocomposite membranes via interfacial polymerization reaction. The synergistic effect of these three materials on angstrom-scale molecular transport both in organic solvent and aqueous environment was elucidated using a series of complementary techniques. We demonstrate such nature-inspired nanocomposite membranes enable structural stability even in polar aprotic solvents, and unparalleled ultra-fast, low-pressure, precise separations in both nanofiltration modes, which easily surpass state-of-the-art membranes relying on unsustainable materials. The multi-functionality of saccharide nanocomposites was elegantly harnessed to impact separation applications that contribute towards a better living environment.     

Improvement of piezoelectricity of (Na,K)Nb-based lead-free piezoceramics using [001]-texturing for piezoelectric energy harvesters and actuators

0.96(Na_0.5K_0.5)(Nb_0.93Sb_0.07)O₃?(0.04?x)BaZrO₃?x(Bi_0.5Ag_0.5)ZrO₃[NKNS?(0.04?x)BZ?xBAZ] ceramics are well textured along the [001] direction using 3.0 mol% NaNbO₃ seeds. The textured-NKNS?0.02BZ?0.02BAZ thick film has a rhombohedral-orthorhombic-tetragonal (R-O-T) structure with a large proportion of the O-R structure (> 80%). This specimen exhibits the largest values for d₃₃ (805 pC/N) and d₃₃ ×g₃₃ (29.5 ×10^?12 m²/N), which are the largest d₃₃ and d₃₃ ×g₃₃ values of NKN-based piezoceramics to date. It exhibits a large strain (0.17% at 4.0 kV/mm). Therefore, it is an outstanding piezoceramic material for piezoelectric energy harvesters (PEHs) and actuators. A PEH and actuator are fabricated using this specimen. The PEH shows a large power density (4.3 mW/cm³), which is the largest value among the PEHs produced by lead-free piezoceramics. The actuator exhibits a large acceleration (50.8 G) and displacement (3.9 mm), which are the best actuating properties among the actuators produced by lead-free piezoceramics. Therefore, texturing is an excellent technique for improving the piezoelectricity of NKN-based piezoceramics.     

Influence of anisotropy of nickel-based single crystal superalloy in atomic and close-to-atomic scale cutting

Nickel-based single crystal superalloy is widely used in the field of aerospace and nuclear reaction equipment due to its good properties. Ultra-precision machining technology is an important means to ensure the surface quality of parts. However, the anisotropy of materials has great influence on the evolution of surface and subsurface defects and the removal of materials in the process of machining. In this paper, The MD (molecular dynamics) modeling and simulation verification of cutting anisotropic nickel-based single crystal superalloy workpiece with silicon nitride tool is carried out by using the mixed potential function simulation. Through cutting simulation and visualization, the types, number, deformation area and dislocation evolution of the machined surface defects and inside of the workpiece defect of nickel-based single crystal superalloy with different crystal orientations are analyzed. The evolutionary mechanism of the machined surface defects and the law of material removal are discussed. The research content provides a theoretical basis for parameter optimization and improvement of machining quality in the atomic and close-to-atomic scale (ACS) cutting process, and technical support for efficient and precise machining process of the nickel-based superalloy.     

Improvement of epitaxial growth and flux pinning of MOD-derived YBa2Cu3O7−δ nanocomposites films by self-seeding and multi-element doping strategies

YBa₂Cu₃O_7?δ (YBCO) nanocomposite films were fabricated by low-fluorine metal-organic deposition (LF-MOD) route, combining self-seeding and multi-doping strategies with elements of Zr, Hf, Sn and Mn. Under the same growth conditions, due to the self-seeding layer as a template for the c-axis growth of doped films, all the multi-doped films with 200 nm self-seeding layers exhibit good c-axis orientation, even for the heavy doping of 16 mol%. EDS confirmed the four doping elements in the multi-doped YBCO films appear independently, leading to higher density of nano-scale heterogeneous phases than the case of Zr single doping. The pinning force density (F_p) and critical current density (J_c) are improved significantly, which indicates that the optimal doping content is achievable as high as 12 mol% in the case of multi-doping. The multi-12% YBCO films have the highest Fp,max of 6.13 GN/m3 at 77 K, which is about 3.3 times higher than that of the undoped films, and the Jc can reach 4.3 MA/cm2 at 30 K, compared to 3.1 MA/cm2 for the undoped films.     

Microstructure and superconducting properties of bulk EuBCO-Ag with and without holes

Bulk single-grain EuBCO-Ag superconductors with holes and without holes grown using a top-seeded melt-grow process are analysed. It turns out that the levitation force and the trapped magnetic field at 77 K are higher for the sample with holes (0,85 N and 1 T for the sample with a diameter of 28 mm and a height of 10 mm). Careful complex microstructural analyses undertaken by polarised light optical microscopy and scanning electron microscopy show that the reason for this behaviour is mainly the lower porosity of the sample with holes and the lower density of the of a/c-oxygenation cracks in non-porous areas along the holes. It also appears that other microstructural features, such as higher volume fraction of Eu₂BaCuO₅ particles in the a-growth sector than in the c-growth sector, uniform distribution of Ag particles in samples, presence of tetragonal EuBa₂Cu₃O_7?x regions are similar on both types of samples and cannot significantly affect macroscopic superconducting properties. The influence of porosity on the local critical current density and transition temperature is also illustrated.     

Microstructure and fracture behaviour of Ti<Subscript>3</Subscript>Al/TC4 dissimilar materials joints welded by electron beam

Electron beam was used to join TC4 alloy to Ti₃Al-based alloy. The composition of the weld was analysed by XRD and TEM and the results showed that the weld mainly composed of α′ martensites. The change of heat input had little influence on the composition of the weld but can make the grain size increasing. The fracture path of the joints was mainly decided by the microstructure of the weld and started from coarse grain zone to HAZ and base metal of Ti₃Al alloy.     

Alloying effects on properties of Al2O3 and TiO2 in connection with oxidation resistance of TiAl

In the present work, a first-principles method is used to calculate the oxidation energies of Al₂O₃ and TiO₂ as well as the formation energy of oxygen vacancy in TiO₂ containing various alloying elements, in order to shed some light on the alloying effects on the oxidation resistance of γ-TiAl. Our calculations demonstrate that almost all alloying elements increase the oxidation energies of Al₂O₃ and TiO₂. The alloying elements with number of d electrons from 2 to 5 in the forth and fifth rows of the periodic table (e.g., Zr, Nb, Mo, Hf, Ta, W) increase significantly the oxidation energy difference between Al₂O₃ and TiO₂, i.e., reduce the relative stability of Al₂O₃ to TiO₂. On the other hand, these alloying elements increase the formation energy of oxygen vacancy in TiO₂. The effects of other alloying elements are less significant or opposite. Observing the experimental mass gains of TiAl alloys and unalloyed TiAl due to oxidation, we find that the elements reducing the relative stability of Al₂O₃ to TiO₂ and increasing the formation energy of oxygen vacancy enhance the oxidation resistance of TiAl whereas others do not. Such correlations are rationalized by analyzing the alloying effects on the internal oxidation of Al in the γ-TiAl matrix and the diffusion of oxygen in TiO₂ surface scale.     

Effect of homogenizing heat treatment on the compressive properties of closed-cell Mg alloy foams

Closed-cell AZ31 Mg alloy foams were successfully prepared by melt-foaming method. Homogenizing heat treatment was applied on the foams and the effects of heat treatment on compressive properties of closed-cell Mg alloy foams were investigated systematically. The results showed that homogenizing heat treatment enhanced the compressive properties in terms of yield strength, mean plateau strength, available energy absorption capacity and ideality energy absorption efficiency of the foams. In addition, homogenizing heat treatment greatly reduced the stress drop rates of the foams. Specimens homogenized at the temperature of 753 K for 24 h possessed good combination of yield strength, compressive stability, available energy absorption capacity and ideality energy absorption efficiency under the present experiment conditions. And the reasons were discussed.     

Phonon spectra and magnetic behaviors of hydrothermally synthesized Sm-doped ZnO nanorods

Herein one-dimensional Sm-doped ZnO nanostructures have been successfully fabricated by a simple hydrothermal method at a low temperature of 90 °C. The effect of Sm doping on the microstructure, photoluminescence and magnetism of ZnO nanorods is also investigated. FE-SEM images show that the average diameter of the Sm-doped ZnO nanorods is obviously smaller than that of ZnO nanorods. Photoluminescence spectrum of Sm-doped ZnO nanorods shows a slightly red-shifted decrease of UV emission and an enhancement of photoluminescence performance of visible emission. Raman spectrum of Sm-doped ZnO nanorods reveals that the peak intensity corresponding to the E₂ high mode decreases significantly compared with that of the pure ZnO nanorods, indicating the restraint of crystallization. Room temperature ferromagnetism is observed from magnetization curves of both ZnO and Sm-doped ZnO nanorods. The increase of the saturation magnetization induced by the Sm doping in the ZnO nanorods reveals an association with the increase of oxygen vacancies and oxygen interstitials.