查看更多>>摘要：Hybrid materials composed of inorganic magnetic cobalt-manganese mixed nanoferrites and PMMA polymeric shell have been fabricated by applying an in-situ polymerization process using pre-prepared inorganic core particles (8-9 nm). The ability of the hybrid heating under action of alternating magnetic field and laser radiation (in a separate and synergy mode) was evaluated and compared with stock nano-particles. It was found that hybrid materials show a high response to both stimulants and the highest temperature was achieved by using both AMF and laser exposure under synergic mode (twice the value for the AMF alone). The specific absorption rate of composite material was around 30 W/g for the optimized field parameters and both laser wavelengths (808 and 1122 nm). The great response of the hybrid material for contactless action of AMF and NIR radiation makes the proposed material very interesting for future biomedical and EMI shielding applications.
查看更多>>摘要：As inspired by the surging demand for high performance energy storage systems, researchers have been designing and exploring advanced electrode materials exhibiting higher energy and power densities. In this study, a novel combination of nickel-cobalt sulfide and oxide was reported for high performance super-capacitors. The porous α-Ni(Co)S@NiCoO_2 composites with core-shell structure were derived from the well-designed precursor with Ni_2CoS_4 and ZIF-67 serving as the self-sacrificing templates through a two-step calcination process at elevated temperatures. Such a heterostructure exhibited an ultra-high specific capacity of 502.4 mA h g~(-1) at a current density of 1 A g~(-1), which was attributed to the unique porous core-shell structure and the ingenious combination of bimetallic sulfide and oxide. Furthermore, a hybrid supercapacitor based on the α-Ni(Co)S@NiCoO_2 composite and commercial activated carbon achieved a high energy density of 82.4 Wh kg~(-1) at a power density of 847.5 W kg~(-1). The prominent electrochemical performance exhibited by the α-Ni(Co)S@NiCoO_2 heterostructure in this study was demonstrated to be promising to practically serve as advanced electrode materials in supercapacitors.
查看更多>>摘要：The balance between the mechanical properties and corrosion resistance of high strength 7xxx Al alloys is an important topic. This study introduced pre-rolling into the solution and aging treatments for a recently developed 7A99 Al. The cold rolling after solution but before aging was considered as the first group, and the cold rolling before solution was the second group. For the first group, a great deal of strain energy was stored in the alloy, which contributed the occurrence of recrystallization during subsequent solution process and a finer grain structure. For the second group, the dislocations induced by cold rolling before aging accelerated the coarsening of η' and η precipitates. Moreover, T76 aging also caused the larger size of precipitates due to its higher temperature than T6 aging. The pitting corrosion of 7A99 Al tended to initiate at Al_7Cu_2Fe intermetallic, and the dissolution of MgZn_2 phase along grain boundaries facilitated the in-tergranular corrosion. The cold rolling after solution process and T76 treatment both improved the resistance on stress corrosion cracking, since the grain boundary precipitates had large size, discontinuous distribution and high Cu content. The combining of cold rolling before solution and T6 treatment contributed to the enhancement of strength due to the fine grain strengthening, solution strengthening and precipitates strengthening, and the corresponding yield strength and ultimate tensile strength reached as high as 628 and 665 MPa. Compared to T6 treatment, the strength of T76 treated samples was reduced only by 3-5%, which is an advantage of the proposed method.
查看更多>>摘要：The tendency of AA3003 towards localized corrosion is one of the most challenging issues for its broader use. Intermetallic phases (IMPs) in AA3003 play dual contradictory roles: strengthening effect and initiating pitting. Solving this contradiction contributes to improvement of corrosion resistance and fully utilizing the potential of materials. Herein, a superhydrophobic surface with IMPs in-situ pinning effect was fabricated via a chemical etching approach combined with stearic acid (STA) modification. Thus, IMPs can provide sound support for the superhydrophobic surface and meanwhile eliminate the adverse effect of promoting localized corrosion. Formation mechanism of etching structure was attributed to the synchronous chemical reaction of IMPs and matrix phases in the etchant. Further modification with STA changed mico/nano hierarchical surface from hydrophilicity to superhydrophobicity. The as-prepared surface exhibited a maximum static contact angle of-169° and a sliding angle of ~1 °, possessing excellent superhydrophobicity. Besides, the wettability, self-cleaning, chemical stability, mechanical durability, and corrosion resistance properties of the superhydrophobic surface were comprehensively investigated. The results showed that the corrosion inhibition efficiency exceeded 99% in 3.5 wt% NaCl solution. The pinning direction of IMPs in superhydrophobic surface influenced its properties. It is anticipated that the construction of superhydrophobic surfaces will broaden its promising applications.
查看更多>>摘要：The development of novel lead-free materials operating at high temperature and able to replace lead-based compounds and their derivatives in different devices is currently a remarkable challenge. In spite of having a high Curie temperature, the ferroelectric Bi_4Ti_3O_(12) is rarely used as a piezoelectric due to its high conductivity. In this work, Bi ions in Bi_4Ti_3O_(12) were partially replaced with Yb and Er aiming to compensate oxygen vacancies and improve others physical properties. In particular, Bi_(3.8-x)Er_(0.2)Yb_xTi_3O_(12) compounds with x = 0.05, 0.1, and 0.2 were prepared by a low-cost solid-solid state reaction process, and their structural, optical and electrical properties were investigated. It was observed that, at low temperatures, the conductivity, impedance and permittivity are mainly governed by grain effects, and by grain boundaries and grains effects at high temperatures. The electrical conductivity at 700 K decreases with Yb content and shows a minimum for x = 0.2. The relative permittivity at high temperatures is colossal while the tangent loss is negligible. High permittivities accompanied with low loss factor were obtained for Bi_(3.6) Er_(0.2)Yb_(0.2)Ti_3O_(12). These results open a wide application domain for this particular compound.
查看更多>>摘要：In this study, α-Fe_2O_3/rGO was smoothly synthesized by a one-step method and employed to activate persulfate (PS) for the degradation of Bisphenol A (BPA) under sunlight. During the degradation experiment, the degradation rates of BPA for PS, α-Fe_2O_3/8% rGO, and α-Fe_2O_3/8% rGO/PS were 6.6%, 47.6%, and 99.1%, respectively, indicating that the introduction of α-Fe_2O_3/rGO and PS significantly enhanced the photo-catalytic efficiency because that photocatalytic process and PS activation coupling system not only inhibited the recombination of photo-induced carrier pairs, but also reduced the energy consumption of PS activation. Moreover, electron spin resonance spectroscopy (ESR) and trapping experiments were utilized to explore the active species generated during the reaction. The results showed that OH and-So_4~(2-) were the principal oxidative species in this reaction system. These results showed that Fe-loaded rGO has great potential for activating PS to decompose pollutants in water.
查看更多>>摘要：Secondary hot-working on dual phase titanium alloys are essential for microstructural modification to tailor mechanical properties, which is typically challenging due to a narrow available processing window, especially during industrial scale manufacturing. Poor workability, strain induced porosity and adiabatic temperature rise in α+β phase region (i.e., sub-transus) are some of the main challenges faced. Cyclic thermal treatment (CTT) is an emerging technology showing potentials for microstructure modification (i.e., globularisation) in Ti-6A1-4V with significantly reduced mechanical work in the α+β region. This study summarises the results of CTT investigations conducted on a wrought Ti-6A1-4V alloy subjected to various thermo-mechanical conditions to develop different initial microstructures. Samples with uniform strain distributions were extracted from pre-forged samples and subsequently subjected to CTT using both conventional electric furnace (i.e., for slow heating and cooling rates), and induction heating (i.e., for faster heating and cooling rates). CTT of the samples forged at sub-transus temperature in conventional furnace led to maximum (i.e. -100%) globularisation and significant coarsening of a grains, resulting in an equiaxed bimodal microstructure. On the other hand, CTT with induction heating method has resulted in a maximum of 80% globularisation fraction in samples forged to 60% reduction, and -35% globularisation fraction in those forged to 20% reduction. The globularisation mechanisms during CTT of the sub-transus forged samples was dominated by the boundary splitting and thermal grooving. A Johnson-Mehl-Avarmi-Kolmogorov (JMAK) based model has been developed to predict the evolution of globularisation and grain growth during CTT. The developed JMAK model was then successfully incorporated into DEFORM~R software as post-processing user subroutines. The predicted microstructure evolution by Finite Element (FE) simulations shown a good convergence towards the experimentally measured data following CTT.
查看更多>>摘要：Strain glass alloys are promising candidates of high performance damping materials for their broad damping peaks. To realize the practical applications, the large damping capacity and broad ambient temperature range are highly desirable. However, the high damping behavior covering ambient temperature has not yet been achieved in strain glass systems, and how to obtain a maximum damping capacity in the same strain glass system remains unclear. Here, we reported the broad ambient temperature damping of Ni_(73-x)Fe_xGa_(27)(x = 23.5-24.5) strain glass alloys. The damping capacity of Ni_(73-x)Fe_xGa_(27) strain glass alloys increases as the compositions move towards the martensite/strain-glass phase boundary, and the maximum damping value (-0.12) is achieved in Ni_(49.5)Fe_(23.5)Ga_(27) strain glass alloy within the phase boundary. The boundaries of martensitic nano-domain are very mobile in phase boundary region, which leads to broad and high damping peak around ambient temperature. Our results provide an effective way to design high performance damping materials.
查看更多>>摘要：To improve the application of transition metal oxides (TMOs) in lithium-ion batteries (LIBs), this study aims to construct electrodes using three strategies, i.e., engineering nano-sized TMOs, introducing different TMOs as hybrid heterostructures, and compositing carbonaceous structures with TMOs. This study presents an efficient procedure to synthesize bimetallic MOFs (Fe@Z67s) as precursors. During the synthesis of MOFs, two key parameters are investigated, i.e., the use of Ar inert gas (O_2-free environment) and the optimization of the iron molar content. After successive carbonization and oxidation, Fe@Z67s are metamorphosed into a hierarchical porous nitrogen-doped carbon (NC) comprising cobalt-based nanoparticles (Co/Co_3O_4/ CoFe_2O_4(CCF)). Under the optimized conditions, the resultant L-CCF/NC-Ar electrode (derived from the synthesized Fe@Z67 under the O_2-free environment (Ar) with a low amount of iron (I)}, discloses the best electrochemical performance as LIB anode. This engineered electrode delivers a remarkable reversible capacity of 1020 mA h g~(-1) after 500 cycles with an excellent capacity retention of 95% at a high current density of 1 A g~(-1). The outstanding electrochemical performance of the developed electrode can be ascribed to the synergistic effect of an optimal ratio of TMOs hybrid/ porous graphitic carbon, hollow nanostructured anode material, high surface area, appropriate N-doping, and the homogeneous distribution of the active sites.
查看更多>>摘要：Highly transparent and submicrometer-grained Yb:Y_2O_3 ceramics were obtained by hot-pressing method with ZrO_2 sintering additive. Hot-pressing method provides extra driving force to promote the densification of Yb:Y_2O_3 transparent ceramics, resulting in high transmittance achieved. The transmittances of all samples were ranging from 80.5% to 81.8% at 1100 nm and 72.7-77.7% at 600 nm. The ceramic samples in this work were sintered at a low temperature of 1600 °C for 3 h, providing dense microstructures with average grain size less than 1 um, which are smaller than those of Yb:Y_2O_3 ceramics prepared by other traditional sintering techniques. The microhardness and fracture toughness were ranging from 8.16 to 7.99 GPa, and from 0.94 to 0.88 MPa-m~(1/2), respectively, which are higher than the comparison samples fabricated by pressureless sintering. The absorption cross-sections of the 1 at% Yb-doped sample at 950 and 976 nm were 0.93 × 10~(-20) and 1.22 × 10~(-20) cm~2, respectively. The fluorescence decay lifetime at 1032 nm was in the range of 0.79-1.36 ms. According to the available literature, this is the first report about Yb:Y_2O_3 transparent ceramics fabricated by hot-pressing sintering without any combined sintering process. The ceramics obtained may have potential use for solid-state lasers partly replacing single crystals.
NSTL
Elsevier