Carbon nanotubes (CNTs)-based composites have attracted significant research interest in recent years, owing to their important applications in various technological fields. In this investigation, we ...describe a general approach to make CNTs-based nanocomposites via self-assembly. The method allows one to prepare binary composites as well as complex systems such as ternary or even quaternary composites where nanoparticles of active phases (e.g., metals and metal oxides) are used as primary building blocks. Six different kinds of binary, ternary, and quaternary nanocomposites, TiO2/CNTs, Co3O4/CNTs, Au/CNTs, Au/TiO2/CNTs, TiO2/Co3O4/CNTs, and Co/CoO/Co3O4/CNTs, have been reported herein in order to draw common features for various assembly schemes. To understand the interconnectivity between the active phases and CNTs, we have devised a range of experiments and examined the resultant samples with many instrumental techniques. On the basis of this work, we demonstrate that highly complex inorganic−organic nanohybrids with good controls in particle shape, size, and distribution can be fabricated from presynthesized nanobuilding units. Concerning their workability, we further show that self-assembled TiO2/CNTs are sufficiently robust and the electrochemical performance of TiO2 is significantly enhanced when it is used as a cathode material in Li-battery application.
The local inhomogeneity along the thickness direction of the extruded plate of spray-formed aluminum alloy 7055 were investigated. The thermal extrusion process was simulated by using DEFORM-3D ...software to understand its formation mechanism. In order to reduce the extrusion-induced inhomogeneity and improve the mechanical properties, the evolution of the secondary phase during different heat treatments and its influence on the peak aged hardness and tensile strength of the alloy were emphatically analyzed. The results show that the strain rate and temperature during the thermal extrusion process tend to decrease from the surface to the center, which leads to the local inhomogeneity of the microstructure and properties in the thickness direction. Such inhomogeneity can be reduced by heat treatments combining long-time or slow-heating solution treatments (F2 and F3) with peak ageing at 120 °C, due to similar content of S (Al2MgCu) phase after solution treatment and η′ phase (peak-ageing) in different regions of the alloy. The alloy solution treated with a slow heating rate (F3) and then peak aged shows highest hardness and tensile strength, because the slow heating process during the solution treatment promotes the precipitation of Al3Zr particles, and there are less S (Al2MgCu) phases after solution treatment which is conducive to the η′ phase precipitation during the subsequent aging process.
This paper describes the homogeneous catalysis and highly efficient recycling of aqueous catalyst for the hydroformylation of higher olefins in the methanol/water mixed solvent for the first time. ...When sufficient methanol is added into aqueous HRh(CO)(TPPTS)
3
/TPPTS solution and 1-hexene, the reaction mixture becomes a single phase at reaction temperature (TPPTS: Trisodium triphenylphosphine-3,3′,3″-trisulfonate), which makes the 1-hexene hydroformylation proceed homogeneously. The turnover number (TON) is 11880 during an hour, and TON is up to 10428 during half an hour at a substrate to catalyst ratio of 12000. After the reaction, the methanol with low boiling point can be readily recovered by distilling the product mixture at the reaction temperature. And then, what's left is the aqueous organic two-phase mixture. The aqueous catalyst solution can be separated from the products by a simple decantation. The recovered aqueous catalyst solution as well as methanol can be recycled for seven runs without significant loss of activity and selectivity for aldehydes. Moreover, the average rhodium leaching in products is less than 0.09 wt%.
Graphic Abstract
Amorphous Si (a-Si) thin film anodes were prepared by pulsed laser deposition (PLD) at room temperature. Structures and properties of the thin films were investigated using X-ray diffraction (XRD), ...field emission scanning electron microscopy (FESEM) and electrochemical measurements. Galvanostatic charge/discharge tests of half cells using lithium counter electrode were conducted at a constant current density of 100
μA/cm
2 in different voltage windows. Cyclic voltammetry (CV) was obtained between 0 and 1.5
V at various scan rates from 0.1 to 2
mV/s. The apparent diffusion coefficient (
D
Li) calculated from the CV measurements was about ∼10
−13
cm
2/s. The Si thin film anode was also successfully coupled with LiCoO
2 thin film cathode. The a-Si/LiCoO
2 full cell showed stable cycle performance between 1 and 4
V.
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•Influence of Zn/Mg ratios on the microstructure and mechanical properties was investigated systematically.•The precipitation behavior of dual precipitates (T′ and η′ phase) has been ...discussed.•T′ phase and η′ phase can co-exist, where a higher Zn/Mg ratio improves the precipitation of η′ phase.•A strength model was established to predict the strengthening effect of dual precipitation (T′ and η′ phase).
The effects of Zn/Mg ratios on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys aged at 150 °C have been investigated by using tensile tests, optical metallography, scanning electron microscopy, transmission electron microscopy and atom probe tomography analyses. With increasing Zn/Mg ratios, the ageing process is significantly accelerated and the time to peak ageing is reduced. T′ phase predominates in alloys of lower Zn/Mg ratios while η′ phase predominates in alloys with a Zn/Mg ratio over 2.86. Co-existence of T′ phase and η′ phase with a large number density is beneficial to the high strength of alloys. Such precipitates together with narrow precipitate free zones cause a brittle intergranular fracture. A strength model has been established to predict the co-strengthening effect of T′ phase and η′ phase in Al-Zn-Mg-Cu alloys, including the factors of the grain boundary, solid solution and precipitation.
Pre-ageing and pre-stretching before artificial ageing can significantly affect the precipitation during the subsequent artificial ageing in Al–Zn–Mg–Cu alloys, and their effects are closely relevant ...to the alloy composition and Zn/Mg ratio due to the different predominate precipitates. The diverse effects of pre-ageing and pre-stretching on the mechanical properties and microstructures of Al–Zn–Mg–Cu alloys with five different Zn/Mg ratios have been systematically studied with transmission electron microscopy, hardness measurements and tensile tests. The results reveal that pre-ageing can effectively enhance the strength due to the improvement of number density of precipitates. Different pre-aging time causes similar improvement of strength but different elongation values in peak-aged alloys A2 (T′ phase strengthened) and A5 (η′ phase strengthened), which can be explained by different size and density of precipitates and PFZ width. The effects of pre-stretching on age-hardening behavior of the alloys with various compositions are significantly different. It results in a reduction in hardness in the lowest Zn/Mg ratio alloy A1 (T′ phase strengthened) due to accelerated coarsening of precipitates; on the contrary, it results in a remarkable improvement of the hardness of the highest Zn/Mg ratio alloy A5. Pre-stretching causes different strengthening effect in alloy A5, and the maximum enhancement takes place with 2% pre-stretching because the precipitates become denser and smaller. Additionally, both pre-ageing and pre-stretching are effective ways to reduce PFZ width by promoting the precipitation near the grain boundary.
●Effects of pre-ageing/stretching are depending on the alloy composition and Zn/Mg ratio.●Pre-ageing can improve the strength without obvious loss of elongation in alloys mainly strengthened by T'/η′ phase.●Pre-stretching has an opposite effect on the age-hardening behavior of alloys A1 and A5.
Effects of Ag addition on the age hardening and precipitation behavior of aluminum alloy 7075 were investigated. The transmission electron microscopy (TEM) and atom probe tomography (APT) were used ...to study the aggregate distribution and identify the role of Ag in precipitation hardening of the alloy. The hardness and strength of the Ag–containing alloy were increased by more than 10% due to a higher number density of fine aggregates, which was 2.5 times that of the Ag–free alloy 7075. Both T–type and η–type precipitates existed in the alloys, and two precipitation sequences occurred simultaneously as: SSS → η–type cluster → GP zone → η′ → η → T, and SSS → T–type cluster → GP zone→ T′ → T. Particularly, Ag promoted the formation of T–type clusters due to the interaction among Ag, Mg and Zn atoms as well as vacancies at the early stage of aging. The Mg–Ag, Zn–Ag, and vacancy–Ag co–clusters acted as nucleation sites for the subsequent precipitates (η′, T′, etc.). This also caused the increase of Mg concentration in T–type clusters at the beginning of aging and the narrowing of the precipitation free zone (PFZ) near grain boundaries at the peak aging.
•Ag accelerates the aging precipitation process of the alloy 7075.•The peak-aged alloy 7075 + Ag exhibits higher mechanical properties.•Ag increases the number density of aggregates in aged 7075 alloy.•Both T/η-types precipitates exist in the alloys 7075 and 7075 + Ag during aging.•Strong interacts of Mg–Ag/vacancy promote precipitation of T in alloy 7075 + Ag.
The precipitation behavior of spray-formed aluminum alloy 7055 during high temperature aging at 360–440 °C was studied by using scanning electron microscopy and transmission electron microscopy, ...together with hardness and electrical conductivity measurements. The nucleation, growth and dissolution mechanism of η phase were analyzed based on precipitation thermodynamics. The results show that the main precipitates of the alloy during high temperature aging is η phase. At the initial rapid heating-up stage, the nucleation is dominant to influence the size and number density of η phase; during the subsequent isothermal aging, the growth rate has a dominant effect on η phase. The existence of η phase is related to its critical size at a given temperature. For the spray-formed aluminum alloy 7055, a most suitable high temperature aging treatment is 400 °C for 2 min. In this condition, the alloy forms more η phases in finer sizes, and its precipitation free zone around grain boundaries becomes narrower. Such microstructure is benefited from the balance of nucleation and growth of η phase, which in turn improves the hardness and conductivity of this alloy.
•The precipitation behavior of spray-formed aluminum alloy 7055 were studied.•Nucleation and growth rate of η phase during aging at 360–440 °C were calculated.•Nucleation or growth dominated differently during aging process.•The most suitable aging treatment at high temperatures was 400 °C for 2 min.
The ageing precipitates and strengthening effects of Al-Zn-Mg-Cu alloys with different Zn contents were investigated. The results showed that increasing Zn contents can significantly improve the ...age-hardening response and influence the type of precipitates as well. The low Zn-containing alloy (1.70 at.%) is strengthened by nano-scale T′ phases in the peak aged condition. However, the microstructure of the high Zn content (2.34 at.%) alloy in the peak aged condition consists of a higher density of globular T′ phases and a small proportion of plate-like η′ phases. The results of atom probe tomography revealed that clusters formed at the early stage of ageing with a Zn/Mg atomic ratio higher than 1.3 transform into η′ phases and these clusters with a lower Zn/Mg ratio transform into T′ phases. The composition of a T′ phase varies with its size, where the concentrations of Zn and Mg increase with its increasing radius, while the concentration of Al presents an opposite trend.
•Co-precipitation of T´ and η´ phase in Al-Zn-Mg-Cu alloys was investigated.•The precipitation of η´ phase was promoted by the increase of Zn content.•Clusters with different Zn/Mg ratios showed different phase transformation path.
•The effect of a novel combinatorial pre-treatment on the hardening behavior and microstructure evolution was investigated.•GP I zones formed during natural ageing are helpful to the uniform ...distribution of dislocations introduced by pre-stretching.•The synergetic effect of combinatorial pre-treatment was compared in T’/η’ phase-strengthened Al-Zn-Mg-Cu alloys.•The peak hardness of combinatorial pre-treated alloys was unaffected by the pre-stretching strain.
Al-Zn-Mg-Cu alloys with different major strengthening precipitates are subjected to a novel combinatorial pre-treatment, including natural ageing and pre-stretching. The evolution of hardness and microstructure during the combinatorial pre-treatment and subsequent artificial ageing has been investigated. The results reveal that the growth rate of hardness in alloy B (Zn/Mg = 10.0) is much higher than that of alloy A (Zn/Mg = 1.5) due to the fast precipitation kinetics of η′ phase compared with T′ phase. Both GP I zones and dislocations introduced by the combinatorial pre-treatment can act as heterogeneous nucleation sites for precipitation, resulting in more precipitates and higher hardness than pre-stretched alloys A and B. Dislocations distribute uniformly in combinatorial pre-treated alloys owing to the existence of GP I zones and dislocations, which promote the precipitation and refine the precipitate size. Moreover, these alloys with distinct pre-stretching (2%–10%) show similar precipitation behavior and peak hardness, and it indicates that the dislocation-induced precipitation will not be affected by the density of dislocations when plenty of GP I zones pre-exist.
