Three groups of AlSiTiCrNiCu high entropy alloy (HEA) particles reinforced Al606l composites were fabricated by spark plasma sintering at 520 and 570 °C (S520, S570) and by hot-pressed sintering at 570 °C(H570). The AlSiTiCrNiCu (AST) particles used as reinforcements were synthesized by mechanical alloying. The influences of the sintering process on the microstructure and mechanical properties of composites were investigated. The results showed that the AST particles had a near-equiatomic composition with a single BCC structure. The sintering temperature and time had a coupling influence on the interfacial microstructure. S520 had hardly reaction products and slight interfacial diffusion, and the AST particles were completely high entropy. Intense interfacial reactions happened on S570 and H570 with the same reaction products. The element diffusion of S570 was focused on the edge of the AST particles with partial loss of high entropy. Complete element diffusion and entire loss of high entropy of AST particles happened on H570. The differences in the microstructure caused by the three preparation methods led to the changes in mechanical properties and fracture mechanisms of composites.
We used different SiC particle size as raw materials and via reaction bonding technique to prepare porous SiC membrane supports. The phase composition, microstructure, bending strength, open porosity, and pore size distribution were investigated as a function of SiC particle size and firing temperature. It is found that the reduction of SiC particle size not only dramatically enhances the bending strength of porous SiC membrane supports, but also slightly reduces the firing temperature duo to smaller SiC particle with higher specific surface area and higher reaction activity. Besides, the open porosity and pore size distribution are dependent on the firing temperature, but insensitive to the SiC particle size due to the pore related characters mainly controlled by the binder. The bending strength increases with the increasing of the firing temperature and with the decreasing of SiC particle size. When the firing temperature was 1 500 °C and SiC average particle size was 447.75 µm, the optimal performance were achieved, the bending strength was 15.18 MPa, the open porosity was 36.02 %, the pore size distributed at 3.09–112.47 µm, and the mean pore size was 14.16 µm.
Highly monodisperse carbon quantum dots (CQDs) were synthesized by a solvothermal method using L-ascorbic acid as carbon source and different simple alcohols (methanol, ethanol, ethylene glycol, and isopropanol) as reaction solvents at 180 °C for 4 hours. The performance of CQDs was characterized by transmission electron microscope (TEM), Fourier infrared spectrometer (FTIR), UV-visible spectrophotometer, and fluorescence spectrophotometer. The results show that the prepared CQDs are wavelength-dependent, and have good hydrophilicity and similar surface compositions. However, there are more carbon and oxygen-containing functional groups on the surface of CQDs prepared with ethanol (CQDs-ET), and the type and number of functional groups will directly affect the fluorescence emission of CQDs. Also, it is found that the luminescence mechanisms of CQDs prepared by this solvothermal method are mainly based on the defect state of the oxygen group surface. And alcohol solvents do not directly participate in the formation of carbon nuclei during the reaction process, but it will affect the number and type of surface groups. Therefore, the influence of surface groups on the CQDs performance is greater than that of carbon nuclei in this experiment.
The electronic structure and optical property of stacked GaN-WS2 heterostructure are explored with HSE06 calculation based on density functional theory. The direct band gap of GaN-WS2 heterostructure is 1.993 eV, which is obviously a type-II band alignment semiconductor. Furthermore, the optical property of GaN-WS2 heterostructure such as absorption coefficient is analyzed. These new findings enable GaN-WS2 heterostructure to be promising candidates for photovoltaic cells and electronic devices in visible light.
To solve the problem of the low added value Zn-containing rotary hearth furnace (RHF) dust, two deep eutectic solvents (DESs) were employed, such as choline chloride-urea (ChCl-urea) and choline chloride-oxalic acid dihydrate (CC—OA) solvent and Zn-containing RHF dust (water-washed) as the research target. Then, we prepared ZnO nanoparticles using two DESs or their combination, namely, ChCl-urea (Method A), CC—OA (Method B), first CC—OA and then ChCl-urea (Method B-A) and first ChCl-urea and then CC-OA (Method A-B), respectively. The effects of these methods on the properties of as-obtained precursors and ZnO nanoparticles were investigated in detail. The results indicated that the precursor obtained by Method A was Zn4CO3(OH)6·H2O, and those by Methods B, B-A, and A-B were all ZnC2O4·2H2O. Moreover, the decomposition steps of the last three methods were similar. The ZnO contents of 95.486%, 99.768%, 99.733%, and 99.76% were obtained by Methods A, B, B-A, and A-B, respectively. Methods A, B, and B-A led to the formation of spherical and agglomerated ZnO nanoparticles with normal size distributions, where Method B showed the best distribution with an average diameter 25 nm. The ZnO nanoparticles obtained by the Method A-B did not possess good properties.
The waste coffee-grounds carbon (WCGC) was prepared with H3PO4 treated using waste coffee-grounds as precursor. Its adsorption ability was studied using phenol as test molecule. The influence of H3PO4 treated, calcined temperature, the initial phenol concentration, the doge of carbon and original pH values on phenol adsorption ability were investigated. Characterization of WCGC was performed by N2 adsorption isotherms, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. First, the second order and Weber-Morris model reaction rate models were used to estimate the WCGC adsorption ability. The results show that the produced WCGC (700 °C, 2 h) has been graphitized and the layered structure increased BET surface to 435.98 m2/g and adsorption phenol ability. The initial phenol concentration is 50 mg/L, the amount of WCGC (700 °C, 2 h) is 0.2 g, and the phenol adsorption rate is 97% after 270 min and no intermediate product formation. The adsorption kinetics of the selected WCGC is best fitted by the Weber-Morris model.
An efficient and promising approach for effectively dispersing multi-walled carbon nanotubes (MWCNTs) in cementitious composites has been investigated. The naturally occurring organic extracts from species of indigenously known ‘Keekar’ trees scattered along tropical and sub-tropical regions; is found as an exceptional replacement to the non-natural commercial surfactants. In the initial phase of investigation, ideal surfactant’s content required for efficient dispersion of MWCNTs in solution was determined using ultraviolet spectroscopy. The experimental investigations were then extended to five different cement composite formulations containing 0.0, 0.025, 0.05, 0.08 and 0.10% MWCNTs by weight of cement. It was observed that the natural surfactant produced efficient dispersion at much reduced cost (approx. 14%) compared with the commercial alternate. The estimated weight efficiency factor φ was found 6.5 times higher for the proposed sustainable replacement to the conventional along with remarkable increase of 23% in modulus of rupture on 0.08 wt% addition of MWCNTs. Besides strength enhancement, the dispersed MWCNTs also improved the first crack and ultimate fracture toughness by 51.5% and 35.9%, respectively. The field emission scanning electron microscopy of the cryofractured samples revealed efficient dispersion of MWCNTs in the matrix leading to the phenomenon of effective crack bridging and crack branching in the composite matrix. Furthermore, the proposed scheme significantly reduced the early age volumetric shrinkage by 39%.
Highly stable and permeable silicone emulsions were prepared by encapsulating N-octyl triethoaysilane microdroplets into micelles of NH2-PDMS/SiO2. The conversion of siloxane to sub-1 µm emulsions, on one hand, endows the concrete with a highly hydrophobic internal surface. While, its outside surface maintains relatively high surface energy, which is beneficial for the post-coating of other polymers. As a result, the coated concreted can simultaneously acquire water repellency and low permeability. The utilization of water-dispersed silicone emulsions, on the other hand, is beneficial for the environmental protection. Thus, this work offered a green procedure for the comprehensive protection of concrete.
Graphene-modified asphalt (GMA) for road application was prepared via using metal-free phthalocyanine-dispersed to modify an SK-70# base asphalt with graphene. The preparation parameters are as follows: the content of graphene is 0.26% based on the mass percentage of absolute ethanol, the content of nonmetal phthalocyanine is 190% based on the mass percentage of graphene, and then the GMA is prepared via unique high-speed shearing with continuing to ventilate nitrogen, which can prevent the aging of modified asphalt in the high-speed shearing process, and effectively evaluate the modifier. The penetration, softening point, force ductility, and fracture energy of GMA were significantly improved based on the base asphalt. Thus, the incorporation of graphene could enhance the base asphalt’s high- and low- temperature stability. The modification mechanism was researched via metallographic microscopy, computed tomography (CT), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM). Adsorption and physical dispersion of the asphaltenes and resins in the phthalocyanine-graphene system were confirmed.
Titanium (Ti) nitrides were in situ grown on Ti6A14V alloy (TA) using a glow discharge plasma nitriding (GDPN). The morphology, chemical composition, phase and mechanical property of the obtained nitrided TA were analyzed using a scanning electron microscope (SEM), energy dispersive spectroscope (EDS), X-ray diffraction (XRD), and nanoindentation tester, respectively. The tribological performances of un-nitrided and nitrided TAs were evaluated using a ball-on-plate wear tester, and the wear mechanism was also discussed in detail. The results show that the nitrided layer with the compound and diffusion layers is formed on the nitrided TA, which is composed of δ-TiN and α-Ti phases. The nanohardness and elastic modulus of nitrided TA are 6.05 and 143.13 GPa, respectively, higher than those of un-nitrided TA. The friction reduction and anti-wear performances of nitrided TA are better than those of un-nitrided TA, and the wear mechanism is primary abrasive wear, accompanying with adhesive wear, which is attributed to the formation of Ti nitrides with the high nanohardness and elastic modulus.
To solve the problem of the poor plasticity and to meet the requirements of high temperature for forming titanium alloy, mechanical properties of TC2 titanium alloy under the compound energy-field (CEF) with temperature and ultrasonic vibration were studied. The effects of CEF on tensile force, elongation, microstructure and fractography of the TC2 titanium alloy were compared and analyzed. The results show that, under the same thermal conditions, the deformation resistance of TC2 titanium alloy decreases with the increase of ultrasonic vibration energy. The formability is also improved correspondingly due to the input of ultrasonic vibration energy and its influence on the microstructure of the material. However, when the ultrasonic vibration energy is larger, the fatigue fracture will also appear, which reduces its formability.
To investigate the dynamic recrystallization behavior of 7xxx aluminum alloys, the isothermal compression tests were carried on the 7056 aluminum alloy in the temperatures range of 320–440 °C and in the strain rates range of 0.001–1 s−1. In addition, the microstructure of samples were observed via electron back scanning diffraction microscope. According to the results, true stress and true strain curves were established and an Arrhenius-type equation was established, showing the flow stress increases with the temperature decreasing and the strain rate increasing. The critical strain (ε c) and the critical stress (σ c) of the onset of dynamic recrystallization were identified via the strain hardening rate and constructed relationship between deformation parameters as follows: ε c=6.71×10−4 Z 0.137 3 and σ p=1.202σ c+12.691. The DRX is incomplete in this alloy, whose volume fraction is only 20% even if the strain reaches 0.9. Through this study, the flow stress behavior and DRX behavior of 7056 aluminum alloys are deeply understood, which gives benefit to control the hot working process.
The microstructure evolution and its effects on the mechanical performance of 2000 MPa bridge cable steel wires were investigated by transmission electron microscope (TEM), electron backscatter diffraction (EBSD), X-ray diffractometer (XRD) and mechanical tests. Experimental results reveal that, with the increasing strain from 0 to 1.42, a fiber structure and a <110> fiber texture aligned with the wire axis are gradually developed accompanied by cementite decomposition and the formation of sub-grains; the tensile strength increases linearly from 1 510 to 2 025 MPa, and the reduction of the area is stable with a slight decline from 44% to 36%. After annealing at 450 °C for different times, pronounced changes in the microstructure occur. Cementite lamella fragment into coarser globules corresponding to a remarkable spheroidization process, while ferrite domains recover and recrystallize, and this process is associated to modifications in the mechanical properties. Furthermore, based on the observations on dislocation lines crossing through cementite lamellae, a possible mechanism of cementite decomposition is discussed.
The 2024 anodized aluminum alloy film was sealed by KAl(SO4)2 solution and the effect of sealing on corrosion resistance was investigated by means of potentiodynamic polarization curves, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy. The experimental results show that the optimal parameters for KAl(SO4)2 sealing are 35 °C, with the pH value of 8, the concentration of 8 g/L, and the sealing time of 3 min. The corrosion resistance of the KAl(SO4)2 sealed sample can be significantly improved than that of unsealed one, and is obviously superior to that of the conventional hydrothermal sealed sample. Furthermore, X-ray photoelectron spectroscopy demonstrates that more Al(OH)3 will be formed in the process of KAl(SO4)2 sealing, which will shrink the diameter of the microporous and therefore results in the excellent corrosion resistance.
Fe-Al-Ta eutectic composites with solidification rates of 6, 20, 30, 80 and 200μm/s were obtained by a modified Bridgman directional solidification technique and alloying. Moreover, tensile property and fracture behavior of Fe-Al-Ta eutectic composites were studied at 600 °C. The relationship between mechanical property and microstructure at high temperature was studied. Microstructure of Fe-Al-Ta eutectic is composed of Fe2Ta (Al) Laves phase and Fe (Al, Ta) matrix phase. In addition, the tensile strength at high temperatures is higher than that at room temperature. The tensile strength is increased with the increase of solidification rate. Moreover, fracture morphology transforms from cleavage fracture to dimple fracture as the solidification rate is increased at high temperatures.
Wettability of Zn-Al alloy melt on the pure iron substrate at 450 °C was studied. The effect of Al content (Zn, Zn-1Al, Zn-2Al, Zn-3Al, Zn-4Al, and Zn-5Al) on the wetting behavior and interfacial reaction was investigated by high-temperature contact angle measuring device and scanning electron microscope (SEM). The results show that, with the increase of Al content, the initial contact angle of the molten alloy on the substrate decreases gradually and the wettability increases gradually. Compared with the initial contact angle, the final contact angle is slightly reduced, because the Fe-Al inhibition layer is preferentially formed at the interface when adding Al to the alloy. The presence of Al will promote the occurrence of the reactive wetting, leading to an insignificant wetting spreading process, and the final contact angle negligibly differs from the initial contact angle. The adhesion work and charge density distributions of interface systems were calculated based on the first-principles. The results show that the adhesion work of the Fe/Zn and Fe/(Zn-Al) interface model is 2.017 1 J/m2 and 13.794 4 J/m2, respectively. The addition of Al greatly increases the adhesion work between alloy melt and iron substrate. Compared with the Zn-Fe and Al-Fe interface models, it can be seen that a significant charge migration phenomenon occurs between the interfaces. The amount of charge migration in the Al-Fe interface model is much larger than that in the Zn-Fe interface model, indicating that the bonding between Al-Fe atoms can occur more easily and the interaction between Al-Fe interfaces is stronger. This is also the reason why the addition of Al increases the adhesion work between interfaces.
The influence of rare earth Y on the microstructure and mechanical properties of Al-Zr alloy produced by dynamic ECAE was studied by OLYMPUS-BX51M optical microscope (OM), S4800 energy disperse spectroscopy (EDS) and SANS CMT5105 electronic universal material testing machine, and the corresponding equivalent conductivity was also investigated by using QJ48 DC electric bridge. The results show that the tensile strength of Al-Zr conductor first increases and then decreases with the increase of the aging time and temperature, and the highest tensile value can be obtained under the aging temperature of 160 °C for 4 h. The ductility and the resistivity of the Al-Zr alloy have inverse proportion to the aging time. The rare earth Y has significantly improved the electrical and mechanical properties of Al-0.3%Zr heat-resistant alloy. In this study, the tensile strength and the elongation of the Al-0.3%Zr-0.2%Y alloy, after aging treatment at 220 °C for 14 h, are about 278.49 MPa and 6.7%, respectively, and the equivalent conductivity is about 59.6 IACS. Hence the synthetical properties of the Y-containing alloy are significantly improved compared with traditional Al-0.3%Zr alloy.
The deformation behavior of equal channel angular pressing (ECAP) was discussed by using plasticity method. The node mapping method is employed to realize the analysis of multi-pass ECAP by using three-dimensional FEM methods for pure aluminum. The single-pass ECAP is a non-uniform shear deformation process in the cross-section of the workpiece. The uniform deformation processing routes are obtained during multi-pass ECAP process. In addition, the density of dislocations and defects of crystal lattice are also largely changed for different processing routes. The grain microstructure is gradually refined with the increase of the pressing passes. The grains and their distribution obtained by route Bc are more useful for producing the material with high angle grain boundaries. The grain microstructure of the cross section of the pressed material decreases with the increase of strain, and some grains exhibit transformed grain boundary (PTB) fringes. The dislocation density in the grain decreases, and the grain boundary presents equiaxed distribution.
Two isomeric fluorene-based heteroundecenes of bis(thienocyclopenthieno[3,2-b]thieno) fluorene (BT2T-F) and bis(dithieno[3,2-b:2’,3’-d]thiophene)cyclopentafluorene (B3T-F) have been designed and synthesized. The side chains of 4-hexylphenyl anchor on the 5th and 8th positions in B3T-F while on the 4th and 9th positions in BT2T-F, in which the former is closer to the center of the fused ring. The corresponding acceptor-donor-acceptor (A-D-A) type small molecule acceptors (SMAs) of BT2T-FIC and B3T-FIC were prepared by linking BT2T-F and B3T-F as fused ring donor units with the acceptor unit of 2-(5,6-difluoro-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC-2F), respectively. B3T-FIC presents a superior crystallinity with intense face-on π-π stacking in its neat film while BT2T-FIC is more disordered. When blended with PBDB-T-2Cl as a polymer donor, the optimized PBDB-T-2Cl:BT2T-FIC device exhibits an averaged power conversion efficiency (PCE) of 10.56% while only 7.53% in the PBDB-T-2Cl:B3T-FIC device. The improved short-circuit current (J sc) and fill factor (FF) of the PBDB-T-2Cl:BT2T-FIC device are the main contribution of its higher performance, which is attributed to its more efficient and balanced charge transport and better carrier recombination suppression. Given that BT2T-FIC blend and B3T-FIC blend films both take a preferential face-on orientated π-π stacking with comparable distances, the suitable SMA domain size obtained in the BT2T-FIC blend could account for its more efficient photovoltaic performance. These results highlight the importance of side-chain strategy in developing efficient SMAs with huge fused ring cores.