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Polyvinylidene fluoride/graphene oxide (PVDF/GO) composite nanofibers were fabricated by electrospinning technology, to enhance the output performance of triboelectric nanogenerators (TENG) based on PVDF. These nanofibers were assembled into vertically contact-separate TENG to investigate the influence of GO mass fraction on the output performance of TENG. By utilizing the COMSOL software, the output performance of the TENG was simulated and analyzed, and the variations of electric potential and electric energy density at different electrode distances were observed. This study provides theoretical support for the working principle of TENG. Moreover, the morphology and structure of the PVDF/GO composite nanofibers were characterized using scanning electron microscopy, while the output performance of the TENG based on PVDF/GO composite nanofibers was characterized using a digital oscilloscope. The results indicate that the TENG based on PVDF/GO composite nanofibers exhibits excellent output efficiency when the GO mass fraction is 0.06%. The output voltage is approximately 350 V, and the short-circuit current is around 28 µA, and under impedance matching conditions, the maximum peak power is approximately 9.66 mW, with a power density of approximately 3.86 W/m². The TENG prepared by PVDF/GO composite nanofibers exhibits excellent output performance, capable of powering 120 LEDs, hereby demonstrating potential application prospects in the field of energy harvesting. [ABSTRACT FROM AUTHOR]

The aging precipitation behavior of 6061 aluminum alloy that underwent iron casting and water-cooled copper casting and 6061 aluminum with Mn and Zr elements added was studied. Firstly, the hardness curves, tensile properties, and fracture morphology of four aging alloys—6061 (iron mold casting), 6061 (water-cooled copper mold casting), 6061-0.15Mn-0.05Zr (iron mold casting), and 6061-0.15Mn-0.05Zr (water-cooled copper mold casting)—were studied. The results of the aging hardness curve show that the aging precipitated phase of the 6061 alloy cast with a water-cooled copper mold is dispersed. The addition of Mn increases the amount of coarse inclusion α-(AlMnFeSi) in the alloy, resulting in a decrease in the age hardening property. The addition of Zr is related to the nucleation and growth of the G.P. region in the early aging period, mainly changing the formation rate and quantity of the G.P. region, leading to the advancement of peak aging and an increase in hardness. After the G.P. region gradually transforms into the β phase, the hardness of the alloy increases with the increase in the volume fraction of the β phase. When the β″ phase is coarsened to the point where the fault line can be bypassed, the transitional metastable β′ phase begins to precipitate, and the coherent distortion around it weakens, indicating over-aging. Finally, the equilibrium phase Mg2Si is formed. The results of the tensile tests indicate that the tensile strength and yield strength of the 6061-0.15Mn-0.05Zr alloy produced by water-cooled copper casting after aging are 356 Mpa and 230 Mpa, respectively. These values are 80 MPa and 75 MPa higher, respectively, than those of the 6061 aluminum alloy produced via iron casting. However, the elongation is by 5%. The fracture morphology of the tensile sample of the aging alloy shows that dislocation slip in the alloy results in dislocation plugging, stress concentration, and the initiation of crack cleavage on the surface. The fracture of the water-cooled copper mold-casting alloy is a ductile fracture of the microporous aggregation type, and the macroscopic fracture exhibits an obvious "neck shrinkage" phenomenon. The fracture analysis is consistent with the mechanical properties. The DSC curve shows that there is no enrichment process of solute atoms during the heating process, and the aging precipitation process after homogenization is as follows: G.P. zone → β″ phase → β′ phase. The aging precipitation process of the water-cooled copper casting alloy after homogenization treatment is as follows: β″ phase → β′ phase (no precipitation in the G.P. zone was observed). The results of the differential scanning calorimetry (DSC) analysis show that the main strengthening phase in the experimental alloy system is the β″ phase. The activation energies for the β″ phase precipitation were calculated and found to be 147 KJ/mol, 217 KJ/mol, 185 KJ/mol, and 235 KJ/mol, respectively. Additionally, a kinetic equation for the β″ phase precipitation during alloy aging was fitted. [ABSTRACT FROM AUTHOR]

High‐density NiFe2O4 ceramics with homogeneous microstructure were produced by slip casting and pressureless sintering. The slurry stability, sintering behavior, and microstructure of NiFe2O4 ceramics were investigated. A stable slurry can be obtained by adding 12.5 wt% NiFe2O4 nanoparticle and 5 wt% nano‐binder at a slurry pH around 11.0. The linear shrinkage and linear shrinkage rate for both NiFe2O4 ceramic green bodies shaped by cold press molding and slip casting showed nearly the same trends. The temperature associated with the maximum linear shrinkage rate of slip casted green body was 1263.5°C, which was lower than that of cold press molded sample (1272.0°C). The sintering activation energy of slip casted green body was also lower than that of cold press molded sample (279.18 vs 288.47 kJ mol−1), owing to high density and homogeneity of slip‐casted green compact. A high‐density NiFe2O4 ceramics with uniform grain size distribution can be produced by slip casting and pressureless sintering at 1350°C for 6 hours, attributed to the ability of slip casting to minimize agglomerates and micropores. It demonstrated that slip casting was more suitable to prepare high‐density NiFe2O4 ceramics with good homogeneity. [ABSTRACT FROM AUTHOR]

In this work, the effect of alloying element Zn on microstructure and prosperity of 5083 Al alloy was investigated. The grain sizes of 5083 and 5083 + Zn alloys were refined to <200 nm by appropriate rolling processes. The microhardness and tensile tests were conducted. The results showed that the dislocation density evaluated by microhardness of rolled 5083 + Zn alloys increases from 1.90 × 10 to 2.57 × 10 with increasing Zn contents. The tensile tests showed that the ultimate tensile strength of rolled 5083 alloy doubled when Zn was introduced, while the uniform elongation pronounced decreased. The yield strength of 5083 + Zn alloys increases with Zn contents. However, the strain hardening rate for the rolled alloys was decreased with increasing Zn contents. Solid solution strengthen and precipitation strengthen due to addition of Zn were responsible for the increase in yield strength and ultimate tensile strength. [ABSTRACT FROM AUTHOR]

TiO2-doped NiFe2O4 samples were prepared via ball-milling and two-step sintering processes. Besides NiFe2O4 phase, two new phases, NiTiO3 and Fe2TiO5, formed in TiO2-doped samples. The temperature of sintering onset for 1.0 wt% TiO2-doped samples is 230°C lower than that of undoped samples. Early-stage synthesis process of TiO2-doped NiFe2O4 ceramics is controlled by grain boundary diffusion mechanism. Increasing TiO2 content from 0 to 1.0 wt%, the apparent activation energy decreased from 813.919 KJ/mol to 639.361 KJ/mol. The values of relative density and bending strength reached their maximum value with 1.0 wt% TiO2. Saturation magnetization, residual magnetization ratio and coercivity decrease with increasing TiO2 content. [ABSTRACT FROM AUTHOR]

NiO-FeO-ZrO composites were fabricated by a two-step sintering process. No phase transformation for ZrO was observed. The as-prepared NiO-FeO-ZrO ceramic showed excellent mechanical properties because of the introduction of ZrO fiber. The values for both the bending strength and fracture strength of 3 wt.% ZrO-reinforced NiFeO samples reached the maximum values of ~89.0 MPa and ~4.67 MPa m, respectively, The toughness mechanism is mainly attributed to fibers' fracture, crack deflection, fibers' pull-out, and fibers' debonding. The conductivity of ZrO-reinforced NiFeO is dependent on temperature and ZrO content. When the electrolytic temperature is up to 950 °C, the conductivity value of the sample reinforced with 4 wt.% ZrO fibers is 0.63 S/cm, which has been improved by 37.8% compared with the conductivity value of 0.45 S/cm for the un-doped samples. The main conductive mechanisms of ZrO fiber in the matrix are the one based on the substitution of Zr ions to produce quasi-free electrons, and the other based on oxygen ionic conducting mechanism. [ABSTRACT FROM AUTHOR]

NiFe2O4 nanoparticles were synthesized via solid-state reaction. The effects of the reaction parameters, namely dispersant content, calcination temperature and annealing time on particle size and morphology were investigated. Magnetic properties of NiFe2O4 nanoparticles were tested. The formation mechanism of nanoparticles by solid-state reaction was also discussed. The results indicated that the synthesized nickel ferrite particles were of nanometer size with different morphologies by slight variation of the reaction conditions. The solid-state reaction technique is a simple, convenient, inexpensive and effective preparation method of NiFe2O4 in high yield. [ABSTRACT FROM AUTHOR]

This article introduces a new technique of electroless copper deposition on carbon fibers in the absence of precious metal as the catalyst. Copper layers were electrolessly deposited on the surface of carbon fiber without using the conventional palladium or silver catalyst to initiate redox reactions leading to metallization. This new technique shows that nickel seeds can serve as excellent catalysts to expedite the redox reactions. By performing experiments, parameters such as activation temperature, nickel ion concentration, and pH value were optimized, and an orbicular copper plating layer of carbon fiber was obtained in the copper sulfate salt-based conventional electroless solution. The surface morphology of copper coating was characterized by scanning electron microscopy and X-ray diffraction. The results indicate that uniform and smooth copper coating could be obtained by the new precious-metal free activation process. The resulting copper coating thickness is about 1 μm. [ABSTRACT FROM AUTHOR]

NiFeO samples with small amounts of MnO were prepared via ball-milling process and two-step sintering process from commercial powders. Sintered density, average grain size, and microstructure of Mn-doped 18NiO-NiFeO composite ceramics have been investigated by means of x-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Bending strength was measured by three-point method. The results show that the crystalline structures of the ceramic matrix are still NiFeO spinel structure and Mn ions homogeneously distribute in both the grains interiors and the grain boundaries. When 1 wt.% MnO was added, the values of relative density and bending strength of composite ceramics reached their respective maximum of 93.6% and 38.75 MPa, respectively. It is preliminarily found that MnO can reduce the sintering temperature obviously because of partial substitution of Fe with Mn in NiFeO lattice. [ABSTRACT FROM AUTHOR]

Electroplating technique was applied to coat carbon fibers with nickel. Before plating, the initial fibers were pretreated to improve the wettability in bath. The electroplating parameters were optimized to obtain high-quality nickel-coated carbon fibers, and the effects on plating were studied. The coated carbon fibers were characterized by SEM, XRD, and XPS. The coatings are uniform, smooth, bright, and adherent to carbon fibers not only along length but also along the diameter of the filaments, and mainly composed of pure nickel. Metal-carbon-oxygen bonds are present at the interface between nickel coatings and fibers, which provides the interfacial binding force. The results of performance tests showed that the nickel-coated fibers possess a good bonding strength not less than 78.5 kPa, and exhibit excellent oxidation resistance at high temperature. Compared with the initial fibers, the wettability with aluminum is also improved obviously. [ABSTRACT FROM AUTHOR]

luminum foam sandwich was prepared by rolling-bonding/powder metallurgical foaming technology, and the effects of rolling on bond strength of face sheet/powders and powder density were studied. Moreover, the foaming agent, TiH, was heat treated and a certain amount of Mg was added into powder in an attempt to understand how the stability and uniformity of foam was improved. The experimental results show that the foaming precursors with ideal quality were obtained by rolling-bonding process. When rolling reduction is 67%, the consistency of powders reach to 99.87%. Throughout consideration of the bonding of face sheet/core layer powders and deformation characteristic of powders, the optimum rolling reduction is 60%-70%. Cracks and drainage during foaming were inhibited by heat treatment of foaming agent TiH and the addition of a certain amount of Mg. The optimum heat treatment way of TiH is that heat preserving 1 hour at 450 °C; the amount of adding Mg is 1wt%. [ABSTRACT FROM AUTHOR]

The compressive deformation behaviors of closed-cell Al foams manufactured through powder metallurgy route with various relative densities have been studied. The high-density specimens displayed smoother stress-strain curves and more stable compressive behaviors. The stress-strain curves for low-density specimens displayed a regular fluctuation and more than one stress drop were observed. This can be attributed to the different deformation mode due to density variation. The effect of relative density on the stress drop ratio was studied. The results show that the stress drop ratio decreases with relative density. The compressive deformation mode changes as the relative density is <0.15. [ABSTRACT FROM AUTHOR]

The quasi-static compressive mechanical behavior and deformation mechanism of closed-cell magnesium foams were studied, and the effects of the density of magnesium foams on the compressive and energy absorption properties were also discussed. The results show that the compressive process of closed-cell magnesium foams is characterized by three deformation stages: linear elastic stage, collapsing stage and densification stage. At the linear elastic stage, the peak compressive strength ( σ0) and Young’s modulus ( E0) increase as the density increases. Magnesium foams can absorb energy at the collapsing stage. In a certain strain range, the energy absorption capacity also increases as the density of magnesium foams increases. [ABSTRACT FROM AUTHOR]

Closed-cell Al-Si alloy foams have been prepared by melt route. The cell shape anisotropy ratio of Al-Si alloy foams specimens in relative density range of 0.11-0.39 were measured. The quasi-static compressive tests show that Al-Si alloy foams have higher plastic collapse stress in the longitudinal direction (LD) than in the transverse direction (TD). The plastic collapse stress ratio increases with cell shape anisotropy ratio, which is basically in agreement with Gibson and Ashby model. Moreover, energy absorption capacity of Al-Si alloy foams was investigated. The results show that the energy absorption capacity in the LD is higher than that in the TD. [ABSTRACT FROM AUTHOR]

The treatment of goaf subsidence is important for sustainable development. Geopolymer is a new type of cementing material with excellent mechanical properties, durability, corrosion resistance, and other advantages owing to its unique three-dimensional spatial aggregation structure. Herein, a type of preparation technology of fly-ash-based foamed geopolymer suitable for goaf filling was developed by adding a chemical foaming agent to the matrix of fly-ash-based geopolymer. The mechanical properties, chemical composition, and pore structure characteristics of the samples were discussed. When the samples with different contents of fly ash, sodium metasilicate, sodium stearate, H2O2, and NaOH were prepared, a uniaxial compression test was performed to analyze the uniaxial compression failure characteristics and compression strength of the samples. The mineralogical composition of each sample was analyzed by X-ray diffraction (XRD) test, and the microstructure images of different samples were observed using scanning electron microscopy (SEM). The effects of the content of each component on the properties of the samples were discussed. Finally, the CO2 emission, energy consumption, and cost of producing fly-ash-based foamed geopolymer were analyzed. Overall, the material had the advantages of low energy consumption, low CO2 emission, environmental-protection ability, and waste utilization and thus has a broad application prospect in treating subsidence. [ABSTRACT FROM AUTHOR]

A Pd-free activation pretreatment process was developed for electroless Ni-P plating on NiFe2O4 particles. The main influencing factors, including NiCl2·6H2O concentration, pH of electroless bath and temperature, were investigated. Microstructures of the coating layers were characterized by scanning electron microscopy. It was found that a more uniform and compact Ni-P coating layer was successfully formed by electroless plating via Pd-free activation pretreatment than Pd as sited plating. The coating layers plated by Pd-free activation pretreatment were thicker than those by the sensitization and activation pretreatment on average (9 vs. 5 μm). The new process did not need conventional sensitization or activation pretreatments, because the Ni particles dispersed uniformly on the NiFe2O4 substrate became catalytic activation sites for nickel electroless plating. Such improvement was beneficial to shortening the preparation process and reducing the production costs with the use of noble metal Pd. [ABSTRACT FROM AUTHOR]