Modification of the electronic structure of graphene by intercalation of iron and silicon atoms

The ab initio calculations of the electronic structure of low-dimensional graphene–iron–nickel and graphene–silicon–iron systems were carried out using the density functional theory. For the graphene–Fe–Ni(111) system, band structures for different spin projections and total densities of valence electrons are determined. The energy position of the Dirac cone caused by the p _z states of graphene depends weakly on the number of iron layers intercalated into the interlayer gap between nickel and graphene. For the graphene–Si–Fe(111) system, the most advantageous positions of silicon atoms on iron are determined. The intercalation of silicon under graphene leads to a sharp decrease in the interaction of carbon atoms with the substrate and largely restores the electronic properties of free graphene.

     

Effect of ultradisperse TiO<Subscript>2</Subscript>, ZrO<Subscript>2</Subscript>, and cryolite powders on high-chromium cast iron hardening

The quantitative parameters of structural-phase state of Fe–27% Cr–2% Ni–2.8% C cast iron are determined via X-ray diffraction and transmission electron microscopy before and after adding ultradisperse TiO₂, ZrO₂ and cryolite powders. The contributions from individual physical mechanisms in increasing the yield stress of cast irons are quantitatively assessed. It is established that the main contribution to the durability of modified Fe–27% Cr–2% Ni–2.8% C cast iron come from solid-solution, dispersion, and grain-boundary mechanisms of hardening.     

FeNi Layered Double‐Hydroxide Nanosheets on a 3D Carbon Network as an Efficient Electrocatalyst for the Oxygen Evolution Reaction

An efficient electrocatalyst for oxygen evolution has been prepared via the deposition of iron–nickel layered double‐hydroxide (FeNi‐LDH) nanosheets on 3D carbon network as the building scaffold in a one‐step hydrothermal process. It is found that upon the assembling of FeNi‐LDH nanosheets with graphene into the 3D cross‐linked hybrid, the FeNi‐LDH/graphene hybrid features a well‐improved catalytic activity towards the oxygen evolution reaction (OER) with a good stability during the long‐term cycling experiment. Moreover, the hybrid catalyst is also active in the oxygen reduction reaction (ORR), qualifying it as a new type of bifunctional catalyst that can work in metal–air batteries.     

Sonochemical production of intermetallic coatings in heterogeneous media

The production of 5–10 μm fused particles and agglomerates occurs when metal powders in hydrocarbon solvents are exposed to high-intensity ultrasound. The principle mechanism of particle fusion is believed to be interparticle collision caused by the rapid movement of particles propelled by shock waves generated at cavitation sites. An energy-dispersive X-ray (EDX) study of the agglomerates produced during the sonication of mixed-metal powders in decane indicates that not only are the metal particles fused by the action of ultrasound but that intermetallic coatings are also developed. By examination of mixed-metal systems (Ni/Co and Cu/Mo) with substantially different tribological characteristics, it has been determined that the coatings are generated by both adhesive wear and direct impact. The mechanisms of ultrasound-induced coatings are discussed.     

State of the art and recent advances in the ultrasound-assisted synthesis,exfoliation and functionalization of graphene derivatives

Sonochemistry, an almost a century old technique was predominantly employed in the cleaning and extraction processes but this tool has now slowly gained tremendous attention in the synthesis of nanoparticles (NPs) where particles of sub-micron have been produced with great stability. Following this, ultrasonication techniques have been largely employed in graphene synthesis and its dispersion in various solvents which would conventionally take days and offers poor yield. Ultrasonic irradiation allows the production of thin-layered graphene oxide (GO) and reduced graphene oxide (RGO) of up to 1 nm thickness and can be produced in single layers. With ultrasonic treatment, reactions were made easy whereby graphite can be directly exfoliated to graphene layers. Oxidation to GO can also be carried out within minutes and reduction to RGO is possible without the use of any reducing agents. In addition, various geometry of graphene can be produced such as scrolled graphene, sponge or foam graphene, smooth as well as those with rough edges, each serving its own unique purpose in various applications such as supercapacitor, catalysis, biomedical, etc. In ultrasonic-assisted reaction, deposition of metal NPs on graphene was more homogeneous with custom-made patterns such as core-shell formation, discs, clusters and specific deposition at the edges of graphene sheets. Graphene derivatives with the aid of ultrasonication are the perfect catalyst for various organic reactions as well as an excellent adsorbent. Reactions which used to take hours and days were significantly reduced to minutes with exceedingly high yields. In a more recent approach, sonophotocatalysis was employed for the combined effect of sonication and photocatalysis of metal deposited graphene. The system was highly efficient in organic dye adsorption. This review provides detailed fundamental concepts of ultrasonochemistry for the synthesis of graphene, its dispersion, exfoliation as well as its functionalization, with great emphasis only based on recent publications. Necessary parameters of sonication such as frequency, power input, sonication time, type of sonication as well as temperature and dual-frequency sonication are discussed in great length to provide an overview of the resultant graphene products.     

Curcumin-assisted ultrasound exfoliation of graphite to graphene in ethanol

In this paper, we demonstrated a simple and cost-effective method to produce graphene from graphite in ethanol using ultrasound assisted with curcumin. The influence of curcumin concentration, starting graphite amount, sonication power, and sonication time on the graphene concentration was studied schematically. The π-π interaction between curcumin and graphene, being confirmed by FTIR spectrum, facilitate the exfoliation of the graphite into graphene. The concentration of the graphene in the ethanol reached up to 1.44 mg mL⁻¹ and the exfoliated suspension was relatively stable. The content of monolayer, bilayer, and multilayer in the exfoliated graphene suspension were 21%, 37%, and 42%, respectively. The as-prepared graphene sheets were free-defect. This novel approach may not only enable to exfoliate the graphite into graphene but also to make the graphene-curcumin hybrid which might find applications in pharmaceutical industry.     

Comparative visualized investigation of impact-driven high-speed liquid jets injected in submerged water and in ambient air

This paper is a comparative study on the characteristics of high-speed liquid jets injected in surrounding water and air using shadowgraph technique. One of the main objectives is to investigate the effects of liquid’s physical properties, used to generate the high-speed liquid jets, on jet generation’s characteristics. Moreover, comparative investigations on effects of those liquid jets after injected in water and air are reported. The high-speed liquid jets were generated by the impact of a projectile launched by a horizontal single-stage power gun. The impact-driven high-speed liquid jets were visualized by shadowgraph technique and images were recorded by a high-speed digital video camera. The process of impact-driven high-speed liquid jet injection in air and water, oblique shock waves, jet-induced shock waves, shock waves propagation, the bubble behavior, bubble collapse-induced rebound shock waves and bubble cloud regeneration were clearly observed. It was found that different properties of liquid (surface tension and kinematic viscosity) affect the jet maximum velocity and shape of the jet. Bubble behaviors were only found for the jet injected in water. From the shadowgraph images, it is found that the maximum average jet velocity, expansion and contraction velocities of bubble in axial direction increase when the value of the multiplied result of surface tension by kinematic viscosity increases. Therefore, surface tension and kinematic viscosity are the significant physical properties that affect characteristics of high-speed liquid jets.     

Effects of green laser fluence on the characteristics of graphene nanosheets synthesized by laser ablation method in liquid nitrogen medium

We have studied the effects of laser fluence on the characteristics of graphene nanosheets produced by pulsed laser ablation technique. In this work, The second harmonic of a Q-switched Nd:YAG laser at 532 nm wavelength and 5 Hz repetition rate with different laser fluences in the range of 0.5–1.8 J/cm² was used to irradiate the graphite target in liquid nitrogen medium. The products of ablation were characterized using Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray diffraction pattern, UV–Vis absorption spectroscopy, Raman spectrum and transmission electron microscopy. The Raman spectroscopy indicates that the quality of the graphene nanosheets was decreased while their structure defects were increased as the laser fluence was increased from 0.5 to 1.4 J/cm². Our results suggest that the amount of defects and the number of layers in graphene nanosheets can be changed by adjusting the laser fluence. This study could be a useful guidance for producing of high quality of graphene nanosheets by laser ablation method.     

Wear Performance and Mechanisms of Polyphenylene Sulfide/Polytetrafluoroethylene Wax Composite Coatings Reinforced by Graphene

Polyphenylene sulfide (PPS) composite coatings reinforced by graphene were prepared through a spraying method. Wear performance of the composite coatings were evaluated using a block-on-ring test rig, and the results showed that the wear life of the composite coatings were over seven times higher than that of a pure PPS coating. Wear mechanisms of PPS composite coatings reinforced by graphene are discussed. It was concluded that adhesive wear was the major wear mechanism of the pure PPS coating but the wear form of the composite coatings was dominated by abrasive wear due to the graphene filler that has high mechanical strength. In addition, fatigue wear appeared for composite coatings with higher content of graphene. The formation of a uniform thin transfer film on the counterpart ring and fine wear debris for the composites coatings during abrasion were consistent with the improvement of wear performance. The 3D morphology of the surface of the counterpart ring was also used to discuss the wear mechanism of PPS composite coatings.     

Borosiliciding of Fe–Ni alloys and evaluation of their resistance to abrasive wear

X-ray diffraction analysis, Mössbauer measurements and metallographic observations were performed on borosilicide coatings grown at 850°C on Armco iron and the Fe₆₄Ni₃₆ binary alloy using a KBF₄-activated powder mixture of B₄C and Si₃N₄. The phase composition of the coatings was determined, a result allowing to show that the thermochemical treatment gives rise to iron boriding and iron siliciding reactions of different strength, depending on the treated material. The presence of Ni in the base metal allows iron-free nickel silicides to form as important components of the coating. The resistance of borosilicide coatings to abrasive wear is evaluated and discussed.     

Frictional behavior of oxide graphene nanosheets as water-base lubricant additive

Oxide graphene (GO) nanosheets were prepared by modified Hummers and Offeman methods. The products were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), and thermogravimetric analysis (TGA). The tribological properties of GO nanosheets as water-base lubricant additive were investigated using a UMT-2 ball-plate tribotester. By the addition of GO nanosheets in pure water, the antiwear ability was improved and the friction coefficient was decreased. The water with GO nanosheets showed better tribological properties than the water with oxide multiwall carbon nanotubes (CNTs-COOH). It is concluded that the formation of a thin physical tribofilms on the substrate can explain the good friction and wear properties of GO nanosheets.     

Ultrasound-assisted Li+/Na+ co-intercalated exfoliation of graphite into few-layer graphene

In this work, we developed a novel approach for few-layer graphene by employing Li⁺/Na⁺ co-intercalated exfoliation assisted by ultrasound method. The experiments were conducted under the ultrasonic power of 300 W and the frequency of 40 kHz without the participation of any organic solvent. The effect of Li⁺/Na⁺ proportion on the exfoliation of graphite was intensively investigated. The structure and morphology of the as-exfoliated graphene nanosheets (UGN) was determined by a series of characterizations. The results showed that the thicknesses of the as-exfoliated graphene nanosheets were about 2.38–2.56 nm (about 7–8 layers) at the optimal Li⁺/Na⁺ ratio. The potential application of the as-exfoliated graphene nanosheets as additive in grease was evaluated by four-ball friction tester. The results demonstrated that the antifriction and antiwear performances of the grease with 0.06 wt% graphene were significantly improved by 21.35% and 30.32% relative to pure grease, respectively. The friction mechanism was proposed by detecting the worn surfaces.     

Diffusion paths in single-phase ternary metal systems

An analysis of diffusion paths in single-phase ternary metal systems Co–Fe–Ni and Cu–Fe–Ni on the basis of the phenomenological interdiffusion model using effective interdiffusion coefficients is presented. The peculiarities of practical application of effective interdiffusion coefficients of components for calculating diffusion paths in ternary systems are analysed. It is done on the basis of the relationship between effective interdiffusion coefficients and the diffusion paths. The results were found to be in good agreement with experimental data for the ternary systems Co–Ni–Fe and Cu–Ni–Fe. It is shown that deviation of the diffusion path from linearity in ternary single-phase diffusion couple in the system Cu–Ni–Fe mainly depends on the thermodynamic properties of the system.     

Effect of medium on friction and wear properties of compacted graphite cast iron processed by biomimetic coupling laser remelting process

Stimulated by the cuticles of soil animals, an attempt to improve the wear resistance of compact graphite cast iron (CGI) with biomimetic units on the surface was made by using a biomimetic coupled laser remelting process in air and various thicknesses water film, respectively. The microstructures of biomimetic units were examined by scanning electron microscope and X-ray diffraction was used to describe the microstructure and identify the phases in the melted zone. Microhardness was measured and the wear behaviors of biomimetic specimens as functions of different mediums as well as various water film thicknesses were investigated under dry sliding condition, respectively. The results indicated that the microstructure zones in the biomimetic specimens processed with water film are refined compared with that processed in air and had better wear resistance increased by 60%, the microhardness of biomimetic units has been improved significantly. The application of water film provided finer microstructures and much more regular grain shape in biomimetic units, which played a key role in improving the friction properties and wear resistance of CGI.     

Doping effects of transition metals on the superconductivity of (Li,Fe)OHFeSe films

The doping effects of transition metals(TMs = Mn, Co, Ni, and Cu) on the superconducting critical parameters are investigated in the films of iron selenide(Li,Fe)OHFe Se. The samples are grown via a matrix-assisted hydrothermal epitaxy method. Among the TMs, the elements of Mn and Co adjacent to Fe are observed to be incorporated into the crystal lattice more easily. It is suggested that the doped TMs mainly occupy the iron sites of the intercalated(Li,Fe)OH layers rather than those of the superconducting Fe Se layers. We find that the critical current density J_c can be enhanced much more strongly by the Mn dopant than the other TMs, while the critical temperature T_c is weakly affected by the TM doping.     

Fabrication of completely filled carbon nanotubes with copper nanowires in a confined space

Carbon nanotubes (CNTs) filled completely with polycrystalline Cu nanowires were synthesized by laser vaporization of Cu and graphite under high-pressure Ar gas atmosphere. Depending on the Ar gas pressure (0.1–0.9 MPa) and the Cu content (1–40 at.%) in graphite targets for laser vaporization, various products with different morphologies were observed by scanning and transmission electron microscopy. The ratios of the Cu-filled CNTs and carbon nanocapsules particularly increased as Ar gas pressure was increased. The maximum ∼60% fraction of Cu-filled CNTs with outer diameter of 10–50 nm and length of 0.3–3 μm was achieved at 0.9 MPa from graphite containing 20 at.% Cu. Most of the encapsulated Cu-nanowires were surrounded by single, double, or triple graphitic layers. Although the yield of the Cu-filled CNTs was also dependent on the Cu content in the graphite targets, no unfilled CNTs were produced even for low Cu content. The growth of Cu-filled CNTs is explained by the formation of molten Cu–C composite particles with an unusually C-rich composition in a space confined by high-pressure Ar gas, followed by precipitating Cu and C from the particles and subjecting them to phase separation.     

Correlation between the wear resistance of Cu-Ni alloy and its electron work function

This article reports our studies on the performance of isomorphous Cu–Ni alloy during sliding and erosive wear processes with attempt to correlate its wear behaviour with the electron work function (EWF). EWF, mechanical behaviour and wear resistance of the Cu–Ni alloy with respect to the concentration of Ni were measured using ultraviolet photoelectron spectroscopy, micro-indenter, pin-on-disc and air-jet testers, respectively. It was demonstrated that EWF, hardness and Young’s modulus of the alloy increased as the concentration of Ni increased. During solid-particle erosion tests, the wear resistance of the alloy was enhanced with an increase in the Ni concentration, corresponding to an increase in EWF. However, an opposite trend was observed during sliding wear tests, which was ascribed to the formation of oxide scale that affected the sliding wear resistance.     

Research on the mechanics of underwater supersonic gas jets

An experimental research was carried out to study the fluid mechanics of underwater supersonic gas jets. High pressure air was injected into a water tank through converging-diverging nozzles (Laval nozzles). The jets were operated at different conditions of over-, full- and under-expansions. The jet sequences were visualized using a CCD camera. It was found that the injection of supersonic air jets into water is always accompanied by strong flow oscillation, which is related to the phenomenon of shock waves feedback in the gas phase. The shock wave feedback is different from the acoustic feedback when a supersonic gas jet discharges into open air, which causes screech tone. It is a process that the shock waves enclosed in the gas pocket induce a periodic pressure with large amplitude variation in the gas jet. Consequently, the periodic pressure causes the jet oscillation including the large amplitude expansion. Detailed pressure measurements were also conducted to verify the shock wave feedback phenomenon. Three kinds of measuring methods were used, i.e., pressure probe submerged in water, pressure measurements from the side and front walls of the nozzle devices respectively. The results measured by these methods are in a good agreement. They show that every oscillation of the jets causes a sudden increase of pressure and the average frequency of the shock wave feedback is about 5–10 Hz.     

NiCoP/rGO复合材料的合成及其性能研究

以六水合氯化镍、七水合硫酸钴、氧化石墨烯(GO)和赤磷为原料,利用原位水热法,在不添加任何表面活性剂的情况下,合成了磷化钴镍/还原氧化石墨烯(NiCoP/rGO)纳米复合材料,并通过XRD、SEM、TEM、IR、Raman等对该复合材料进行了表征.结果表明,所得复合材料由NiCoP纳米颗粒和还原氧化石墨烯片层结构组成,NiCoP纳米颗粒尺寸大约为20 nm,均匀分布在rGO片层结构表面上,同时探讨了复合材料的形成过程.另外,复合材料的吸附脱除实验表明,所得复合材料对多种染料都具有非常好的吸附作用,因此,在污水处理方面有较大的应用价值.     

Effect of sputtered Cu film’s diffusion barrier on the growth and field emission properties of carbon nanotubes by chemical vapor deposition

Growth of carbon nanotube (CNT) films with good field emission properties on glass is very important for low cost field emission display (FED) applications. In addition to Ni, Co and Fe, Cu can be a good catalyst for CNT growth on glass, but due to diffusion into SiO₂ it is difficult to control the CNTs density and uniformity. In this paper, four metal barrier layers (W, Ni, Cr, Ti) were deposited by dc magnetron sputtering on glass to reduce the Cu diffusion. As-grown CNT films showed various morphologies with the use of different barrier metals. CNTs with uniform distribution and better crystallinity can be synthesized only on Ti/Cu and W/Cu. Voltage current measurements indicate that better field emission properties of CNT films can be obtained on titanium and tungsten barriered Cu, while chromium and nickel are not suitable barrier candidates for copper in CNT-FED applications because of the reduced emission performance. PACS 81.05.Uw; 61.46.Fg; 85.45.Db; 66.30.-h