IF-WS2 Nanoparticles Research Articles

Microwave dielectric properties of inorganic fullerene-like tungsten disulfide nanoparticles

The dielectric response of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanoparticles prepared by a sulfidization reaction of WO3 nanoparticles has been investigated, against commercial platelet 2H-WS2 particles, using a cavity perturbation technique at microwave frequencies at temperatures ranging from 20 to 750°C. The IF-WS2 nanoparticles showed both temperature and frequency dependent dielectric properties. The different dielectric behaviour between the IF-WS2 and 2H-WS2 can be attributed to the different conductivity and structure peculiar to the materials. The microstructure and thermal stability of the IF-WS2 and 2H-WS2 were thoroughly examined, to correlate with the resulting dielectric responses.

Meso-scale modelling of shock wave propagation in a SiC/Al nanocomposite reinforced with WS2-inorganic fullerene nanoparticles

It has been postulated that nanocomposites incorporating IF-WS2 nanoparticles within a strong matrix might form the next generation of highly shock-resistant materials. The present work describes initial analyses into the shock response of such materials via a sequential multi-scale dynamic analysis. Density functional theory is used to calculate the elastic properties of the multilayered WS2 nanoparticles. These properties are then used within an explicit finite element (FE) analysis of wave propagation through an embedded statistical volume element (SVE) of a two-phase nanocomposite consisting of a matrix with IF-WS2 nanoparticles. Some wave front dispersion was noted, particularly where the modulus of the matrix is significantly different from that of the particles. A three-phase nanocomposite consisting of an aluminium matrix with IF-WS2 and SiC nanoparticles was also considered, and showed more apparent wave front dispersion than for the two-phase nanocomposite. Hugoniot shock propagation data have been derived from the simulation outputs. It is concluded that sequential multiscale modelling of these systems is appropriate and can provide useful information about shock wave propagation in the elastic region. The work also provides a foundation for more realistic simulations at higher rate loading, where it will be necessary to incorporate material failure in the models.

Lubrication mechanisms of hollow-core inorganic fullerene-like nanoparticles: coupling experimental and computational works

Inorganic fullerene-like (IF) nanoparticles made of metal dichalcogenides have previously been recognized to be good friction modifiers and anti-wear additives under boundary lubrication conditions. The tribological performance of these particles appears to be a result of their size, structure and morphology, along with the test conditions. However, the very small scale of the IF nanoparticles makes distinguishing the properties which affect the lubrication mechanism exceedingly difficult. In this work, a high resolution transmission electron microscope equipped with a nanoindentation holder is used to manipulate individual hollow IF-WS2 nanoparticles and to investigate their responses to compression. Additional atomistic molecular dynamics (MD) simulations of similarly structured, individual hollow IF-MoS2 nanoparticles are performed for compression studies between molybdenum surfaces on their major and minor axis diameters. MD simulations of these structures allows for characterization of the influence of structural orientation on the mechanical behavior and nano-sheet exfoliation of hollow-core IF nanoparticles. The experimental and theoretical results for these similar nanoparticles are qualitatively compared.

Hydrophobicity study of polytetrafluoroethylene nanocomposite films

In the present work, inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles have been incorporated into polytetrafluoroethylene films using aerosol-assisted deposition process. The hydrophobic behavior of the nanocomposite film has been investigated and the result shows that the hydrophobicity of PTFE films can significantly be improved with the incorporation of IF-WS2 nanoparticles. An oblate spheroid model which takes into the consideration of surface roughness effect has been proposed, to simulate the hydrophobic behavior, based on the surface roughness and peak density of the nanocomposite films. This hydrophobic model can provide a useful guideline to describe and predict the hydrophobicity of nanocomposite films, from the input of parameters such as surface energy, roughness and liquid properties.

Structural transformation of tungsten oxide nanourchins into IF–WS2 nanoparticles: an aberration corrected STEM study

IF–WS2 nanoparticles synthesized starting from tungsten oxide nanourchins have been investigated by using aberration corrected scanning transmission electron microscopy (Cs-STEM). The synthesis process produced IF–WS2 nanoparticles of two different and well differentiated ranges of size. High resolution HAADF–STEM images and their comparison with simulated STEM micrographs reveal the predominance of stacking of the type 1T close to the border of the structure; the observation of this kind of stacking, observed previously in IF–MoS2 but never reported before in the case of the IF–WS2 nanostructures, adds a new dimension to the existing understanding of structure and stacking in the case of the nanostructures of transition metal chalcogenides.

Frictional Characteristics of IF-WS2 Nanoparticles in Simulated Engine Conditions

The efficacy of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanoparticles as engine oil friction modifier additive was investigated using a high-stroke reciprocating piston ring–cylinder bore bench test system. Frictional characteristics of various IF-WS2 nanoparticle concentrations in mineral oil were experimentally analyzed in simulated engine conditions controlling oil temperature, speed, and normal load. Though the effect of IF-WS2 nanoparticles on piston ring and cylinder bore friction was minor in low concentrations, after a running period in a mixed lubrication regime with 10% additive, a considerable reduction in friction coefficient was observed when the IF-WS2 formulated oil was used. This reduction remains to some extent with reference mineral oil after solvent cleaning of the mating components. The results show that a thin tribofilm gradually forms on the piston ring and the cylinder bore surfaces, reducing the friction coefficient in a mixed lubrication regime. However, in order to obtain the friction reduction there seems to be a threshold in the concentration of IF-WS2 in mineral oil and film development period. The effects of lubrication regime, contact load, speed, and surface roughness on tribofilm formation are also discussed. The presence of WS2 tribofilm formed on the piston ring and the cylinder bore surfaces was further verified using Raman spectroscopy.

The Effect of Tungsten Sulfide Fullerene-Like Nanoparticles on the Toughness of Epoxy Adhesives

In this work the effect of inorganic fullerene-like (closed cages) nanoparticles of tungsten disulfide (IF-WS2) on the mechanical properties and especially on the toughness of epoxy resins, was studied. The epoxy resin used was the well-known DGEBA (di-glycidyl ether of bis-phenol A) cured with polyamidoamine. The epoxy/IF-WS2 nanocomposites were prepared by applying a high shear mixing to obtain a uniform dispersion and homogeneous distribution of the IF nanoparticles in the epoxy matrix. Two mixing procedures were used — a low shear of short duration and high shear with a long mixing time. The resulting epoxy nanocomposites were first characterized for their shear and peel strength using appropriate bonded joints. The experimental results demonstrate that enhanced shear strengths and shear moduli were achieved, together with a significant increase in the peel strengths at low concentrations of the IF-WS2 nanoparticles (more than 100% increase at 0.5 wt% IF-WS2). Above the threshold value of 0.5% IF-WS2 the peel strength decreased sharply. The fractured surfaces of the bonded joints were examined by transmission and scanning electron microscopy in order to characterize the fracture mechanisms and analyze the dispersion level of the nanoparticles within the polymer. The electron micrographs indicated that the presence of the nanoparticles in the epoxy matrix induced fracture mechanisms which were different from those observed in the pristine epoxy phase. These mechanisms included: crack deflection; crack bowing; and crack pinning. Evidence for a chemical interaction between the nanoparticles and the epoxy were obtained by infrared measurements in the attenuated total transmittance mode. The data suggests the formation of new carbon–oxygen–sulfur bonds, which are most likely due to the reaction of the outermost sulfur layer of the IF nanoparticles with the reactive epoxy groups. The observed simultaneous increase in both shear and peel strengths at very low IF-WS2 concentrations, found in this work, could lead to the development of high performance adhesives and to new types of structural and ballistic fiber nanocomposites.

Gold Nanoparticles as Surface Defect Probes for WS2 Nanostructures

WS2 inorganic nanotubes (INT) and inorganic fullerene-like nanoparticles (IF) are well-known for their high mechanical strength and as superior solid lubricants. The outermost WS2 layer is considered to be fully bonded; thus, it was suggested that the interactions of these WS2 nanostructures with their surroundings are governed by purely van der Waals (vdW) interactions. However, in the case of IF-WS2 nanoparticles, the faceted surface may contain sites with nonsaturated coordination, which, in turn, react with the surrounding media. Gold nanoparticles (GNP) were used as probes for the IF-WS2 surface defects, mapped by both scanning and transmission electron microscopy. The interaction between the GNP and the reactive surface was investigated using INT-WS2 as a model and was characterized by atomic force microscopy (AFM).

TWO SUITABLE METHODS FOR THE PREPARATION OF INORGANIC FULLERENE-LIKE (IF) WS2 NANOPARTICLES

Two facile and low cost routes were used for the synthesis of IF-WS2 nanoparticles. In this paper, preparation of IF-WS2 nanoparticles with two different methods was investigated. In the first method, WO3 nanoparticles were reacted with H2S gas in N2/H2 reducing atmosphere at 900 oC. The as-synthesized IF-WS2 nanoparticles are spherical shape with an average size of about 70 nm. In the second method, WO3 nanoparticles were reacted with Sulfur powder in H2 reducing atmosphere at 800 oC. All reaction conditions have been optimized. In this method, application of the harmful and poisonous H2S gas was eliminated. The as-prepared IF-WS2 nanoparticles are spherical shape with an average size of about 50 nm. In this research, it was revealed that in the first method, the reduction of WO3 nanoparticles before the reaction with H2S gas is very important in product quality and the output of the reaction will be increased. Also in contrast to that was proposed in the previous similar research, it was revealed that the preparation of IF-WS2 nanoparticles according to the second method can not be considered as large scale method because the product quality is directly dependent on the amount of WO3 nanoparticles that can not be considered exceeding 0.1 g. Besides, the preparation method of WO3 nanoparticles as precursor for the synthesis of IF-WS2 nanoparticles is different from previous similar researches. The solution of ammonium para tungstate (APT) and citric acid (as organic additive) was prepared and then the pH of solution was adjusted at 7 by using ammonium hydroxide. Firstly, the sample was heated to 250 oC for 1 h and secondly was calcined at 500 oC for 2 h to obtain yellow color powder of WO3 nanoparticles with an average size of about 50 nm. The samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

On the Efficacy of IF–WS2 Nanoparticles as Solid Lubricant: The Effect of the Loading Scheme

Fullerene-like WS2 (MoS2) nanoparticles (IF) have been studied in the past as solid lubricants. Using the tribological ball-on-flat experiments, it was shown that the size of the aggregates and their distribution determine the penetration and entrapping of the IF nanoparticles at the interface. It is expected that the wedge clearance at the inlet of the contact, i.e., the oblique-angle entrance to the contact zone between the two mating tribological surfaces, as well as the average surface roughness, can limit the supply of the lubricant into the interface in, e.g., the block-on-ring experiment. In the present series of experiments, the Stribeck curve was designed first using a linear loading scheme and pure oil. It was concluded that a wedge clearance (oblique-angle) in the inlet of the contact zone leads to entrapment of the IF nanoparticles and their compaction, which hamper the supply of the fluid lubricant into the interface. A ball-on-flat and flat block-on-ring friction devices with wedge clearance in the inlet of the contact can distort the efficacy of IF. Procedures for improving the supply of the IF nanoparticles to the contact zone and improving thereby their efficacy are considered.

Friction and wear properties of nanocomposite coatings including inorganic fullerene-like (Mo, W)S2 in environments

A quantity of inorganic fullerene-like IF-MoS2 and IF-WS2 nanoparticles is prepared by solid-gas reaction,pre-cipitation and solvent thermal induced methods.Ni-P?(IF-WS2) composite coatings on aluminum alloy are prepared by elec-troless codeposition.(Ni,Mo)/IF-(Mo,W)S2 gradient nan-ocomposite coatings and IF-(Mo,W)S2/(Ni,Mo)-IF-(Mo,W)S2 multilayer nanocomposite coatings are deposited on alu-minum and titanium alloy substrates by magnetron sputtering and laser sputtering,respectively.The adhesion,friction and wear properties of the nanocomposite coating are evaluated using conventional scratch tester,a ball-on-disk tribometer both in vacuum(10-2 Pa) and in humid air.The Ni-P?(IF-WS2) composite coatings exhibite both higher wear resistance and lower friction coefficient than Ni-P electroless coating.The gradient and multilayer structures improve the adhesion of the coatings to alloy substrates.The(Ni,Mo)/IF-(Mo,W)S2 grad-ient nanocomposite coatings and IF-(Mo,W)S2/(Ni,Mo)-IF-(Mo,W)S2 multilayer nanocomposite coatings all show low friction coefficient and wear rate in different environments.The nanocomposite coatings containing IF-(Mo,W)S2 materials has excellent tribological stability.

Synthesis of inorganic fullerene-likeWS2 nanoparticles and their lubricating performance

A facile, large-scale and low-cost route was used to synthesize inorganic fullerene-like (IF)WS2 nanoparticles by the reaction of sulfur powder (S) and as-preparedWO3 nanoparticles in a hydrogen atmosphere at a heating temperature of500–650 °C. Theas-synthesized IF-WS2 nanoparticles are of a closed hollow cage structure with an average size of about 50 nm. Thecomposition, morphology and structure of the products were characterized by XRD,TEM, FE-SEM, and HRTEM. The influences of the main reaction conditionswere investigated and the possible growth mechanism are proposed. It is worthnoting that through changing the amount of as-prepared composite powder(WO3 and S) and the content of hydrogen, yields ofIF-WS2 in larger scales can accordingly be easily obtained, and such a synthetic route may also beused in the synthesis of other transition IF metal dichalcogenides. Furthermore,tribological experiments emphasized the important role played by these as-synthesizedIF-WS2 nanoparticles in providing excellent lubricating performance, which may bring a muchbrighter future for their applications in the lubricating field, or even arouse great interest ofboth scientists and industrialists for their many other important applications.

The Effect of WS2Nanoparticles on Friction Reduction in Various Lubrication Regimes

A study of the tribological behavior of nested inorganic fullerene-like (IF) nanoparticles of WS2, as a potential additive to base oils is presented. Friction measurement results obtained from three different test rigs over a wide range of normal loads and sliding velocities are shown. Stribeck curves are used to reveal the lubrication regimes where the IF are most effective. It is found that the addition of IF-WS2 nanoparticles to the base oils results in up to 50% reduction in friction coefficient in the mixed lubrication regime. The mechanism of improved friction and wear behavior with the IF additive is discussed.

Modification of contact surfaces by fullerene-like solid lubricant nanoparticles

Recently, it has been established that WS2 and MoS2 nanoparticles (IF) mixed in oil, and impregnated into porous matrix of powdered materials appear to enhance the tribological properties in definite loading range in comparison to typical metal dichalcogenides particles. Modification of the contact surface by IF-WS2 nanoparticles from oil, grease and from pores of densified powdered samples is considered in this work. The role of the IF solid lubricants as a part of a third body is discussed also in this work. The effect of the IF in oil was studied using a pin-on-disk tester. The study of IF in greases and impregnated into the pores of densified matrices was performed using a ring-block tester. The state of the mating surfaces and the nanoparticles before and after the friction test has been studied by TEM, SEM and XPS. It was established that the IF nanoparticles form a protective film allowing an increase in the load capacity of rubbed pairs. The tribological behavior of lithium grease with IF was found to be appreciably better than that of a commercially available grease incorporating MoS2 platelets (2H). It is found that the IF nanoparticles lead to improved tribological behavior of greases with the IF nanoparticles under very high loads. Impregnation of the IF-WS2 into the pores of densified powdered materials provides a reduced friction coefficient and wear rate over a wide load range in comparison to 2H solid lubricant. The main advantages of the IF nanoparticles is ascribed to the release and furnishing of the nanoparticles from the open pores onto the metal surface and their confinement at the interface, which is not possible with dense flat surfaces. It is expected that the spherical shape of IF nanoparticles facilitate their sliding/rolling between the rubbed surfaces.