Fullerene-like WS2 Nanoparticles Research Articles

Biopolymer Nanocomposite Materials Based on Poly(L-lactic Acid) and Inorganic Fullerene-like WS2 Nanoparticles.

In the current study, inorganic fullerene (IF)-like tungsten disulphide (WS2) nanoparticles from layered transition metal dichalcogenides (TMDCs) were introduced into a poly(L-lactic acid) (PLLA) polymer matrix to generate novel bionanocomposite materials through an advantageous melt-processing route. The effectiveness of employing IF-WS2 on the morphology and property enhancement of the resulting hybrid nanocomposites was evaluated. The non-isothermal melt–crystallization and melting measurements revealed that the crystallization and melting temperature as well as the crystallinity of PLLA were controlled by the cooling rate and composition. The crystallization behaviour and kinetics were examined by using the Lui model. Moreover, the nucleating effect of IF-WS2 was investigated in terms of Gutzow and Dobreva approaches. It was discovered that the incorporation of increasing IF-WS2 contents led to a progressive acceleration of the crystallization rate of PLLA. The morphology and kinetic data demonstrate the high performance of these novel nanocomposites for industrial applications.

Fullerene-like Nanoparticles of WS2 as a Promising Protection from Erosive Wear of Gun Bore Nozzles

Background: Erosive wear causes increase in the bore diameter of firearms barrels and nozzles. Most responsible factors for this erosion are friction and heat generated during the shot. Protection from erosive wear is very important for gun tube life cycle, and various protection methods are used: adding phlegmatizers in gunpowder composition or applying protective layers on the gun bore inner surface. Objective: In this research, a possibility is examined to protect the surface of a nozzle exposed to gunpowder erosion applying a layer of tungsten disulfide fullerene-like nanoparticles, IF-WS2, known as outstanding solid lubricant of a great mechanical resistance. Methods: Nanoparticles on the nozzle surface before and after the gunfire tests were observed using scanning electron microscopy/energy dispersive X-ray spectroscopy. Gunfire tests were performed on designed erosion device. Temperatures in the defined position near the affected surface were measured with thermocouples and compared for the nozzles with and without nanoprotection, as well as the nozzle mass loss after each round. Results: For the sample with IF-WS2 lower temperatures after firing and lower mass losses were observed. Mass loss after first round was 25.6% lower for the sample with protective nanoparticles layer, and the total mass loss was about 5% lower after five rounds. After the first round the nozzle without IF-WS2 was heated up to a temperature which was for 150.8°C higher than the nozzle with IF-WS2. Conclusion: Protective function of IF-WS2 is the most pronounced for the first round. The observed results encourage its further application in firearms gun bores protection.

Sliding Wear of WC-Ni-Based Self-Lubricating Composites With the Addition of Fullerene-Like WS2 Nanoparticles Against WC-Ni Cermet

Abstract In this work, WC-Ni-based composites with fullerene-like WS2 nanoparticles were fabricated by pulsed electric current sintering. High pressure could assist in low-temperature sintering of the composite. The sliding wear behavior of the composites against WC-Ni counterbodies was also studied in reciprocating ball-on-plate mode. The friction coefficient of the composite was reduced by the incorporated lubricant. Cross-sectional transmission electron microscopy and energy dispersive X-ray elemental mapping further suggest that the friction reduction is attributed to the formation of a mixed tribofilm on the wear tracks supported by the underlying densified matrix. Wear mechanisms are also discussed here.

Uniform, Scalable, High-Temperature Microwave Shock for Nanoparticle Synthesis through Defect Engineering

Summary Here we demonstrate a thermal shock synthesis method triggered by microwave irradiation for the rapid synthesis of nanoparticles on reduced graphene oxide (RGO) substrate. With properly controlled reduction, RGO has high electrical conductivity while maintaining functional groups, leading to an extremely efficient microwave absorption of ∼70%. The high utilization of microwaves results in the ability to raise the temperature to 1,600 K in just 100 ms, which is followed by rapid quenching to room temperature. The defects on the RGO are crucial for achieving this record-high microwave-induced temperature as these defects play a fundamental role in absorbing the radiation as well as the self-quenching mechanism. By loading precursors onto RGO, we can utilize rapid temperature change to synthesize nanoparticles. The nanoparticles are ∼10 nm with uniform distribution. This facile, rapid, and universal synthesis technique has the potential to be employed in large-scale production of nanomaterials and suggests a new direction for nanosynthesis.

Deposition of metal coatings containing fullerene-like MoS2 nanoparticles with reduced friction and wear

Self-lubricating films are of immense importance in various tribological applications. Nanoparticles are often used as the lubricating component in such films. Inorganic fullerene-like (IF) nanoparticles of WS2 have been used in the past for variety of tribological applications including for self-lubricating polymer and metallic films. IF nanoparticles from MoS2 with superior tribological behavior were reported in the past. However, such nanoparticles, which are available in minute amounts, were not applied for self-lubricating coatings in the past. In the current work, inorganic fullerene-like nanoparticles of MoS2 (IF-MoS2) were co-evaporated with titanium (cobalt) on metal substrates. The films were characterized by different techniques and were shown to have good adhesion to the underlying substrate. Furthermore, tribological tests indicated that such coatings exhibit improved friction coefficient (roughly 0.1) and very small wear under relatively high load.

A new method to prepare composite powders customized for high temperature laser sintering

Composites have the potential to enhance the mechanical properties of components fabricated by additive manufacturing; however, the bottleneck is the limited number of polymeric composite powders available for this manufacturing process. This paper describes a generically new method to create composite powders that are suitable for High Temperature Laser Sintering (HT-LS). C-coated Inorganic Fullerene-like WS2 (IF-WS2) nanoparticles and graphene nanoplatelets (GNPs) have been chosen to demonstrate their incorporation into a high performance polymer matrix: Poly Ether Ether Ketone (PEEK). The morphological and physical property investigations have confirmed that the resulting composite powders exhibit the desired particle morphology, size, distribution and flowability for HT-LS applications. Further preliminary sintering results have demonstrated that they are comparable to the currently available commercial grade of PEEK powder HT-LS applications in terms of powder packing properties and flow ability. The new strategy reported here brings in great potential for the additive layer manufacturing of high performance polymeric composite components with improved mechanical and added functionalities by choosing the proper matrix and filler combination.

Al alloy metal matrix composites reinforced by WS2 inorganic nanomaterials

In the present work, advanced aluminium metal matrix composite reinforced by nanomaterials is reported. The materials used for the experiments are AA6061 aluminium alloy, compounded with inorganic nanotubes (INT) and fullerene-like (IF) nanoparticles of WS2. Aluminium metal matrix composite with different weight percentage (0.1–0.5wt%) of the INT and IF were prepared. Both the AA6061 aluminium and the aluminium metal matrix nanocomposites (MMCs) were re-melted by the stirring-casting method. Mechanical properties and microstructure analysis of the nano-MMCs were conducted.The measurements have shown that the hardness, yielding strength, ultimate tensile strength, and ductility were improved by up to 68% compared to the neat alloy for nanoparticles concentrations the range of 0.2wt%. Metallography microstructure analysis showed that increasing the WS2 INT or IF nanoparticles weight percentage in aluminium metal matrix composite, resulted in a more refined grains. The grain size of the composite matrix was reduced by up to 48.4% compared with that of neat AA6061 alloy ingot. Scanning electron microscope (SEM) analysis showed that addition of 0.5wt% of WS2 nanotubes into the Al matrix resulted in INT agglomeration which had deleterious effect on the tensile strength. The composite materials reinforcement mechanism was studied. This analysis showed that the improved mechanical properties of the metal nanocomposites can be predominantly attributed to the differences in thermal expansion coefficients of the WS2 INT (or WS2 IF nanoparticle) and the AA6061 alloy.

(Invited) Investigation of Single WS2 Nanotubes Leads to New Observations and Potential Applications

Multiwall nanotubes and fullerene-like nanoparticles of WS2 are produced in large amounts, offering numerous opportunities for their investigation and future applications. While many studies focus on the preparation and studying the characteristics of bulk matrices incorporating these nanotubes, the investigation of individual nanotubes permits addressing intriguing issues, encompassing their unique optical, electrical and mechanical properties. In this report, the author will dwell on several new studies. FET of WS2 nanotubes with liquid ionic gating demonstrated that the nanotubes become superconducting at low temperatures (5.8 K).1 The magnetoresisitance exhibited strong Little-Parks oscillations under magnetic field parallel to the tube axis, which originates from the interference of the supercurrent along the circumference of the nanotube. The coupling of the supercurrent with the magnetic field in the chiral tubes produces nonreciprocal second harmonic signal. In another study, the electromechanical characteristics of a torsion device based on single nanotube was studied.2 A high frequency resonator with high quality factor was established. The high quality factor of the WS2-based device was attributed to the interlocking of the layers, which minimize the dissipative losses due to reciprocating motion of the nanotubes walls during torsion. The wetting of single WS2 nanotube retracted from a liquid surface was studied experimentally and by detailed computational anlaysis.3 Nanotubes with different diameter and having open or closed tips were studied. It was found that the water does not wet the outer wall of the nanotubes. However, nanotubes with open end of diameter below say 40 nm exhibited strong interaction with the water surface. Careful analyses indicated that strong capillary action leads to the filling of the hollow nanotube core which leads to large dissipated energy during withdrawal of the nanotube. At the end of the talk, the author will briefly deliberate on the commercial applications of fullerene-like WS2 nanoparticles in advanced lubrication and the industrial prospects of nanotubes thereof.

Inorganic Nanotubes and Fullerene-like Nanoparticles at the Crossroads between Solid-State Chemistry and Nanotechnology.

Inorganic nanotubes (NTs) and fullerene-like nanoparticles (NPs) of WS2 were discovered some 25 years ago and are produced now on a commercial scale for various applications. This Perspective provides a brief description of recent progress in this scientific discipline. The conceptual evolution leading to the discovery of these NTs and NPs is briefly discussed. Subsequently, recent progress in the synthesis of such NPs from a variety of inorganic compounds with layered (2D) structure is described. In particular, we discuss the synthesis of NTs from chalcogenide- and oxide-based ternary misfit layered compounds, as well as their structure and different growth mechanisms. Next we deliberate on the mechanical, optical, electrical, and electromechanical properties, which delineate them from their bulk counterparts and also from their graphene-like analogues. Here, different experiments with individual NTs coupled with first-principles and molecular dynamics calculations demonstrate the unique physical nature of these quasi-1D nanostructures. Finally, the various applications of the fullerene-like NPs of WS2 and NTs formed therefrom are deliberated. Foremost among the possibilities are their extensive uses as superior solid lubricants. Combined with their nontoxicity and their facile dispersion, these NTs, with an ultimate strength of about 20 GPa, are likely to find numerous applications in reinforcing polymers, adhesives, textiles, medical devices, metallic alloys, and even concrete. Other potential applications in energy-harvesting and catalysis are discussed in brief.

Flaky and fullerene-like WS2 nanoparticles as tribologic and toughening additives for epoxy

Just like MoS2, WS2 is known for its outstanding tribologic properties. When used as additives, both were found to considerably improve the tribologic behavior of epoxy, i.e., its coefficient of friction and wear resistance. The best improvements were obtained with WS2 or MoS2 nanoparticles, in particular if they had a fullerene-like morphology. Likewise, fullerene-like WS2 nanoparticles were shown to considerably enhance the fracture toughness of epoxy. It was thus hypothesized that the improved wear resistance could be due to the toughening effect rather than due to reduced friction. Our investigations showed that both flaky and fullerene-like WS2 nanoparticles can improve the fracture toughness of certain epoxy systems, while they can embrittle others. The beneficial effect on the epoxy’s wear resistance could not be confirmed either: The coefficient of friction and wear measured in pin-on-disc tests correlated insignificantly with the type or amount of nanoparticles used or the dispersion technique applied. The fact that the fracture toughness did not correlate with the measured wear suggests that the investigated epoxy system wears by adhesion rather than by abrasion. It is thus possible that tribologic additives like WS2 are unsuited for counteracting this wear mechanism. In a nutshell, both the toughening and the wear-reducing effect of flaky and fullerene-like WS2 nanoparticles seem to depend strongly on the particular epoxy system investigated.

Correlation of epoxy material properties with the toughening effect of fullerene-like WS2 nanoparticles

This work deals with the toughening effect of inorganic, fullerene-like WS2 (IF-WS2) nanoparticles (NPs) on epoxy. It has been hypothesized that this toughening effect depends on the epoxy’s cross-link density, its molecular defect fraction or its reference fracture toughness KIc. Seven different epoxy systems were filled with 0.5% laboratory-made IF-WS2 NPs by mass and investigated in order to analyze which material properties are determining the toughening effect. These NPs were similar to commercially available IF-WS2 NPs, but their agglomerates could not be broken up as successfully and they yielded less toughening effect. The cross-link density of the epoxies measured via dynamic-mechanical thermal analysis agreed reasonably well qualitatively with the theoretical estimation. The glass-transition temperature and the compressive yield stress were not affected significantly by the IF-WS2 NPs. The toughening effect of IF-WS2 depended entirely on the curing agent type and quantity. Polyetheramine-cured epoxies behaved differently from the others in their yielding behavior, but also in the IF-WS2 NPs’ toughening effect: While some of the investigated material properties correlate strongly with the toughening effect for polyetheramine-cured epoxies, the correlation for all investigated epoxies is rather low. Thus, none of the mentioned hypotheses could be clearly confirmed.

Tribological behaviour of Al<SUB align="right">2O<SUB align="right">3/inorganic fullerene-like WS2 composite layer sliding against plastic

With the aim of proposing new materials with good properties for dry sliding contact, aluminium oxide layers Al2O3 with inorganic fullerene-like tungsten disulfide IF-WS2 - were obtained and tested. The results of tribological tests, surface topography measurements and SEM analysis are presented. The top layer of the anodised (porous) aluminium-oxide film was loaded with fullerene-like nanoparticles (NP) of WS2 (IF-WS2). Ethanol (method A) and glycol ethylene (method B) were used as dispersive liquids. The tribological properties were investigated by conducting wear tests of Al2O3/IF-WS2 (inorganic fullerene-like tungsten disulfide) coatings against a TG15 plastic (politertrafluotoethylene - graphite) counter-body under pin-on-plate reciprocating motion in dry contact conditions. Non-parametric statistical ANOVA (by Kruskal-Wallis) showed that Al2O3/IF-WS2 layers (method B) had a higher dispersion of the results of both the friction coefficient and the wear intensity of TG15 material while they were in contact. A lower value of wear intensity and a smaller spread of data predispose the Al2O3/IF-WS2 layer produced by method A more to a sliding contact compared to the layer obtained by method B.

Dispersion of fullerene-like WS2 nanoparticles within epoxy and the resulting fracture mechanics

Abstract Fullerene-like WS2 (IF-WS2) nanoparticles (NPs), some with silane-based surface functionalization, were dispersed within epoxy as toughening agents. Dispersion by sonication resulted in a broad and likely bimodal agglomerate size distribution and in thermo-oxidative degradation. In contrast, three-roll milling gave good and well reproducible dispersion quality as measured by dynamic light scattering (DLS). The fracture toughness increased considerably, independently of the functionalization. Atomic-force microscopy indicated that the epoxy's modulus close to the NPs did not differ from the bulk modulus, thus modulus inhomogeneities cannot explain the toughness increase. Fracture surfaces show curved crack lines several hundred nanometers distant from the NPs, which are likely due to secondary cracks induced at the nanoparticle surfaces. The resulting increase in the fracture surface area and possible shear fracture are likely toughening mechanisms.

Preparation of Ultrahigh Molecular Weight Polyethylene/WS2 Composites for Bulletproof Materials and Study on Their Bulletproof Mechanism

Ultrahigh molecular weight polyethylene (UHMWPE)/WS2 nanoparticle fibers were prepared by adding inorganic fullerene-like (IF) WS2 nanoparticles treated by a coupling agent to the precursor solution of UHMWPE. The influence of WS2 nanoparticles on the microstructure and properties of UHMWPE fibers were characterized by the scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and mechanical property measurements. The bulletproof performance of the UHMWPE/WS2 composite was tested by a bullet-shock test, and the bulletproof mechanism of the UHMWPE/WS2 composite was preliminarily studied. The results showed that WS2 nanoparticles could be uniformly dispersed in the UHMWPE fiber. After incorporating of WS2 nanoparticles, the UHMWPE fibers became stiffer and tougher than the pristine ones. In particular, the modulus of the fibers increased from 1203 to 1326 cN/dtex. The introduction of IF-WS2 nanoparticles led to significantly improved bulletproof performance of UHMWPE fibers.

Tribological coatings for complex mechanical elements produced by supersonic cluster beam deposition of metal dichalcogenide nanoparticles

Fullerene-like MoS2 and WS2 nanoparticles can be used as building blocks for the fabrication of fluid and solid lubricants. Metal dichalcogenide films have a very low friction coefficient in vacuum, therefore they have mostly been used as solid lubricants in space and vacuum applications. Unfortunately, their use is significantly hampered by the fact that in the presence of humidity, oxygen and moisture, the low-friction properties of these materials rapidly degrade due to oxidation. The use of closed-cage MoS2 and WS2 nanoparticles may eliminate this problem, although the fabrication of lubricant thin films starting from dichalcogenide nanoparticles is, to date, a difficult task. Here we demonstrate the use of supersonic cluster beam deposition for the coating of complex mechanical elements (angular contact ball bearings) with nanostructured MoS2 and WS2 thin films. We report structural and tribological characterization of the coatings in view of the optimization of tribological performances for aerospace applications.

Decoupling reduction–sulfurization synthesis of inorganic fullerene-like WS2 nanoparticles in a particulately fluidized bed

A novel decoupling reduction–sulfurization process for the synthesis of inorganic fullerene-like (IF) WS2 nanoparticles has been developed in this work. In this strategy, the raw WO3 nanoparticles are firstly reduced by hydrogen in a fluidized bed, followed by sulfurization with H2S in a reducing atmosphere. The diffusion and reaction are the two kinetic factors playing important roles in controlling the structure of WS2. Under diffusion limitation, the porous β-W phase and inordinate WS2 structure are formed, while the α-W phase and IF-WS2 structure are usually obtained in the reaction-limited condition. The particulate fluidization of the reduced WO3 nanoparticles in the agglomerates forms is realized in this decoupling reduction–sulfurization process. The porous β-W nanoparticles and their particulate fluidization enhance the diffusion of H2S, resulting in the completion of sulfurization reaction in short time. This newly developed approach is efficient and cost-effective, and might be extended to the large-scale synthesis of other inorganic fullerene-like metal sulfides.

Inorganic nanotubes and fullerene-like nanoparticles: Synthesis, mechanical properties, and applications

In this paper the synthesis of inorganic nanotubes (INT) and to a lesser extent, inorganic fullerene-like nanoparticles (IF) of WS2, which have been recently scaled-up, is discussed in some detail. Subsequently the mechanical properties of IF/INT are summarized, in reference to their remarkable possibility to reinforce polymer matrices and serve as superior solid lubricants. The effect of adding minute amounts of such nanoparticles to various polymer matrices is reviewed with reference to thermoplastic and thermosetting polymers. Possible different applications of such nanocomposites are also briefly discussed.

Structural effects on mechanical response of MoS2 nanostructures during compression

In recent years, inorganic nanostructures, such as fullerene-like MoS2 and WS2 nanoparticles, have been shown to be promising candidates for friction and wear reduction in tribological applications. However, it has been demonstrated experimentally that the mechanical response of any given inorganic nanostructure varies depending on its individual structural characteristics such as size, shape, and crystallinity. Here, classical molecular dynamics simulations are performed that investigate the mechanical responses of different types of MoS2 nanostructures during uniaxial compression. The results illustrate the dependence of mechanical behavior on nanoparticle structure and, in particular, indicate that the mechanical properties of MoS2 nanostructures vary significantly with changes in the orientation of the MoS2 walls at the interface.

Mechanical and thermal behaviour of isotactic polypropylene reinforced with inorganic fullerene-like WS2 nanoparticles: Effect of filler loading and temperature

The thermal and mechanical behaviour of isotactic polypropylene (iPP) nanocomposites reinforced with different loadings of inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles was investigated. The IF-WS2 noticeably enhanced the polymer stiffness and strength, ascribed to their uniform dispersion, the formation of a large nanoparticle–matrix interface combined with a nucleating effect on iPP crystallization. Their reinforcement effect was more pronounced at high temperatures. However, a drop in ductility and toughness was found at higher IF-WS2 concentrations. The tensile behaviour of the nanocomposites was extremely sensitive to the strain rate and temperature, and their yield strength was properly described by the Eyring's equation. The activation energy increased while the activation volume decreased with increasing nanoparticle loading, indicating a reduction in polymer chain motion. The nanoparticles improved the thermomechanical properties of iPP: raised the glass transition and heat deflection temperatures while decreased the coefficient of thermal expansion. The nanocomposites also displayed superior flame retardancy with longer ignition time and reduced peak heat release rate. Further, a gradual rise in thermal conductivity was found with increasing IF-WS2 loading both in the glassy and rubbery states. The results presented herein highlight the benefits and high potential of using IF-nanoparticles for enhancing the thermomechanical properties of thermoplastic polymers compared to other nanoscale fillers.

Nanoparticle based and sputtered WS2 low-friction coatings — Differences and similarities with respect to friction mechanisms and tribofilm formation

MoS2 and WS2 are widely known intrinsic low-friction materials that have been extensively used and thoroughly investigated in literature. They are commonly produced in the form of sputtered coatings and show extremely low friction coefficients in non-humid environments, but rapidly degrade in humid conditions. Close nested fullerene-like nanoparticles of these materials have been proposed to have better oxidation resistance due to their closed form with the absence of dangling bonds. In the present study, an electrochemically deposited coating consisting of fullerene-like nanoparticles of WS2 embedded in a Ni–P matrix is tested under various loads and humidity conditions and compared with a sputtered WS2 coating with respect to their tribological behavior. The formation of a tribofilm on both surfaces is known to be crucial for the low-friction mechanism of WS2 and the different mechanisms behind this formation for the two types of coatings are investigated. It is shown that despite the completely different transformation processes, the resulting tribofilms are very similar. This is analyzed thoroughly using SEM, AES and TEM. The friction coefficient is known to be lower at higher normal loads for these materials and in the present study the mechanical and chemical responses of the tribofilm to higher normal loads during sliding are investigated. It was observed that the basal planes become aligned more parallel to the surface at higher loads, and that the tribofilm is less oxidized. It is suggested that these mechanisms are connected and are crucial keys to the wear life of these materials.