Using a new quartz-made reactor, large amounts of fullerene-like (IF) MoS2 nanoparticles were synthesized by reacting MoO3 vapor with H2S in a reducing atmosphere. The nanoparticles were found to be of high crystalline order; with an average size of 70 nm and consist of more than 30 closed shells. Extensive tribological testing of the nanoparticles in two types of synthetic oils- poly-alpha olefins (PAO)- was carried out and compared to that of bulk (2H platelets) MoS2 and IF-WS2. These tests indicated that under high pressure and relatively low humidity, the IF-MoS2 exhibited a friction coefficient as low as 0.03 and the smallest wear rate of the measured systems. However, its performance was found to be lower in comparison to IF-WS2 after 2500 cycles, due probably to its inferior chemical stability. This study indicates that the tribological performance of the IF nanoparticles depends strongly on their crystalline order and size.

Fullerene-like MoS 2 Nanoparticles and Their Tribological Behavior

The excellent shock-absorbing performance of WS2 and MoS2 nanoparticles with inorganic fullerene-like structures (IFs) under very high shock wave pressures of 25 GPa is described. The combined techniques of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, thermal analysis, and transmission electron microscopy have been used to evaluate the diverse, intriguing features of shock recovered IFs, of interest for their tribological applications, thereby allowing improved understanding of their antishock behavior and structure-property relationships. Two possible failure mechanisms are proposed and discussed. The supershock-absorbing ability of the IF-WS2 enables them to survive pressures up to 25 GPa accompanied with concurrent temperatures of up to 1000 degrees C without any significant structural degradation or phase change making them probably the strongest cage molecules now known.

Shock-absorbing and failure mechanisms of WS2 and MoS2 nanoparticles with fullerene-like structures under shock wave pressure.

An integrated WS2@CMK-3 nanocomposite has been prepared by a one-step hydrothermal method and then used as the anode material for lithium-ion and sodium-ion batteries. Ultrathin WS2 nanosheets have been successfully embedded into the ordered mesoporous carbon (CMK-3) framework. Owing to the few-layered nanostructure of WS2, as well as the high electronic conductivity and the volume confinement effect of CMK-3, the material shows larger discharge capacity, better rate capability, and improved cycle stability than pristine WS2. When tested in lithium-ion batteries, the material delivers a reversible capacity of 720 mA h g−1 after 100 cycles at a current density of 100 mA g−1. A large discharge capacity of 307 mA h g−1 is obtained at a current density of 2 A g−1. When used in sodium-ion batteries, the material exhibits a capacity of 333 mA h g−1 at 100 mA g−1 without capacity fading after 70 cycles. A discharge capacity of 230 mA h g−1 is obtained at 2 A g−1. This excellent performance demonstrates that the WS2@CMK-3 nanocomposite has great potential as a high-performance anode material for next-generation rechargeable batteries.

Improved Lithium‐Ion and Sodium‐Ion Storage Properties from Few‐Layered WS2 Nanosheets Embedded in a Mesoporous CMK‐3 Matrix

Inorganic fullerene-like (IF) MoS2 and WS2 nanoparticles were found to be good friction modifiers and anti-wear additives when dispersed in a lubricant. Their tribological performance seems to be related to the structure, size, and shape of these nanomaterials. The present study describes the tribological properties of a new inorganic fullerene IF-Mo
 x
 W1−x
 S2 containing both molybdenum and tungsten disulfide under boundary lubrication. Mo
 x
 W1−x
 S2 amorphous inorganic fullerene nanostructures were synthesized by means of MOCVD using an induction furnace setup. The average diameters range from 25 to 45 nm. Upon variation of the amounts of precursors and S, various solid solutions of IF-Mo
 x
 W1−x
 S2 were obtained. In addition, a morphological, chemical, and structural analysis of the samples was performed using high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). Friction experiments were carried out with a ball-on-flat contact using an environmental tribometer. The results show interesting friction reducing and wear properties of these nanomaterials. The change in the molecule stoichiometry, which led to a variation of particles size but also to a variation of the crystallinity of the particles, affects the tribological performance.

Synthesis and Tribological Performance of Novel MoxW1−xS2 (0 ≤ x ≤ 1) Inorganic Fullerenes

The growing availability of nanotubes and the increased knowledge about their loading in polymers have prompted the incorporation of nanotubes in cementitious matrices. The effects of loading straight tungsten di-sulfide nanotubes (WS2NT) or waved carbon nanotubes (CNT) in cementitious matrices was explored. Their inclusion in these composites at exceptionally low concentrations (0.063 vol% and 0.15 vol% for WS2NT and CNT, respectively) enhanced the composite’s mechanical properties, including compressive and flexural strengths (25–38%). Thermal analysis and electron microscopy indicated that nanotube incorporation in cementitious matrices also accelerated hydration reaction kinetics. It was shown that straight WS2NTs bridged pores and cracks more effectively than the waved CNTs, which resist crack propagation via an anchoring mechanism. A comparison to representative cement nanocomposite systems shows that nanotubes (aspect ratio≫1), offer better reinforcement efficiencies than particulate nanomaterials, yielding high mechanical properties enhancement at low concentration.

The critical role of nanotube shape in cement composites

Two-dimensional compounds (like graphite or MoS2) are capable of bending their layers and forming a closed cage structure, which is denoted the inorganic-fullerene-like (IF) phase in the case of inorganic materials. Simultaneous thermal analysis (TG-DTA) of a number of nanomaterials (IF-MoS2, IF-NbS2, and IF-WS2) and their bulk counterparts was carried out in inert and oxidizing environments at various heating rates. Oxidation occurred at 295 °C for the smallest particle size (100 nm) but the oxidation temperature increased to 440 °C for the largest particle size (3 μm). At low heating rates, the oxidation occurred through sulfates and lower oxides, while at high heating rates mostly one-step oxidation to the highest oxide was observed. The stability in N2 atmosphere depended on the criterion of stability chosen: Choosing the onset temperatures of the decomposition step (between 1200 °C and 1390 °C), the stability decreased in the order WS2
				≈ MoS2 > NbS2; and the bulk material reacted mostly at higher temperatures compared to the IF-phase. Choosing the extent of decomposition as a measure of stability, no specific trend could be found. Surprisingly, a single IF-WS2 sample was found to be most stable by both methods.This study shows that IF nanoparticles are comparably (though somewhat less) stable against oxidation as well as decomposition than the bulk material exhibiting the usual plate-like structure.

How stable are inorganic fullerene-like particles? Thermal analysis (STA) of inorganic fullerene-like NbS2, MoS2, and WS2 in oxidizing and inert atmospheres in comparison with the bulk material

How Stable Are Inorganic Fullerene-Like Particles? Thermal Analysis (STA) of Inorganic Fullerene-Like NbS2, MoS2, and WS2 in Oxidizing and Inert Atmospheres in Comparison with the Bulk Material.

Christoph Schuffenhauer

Papers

How stable are inorganic fullerene-like particles? Thermal analysis (STA) of inorganic fullerene-like NbS2, MoS2, and WS2 in oxidizing and inert atmospheres in comparison with the bulk material

How Stable Are Inorganic Fullerene-Like Particles? Thermal Analysis (STA) of Inorganic Fullerene-Like NbS2, MoS2, and WS2 in Oxidizing and Inert Atmospheres in Comparison with the Bulk Material.