Synthesis And Investigation Of Inorganic Fullerene-like Sulphide (IF-MS₂, M=W,Mo) Nnanomaterials And Nanocomposites

Since the discovery of C60 molecule and carbon nanotubes, intense interests have been aroused to synthesize inorganic materials with fullerene-like (IF) structures and nanotubes. The investigations have opened a challenging new field in nanotechnology, catalyst, energy and functional composites with a wide range of possible applications. Here, We report a new synthetic route to prepare a series of inorganic fullerene-like metal sulphide IF-MS₂(M=W, Mo)nanomaterials and nanocomposites. Based on the investigations of microstructure, influences of various parameters, growth mechanism and properties, many significative results have been obtained.The M/IF-MS₂ (M=W, Mo) have been synthesized by the sulfidization of metal nanospheres under hydrogen atmosphere, in which the metal nanospheres are synthesize by wire electrical explosion (WEE) method.By adjusting various parameters (temperature, mol ratio of M/S, reaction time, hydrogen atmosphere), W/IF-WS₂ with core-shell structure have been synthesize at 380～500oC and the IF shell is about 10～20 nm. Core-shell Mo/MoS₂ nanospheres with inorganic fullerene-like and actinomorphic shell have been obtained at 400～600oC.The shell thinness is about 4～10 nm. Our preparation route evidently decreases the reaction temperature compared with the popular solid-gas method; XRD results indicate that d(002) in IF-WS₂ exhibit 3.3-1.6%expansion and d(002) in IF-MoS₂ exhibit 4.2-1% expansion along the c axis in accordance with the bulk.The core-shell nanospheres show higher thermal stability than 2H and hollow IF particles. The onset temperature of W/IF-WS₂ nanospheres is 414-424oC and Mo/IF-MoS₂ is about 386oC. In the chapter, we discussed the influences of various parameters (temperature, mol ratio of M/S, reaction time, hydrogen atmosphere) on the morphology in details; a growth mechanism of outside-in diffusion has been discussed: at the beginning, the exterior atoms of the metal nanoparticles reacted with liquid or gaseous sulfur, and then one or two closed MS₂ layer was formed. Subsequently, outer sulfur atoms diffused inwards through the defects of outer layer driven by temperature and concentration gradients, causing the similar reactions to take place continuously. During the process, hydrogen plays an important role of preventing particles from oxidization, activating the surface of the tungsten nanospheres and transmitting sulfur atoms in the form of hydrogen sulfide for easily forming smooth and closed MS₂ layer. The sulfur transmission may involve amorphous MS3. At the beginning, sulfur is superfluous and MS3 is formed. Driven by temperature and concentration gradients, MS3 lose sulfur atom to form MS₂. The lost sulfur react with inner mentl and similar reactions take place. The growth mechanism of actinomorphic Mo/2H-MoS₂ follows the principia of crystal lattice matching. (002) layers of MoS₂ are located in every three (110) layers of metal Mo and all grow paralleling to the (110) plane. When the actinomorphic MoS₂ layers are formed, the layers will become the channels for the sulfur to diffuse into. The actinomorphic morphology is a steady structure because the consistent lattice orientation can effectively eliminate strain in layers.The tribological performance of the oil(HD 80W-90),the IF composite oil (oil+1wt.%IF) and the 2H composite oil(oil+1wt.%2H) were investigated by the high temperature terminal face friction and wear tester under 200-5000 N loads. The results show that the the IF composite oil exhibite lower tribological coefficient, better wear-resistant and higher extreme- pressure. Under higher loads IF composite oil show lower tribological coefficients than that of oil (>700N), 2H composite oil (>880N) and hollow IF composite oil (1200²000N). Under 2000N load, the IF composite oil shows best lubricative behavior with minimal tribological coefficients of 0.019 and maintained a steady lubrication during a long time. Under high load of 5000N, core-shell IF nanospheres exhibit better fluidity and can move everywhere to automatically fill up the sunken surface to maintain balanced friction; The IF composite oil exhibits better wear-resistant than 2H composite oil, especially better than HD oil under different conditions; The IF composite oil show highest extreme- pressure(EP) among the three lubricants. The EP values of 2H composite oil and HD oil are about 4500N and 1700N, respectively, while the EP value of IF composite oil exceeds 5500N; Raman spectroscopy under hydrostatic pressure up to 20.5 GPa indicate that the structure of W/IF-WS₂ is changed at the pressure of 5.4GPa and 13.3 G Pa and the transformation is reversible. This indicates theW/ IF-WS₂ nanosphere has excellent behavior of resisting compression. The above excellent behaviors lie in: the nanospheres with closed shell are relatively steady and avoid bonding with metal atoms of contact pairs to form worn particles; enwrapping the tungsten into IF-WS₂ improves the structural rigidity and preserves the spherical shape unchanged even under higher loads.The amorphous MoS₂.5 nanoparticles have been synthesized by a simple oxidation-reduction reaction in an aqueous solution with the diameter of 30⁵0nm. A series of products with different morphologies, such as MoS₂ nanospheres, inorganic fullerene-like (IF) nanospheres, nanorods and Mo with netlike structure can be obtained by annealing the amorphous MoS₂.5 nanoparticles in vacuum under 400-1200oC. During the thermal treatment, the rich sulfur bonds broke first for recrystallization of MoS₂. Driven by thermal kinetics, the IF nanoparticles were obtained by eliminating the unsaturated bonds to form a closed structure under 500-700oC. The final IF product proves that the dot effects are necessary during the formation of closed IF structure from amorphous materials put forward by Tenne. With increasing temperature quickly, MoS₂ rod, Mo2S3 long plate and Mo with netlike structure can be obtained at 800-1200oC. The samples show stronger absorption in 300⁴70nm region and weaker absorption in 510⁶50nm. With different sample obtained at different annealing temperatures the absorption regions show little difference. The IF layer numbers have obvious effect on the optical properties.The IF-MoS₂ with more layers exhibit stronger optical absorbtion.Glass microballoon (GMB) coated with MoS₂ nanoparticles have been obtained via chemical deposition process (oxidation-reduction) in solution. The thinness of MoS₂ shell can be adjusted by adjusting the concentration of precursors. After annealed at 500oC in hydrogen, GMB/MoS₂ microspheres with different thinness (280⁶60nm) have been obtained. The GMB/MoS₂ microspheres show strong obsorption in 290-515 nm and 616-750nm region and weaker absorbtion in 530 -600nm region.All kinds of synthetic routes provided here are easy to control over all reaction processes and especially to realize large-scale preparation; The IF composite oil obtained by adding W/IF-WS₂ as additive shows excellent lubricant performance. It's very important for the upgrade and replacement of the traditional lubricants; The Mo/2H-MoS₂ and GMB/MoS₂ microsphere are expected to have many advantages in applications as catalysts in chemical industry and photocatalysts.