Preparation And Properties Of SiC, MoS₂ Nanomaterial And Their Nanocomposite Material

SiC, one of the third-generation semiconductors, is a wide-band-gap material with high breakdown field, high thermal conductivity, high carrier concentration and drift velocity. It can be used to fabricate electronic devices which are durable at high temperature, frequency,power and strong corrosion, radiation. MoS2 is a narrow-band-gap material in the application of solid lubricant, electronic devices, catalyst, hydrogen storage, shock absorption, photochromic-film and electron probe. The two semiconductors have attracted considerable interests and been under extensive research. With the development of nanoscience, the special physical and chemical properties varied from bulk material aroused the interesting in nano-semiconductors. The subjects of nano-SiC, nano-MoS2 and the relevant composite material in nanosize are the hotspots at present. And researches on the synthesis and properties of them are prosective and significant.In this article, nanosized SiC powders were prepared by electric pulse discharged in liquid using two organic precursors repectively. The method can operate easily, produce continuously and the particle-size distribution of obtained SiC nanoparticles is narrow. X-ray diffraction (XRD), field emission scanning electronic microscopy (FESEM) and transmission electron microscope (TEM) were taken to investigate the crystal structure, particle-size and morphology of the samples. XRD results showed that the main composition of the product wasβ-SiC, and a small quantity of 6H-SiC was also detected. The Si and C during the strong pulse discharge process exited in the SiC nanoparticles as the Si-rich region and C-rich region respectively. The particle-size distribution ofβ-SiC nanoparticles prepared from (CH3)3Si-O-[-Si-(CH3)2-O-]-Si(CH3)3 (DSO-SiC) was 10-60nm with the average particle-size of 22nm;? The particle-size distribution ofβ-SiC nanoparticles prepared from (CH3)3Si-Si(CH3)3 (HD-SiC) was 8-18nm with the average particle-size of 12nm. The forming mechanism of SiC nanoparticles can be explained as follows: the high temperature and high pressure created by strong pulse discharged decomposed the organic liquid. Then atoms (or ions) combined together to form Si and SiC etc. Because the environment of high temperature and pressure disappeared soon after the discharge, the formed SiC nanoparticles had no enough time to grow large.β-SiC was the stable phase at low temperature, so it became the the main composition of the product. Other crystal structures of SiC may come from the stack faults during the forming process ofβ-SiC. The difference on particle-size and uniformity between DSO and HD particles lies on three aspects: 1) Hexamethyl disilane (CH3)3-Si-Si-(CH3)3 is the material with short chains, while dimethyl silicone oil (CH3)3Si-O-[-Si-(CH3)2O-]n-Si(CH3)3 with long chains. High energy could not break all the bonds of the precursors and DSO (long chains) was broken into atomic clusters with different chain length. Then these atomic clusters formedβ-SiC nano-crystallites. So the particles vary from each other and some larger particles were observed. 2) The viscidity of the two precursors is different, which may lead to the difference of the temperature decrease rate. It makes the contrast of particle-sizes between two precursors evident; 3) High viscidity of DSO can not cause the formed ?β-SiC nano-crystallites to be dispersed well in the residual liquid. As a result,β-SiC nano-crystallites are preferred to assemble together. And next spark will made these assembledβ-SiC nano-crystallites grown into bigger ones.Photoluminescence (PL) of nano-SiC were reported by many researchers. To investigate the photoluminescence properties of HD-SiC powder, the air-annealed and vacuum-annealed were both adopted. 400nm PL peak was observed from the vacuum-annealed sample. The intensity of PL peak can be enhanced by increasing the annealing temperature. The intensity of 400nm PL peak was also increasing with the annealing temperature in air-annealing, but it fell after the temperature reached 800℃. In addition, one new PL peak appeared at 470nm in air-annealing. With temperature increasing, the intensity of it strengthened and reached the maximum at 1000℃. Comparing the PL spectra obtained at the two anneal conditions, the possible origin of PL bands were given.Nano-sized SiC-FeSi composite particles were prepared by electric pulse discharged in liquid using (CH3)3-Si-Si-(CH3)3 as the precursor. TEM gave the particle-size and morphology of the two samples. The average size of composite particles made from (CH3)3-Si-Si-(CH3)3 is ca.10nm. Then the SiC-FeSi composite particles prepared from (CH3)3-Si-Si-(CH3)3 were annealed in vacuum. We studied the magnetic properties of the annealed samples. XRD data showed that the particle-sizes of FeSi increased with the annealing temperature. The critical size of superparamagnetic transformation is ca.12.2nm determined by XRD and hysteresis loop.MoO3 nanorods were synthesized by the sonochemical precipitation method through reaction of (NH4)6Mo7O24·4H2O and HCl. The products were characterized by XRD, Raman, SEM and TEM. XRD showed that the precipitation is h-MoO3. When it was annealed in air at 400℃for 2h, the o-MoO3 was obtained. Raman spectra also comfirmed the component of the powder and prove its better crystalline. The particle-size and morphology are given by SEM and TEM. The particles synthesized from 0.1mol/L (NH4)6Mo7O24·4H2O solution are spherical -like with the uniform spokewise nanorods, while the ones synthesized from 0.05mol/L were aggregate nanorods with irregular size. With (NH4)6Mo7O24·4H2O as precursor, MoO3 nanospheres were prepared by chemical precipitation with the assistance of ultrasonic. Size distribution of highly dispersed MoO3 nanospheres was 100-200nm (0.08mol/L (NH4)6Mo7O24·4H2O) and 25-75nm (0.05mol/L), respectively, which is appropriate for the synthesis of IF-MoS2.MoO3 nanospheres and nanorods, which were prepared from two concentration of (NH4)6Mo7O24·4H2O mentioned above, mixed with the S powder dissolved in the mixture of CS2 and CCl4 (volume ration 1︰1). MoS2 could be obtained when the MoO3-S composite was treated under H2 at different temperature. Results from XRD indicated that IF-MoS2 was not formed until temperature was above 600℃. When the MoO3-S composite was annealed for 2h at the temperature ranging from 600℃to 850℃, IF-MoS2 and MoO2 were observed in the samples. MoO2 disappeared and 2H-MoS2 appeared after the sample was annealed at 850℃for 6h. TEM gave the morphology and particle-size of the MoS2 particles annealed at 800℃. The surface of IF-MoS2 nanoparticles synthesized from 0.08mol/L (NH4)6Mo7O24·4H2O looked smooth and spherical-like, while the particles synthesized from 0.05 mol/L (NH4)6Mo7O24·4H2O were sulfured completely with the hollow cage structure. The reasonable explaination was presented on the present formation mechanisms of IF-MoS2 combined the morphology of our as-obtained IF-MoS2. Afterwards, a series of experiments were conduced to test the tribological properties of the as-obtained IF-MoS2 nanoparticles as the oil additives. Results showed that the composite oil possessed the excellent lubricating performance.The SiC-MoS2 composite nanoparticles were synthesized using 3-mercapto- propyltrimethoxysilane as the coupling agent. The composited nanoparticles aggregated heavily and only a small quantity of them dispersed better. The particle-size distribution of them is 15-50nm with the continuous and uniform shell of 5-20nm.