Papers by Author: Chang Sheng Li

Abstract: TiSe₂ nanobelts/nanoplates have been successfully fabricated through a facile and environment-friendly pressureless sintered process using micro-sized Ti and Se elements as raw materials. The morphology and structure of the as-prepared TiSe₂ products were investigated by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy. The experimental results indicated that the morphology of TiSe₂ products were strongly dependent on the reaction temperature and reaction time. As the reaction temperature was set at 600°C and 800°C, long belts-like and plates-like structures of as-prepared TiSe₂ products could be observed, respectively. However, a mixture of nanobelts and nanoplates could be obtained at a reaction temperature of 700°C. It was also found that the reaction time played a crucial role in obtaining the homogeneous distribution nanoparticles, therefore, reasonable reaction process and formation mechanisms of as-prepared TiSe₂ nanoparticles were proposed. Moreover, the tribological properties of the TiSe₂ nanobelts/nanoplates were investigated. The test results showed that the addition of TiSe₂ nanoparticles could improve the tribological properties of base oil. Furthermore, the friction coefficient of base oil containing TiSe₂ nanoplates was lower and more stable than those of TiSe₂ nanobelts and pure base oil.

Abstract: Nb_1-xTi_xSe₂ (x=0～1) micro/nano-particles have been successfully prepared via solid-state thermal (750°C) reaction between microsized Nb, Ti with Se powders under seal environment in a seal quartz tube and characterization by X-ray diffractometer and scanning electron microscopy. It was found that the morphologies of the as-prepared products changed from microplates to micro-nanoparticles or aggregations composed of layer structure with the doping of Ti. And the amount of regular hexagonal microplates evidently reduced and nanoscaled particles increased with the increase of the contents of Ti dopant within a certain limit (1-20 atwt. %). The tribological properties of the as-prepared products as additives in paraffin were investigated by UMT-2 multispecimen tribotester. By the addition of Nb_1-xTi_xSe₂ micro/nanoparticles in paraffin, the antiwear ability was improved and the friction coefficient was decreased. The paraffin with Nb_1-xTi_xSe₂ micro/nanoparticles showed better tribological properties than that with pure NbSe2. A combination of the molecule-bearing mechanism of sliding friction, and fill in-repair work between the rubbing surfaces can explain the good friction and wear properties of Nb_1-xTi_xSe₂ micro/nanoparticles.

Abstract: The high temperature self-lubrication Ni-Cr-W matrix composites were prepared by powder metallurgy and sintered by hot isostatic pressing (HIP). Atomized Ni-Cr-W powder was mixed with friction components of MoS₂ and Graphite. The mixed powders were cold pressed 450MPa and sintered at 1100°C~1200°C in the presence of argon atmosphere for 1 hour under 180MPa hot isostatic pressing with respect to their application in slide bearing bushing. The tribological properties are investigated on UMT-2 tester in ball-on-disc against alloy steel ball. The results showed that the appropriate addition of MoS₂ show excellent antifriction and wear resistance. And the friction coefficients and wear rates decrease over the wide temperature range of 25°C~600°C compared that of the composites by pressureless sintered method. The results indicated that HIP technology had an obviously strengthening effect on the density, and anti-press strength.

Abstract: In this paper, calcium carbonate particles with unusual morphologies could be successfully synthesized by a precipitation reaction of sodium carbonate with calcium chloride in the presence of a novel polymer-surfactant aggregate consisting of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) and sodium dodecyl sulfonate (SDS). The as-prepared products were characterized with scanning electron microscopy and X-ray diffraction. The results showed that the SDS concentrations, the molar ratio of CO₃^2- to Ca²⁺ (R), and the reactive temperature in the mixed system turned out to be important parameters for control of morphologies of the as-prepared CaCO₃ particles. Various unusual crystal morphologies, such as hollow microsphere, cubic, and rombehedra, etc., can be obtained depending on the experimental conditions. Moreover, the formation mechanisms of calcium carbonate with different morphologies were discussed.

Abstract: Face centered cubic Ti3Si nanoparticles were synthesized by mechanical alloying process and the structural and compositional evolutions during the mechanical alloying process were investigated by X-ray diffraction and High Resolution Transmission Electron Microscopy. The results showed that the lattice parameter ratio c/a and the unit cell volume of Ti(Si) were found to decrease with increasing milling time, indicating that the shrinkage of Ti lattice was caused by diffusion of Si atoms into Ti. After milling 51h, amorphous compounds were obtained by alloying Ti and Si powders, and the following mechanical alloying process crystallized the amorphous alloy to crystalline Ti3Si nanoparticles. These nanoparticles were predominantly crystalline with traces of the remnant amorphous phase.

Abstract: large-scale and elegant one-dimension tubular nanostructure TaS2, have been generated successfully employing solid-phase reaction growth with tantalum and sulfur powders. Detailed experimental procedures, and the characterization of associated product, have been evaluated using transmission electron microscopy (TEM) and other techniques. The results show that the reaction yielded a lot of one dimension nanostructures of TaS2 with average diameter of one hundred nanometers and length of several micrometers (or several ten micrometers). Moreover, effect of TaS2 nanostructure, as additive in commercial lubricating oil T40, was initially measured by UMT Multi-specimen Test System (UMT-2). The results show, as additive, antiwear and bearing weight ability of 1-D TaS2 nanostructure, excelled ordinary lubricating oil at atmosphere.

Abstract: The metal elements, such as Fe, Mn, Co, Ni, Ni-Mn, Co-Mn and Fe-Mn, were mixed and milled with pre-cross-linked polysilazane Ceraset® and subsequent pyrolysis. The metals act as active fillers to increase the density of composite. The phases and microstructures of metal/ceramic composites were studied using XRD, SEM and EDS, and the magnetic property was measured with Magnetic Property Measurement System at –196oC. The results show that there are two main domains in composites, one is metal-rich domain and another is metal-poor domain. The density of composite is larger than that of polymer-derived SiCN ceramic, but the hardness varies little. The compound generated by the reaction between metal and matrix has great effect on the magnetic properties of composites, which are filled with different metals.

Abstract: It is well known that metal dichalcogenides MS2 (M=Mo, W, Nb, Ta, TiS, Zr ,Hf, S=S, Se) have lamellar structure, the bonds of adjacent lamellae are weak van der Waals interactions and inter-lamellar are strong covalent interactions. The structures make adjacent lamellae easy to slip and it shows low friction coefficient during friction process. MS2 are often used as solid lubricants in high/low temperature, heave load and vacuum, in which oil is failure. WS2 has better high temperature properties than MoS2, although little natural WS2 mineral has been deposited, and people must synthesize it by chemical means, so its price is nearly 5 times expensive than that of MoS2. Until now little study is made comparing with MoS2. Furthermore the research papers about tribological behavior of NbS2, TaS2, TiS2, ZrS2, HfS2 are not seen. In this study the thermal decomposition method is used to produce fullerene-like MS2 nanotubes. The morphology, microstructure and tribological behavior of MS2 nanotubes are investigated by means of SEM, TEM, XRD and AFM. The results show that the diameter of MoS2, WS2 and NbS2 nanotube is less than 100nm, and the length is more than 2μm. The MoS2, WS2 nanotube has lower friction coefficient than MoS2 powder tested by AFM using Si3N4 probe. Similar results are also found for NbS2 nanotube. The macroscopic friction test for pin on disc tester shows nearly the same results. TEM image shows that MS2 nanotubes have rolling debris between two antagonist surfaces, and MoS2 powder only has flattened debris. It may be the fullerene structure brings the chemical stability and lead low friction.

Abstract: MS2(M=Mo, W, S=S, Se) are often used as solid lubricants in high/low temperature, high load, vacuum, in which oil lubrication is failed. Although WS2 is much more expensive than MoS2, it has better high temperature properties than MoS2. Thermal decomposition method is used to produce fullerence-like WS2 nanotube on Al2O3 template using (NH4)2WS4. The fabricated WS2 nanotube’s diameter is about 100nm and its length is longer than 2µm.The morphology, microstructure and tribological behavior of WS2 nanotube are investigated by means of SEM, TEM, XRD and AFM. The friction force between Si3N4 probe of AFM with WS2 nanotube is lower than that with MoS2 powder. Similar results are also found in pin-disc tester by GCr15 pin and lubricants coating disc. The results of HETEM show that WS2 nanotube has rolling debris between the two antagonist surfaces, and MoS2 powder only has flattened debris. It may be the fullerence structure brings the chemical stability and leads to low friction.