Papers by Author: Shi Gen Zhu

Abstract: This study prepared a Graphene/TiO₂(G/TiO₂) thin films by using a sol–gel method The structure and morphology of the materials were characterized using X-ray diffraction (XRD), atomic force microscope (AFM) and thermo gravimetric- differential scanning calorimeter techniques (TG/DTG).AFM images showed that the G/TiO₂ film is typically amorphous hot-treated at 300°C. When the temperature was increased to 500 °C, G/TiO₂ thin films are all crystalline. The XRD results showed that G/TiO₂ thin films contained crystalline phase of anatase after calcining at 500°C. TG/DTG measurement showed that the change of the crystal phase did not occur in gel until to 500°C.

Abstract: Various rare earth (La³⁺) doped titaniumdioxide(TiO₂) thin films (La³⁺-doped TiO₂) have been successfully prepared on a glass substrate by a sol–gel dip coating route using titanium tetraisopropoxide and lanthanum chloride as the initial materials. After the La³⁺-doped TiO₂ thin films were calcined at 500°C for 1h, the effect of La³⁺-doping on the properties of films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric- differential scanning calorimeter techniques (TG/DTG). The XRD results showed that all La³⁺-doped TiO₂ thin films contained only a single crystalline phase of anatase TiO₂ after calcining at 500°C for 1h. Moreover, the XRD results also revealed that the crystallinity and crystalline size decreased with increased La³⁺-doping. SEM micrographs showed that all La³⁺- doped TiO₂ thin films have smooth surfaces containing granular nanocrystallines and are without cracks. TG/DTG measurement showed that there was a significant weight loss of the TiO₂ precursor calcined in the temperature range from ambient to 660 °C, which was due to the volatilizing of water and organic and the phase transformation.

Abstract: Rare earth doped titaniumdioxide (TiO₂) thin films (rare earth-doped TiO₂) have been successfully prepared on a glass substrate by a sol–gel route. After the rare earth-doped TiO₂ thin films were calcined at 773K for 1h, the effect of rare earth-doping on the properties were investigated using X-ray diffraction (XRD), scanning electronmicroscopy (SEM), ultraviolet–visible spectroscopy and thermogravimetric techniques (TG/DTG). The XRD results showed that rare earth-doped TiO₂ thin films contained only a single crystalline phase of anatase TiO₂ after calcining at 773K for 1h. SEM micrographs showed that rare earth-doped TiO₂ thin films have smooth surfaces containing granular nanocrystallines and are without cracks. The UV–vis absorption spectra showed that the absorption of the rare earth-doped TiO₂ thin films has a red-shift. From ambient to 1273K, it is about 12% of mass loss because of the volatilizing of water and organic and the phase transformation.

Abstract: The effects of doping with VC (grain growth inhibitors) on the microstructural characteristics and mechanical properties of WC-Al₂O₃ compacts prepared by hot-pressing sintering were investigated. VC suppressed the rate of densification during isothermal sintering, but eventually increased the sintered density with extended holding time. Microstructure observation results revealed that the grain growth of WC was significantly retarded with the addition of VC. Meanwhile, the activation energy for grain growth during isothermal sintering increased from 380.75 to 446.68 kJ/mol, which is consistent with the inhibition mechanism of VC.

Abstract: The method of electric contact heating for nodular cast iron was based on the application of the contact resistance heating between the electrode and work piece to change the characteristics of the surface. The effects of processing parameters on the width and depth of modified layer were analyzed, and among the experimental factors, the electric current had the largest effect than the others. Optical microscope was used to describe the microstructure transformation and identify the phases in the modified layer. Results showed that a cementite-martensite microstructure in the melted zone and a martensite-ledeburite-ferrite microstructure with graphite nodules in the hardened zone have been observed; especially two typical hardened shells around graphite are achieved in the hardened zone, which are ledebruite-martensite shell and single martensite shell around graphite. The effects of the changed microstructures were additionally verified by microhardness measurements in the modified zone. The microhardness of the nodular cast iron was found to be significantly increased after electric contact heating.

Abstract: The master sintering curve (MSC) of nanocomposite WC-MgO was constructed based on the combined-stage sintering model. Nano-sized WC-4.3wt%MgO powder with average particle size of 35nm was synthesized by high-energy ball milling, and then uniaxially pressed at the pressure of 500MPa to fabricate green compacts. The shrinkage response of the compacts, used to construct the master sintering curve, were studied by dilatometric runs at two constant heating rates of 5°C/min and 10°C/min up to 1900°C. Using the estimated activation energy, the master sintering curves were established and compared to acquire an optimum value (Q=361.8 kJ/mol). The obtained MSC was validated by non-isothermal sintering with the identical green compacts. The results demonstrate that the MSC can be applied successfully to predict and control shrinkage level and final density during heating up regardless of heating rates.

Abstract: The distinguished characteristic of casting process of natural yellow clay-bonded green sand is a strippable sintering layer formed at the interface of casting and mould. Hot shake-out can be realized because this sintering layer can firmly attach to the casting surfaces to protect castings at elevated temperature. Better surface quality of castings is achieved after the sintering layer easily shed from the casting surface at room temperature. In this study, a series of tests were carried out to reveal the characteristic of this sintering layer. First, thermal gravimetric/differential thermal analysis (TG/DTA) method was used for detailed analysis the thermal property of natural yellow clay-bonded green sand. And, X-ray diffraction (XRD) analysis was employed to define the phase composition at variable temperatures. Then, sintering experiments were carried out on mixtures of natural yellow clay-bonded sand with iron powder or iron oxides under different conditions. Finally, the mechanical performances of sinter layer of natural yellow clay-bonded sand at elevated and room temperatures were investigated. The result revealed that natural yellow clay-bonded green sand is a kind of low grade molding sand, and iron oxides participate in the forming of sintering layer. The sintering layer of natural yellow clay-bonded sand were proved both excellent plastic at elevated temperature and brittle at room temperature, which coincides with its behavior in the casting process.

Abstract: In this work, the effects of mechanical milling on the extent of reduction were investigated to give an overview of potential improvements in the preparation of WC. A mixture of graphite and tungsten oxide (WO3) was mechanically milled together for 10 h. The as-milled powder and un-milled powder were investigated by thermal analysis, isothermal treatment, and X-ray diffraction to determine the effect of milling on the carbothermal reduction of WO3 to tungsten carbide (WC). The as-milled powder underwent a rapid reduction reaction at about 150°C lower than the un-milled powder. The reduction sequence to WC was illustrated to differ for the two powders. The milled powder showed complete reduction to WC in 1 h at 1215°C whereas the un-milled powder was incompletely reduced. Finally, WC powder was readily achieved by carbothermic reduction of mechanical activated WO3 and graphite, leaving its grains nano-sized.