Papers by Author: Xiao Nong Cheng

Abstract: Recently, noble metal nanoparticles (Au or Ag NPs) decorated graphene (GE) sheets are used as good surface-enhanced Raman scattering (SERS) substrates for detection of molecules. Ultrathin GE film covered by Ag NPs has been designed for the SERS substrate in this paper. The films were prepared firstly by dip-coating method with graphene oxide (GO) and AgNO₃ or Ag NPs colloid as raw materials and secondly reduced by thermal annealing at 600 °C in H₂/Ar atmosphere. The structure and SERS activity of the obtained films have been investigated in detail. Results indicated that Ag NPs can be decorated on graphene sheets through the electrostatic adsorption between the GO sheets and positively charged Ag⁺ or Ag NPs. Compared with the film obtained with AgNO₃, Ag NPs/GE film prepared with Ag NPs colloid showed the higher SERS sensitivity with rhodamine 6G (R6G) as the probing molecules, the enhanced factor for 1×10^-5 M of R6G adsorbed on the surface of Ag NPs/GE substrate is about 9.1×10⁷.

Abstract: Intergranular corrosion behavior of 00Cr12 ferritic stainless steels with different amounts cerium was evaluated. For this evaluation, electrochemical measurements - polarization curves - were obtained for tested materials, and optical microscope was used to observe corrosive microstructure. Experimental results shows: cerium reduces grain sizes and improves intergranular corrosion resistance of test materials. Through mechanism analysis: cerium reduces grain sizes, increases grain boundary density, therefore might improve distribution aspects of carbides and nitrides, chromium depletion situation near grain boundary would be improved, this work worth further study.

Abstract: To synthesize morphology- controlled nano- copper with excellent lubrication properties as lubricant’s additive, chemical reduction synthesis method was used coalescing in situ via liquid paraffin as resolvent and modification with polyethylene glycol (PEG-2000). The as- prepared Cu nanopieces with 35.59 nm average length and 21.03 nm average width were characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The tribological behavior of Mobil 1 5W-30 lubricating oil with nano- Cu were measured by ball- on- disk UMT- Ⅱ tribometer and analyzed by SEM and EDS. It is found that the tribological performance of Mobil 1 5W- 30 with nano- Cu is improved, and the optimization addition is 0.4% (Cu wt) with the lowest friction coefficient.

Abstract: The anti-perovskite structured Mn₃XN(X=Cu,Al,Ag,Zn,Ga,Sn,In) have wide perspective and practicability with unique advantages compared with other materials as a new negative thermal expansion (NTE) material. Because of its simple preparation and unique properties of NTE, this kind of compounds aroused scientists’ attention. The metallic nitrides Mn₃Zn_1-xSn_xN (x=0.1, 0.2, 0.3, 0.4, 0.5) were prepared by solid-state sintering. The anti-perovskite compound Mn₃Zn_1-xSn_xN has a cubic crystal structure with space group Pm3m. It shows that Zn element is partial replaced by Sn element. The Sn doping in Mn₃Zn_1-xSn_xN compound can cause the thermal expansion behavior of the compound to change between positive and negative by analyzing the curve of thermal expansivity with the temperature. Mn₃Zn_0.7Sn_0.3N shows a very strong NTE. Its negative thermal expansion coefficients were -4.39×10^-4/K from 345.4 °C to 476.2 °C. In addition, the variation of the thermal expansion curve for Mn₃Zn_0.8Sn_0.2N is almost negligible with the increasing of temperature to 600 °C, exhibiting nearly zero thermal expansion behavior. Therefore, the thermal expansion of Mn₃Zn_1-xSn_xN could be tuned via different contents of Sn in Mn₃ZnN.

Abstract: A porous biomorphic woodceramic was prepared from bagasse powders infiltrated with the epoxy resin followed by sintering in vacuum. The microstructures and chemical structures of the woodceramics were studied by SEM and FTIR, respectively. The effect of the sintering temperature and content of bagasse on the carbon yield ratio, volume shrinkage ratio, and volume electrical resistivity of the woodceramics were studied. Experimental results show that the pores in woodceramics present the irregular distribution but the main structural features of the tracheidal cell structures are retained. The woodceramic is a carbon material containing C–O–C, C=C, C=O and C–H bonds. The carbon yield ratio of the woodceramics decreases with the increase of the content of bagasse. While the volume shrinkage ratio and volume electrical resistivity increase with the increase of the content of bagasse.

Abstract: Equal channel angular pressing (ECAP) of a quenched commercial pure titanium (CP-Ti) (grade 2) has been successfully performed at liquid nitrogen temperature with an imposed equivalent strain of about ∼0.5, and its microstructures, tensile properties and dislocation strengthening were investigated. High-resolution transmission electron microscopy (HRTEM) shows that the ECAPed CP-Ti presented a microstructure containing lattice distortions, dislocations, stacking defects and deformation twins. Tensile tests indicate that the ECAPed CP-Ti had yield strength of ~700 MPa (40 % higher than that of the unECAPed CP-Ti) and a high level of tensile ductility (~28%). X-ray diffractometer (XRD) data indicate that the ECAP processing not only broaden the XRD peaks significantly but also decreased texture considerably. The theoretical analysis by using Taylor equation based on the coherent diffraction domain size and the lattice micro-strain obtained from XRD line broadening analysis illustrates that ECAP-resulted dislocation made a strengthening contribution of about ~35.1 %.

Abstract: The CaCu_3-xZn_xTi₄O₁₂ (CCZTO) (x=0, 0.06, 0.1, 0.2) ceramics were prepared by Sol–gel method. The XRD pattern shows that crystal structure of the sample with no Zn is basically single-phase. The SEM results indicate that the samples have porous structures and the gain size decreases with the content of Zn increasing. The dielectric properties of CCZTO were analyzed by Agilent 4294A. The experimental results show that the dielectric constants are less than that in other papers reported obviously because of their mesoporous structures. With the little doping amount(x=0.06, 0.1), a sharp decrease happened in the dielectric constant (ε_r). The higher ε_r was found when x=0.2, but its dielectric loss (D) had greatly increased and frequency stability of dielectric property became worse. The uniformity of gains was put forward to explain the results which showed great impact on the dielectric constant.

Abstract: Temperature field during laser surface melting the pure Al was numerically simulated by the Laplace integral transform technique using the MathCAD software. The influences of laser power densities on the surface temperature of the pure Al were analyzed. Mathematical expressions for the temperature distribution of the heating and cooling process on the pure Al surface were obtained.

Abstract: Negative thermal expansion (NTE) material ZrWMoO8 was prepared by hydrothermal method. The phase structure and morphology of the obtained precursor and final product were examined by XRD and SEM, respectively. To study its negative thermal expansion property, two methods were utilized. One is based on the in-situ XRD results and the thermal expansion coefficient (CTE) was calculated by the cell parameters obtained at different temperatures. Another is based on the thermo-mechanical analysis (TMA) and the CTE was calculated by the length of ZrWMoO8 bar at different temperatures. The differences between these two methods were also discussed.

Abstract: TiO2 thin film containing SrFe12O19 powders on the surface of 316L stainless steel and NiTi alloy was prepared through sol-gel method and micro-magnetic field was established by the magnetization process applied on the coating. The coating film was characterized by x-ray diffraction (XRD) and the surface morphology of the coating was observed by scanning electron microscope (SEM). This blood compatibility thin film was evaluated by dynamic cruor time of blood test.The results show that dynamic cruor time of blood is prolonged by the micro-magnetic field of the thin film, indicating improved blood compatibility.