Er Jun Guo

Synthesis of ZnO nanowire arrays/3D graphene foam and application for determination of levodopa in the presence of uric acid

Three-dimensional (3D) graphene foam (GF) was prepared by chemical vapor deposition (CVD) using nickel foam as the template. ZnO nanowire arrays (ZnO NWAs) were vertically grown on the 3D GF by hydrothermal synthesis to prepare ZnO NWAs/GF. This hybrid combines the properties of ZnO NWAs and 3D GF, which has favorable electrocatalysis and outstanding electrical conductivity. The vertically aligned ZnO NWAs grown on the GF enlarged the electroactive surface area, which was investigated from the Fe(CN)63-4+ redox kinetic study. The ZnO NWAs/GF was used as an electrochemical electrode for the determination of Levodopa (LD) in the presence of uric acid (UA). The electrochemical responses of the ZnO NWAs/GF electrode were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results show that the sensitivity of the electrode for LD is 3.15μAμM-1 in the concentration range of 0.05-20μM and the measured detection limit of the electrode for LD is 50nM. The electrode also shows good selectivity, reproducibility and stability. The proposed electrode is succsefully used to determine LD in human plasma samples and it is potential for use in clinical research.

Numerical simulation of macrosegregation with grain motion during solidification of Mg-4wt.%Y alloy

A two-phase solidification model was used that incorporates the descriptions of natural convection, heat transfer, solute transport and solid movement at macroscopic scale with microscopic relations for grain nucleation and growth. The implementation of the two-phase model was validated by comparisons with a consensus of previous numerical simulation for Sn-5wt.%Pb alloy and with experiment for Mg-4wt.%Y alloy cast in one-side-chilled resin sand mould. With free movement of globular grains in the bulk liquid, effects of melt superheat and nucleation density on fluid flow behavior and macrosegregation during solidification of Mg-4wt.%Y alloy were numerically investigated. It was found that a lower melt superheat and a higher nucleation density decrease the severity of macrosegregation by weakening the flotation of grains.

Effect of Hydrothermal Reaction Conditions on the Sizes and Morphologies of ZnO Nanorods

The influence factors of hydrothermal treatment on the formation process of ZnO nanorods are investigated involving with hydrothermal temperature, time and precursor concentration. The as-obtained products were characterized by Scanning Electron microscope (SEM) and X-ray diffraction (XRD), respectively. XRD result indicates that the obtained ZnO nanorods are high-quality single crystals. SEM results indicate that both the diameter and the length of ZnO nanorods increase with increasing the hydrothermal time and temperature. The precursor concentration prominently determines the morphologies of ZnO nanostructure from initial particle morphology to rod-like, and to final slice-like morphology.

Abrasion Behavior of WC Reinforced Cast Iron Surface Composite Fabricated by Cast-Infiltration Method

In this paper, WC particles and NH4HCO3 powders were mixed evenly, and then pressed under 150MPa. The WC porous preforms were obtained after the compacts being heat treated to eliminate NH4HCO3. The volume ratios of WC in the preforms were 30%, 40% and 50% respectively. WC/Fe composites were fabricated by infiltrating liquid cast iron into the WC porous preforms. Optic microscope and scanning electron microscope were employed to observe the microstructure of the matrix alloy and the composites. The results showed that matrix alloy without WC addition had pores in the surface. The microstructure of the composites with WC volume fractions of 30%, and 40% were denser than that of 50%. Hardness and wet sliding wear behaviors of the composites were investigated at room temperature. The addition of WC particles could effectively improve the hardness and the wear resistance of the composites. The influence of volume fractions on hardness of the composites was similar to that on wear resistance. The hardness and the wear resistance of the 40vol.%WC/Fe composite was better than those of the 30vol.%WC/Fe composite. And the properties of the 50vol.%WC/Fe composite were the worst.

Physical Simulation on Chill of Thick Walled Ductile Iron Casting for Spent-Nuclear-Fuel Container

Forced cooling measures need to be adopted in order to ensure the thick walled ductile iron casting solidification within the stipulated time. In this paper, the thick walled ductile iron casting for spent-nuclear-fuel container is used as the research object. The technology of outside mold has been identified in the actual production process. Through physical simulation experiment, the thickness of the outside the chills can be determined, and the cooling effect of chills is verified. The results show that cooling conditions have a decisive effect on the eutectic solidification, the residence time of eutectic platform and the time of casting solidification.

Modeling of Heat Transfer in Spent-Nuclear-Fuel Container during Forced-Chilling Process

Application of spheroidal graphite cast iron in the production of spent-nuclear-fuel container contributes to improve the strength and toughness of the casting, because of the nodular shape of graphite. For a large-scale container, a forced-chilling technique is used to accelerate solidification process and raise spheroidization rate. In this paper, modeling of heat transfer in the container is performed. Influences of cooling media, inflow flux of coolant and thickness of sand layer upon the variations of cooling rate are systematically analyzed. Calculated results indicate that water as a coolant is more capable of enhancing the cooling course than air. Increasing inflow flux conducts an effective cooling job, whose influence is more apparent for air-cooling than for water-cooling. The role of decreasing the thickness of sand layer is most pronounced for raising solidification rate. The predicted cooling curves are compared with experimental measurements to validate the model.

Research Materials of Chills Effect on the Solidification Process of ZM5 Shell

A commercial software, MAGMASOFT, was used to simulate the ZM5 shell with different materials of chills. The calculated results of solidification are obtained. Shrinkage porosity is predicted by means of a built-in porosity criterion. It shows that using the different materials of chills, such as copper, gray iron and steel, a large amount of shrinkage porosity defects are formed in ZM5 shell. However, with graphite as the material of chills, shrinkage porosity defects of ZM5 shell can be effectively reduced.