Advanced Materials Research Vols. 197-198

Abstract: Crystallization rule of mould powder for high-speed continuous casting was studied and the suitable composition powder was done. The analysis of experiment shows: in the given range, the influencing order of different fluxing agents for the crystallization temperature is: Li₂O> BaO> B₂O₃> Na₂O> CaF₂> MgO. According to different solidification characteristics of steel and the requirements to the performance of mould power, component design of mould powder for high-speed continuous casting was done from the perspective of the crystallization characteristics.

Abstract: This paper demonstrates the natural frequency varying rule with differently critical design parameters for the free vibration characteristics and change features of structural response with different geometric parameters under the simple harmonic excitation.

Abstract: An experimental investigation on the effect of hydrogen fraction on the combustion characteristics of a spark ignition engine fueled with low heat value gas-hydrogen blends was studied. The results show that engine indicated thermal efficiency, indicated mean effective pressure and maximum combustion pressure are increased with the increase of hydrogen fraction in the blends. And hydrogen addition shows remarkable influence on engine power and emissions. At the same excess air ratio, HC emissions decrease, CO and NO_x emissions increase with the increase of hydrogen fraction in the blends. And engine power is influenced by both hydrogen fraction and heat value in low heat value gas-hydrogen blends combining. Hydrogen significant extends the lean burn limit of combustion of low heat value gas.

Abstract: β' phase precipitation in a cold rolled Cu-Zn alloy under high density electric current pulses was studied in the present work. The results showed that the precipitation of β' phase was controlled by the angle between the current direction and rolling direction. When the angle was 45º, the application of electric current could refine α phase without β' phase precipitation, while at 0º or 90º, β' phase precipitated from α phase boundaries and distributed along the rolled direction. It was proposed that the precipitation of β' phase during the application of high density electric current was determined by the electron wind force and anisotropic electrical resistivity of the grain boundaries.

Abstract: The present study developed a subsurface microhardness gradient technique to estimate hydrogen diffusivity of stainless steels, as per the similarity between concentration distribution and hardness gradient. Cathodic charging were performed on 304 stainless steels for 24 h in a 0.5 mol/L H₂SO₄ solution using a current density of 100 mA/cm², with 0.25g/L Na₂S as the hydrogen recombination poison. Microhardness in the cross-sectional region had an increase than the uncharged materials due to the hardening mechanism as found by martensite transformation. Hydrogen diffusivity was estimated using the microhardness data and the diffusion equation. The estimated diffusivity of hydrogen at 306 K in 304 stainless steels is 3.28×10^-13 m²/s, which has good agreements with the one measured by time-lag electrochemical method in a previous research.

Abstract: Hydrogen is a clean, abundant, no-toxic, renewable fuel and packs more energy per unit mass than others. It is important to find a efficient way to store it. Hydrogen molecules adsorbed on the Al doped BN sheets are investigated by using density function theory (DFT) calculations. The results indicate that the H₂ molecule is very easy to be absorbed on the doped BN sheet of B substituted by an Al atom (Al_B-BN), which is most stable structure in all the Al doped configurations. Therefore, AlB-BN is a promising material in storage H₂.

Abstract: In order to find the reason of the weak performance of a H₂/O₂ proton exchange membrane fuel cell (PEMFC) stack, a series of fault analysis and diagnosis tests were conducted. According to the test data, the problematic points were focused, and the fault types of the specific single cells were analyzed. It is found that a minimum of three groups of diagnosis tests based on three relatively high load resistances and a voltmeter could judge the working condition of the PEMFC stack and confirm the fault types of its single cells. The method is useful for quick detecting and handling of PEMFC stack in Industrial field and home usage.

Abstract: Pd (0.1-1 wt%) loaded Ni/Mg(Al)O catalysts have been prepared by co-precipitation and impregnation methods, and their catalytic activities were tested in the catalytic reforming of tar components from hot coke oven gas (COG) with lower steam/carbon (S/C) molar ratio. The 0.5%Pd-12%Ni/Mg₃(Al)O bimetallic catalyst derived from hydrotalcite showed excellent catalytic activity. The effect of reaction temperature on the catalytic performance was investigated in detail. Toluene could be completely converted into small gas molecules of CH₄, CO and CO₂ over the catalyst at S/C=0.42 and 600°C under atmospheric pressure.

Abstract: Thermodynamic analysis was carried out for theoretical reaction of hydrogen produced from dimethyl ether (DME) auto-thermal reforming by using the minimum of GIBBS energy. The volume content of various gases were calculated at adiabatic condition as function of air to DME ratio (0.2~0.8), H₂O to DME ratio (1~6) and pressure (0.1~0.6MPa). The result proves that the volume content of H₂ decrease with the increasing of pressure. With the increasing of the H₂O to DME ratio and the O₂ to DME ratio the volume of H₂ increases first then decreases. With the increasing of the H₂O to DME ratio the volume of CH₄ and CO decreases, the volume of CO₂ increases. The model reliability was verified experimentally on self-designed equipment. The experiments data are closed to simulation results.

Abstract: A model of PEMFC is developed that captures dynamic behavior for control purposes. It analyzes in detail the influence factor of voltage of PEMFC. The model is mathematically simple, and accounts for the essential phenomena that influence the PEMFC performance. The partial pressure of hydrogen and oxygen can be found using the laplace transform and differential form of ideal gas state equation. It is assumed that the mixture ratio of hydrogen and oxygen in the reaction are constant, the dynamic lumped model of PEMFC is proposed. The model is verified by comparing the experiment data with simulation result of model. On the basis of the dynamic model, the partial pressure and voltage are analyzed when when the load current suddenly changes.The research about lumped model has important significance to the research of the distributed generation network in various performances and has guiding meaning to the structure design of fuel cell.