Understanding active sites and mechanism of oxygen reduction reaction on FeN4–doped graphene from DFT study

First-principle density functional theory (DFT) calculations are performed to study the active sites in FeN₄G electrocatalysts, as well as ORR activity and mechanism. The possible intermediates and transition states existing in the possible reaction paths from Langmuir-Hinschelwood (LH) mechanism are investigated. The results show that the associative pathways of OOH1 formation is prior to that of O₂1 dissociation. The condition of proton adsorbed on top N sites (T2) is more beneficial to the reduction of O-contained species adsorbed on top Fe site (T1) compared to the conditions of proton adsorbed on top C sites (T3). However, the dissociation of O₂1, OOH1 and H₂O₂1 is more likely to occur on the paired T1-T3 sites, since their lower energy barriers compared to other paired sites. The most favorable four-electron reduction pathway follows the mechanisms: O₂1→ OOH1→ O1+H₂O→ OH1+H₂O→ 2H₂O. The rate determining step for ORR on FeN₄G is the reduction of O1 into OH1 (barrier, 0.47 eV). The most feasible pathway for ORR is downhill at a high electrode potential (0.76 V vs. SHE at pH = 0) according to the free energy diagram. Compared to the ideal catalyst, the adsorption energy of OOH1 on FeN₄G is much lower in free energy, while those of OH1 and O1 are slightly higher. Additionally, the elementary reaction rate for OOH1→O1+H₂O is much larger than that of OOH1→H₂O₂ based on the parameter of activation barrier. Therefore, the formation of H₂O₂ (l) is unfavorable on FeN₄G catalysts.     

Modeling of damage in materials during hot deformation based on the Zener-Hollomon parameter

By introducing the Zener-Hollomon parameter, which synthetically considers the influence of deformation tem-perature and strain rate into damage mechanics, a damage evolution model was developed to simulate the damage evolution of metallic materials during hot deformation. The errors between the prediction damage values and the experimental ones are within 6%.     

阻燃镁合金的研究现状及进展

综述了阻燃镁合金的研究开发现状,尤其是Ca、Be、Zn和稀土在镁合金中的阻燃作用及其阻燃机理,指出了阻燃镁合金研究目前还存在的问题和今后的研究重点。     

Improving the mechanical properties of polypropylene via melt vibration

The effect of melt vibration on the mechanical properties of polypropylene prepared by low-frequency vibration-assisted injection molding (VAIM) has been investigated. With the application of melt vibration technology, the mechanical properties of polypropylene are improved. The yield strength increases with the increment of the vibration frequency, and a peak stands at a special frequency for VAIM; the elongation at break decreases first and then increases with increasing vibration frequency, and a valley stands at a special frequency. The tensile properties increase sharply at an enlarged vibration pressure amplitude with sharply decreased elongation at break. The Young's modulus and impact strength also increase with the vibration frequency and pressure vibration amplitude. When it is prepared at 59.4 MPa and 0.7 Hz, the maximal yield strength is approximately 40 MPa versus 33.7 MPa for a conventional sample; an 18.7% increase in the tensile strength is produced. Self-reinforcing and self-toughening polypropylene molded parts have been found to be prepared at a high vibration frequency or at a large pressure vibration amplitude. Scanning electron micrographs have shown that, in the vibration field, the enhancement of the mechanical properties is attributable to more pronounced spherulite orientation and increased crystallinity in comparison with conventional injection moldings. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Eco-friendly fermentation module for maximization of hydrogen harvesting from fatty restaurant waste diluted with grey water

Valorization of fatty restaurant waste (RW) is an economically and environmentally promising approach due to the enriched high biodegradable organic content of this substrate. However, the lipid fraction has an adverse impact on the hydrogen fermentation process. Thus, three staged hybrid reactors (HR1, HR2 and HR3) connected in series were investigated for lipid degradation and H₂ harvesting from the codigestion of fatty RW and grey water. A hydrogen harvesting volume of 0.3 ± 0.02 L/L.d., was recorded in HR1, and lower values of 0.22 ± 0.1 and 0.11 ± 0.06 LH₂/L.d were obtained in HR2 and HR3, respectively. The phyla Actinobacteria (6.4%), Bacteroidetes (10.9%), Chloroflexi (45.1), and Proteobacteria (22.4%), which degrade carbohydrates, lipids and proteins, were dominant in HR1 and highly reduced in HR2 and HR3. Nevertheless, the abundance of the phylum Firmicutes was 16.6% in HR1 and increased to 21.7% in HR3. Staging of the anaerobic digesters highly distributed the hydrolytic and acetogenic syntrophic microbes, creating a unique fermentation medium for H₂ harvesting from RW diluted with grey water.     

形态控制技术获取自增强制件研究

在成型过程中向成型设备或模具分别输入具有不同振频和振幅的振动场、不同拉伸比的拉伸应力场、不同剪切速率的剪应力场、以及先剪切后拉伸的复合应力场等,成功地改变了聚合物凝聚态结构;改变了结晶聚合物的结晶度、取向度、晶粒尺寸、晶胞参数;生成了不同的串晶结构、串晶互锁结构。分别得到了具有突出高强度、高模量的试样,自增强同时又自增韧的试样,在单方向应力场中获得双向自增强结构的试样,以及在极少量高分子组分诱导下性能大幅度提高的试样。     

低频振动场对HDPE性能的影响

利用低频熔体振动注射成型技术获得自增强高密度聚乙烯。实验结果表明,采用振动注射成型工艺,试样屈服拉伸强度由26.5MPa提高到36.1MPa;试样的芯层中可获取沿流动方向生成的串晶或行式排列的片晶结构;压力振动注射有利于分子在(110)晶面择优取向,使结晶更加完善;振动注射提高了试样的结晶度,芯层结晶度最大提高了10.2%。