Advanced Materials Research Vol. 509

Abstract: Silicon rubber is a potential material for gaskets in proton exchange membrane (PEM) fuel cell. So its long term stability and durability is crucial to the electrochemical performance of fuel cell especially in an acidic, high temperature, humid environment. In present paper, the aging process of silicon rubbers has been studied in one simulated PEM fuel cell medium and two accelerated durability test (ADT) mediums for short time test at 70oC and 90oC, respectively. Effect of exposure time, temperature and exposure medium on aging of silicone rubber is also compared. Weight loss is measured by electronic balance; topographical changes on samples’ surfaces are monitored by optical microscopy; Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of samples before and after exposure over time. The results show that the weight loss increased over time. Surface conditions of samples change over time from initially smooth to rough, crack appearance and finally crack propagation through Optical microscopy. ATR-FTIR results show that the surface chemistry changed significantly via de-crosslinking and chain scission in the backbone for materials over time. The aging degree is severe at high temperature or in high concentration acidic solution over time.

Abstract: New materials for high performance tribological applications have been one of the major incentives for the development of aluminum-based metal matrix composites (MMCs). MMCs have received attention because of their improved specific strength, good wear resistance, higher thermal conductivity than ceramics, lower coefficient of thermal expansion, etc. Traditionally, lubricant externally added plays an important role in reducing wear in the application of wear resistance materials. However, self-lubricating materials are more desired than materials to which lubricant needs to be applied periodically, especially for wear parts difficult to be accessed, since solid lubricant contained in the former can be released automatically during the wear process and reduces wear.

Abstract: Carbon nano tubes (CNTs) has found applications in many fields due to its enormous versatility, however, very few report has been given on its promotive effect as support on the adsorption of NOx with solid tungstophosphoric acid (H3PW12O40), and no results on the use of surface modified CNTs in this process can be found in literatures. In this study, we have conducted systematic works on this issue and found some relations between pre-treatment method of CNTs and NOx adsorption efficiency of H3PW12O40/CNTs, and the relations between differernt impregnating solvent used in loading process and NOx adsorption efficiency of H3PW12O40/CNTs, which may be very helpful to the development of new effective adsorbent/catalyst for the adsorption-conversion of NOx. The main conclusions derived are as follows: absolute ethyl alcohol was the superior solvent to water for HPW loading on CNTs; the resultant –OH containing CNTs shows better promotive effect on the adsorption of NOx than that containing –COOH when using absolute ethyl alcohol as solvent; in both cases, with the increase of H3PW12O40 loading, the NOx adsorption efficiency tends to reach a peak value close to that in the case of pure H3PW12O40, before dropping down; compared to pre-treated activated carbon fiber, modified CNTs, especially CNTs–OH, is favorable to be used as support of H3PW12O40 for effective adsorption and even further conversion of NOx.

Abstract: The effects of temperature, stress level and hygrothermal aging on the creep-recovery behaviors of anisotropic conductive adhesive film (ACF) were investigated experimentally using a dynamic mechanical analyzer (DMA). It is found that the initial strains, instantaneous strains, and creep or recovery rates increase with increasing temperature，however decrease with increasing hygrothermal aging time. The change of creep or recovery rates at low temperature is apparent, however the creep or recovery rates increase obviously at temperatures above 25 oC with increasing stress level. For the hygrothermal aged ACF, the time to reach steady creep stage or steady recovery stage is reduced significantly compared with the unaged sample. The strain jumps at instantaneous loading decrease visibly and the strain jumps at instantaneous unloading decrease slightly with increasing aging time. And the strain jumps at instantaneous loading and unloading increase with increasing stress level for the unaged and aged ACFs.

Abstract: The precipitation of copper during aging at 600oC in high-purity Fe-Cu alloy was examined by means of transmission electron microscopy (TEM).Nano-scale copper-rich clusters with a B2-like structure were observed during heat treatment. These micro structural features play an important role in precipitation strengthening. In addition, the precipitation process has been analyzed in terms of the evolution of microstructure by a Monte Carlo method. A description of the coherent precipitation of copper in iron, based on a vacancy diffusion mechanism, thermally activated jump frequencies and cohesive energy is discussed in order to deal with simultaneous precipitation of metastable and stable phases in Cu-containing steel during aging. This analysis gives an estimation of the precipitation dynamics, as well as the evolution of Cu precipitates across a wide range of temperatures.

Abstract: Cu₂O/Cu composite particles were successfully synthesized by a novel facile template-free chemical reduction route at room temperature. X-ray diffraction (XRD) results showed that the sample mainly consisted of the Cu₂O phase coexisting with a few Cu phases. Scanning electron microscopy (SEM) images indicated that the regular particles with a cubic shape about 2-3 μm is Cu₂O. In addition, the electrochemical behavior of the Cu₂O/Cu composite electrode and copper electrode during the charging and discharging process were both investigated. It was found that the first discharge capacity of Cu₂O/Cu composite electrode was up to 650 mAh•g^-1, which is much higher than the theoretical capacity of Cu₂O (about 375 mAh•g^-1). The additional capacity is attributed to the electrodeposition of lithium on pure copper, confirmed by the electrochemical property of copper as the anode material of the lithium-ion battery. The copper electrode presented a high discharge capacity of 280 mAh•g^-1 during the first cycle. However, a large irreversible capacity as same as the cuprous oxide electrode was observed during the first charging process. It is indicated that deposition of lithium on the Cu particle surface acts as a barrier preventing the contact between the Cu and the electrolyte. Furthermore, the Cu₂O/Cu composite electrode can exhibit reversible capacity of 210 mAh•g^-1 at a charge-discharge rate of 30 mA•g^-1 after 40 cycles.

Abstract: Mg alloys were increasingly attracting attention as a potential implant biomaterials because that there will be no need for a second surgery. However, the majority of conventional Mg alloys have been developed for automotive components and were not suitable for Mg based implants. In this paper, a new Mg-RE based materials was developed for implant biomaterials, avoiding the negative influences of previous systems. Microstructure, mechanical and corrosion properties were investigated. The result exhibited that the mechanical properties and degradable rate were sufficient to satisfy the requirement of Mg-based implants. Furthermore, the deformability of the alloy was also investigated. The fine stent pipe was prepared by cold-drawing technology. The primitive results demonstrated that this new alloy was an ideal stent materials.

Abstract: To reduce fuel consumption and greenhouse gas emission, dual phase (DP) steels have been considered for automotive applications due to their higher tensile strength, better initial work hardening along with larger elongation compared to conventional grade of steels. In such applications, which would create potential safety and reliability issues under dynamic loading, the mechanical behavior of DP steel considering the strain rate must be examined. In the present study, the dynamic tensile behavior of DP600 steel sheets was investigated using a high-speed tensile testing machine at various strain rates. And the quasi-static tensile testing was also conducted on the steel to understand the effect of the strain rate on the tensile property. The fracture mechanisms of the steel were also analyzed. The results show that the mechanical properties of DP600 steel are noticeably influenced by the strain rates. As the strain rate increases, the strength of the steel increases and the obvious yield phenomenon can be observed when the strain rate is above 0.01 s^-1. The fracture elongation of DP600 steels decreases with increasing strain rate from 0.001 to 1 s^-1, then increases up to the strain rate of 100 s^-1 and reaches the lowest value at the strain rate of 1000 s^-1. DP600 steel sheet exhibit typical ductile fracture characteristics with dimples morphology of the facture surface when tensile deformed at various strain rates.

Abstract: LiFePO4 compound has been paid considerable attention as a promising positive electrode material. In this work, LiFePO4 compound was synthesized by the solid carbon thermal reduction reactions，where Fe2O3, Fe(OH)3 and FeSO4 is used as the iron resource respectively. All the synthesized products are pure phases except that using FeSO4 as the iron resource. The SEM images show porous morphologies, but different iron resource samples show different degree of pore ratio. According to the results of charge/discharge curves, capacity of the sample prepared by Fe(OH)3 as the iron resource shows superior to those of other samples. The result is attributed to more pores in the sample, which is benefit to electrolyte penetrating, short Li-ion diffusion distance.