Advanced Materials Research Vols. 562-564

Abstract: Microstructure and mechanical properties in QT-Treated 9Ni steel were investigated. The detail microstructures were observed by optical microscope (OM) and transmission electron microscope (TEM). The volume fraction of austenite was estimated by XRD. Tensile test at room temperature and Charpy-V-Notch (CVN) impact test at -196°C were carried out. The results showed that the microstructure of QT-treated 9%Ni steel was composed of tempered martensite and reversed austenite. The brittle cementite was absorbed gradually by the increasing reversed austenite as the tempering temperature increased. The optimum tempering temperature range was 560°C~580°C. The reversed austenite could improve the cryogenic toughness of 9Ni steel through the combination of the scavenging effect and the TRIP effect.

Abstract: Polybenzoxazine was one of the most widely employed matrix for advanced composites, due to their low viscosity, good dimensional stability, high glass transition temperature (Tg) and wide molecular design flexibility. To obtain high perfomance resin matrix, a fundamental understanding of the formation of crosslinking network structure and the relationship between structure and properties was essential. Therefore, the blends of benzoxazine precursor with different functionality were designed to achieve various network molecular architectures, and the effects of inhomogeneous structure of polybenzoxazine on mechanical and thermal properties were investigated. The bifunctional benzoxazine precursor (BA-a) based on bisphenol-A, formaldehyde and aniline, and the monofunctional benzoxazine monomer (Ph-a) based on phenol, formaldehyde and aniline were synthesized respectively. The blends of BA-a and Ph-a, in which the mole ratio was 1:0, 2:1, 1:1 and 1:2, repectively, were thermally cured through ring-opening reaction to obtain polybenzoxazines with various network structures. The fracture surface morphology of various polybenzoxazines was observed by atomic force microscopy (AFM). The hard phase with highly crosslinking density was dispersed in the soft phase with slightly crosslinking density, which led to the generation of inhomogeneous structure of polybenzoxazine. Dynamic mechanical thermal analysis (DMTA) of carbon fiber reinforced polybenzoxazine showed two glass transition temperatures (Tg), which corresponded to the soft phase and hard phase, respectively.With increasing the mole ratio of Ph-a, the increase of hard phase resulted in the enahncement of flexural modulus of polybenzoxazine, whereas the tensile and flexural strength of polybenzoxazine decreased due to the reduction of the crosslinking density of soft phase. Derivative thermogravimetric (DTG) analysis exhibited three major degradation steps, which characterized the decomposition, weight-loss and charring, respectively. Thermogravimetric analysis (TGA) showed that the onset degradation temperature and char yield at 850 oC increased with the increase of Ph-a mole ratio, indicating higher thermal stability and lower decomposition rate, which was attributed to the increase of hard phase with highly crosslinking density.

Abstract: As a modifier, desulfurization waste can improve the performance of traditional adobe materials. The results show that it was possible effectively to modify properties of adobe materials by means of DHG and DFA. When the molding pressure is 15 MPa, the compressive strength of modified adobe materials arrived at 7.5MPa at 28 days. Moreover, modified adobe materials remain a better volume stability and water resistance observed in the drying shrinkage (0.6mm/m) and softness coefficient (0.52), respectively.

Abstract: The objective of this study was to examine the time dependent mechanical properties of epoxy without/with nano particles composites and how the nano particles in the epoxy affect the relaxation properties of epoxy. Furthermore, viscoelastic constitutive models of epoxy and epoxy composite were established and the corresponding mechanical parameters were obtained by using inverse iterative finite element procedure. The ramp-hold indentation tests were used to investigate the time dependent mechanical properties of epoxy with and without Al2O3 nano particles. Experimental results showed that adding Al2O3 nano particles in to epoxy can reduce the relaxation effect of epoxy.

Abstract: A facile method for manufacturing super hydrophobic surfaces is presented using the stainless steel wire mesh as templates. The rough surfaces of polymers including polycarbonate, polypropylene and PMMA are prepared with hot embossing on different specifications of stainless steel wire mesh. Scanning electron microscopy (SEM) results reveal that the surfaces roughness of the polymers can be controlled by selecting templates. Contact angle measurement shows that the water contact angles(WCA) rise with the increase of surface roughness, especially, the water contact angle on the PC surfaces prepared with specifications of 635mesh screen can reach to 152.3°, alias super hydrophobic surfaces.

Abstract: Outdoor electrical insulators form an important link in an electric power system. Along with the traditional insulators like glass and porcelain, presently the polymeric insulators are also used world widely. These polymeric insulating materials are very sensitive to various environmental parameters such temperature, raining, pollution, UV-radiations and icing etc. which seriously effect their electrical, chemical and hydrophobic properties. This paper shows a dynamic change of hydrophobicity on the surface of polymeric insulator under different environmental and contamination stresses. The hydrophobicity decrease of polymeric insulating surface due to rain and icing, hydrophobicity transfer status though different pollution layers and hydrophobicity recovery at different temperatures, humidity and wind speed are carried out in this paper. The hydrophobic characteristics are studied by measuring static contact angle on the surface on polymeric insulating material.

Abstract: An electrochromic copolymer based on pyrrole and 3,4-ethylenedioxythiophene (EDOT) are electrodeposited on ITO electrode in aqueous micellar solution. The copolymer show blue grey in neutral state (-0.8V) and light blue in oxidized state(0.8V). The λmax of the copolymer in neutral state is 530nm and the onset energy for π-π* transition (Eg) is calculated to be 1.68eV by the onset wavelength. And successive cycle voltammagrams indicate that the incorporation of EDOT units into the Ppy improves the electrochemical stability of the copolymer films, which retains 89% of electroactivity after 500 cycles, the copolymer could be as a promising candidate material for electrochromic devices.

Abstract: Isothermal oxidations of U71Mn steels under pure oxygen, between 1027K and 1473K, are experimentally analyzed in this study. The results showed that Oxidation kinetics at different temperature from 1173K to 1473K are similar: mass increase per unit area as function of oxidation time follows parabolic role. Oxidation rate constants of the steel under pure oxygen, from 1173K to 1473K, keep exponential law as function of oxidation time.

Abstract: In order to ameriolate the electrochemical hydrogen storage performances of La–Mg–Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La_0.75−xZrxMg_0.25Ni_3.2Co_0.2Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys were prepared by melt spinning. The influences of substithting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated. The structure characterized by XRD and TEM displays that the as-spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun Zr-free alloy displays an entire nanocrystalline structure, while an like amorphous structure is detected in the as-spun alloy substituted by Zr, implying that the substitution of Zr for La facilitates the amorphous formation. The substitution of Zr for La markedly enhances the electrochemical cycle stability of the alloys, whereas the impact generated by such substitution on the high rate discharge ability (HRD) of the alloys is different with the variation of the spinning rate. The HRD of the as-spun (5 m/s) alloys yields the largest value with the change of Zr content, but that of the as-spun (20 m/s) alloys always declines with the growing amount of Zr substitution.

Abstract: The affect of adding of Zn on the microstructure and corrosion properties was investigated in this work. Vacuum induce melting was used to obtain the Mg-2Ca-xZn (wt.%) (x = 0%, 1%, 2% and 3%) alloys. Erode test was carried out in the Hank’s simulated body fluid for the alloys and the increasing of weight is carefully measured. The microstructure of the alloys was observed with optical microscope and SEM. It is found that and the Mg-2Ca-1Zn alloy is with the best corrosion resistance. Hardness increases as the adding of Zn in the alloys.