Advanced Materials Research Vols. 535-537

Abstract: The toughening modification of PLA(polylactic acid) and PLA/ethylene-maleic anhydride-methylacrylic acid glycerid shrink commonly terpolymer (E-AA-GMA) with different proportions of EVA was studied in the paper.We tested the breaking elongation rate and impact strength of the modified materials. The results showed that EVA had toughening role for PLA , and the toughening present a trend of improving slowly along with EVA increased. The EVA's toughening effect was more apparent when PLA with the compatibilizer (E-AA-GMA).The results of SEM analysis showed that the compatibility of blend material with the compatibilizer was better than the one without.

Abstract: In this work, effect of carboxymethyl chitosan (CMCS) on vulcanization kinetics of natural rubber was studied using the Rheometer MDR2000.The results showed that both the rate constants of induction period and curing period of natural rubber (K-N) was greater than that of natural rubber added CMCS and the dosage is 0.05% of fresh latex (CMCS-1), but less than that of natural rubber added CMCS and the dosage is 0.1% of fresh latex (CMCS-2), and the activation energy 100.8kJ/mol of induction period of K-N is greater than the activation energy 96.7kJ/mol, 93.7kJ/mol of induction period of CMCS-1, CMCS-2, respectively and that the activation energy 104.4 kJ/mol of curing period of K-N is less than the activation energy111.9kJ/mol of curing period of CMCS-1, and bigger than the activation energy 103.4 of CMCS-2 at the same temperature.

Abstract: A series of main-chain liquid-crystalline polymers containing maltose were synthesized by interfacial condensation reactions of sebacyl chloride, 4,4’-Dihydroxy-2,2’-dimethyl Benzalazine(DDBA), and 1-O-[4´-O-(α-D-glucopyranosyl)-ß-D-glucopyranosyl]-methanol(MM). The effects of MM on characteristics of liquid-crystalline properties were studied. P1- P3 exhibited nematic mesophase on heating and cooling cycle, while P4- P7 exhibited both chiral smectic A and nematic mesophases on heating cycle and nematic mesophase on cooling cycle. P8 did not exhibit any mesophase on heating and cooling cycle. The glass-transition temperature decreased with increasing concentration of MM.

Abstract: The paper discusses the possibility of manufacturing dental implants through Selective Laser Melting (SLM) of a Ti-6Al-4V alloy powder. Among all possible biomaterials, this alloy is widely used in biomedical applications due to high biocompatibility. Selective Laser Melting allows to obtain biomaterials with peculiar characteristics in terms of porosity gradient, roughness, customized geometry, and mechanical properties. Influence of input process parameters on porosity and analysis of Selective Laser Melting capabilities in implant dentistry have been focused. Porosity is a key parameter in dental implants as it affects stiffness, which is related to Young’s modulus. Ti-6Al-4V bulk material presents a Young’s modulus of 110 GPa, whereas the bone one ranges from 10 to 26 GPa. The relative difference of mechanical properties causes the phenomenon of stress shielding, which has a detrimental effect on the longevity of dental implants. Total porosity is important in reducing the effective modulus of porous metals. Biomaterials specimens obtained during experimental phase have been examined in terms of porosity (in inverse ratio to relative density), microstructure, microhardness and roughness. According to test results discussed in this paper, Selective Laser Melting is proved to be an efficient technology for the construction of Ti-6Al-4V dental implants, because biomaterials with adequate properties can be obtained changing processing parameters. Other fabrication techniques fail to produce biomaterials for dental implants with the desired features.

Abstract: Magnetic properties of polycrystalline Bi_0.5Ca_0.5MnO₃ are investigated by means of magnetization and electron spin resonance (ESR). The charge ordering (CO) and antiferromagnetic (AFM) transitions are determined from the temperature dependence of magnetization and ESR parameters. It is found that weak ferromagnetic (FM) spin correlations exist in the paramagnetic (PM) state. With temperature decrease, FM spin correlations are suppressed by gradually increased AFM spin correlations in the CO state and frozen in the long range AFM state at the AFM transition temperature TN. Our study suggests that the competition between FM and AFM spin correlations is accompanied by a change of spin-orbit coupling and spin-lattice interaction.

Abstract: The complex of ZnL2Cl4 was synthesized by using zinc chloride hydrate and ligand 2-[(4-Methylpiperazin-1-yl)iminomethyl]phenol(L) under reflux conditions and anhydrous ethanol as solvent. The complex was characterized by elemental analysis, Infrared spectroscopy, solid fluorescence. Experimental results showed that the free ligand was thermally stable, and emitted intensive blue fluorescence at the peak wavelength of 493 nm. Compared with the fluorescent emission of free ligand, the complex of ZnL2Cl4 is blue-shifted to 448 nm in solid-state and exhibiting stronger blue fluorescence.

Abstract: The YBa₂Cu_3-x(doped element)_xO_7-δ samples were prepared by solid-state reactions and studied by means of XRD, positron annihilation technique and simulation calculation. The results show the local electron density n_e saturation and variations of oxygen content, which can be explained by the cluster effect. Another important new result is that the superconductivity does not depend directly on the valence electron density with different dopant. The T_c seems to lose the association with the n_e variation. The dopants can be regarded as a kind of defects is similarly an adding or a losing oxygen ion. Oxygen interstitials reflect fractal distributions of dopants. The oxygen content and distribution reflect the superconductivity of the samples.

Abstract: Nowadays the penetration of PV-generated power energy into the utility grid is increasing exponentially. This paper focuses on two-stage three-phase grid-connected PV systems, which includes modeling of three-phase grid-connected PV systems, grid-connected control strategy of inverter. The inverter based on the grid-voltage oriented vector control used SVPWM-based synchronous current vector PI controllers to control the grid-current of the common point in three-phase grid-connected system. Theoretic analysis and experimental results on a 2.5KW prototype verify the presented algorithm.

Abstract: The discovery of ferromagnetism (FM) in wide band-gap semiconductors doped with transition metals (TM), known as DMSs, has attracted much interest. Among DMSs, the system of Mn-doped ZnO is considered as the most promising candidates. This paper focuses primarily on the recent progress in the experimental studies of ZnO:Mn DMSs.

Abstract: Phase separation of the poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester(PCBM) active layer (ATL) was investigated by varying their relative ratio in the organic solar cells (OSCs).With the help of the UV/visible spectrophotometer, optical microscopy and scanning electron microscope,we found that the cluster of PCBM at the interface or surface was affected by Al cathode, the composition of the blends and thermal annealing. The disc-like shape crystals of PCBM substituted for the needle-like ones at higher PCBM compositions at the ATL/Al interface, which led to stronger contacts and bigger contact area. It could make short circuit current density increase, but may affect the blend morphology and result in parallel resistance and open circuit voltage decreased with the PCBM ratio increasing from 40 to 60%. The microstructure of the P3HT:PCBM ATL, determined by the composition dependent phase separation, supported the optimized performance of the OSCs with the composition of 40–50% PCBM.