Advanced Materials Research Vol. 716

Abstract: Novel proton conducting nanocomposite membranes included binary and ternary mixtures of acid modified nanotitania particles particles with polymers such as poly (vinyl alcohol) (PVA),pol (vinyl phosphonic acid), sulfonated polysulfone (SPSU) and poly (1-vinyl 1,2,4-triazole) (PVTri) . The interaction of functional nanoparticles with the host matrix were searched by FT-IR spectroscopy. The homogeneous distribution of functional nanoparticles in the membranes was confirmed by SEM micrographs. The spectroscopic measurements and water/methanol uptake studies suggested a complexation between polymers and sulphonic acid that inhibited the leaching out of acidic units. The TGA results verified that the presence of modified nanoparticles in the composite membranes the thermel stability of the membranes enhanced up to above 200 °C.

Abstract: With the Grafting to method, the hyperbranched polyurethane/multi-walled carbon nanotubes composites (MWNT-HBPU) was prepared. The reaction mechanism was covalently grafting hyperbranched polyurethane to multi-walled carbon nanotubes,through the reaction of the isocyanate groups of multi-walled carbon nanotubes (MWNT-NCO) and the hydroxyl groups of homemade hyperbranched polyurethane (HBPU). The structure and properties of the composites was studied by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), Thermal gravimetric analysis (TG) and Differential scanning calorimetry (DSC). The test results of FT-IR and TG showed that the prepared product was MWNT-HBPU; the DSC results demonstrated that the glass transition temperature of HBPU was significantly increased from 91.9°C to more than 99.7°C by the addition of MWNT-HBPU; the dispersion of the MWNT-HBPU was much better than the pure MWNT in solvents, such as N, N-dimethylformamide , Dimethyl sulfoxide etc.

Abstract: A novel synthesis of nanosized spinel LiMn₂O₄ cathode has been developed by a combination of high-gravity technology and microwave technology. Spinel lithium manganate precursor were prepared by co-precipitation method in a rotating bed with helix channels (RBHC). Calcination of the precursor in the microwave field produces uniformly sized, nanoparticles of spinel LiMn₂O₄ as the final product. The phase structures and morphologies were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM), transform electron microscopy (TEM). The results show that nanosized spinel LiMn₂O₄ powders with high crystallinity, uniform particle size, and the average size of about 60 nm can be synthesized by the integration of high-gravity technology and microwave technology.

Abstract: Lead free piezoelectric ceramics 0.98(Na_0.5K_0.5)NbO₃-0.02(Na_0.5Bi_0.5)TiO₃ [abbreviated as 0.98NKN-0.02NB with the addition of 0~1.0 wt% Na₂CO₃ have been synthesized by the conventional mixed oxide process. The effects of amount of Na₂CO₃-content on the electrical properties and crystalline structures were investigated. The specimens of 0.98NKN-0.02NBT ceramics added with Na₂CO₃ maintain an orthorhombic phase. In the case of low Na₂CO₃ content ( 0.3 wt%), the grain growth became remarkable. The increase of grain size favors improving the piezoelectric properties, which is known as grain size effect. The grain size effect compensates the decrease of the electromechanical coupling factor due to the hard doping effect. For 0.98NKN-0.02NBT ceramics by doping 0.3 wt% Na₂CO₃, the electromechanical coupling coefficients of the thickness mode k_t and the planar mode k_p reach 0.51 and 0.33, respectively, after sintering at 1100 °C for 3 h. Moreover, the addition of excess Na₂CO₃ is a helpful method on ceramic processing to improve the dielectric tangent loss and the mechanical quality factor. Our results show that 0.98NKN-0.02NBT with the addition of 0.3 wt% Na₂CO₃ is a good lead-free piezoelectric ceramic.

Abstract: Based on a unified form of the plate kinematics in terms of the transverse shear functions and the Heaviside step function, the analytical solutions of laminated plates corresponding to a number of higher-order shear deformation plate theories are solved in this paper. The accuracy assessment of these higher-order laminated plate theories is conducted by comparing the resulting analytical solutions with the elasticity solutions and finite element results. The accuracy study shows that the interlaminar shear stress continuity condition is very important for the accurate prediction of the transverse shear stresses across the laminated plate thickness. The comparison study also indicates that the new laminated plate theory accounting for the interlaminar transverse shear stress continuity proposed by the authors yields both very accurate displacements and accurate stresses. This new higher-order laminated plate theory can be efficiently used in the finite element analysis of laminated composite plates since it uses the same five field variables as those used in the first-order shear deformation plate theory.

Abstract: In this contribution, the surface electrical properties of graphene oxide (GO), chemically reduced graphene oxide (RGO) and thermally exfoliated graphene oxide (EGO) were characterized by zeta potential. Their surface morphologies were observed by scanning electron microscope. Then they were immobilized on glass carbon electrodes and their electrochemical behaviors for different charged redox systems were also investigated by using the cyclic voltammetry (CV) method. Results indicated that the density of surface negative charge on GO is much more than those on RGO and EGO. Furthermore, the electrochemical performances of electrodes modified with GO, RGO and EGO for detecting the model analyte Cu²⁺ by CV were compared. The results demonstrate that negative charge on the surface of graphene materials affects their performances as electrochemical sensors significantly.

Abstract: In this work, a high strength, high toughness low carbon steel weld was developed by controlling the contents of B and Ti which are the minor but critical elements to the weld microstructure. The weld with the low B - Ti content exhibited the high strength close to 1 GPa and the excellent toughness over 70 J at 40 °C. The weld microstructure consisted of the multiphase which composed acicular ferrite, bainite, martensite, under welding condition. A weld with the high B - Ti content was fully martensite and exhibited the high strength over 1 GPa but the poor toughness below 15 J at 40 °C. The present results inform that, when the low carbon steel weld contains the substantial amount of various alloying elements to obtain the high strength, the B content should be low as possible so that a substantial amount of acicular ferrite is ensured by screening the hardenability improving effects from other elements. The Ti content was found to affect the size of the multi-component oxides such that the less the Ti content, the smaller the oxide size which is critical to the acicular ferrite nucleation.

Abstract: Different structures of new types of the flexible electrodes were fabricated from 3-dimensional stainless steel of fibres. Their electrochemical behaviour was characterized using AC impedance spectroscopy where the data presented in impedance plots exhibit different curves. Two or three layers simulation models are proposed to analysis charge transport behaviour and to elucidate dominant characteristics of the samples. The result shows that the bottom layer is more influential on ion exchange and charge transport than other layers.

Abstract: Block copolymer PLA₂₀₀-b-PPEGMEMA₂₂₅ were prepared via ring-open polymerization and RAFT process. Further stabilization of the micellar system was performed in water using a dimethacrylate (EDGMA), and the RAFT to cross-link the interface. The interface-cross-linked micelle was found to present better properties than the uncross-linked block copolymer micelle during the drug loading and releasing experiment. Both block copolymers and cross-linked micelles show no toxicity on COS-7 cell line.

Abstract: In this research, efforts were made to study the modification of microstructure of pure Ni matrices. Modification was attempted using glucose as carburizing medium under a control of heat treatment conditions. Nickel plates were carburized under vacuum conditions at 380°C and 650°C for 3 hours. In order to determine the parameters of the carburizing, thermal properties of glucose along with the thermochemical behavior were examined by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA). The characterization of the microstructure of the carburized specimens was investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). For analyzing the effect of temperature treatment on corrosion resistance, electrochemical corrosion tests were conducted. It was observed that the polarization curves for carburized samples at 380°C were shifted to lower corrosion current densities. Consequently, lower corrosion rates were achieved for these samples preventing the formation of extensive corrosion over their surfaces comparing with carburized Nickel substrates at 650°C.