Advanced Materials Research Vols. 239-242

Abstract: Fine CdS nanodots (~5 nm) have been prepared in aqueous solution under the control of ds-DNA via a novel alternating dialysis procedure, which have been characterized by TEM, UV-vis, fluorescence (FL) and resonance light scattering (RLS) spectra. The resultant well-dispersed CdS nanodots present a strong FL peak at 339 nm and RLS bands around 394 nm. Interestingly, it was found that the quenching of FL and the enhancing of RLS intensity are dependent on the concentration of Hg²⁺, both of which showed good linear relationship over the range of 0.01-100 mmol/L, with a detection limit (3s) as low as 0.91 nmol/L. Good selectivity of this method for Hg²⁺ analysis has also been checked over other metal ions.

Abstract: The optical fibers with epoxy acrylates and urethane acrylates UV-curable coatings were embedded in composites. It’s found that after high-temperature heated, when the coating’s glass transition temperature was higher than the heating temperature, the microstructure of the coating would not change, but when the coating’s glass transition temperature was lower than the heating temperature, the coating would detached from optical fiber. FBG (fiber Bragg grating) sensors with coating and naked FBG (without coating) sensors were embedded in composite materials to monitor impacting damage. It was found that when the coating broke away from the optical fiber which was embedded in the composites, the sensitivity of the FBG sensors would reduce.

Abstract: In this study, papercut-like carbon sheets with an average size of about 20 nm in thickness have been successfully synthesized by the pyrolysis of tetrachloromethane and calcium carbide in an autoclave in 600 °C in the existence of alloy (Fe-Co-Ni). The X-ray powder diffraction (XRD) reveals amorphous carbon nature of the as-prepared sample. The thermal stability of the as-prepared sample was also studied.

Abstract: With the effects of electronic structure and atomic size being introduced, a revised model to calculate the viscosity of the bulk metallic glass alloys was proposed and the viscosity of ternary Zr-Al-Cu, Zr-Ni-Al and quaternary Zr-Al-Ni-Cu systems are calculated in this paper, and the computed results agree well with the empirical one. The sequence of viscosity of different systems is: V_Zr-Al-Cu <V_Zr-Al-Ni<.V_Zr-Al-Ni-Cu. To Zr-Al-Cu and Zr-Ni-Al, the highest viscosity locates in the composition range of X_Zr=0.37-0.86, X_Cu=0-0.40 and X_Zr = 0.45-0.79, X_Al = 0.12-0.50, respectively. And to the Zr-Ni-Al-Cu system with 66.67% Zr, the highest viscosity is obtained in the region of X_Al= 0.63-0.80, X_Ni = 0.14-0.24.

Abstract: Sm_0.5-xBa_xSr_0.5Co_0.8Fe_0.2O_3-δ powders were synthesized by a sol-gel method. The crystal structure and thermal expansion coefficient of Sm_0.5-xBa_xSr_0.5Co_0.8Fe_0.2O_3-δ (SBSCF, x=0.00, 0.05, 0.10) were investigated. All samples were the perovskite structure with an orthorhombic symmetry and exhibited a similar thermal expansion behavior. The electrochemical properties of SBSCF-SDC composite cathodes were studied using A.C. impedance method. The substitution of Ba²⁺ for Sm³⁺ had a significant effect on the area specific resistance of the composite cathodes. The area specific resistance (ASR) decreased with the increase of Ba²⁺ substitution. This result suggested that the electrochemical performance of Sm_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ based cathode improved as Sm³⁺ is partially substituted by Ba²⁺.

Abstract: Coating craft process is often used on the hole surface, thus it must affect the degree of the stress concentration near the hole edge. Airy stress function methodology is used to obtain the analytical stress solution for a plate with a small coating circular hole in the center and subjected to the uniaxial uniform tension in this paper. With the help of the finite element software MSC.Patran & Nastran, the K3alloy plate is numerically analyzed, and its coating material is a ZrO₂, and with the comparison of the acquired analytical solutions, it can be found that the numerical results coincide with the analytical ones very well. The results show that coating affects greatly the stress distribution near the hole edge, and the stress concentration factor in the coating increases with the coating thickness but decreases in the plate, and it increases with the shear modular ratio of the coating to the plate but decreases in the plate. The effect of the coating on the stress distribution near the hole and the stress concentration cannot be neglected.

Abstract: Fluorocarbon coating was exposed to artificial weathering environment produced by the xenon lamp/condensation weathering equipment for different time periods. The degradation process was studied by electrochemical impedance spectroscopy (EIS), Fourier Transform Infrared Spectrometry (FTIR) and optical microscope. The results show that the resistance of the coatings decrease ，while the capacitance and soakage become larger with the increase of the aging time. This demonstrates that the early aging of the coating influences its protective properties for the corrosion medium. The reason is the changes of the coating’s surface state and chemical structure accelerate the penetration of medium into the coatings, and therefore accelerate the corrosion of metal occurs under the coating.

Abstract: Carbon dioxide corrosion is a very complex electrochemical process. Compositions of formation water in different gas and oil wells are various, which effects on the carbon dioxide corrosion of tubular steel. HCO₃^- and SO₄^2- were studied in order to further understand their role on the corrosion process. The results show marked difference when they are the main composition while others conditions is the same. HCO₃^- mitigates the corrosion, because its participation in cathodic and anodic reactions accelerates passivation. However, corrosion in formation water mainly containing Na₂SO₄ is severe, which presents higher general corrosion rate and more dangerous localized corrosion.

Abstract: A SiO₂/TiO₂ supported on glass fibers photocatalyst with visible light activity were synthesized by sol-gel technology, butyl titanate as a Ti source, and tetraethylorthosilicate (TEOS) as a Si source. The photocatalytic activitie under visible light of SiO₂/TiO₂ supported on glass fibers were evaluated by the photocatalytic decomposition of methylene blue. The samples were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS). The results show that the optical absorption edges of the SiO₂/TiO₂ showed red shift with increasing the dopant of SiO₂. The sample of SiO₂/TiO₂ supported on glass fiber (atomic ratio of Si/Ti=0.05) has the highest catalytic efficiency under visible light irradiation.

Abstract: The cavitation erosion behavior of ZQAl9-4-4-2 nickel-alum inium bronze in 2.4%NaCl solution was investigated by using a magnetostrictive – induced cavitation facility. The micrographs of damaged surface were observed by scanning electron microscope (SEM) and transmission electron microscopy(TEM). The results showed that the cavitation microcrack in the a phase adjacent to the k phase. They propagated and connected with each other in the a phases, resulted in the removal of a phases and detachment of the k phase from the matrix in the following test period followed. The microcracks tended to propagate parallelly to the eroded surfaces.