Key Engineering Materials Vol. 807

Abstract: Eu³⁺ and Tb³⁺ ions singly activated Gd₂O₂S hollow spheres have been successfully synthesized via solvothermal method by using Gd (NO₃)₃, Eu (NO₃)₃, Tb (NO₃)₃ and thiourea as raw materials. Detailed characterization of the as-prepared samples were obtained by X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), transmission electronic microscope (TEM) and photoluminescence (PL) spectroscopy. The results demonstrate that at 220 ^oC for 24 h, the molar ratio of thiourea/Gd³⁺ has no significant impact on the phase composition of Gd₂O₂S products. With the reaction time increased from 6 h to 24 h, the morphology of Gd₂O₂S samples changed from ellipsoidal to near-spheroidal structure, but still remained hollow structure. PL results show that the strongest emission peaks for Gd₂O₂S:Eu³⁺ and Gd₂O₂S:Tb³⁺ samples were centered at 625 nm and 545 nm, corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ ions and ⁵D₄→⁷F₅ transition of Tb³⁺ ions, respectively. The quenching concentrations for Eu³⁺ and Tb³⁺ ions were 12% and 6%, which can be attributed to the exchange interaction for Eu³⁺ and Tb³⁺ ions, respectively.

Abstract: HAuCl₄ was reduced by glucose as reducing agent and dispersant under UV radiation and acetone as photo sensitizer. The experimental samples were characterized by the transmission electron microscopy and UV-visible spectrophotometer, and the results show that these gold nanoparticles’ size is uniform, monodisperse distribution of spherical particles of average diameter of 5.8 nm, and gold nanowires with two-dimensional network structure were successfully prepared. The influence of glucose concentration on reaction under this condition and the mechanism of nucleation and growth of the photochemical reduction were discussed.

Abstract: The TiO₂ nanoparticles with different Yb doping amount were prepared by a facile sol-gel method. The samples were characterized by XRD, TEM, XPS, UV-Vis, and PL, etc. The influence of Yb-doping on structure and visible light photocatalytic activity of mixed phase TiO₂ was evaluated by photocatalytic degradation of methylene blue (MB) under the irradiation of fluorescent lamp. The results show that ytterbium appeared two kinds of Yb³⁺ and Yb²⁺ valence state on the surface of TiO₂. Ytterbium doping can restrain the phase transfer from anatase to rutile, prevent the grain growth, and increase the surface hydroxyl content. Appropriate amount of Yb doping and the proportions of rutile and anatase mixed phase can effectively inhibit the recombination of photogenerated electron and hole, expand the wavelength range of absorption spectrum, and improve the photocatalytic performance of TiO₂. Meanwhile, the photocatalytic activity of the Yb-TiO₂ samples was the best under the irradiation of fluorescent light when the sintered temperature T=500°C and n(Yb):n(Ti)=0.009, it was 95.2% within 6 h and significantly higher than 56.4% of pure TiO₂ under the same experimental conditions.

Abstract: This article outlines the various processes for CNT growth. The surface morphology of carbon nanotubes on carbon nanotubes was characterized by scanning electron microscopy (TEM) and transmission electron microscopy (TEM). Bifurcated carbon nanotubes were founded. Mechanism analysis was studied of bifurcated carbon nanotubes from chemical crystallization bifurcation and nonlinear dynamic bifurcation. At present, 5nm or 7nm chip fabrication is limited by quantum effects, which makes Moore's Law invalid. Bifurcated carbon nanotubes may be the development direction of new transistors.

Abstract: High purity metal vanadium powder was milled by high energy ball milling, and the grain size and morphology of vanadium powder was observed by electron probe, and the stress-strain curve was measured by CMT5305 universal testing machine for research of the mechanical property. In order to investigate the effect of sintering process on the property of product, the vanadium powder was sintered by the hot pressing sintering process and the cold isostatic pressing with vacuum sintering process respectively. The experimental results show that for the cold isostatic pressing with vacuum sintering process, the density of raw compact increases with the increase of pressing pressure. When the pressure increases to 280 MPa, the density and relative density of raw compact are 3.99 g·cm^-3 and 66.94% respectively, the density and relative density of product after sintering are 5.28 g·cm^-3 and 88.59% respectively. With the pressure increasing from 80 MPa to 200 MPa, the compressive strength increases significantly from 0.4 MPa to 6.0 MPa, the pressure increases to 280 MPa, the compressive strength slowly increases to 7.4 MPa. For the hot pressing sintering process, the relative density of product is higher than that of cold isostatic pressing with vacuum sintering process, and the density and relative density reach to 5.51 g·cm^-3 and 92.91% respectively under 280 MPa pressure.

Abstract: In this paper, a low nickel superalloy used for automotive valves was treated at different heat treatments. The metallographic structure and hardness with various heat treatment process were studied. Optimized process guarantees test superalloy can meet the technical requirements.

Abstract: In this research, CO₂ gas was used as carbon and oxygen source to prepare carbon-doped TiO₂ (C-TiO₂) films on stainless steel by reactive magnetron sputtering. In order to grasp the relationship between sputtering process, microstructure and mechanical and photocatalysis properties of C-TiO₂ thin film, a orthogonal experiment design validated by following mechanical analysis and photo-degradation experiments was employed to determine the optimal reactive sputtering parameters, including substrate temperature, sputtering power and CO₂ gas flow rate. nanoindentation and nanoscratch tests were employed to analyze the hardness, modules and adhesion strength of as-deposited C-TiO₂ films, respectively. Taking the hardness, modules and adhesion between the film and the substrate as a reference of integrated mechanical properties, range analysis of as-prepared C:Ti-O films were done to search the optimal combination of sputtering parameters. The photocatalytic activities of as-prepared C-TiO₂ films using methyl orange (MO) as colored dye indicator were also evaluated by measuring absorbance and calculating the MO’s decolorization rate under different UV light irradiation time. The results of photocatalysis experiment compared with a blank group proved that C-TiO₂ films sputtered at the optimized reactive sputtering parameters can achieve both superior photocatalysis and mechanical properties.

Abstract: Using hydrated manganese sulfate and general type graphene (GR) as raw materials, Mn₃O₄/GR composite has been successfully prepared by the liquid phase chemical co-precipitation method at room temperature. X-ray diffraction (XRD) was used to investigate the phase structure of Mn₃O₄ powder and Mn₃O₄/GR composite; The electrochemical performances of the samples were elucidated by cyclic voltammetry and galvanostatic charge-discharge test in 0.5 mol/L Na₂SO₄ electrolyte. The results show that the Mn₃O₄/GR composite possesses graphene phase and good reversibility; the composite also displays a specific capacitance of 318.8 F/g at a current density of 1 A/g.

Abstract: Spin-coating process is one of the important parts in the fabrication of semiconductor integrated circuits (IC). Numerical simulations and experiments based on Fluent were carried out, including discussing geometric parameters of spin-coating pallet that affect wafer deformation. The numerical results indicated that under the same effect of vacuum negative pressure, when wafer-supporting stage diameter (D) was smaller than 30mm, the wafer deformation was mainly warpage deformation; and when D was greater than 45mm, spin-coating pallet deformation affected the wafer deformation increasingly and downwarping deformation was occurred at the wafer edge. At the same exit velocity, the deformation around the wafer center and the vacuum degree were both increased with the increase of vacuum suction diameter (d). When the area of the wafer-supporting stage was 1/2~3/5 of the wafer and d was about 3mm, the wafer deformation was the smallest.