PARTICLE SIZE AND MICROSTRUCTURE OF Ni NANOPOWDERS PREPARED BY ANODIC ARC PLASMA

Pure Ni nanopowders were successfully prepared by the method of anodic arc discharged plasma with homemade experimental apparatus. The particle size, mircostructure and morphology of the particles by this process were characterized via X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED); The specific surface area and pore parameters were investigated by multi-point full analysis of nitrogen adsorption-desorption isotherms at 77K by BrunauerEmmett-Teller (BET) surface area analyzer; The chemical composition were determined by X-ray energy dispersive spectrometry (XEDS) equipped in SEM and element analyze instrument. The experiment results indicate that the samples by this method with high purity, the crystal structure of the particles is as same as the bulk material, is fcc structure, with average particle sizes about 47nm, ranging from 20 to 70nm, and distributed uniformly in spherical chain shapes, the specific surface areavis 14.23m^2/g, pore volume of pore is 0.09cm^3/g and average pore diameter is 23nm.     

MONTE CARLO SIMULATION OF SPIN-POLARIZED SECONDARY ELECTRONS FROM IRON

A Monte Carlo model considering the electron spin direction and spin asymmetry has been developed. The energy distribution of the secondary electron polarization and the primary energy dependence of the polarization from Fe are studied. The simulation results show that: (1) the intensity of the spin-up secondary electrons is larger thanvthat of thevspin-down secondary electrons, suggesting the secondary electrons are spin polarized; (2) the spin polarization of secondary electrons with nearly zero kinetic energy is higher than the average valance spin polarization, Pb=27% for Fe. With increasing kinetic energy, the spin polarization of the secondary electrons decreases to the value of Pu remaining constant at higher kinetic energies; (3) the spin polarization increases with an increase in the primary energy and reaches a saturation value at higher primary energy in both the Monte Carlo simulation and experimental results.     

THE BAND STRUCTURE AND WORK FUNCTION OF TRANSPARENT CONDUCTING ALUMINUM AND MANGANESE CO-DOPED ZINC OXIDE FILMS

Al and Mn co-doped-ZnO films have been prepared at room temperature by DC reactive magnetron sputtering technique. The optical absorption coefficient, apparent and fundamental band gap, and work function of the films have been investigated using optical spectroscopy, band structure analyses and ultraviolet photoelectron spectroscopy (UPS). ZnO films have direct allowed transition band structure, which has been confirmed by the character of the optical absorption coefficient. The apparent band gap has been found directly proportional to N^2/3, showing that the effect of Burstein-Moss shift on the band gap variations dominates over the many-body effect. With only standard cleaning protocols, the work function of ZnO: (Al, Mn) and ZnO: Al films have been measured to be 4.26 and 4.21eV, respectively. The incorporation of Mn element into the matrix of ZnO, as a relatively deepd onor, can remove some electrons from the conduction band and deplete the density of occupied states at the Fermi energy, which causes a loss in measured photoemission intensity and an increase in the su,rface work function. Based on the band gap and work function results, the energy band diagram of the ZnO: (Al, Mn) film near its surface is also given.     

EFFECT OF THE DEFECT STATES DENSITY ON OPTICAL BAND GAP OF CdIn2O4 THIN FILM

Transparent conducting oxides Cdln2O4 thin films were prepared by radio-frequency reactive sputtering from a Cd-ln aUoy target in Ar O2 atmosphere. By transmission spectrum and Hall measurement for different samples prepared at different substrate temperatures, it could be found that the carrier concentration would increase with the decrease of substrate temperature, but absorption edge showed an abrupt variation from a blue shift to a red shift. TheoreticaUy, the paper formulated the effect of high-density point defects on band structures; it embodied the formation of band tailing, Burstein-Moss shift and band-gap narrowing. The density of holes will influence the magnitude of optical band gap and transmittance of light. Since extrapolation method does not fit degenerate semiconductor materials, a more accurate method of obtaining optical band gap is curve fitting. In addition, ionized impurities scattering is the main damping mechanism of the free electrons in Cdln2O4 films, the density of ionized impurities induced by altering substrate temperature will affect the carriers mobility.     

STUDY ON HOT SAND COOLING EQUIPMENT WITH DAMPING SAND CASCADE AND VERTICAL SPOUTED-FLUIDIZED BED

1. Introduction In mass production foundry, because of short production period, much repeatly using times of molding sand, heat released by liquid metal during solidification in the sand mould will make the tem- perature of sand attain to 60-70°C[1], tha…     

Corrosion characteristics of boronized AISI 8620 steel in oil field water containing H<Subscript>2</Subscript>S

The corrosion behaviours of non-boronized and boronized AISI 8620 steels in both oil field water and H₂S-saturated oil field water have been investigated by means of immersion test, electrochemical method, X-ray diffraction and scanning electron microscopy. The experimental results show that boronized steel has better corrosion resistance to as-received oil field water and H₂S-saturated oil field water than the non-boronized steel. Both non-boronized and boronized steels have reacted with H₂S and form corrosion film of FeS, which could not retard the corrosion process due to pores and cracks in the FeS film, and large scale of pitting corrosion is found on non-boronized AISI 8620 steel surface. The immersion corrosion of non-boronized AISI8620 in both corrosion solutions can be divided into two stages: the rapid corrosion stage with high slope and the gradual corrosion stage with low slope, corresponding to uniform corrosion and corrosive product scaling off the surface, respectively. The better corrosion resistance shown by boronized AISI 8620 steel is ascribed to lower corrosion current as compared with the non-boronized AISI8620 steel.     

Interactions between Nb-silicide based alloy and yttria mould during directional solidification

Pure yttria moulds have been prepared for directional solidifications of Nb-22Ti-16Si-6Hf-2Al-2Cr (at. %) alloy with a withdrawal rate of 1 × 10^-4 m s^-1 at 1850 °C and 1900 °C. This study demonstrates that a mild interface reaction occurred between the yttria mould and hafnium, the most reactive element in the alloy. A sequential reaction layer of HfO₂ and Y₂O₃ was formed at metal-mould interface, and its thickness depended on both heating temperature and holding time. HfO₂-Y₂O₃ inclusions were dispersed in the metal matrix, and the majority of them concentrated around the solid-liquid interface rather than in steady state growth region. Some inclusions were merged with each other. The reaction mechanism between Nb-silicide based alloy and yttria mould also has been described.     

Evidence of room temperature ferromagnetism in Co-doped transparent CuAlO2 semiconductor

We synthesized CuAl_1−xCo_xO₂ (x = 0.00-0.07) thin films by solid-state reaction from Cu₂O and Al₂O₃ on a sapphire (0 0 1) substrate by a simple and cost-effective spin-on technique. X-ray diffraction and Raman spectroscopy confirm the formation of single impurity-free delafossite CuAlO₂ structure for all the compositions. We observed diamagnetism for pristine CuAlO₂ and ferromagnetism for Co-doped CuAlO₂ at room temperature. Specially, the coercivity (H_c) and saturation magnetization (M_s) are significantly enhanced with Co composition from 1 at.% to 5 at.% but show the reverse tendency with higher Co content.     

Microstructural control of TiAl-Nb alloys by directional solidification

The lamellar microstructure of TiAl-Nb alloys with and without low boron additions is controlled using double directional solidification (DS). In alloys without the addition of boron, the β phase is seeded during double DS. Complete peritectic transformation occurs in both the dendritic and interdendritic regions, which can lead to the successful alignment of both the high-temperature α phase and the lamellar microstructures. Well-aligned lamellar microstructures can be easily achieved if the alloy composition is close to the peritectic point on the hypo-peritectic side. In alloys with low boron additions, however, the competitive growth of the α phase breaks the continuity of the lamellar microstructure in the region ahead of stable growth, which finally results in columnar grain coarsening and unsuccessful alignment of the lamellar microstructures.