Materials Science Forum Vol. 750

Abstract: It is well known that SiC doping in superconducting MgB₂ improves the upper critical magnetic field (B_c2) and the critical current density (J_c) under high magnetic field. However, the relationship between SiC doping and the flux pinning mechanism has not been clarified. In this study, several MgB₂ samples with and without SiC doping were prepared by the conventional in situ powder-in-tube method. The critical current densities and the force-displacement characteristics of fluxoids in samples were investigated by an ac inductive measurement (Campbell’s method). The Labusch parameter (α_L) and the interaction distance (d_i) were estimated from the obtained force-displacement profile. It was found that SiC doping enhances the values of α_L, but does not change the characteristics of the magnetic field dependence of α_L apparently. Namely, α_L vs. B^3/2 characteristics in the pure samples and SiC doped samples are almost the same. Such a result of α_L properties implies that the pinning mechanism in the SiC doped samples could be consistent with the conventional pinning theory. On the other hand, d_i, which is considered to be proportional to the size of pinning potential, decreases rapidly with increasing magnetic field, especially in the pure samples. For high magnetic field region, the variations of d_i were deduced to be caused by flux creep. The depth of pinning potential, U₀, was estimated by using the values of α_L and d_i. The values of U₀ give evidence of that SiC doping can prevent the flux bundles moving to another pinning center under high magnetic field.

Abstract: DLC/SiC films (SiC as a transition layer) were prepared on the surface of magnesium alloy (AZ31) using a plasma immersion ion deposition (PIID) process. A dense and smooth DLC film can be observed by SEM. The surface hardness can be improved to 11.45GPa by deposition of the DLC film. Electrochemical tests show that the corrosion potential of AZ31 with DLC film is increased from -1.7V to -0.6V, which indicates that the DLC film improves the corrosion resistance of Mg alloy.

Abstract: N-doped TiO2 films were prepared by using N ion beams to bombard TiO2 films surface. By controlling the metal ultrahigh vacuum gat valve, only the N ion beams working pressure was adjusted from 0.1 to 0.9 Pa, with the step size of 0.2 Pa. The composition, chemical bond structure, and optical properties of N-doped TiO2 films were investigated. The result indicated that with increasing the ion source working pressure, more N ions were generated and bombarded with the surface TiO2 films, which could result in more N ions were doped into the films. So with increasing the ion source working pressure from 0.1 to 0.9 Pa, the N/Ti and O/Ti atom ratio increased and decreased monotonously from 0.37 to 0.49 and 1.49 to 0.61, respectively. Meanwhile, because of more N doped into films, the mean absorbency of N doped TiO2 films in the visible range also increased monotonously from 4.8% to 45.8%.

Abstract: The thermal stability and glass-forming ability (GFA) of Zr70Ni30−xAlx (x = 5 − 19) metallic alloys were investigated. Alloy with x = 8 has the largest critical diameter (dc) of 2 mm in the alloy series, which possesses the largest supercooled liquid region, Trg and γ value, simultaneously. Further addition of 2 − 4 at.% Nb to Zr70Ni22Al8 alloy by replacement of Zr increases the dc up to 6 mm. In addition, Zr70Ni22Al8 bulk metallic glass exhibits large compressive plastic strain of 13.8% with yielding stress of 1547 MPa and Young’s modulus of 79 GPa. Addition of Nb increases the strength but lowers the plasticity.

Abstract: The structure and magnetic properties of the melt-spun Fe80–xPtxB20 (x = 0 – 20) alloys have been investigated. The amorphous phase was obtained for the alloys with x = 0 and 5, while the mixed structure consisting of amorphous and fcc-FePt phases was formed for the alloys with x = 10, 15 and 20. The annealed alloys consist of α-Fe + Fe3B phases for x = 0 and 5, Fe3B + Fe2B + fcc-FePt phases for x=10, and Fe2B + fcc-FePt + L10-FePt phases for x = 15 and 20, respectively. The alloys with x = 15 and 20 exhibited hard magnetic characterization after annealing. The coercivity increased with increasing Pt content.

Abstract: The structural defects including dislocations and grain boundaries (GBs) in upgraded metallurgical grade silicon (UMG-Si) prepared by vacuum directional solidification were investigated. The results demonstrated that higher withdrawal rates increased the dislocation density. The state of melt growth changed from quasi-equilibrium to non-equilibrium, and the GB type was also highly related to the withdrawal rate, especially for ∑3 boundary. The change of total interfacial energy and increase of carbon concentration may be a possible driving mechanism for this phenomenon.

Abstract: The removal of impurities in the process of refining metallurgical grade Si by metallurgical method has been one of the most important research. In this paper, a bubble adsorption effect was proposed to refine the primary silicon in the Al-Si melt. The experimental results show that the impurities content in the primary silicon is related to the volume of bubble in the alloys, the more bubbles exist in the alloys, the less impurities are detected in the primary silicon, and the least impurities content is 84.23ppmw except for Al compared to 777.47ppmw in metallurgical grade Si.

Abstract: A new method to prepare micro-nanopowder with incorporating jet milling and electrostatic dispersion was presented in this study. The dispersivity of the powder could be improved during the process of jet milling by having the particles charged with identical charge. Both micro-nanopowders with high dispersion, calcium carbonate (CaCO3) and magnesium zinc ferrite (MgZnF) were prepared respectively. The theoretic studies on this method and the analyses on the effects of preparation parameters on dispersivity, showed that jet milling /electrostatic dispersion (J/E) method to prepare micro-nanopowder in the air without any additive is achievable. The charge voltage and air current pressure would strongly affect the characters of the powder. The charge to mass ratio (q/m) of both powders reached its peak under the charge voltage at 50 kV and air current pressure at 0.3MPa.

Abstract: Bi4-xLnxTi3O12 (Ln = La, Nd or Gd; x = 0, 0.25, 0.5, 0.75 or 1.0) fine powders were prepared by the chemical coprecipitation method. Suitable calcination temperature for each powder was determined. The effects of Ln-substitution on the sintering behaviors, crystal structures, lattice constants and microstructures of sintered bodies were investigated. The crystallization temperature was significantly influenced by lanthanide elements and their amounts, and thus, a suitable temperature for calcination was determined for each substitution. Each calcined powder was milled and fired at 950, 1000, 1050 or 1100°C for 2 hr. It was found that the Ln-substitution drastically inhibited both sintering and grain growth, although the effect was not consistent with the order of Ln ionic radii.

Abstract: In order to develop the ‘Bio-filter’, Si3N4 porous bodies with micro-macro complex pore structure were fabricated. The micro-pores were successfully introduced by inserting PE meshes between the green tapes. Micro-pore size was controlled by adding a small amount of the β-Si3N4 ‘seed’ particles to the α-Si3N4 raw powder. It is expected that the aerobic microbes colonize along the micro-pores consuming dissolved oxygen, which makes the anaerobic ones colonized within the micro-pores to develop the microbe consortium. In this study, this concept was verified by using the S. cerevisiae and B. bifidum as the aerobic and anaerobic microbes, respectively.