Materials Science Forum Vols. 654-656

Abstract: The inductor for a power supply is expected to have higher efficiency and capability of dealing satisfactorily with large current. Additionally, high corrosion resistance characteristics are also required for commercial inductors in practical use of. Thereby, we focused on Fe-based glassy metal alloys with both high magnetization and low magnetic anisotropy ［1］, and developed the novel glassy metal alloys with a chemical composition Fe97-x-yPxByNb2Cr1. In this glassy metal alloy, 1 at % Cr is the optimum composition for the realization of higher corrosion resistance as well as a high magnetic flux density. The glassy Fe97-x-yPxByNb2Cr1 (x=5-13, y=7-15) alloy exhibits the high glass-forming ability leading to the large thickness of 110-150 μm and low coercive force of 2.5-3.1 A/m due to higher structural homogeneity in wide range of composition. The large critical thickness of this alloy should be caused by the high glass-forming ability (GFA) due to the existence of the super cooled liquid region (Tx) of roughly 30 K. Therefore a Fe77P7B13Nb2Cr1 powder/resin composite core displays a much lower core loss of 650 W/m3 than the conventional amorphous Fe75Si10B12Cr3 powder/resin composite core by approximately 1/3.

Abstract: Nanocrystalline Fe-Si-B-P-Cu wide ribbons, with 15-30mm width, using industrial raw materials have been investigated. A homogeneous nanocrystalline structure composed of α-Fe grains with around 10 nm in diameter was realized after crystallization and the nanocrystalline alloys exhibit the high Bs of 1.74-1.82 T, the low Hc of 6.5-7.2 A/m and the low W at 50Hz-1.7T of 0.42-0.60W/kg. Therefore, the nanocrystalline Fe-Si-B-P-Cu soft magnetic alloy has a large economical advantage of low material cost by using industrial raw materials.

Abstract: Nanocrystalline Fe-Co alloy powders, which were prepared by high-energy mechanical milling, were nitrided under the mixing gas of NH3/H2 in the temperature range from 380°C to 510°C. X-ray diffraction (XRD) was used to analyze the grain size and reaction during the processing. The magnetic properties of the nitrided powders were measured by Vibrating Sample Magnetometer (VSM). The results show that with the appearance of Fe4N phase after nitride treatment, and the grain-size of FeCo phase decreases with the increase of nitridation temperature between 380°C to 450°C.The saturation magnetization of nitrided alloy powder treated at 480°C is about 18% higher than that of the initial Fe-Co alloy powder, accompanied by the reduction of the coercivity. Transmission electron microscope (TEM) was used, attempting to further analyze the effect of Fe4N phase on microstructure and magnetic properties of the powder mixtures.

Abstract: In the present work, an extensive research program has been undertaken to characterise a wide spectrum of properties of nano-metals. In particular, the effect of grain refinement on such properties as fatigue, corrosion and wear resistance, conductivity and thermal stability has been studied for various nano-metals (aluminium, copper and iron alloys). The results have revealed that nano-grain refinement also improves physical properties of single phase metals. A disadvantageous effect of large (micron sized) particles, which do not undergo refinement during the processing, has been also recognized.

Abstract: Nanocrystalline materials with high strength have been reported in large numbers. In particular, there has been considerable research on electrodeposited nanocrystalline Ni (nc-Ni) and nc-Ni alloys. However, reported data vary widely especially in ductility. Therefore, it is necessary to obtain the true characteristic value of nc-Ni and nc-Ni alloys. In the present study, nc-Ni and nc-Ni-W was electrodeposited under different conditions in order to obtained bulk nc-Ni and nc-Ni-W with high tensile strength and good ductility. At first, bulk nc-Ni-W was fabricated using a sulfamate bath. Although the resulting bulk nc-Ni-W had inhomogeneous grain size and W-concentration, this sample exhibited plastic deformation behavior. Then, nc-Ni was fabiricated by four types of sulfamate baths. As a result, the nc-Ni obtained from a sulfamate bath containg added saccharine and 2-butyne-1,4-diol exhibited brittle behavior. In contrast, bulk nc-Ni obtained from sulfamate bath with a grain size of about 60 nm exhibited a tensile strength of about 1000 MPa and ductility of 8.8 %.

Abstract: The tensile specimen of nanocrystalline Ni–W alloys with 50 μm × 20 μm in area and 4 mm in gauge length was made by using an electrodeposit together with ultraviolet light lithographic technique. The composition and grain size were Ni-16.9 at.% W and about 6 nm, respectively. Tensile testing of the alloy was carried out. The nominal tensile strength and Young’s modulus were about 2.7 GPa and 123 GPa, respectively. The elastic strain and plastic strain were about 2 % and 1 %, respectively. The stress-strain curve showed work hardening. The macroscopic fracture part yielded necking and the microscopic fracture surface showed dimple pattern. As mentioned above, this electrodeposited nanocrystalline Ni-W alloy showed high strength, low elastic modulus and high ductility.

Abstract: Nanocrystalline and microcrystalline Fe-10Cr alloys were prepared by high energy ball milling followed by compaction and sintering, and then oxidized in air for 52 hours at 400°C. The oxidation resistance of nanocrystalline Fe-10Cr alloy as determined by measuring the weight gain after regular time intervals was compared with that of the microcrystalline alloy of same chemical composition (also prepared by the same processing route and oxidized under identical conditions). Oxidation resistance of nanocrystalline Fe10Cr alloy was found to be in excess of an order of magnitude superior than that of microcrystalline Fe10Cr alloy. The paper also presents results of secondary ion mass spectrometry of oxidized samples of nanocrystalline and microcrystalline Fe-Cr alloys, evidencing the formation of a more protective oxide scale in the nanocrystalline alloy.

Abstract: This paper introduces a novel process for growing one-dimensional nanomaterials. That is, firstly, preparing a pure metal nanocrystalline film by using pulse electro-deposition, then, using this film as a catalyst for synthesizing variant one-dimensional carbon nanomaterials and one-dimensional metal oxide nanoneedles. Comparing with the nanoparticle catalyst, the growth mechanism of the present one-dimensional nanomaterials belongs to the “base growth model”, and it has advantages such as a much simpler process and no post purification requirement. In addition, the present method provides a possibility for diameter control of the one-dimensional nanomaterials through grain size control of the nanocrystalline film by adjusting the pulse electro-deposition parameters.

Abstract: We report the development of new nanoparticle phosphors and quantum dot structures designed for applications to enhance the color rendering and efficiency of high brightness white LEDs, as well as for bio-sensing applications. The intrinsic problem of self-absorption, high toxicity, and high sensitivity to thermal quenching of conventional quantum dot systems has prevented their adoption to LED devices. Doped Cd-free quantum dots may circumvent these issues due to their distinct Stokes shift and improved stability at high temperature. We report on the modification of Mn-doped ZnSe/ZnS core-shell quantum dots for application to the (blue diode + yellow emitter) white LED system. Band gap tuning for 460 nm excitation, inorganic shell growth and in-situ monitoring for enhanced efficiency, and analysis of thermal stability will are reported.

Abstract: Magnetoplumbite-type (M-type) strontium ferrite particles with two stoichiometric ratios (SrFexO19; x = 9.2 and 11.6) have been synthesized via the sol-gel technique employing ethylene glycol as the gel precursor. The prepared samples were characterized using x-ray diffractometry (XRD), thermogravimetric analysis (TGA), photoluminescence (PL) spectrophotometry, field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectrometry (EDS) and superconductivity quantum interference device magnetometry (SQUID). X-ray powder diffraction patterns showed that the samples were single-phase with the space group of P63/mmc and cell parameter values of a = 5.88 Ǻ and c = 23.03 – 23.04 Ǻ. EDS results confirmed the composition being mainly of M-type SrFe12O19. The photoluminescence property of strontium ferrite was examined at excitation wavelength of 260 - 290 nm and significant PL emission peaks centered at 334 nm were detected. Both as-prepared strontium ferrites exhibited significant oxygen vacancies which were detectable via TGA where the sample with the Sr/Fe ratio of 1:11.6 exhibited the highest oxygen vacancies in its structure.