Materials Science Forum Vols. 534-536

Abstract: In the previous work, we reported a P/M soft magnetic material with super low core loss value of W10/1k = 68 W/kg which is lower than that of 0.35mm-thick flat rolled soft magnetic laminated steel sheets. But this material lack of strength characteristics due to spherical particles produced by a gas-atomizing method. That is, the value of transverse rupture strength (TRS) was only 20MPa when a non-hygroscopicity resin was used as binder. In order to achieve both low core loss and high strength, the iron powder (shape, surface morphology) and binder strength was improved, and we were able to obtain a material with TRS of 80 MPa and core loss (W10/1k) of 108 W/kg of. Furthermore, by using this binder system, we were able to obtain a TRS of over 50MPa for the material with spherical particles (W10/1k = 81 W/kg).

Abstract: Magnetic core components are often made from laminated sheet steel, but they are difficult to manufacture in near net shape, resulting in large core losses at higher frequencies. In this study, the pure iron powder was treated with aqueous phosphoric acid to produce phosphate insulating layer on the surface. After drying the powder, it was mixed with 0.5wt% Zn stearate and compacted in a mold with a diameter of 20mm at 800MPa. The powder compacts were then heat treated at 500°C for 1 hour. The results showed that insulated iron powder was obtained with uniform phosphate layer by chemical reaction. With increased amount of phosphate layer, the core loss and density of compacts were decreased. It was also found that the addition of ethyl alcohol during insulating reaction resulted in improved core loss value.

Abstract: The coercivity of Sm2Co17-based permanent magnets at high operating temperature gradually increased with increasing Cu and Zr content, but decreased as the Fe content increased. The magnet Sm(Co0.7Fe0.1Cu0.16Zr0.04)6.7 that was studied had a room temperature intrinsic coercivity of about 30 kOe. For this magnet, the temperature coefficient of coercivity RT − 500 o C β and Hci at 500oC are -0.148%/oC and 8.6kOe. The magnet is composed mainly by 2:17R cell interior, 1:5 cell boundary phase, as well as 2:17H lamellar phase. There is a maze-like domain structure in the magnet. The HRXRD evidence shows that the phase transformation at high temperature leads to the degraded magnetic properties of the magnets.

Abstract: The magnetic inductance of nanocrystalline Fe73Si16B7Nb3Cu1 and an amorphous FeSiB sheet has been investigated to identify the radiofrequency identification (RFID) performance. Planar flow cast amorphous ribbons were pulverized and classified using a stack of sieve. The powder was mixed with binder and solvent and tape-casted to form 0.6-0.8 mm thick films. The inductance of the sheet was measured to investigate the RFID characteristics of the nanocrystalline and the amorphous materials. Results showed that the atmosphere for annealing significantly influenced on the inductance of the material. The surface oxidation of the particles was the main reason for the reduced inductance. The maximum inductance of Fe73Si16B7Nb3Cu1 alloy was about 88μH at 17.4 MHz, which was about 65% greater compared to the amorphous FeSiB alloy. The higher inductance in the nanocrystalline alloy indicates that it may be used as a potential replacement of current RFID materials.

Abstract: Nd2Fe14B/α-Fe nanocomposite powders with a nominal composition of Nd12Fe82B6 were prepared by HDDR combined with mechanical milling. The microstructure of both the as-disproportionated and the subsequently desorption-recombination annealed alloy powders was studied by Mössbauer spectrometry and TEM. The magnetic properties were investigated by VSM using bonded magnet samples. The results showed that the annealing temperature had significant influence on both the recombination kinetics and the grain size of the Nd2Fe14B/α-Fe nanocomposite phases, and the bonded magnet samples presented the best magnetic properties when the nanocomposite powders were prepared by annealing at 760°C for 30 min.

Abstract: In order to obtain specific magnetic properties, it is of paramount importance to increase the alloy density of components fabricated by powder metallurgy. An alternative to increase the density of alloys such as Fe-49Co-2V would be the use of elemental Fe and Co instead of the prealloyed powder. Trying to give some insight on the industrial application of this strategy, this paper investigates the replacement of more conventional pre-alloyed Fe-49Co-2V powders with elemental Fe and Co. A previous analysis shows that it is possible to achieve higher densities using elemental Fe and Co powders sintered at the same temperature than Fe-49Co-2V. It is also shown that this leads to a noticeable improvement in some important magnetic properties such as permeability and magnetic induction.

Abstract: This study describes the development of a high throughput purification process of nucleic acid using amino-functionalized silica coated ferrite nanoparticles. The magnetic ferrite nanoparticles were synthesized and coated by a silica precursor in controlling the coating thicknesses and sizeses. The surface modification was performed with amino-functionalized organic silanes on silica coated magnetic nanoparticles. The spectroscopic measurements such as a FT-IR (ATR-method) and Vibrational Sample Magnetometer (VSM) were used to characterize the chemical structures and magnetic strengths. To elucidate the relationship between surface area, pore size distribution and reactivity of the materials, BET and Zeta potential were used. The use of functionalized self-assembled magnetic ferrite nanoparticles for a nucleic acid separation process provides a lot of advantages compared to the conventional silica based process.

Abstract: MgO insulation coating with thickness of ca. 50nm was evaporated on the surface of iron powder and fabricated soft magnetic composite(SMC) with low iron loss. The MgO insulation coating had greater heat resistance than conventional phosphate insulation coating, which enabled stress relieving annealing at higher temperature (600C). Electrical and magnetic properties of SMC was examined. The electrical resistivity of the SMC annealed at 700C was 21μΩm. The iron loss at 50Hz for Bm = 1.5T was 5.34W, which was 40% of conventional SMC and was at the same level with laminated steel plate (t0.35). These results show that MgO insulation coating has enough heat resistance and adhesiveness to powder surface to obtain SMC with low iron loss.