A Study on Alnico Permanent Magnet Powders Prepared by Atomization

Alnico powders were prepared by gas atomization process. Composition of the Alnico powders was Fe37.1 A18.2Ni17.6-Co26.6 Cu3.3 Ti7.2 (wt pct) which was the same as that of commercially available Alnico magnets. Averageparticle size of the powders was 119μm. Effects of heat treatment in magnetic field on magnetic properties of thepowders were investigated. The optimum process of heat treatment was found as follows, heated at 870℃ for 1min first, then cooled down to 700℃ at cooling rate 0.3℃/s in magnetic field, and finally aged isothermally for 4 h.Magnetic properties of the Alnico powders were measued and the results were that intrinsic coercivity i_H_c was 1.0kOe and remanence M_r was 36.5 emu/g.

Microstructure of pre-sintered permanent magnetic strontium ferrite powder

The microstructure and characteristics of pre-sintered strontium ferrite powder were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The present study shows that the pre-sintered strontium ferrite powder is provided with a certain particle size distribution, which results in high-density magnets. The strontium ferrite particle has a laminar hexagonal structure with a size similar to ferrite single domain. Ferric oxide phase due to an incomplete solid phase reaction in the first sintering is discovered, which will deteriorate the magnetic properties of ferrite magnet. In addition, the waste ferrite magnets with needle shape arranging along C axis in good order into the powders are found, which have no negative effects on finished product quality.

Enhanced soft magnetic properties of iron powders through coating MnZn ferrite by one-step sol–gel synthesis

The MnZn ferrite coating formed on the surface of iron-based soft magnetic powders via facile and modified sol–gel process has been fabricated to obtain better magnetic performance due to its higher permeability compared with traditional nonmagnetic insulation coatings. The influence of the MnZn ferrite contents on the magnetic performance of the soft magnetic composites(SMCs) has been studied. As the MnZn insulation content increases, the core loss first experiences a decreasing trend that is followed by progressive increase, while the permeability follows an increasing trend and subsequently degrades. The optimized magnetic performance is achieved with 2.0 wt% MnZn ferrite, which results from the decrement of inter-particle eddy current losses based on loss separation. A uniform and compact coating layer composed of MnZn ferrite and oxides with an average thickness of 0.38 ± 0.08 μm is obtained by utilizing ion beam technology, and the interface between the powders and the coating shows satisfied adhesiveness compared with the sample directly prepared by mechanical mixing. The evolution of the coating layers during the calcination process has been presented based on careful analysis of the composition and microstructure.

Synthesis of Fe_3O_4 Magnetic Powder from Spent Pickling Liquors

Spent pickling liquors pose a serious environmental problem in most industrialized countries, mainly owing to their corrosive properties and their ferrous iron and hydrochloric acid content. In this paper, spent pickling liquor was used as an inexpensive raw material to prepare Fe304 magnetic powder via an oxidation method. Being able to recover the dissolved iron from spent pickling liquors would not only salvage a valuable material but also render the effluent environmentally benign. The structure of the Fe_3O_4 magnetic powder was characterized by X-ray diffraction. The morphology and size were characterized by scanning electron microscopy and transmission electron microscopy. Their magnetic properties were tested at room temperature by a vibrating sample magnetometer. In addition, the saturation magnetization of Fe_3 O_4 products can be further enhanced to 96.1 emu/g after purification.

DYNAMIC COMPACTION OF PURE COPPER POWDER USING PULSED MAGNETIC FORCE

The compaction of pure Cu powder was carried out through a series of experiments using dynamic magnetic pulse compaction, and the effects of process parameters, such as discharge energy and compacting direction, on the homogeneity and the compaction density of compacted specimens were presented and discussed. The results indicated that the compaction density of specimens increased with the augment of discharge voltage and time. During unidirectional compaction, there was a density gradient along the loading direction in the compacted specimen, and the minimum compaction density was localized to the center of the bottom of the specimen. The larger the aspect ratio of a powder body, the higher the compaction density of the compacted specimen. And high conductivity drivers were beneficial to the increase of the compaction density. The iterative and the double direction compaction were efficient means to manufacture the homogeneous and high-density powder parts.

The structural and magnetic properties of barium ferrite powders prepared by the sol-gel method

In this paper, M-type hexagonal barium ferrite powders are synthesized using the sol-gel method. A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 ℃ using thermo-gravimetric analysis and differential scanning calorimetry. The effects of the additives and the cacinating temperature on the magnetic properties are investigated, and the results show that single-phase barium ferrite powders can be formed. After heat-treating at 950 ℃ for 4h with 3 wt% additive, the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g, respectively.

Effects of temperature on the mechanical properties of Ti6Al4V powder compacts prepared by magnetic pulse compaction

The effects of temperature （0-500°C） on the compressive strength,hardness,average relative density,and microstructure of Ti6Al4V powder green compacts prepared by magnetic pulse compaction were investigated.The results show that with increasing heating temperature,the compressive strength first increases and then decreases with the maximum value of 976.74 MPa at 400°C.The average relative density and hardness constantly increase,and their values reach 96.11% and HRA 69.8 at 500°C,respectively.The increase of partial welding is found among the junctions of particles inside the compacts; there is no obvious grain growth inside the compacts within the temperature range.

Effects of Rare Earth Doping on the Properties of γ-Fe_2O_3 Magnetic Powder

The effects of rare earth doping on the formation process of α-FeOOH crystallite and the properties of γ-Fe2O3 magnetic powder were investigated. The growth of needle α FeOOH crystallite was completed by the basic process. The experimental results show that the rare earth doping can increase the aspect axial ratio of needle α-FeOOH grains. its anti-sintering capability during the heat-treatment and the thermostability of γ-Fe2O3 magnetic properties. The magnetic properties of γ-Fe2O3 doping with rare earth are as follows: the coercivity Hc=36.3 kA/m (445 Oe), the ratio saturation magnetization σs=90.4μWbm/kg (72 emu/g), the ratio remanent magnetization σr=54 μWbm/kg (43 emu/g), and the temperature coefficient of remanent magnetization of γ-Fe2O3 doping with 0.1 mol% Dy can reach -5 ×10-4℃-1.

Microstructure and mechanical properties of Ti6Al4V powder compacts prepared by magnetic pulse compaction

Ti6Al4V powder compaction was performed by using magnetic pulse compaction in air at 200℃.Effects of process parameters such as voltage,capacitance,discharge times on the microstructure,compressive strength,hardness and relative density of compacts were investigated.The experimental results show that the relative density,hardness and compressive strength of compacted specimens increase with increasing voltage.In addition,the relative density and compressive strength of compacted specimens increase with the augmentation of capacitance in the range investigated.The relative density increases,the hardness firstly increases and then tends to be a fixed value;and the compressive strength firstly increases and then decreases from one to five times compaction.Both values of the hardness and compressive strength reach the maxima of HRA 69.1 and 1 062.31 MPa,at three times compaction,respectively.There are pores in and between particles.

Evaluation of Mean Crystallite Size on Magnetic Powder by Scanning Electron Microscopy and Synchrotron Diffractometry

This paper presents the results of investigations carried out with Pr-based magnetic powders. The magnetically hard powders were produced from homogenised alloys using a high temperature hydrogen pulverization process. Alloys and powders were investigated by scanning electron microscopy and by energy dispersive X-ray analysis. Mean crystallite size of the pulverized material was estimated using synchrotron powder diffractometry and the Scherrer method. A comparison between these two investigation techniques has been carried out. The effects of copper on the properties of the magnetic powders have been studied. It has been shown that the addition of this alloying element had a marked effect on the microstructure of the powders.

Magnetic Properties of Nanocrystalline Fe_(60)Cr_(40) Powders Prepared by Mechanical Alloying in Vacuum and Air

Magnetic properties of nanocrystalline Fe_~60 Cr_~40 powders prepared by mechanical alloying in vacuum and air were investigated by utilizing the measurements of magnetization, X-ray diffraction, and ~ ~57 Fe Mssbauer spectrum. The results show that the Fe_~60 Cr_~40 powders keep the bcc structure during milling in air and vacuum. The saturation magnetization of the Fe_~60 Cr_~40 powders milled in vacuum and air decreases with the increase of the milling time up to 45 h. The decrease of saturation magnetization of the Fe_~60 Cr_~40 powders milled in vacuum is due to the formation of Fe-Cr solid solution, while in air it is due to the formation of paramagnetic disorder structure and solid solution.

Effects of Heat-treatment on Microstructure and Magnetic Properties of Ba Ferrite Ultrafine Powders Prepared by Sol-gel

Barium (Bag) ferrite ultra fine powders were synthesized by using sol-gel in which polyethylene glycol 200(PEG200) was used as gelling agent. The transition of Ba ferrite was studied by thermal gravimetric and differential thermal analysis (TG-DTA) technology. The micro structural changes were analyzed using X-ray diffraction (XRD) and atomic force microscopy (AFM) for the specimens annealed at different temperatures. The transition temperatures were 414.55°C and separately corresponding to BaFe2O4 and BaFe,2O19. There were three types of microstructures for Ba ferrite ultrafine powder specimen annealed at 800°C. For the specimens annealed at different temperatures, there were different kinds of Ba ferrites. The ferrite powder consists of BaFet2O19 and BaFe2O4 for the specimen annealed at 800°C, and only BaFe^O^ can be found in the specimen annealed at 1000°C. The magnetic properties, a , and H c of BaFC|2O19 ultrafine powders are different from that of BaFe12O19 bulk material.

Effect of Particle Size and Distribution of Rapidly Quenching NdFeB Magnetic Powder on Magnetic Properties of Polymer-Bonded NdFeB Permanent Magnet

The effect of particle size and distribution of rapidly quenching NdFeB magnetic powder on the magnetic properties of polymerbonded NdFeB permanent magnet was studied. The results show that the particle size and the distribution of rapidly quenching NdFeB magnetic powder have significant effects on the magnetic properties of polymerbonded NdFeB permanent magnet. As long as the size and the distribution of rapidly quenching NdFeB powder are within the right range, high magnetic properties of polymerbonded NdFeB permanent magnet can be obtained. This is mainly because the rapidly quenching NdFeB magnetic powder has high hardness and is scaleshaped. The larger the size of rapidly quenching NdFeB particles is, the more difficult it is to obtain high density of bonded NdFeB magnet. However the structure will be destroyed if the size is too small. It results in the deterioration of magnetic properties. The mechanism is also discussed.

Structure,room-temperature magnetic and optical properties of Mn-doped TiO_2 nano powders prepared by the sol-gel process

TiO2 nano powders with Mn concentration of 0 at%-12 at% were synthesized by the sol-gel process, and were annealed at 500 ℃ and 800 ℃ in air for 2 hrs. X-ray diffraction （XRD） measurements indicate that the Mn-TiO2 nano powders with Mn concentration of 1 at% and 2 at% annealed at 500 and 800 ℃ are of pure anatase and rutile, respectively. The scanning electron microscope （SEM） observations reveal that the crystal grain size increases with the annealing temperature, and the high resolution transmission electron microscopy （HRTEM） investigations further indicate that the samples are well crystallized, confirming that Mn has doped into the TiO2 crystal lattice effectively. The room temperature ferromagnetism, which could be explained within the scope of the bound magnetic polaron （BMP） theory, is detected in the Mn-TiO2 samples with Mn concentration of 2 at%, and the magnetization of the powders annealed at 500 ℃ is stronger than that of the sample treated at 800 ℃. The UV-VIS diffuse reflectance spectra results demonstrate that the absorption of the TiO2 powders could be enlarged by the enhanced trapped electron absorption caused by Mn doping.

Fabrication of ultrafine Nd-Fe-B powder by a modified reduction-diffusion process

In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was <<1 μm. Most Nd2Fe14B particles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were iHc=～5.9 kOe, Br=～5.5 kG, and (BH)max=～6 MGOe.

Preparation of Immuno-magnetic Beads and Their Separation & Detection to Ovary Cancer Cells

The organic monomer-molecule with nanometer magnetic powder by means of reforming the surface of nanometer magnetic powder have been synthesized. Magnetic beads in diameter of 2 mum or so am obtained by controlling conditions. Ovary cancer cells of ascites are separated and ovary cancer cells of blood arc detected by using immuno-magnetic beads linked with ovary cancer cell mono-antibodies. Results show that the specificity is 85% sensitivity is 87%, accuracy is 84%, cells acquiring purity is 90%, cells activity is 92% and detection sensitivity is 25 x 10(-7).

Synthesis of Ultrafine Fe_3O_4 Powder via a Novel Ageing Process

Ultrafine Fe3O4 powder was successfully synthesized via a novel ageing process from a precursor FeO（OH）, which was the hydrolysate of FeCl3 in the urea solution. The structure of as-synthesized powder was characterized by X-ray diffraction （XRD）, and the morphology of these nanoparticles was investigated using a transmission electron microscope （TEM）. Pure phase Fe3O4 was obtained and the mean diameter of these nanoparticles was about 21 nm.Furthermore, the study indicated that the precursor FeO（OH） played an important role in the formation of Fe3O4 nanoparticles. The mechanism was also discussed.

Grain Growth Behavior in Sintered Nd-Fe-B Magnets

The Nd2Fe14B grain growth behavior in sintered Nd-Fe-B magnets was quantitatively described.The effects of sintering temperature and time,and alloy powder size and its distribution on grain growth process were analyzed.Hence,possible grain growth mechanisms in these magnets were qualitatively discussed.The Nd2Fe14B grain growth proceeded at quite a high rate in the initial 0~1 h of sintering and from then onwards the grain growth rate decreased.A large average particle size or a wide particle size distribution of initial alloy powders was found to remarkably accelerate the grain growth process and even result in the occurrence of abnormal grain growth.On the basis of experimental results,two grain growth mechanisms were considered to operate during sintering of Nd-Fe-B magnets,that is,dissolution and re-precipitation of Nd2Fe14B particles,and Nd2Fe14B particle growth by coalescence.It was believed that Nd2Fe14B particle growth by coalescence not only produced a large average grain size and a wide grain size distribution,but also was the fundamental reason for the formation of abnormally large grains in the microstructure of sintered Nd-Fe-B magnets.

EFFECT OF Si CONTENT ON ORDERING DEGREE AND ELECTROMAGNETIC CHARACTERISTICS IN FeSiAl ALLOYS

FeSiAl alloys ribbons synthesized by melt-quench were annealed in vacuum at 873 K for 60 rain. The flaky powders were prepared by milling the annealed ribbons for 70 h. After milling, the powders were heat treated at 573 K for 90 rain. The ordering degree of the powders lattice structure was analyzed by X-ray diffraction （XRD）. The measurement of specific saturation magnetization was carried out by vibrating samples magnetometer （VSM）. Complex permittivity and complex permeability in the frequency band of 0.5-18 GHz were measured with the vector network analyzer. The ordering degree of the superlattice structure increased from 0.2＇7 to 0.49. Complex permittivity and complex permeability decreased with increasing Si content. After ordering, the specific saturation magnetization decreased from 134.2 to 85.0 A.m2.kg-1. For use in anti-EMI material, the total contents of Si and Al in FeSiAl alloys should be controlled at a low level.