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.

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.

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.

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).

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.

Solution combustion synthesis of Fe-Ni-Y_2O_3 nanocomposites for magnetic application

Fe-Ni-Y2O3 nanocomposites with uniform distribution of fine oxide particles in the gamma Fe Ni matrix were successfully fabricated via solution combustion followed by hydrogen reduction. The morphological characteristics and phase transformation of the combusted powder and the Fe-Ni-Y2O3 nanocomposites were characterized by XRD, FESEM and TEM.Porous Fe-Ni-Y2O3 nanocomposites with crystallite size below 100 nm were obtained after reduction. The morphology, phases and magnetic property of Fe-Ni-Y2O3 nanocomposites reduced at different temperatures were investigated. The Fe-Ni-Y2O3 nanocomposite reduced at 900 °C has the maximum saturation magnetization and the minimum coercivity values of 167.41 A/(m2·kg)and 3.11 k A/m, respectively.

Effects of two silicone resin coatings on performance of FeSiAl magnetic powder cores

Two silicon resins with excellent thermal stability,JH1123 and JH7102,are used as the insulated agents and binders for the gas-atomized FeSiAl powder,and corresponding magnetic powder cores(MPCs)are fabricated.The insulation capability and application prospects of the two silicon resins are evaluated by comparing the magnetic properties of the coated powder and MPCs.The scanning electron microscopy,energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy results show that uniform insulation layers are both formed on the powder surfaces.JH1123 has stronger binding ability,and the JH1123-coated powder exhibits severe agglomeration,with d50(average particle size)approximately twice that of the JH7102-coated powder.Both as-prepared MPCs exhibit outstanding soft magnetic properties.Wherein,the permeability of FeSiAl@JH1123 is up to 74.0,which is 35.5%higher than that of FeSiAl@JH7102 because JH1123 can further improve the density of the MPCs.As for FeSiAl@JH7102,it has better direct current bias and lower core loss of 716.9 mW cm^(−3) at 20 mT and 1000 kHz due to its lower coercivity and greater anti-magnetic saturation ability.A comprehensive comparison shows that FeSiAl@JH1123 is suitable for medium and high frequency applications,while FeSiAl@JH7102 is more suitable for high frequency applications.This indicates that the use of JH1123 and JH7102 silicon resins for binding and insulated coating not only simplifies the preparation process of MPCs,but also enables the controlled production of MPCs for different applications.

Development of Technology and Equipment for Non-destructive Testing of Defects in Sewing Mandrels of a Three-roll Screw Mill 30-80

The conditions of heating and cooling of piercing mandrels made of 4X5MFS steel of a three-roll screw mill 30-80 in the production of a closed cavity of steel vessels of small volume are determined.It is established that multiple cycles of heating up to 600℃ and cooling with water up to 80℃ for about 7 seconds/1 cycle lead to the formation of ridges,shells and cracks on the surface and in the volume of the tool.The loss of structural strength of the material leads to the breakdown of the mandrel during the stitching process.The technique and equipment of magnetic powder control have been developed to establish the dynamics of the growth of internal and external defects of mandrels.An equation is obtained that allows determining the increase in the number of defects in the sewing tool of a screw rolling mill.The technology of non-destructive testing made it possible to develop a rational plan for replacing the sewing mandrels,which allows for predicting the appearance of defects leading to a complex breakdown of the deforming tool at the NPO Pribor machine-building enterprise.

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.

Novel CoFeAlMn high-entropy alloys with excellentsoft magnetic properties and high thermal stability

High-entropy alloys(HEAs),which are composed of 3d transition metals such as Fe,Co,and Ni,exhibit an exceptional combination of magnetic and other properties;however,the addition of non-ferromagnetic elements always negatively affects the saturation magnetization strength(M s).Co_(4)Fe_(2)Al_(x)Mn_(y) alloys were designed and investigated in this study to develop a novel HEA with excellent soft magnetic properties.The Co_(4)Fe_(2)Al_(1.5)Mn_(1.5) HEA possesses the highest M s of 161.3 emu g^(-1) thus far reported for magnetic HEAs,a low coercivity of 1.9 Oe,a high electrical resistivity of 173μΩ cm,a superior thermal stability up to 600℃,which originates from the novel microstructure of B2 nanoparticles distributed in a DO_(3) matrix phase,and the crucial transition of Mn from antiferromagnetism to ferromagnetism with the assistance of Al.The Co_(4)Fe_(2_)Al_(1.5)Mn_(1.5) HEA was selected to produce micron-sized powder and soft magnetic powder cores(SMPCs)for application in the exploration field.The SMPCs exhibit a high stable effective perme-ability of 35.9 up to 1 MHz,low core loss of 38.1 mW cm^(-3)(@100 kHz,20 mT),and an excellent direct current(DC)bias performance of 87.7%at 100 Oe.This study paves the way for the development of soft magnetic HEAs with promising applications as magnetic functional materials.

变形和能量注入协同作用制备可控非晶纳米晶结构超高饱和磁化强度FeCoB粉末

非晶纳米晶磁粉芯(ANMPCs)是电子元器件在高频应用的关键软磁材料.但其相对较低的饱和磁化强度无法满足器件的小型化要求.强Fe-Co交换耦合非晶纳米晶粉是制备高磁化强度ANMPCs的潜在材料.本文采用机械球磨法制备了一系列(Fe_(0.8)Co_(0.2))_(87)B_(13)软磁粉末,这些粉末的非晶相、纳米晶相含量和粒径可调.在球磨过程中,出现了合金化、玻璃化和纳米化三个阶段以及粉末形貌和尺寸的非线性变化,进而导致ANMPCs软磁性能的非单调变化.磁粉具有超高饱和磁化强度达239 emu g^(-1),有效磁导率为33.球磨150 h后,FeCoB粉末非晶-纳米晶双相结构达到动态平衡,同时粒径达亚微米尺度,从而提高了粉末高频稳定性且降低了磁芯损耗.在变形和能量注入的协同作用下,机械球磨实现了含极高铁磁元素的非晶-纳米晶双相粉末可控制备、提高了高磁化强度ANMPCs综合软磁性能.

Magnetic property recovery in Nd-Fe-B bonded magnet wastes with chemical reaction and physical dissolution

The main difficulty for the recovery of Nd-Fe-B bonded magnet wastes is how to completely remove the epoxy resins.In this study,chemical reaction and physical dissolution were combined to remove the epoxy resins by adding ammonia-water and mixed organic solvents.Ammonia-water can react with the epoxy functional group of epoxy resin to generate polyols.Mixed organic solvents of alcohol,dimethyl formamide(DMF),and tetrahydrofuran(THF) can dissolve the generated polyols and residual epoxy resins.Under the optimum processing conditions,the epoxy resins in the waste magnetic powders are substantially removed.The oxygen and carbon contents in the recycled magnetic powder are reduced from 13500 × 10^(-6) to 1600 × 10^(-6) and from 19500 × 10^(-6) to 2100 × 10^(-6) with the reduction ratio of88.1% and 89.2%,respectively.The recycled magnetic powder presents improved magnetic properties with MS of 1.306 × 10^(-1) A·m^(2)/g,Mr of 0.926 × 10^(-1) A·m^(2)/g,Hcj of 1.170 T,and(BH)max of 125.732 kJ/m^(3),which reach 99.8%,99.4%,95.9%,and 96.9% of the original magnetic powders,respectively.

Effects of embedding direct reduction followed by magnetic separation on recovering titanium and iron of beach titanomagnetite concentrate

Embedding direct reduction followed by magnetic separation was conducted to fully recover iron and titanium separately from beach titanomagnetite （TTM）. The influences of reduction conditions, such as molar ratio of C to Fe, reduction time, and reduction temperature, were studied. The results showed that the TTM concentrate was reduced to iron and iron-titanium oxides, depending on the reduction time, and the reduction sequence at 1 200℃ was suggested as follows ： Fe2.75 Ti0.25O4→Fe2TiO4→FeTiO3→FeTi2O5. The reduction temperature played a considerable role in the reduction of TTM concentrates. Increasing temperature from 1 100 to 1 200℃ was beneficial to recovering titanium and iron, whereas the results deteriorated as temperature increased further. The results of X-ray diffraction and scanning electron microscopy analyses showed that low temperature （≤1100℃） was unfavorable for the gasification of reductant, resulting in insufficient reducing atmosphere in the reduction process. The molten phase was formed at high temperatures of 1250-1 300℃, which accelerated the migration rate of metallic particles and suppressed the diffusion of reduction gas, resulting in poor reduction. The optimum conditions for reducing TTM concentrate are as follows： molar ratio of C to Fe of 1.68, reduction time of 150 min, and reduction temperature of 1 200℃. Under these conditions, direct reduction iron powder, assaying 90.28 mass% TFe and 1.73 mass% TiO2 with iron recovery of 90.85%, and titanium concentrate, assaying 46.24 mass% TiO2 with TiO2 recovery of 91.15%, were obtained.

Electromagnetic shielding effectiveness of amorphous metallic spheroidal-and flake-based magnetodielectric composites

Flexible,lightweight,conductive materials,having both high rf losses and high permeability,are extremely desirable for applications as electromagnetic(EM)shielding.Gas atomized spherical FeSi-based ferromagnetic metallic particles,having a mean diameter of 14.6μm with a standard deviation of 7.3μm,were measured to have a room temperature saturation magnetic flux density of 1.49 T with a coercivity of 160 A/m.Ball milling of the amorphous particles led to aspect ratios from 1:1(spherical)to>100:1(flake-like).Flake-like particles,suspended in paraffin,were found to not only increase the surface area of fillers enhancing the polarization mechanism but also increase the complex permeability and complex permittivity,and thus provide broadband shielding effectiveness.A loading factor of 40 vol.%of the∼15μm diameter powders provided the largestΔW_(RL=-20 dB)of 9.49 GHz(i.e.,6.55<f<16.04 GHz)at a coating thickness of 2 mm.Overall,powder composites show a wide absorption potential above 18 GHz for<1.5 mm thicknesses.The optimized flake-based composites exhibit strong EM wave absorption with an SE of-40 dB and SE<-10 dB of 17.57 GHz at 40 vol.%filler at a thickness of 1.6 mm.

Preparation of Chromium-iron Metal Powder from Chromium Slag by Reduction Roasting and Magnetic Separation

Chromium slag（CS）has become one of the most hazardous solid waste containing chromium and iron.Based on its characteristics,the technology of reduction roasting and magnetic separation was employed to treat CS.The major impurity element of CS is magnesium and it exists in magnesium ferrite phase,which is hard to recover iron in the absence of additives.During reduction roasting,additives（Al2O3and CaF2）could destroy the structure of magnesium ferrite and improve the iron grade and recovery.The final product,i.e.chromium-iron powder,contains 72.54% Fe and 13.56% Cr,with the iron recovery of 80.34% and chromium recovery of 80.70%.

Structure and magnetic properties of melt-spun Sm-Fe-Nb ribbons and their nitrides

SmFe（10-x）Nbx（x = 0, 0.1, 0.2, 0.3） ribbons and their nitrides were prepared by melt-spinning, followed by annealing and subsequent nitriding. The structure and magnetic properties were investigated by means of X-ray diffraction（XRD） using the Rietveld method, vibrating sample magnetometer（VSM）, transmission electron microscope（TEM） and Mossbauer spectroscopy. XRD analysis shows that the addition of Nb can impede the precipitation of Sm2 Fe（17） and a-Fe phases and the Nb atoms occupy 2 e site in the alloys. At 300 K, the mean hyperfine fields of 2 e site are 29.58 T with Nb doping at x = 0.1 and the corresponding Curie temperature is 552 K. The optimal properties of remanence of Br = 0.9 T, intrinsic coercivity of H（cj）= 741.5 kA·m^-1, and maximum magnetic energy product of（BH）（max）= 124.2 kJ·m-（-3） are gained at x = 0.10 in the nitrides.

Magnetic modification of diamagnetic agglomerate forming powder materials

A simple method for the magnetic modification of various types of powdered agglomerate forming dia- magnetic materials was developed. Magnetic iron oxide particles were prepared from ferrous sulfate by microwave assisted synthesis. A suspension of the magnetic particles in water soluble organic solvent （methanol, ethanol, propanol, isopropyl alcohol, or acetone） was mixed with the material to be modified and then completely dried at elevated temperature. The magnetically modified materials were found to be stable in water suspension at least for 2 months.

Tracing soil erosion with Fe_(3)O_(4) magnetic powder: Principle and application

Magnetic powder is regarded as an effective and economical tracer for estimating soil erosion.However,the principle and application for using magnetic powder to estimate soil erosion are still not fully developed.In this study,magnetic powders with mean diameters of both 30 and 1μm were mixed into three soils at different mass proportion.The relationship between magnetic susceptibility and the mass proportion of the introduced magnetic powder in the tagged soil,and the binding ability of magnetic powder to soil particles after both dry and wet sieving were investigated.The accuracy of tracking soil loss by using magnetic powder as a tracer was assessed.The results showed that there was a significant linear relationship between the magnetic susceptibility and the mass proportion of the introduced magnetic powder in the tagged soil.The relationship between the amount of soil captured by a magnet and the mass proportion of magnetic powder in the tagged soil indicated that soils were readily magnetized by magnetic powder,especially fine fractions.The magnetic susceptibility of magnetic powder in different sizes of soil aggregates was variable.A majority of magnetic powder of both 30 and 1μm diameters was strongly bound with fine particles<0.05 mm in dry and wet sieving.Using the estimated tracer mass proportions,the relative errors between measured and estimated soil losses with enrichment correction factor were less than 18.3%under the simulated rain events.This study not only reveal the principle of Fe_(3)O_(4) powder in soil erosion,but also improve its estimated precision of soil loss,which can make the tracing method by Fe_(3)O_(4) magnetic powder more useable in future.