Effect of Heat Treatment on Structure and Magnetic Performance of Ni-Fe-P Alloy Obtained by Electroless Plating

The electroless deposition of Ni68-Fe10.5-P21.5 alloy has been investigated. The crystallization behavior of the deposit was comparatively studied by using differential scanning calorimetry and X-ray diffractometry. The deposit transforms into a square Ni3P phase at 380. 0 ℃, then changes into a cubic FeNi3 phase at 490. 0 ℃. The microhardness, the size of the formed grains and the magnetic performance of the deposit increase with the increase of the heat treatment temperature below 500 ℃, then they decrease after this temperature. The effect of heat treatment time at 500 ℃ on the surface micromorphology, the structure and the magnetic performance of the deposit were also studied. The resuits show that with the increase of heat treatment time, the extent of crystallization of the deposit increases and the size of the formed grains becomes uniform. The results also show that the magnetic performance of the deposit under heat treatment for 40 min is maximal and then decreases with the increase of heat treatment time. The property change of the deposit is related to the crystal structure and the size of the formed grains of the deposit.

Microstructure and magnetic performance of Ni-substituted high density MnZn ferrite

The effects of NiO on microstructure and magnetic properties of Mn-Zn ferrite with a nominal composition of Zn_(0.32)Mn_(0.60-x)Ni_(x)Fe_(2.08)O_(4)were investigated.The calcined powder of Mn-Zn ferrite was characterized by X-ray diffraction(XRD),the fracture surface of Mn-Zn ferrite was checked by scanning electronic microscope(SEM),and then the magnetic properties were measured.As a result,the substitution of Ni can cause the crystal lattice constant of MnZn ferrite to decline,and the grain size to decrease,therefore improve the magnetic performance of MnZn ferrite whose density exceeds 5.0 g·cm^(-3).

EFFECT OF ELECTROLESS DEPOSITION CONDITIONS ON THE STRUCTURES AND THE MAGNETIC PERFORMANCES OF THE Co-Fe-P ALLOY

Electroless Co-Fe-P alloys were deposited from an alkaline bath, containing boric acid as a buffer agent and sodium citrate as a complexing agent. As a result, with the increase of pH of the bath, the iron content of the deposit increased, whereas the cobalt and phosphorus contents decreased. The structure of the deposit was investigated using X-ray diffraction （XRD） and transmission electron microscope （TEM）. The deposit consisted of hexahedron phase Co, cubic phase Fe-Co, and amorphous phase （crystalline）. The magnetic performances of the deposit were studied using vibrating sample magnetometer （VSM）. The more the content of Fe and the less the content of P （the content of Co being less）, the better the magnetic performances of the deposit. The Co-Fe-P deposit was suitable for use as soft magnetic material.

Performance improvement of Fe-6.5Si soft magnetic composites with hybrid phosphate-silica insulation coatings

Fe-6.5Si soft magnetic composites(SMCs)with hybrid phosphate-silica insulation coatings have been designed to improve their comprehensive property via chemical coating combining sol-gel method in this work.The microstructure and magnetic performance of the Fe-6.5Si SMCs with hybrid phosphate-silica insulation coatings were investigated.The hybrid phosphate-silica coatings with high heat resistance and high withstand pressure,formed on the surface of the Fe-6.5Si ferromagnetic powders,were found stable in the composites.Compared with Fe-6.5Si SMCs coated by single phosphate or single silica,Fe-6.5Si SMCs with hybrid phosphate-silica show much higher permeability and lower core loss.The work provides a new way to optimize the magnetic performance of soft magnetic composites.

Crystal structures and magnetic performance of nanocrystalline Sm-Co compounds

A variety of intermetallic compounds in the binary Sm Co system were reviewed, and the contents were focused on the crystal structures, magnetic properties and the nanoscale effects. The representative nanocrystalline Sm-Co compounds were introduced in details, the diagrams for their lattice structures and the atomic sites and occupancies were provided. Moreover, the magnetic properties of the nanocrystalline Sm-Co compounds were compared with those of the conventional polycrystalline counterparts. It showed that the nanocrystalline Sm Co compounds exhibit special phase stability and remarkably enhanced magnetic performance, which are promising candidates for the matrix phases to develop permanent magnets, particularly the advanced high-temperature magnetic materials.

Sodium Nitrate Passivation as a Novel Insulation Technology for Soft Magnetic Composites

Sodium nitrate passivation has been developed as a new insulation technology for the production of FeSiAl soft magnetic composites (SMCs). In this work, the evolution of coating layers grown at different pH values is investigated involving analyses on their composition and microstructure. An insulation coating obtained using an acidic NaNO_(3) solution is found to contain Fe2O_(3), SiO_(2), Al2O_(3), and AlO(OH). The Fe2O_(3) transforms into Fe3O4 with weakened oxidizability of the NO_(3)– at an elevated pH, whereas an alkaline NaNO_(3) solution leads to the production of Al2O_(3), AlO(OH), and SiO_(2). Such growth is explained from both thermodynamic and kinetic perspectives and is correlated to the soft magnetic properties of the FeSiAl SMCs. Under tuned passivation conditions, optimal performance with an effective permeability of 97.2 and a core loss of 296.4 mW∙cm−3 is achieved at 50 kHz and 100 mT.

GA-BASED PID NEURAL NETWORK CONTROL FOR MAGNETIC BEARING SYSTEMS

In order to overcome the system non-linearity and uncertainty inherent in magnetic bearing systems, a GA（genetic algnrithm）-based PID neural network controller is designed and trained tO emulate the operation of a complete system （magnetic bearing, controller, and power amplifiers）. The feasibility of using a neural network to control nonlinear magnetic bearing systems with unknown dynamics is demonstrated. The key concept of the control scheme is to use GA to evaluate the candidate solutions （chromosomes）, increase the generalization ability of PID neural network and avoid suffering from the local minima problem in network learning due to the use of gradient descent learning method. The simulation results show that the proposed architecture provides well robust performance and better reinforcement learning capability in controlling magnetic bearing systems.

Excellent magnetic softness-magnetization synergy and suppressed defect activation in soft magnetic amorphous alloys by magnetic field annealing

Fe-based amorphous alloys with high saturation magnetic flux density(B_(s))are increasingly attractive from both scientific and technological points of view,however,they usually suffer from the trade-off between magnetization and softness.In this work,we explore the soft magnetic properties(SMPs),magnetic and atomic structures,and defect activation during creep deformation of as-quenched and annealed Fe_(82.65-x)Co_(x)Si_(2)B_(14)Cu_(1.35)(x=0-20)amorphous alloys(AAs).Improved magnetic softness-magnetization synergy has been realized in all these alloys by field annealing.Particularly,superb SMPs with superhigh B_(s) of 1.86 T,low coercivity of 1.2 A/m and high effective permeability of 16300 are obtained in the Fe_(66.65)Co_(16)Si_(2)B_(14)Cu_(1.35) AA.The locally regularized arrangement of domains,homogenized structure with less structural/magnetic defects and suppressed crystal-like ordering by field annealing contribute synergistically to the superb SMPs.Besides,the relaxation time spectra obtained from creep deformation indicate less liquid-like and solid-like defects activated in the field-annealed AA,which is correlated with the structural homogenization and superb SMPs.This work provides new and comprehensive insight into the interplay among external field,heterogeneous structure,SMPs and defect activation of Fe-based AAs,and offers a promising pathway for softening amorphous alloys with high Bs.

Fabrication and application prospects of Pr-Fe-B/Alnico nanocomposite alloys

The potentials of rare earth-based nanocomposite alloys have never been realized due to strict microstructural constraints.Owing to the easy demagnetization it is challenging to increase the soft magnetic phase content.To avoid the easy demagnetization,Pr-Fe-B/Alnico magnets were fabricated and reported in this manuscript.The content of the Alnico phase is increased from 0 to 25 wt%,while the content of Pr element is reduced to below the sub-stoichiometry of the 2:14:1 main phase.The maximum magnetic energy product,which is the figure-of-merit for permanent magnets,is increased from 122 kJ/m^(3) for the standard alloy to 146 kJ/m^(3) for the alloy with 15 wt% Alnico which shows a significant improvement considering the fact that the Curie point of the magnet is also increased by~66 K.The special microstructure contains distinctly and heterogeneously distributed 2:14:1 and Alnico phases.The dimensions of neither the 2:14:1 nor the Alnico phases meet the dimensional requirements of the nanocomposite magnets,but still the smooth demagnetization curves are noted for the alloys.The behavior of effective anisotropy,the performance of the magnets in applied magnetic field and the magnetic interactions among the various constituent grains were quantitatively studied by reversible susceptibility,irreversible susceptibility and re coil loop openness.This study may provide some guiding principles for the development of nanocomposite magnetic alloys with excellent magnetic properties by using much less RE elements.

Metal-organic framework derived magnetic nanoporous carbon as an adsorbent for the magnetic solid-phase extraction of chlorophenols from mushroom sample

In this work, a metal-organic framework derived nanoporous carbon （MOF-5-C） was fabricated and modified with Fe3O4 magnetic nanoparticles. The resulting magnetic MOF-5-derived porous carbon （Fe304@MOF-5-C） was then used for the magnetic solid-phase extraction of chlorophenols （CPs） from mushroom samples prior to high performance liquid chromatography-ultraviolet detection. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and N2 adsorption were used to characterize the adsorbent. After experimental optimization, the amount of the adsorbent was chosen as 8.0 mg, extraction time as 10 min, sample volume as 50 mL, desorption solvent as 0.4 mL （0.2 mL × 2） of alkaline methanol, and sample pH as 6. Under the above optimized conditions, good linearity for the analytes was obtained in the range of 0.8-100.0 ng g 1 with the correlation coefficients between 0.9923 and 0.9963. The limits of detection （SIN= 3） were in the range of 0.25-0.30 ng g-1, and the relative standard deviations were below 6.8%. The result showed that the Fe304@MOF-5-C has an excellent adsorption capacity for the analytes.