Chemical synthesis of SmCo5/Co magnetic nanocomposites

A three-step chemical synthesis of SmCo5/Co nanocomposites was developed. Firstly, the Co-Sm（OH）3-Ca（OH）2 precursors were prepared by co-precipitation.Secondly, SmCo5 particles were obtained by reductive annealing of the precursors. At last, the SmCo5/Co nanocomposites were achieved by chemical deposition based on SmCo5 particles. The SmCo5/Co nanocomposites contain hard magnetic phase of SmCo5 with about 100 nm in size and soft magnetic phase of Co with about 8 nm in size,exhibiting independent two-phase structure without alloying. Compared to that of single-phase SmCo5 particles, the saturation magnetization of SmCo5/Co nanocomposites is increased by 27.5%. The synthesis provides a new route to fabricate SmCo-based nanocomposites.

Solution processed MnBi-FeCo magnetic nanocomposites

Advanced permanent magnets based on rare-earth-free MnBi intermetallic alloys are considered energy-critical materials due to their applications in high temperature power electronics and green energy-related generators and motors, owing to their positive temperature coefficient of magnetic anisotropy. However, a direct method to achieve high saturation magnetization, without the significant loss of coercivity, is critical for attaining high performance MnBi magnets. Here, we demonstrate the synthesis and processing of magnetic nanocomposites, consisting of metal-redox MnBi nanoparticles and electro-spun FeCo nanowires. The composition ratio, processing dependent magnetism, and increased coercivity with increasing temperature, were studied in MnBi-FeCo nanocomposites. The magnetic performance of nanocomposites was dictated by interfacial coupling between magnetically hard MnBi and semi-hard FeCo nanowires, as well as the composition ratio and processing conditions. Solution processed MnBi-FeCo nanocomposites allow the potential for the development of high temperature and high performance rare-earth-free permanent magnets.

Synthesis and Characterization of Heterocyclic Functionalized Polymers by Click Reaction: Preparation of Magnetic Nanocomposites and Studies on Their Thermal, Mechanical, Photophysical and Metal Ions Removal Properties

This work reports synthesis and characterization of heterocyclic functionalized polymers, poly（triazole-etherimidazole）s（PTAEI）, from a dialkyne-terminated compound, 3-（4,5-bis（4-（propargyloxy）phenyl）-1H-imidazol-2-yl）-9-ethyl-9H-carbazole, by using click reaction. PTAEIs were characterized and their properties such as solubility, thermal, mechanical, photophysical and metal ions adsorption were investigated. These polymers had weight average molar masses（Mw） in the range of 19100-26700 g/mol, exhibited excellent solubility in polar aprotic solvents and formed low-colored flexible thin films by solution casting method. They exhibited good thermal stability with glass transition temperatures（Tg） between 160 °C and 211 °C and 10% weight loss temperatures（T10%） in the range of 308-426 °C. Nanocomposites of PTAEIs with epoxide-terminated Fe3O4 showed that strong interfacial interaction between inorganic particles and the polymer matrix contributed to the enhanced thermal and mechanical properties. The photoluminescence intensity of the PTAEIs increased and the spectra red shifted with increasing Fe3O4 content. The PTAEIs and nanocomposites were tested for their extraction capability of metal ions from aqueous solutions either individually or in the mixture.

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.

Absorption performance of DMSA modified Fe_3O_4@SiO_2 core/shell magnetic nanocomposite for Pb^(2+) removal

The purpose of this study is to explore the adsorption performance of meso-2,3-dimercaptosuccinic acid(DMSA)modified Fe3O4@SiO2 magnetic nanocomposite(Fe3O4@SiO2@DMSA)for Pb2+ions removal from aqueous solutions.The effects of solution pH,initial concentration of Pb2+ions,contact time,and temperature on the amount of Pb2+adsorbed were investigated.Adsorption isotherms,adsorption kinetics,and thermodynamic analysis were also studied.The results showed that the maximum adsorption capacity of the Fe3O4@SiO2@DMSA composite is 50.5 mg/g at 298 K,which is higher than that of Fe3O4 and Fe3O4@SiO2 magnetic nanoparticles.The adsorption process agreed well with Langmuir adsorption isotherm models and pseudo second-order kinetics.The thermodynamic analysis revealed that the adsorption was spontaneous,endothermic and energetically driven in nature.

Effect of high magnetic field on the crystallization of Nd_2Fe_(14)B/α-Fe nanocomposite magnets

Nd8.1Dy0.9Fe76.95Co8.55B5.5 nanocomposite magnets annealed with and without a 10 T magnetic field were investigated in this article. The ribbons with coexisting amorphous and crystalline phases were selected to do this study. The resuits of Moessbauer spectroscopy revealed that the content of α--Fe increased when annealed in high strength magnetic field. The size of the grains also increased considerably after the application of magnetic annealing. All these led to the decrease of the magnetic properties, especially the coercivity of the ribbons.

Effect of Gallium Addition on Magnetic Properties of Nd_2Fe_(14)B-Based/α-Fe Nanocomposite Magnets

The influence of Ga addition on the crystallization behavior and the magnetic properties of nanocomposite Nd2Fe14B-based/α-Fe magnets was investigated. It was found that the addition of 0.2% did not change the crystallization temperature of amorphous alloy, but the magnetic properties were improved significantly because of the strong exchange coupling interaction between the hard and soft magnetic phases. The optimum magnetic properties with iHc = 600. 3 kA· m^-1, B r = 0.75 T, and （BH）max = 88.03 kJ· m^-3 were obtained in bonded Nd9.5（FeCoZr）83.8 Ga0.3 B6.5 magnet with 15 m·s^- 1 wheel speed and 670 ℃ annealing treatment. The apparent improvement of magnetic properties originates from the grain refinement calculated using the Scherrer formula from corresponding XRD patterns and the excellent rectangularity of the demagnetization curve.

Effect of Zirconium Content on Microstructure and Magnetic Properties of Nanocomposite Bonded Magnets

Five kinds of bonded magnets with compositions of Nd(10.5)Fe(78.4-x)Co(5)Zr(x)B(6.1) (atom percentage x = 0, 1.0, 1.5, 2.0, 2.5) were prepared by rapid quenching, post heat treatment and mould-pressing. The microstructure and crystallization behavior were studied by X-ray diffraction (XRD), differential thermal analysis (DTA) and atomic force microscopy (AFM). The results suggest that high content of Zr can increase the glass formation ability (GFA) of alloys. When the content of Zr is controlled at a certain level, Fe,Zr with high melting point is formed in the alloys, and grain size is reduced consequently. At the same time, because of Zr addition, the coercivity and squareness of demagnetization loop are obviously improved, and the energy product is accordingly increased. As a result, optimal magnetic properties of Nd(10.5)Fe(78.4-x)Co(5)Zr(x)B(6.1) (B(t) = 0. 659 T, H(cj) = 628 kA center dot m(-1), H(cb) = 419 kA center dot m(-1) (BH)(m) 73 kJ center dot m(-3)) are obtained when x = 2.

Preparation and Magnetic Properties of Melt-Spinning Nd_2Fe_(14)B/α-Fe Nanocomposite Magnets

Nd_(11)Fe_(71)Co_8V_(1.5)Cr_1B_(7.5) magnet was prepared by melt-spinning and subsequently annealed. The effects of the wheel speed on the magnetic properties and microstructure were studied. The results reveal that fine nanocomposite microstructure consisting of Nd_2Fe_(14)B and α-Fe phases can be developed at an optimum wheel speed of about 21 m·s^(-1). After optimal annealing (640 ℃×4 min), magnetic properties of B_r=0.64 T, (()_jH_c)=903.5 kA·m^(-1) and (BH)_(max)=71 (kJ·m^(-3)) were obtained for the bonded magnets. The addition of Cr element significantly reduces grain size, increasing the intrinsic coercivity and maximum magnetic energy product.

Computer Simulation of Effect of Intergrain Exchange Interaction on Magnetic Properties of Nanocomposite Magnets

Effects of the intergrain exchange interaction on magnetic properties of nanocomposite magnets were investigated by using the computer simulation based on the micromagnetic theory. The simulation was carried out under the assumptions that the strength of the intergrain exchange interaction is weaker than that of the intragrain exchange interaction, that inhomogeneous nanostructures result in the distribution of the strength of the intergrain exchange interaction, and that there exists nonmagnetic intergranular phase (NMIP) between grain boundaries. The distribution of the strength of the intergrain exchange interaction was simulated by the lognormal distribution with the standard deviation of σ.The calculations for Nd 2Fe 14B/α-Fe nanocomposite magnets reveal that a suitably weak intergrain exchange interaction and small grain size enable us to improve magnetic properties. It is also found that a Nd 2Fe 14B/α-Fe nanocomposite magnet has a potential of a (BH) max value exceeding 300 kJ·m -3. On the other hand, the calculations for Nd 2Fe 14B/Fe 3B nanocomposite magnets reveal that the distribution of the strength of the intergrain exchange interaction deteriorates magnetic properties significantly. Particularly, this tendency is remarkable, when the grain size L is larger than its optimum value, 11 nm. The existence of nonmagnetic boundary layers accelerats this tendency. At σ=0.2, the calculated demagnetization curve for the model magnet composed of Nd 2Fe 14B(36%)/Fe 3B(54%)/NMIP(10%) (Valume fraction) grains (L=15 nm) agrees with that obtained experimentally for a Nd 2Fe 14B/Fe 3B nanocomposite magnet. These results suggest importance of refinement of grain size, suppression of a nonmagnetic intergranular phase, and preparation of homogeneous nanostructure for superior magnetic properties.

Structure and Magnetic Properties of Nd-Fe-B/α-Fe Nanocomposite Magnets by Co, Nb, Dy Substitutions

Structure and magnetic properties of the nanocomposite magnets prepared by mechanical al loying procedure with composition 55 wt pct Nd (Fe0.92B0.08)5.5+45 wt pct α-Fe,55 wt pct Nd(Fe0.8-.Co0.12Nbx B0.08)5.5+45 wt pct α-Fe (x=0.00, 0.01- 0.03) and 55 wt pct (Nd0.9Dy0.1) (Fe0.77Co0.12Nb0.03B0.08)5.5+45 wt pct α-Fe were studied. It was found that substitution of Co for Fe could significantly improve the permanent magnetic properties of the nanocomposite magnets and typically, the maximum magnetic energy product was increased from 104.8 kJ/m3 (13.1 MGOe) to 141.6 kJ/m3 (17.7 MGOe). In contrast to the case of conventional nominally single-phase magnets, the addition of Nb results in promoting the growth of α-Fe grain and is thus unfavorable for the improvement of permanent magnetic properties of the nanocomposites. Although the addition of Dy can increase the coercivity of the magnets, the increase of magnetic anisotropy of hard phase leads to decrease of the critical grain size of soft phase. Additionally it causes the difficulty of preparing the nanocomposites because it is more difficult to control the grain size of soft phase to meet the requirement of appropriate exchange coupling between hard and soft grains

Microstructure and Magnetic Properties of Nd_(8.5)Fe_(77.1)B_(6.4)Co_4Zr_3Nb_(0.5)V_(0.5) Ribbons

Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for 4 min, which enhanced the interaction coupling between grains and improved the magnetic properties. The results of three-dimensional atom probe (3DAP) revealed that V-enriched intergranular phase existed at the grain boundaries, suppressing the grain growth during crystallization process. The remanence and coercivity for annealed ribbons reached to 80 emu·g-1 and 567 kA·m-1, respectively.

Microstructure and magnetic properties of directly quenched Nd_2Fe_(14)B/α-Fe nanocomposite materials at different temperatures

Directly quenched Nd9.5Fe81Zr3B6.5 nanocomposite permanent magnets were prepared under different melt treatment conditions, i.e., the melt temperature was varied prior to ejection onto the quenching wheel. The effect of quenching temperature on the microstructure and magnetic properties of the alloys was studied by X-ray diffractometry, transmission electron microscopy and magnetization measurements. It is found that a finer and more uniform microstructure can be obtained directly from the melt quenched at lower temperature. With increasing initial quenching temperature, the optimal quenching speed decreases and the microstructure of the ribbons becomes coarser and more irregular. As a result, the magnetic properties of the alloys are deteriorated. It is believed that the break of the pre-existing Nd2Fe14B clusters and decrease in number of the developing nuclei of Nd2Fe14B phase with increase in quenching temperature may be the causes for the change of the microstructure and the magnetic properties of the ribbons.

Effect of super heat treatment on crystallization behavior and magnetic properties of Nd_(4.5)Fe_(77)B_(18.5) nanocomposites

Melt-spun Nd4.5Fe77B18.5 ribbons were prepared under various superheat temperatures.The microstructure characteristics,crystallization behavior,and subsequent magnetic properties of Fe3B/Nd2Fe14B nanocomposite magnets were investigated using X-ray diffraction,differential thermal analysis,and vibrating sample magnetometry.It was shown that melt spinning at different quenching temperatures caused the as-quenched ribbons to have distinctive crystallization behavior.Depending on superheat temperature,phase tra...

Faujasite zeolite decorated with cobalt ferrite nanoparticles for improving removal and reuse in Pb^2+ions adsorption

Water pollution caused by heavy metals ions has been gaining attention in recent years,increasing the interest in the development of methodologies for their efficient removal focusing on the adsorption process for these purposes.The current challenge faced by adsorption processes is the adequate adsorbent immobilization for removal and reuse.Thus,the present work aimed at producing a faujasite zeolite nanocomposite decorated with cobalt ferrite nanoparticles for Pb^2+ions adsorption in an aqueous medium improving magnetic removal and reuse.As a result,a high surface area(434.4 m^2·g^-1)for the nanocomposite and an 18.93 emu·g^-1 saturation magnetization value were obtained,indicating magnetic removal in a promising material for adsorption process.The nanocomposite regeneration capacity evaluated by magnetic recovery after 24 h suspension presented a high Pb^2+ion adsorptive capacity(98.4%)in the first cycle.Around 98%of the Pb^2+ions were adsorbed in the second cycle.In this way,the synthesized faujasite:cobalt ferrite nanocomposite reveals itself as a promising alternative in adsorption processes,aiming at a synergic effect of FAU zeolite high adsorptive activity and the cobalt ferrite nanoparticles magnetic activity,allowing for adsorbent recovery from the aqueous medium via magnetic force and successive adsorptive cycles.

Nanocrystalline and nanocomposite permanent magnets by melt spinning technique

The melt-spinning technique offers an opportunity for tailoring magnetic properties by controlling the structures and microstructures in both single-phase and composite magnets.This review first broadly discusses the principle of cooling control,amorphization,crystallization,annealing,and consolidation of the melt-spun ribbons.The phase,microstructure,and magnetic properties of popular single-phase nanocrystalline magnets are reviewed,followed by the nanocomposite magnets consisting of magnetically hard and soft phases.The precipitation-hardened magnetic materials prepared by melt spinning are also discussed.Finally,the role of intergrain exchange coupling,thermal fluctuation,and reversible/irreversible magnetization processes are discussed and correlated to the magnetic phenomena in both single-phase and nanocomposite magnets.

Effect of annealing time on the exchange coupling interactions and microstruc-ture of nanocomposite Pr_(7.5)Dy_1Fe_(71)Co_(15)Nb_1B_(4.5) ribbons

The influence of annealing time on the magnetic properties and microstructure of nanocomposite Pr7.5Dy1Fe71Co15Nb1B4.5 ribbons was systematically investigated by the methods of vibrating sample magnetometer （VSM）, X-ray diffraction （XRD） and high resolution transmission electron microscopy （HRTEM）. Interaction domains derived from strong exchange coupling interactions between hard and soft magnetic grains were imaged using magnetic force microscopy （MFM）. Maximum remanence, intrinsic coercivity, and maximum energy product values were obtained in the ribbons annealed at 700℃ for 15 min, which were composed of Pr2（Fe, Co）14B, α-（Fe, Co）, and slight Pr2（Fe, CO）17 phases. Although Jr, Hci, and （Bn）max decreased gradually with further increase of annealing time, it is emphasized that comparatively high Jr and Hci and （BH）max were obtained in a wide annealing time period of 15 to 360 min. The shape of initial magnetization curves and hysteresis loops change as a function of annealing time, indicating different magnetization reversal routes, which can be fully explained by the corresponding microstructure.

Preferred Orientation in Nanocomposite Permanent Magnet Materials

Melt-spun （Nd11.4Fe82.9B5.7）0.99M1 ribbons （M = Zr, Nb, Ga, Zr＋ Ga, Nb ＋ Ga）were prepared by melt-spinning technique. Ga addition is found to be effective for the orientation of c-axis of Nd2Fe14B grains perpendicular to the ribbon plane. Better magnetic properties can be achieved by adding both the two kinds of elements Zr ＋ Ga, Nb ＋ Ga, and it is found that the preferred orientation is further improved. The alignment degree changes with ribbon thickness and is highest when ribbon thickness is 120 μm. Heat treatment can improve the texture degree, but lead to coarser grains. Cryogenic treatment is first applied for the treatment of nanocomposite Nd2Fe14B/α-Fe melt-spun ribbons. The effects on magnetic properties and texture degree of nanocomposite magnets after cryogenic treatment were studied. The result shows that cryogenic treatment is beneficial to the enhancement of texture degree of melt-spun ribbon and the grain size has no obvious change.

Influence of dynamic crystallization on exchange-coupled NdFeB nanocrystalline permanent magnets

Dynamic crystallization was introduced to improve the magnetic properties of NdFeB nanocrystalline permanent magnets by optimizing microstructure.The microstructure was studied by X-ray diffraction(XRD)and transmission electron microscopy(TEM).It has been determined that,compared with the conventional heat treatment,dynamic crystallization can shorten the crystallization time.Moreover,dynamic crystallization can refine grains,enhance the exchange-coupled interaction among grains,and promote the magnetic properties.As a result,the optimal magnetic properties of Nd_(10.5)(FeCoZr)_(83.4)B_(6.1)(B_(r)=0.685 T,H_(ci)=732 kA·m^(-1),H_(cb)=429 kA·m^(-1),(BH)_(m)=75 kJ·m^(-3))are obtained after dynamic crystallization heat treatment at 700℃for 10 min.

Microstructural characteristics of Nd_2Fe_(14)B/α-Fe nanocomposite ribbons bearing Nb element

The effects of Nb on the microstructure and magnetic properties of （Nd0.9Dy0.1）9.5Fe79_xCo5NbxB6.5 （x = 0, 1） nanocomposite magnets were investigated. A fine and uniform microstructure was achieved for the ribbons annealed at 710℃ for 4 min, enhancing the interaction coupling between grains and improving the magnetic properties. The results of three-dimensional atom probe （3DAP） indicated that Fe-Nb-B inter- granular phase existed at the grain boundaries, suppressing the grain growth during the crystallization process. The coercivity was improved from 224 to 643 kA/m for the modification of the microstructure.