Dependence of Magnetic Properties of Rapidly Quenching (Nd,Pr)_x (FeCoZr)_(94-x)B_6 Bonded Magnets on Rare Earths Content

By using sub-overquenching and annealing method which has a wide processing window, (Nd, Pr), ( Fe-CoZr)(94-x)B-6(x = 12, 10.5, 10, 9) bonded magnets were prepared and the effect of rare earths content on magnetic properties was investigated. Being spun at sub-ove.quenching speed the as-spun ribbons consist of amorphous phases mixed with fine crystallites. After crystallization under optimum annealing conditions and bonded with 3.25% (mass fraction) epoxy, the magnets obtained the optimum magnetic properties. The rare earths content directly determines the magnetic properties. With the reduction of rare earths content, B-r increases but H-ci and (BH)(max) decrease. x = 10 is the critical value for the magnetic proper-ties change. Below this value, Br increases slowly meanwhile H-ci and (BH)(max) decrease strongly because alloy contains extra fractions of soft magnetic phase which are not coupled with the hard magnetic phase.. This experimental result is consistent with the calculated results using the model of volume fraction of soft magnetic phase coupled completely suggested.

Effect of rare earth doping on thermo-physical properties of lanthanum zirconate ceramic for thermal barrier coatings

The effect of rare earth doping on thermo-physical properties of lanthanum zirconate was investigated. Oxide powders of various compositions La2Zr2O7 were synthesized by coprecipitation-calcination method. High-temperature dilatometer, DSC, and laser thermal diffusivity methods were used to analyze thermal expansion coefficient （TEC）, specific heat, and thermal diffusivity. The results showed that CeO2 doped pyrochlores La2（Zr1.8Ce0.2）2O7 and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had higher TEC than La2Zr2O7 and La1.7Dy0.3Zr2O7. La2（Zr1.8Ce0.2）2O7, La1.7Dy0.3Zr2O7, and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had lower thermal conductivity than undoped La2Zr2O7. The Dy2O3, Nd2O3, and CeO2 codoped composition showed the lowest thermal conductivity and the highest TEC. Thermo-physical results also indicated that TEC of rare earth oxide doped La2Zr2O7 ceramic was slightly higher than that of conventional ZrO2-8Wt.% Y2O3 （8YSZ）, and its thermal conductivity was lower than that of 8YSZ.

Preparation and Properties of Rare Earth Modified Carbon Black/Natural Rubber Composites

The oxides Eu, Ho, Er and Dy were used to prepare the hydroxides of rare earth modified carbon black. Then natural rubber latex （NRL） was added into the reactor. The system reacted at 85 ℃ with stirring for 1 h to prepare powdered HAF-Ln（OH）3/NR composites. The effects of the kind and content of Ln on the particle size distribution of P [ NR/HAF-Ln （OH）3 ] and mechanical properties of its vulcanizate were studied respectively. It is found that rare earth can help to get the powder of the composite, the product particle with a diameter less than 0.9mm will be get when the composites containing the compound of Ho, Er and Dy with dosage of 1.0, 1.0, O. 5 percent, respectively. The adding of Ln can improve the tensile strength and tear strength of the vulcanizate effectively, what＇s more, Er and Dy can decrease the permanent set of vulcanizate significantly. The SEM studies shows that P[ NR/HAF-Dy （OH）3 ] vulcanizate shows superior mechanical properties that depend primarily on the absence of free carbon black, the fine dispersion of carbon black in the rubber matrix and better polymer-filler interaction.

Effect of rare earth La_2O_3 on the microstructure and mechanical properties of TiC/W composites

In this study, La2O3 was investigated as an additive to TiC/W composites. The composites were prepared by vacuum hot pressing, and the microstructure and mechanical properties of the composites were investigated. Experimental results show that the grain size of the TiC/W composites is reduced by TiC particles. When 0.5 wt.% La2O3 is added to the composites, the grain size is reduced further. According to TEM analysis, La2O3 can alleviate the aggregation of TiC particles. With La2O3 addition, the relative density of the TiC/W composites can be improved from 95.1% to 96.5%. The hardness and elastic modulus of the TiC/W ＋ 0.5 wt.% La2O3 composite are little improved, but the flexural strength and the fracture toughness increase to 796 MPa and 10.07 MPa·m^1/2 respectively, which are higher than those of the TiC/W composites.

Rare earth effect on the microstructure and tribological properties of FeNiCr coatings

FeNiCr alloys with various amounts of La2O3 powders were thermally sprayed onto steel substrate.Electron probe microscopy analysis （EPMA）,X-ray photoelectron spectroscopy （XPS）,and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration were employed to investigate the properties of the sprayed coatings.The results show that rare earth can refine the microstructure effectively and make the element distribution uniform,which leads to the improvement in the properties of the coatings.Meanwhile,the wear rate of the FeNiCr alloy with 1.5% La2O3 is smaller than those of the other coatings.Interestingly,the rare earth can reduce the friction coefficient and act as a self-lubricant in the oxide debris layer formed on the worn surface in friction.The wear mechanism of the coatings is oxidation wear,and a large amount of counterpart material is transferred to the coatings.

SPECTRAL VARIATION AND CHARACTERISTICS OF LOW VALENCY RARE EARTH IONS IN COMPLEX OXIDESⅢ.EFFECT OF THE CRYSTAL ENVIRONMENT AND CHEMICAL FACTORS ON LUMINESCENCE PROPERTIES OF EUROPIUM (Ⅱ) ION

In this paper,the influence of crystal-field on the Luminescence properties of Eu^(2+) in complex oxides are studied theoretically by using purely electrostatic model,the dependence of the 4f^65d levels on Eu-O bond distance is given.Quantum chemistry calculation shows that the splitting extent of 4f^65d energy band in cubic or in octahedral fields will be inversely proportional to R^5,where R is the distance of Eu^(2+) to oxygen ligand.The value of R affects slightly the location of the centre of 4f^65d energy band.According to the exper- imental spectrum data,we have discussed the influence of the host chemical composition,the replaced sites of Eu^(2+) and degree of covalency of Eu-O bond on luminescence properties of Eu^(2+).Some regularity of fluorescence spectrum was observed. In alkali-alkaline earth-phosphates,the splitting extent of 4f^65d band (△E) becomes smaller as the Eu-O bond distance (R) increases.In Na_(3-x)(PO_4)_(1-x)(SO_4)_x and Na_(2-x)CaSi_(1-x)P_xO_4 hosts,d-d emission peak of Eu^(2+) will shift to shorter wavelength with the increase of x's value. The crystal structure data show that Eu^(2+) in K_2Mg_2(SO_4)_3 is affected more strongly by crystal-field and covalancy than in KMgF_3,so K_2Mg_2(SO_4)_3:Eu^(2+) emits blue light (E_(em)~m=400nm) and KMgF_3:Eu^(2+) produces ultraviolet fluorescence.

Electronic and Optical Properties of Rare Earth Oxides: <i>Ab Initio</i>Calculation

In this work, we have investigated the electronic and optical properties of the technologically important rare earth oxide compounds—X2O3 (X: Gd, Tb) using the density functional theory within the GGA. The band structure of X2O3 have been calculated along high symmetry directions in the first brillouin zone. The real and imaginary parts of dilectric functions and the other optical responses such as energy-loss function, the effective number of valence electrons and the effective optical dielectric constants of the rare earth sesquioxides (Gd2O3 and Tb2O3) were calculated.

Effect of niobium on glass-formation ability and soft magnetic properties of Gd-doping glassy alloys

The effect of niobium on glass-formation ability and soft magnetic properties were studied in Fe-Gd-B glassy alloys. The glassy alloys exhibited high glass-formation ability when the element of Nb was added. Bulk glassy rod （Fe0.87Co0.13）68.5Gd3.5Nb3B25 with a diameter up to 3 mm was produced by copper mold casting. The size of the atom might play an important role in increasing glass-formation ability. The coercive force of glassy （Fe0.87Co0.13）71.5.xGd3.sNbxB25 （x=1.2, 1.5, 2, 2.5, 3, 4） alloys decreased after the addition of niobium element and was in the range of 1.5-2.9 A/m. The permeability spectrum of （Fe0.87Co0.13）70.3Gd3.5Nb1.5B25 glassy ribbon showed that the relaxation frequency （f0） was 6.1 MHz.

Synthesis, Electrical and Magnetic Properties of Fe304 Doped by Dy^3＋

The Dy^3＋ -doped Fe3O4 samples were synthesized by sol-gel method, and the effects of dopant on the electrical and magnetic properties were investigated. According to XRD analysis, the high concentration doping of dysprosium ions in Fe3O4 can not be obtained due to the difference of ionic radius, and Fe^3 ＋ ions are replaced by only a small amount of dysprosium ions. The magnetic property was characterized by VSM. The substitution results in the change of saturation magnetization, which may be due to the complex effects of increasing magnetization resulted from Dy^3＋ substitution and decreasing magnetization resulted from the impurity. The electrical property was characterized by four-probe method. With the increasing eoped content, magnetoresistance also increases, then decreases, and increases again. The spin-polarization of doped samples is lower than that of Fe3O4. Lower spin-polarization results in lower tunneling magnetoresistance. Fortunately, barrier was obtained by the second phase at the same time when sample was synthesized. The increase of appropriate barrier height leads to the change of tunneling magnetoresistance.

Effect of Zr on Microstructure and Magnetic Properties of Nanocrystalline (Nd, Pr)FeB/α-Fe Composite Alloys

For nanophase (Nd, Pr)FeB/α-Fe composite alloys were prepared by melt spinning, the appreciable addition of Zr reduces their average grain size. Observed by atom force microscopy (AFM), the average grain diameter of crystallized ribbons on their free surface, reduces from 175 nm of Zr-free alloy to 79 nm of Zr-1at%, by about 55%. If the concentration exceeds 1%, the effects of Zr on fining grain size are evidently weakened. The average grain size on free surface of Zr-1.5at% is 72 nm. With the addition of 1at% Zn, the bonded magnets has the best combination of properties: B_r=0.675 T, H_(ci)=616 kA·m^(-1), (BH)_(max)=77 kJ·m^(-3). Below 1at%, the coarser grains lead to a lower magnetic property. Beyond 1at%, the layer of Zr-rich intergranular phase will thicken, which results in weakening of the exchange coupling among adjacent grains, and then causes degrading of magnetic properties of magnets.

Thermal Stability and Magnetic Properties of (Fe,Co)-Zr-Nd-B Amorphous Alloys

A new type of Fe-based amorphous alloy containing rare earth element was prepared by melt spinning technique. The glass-forming ability (GFA),thermal stability and magnetic properties were investigated in the composition range of Fe_(70)Co_8Zr_(7- x )Nd_ x B_(15) ( x =0% to 6%,atom fraction). They exhibit the glass transition and supercooled liquid region before crystallization. The width of supercooled liquid region obtained for the series of Fe_(70)Co_8Zr_(7- x )Nd_ x B_(15) exceeds (40 K,) among which the maximum width for Fe_(70)Co_8Zr_5Nd_2B_(15) amorphous alloy reaches 61 K. Another main attraction is that the selected Fe-based amorphous alloys have good soft magnetic properties. The saturation magnetization ( J _s) is in the range of 1.10 to 1.37 T,and coercive force ( H _c) in the range of 2.28 to 8.15 A·m (-1) for Fe_(70)Co_8Zr_(7- x )Nd_ x B_(15) amorphous alloys. It is found that the saturation magnetization ( J _s) increases with the increment of the relative content of the Nd for the Fe_(70)Co_8Zr_(7- x )Nd_ x B_(15) alloys. The H _c values for the glasses with Nd content of 1%,2% and 3% are below 3 A·m (-1). The research indicates that Fe_(70)Co_8Zr_5Nd_2B_(15) amorphous alloy has good high GFA and good soft magnetic properties,of which the width of supercooled liquid region,J _s,and H _c are 61 K,1.25 T and 2.28 A·m (-1),respectively.

Structural Analysis and Magnetic Properties of Gd-Doped Li-Ni Ferrites Prepared Using Rheological Phase Reaction Method

A series of Gd-doped Li-Ni ferrites with the formula of LiNi0.5GdxFe2-xO4 where x = 0.00 - 0.08 in steps of 0.02, were prepared by thermolysis of oxalate precursors obtained by rheological phase reaction. The structure, morphology, and the magnetic properties of the samples were characterized by powder X-ray diffraction （XRD）, atomic force microscopy （AFM） and a vibrating sample magnetometer （VSM）. A single spinel phase was obtained in the range of x = 0.00 - 0.04. The lattice parameters of the Gd-doped samples were larger than that of pure Li-Ni ferrite, and increased in the range of 0.00 ≤ x ≤ 0.04, then decreased up to x = 0.08, because of the formation of the secondary phase （Gd- FeO3）. All samples were spheric particles with an average size of about 100 nm, but agglomerated to some extent. The hysteresis loops indicated that the saturation magnetization decreased gradually with increasing Gd content, while the variation of coercivity was related to the microstructure of the Gd-doped samples.

Review on Rare Earth/Polymer Composite

The special properties of rare earth/polymer composite were described. More emphasis was put on the radiation shielding and magnetic properties. In the application to X-ray shielding, rare earth/polymer composite can make up the feeble absorbing area. If the rare earth content is high enough, it can demonstrate strong ability for thermal neutron absorption; The composite has strong paramagnetism. The feasibility of preparing magnetic rare earth/polymer composite was discussed. In addition, three preparation methods were introduced: simple polymerization, mixing and reaction processing. The effect of the rare earth/polymer composites pre-sturcture and the coordinate number of rare earth ions on the light property was analyzed. Rare earth/polymer composite may have the structure and property simlar to those of the ionomer. The feasibility of the in-situ preparation of the rare earth/polymer nano structure is indicated. Besides, the relationship between structure and properties of the rare earth/polymer composite was discussed. The problems associated with such composite materials were also presented.

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.

Preparation of Dysprosium Ferrite/Polyacrylamide Magnetic Composite Microsphere and Its Characterization

Using the technique of microemulsion polymerization with nano-reactor, dysprosium ferrite/polyacrylamide magnetic composite microsphere was prepared by one-step method in a single inverse microemulsion. The structure, average particle size, morphology of composite microsphere were characterized by FTIR, XRD, TEM and TGA. The magnetic responsibility of composite microsphere was also investigated. The results indicate that the magnetic composite microsphere possess high magnetic responsibility and suspension stability.

Influence of rare earth ion substitutions on the structural,optical,transport,dielectric,and magnetic properties of superparamagnetic iron oxide nanoparticles

Superparamgnetic Fe_3O_4 and RE:Fe_3O_4(RE=Dy,Nd,La)nanoparticles with an average crystallite size in the range of 15–24 nm,were synthesized by co-precipitation method.The samples were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),vibrating sample magnetometer(VSM),UV–Vis spectroscopy,LCR bridge,and two-probe technique.X-ray diffraction patterns of all the investigated samples reveal the typical phase of magnetite structure,with a small contribution of orthoferrite(NdFeO_3)as a secondary phase in Nd:Fe_3O_4 sample.The saturation magnetization(M_s)of the samples has values in the range from 41.8 to 52.3 emu/g,and decreases with RE ion doping depending on the ionic radius.Negligible values of the coercivity H_c and remanenceM_r,indicate the superparamagnetic nature of the investigated samples.The calculated values of indirect optical band gap of Fe_3O_4 and RE:Fe_3O_4 nanoparticles are in the range of0.9–1.25 eV.The dielectric constant of the samples decreases,while their activation energy increases with the increasing of ionic radii of dopants.

Microstructure and magnetic properties of bulk magnets Nd_(14-x)Fe_(76+x)Co_3Zr_1B_6(x=0,0.5,1) prepared by spark plasma sintering

Melt-spun ribbons with nominal composition of Nd14–xFe76+xCo3Zr1B6(x=0,0.5,1) were consolidated into isotropic bulk magnets by spark plasma sintering method.It was found that the Nd content and sintering temperature had significant influence on the density and magnetic properties of the sintered magnets.Homogeneous microstructure and fine grain(50–100 nm) were obtained when sintering below 700 ℃,and the initial magnetization curve showed that the coercivity was controlled by the pinning mechanism.However,ab...

Influence of Zr Additions on Microstructure and Magnetic Properties of Nanocomposite Nd_(10.5)Fe_(78-x)Co_5Zr_xB_(6.5) (x=0～5) Alloys

The influence of Zr addition on the microstructure and magnetic properties of nanocomposite Nd_(10.5)Fe_(78-x)Co_5Zr_xB_(6.5) (x=0～5) alloys was investigated. It was found that the intrinsic coercivity could be significantly improved by the addition of 2% (atom fraction) Zr. The presence of small amount of amorphous phase is responsible for the low intrinsic coercivity for Zr-free alloy. The small amount addition of Zr may suppress the growth of grains of α-Fe and Nd_2Fe_(14)B phases. The more homogeneous microstructure with an average grain size of 20 nm can be obtained for Nd_(10.5)Fe_(76)Co_5Zr_2B_(6.5) alloy.

Effects of Dysprosium Oxide Doping on Microstructure and Properties of Barium Titanate Ceramic

Different amounts of dysprosium oxide were incorporated into barium titanate powders synthesized by hydrothermal method. Relations of substitution behaviors and lattice parameters with solid-solubility were studied. Furthermore, the influences of dysprosium oxide doping fraction on grain size and dielectric properties of barium titanate ceramic, including dielectric constant and breakdown electric field strength , were investigated via scanning electron microscope, X-ray diffraction and electric property tester. The results show that dysprosium oxide can restrain abnormal grain growth during sintering and that fine-grained and high density of barium titanate ceramic can result in excellent dielectric properties. As mass fraction of dysprosium oxide is 0.6%, the lattice parameters of grain increase to the maximum because of the lowest vacancy concentration. The electric property parameters are cited as following： dielectric constant （25 ℃ ） reaches 4100, the change in relative dielectric constant with temperature is - 10% to 10% within the range of - 15 - 100 ℃, breakdown electric field strength （alternating current） achieves 3.2 kV·mm^-1, which can be used in manufacturing high voltage ceramic capacitors

Influence of zirconium addition on the microstructure and magnetic properties of nanocomposite Nd_(10.1)Fe_(78.2-x)Co_5Zr_xB_(6.7) permanent magnets

Nanocomposite Nd10.1Fe78.2-xCo5ZrxB6.7 （x= 0, 1.5, 2.5, 2.7, 3, 4） permanent magnets were prepared by melt-spun and annealing. The microstructure and magnetic properties of the permanent magnets were investigated. The resuits reveal that the addition of Zr element significantly reduces the grain size and improves the thermal stability of the amorphous phase. A fme nanocomposite microstructure with an average grain size of about 35 nm can be developed at a wheel speed of 16 m·s^-1 with the content of Zr up to 2.7 at.%. After optimal annealing （710℃ x 4 min）, the magnetic properties of the Ndl0.1Fe75.5Co5Zr2.TB6.7 bonded magnets were achieved as follows： Br= 0.72 T, jHc = 769 kA·m^-1, and （BH）max = 85.0 kJ·m^-3.