Preparation and magnetic properties of anisotropic Nd_2Fe_(14)B/Sm_2Co_(17) hybrid-bonded magnets

In the present work, anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets were prepared with different Nd-Fe-B contents. It is found that the particle distributions and ratios between the two magnetic phases have important roles in the magnetic properties, microstructures and thermal stability of the magnets. With increase of Nd-Fe-B content, the saturation magnetization of the anisotropic hybrid magnet increases significantly, however, coercivity decreases, and the demagnetization curves show magnetically single-phase behavior. The anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets exhibit a maximum energy product and remanence of 14.15 MGOe and 99.53 A·m~2/kg, respectively, when the NdFe-B content is 70 wt% at room temperature. Furthermore, the hybrid magnets also have better thermal stability at elevated temperatures due to the interaction between the two magnetic particles.     

Magnetic properties and microstructure of Fe_(69.5-x)Nd_7B_(21)Nb_(2.5)Ga_x(x=0-1)alloys

The Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)permanent magnets in the form of rods were prepared by annealing the bulk amorphous alloys.The magnetic properties,phase evolution and microstructure of the alloys were investigated systematically.It is found that the glass forming ability(GFA), microstructure and magnetic properties are sensitive to Ga content for Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)bulk alloys.The annealed alloys are mainly composed of soft α-Fe,hard Nd_2 Fe_(14)B and nonmagnetic Nd_(1.1)Fe_4 B_4 phases.When x = 0.3,the optimally annealed magnets exhibit magnetic properties of the remanence Br = 0.63 T,intrinsic coercivity H_(cj) = 368.68 kA/m and maximum energy product(BH)_(max) = 33.73 kJ/m~3.Furthermore,magnetic field heat treatment at the temperature close to Curie temperature of Nd_2 Fe_(14)B phase was applied to the annealed Fe_(69.2)Nd_7 B_(21)Nb_(2.5)Ga_(0.3) magnet.The results of X-ray diffraction(XRD)and transmission electron microscopy(TEM)indicate that the magnetic field heat treatment can be beneficial for the precipitation of α-Fe.Thus,the B_r,H_(cj) and(BH)_(max) are enhanced by 8.7%,6.3% and 16.3%,respectively.     

THERMODYNAMIC OPTIMIZATION AND CALCULATION OF THE Fe-Pr SYSTEM

Based on the phase diagram of the Fe-Pr system available,the thermodynamic optimization and calcula-tion of the system have been carried out by the least square method.The lattice stabilities of Fe and Pr aredescribed by the expression recommended by SGTE organization.The liquid phase is described by thesubregular solution model.The intermetallic compounds,Fe_(17)Pr_2 and Fe_2Pr,are treated as stoichiometriccompounds.The optimized parameters describing phases in the system are presented.The comparision be-tween the calculated and experimentally determined phase diagram shows that the agreement is generally verygood except for the liquid δ-Fe equilibrium.It is suggested to measure this part of phase diagram again.     

Solid-state reaction synthesis and chemical stability studies in Nd-doped zirconolite-rich ceramics

In this study, Nd-bearing zirconolite-rich ceramics were prepared by solid-state reaction process using CaF_2,ZrO_2, Ti,TiO_2, Fe_2 O_3 and Nd_2O_3 as the raw materials. Neodymium was used as trivalent actinide surrogate and designed to substitute the Ca and Zr sites of zirconolite with general stoichiometry of Ca_(1-x)Zr_(1-x)Nd_(2 x)Ti_2O_7(0≤x≤0.3). Density of Fe-Nd-O sample reaches a maximum value of 4.13 g/cm~2 after being sintered at 1325 ℃ for 42 h. Three major phases, namely zirconolite, perovskite and pseudobrookite, are observed in all these samples. The EDX result shows that Nd_2O_3 can be successfully incorporated into the lattice structure of the prepared zirconolite-rich minerals and replace the Ca sites of zirconolite and perovskite with Fe~(3+) as the charge-compensating ion. Furthermore, the thermal conductivities are all in the range of 1.51-1.67 W/(m·K). The normalized elemental leaching rates of Ca and Nd in the Fe-Nd-0.2 sample keep in low values of 6.20 × 10~(-2) and 4.86 x 10~(-4) g/(m~2·d) after 42 d.     

Prediction of Activities in Fe-Based Ternary Liquid Alloys by Hoch-Arpshofen Model

 Thermodynamic properties for an alloy system play an important role in the materials science and engineering. Therefore, theoretical calculations having the flexibility to deal with complexity are very useful and have scientific meaning. The Hoch-Arpshofen model was deduced from physical principles and is applicable to binary, ternary and larger system using its binary interaction parameters only. Calculations of the activities of Fe-based liquid alloys are calculated using Hoch-Arpshofen model from data on the binary subsystems. Results for the activities for Fe-Au-Ni, Fe-Cr-Ni, Fe-Co-Cr and Fe-Co-Ni systems at required temperature are presented by Hoch-Arpshofen model. The average relative errors of prediction are 78%, 45%, 49% and 27%, respectively. It shows that the calculated results are in good agreement with the experimental data except Fe-Au-Ni system, which exhibits strong interaction between unlike atoms. The model provides a simple, reliable and general method for calculating the activities for Fe-based liquid alloys.     

Revealing Liquid Metal Target Malfunctions by Means of Vibrations and Sound Pressure Monitoring

In the following paper an experiment dedicated to the accident protection system of a Liquid Metal Target is presented.The test was carried out at the liquid metal test stand(LIMETS)at PSI in which the malfunctioning of a target during operation was simulated.It could be demonstrated that measurements and the proper(on-line)analysis of target vibrations and surrounding sound pressure fields allow the detection of a malfunctions like deformation or detaching of structural elements immeresed in the flow.Amplitudes of acceleration sensors and microphones signals as well as frequencies of the disturbances’signals are prospective parameters to be used in an automated accident protection system as indicators for a target malfunction.     

Preparation of AZ91D Slurries for Semi-Solid Forming Using Al8 ( Mn, Fe) 5 Precipitates

During the solidification of the AZ91D-alloys, the Al8(Mn, Fe)5 phase is generally precipitated in the melt in advance of the precipitation of the primary α-Mg. The basic principle for manufacturing AZ91D-alloy slurries for semi solid forming is to use the Al8(Mn, Fe)5 precipitates as the heterogeneous nucleation sites for primary α-Mg phases. Microscopic analysis for the location of the Al8(Mn, Fe)5 precipitate explains that the Al8(Mn, Fe)5 precipitate is the effective heterogeneous nucleation site for the primary α-Mg phase. It was also observed that increase of the Mn content in the melt and the cooling rate below to the solid/liquid two-phase region resulted in smaller and more globular primary α-Mg due to the increase of heterogeneous nucleation sites. It was found that the average α-Mg diameter grew as a function of t0.278, where t is the holding time at the solid/liquid two-phase region. This would be attributed to the Ostwald type ripening and coalescence between primary α-Mg phases. The cooling rate below to the solid/liquid two-phase region, Mn content in AZ91D alloy, and the holding time and temperature affected on the quality of slurry.     

Selective microwave absorption in Nd3+ substituted barium ferrite composites

Microwave(MW) frequency based wireless communications and electronic devices became prospective due to several ramifications.To meet this need,a series of neodymium ions(Nd3+) substituted barium ferrite composites with composition(20)BaO:(80-x)Fe_2 O_3:(x)Nd_2 O_3(0≤x≤3 mol%) was prepared at1100℃using solid-state reaction method.We evaluated the effect of various Nd3+ions contents on the surface morphology,structure,and magnetic properties of the as-synthesized barium ferrite composites.Meanwhile,microwave reflection loss,complex permittivity and permeability were determined using the transmission/reflection line method in the X-band(8—12 GHz).SEM image of the composites shows that the surface morphology consists of rough and porous microstructures.XRD patterns of the un-doped composites reveal the existence of BaFe_(12)O_(19)(hexagonal) and Fe_(21.333)O_(32)(tetragonal) crystalline phases.Furthermore,a new hexagonal crystalline phase of Ba_6 Nd_2 Fe_4 O_(15) with the crystallite sizes between 15 and 67 nm is observed due to Nd3+ions substitution in the composite.The saturation magnetization of the composite containing 2 mol% of Nd3+does not exhibit any significant alteration compared to the one devoid of Nd3+.The complex relative permitivity and permeability of the achieved composites enriched in Ba_6 Nd_2 Fe_4 O_(15) and BaFe_2 O_4 phases disclose significant MW frequency dependence.The composites also display selective MW absorption in the X-band which could be useful for diverse applications.     

Co-Al二元系中的fcc/hcp马氏体相变和形状记忆效应

It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few systematic works on the SM effect in Co and Co-based alloys. In this study, the fcc/hcp martensitic transformation and the SM effect were investigated in Co-Al binary alloys(mole fraction of Al=0～16%).The γ/ε martensitic transformation temperatures were found from the DSC measurements to decrease with increasing Al content, while the transformation temperature hystereses were observed to increase from 60 ℃ at x(Al)=0 to 150 ℃at x(Al)= 16%. The SM effect evaluated by a conventional bending test was enhanced by the addition of Al over 4%(mole fraction) and Co-Al alloys containing over 10%(mole fraction) exhibit a good SM effect associated with the hcp →fcc reverse transformation above 200 ℃. The SM effect was significantly improved by precipitation ofβ (B2) phase and the maximal shape recovery strain of 2. 2% was obtained, which can be explained by precipitation hardening. The crystallographic orientations between theβ, ε and γ phases were also determined. Finally, the magnetic properties were investigated and it was found that the Curie temperature and saturation magnetization of Co-14% Al(mole fraction) are 690 ℃and 120 emu/g, respectively. It is concluded that the Co-Al alloys hold promise as new high-temperature and ferromagnetic SM alloys.     

自组装Cu-Fe基复合材料的设计与开发

The Cu-Fe base alloys with liquid immiscible were prepared by gas atomization technique and conventional solidification process, the self-assemble composite microstructures in powders and bulk materials can be obtained under gravity conditions, respectively, and the minor liquid phase always forms the center of composite microstructure. It is shown that the formation of the core-type macroscopic morphology is strongly connected with the existence of a stable miscibility gap of the liquid phase in the Cu-Fe base alloys. This result can be explained by a mechanism that the minor droplets as the second phase are forced to move into the thermal center due to Marangoni motion, which is caused by the temperature dependence of interracial energy between two liquid phases.     

Oxidation Behavior of Fe-based Amorphous Ribbons

The oxidation behavior of Fe-based amorphous ribbons was tested by annealing at 380 ℃in air for different time with heat treatment furnace and analyzed by X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM).The mechanism of oxides formation of the amorphous ribbons was discussed in detail.The results showed that the oxides were mostly B_2O_3,SiO_2 and Fe_2O_3or FeO.With the increase of annealing time and holding temperature,the fraction of the oxides on the ribbon surface increased and the size of the oxides became larger due to the generation of new oxides and the coalescence of small oxides.The oxides have different shapes,such as round,rod and needle-shaped.Experimental results also showed that the oxides nucleated at fish scale,air pocket and impurities in priority,and the growth of the oxides was controlled by the diffusion of atoms.With the increase of the distance to the ribbon surface,the oxygen concentration decreased dramatically.Due to the low binding energy of B_2O_3 and the large diffusion coefficient of B atom,the B element was oxidized firstly compared with other elements.Moreover,the oxidation depths of the B_2O_3 and SiO_2 were larger than that of Fe_2O_3.     

Preparation and Microstructure Evaluation of Directionally Solidified Nd-Fe-B Ingots by Electromagnetic Cold Crucible

In this paper Nd-Fe-B ingots with hyper-peritectic composition were prepared through continuous and directional solidification by a novel electromagnetic cold crucible approach.A group of experiments were carried out in order to investigate the effects of input power and withdrawal velocity on the microstructure and growth orientation of Nd-Fe-B phases.It was found that the peritectic Nd₂Fe₁₄B phase grows with a planar interface at lower withdrawal velocity and changed into the dendritic interface at higher withdrawal velocity.The result was explained by the theory of constitutional supercooling.Meanwhile the volume fraction of ferromagnetic T₁ phase was found to be increased first and then decreased with the increasing of withdrawal velocity during the growth process of the ingots.     

Magnetic Properties of Ga Doped Nd-Fe-B Sintered Magnets

The magnetic properties of Nd_(16)Fe_(77)B_7 and Nd_(16)Fe_((61-x))Co_(16)Ga_xB_7(x=0,1,2,4,7)have been measured.Itis found that the remanent magnetization(Br),maximum energy product(BH)_(max)and the Curie temperature(T_c)decrease with the increase of Ga content.The coercive force(He)increases with the increase of Ga contentwhen x is less than 2,but decreases when x>2.At x=2,the coercive force reaches its maximum value.It is alsofound in all the samples investigated that there is a linear relationship between H_c~(1/2)and T~(2/3),which can not beexplained by Gaunt's wall barrier model.The temperature dependence of the calculated values of H_v and(4bf)has been discussed.     

Enhanced magnetic properties of anisotropic Nd-Fe-B nanocomposites by Fe(C)coating

Nanostructured anisotropic Nd-Fe-B/Fe(C) composite powders were prepared by coating Fe(C) softmagnetic nanoparticles on HDDR Nd-Fe-B hard magnetic powders using iron pentacarbonyl Fe(CO)_5 as soft-phase precursor.The effect of Fe(CO)_5-loading amount on soft-phase purity,coating morphology and magnetic properties of the composite powders was investigated.Dense and continuous Fe(C) softphase coatings with average particle sizes of 58-68 nm are obtained at Fe(CO)_5 loading amounts of x 12 wt%,leading to enhanced remanence and improved energy product of the coated powders.Positive value in δM-plots and single-phase-like demagnetization curves are observed in the Nd-Fe-B/Fe(C) composite powders,indicating the exchange coupling effect between the coated Fe(C) soft phases and the Nd-Fe-B hard phase.     

Synthesis,structure and magnetic properties of Sm_(1.2)Ho_(0.8)Fe_(17)H_x(x=0;4.4)

Intermetallic compounds based on rare-earth metals and iron are by far the most promising materials for permanent magnets.In this work,the multicomponent compound Sm_(1.2)Ho_(0.8)Fe_(17) was prepared by induction melting.The hydride Sm_(1.2)Ho_(0.8)Fe_(17)H_(4.4) with a high hydrogen content was obtained by direct hydrogenation of the intermetallic compound.The rhombohedral Th_2 Zn_(17)-type of structure(space group R3 m) is inherent to parent compound and hydride as well.The effect of hydrogenation on the magnetic properties of Sm_(1.2)Ho_(0.8)Fe_(17) was investigated.Curie temperature of the hydride Sm_(1.2)Ho_(0.8)-Fe_(17)H_(4.4) is higher than that of parent compound by ΔT_C=138 K.The hydrogen embedded in Sm_(1.2)Ho_(0.8)Fe_(17) crystal lattice increases the saturation magnetization(σs) at T=300 K,but does not significantly affect σ_S at T=4.2 K.The ferrimagnetic structure is retained in magnetic fields up to 58 T in the parent compound,while,in the hydride,there is a spin-reorientation phase transition observed at 55 T.It is found that the parameter of the intersublattice exchange interaction decreases significantly in the hydride Sm_(1.2)Ho_(0.8)Fe_(17)H_(4.4)(and in the nitride Sm_(1.2)Ho_(0.8)Fe_(17)N_(2.4)) which is associated with boosting of the unit-cell volume and distances between magnetic ions.     

Crystal Growth and Spectral Properties of Yb3+:KY(WO4)2

Laser crystal Yb∶KYW was grown by the Kyropoulos method. A grown crystal was identified as β-Yb∶KYW by XRD. By TG-DTA the melting point and transition point of the crystal are 1045 and 1010 ℃, respectively. Infrared spectrum and Raman spectrum were measured, and the vibrational frequencies of infrared and Raman active modes for Yb∶KYW crystal were assigned. Absorption spectrum of Yb∶KYW shows that there are two intensive absorption peaks at 940 and 980 nm, respectively, and the absorption cross section is 1.34×10-19 cm2 at chief peak of 980 nm. There exist three intensive emission peaks in Yb∶KYW at 990, 1010 and 1030 nm, respectively, and the emission line width of the chief peak 1030 nm runs up to 16 nm. It was calculated that the peak emission cross section is 3.1×10-20 cm2 at 1030 nm.     

Optical properties and radiative rates of Nd3+ doped zinc-sodium phosphate glasses

Preparation using melt quenching technique and optical characterizations of Nd~(3+) doped Zn-Na phosphate glasses are presented. The structure of the present glasses was studied using X-ray diffraction and FT-IR spectroscopy. UV-vis spectra of the present glasses were analyzed at different concentrations of Nd_2 O_3. The effect of neodymium concentration on the density and energy band gap was investigated. The density of the present glasses slightly increases with the increasing of Nd_2 O_3. A small variation of energy band gap with the increasing of neodymium content is observed as well, while E_g values decrease with the increase of Nd_2 O_3 content. The E_g values lie between 4.36 and 4.69 eV. Based on the measured optical spectra, Judd-Ofelt theory was used to determine the optical parameters such as line strengths, optical intensity parameters(Ω_t), transition probabilities, and transition lifetimes. Hypersensitive transitions were identified in the absorption spectrum, the greatest line strengths are recorded at the transitions~2 G_(7/2)+ ~4 G_(5/2), ~4 S_(3/2) + ~4 F_(7/2) and ~4 D_(1/2) + ~4 D_(3/2)+ ~4 D_(5/2) + ~2 I_(11/2) with wavelengths of 580, 475 and 355 nm,respectively. Lifetimes of the important ~4 F_(3/2) laser-level were determined; which show decreasing trend with the increasing of Nd_2 O_3 content and are found to be between 0.838 and 1.595 ms. The uncertainty of the present results was estimated. The RMS deviations were determined, which show lower values than those in the literature.     

Role of Nd_2O_3 nanoparticles addition on microstructural and superconducting properties of YBa_2Cu_3O_(7–δ) ceramics

The effects of Nd_2O_3 nanoparticles addition on microstructure,transport and AC susceptibility properties of YBa_2Cu_3O_(7–δ)(Y123) superconductors were systematically investigated using X-ray diffraction(XRD),scanning electron micrograph(SEM),four point probe measurement and AC spectrometer.It was found that the added samples were predominant by Y-123 phase beside small amount of Y-211 and unreacted Nd_2O_3 secondary phases.All added samples preserved the orthorhombic structure similar to the pure sample and no orthorhombic-to-tetragonal transition occurred.The samples became more porous and their grain size significantly decreased with addition of Nd_2O_3.The addition of nano-Nd_2O_3 disturbed the grain growth of Y123,thus resulting in the degradation of superconducting properties of the samples.The superconducting transition temperature(Tc onset) of samples decreased from 92 K for x=0.0 to 78 K for x=1.0 wt.%,which could be attributable to oxygen vacancy disorder.From AC susceptibility result,the inter-and intra-granular loss peaks became wider and broader with increase of Nd_2O_3 addition due to the weakening of grains coupling.On the other hand,the inter-granular critical current density,Jcm,was found to increase with Nd_2O_3 addition and had the highest value at x=0.6,confirming that Nd_2O_3 nanoparticles acted as pinning centers in Y123 matrix.     

Pairs of Ln(Ⅲ) dopant ions in crystalline solid luminophores: an ab initio computational study

Formation of dopant ions clusters in solid(glass) luminophores may affect efficiency of non-radiative energy transfer processes between dopant(photoactivator) ions via shortening of the effective distance between them. This study was based on the assumption that the distance between the dopant ions affects the energy of crystal volume at proximity. According to this idea, semi-empirical and ab initio density functional theory(DFT) calculations were performed on various supercells of YVO_4:Eu~(3+) as a model system. It was noted that a shorter Eu–Eu distance resulted in lower total energy of the system, compared to an analogous structure with distant Eu~(3+) ions. As lower energy configurations are preferred, the observed phenomenon was considered to be related to dopant ions clusters formation. Additionally, the values of energies obtained from DFT calculations were used to estimate the percentage of dopant ions occurring as pairs, for different dopant concentrations. The estimation agreed quite well with the available literature data.     

Corrosion Behavior of Ferritic/Martensitic Steels CNS-I and Modified CNS-II in Supercritical Water

 The corrosion behaviors of CNS-I and modified CNS-II were evaluated by exposing to superciritical water (SCW) at 550 ℃ and 25 MPa with a dissolved oxygen concentration of 200×10-9 for up to 1000 h. Detailed corrosion results of these two alloys were provided, including the growth rate of the oxide scales, microstructure of the oxide scales, distribution of phases and alloying elements. The mass gains of CNS-I and modified CNS-II were 60973 mg/dm2 and 45942 mg/dm2, respectively, after exposing to SCW for 1000 h. A duplex oxide scale with an outer porous magnetite layer and an inner relatively dense magnetite/spinel-mixed layer was identified on CNS-I and modified CNS-II after the test. The oxide scales were rather porous at the beginning of the test but the porosity decreased with increase of the exposure duration. It was found that Fe was enriched in the outer oxide layer, Cr was enriched in the inner oxide layer and O existed at a very high concnetration in the whole oxide scale. Other alloying elements such as Mo, W, Mn were depleted from the outer oxide layer and showed slightly enrichment in the inner oxide layer. The distributution of Ni was different from other elements, it was enriched in the interface bewteen the base metal and the oxide scale and depleted in the outer and inner oxide layers.