Effect of Magnetic Field on Synthesis of Nano-FeOOH by Low-Temperature Neutralization Method

Using XRD,TEM and VSM methods,the phase,morphology and magnetic property of iron hydroxide oxide(FeOOH)which has been prepared by low-temperature neutralization reaction under different magnetic fields were analyzed.It can be found that the magnetic field had a great influence on the product.Acicular goethite(α-FeOOH)was synthetized without magnetic field.When the magnetic flux density was increased to 0.1T,γ-FeOOH was obtained.If the magnetic field intensity was raised to 0.5T,the product was all composed ofσ-FeOOH.Moreover,the crystallization of FeOOH was greatly influenced by magnetic field as well.Thermodynamic calculation results show that the magnetic free energy of chemical reaction reached to more than hundreds KJ/mol when the magnetic field is applied.It meaned that the application of magnetic field was conducived to producing the products with higher susceptibility.Even under the low magnetic field,due to the stability of the reaction products was broken by the magnetic field,the magnetic free energy was also effective.     

Large Magnetostriction of Fe-Ga Alloys by Solidification With a Static Magnetic Field

A simple but effective process to fabricate the bulk and practical Fe-Ga alloys at low fields is proposed just by applying a static magnetic field to their solidification process.We have introduced a static 1-T magnetic field to solidify the Fe-17%Ga alloys.The results indicate that the magnetostriction of a polycrystalline textured Fe-17%Ga alloy is increased about threefold by solidifying with a 1-T magnetic field compared to that without a magnetic field.This large magnetostiction could be attributed to the increasing volume fraction and the strong texture of the disordered a-Fe phases.The systematic analysis shows that they are originated from the undercooling and orientation effects induced by the imposed magnetic field during the solidification process.     

Effect of a High Magnetic Field on the Microstructure During Directionally Solidified Sn-20wt.%Pb Hypoeutectic Alloy

The microstructures of Sn-20wt.%Pb hypoeutectic alloy directionally solidified under a longitudinal magnetic field were investigated.The results show that the application of a high magnetic field has a great influence on the morphology of primary P-Sn phase at a temperature gradient of G_L=52 K/cm.At a certain growth speed,with the increase of magnetic field intensity,the magnetic field causes the primaryβ-Sn phase irregular and to be deformed,further,the magnetic field promotes the columnar to equaixed transition(CET).Further,the thermoelectric magnetic force(TEMF)imposed on the dendrite under a high magnetic field has been calculated and the results show that the numerical magnitude of the TEMF during directional solidification under a 10 Thigh magnetic field is about 10~4N/m~3 and this force should be responsible for the occurrence of the CET in the Sn-Pb alloy.This may act as an experimental proof that the coupling of temperature gradient and high magnetic field will induce the occurrence of the CET in Sn-Pb alloy.Above phenomena may be attributed to the thermoelectric magnetic force(TEMF)in solid.     

Free Surface Behavior Under Alternating and Static Magnetic Field

In order to reasonably control the free surface oscillations,by using GalnSn low-melting alloy,the fluctuation and distortion behaviour of metal free surface is investigated under AC magnetic field.By simultaneously superposing DC magnetic field,the damping effect of DC magnetic field on free surface fluctuation is also investigated.In the cylindrical pool,the azimuthal and radial oscillation mode can be found simultaneously due to AC magnetic field.Moreover,the free surface is more stable in square pool than that in the cylindrical pool.Increase coil AC current,the free surface fluctuation is aggravated.A series of surface waves can be observed on free surface with compound magnetic field.Reasonable DC magnetic field can effectively damp the oscillations on the free surface in cylindrical pool.However,the DC magnetic field cannot effectively damp the surface oscillations in square pool.The DC magnetic field has no significant damping effect on the oscillations induced by the lower frequency magnetic force.     

Effect of Longitudinal Magnetic Field on Microstructures of Directionally Solidified Ni-Based Superalloy

The effect of a longitudinal static magnetic field on the microstructures of the superalloy DZ417G during directional solidification at the low withdrawal velocity was investigated experimentally.The experimental results showed that the application of a high static magnetic field significantly changed the interface shapes and microstructures of the superalloy.In practice,when the magnetic filed is applied,the well-ordered columnar dendrite structures still existed in the entire sample as the increase of magnetic field from 0 to 0.3 T.With the increase of magnetic field,the columnar to equiaxed transition(CET)occurred and reaches a maximum under a 0.5 T magnetic filed,and then decrease with the magnetic filed still increase.When the magnetic field is higher than 1.2 T,equiaxed grains zone on the edge of sample increased again and gradually extended from the edge to the center of the sample.Moreover,the macrosegregation may occur along with the appearance of the equiaxed grains.These phenomena should be contributed to interaction of the EMD and TEMC in liquid phase and TEMF in solid phase.     

Phase structure and magnetocaloric effect of （Tb1-xDyx）Co2 alloys

Phase structure and magnetocaloric effect of （Tb1-xDyx）Co2 alloys with x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were investigated using X-ray diffraction analysis, differential thermal analysis, and magnetization measurement. The samples were single phase with cubic MgCu2- type structure; with the increase of Dy content, Tc decreased from 240 K （TbCo2） to 130 K （DyCo2）, and the maximum magnetic entropy change ｜ △SM,max｜ increased from 3.133 to 8.176 J/kg-K under low magnetic field of 0-2 T. The Arrott plot and the change of ｜△SM,max｜ showed that magnetic phase transition from second order to first order occured with the increase of Dy content between x=-0.6 and 0.8.     

Effects of High Magnetic Field on Microstructure and Properties of Low Aspect Ratio Bi₂Sr₂CaCu₂O_x/AgMg Wire

Here,we report the effect of an 8 T magnetic field on the microstructure and properties of a reetangular Bi₂Sr2CaCu20x/AgMg（Bi2212/AgMg）conductor with low aspect ratio.The magnetic field was applied during split melt process with the field direction perpendicular and parallel to the wide surface of the conductors.After heat treatment,the conductors were electrically characterized using four-point critical current measurements as a function of magnetic field and magnetic field orientation relative to the conductor.The superconducting transition and magnetization hysteresis were measured using a SQUID magnetometer.The microstructure was characterized using scanning electron microscopy.It was found that the presence of magnetic field during split melt processing enhances the electrical transport and magnetic behavior.The magnetic field increases the Bi2212 grains alignment and long range texture within filaments and bridges between filaments by textured growth of Bi2212 phase.     

Effects of Magnetic Field on Fracture of AI-Li Alloy Containing Cerium

The effects of magnetic field on fracture feature and microstructure of Al-Li alloys containing Ce were investigated. Experiment results show that the fracture features and the microstructures are changed with the magnetic field. The fracture surface of the alloys is mainly quasi-cleavage without applying magnetic field. With a magnetic field, the fracture of quasi-cleavage changes to more secondary cracks and less quasi-cleavage plates on fracture surface. Grains become thinner and uniform with applying magnetic field. The influence of magnetic field on atom diffusion was discussed.     

Preparation of Nanoscale Sm2Co17 Flakes by Ball Milling in Magnetic Field

A new preparation method of Sm2Co17 nanoflakes was investigated. Hard magnetic Sm2 Co17 nanoflakes with thickness of 20-100 nm were obtained by milling in heptane and oleic acid under a magnetic field of 1.5 T for 0.5-20 h. It was shown that higher anisotropic magnetic properties would be induced by the flake-shape anisotropy when the prepared Sm2 Colt particles are milled with a magnetic field. The magnetic anisotropy of flakes after being aligned under the magnetic field of 1.5 T could be further enhanced, and the value of （BH）m was 128 kJ · m a Both anisotropy and properties are better than those of the nano-particles milled without a magnetic field.     

Effect of Various Field Shapers on Magnetic Pressure in Electromagnetic Inward Tube Forming

In this paper,the influence of various field shapers and their shapes on the distribution of the magnetic flux densities and applied forces on the work-piece in the electromagnetic inward tube forming are studied numerically using the FEA software MAXWELL.First the model was verified with experimental results and thereafter four kinds of field shapers(conical,cylindrical,concave and convex)were considered.Effects of their geometries,such as air gap between field shaper and tube work-piece,height of the step in single and multiple stepped field shaper on magnetic flux densities and magnetic pressures were studied.The results of this research can be applied to design field shaper,tube compression technology,and improve the efficiency of the coil.It is seen that magnetic force decreases if height of step in convex field shaper increases but effective forming region enlarges.Decreasing air gap has also a positive influence on magnetic field increase.Though the object of this research is limited to field shaper for inward tube forming,the results can also be applied to the field shaper for tube bulging.     

Influence of the substitution of Sm, Gd, and Dy for La in La0.7Sr0.3MnO3 on its magnetic and electric properties and strengthening effect on room-temperature CMR

A series of La0.7-xSmxSr0.3MnO3, La0.7-xGdxSr0.3MnO3, and La0.7-xDyxSr0.3MnO3 (x=0.00, 0.10, 0.20, 0.30) samples were prepared by the solid-state reaction method. The influence of the substitution of Sm, Gd, and Dy for La on the magnetic and electric properties and on the magnetoresistance (MR) was studied through measurements of M-T curves and p-T curves. The results showed that: lattice distortion in-duced by substitution of Sm, Gd, and Dy for La and extra magnetism of substitution had great influence on the magnetic and electric proper-ties of perovskite manganites; substitution of magnetic rare earth element for La was an effective way to change Curie temperature and to strengthen MR in perovskite manganites; and appropriate substitution proportion would generate large MR near room temperature.     

微波合成固体氧化物燃料电池阴极材料La1-xSrxMnO3的研究

采用微波技术合成了固体氧化物燃料电池阴极材料La1-xSrxMnO3样品，分别选择x=0.1,0.2,0.3,0.4和0.5合成了La0.9Sr0.1MnO3,La0.8Sr0.2Mn3,La0.7Sr0.3MnO3,La0.6Sr0.4MnO3和La0.5Sr0.5MnO3，用X射线衍射分析检测了样品的结构与组成，用电子扫描电镜考查了样品的形貌和粒度，电导率测量结果表明，样品的组成和烧结温度影响电导率。在系列样品中，组成为La0.7Sr0.3MnO3电导率最高；烧结温度1200℃和1300℃相比较，1300℃烧结后样品的电导率大幅度提高。     

Magnetic Coupling in La0.67 Ca0.33 MnO3／La0.67 Sr0.33 CoO3／La0.67 Ca0.33MnO3 Trilayer Films

The perovskite La0.67 Ca0.33 MnO3/La0.67 Sr0.33 CoO3/La0.67 Ca0.33 MnO3 trilayers were fabricated by a facing-target sputtering technique and their magnetotransport properties were investigated. The magnetoresistance is dependent on spacer thickness and dramatically decreases when La0.67 Sr0.33 CoO3 layer is thick enough because of its short-circuiting effect. Different from La0.67 Ca0.33 MnO3 single layer, trilayer films with thin La0.67 Sr0.33 CoO3 spacer have the enhanced metal-semiconductor transition temperature (TMS) of La0.67 Ca0.33 MnO3 layers. The magnetic coercivity Hc shows a nonmonotonic behavior with changing the spacer layer thickness at 230 K. The waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom Lao.67 Ca0.33 MnO3 layers across the spacer La0.67 Sr0.33 CoO3 layer.     

Magnetic properties and magnetocaloric effects of manganite (La_0.8Ho_0.2)_2/3Ca_1/3MnO₃ and (La_0.5Ho_0.5)_2/3Ca_1/3MnO₃

We reported the magnetic properties and magnetocaloric effects(MCE) of(La0.8Ho0.2)2/3Ca1/3MnO3 and(La0.5Ho0.5)2/3Ca1/3MnO3 nanoparticles by sol-gel technique.With this method,we were able to obtain the samples with particle diameters ranging from 50 to 200 nm.In the(La1-xHox)2/3Ca1/3MnO3 compound,an external magnetic field induced a magnetic transition from an paramagnetic phase to a ferromagnetic phase above Ts=105-135 K,leading to magnetocaloric effects.The maximum value of ΔSM was 1.19 J/(kg·K) at 100 K and 2.03 J/(kg·K) at 152 K for a magnetic field change of 5 T.Because both samples had large relative cooling power(RCP) and wide δTFWHM,the study on systems with the(La1-xHox)2/3Ca1/3MnO3-related magnetic transitions may open an important field in searching good magnetic materials.     

Preparation of La0.9RE0.1MnO3 Ultra-fine Particles Used for CH4 Oxidation

Ｐｅｒｏｖｓｋｉｔｅ ｔｙｐｅｏｘｉｄｅｓ (ｇｅｎｅｒａｌｆｏｒｍｕｌａＡＢＯ3 )ｈａｖｅｂｅｅｎａｔｔｒａｃｔｉｎｇｍｕｃｈａｔｔｅｎｔｉｏｎｆｏｒｍｏｒｅｔｈａｎｔｗｏｄｅｃａｄｅｓｄｕｅｔｏｔｈｅｉｒｐｏｔｅｎｔｉａｌｃｏｍｍｅｒｃｉａｌａｐｐｌｉｃａｔｉｏｎｓａｓｃａｔａｌｙｓｔｓｆｏｒｖａｒｉｏｕｓｒｅａｃｔｉｏｎｓ :ｏｘｉｄａｔｉｏｎｏｆＣＯ[1～ 3 ] ａｎｄｌｉｇｈｔｈｙ ｄｒｏｃａｒｂｏｎｓ[4～ 7] ,ｃｏｍｂｕｓｔｉｏｎｏｆｎａｔｕｒａｌｇａｓｏｒＣＨ4 [8～ 1 1 ] (ｔｏｃｏｎｔｒｏｌＮ…     

Magnetic Transition of La0.8Sr0.2Mn1-xCoxO3（x =0, 0.3, 0.5, 1.0）

A series of rare earth compound oxides with the formula of La0.8Sr0.2Mn1-xCoxO3（ were prepared by the method of citric acid. Structures, figures and magnetic properties of the x=0.0, 0.3, 0.5, 1.0） samples were analyzed by means of XRD, SEM and SQUID. Experiment results prove that all the samples are hexagonal, but their figures and magnetic properties are different. La0.8Sr0.2MnO3 is ferromagnetic. La0.8Sr0.2Mn0.7CO0.3O3 and La0.8Sr0.2Mn0.5Co0.5O3 are ferrimagnetic. La0.8Sr0.2CoO3 is antiferromagnetic. SEM results indicate that the structure of the first three are three-dimensional reticulations which are made up of some small ellipsoids which link up at the head and the end. The fourth sample looks like some dispersed small balls.     

Phase structure and magnetocaloric effect of (Tb1-xDyx)Co2 alloys

Phase structure and magnetocaloric effect of (Tb1-xDyx)Co2 alloys with x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were investigated using X-ray diffraction analysis, differential thermal analysis, and magnetization measurement. The samples were single phase with cubic MgCu2- type structure; with the increase of Dy content, Tc decreased from 240 K (TbCo2) to 130 K (DyCo2), and the maximum magnetic entropy change |ΔSM,max| increased from 3.133 to 8.176 J/kg-K under low magnetic field of 0-2 T. The Arrott plot and the change of |ΔSM,max| showed that magnetic phase transition from second order to first order occurred with the increase of Dy content between x=0.6 and 0.8.     

Large Magnetic Entropy Effect in La2／3Ca1／3MnO3

The magnetocaloric effect in the colossal magnetoresistance material La2/3Ca1/3MnO3 was studied. From the measurements of temperature dependence of magnetization in various magnetic fields, the large magnetic entropy change associated with the ferromagnetic-paramagnetie transition was discovered. This result suggests that perovskite manganites are suitable candidates as working substance in magnetie refrigeration technology.     

Properties of La0.9Sr0.1MnO3 and tourmaline compound catalytic materials for methane combustion

A novel catalytic material Lao.9Sr0.1MnO3 and tourmaline compound catalytic material was synthesized in the base of traditional catalytic material La0.9Sr0.1MnO3 which exhibited excellent catalytic activity for methane combustion. Different contents of toumaaline were added to give a series ofLa0.9Sr0.1MnO3 and tourmaline catalytic material through a sol-gel method. Samples above were characterized and analyzed by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, Brunauer-Emmett-Teller method （BET）, temperaalre programmed reduction （TPR）, catalytic activity test and contact angle test. The as-prepared sample with 2% （m/m） tourmaline showed good homogeneity surface morphology and displayed the optimal catalytic activity. The light-off temperature reduced by 10 ℃ and the T90 decreased by 15 ℃. In addition, the mechanism of the reinforcement of catalytic activity was explored.     

改善钙钛矿材料室温下磁电阻效应的有效途径

将Ag2O与La0.67Ca0.25Sr0.08MnO3均匀混合经高温烧结后形成La0.67Ca0.25Sr0.08MnO3/xAg两相复合体系。随Ag掺入量的增加,样品的电阻率明显下降,磁化强度有小量下降,TC及电阻率的峰值温度TP没有明显变化。304K温度下,从x=0.25样品中得到最大磁电阻效应,磁电阻比约为41%,分别是La0.67Ca0.25Sr0.08MnO3和La0.67Sr0.33MnO3样品的1.6及10倍。磁电阻的本征效应和传导电子在界面处的自旋相关散射作用是产生室温下增强磁电阻效应的主要原因。结果说明,利用离子的掺杂效应调整居里温度到室温附近,再结合金属/钙钛矿复合体系界面属性丰富的特性来制备庞磁电阻材料是提高室温磁电阻有效的途径,这对应用研究具有十分重要的意义。