Magnetocaloric Properties of （Gd1-x Tbx ）3 Al2 Compounds Near Room Temperature

Recentlytherehasbeenaninterestinmagneticrefrigerationstudiesduetoitspotentialasanenergysavingtechnology[1～ 5] .Theefficiencyofmagneticre frigerationcriticallydependuponmagneticrefriger ants .Forthebestrefrigerantperformance ,verylargeisothermalmagneticentropychangeΔSisrequired ,andthemaximumvalueofΔSmustexistoverawiderrangeoftemperatures[2 ] .Recentdiscoveryofgiantmagnetocaloriceffect(MCE)ΔSinfirst ordertransi tionmaterialsgivesfurtherimpulsetowardsthedevel opmentofbothnewmaterialsandmag…     

Structure and Magnetocaloric Effect in Tb（ Co1-xSnx）2 Alloys

Recently,researchonmagnetocaloriceffect(MCE)hasattractedagreatdealofinterestinrare earth(RE)basedcompoundsbecauseoftheirenergy efficiencyandenvironmentalsafetyformagneticrefrig eration.Afirst ordermagneticphasetransitionwas foundintheintermetalliccompoundsRECo2(RE=Er,Ho,Dy)withMgCu2typestructure[1,2],leadingtoa largemagneticentropychangeforthesecompounds,whereasasecond ordertransitionwasfoundinTbCo2andGdCo2.IntheintermetalliccompoundsRECo2,theloweringofd electronconcentrationbythesubst…     

Influence of the Erbium Substitution for Gd in Gd5Si1.8Ge2.2Alloys on the Magnetocaloric Effect in Low-Field

The phases and magnetocaloric effect in the alloys (Gd1-xErx)5Si1.8Ge2.2 with x=0,0.1,0.2 and 0.3 were investigated by X-ray diffraction analysis and magnetization measurement. The samples were single phase with the monoclinic Gd5Si2Ge2-type structure. With the increase of Er content, the Curie temperature (Tc) decreased obviously from 253K of the alloy with x=0 to 114K with x=0.3. The maximum magnetic entropy changed in the samples of (Gd1-xErx)5Si1.8Ge2.2 with x=0.0,0.1,0.2 and 0.3 were 6.88,8.32,9.59 and 10.24 J·kg-1·K-1 respectively in the applied field change of 0~2.0T.     

Line Faults in Gd_5Si_2Ge_2-Type Phase

Line Faults in Gd_5Si_2Ge_2-Type Phase     

Study on Characteristics of Crystal Growth of NdFeB Cast Alloys

IthasbeenfoundthatthemicrostructuresofcastalloyshavegreatinfluenceonmagneticpropertiesinsinteredNdFeBmagnets .SothecharacteristicsofNdFeBcastalloys ,includingtheshapeofcrystal ,thecompositionanddispersionofphases ,havebeenstud iedbythepeople[1～4 ] .However ,therearefewre portsonthecharacteristicsofcrystalgrowth[5] .Inthispaper ,crystalgrowthorientationofcastalloyspre paredbydifferentprocessingwasinvestigatedusingX raydiffraction ,andtheinfluenceofcoolingrateoncrystalgrowthorientationwasana…     

Magnetic Entropy Change of （Gd1-xREx）5Si4（RE = Dy, Ho） Alloys

Magnetic Entropy Change of (Gd_(1-x)RE_x)_5Si_4(RE=Dy, Ho) Alloys     

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.     

Effects of manganese doping on magnetocaloric effect in Ge-rich Gd_5Ge_（2.05）Si_（1.95） alloy

The structure, magnetic and magnetocaloric properties of the Ge-rich Gd5Ge2.05-xSi1.95-xMn2x (x=0.01 and 0.03) alloys were investigated by scanning electron microscopy, X-ray powder diffraction, differential scanning calorimeter (DSC) and magnetization measurements. The results of energy dispersive X-ray analysis (EDX) and X-ray diffraction analyses showed that the composition and crystal structure of the alloys were desired. DSC measurements were performed to determine the transformation temperatures for each alloy. Both alloys exhibited the first order phase transition around room temperature. The alloys showed an anti-ferromagnetic transition around 60 K. The isothermal magnetic entropy changes of the alloys were determined from the isothermal magnetization measurements by using the Maxwell relation. The maximum values of isothermal magnetic entropy change of the Gd5Ge2.05-xSi1.95-xMn2x alloy with x=0.01 was found to be -12.1 and -19.8 J/(kg·K) using Maxwell equation around 268 K in applied fields of 2 and 5 T, respectively.     

Magnetocaloric Effect of Alloys Gd（Al1-x Cox ）2

The magnetocaloric effect in alloys Gd（Al1-xCox）2 with x = 0, 0.05, and 0.10 were investigated using X-ray diffraction （XRD） and magnetization measurements. It was found that three alloys crystallized in a single phase with MgCu2-type structure. The lattice parameter and Curie temperature decreased with increasing Co content, whereas the magnetic-entropy change increased. With a magnetic-field change of 2 T, the maximum of the magnetic-entropy change reached 4.6 J·kg^-1·K^-1 near Curie temperature at approximately 95 K in the alloy GdAl1.8Co0.2, which appeared to be an alternative candidate for active magnetic refrigerants working in the temperature range centered at 100 K.     

电池用含稀土铝合金阳极性能的研究

通过向 99.99%的纯铝中添加稀土及其它一些合金元素 ,如Ga,In ,Mg ,Sn ,Zn等 ,制得一系列含稀土的合金。在 2 5℃ ,4mol·L- 1 的KOH溶液中测定了它们的开路电位、自腐蚀速度与电化学性能。结果表明 :稀土元素能显著提高铝合金的抗腐蚀能力和阳极效率 ,Al 5Zn 0 0 1 5In 0 .1Sn 1Mg 0 .3RE具有较好的综合性能。     

Evolution of Sm2Fel7 Alloys during Hydrogenation-Disproportion Process

The evolution of phase compositions, phase change and microstructure in Sm2Fe17 alloys during hydrogenationdisproportion process were systematically studied with XRD, SEM, EDX methods. Research indicates that HD process of Sm2Fe17 alloys is as follows： Sm2Fe17 alloy absorbs hydrogen first in the atmosphere of hydrogenation with a pressure of 0.1 MPa. Disproportionation begins at T ≥ 500 ℃, then the alloys tuna into lots of SmHx and α-Fe phases which are partly in microcrystal or amorphous structures. Along with the increase of temperature, the microcrystal and amorphous structures transformed into crystal structure and this transformation thoroughly completed at 750 ℃. The size of obtained crystal grain is about 20 - 100 nm. Based on the experimental data, a microstructural transformation model of Sm2Fe17 alloys during hydrogenation-disproportion process was made.     

Evaluating Acceleration Ability of Electrons of SiO_2 and ZnS in ZnS∶Er Electroluminescence

SinceCoeyandSun[1]discoveredtheinterstitial compoundSm2Fe17Nx,ithasattractedmanyresearch ers′attention.Asakindofpermanentmagneticmate rial,Sm2Fe17Nxexhibitsfairlyhighsaturationmagneti zation(1.54T)[2],highanisotropyfield(14T)under roomtemperatureandhighC…     

用于室温磁制冷样机工质盘的Gd1-xCx合金

对Gd1-xCx(x=0、0.02、0.035、0.05)合金的磁热性能及显微硬度的分析测试表明,C的加入可大幅提高材料的维氏硬度;在一定成份范围内, C元素的加入对Gd的居里温度影响不大;2%(原子分数) C的加入几乎不降低Gd的绝热温变峰值, Gd0.95C0.05的最大磁熵变有所降低但降幅不大,综合比较,Gd0.98C0.02合金是制作工质盘理想的磁致冷材料.     

Effect of Annealing on Rare Earth Based Hydrogen Storage Alloys

Rare earth-based hydrogen storage alloy used as negative electrode materials for nickel-metal hydride (Ni-MH) batteries are used commercially.The effect of annealing treatment with different annealing temperature and time on the MLNi3.68 Co0.78 Mn0.35 Al0.27 and MMNi3.55 Co0.75 Mn0.40 Al0.30 alloys were investigated.The crystal microstructure,pressure-composition-isotherms (p-C-T) and electrochemical properties of alloys were examined by X-ray diffraction (XRD), automatic PCI monitoring system and electrical performance testing instruments.The optimum annealing treatment conditions of two kinds of alloys were determined.     

Composition Range of Amorphous Mg-Ni-Y Alloys

Based on the thermodynamic point of view, a method for predication of the composition range of amorphous ter-nary alloys was proposed. The composition range of amorphous ternary alloys is determined by the comparison of the excess free energy of the amorphous alloy and the free energy of competing crystalline states. The free energy is extrapolated from the data of three binary alloys by using Toop‘s model. The method was applied to predict the composition range of amor-phous Mg-Ni-Y alloys. The theoretical results are in good agreement with the available experimental results. It indicates that the present method can be used to predict the composition range for amorphous ternary alloys.     

Effect of Rare Earths on Hot Cracking Resistant Property of Mg-Al Alloys

The effect of rare earths （RE） ranging from 0.1% to 1.2%（mass fraction） on hot cracking resistant property of Mg-Al alloys was investigated. The results show that hot cracking resistant property of Mg-Al alloys remarkably declines with an increase of RE addition. The causes of the decline are as follows： First, grain coarsening of Mg-Al alloys caused by RE addition reduces the fracture strain required for hot crack initiation. Second, RE reduces the eutectic microstructure of Mg- Al alloys, and as a result, shortens the time that the feeding channel remains open, making it difficult to feed the alloy. Furthermore, RE elevates the eutectic reaction temperature, which leads to the decrease in the strength of the interdendritic liquid film at the late stage of solidification. Third, when a-Mg dendrites form continuous skeletons, the interdendritic Al11 RE3 phase tends to block the feeding channels and increases the difficulty of feeding. Last, the shrinkage ratio discrepancy between Al11RE3 phases and α-Mg matrix is prone to cause shrinkage stress and promote hot crack initiation.     

Phase Transformation Behaviors and Effects of Terbium in Polycrystalline Ni-Mn-Ga Magnetic Shape Memory Alloys

The phase transformation behaviors of two kinds of magnetic shape memory alloys NisoMn25 x Ga25-x and Ni50 Mn29Ga21-x Tbx were studied. When the composition of Ni in these alloys was constant, increasing Mn and reducing Ga contents make martensitic transformation temperatures rise obviously. Simultaneously, thermal hysteresis of phase transformation reduce but Curie temperature una|ters. When terbium was added, phase transformation temperature went up further and Curie temperature kept constant. The alloys still show strong ferromagnetism and properties of thermoelastic martensite phase transformation.     

Thermodynamical Evaluation on Magnetocaloric Effect of Magnetic Refrigerating Materials Near Room Temperature

The relationship between isothermal magnetic entropy change △S and adiabatic temperature change △Tad was deduced according to the principles of thermodynamics. The MCE and the engineering application were discussed for Gd and several new kinds of magnetic refrigerating materials near room temperature, Gd5Si2Ge2, MnFeP0.45As0.55 and LaFe11.2Co0.7Si1.1. Isothermal entropy change is proportional to adiabatic temperature change with a factor of T/C (T is temperature, C is heat capacity). When the comparison of magnetacoloric effect is made for two different materials, we should consider isothermal entropy change as well as adiabatic temperature change.     

AZ91镁合金稀土表面改性的研究

研究了采用稀土多元共渗方法提高AZ91镁合金表面耐腐蚀性能的作用。结果表明,该方法可以有效地改善镁合金表面耐全面腐蚀、点蚀的性能,提高镁合金表面在温热潮湿环境下的稳定性。经过稀土渗入处理后的镁合金,显微组织均匀、致密,有利于耐蚀性的提高。     

磁热效应合金Gd5(Ge1-xMx)4的结构

用磁控电弧炉在氩气气氛中熔炼了Gd5(Ge1-xMx)4(M=Mo、Al、Cr和Ga)系列合金。对样品的结构、显微组织和磁热性能进行了研究,研究发现随着M元素含量的增加,晶体结构会发生由5∶4型正交结构→5∶2∶2型单斜结构→5∶4型正交结构的转变,晶态组织出现非共晶→共晶→非共晶的转变,样品的磁热效应会随着M元素的含量增大而增大。