Phase Structure and Electrochemical Properties of Rare Earth Based Hydrogen Storage Alloys

The rare earth based hydrogen storage alloys MmxM1 1 - x ( Ni3.55 Co0.75 Mn0.4 A10.3 ) ( x = 0 ～ 0.5 ) were investigated in this work.Adjusted Ml: Mm ratio to change the content of La,Ce,Pr and Nd in the alloys and then to change the phase structure, the influences of phase structure on the electrochemical properties were analyzed.The results indicate that the main phase of all alloys is LaNi5 with CaCu5 type structure and the crystal lattices constants of LaNi5 are changed with increasing x value, i.e, decreased a-axis, increased c-axis and axis ratio and nonlinear decreased crystal volume.The crystal volume of the alloy with x = 0.3 is larger than others.There is second phase A1LaNi4 in alloys when x≥0.3, which decrease the discharge capacity, but increase the cycling stability and high rate discharge ability.Compared comprehensively, the alloy with x = 0.3 shows the higher discharge capacity and the better cycling stability.

Study on Phase Structure and PCT Characteristics of Rare Earth Based Hydrogen Storage Alloys

The rare earth based hydrogen storage alloys Mm_xMl_ 1-xNi_ 3.55Co_ 0.75Mn_ 0.4Al_ 0.3(x=0～0.50) were investigated in this work. The influences of phase structure on the PCT characteristics were analyzed by means of electrochemical measurements. The results indicate that there is a strict relationship between crystal volume and PCT characteristics.

Phase structure and electrochemical properties of laser sintered La_2MgNi_9 hydrogen storage electrode alloys

Phase structure and electrochemical properties of laser sintered La2MgNi9 alloys were studied. The sintered alloys contained a main phase, LaNi5, and a ternary La-Mg-Ni phase, with a PuNi3 structure and a small amount of LaMgNi4. The ternary La-Mg-Ni phase with a PuNi3 structure had the composition of La1.8Mg1.2Ni9 and La2MgNi9, for alloys laser sintered at 1000 and 1400 W, respectively. Owing to further reactions between LaNi5 and LaMgNi4, the amount of the PuNi3 phase increased for alloys sintered at 1400 W. Both alloys had good activation property （three charge/discharge cycles）. The discharge capacities of the sintered alloys were 321.8 and 344.8 mAh/g, respectively. Compared with the alloy laser sintered at 1000 W, the poor cyclic stability of the alloy sintered at 1400 W was mainly attributed to the lower corrosion resistance of the La2MgNi9 phase.

Phase Structure and Electrochemical Characteristics of Ml(Ni_(3.55)Co_(0.75)Mn_(0.40)Al_(0.30))_(5x)(x=0.88,0.92,0.96,1.00) Hydrogen Storage Alloys

The phase structure and electrochemical characteristics of Ml （（Ni3.55Co0.75Mn0.40Al0.30）sx （ x = 0.88, 0.92, 0.96, 1.00） hydrogen storage alloys were studied. The effect of the stoichiometric ratio on the phase structure and electrochemical characteristics was analyzed. The results of XRD reveal that all the alloys consist mainly of LaNi5 phase with the hexagonal CaCu5 structure. But a few of the diffraction peaks of La2Ni7 phase on XRD pattern are observed when x ≤ 0.92, and with decreasing x, the intensity of La2Ni7 diffraction peaks increases and the values of lattice parameters a and cell volume increase, c and c/a of LaNi5 phase decrease gradually. When x≥0.96, La2Ni7 phase disappears and the alloys become single CaCu5-type. The electrochemical tests show that the maximum discharge capacity, high rate dischargeability and low temperature dischargeability are improved to different degrees by adjusting the stoichiometric ratio.

Effects of annealing on microstructures and electrochemical properties of La_(0.8)Mg_(0.2)Ni_(2.4)Mn_(0.10)Co_(0.55)Al_(0.10) alloy

The La0.8Mg0.2Ni2.4Mn0.10Co0.55Al0.10 alloy was prepared by induction melting. The structural and morphological characterizations were performed by means of X-ray powder diffraction （XRD） and scanning electron microscopy （SEM）. The electrochemical measurements were performed using LAND and CH/660b electrochemical workstation. The main phases of the alloy were LaNi5 and （La,Mg）Ni3. After annealing, the maximum discharge capacity, cycle stability and high rate dischargeability （HRD） were improved obviously. The maximum discharge capacity reached 373.80 mAh/g （T=1173 K）, the C100/Cmax（%） was 72.63% （T=1173 K）, and the value of HRD reached 51.8% at a discharge current density of 1150 mA/g （T=1173 K）. The cyclic voltammetry （CV） and potentiodynamic polarization were also studied.

Influences of molybdenum substitution for cobalt on the phase structure and electrochemical kinetic properties of AB_5-type hydrogen storage alloys

The effects of the partial replacement of Co with Mo on the phase structure and electrochemical kinetic properties of La0.35Ce0.65Ni3.54Co0.80-xMn0.35Al0.32Mox （x=0.00, 0.10, 0.15, 0.20, 0.25） hydrogen storage alloys prepared by arc-melting method were sys-tematically studied in this paper. The X-ray diffraction （XRD） showed that after partial substitution of Mo for Co, the alloys remained a single LaNi5 phase with a hexagonal CaCu5-type structure. The P-C isotherms indicated that the equilibrium pressure gradually decreased with in-creasing of Mo content. Electrochemical studies showed that the substitution of Mo for Co could greatly increase discharge capacity, improve activation ability and reduce self-discharge of alloy electrodes. The alloy with x=0.25 exhibited a higher rate dischargeability （HRD1200= 50.9%）. Moreover, Mo is a vital element in favor of kinetic properties of AB5-type hydrogen storage alloys. As Mo content increased, the ex-change current density I0, the hydrogen diffusion rate gradually increased.

Phase structure and hydrogen storage properties of REMg8.35Ni2.18Al0.21 （RE=La, Ce, Pr, and Nd） hydrogen storage alloys

REMg8.35Ni2.18Al0.21 （RE=La, Ce, Pr, and Nd） alloys were prepared by induction melting and following annealing. X-ray diffraction （XRD） and scanning electron microscopy （SEM） results showed that the alloys were composed of Mg2Ni, （La, Pr, Nd）MgzNi, （La, Ce）2MgxT, （Ce, Pr, Nd）Mg12 and Ce2Ni7 phases. The above phases were disproportioned into Mg2NiH4, MgH2 and REHx （x=2.5 1 or 3） phases in hydriding. CEH2.51 phase transformed into CEH2.29 phase in dehydriding, whereas LaH3, PrH3 and NdH3 phases re- mained unchanged. The PrMg8.41Ni2.14Al0.20 alloy had the fastest hydriding kinetics and the highest dehydriding plateau pressure while the CeMg8.35Ni2.18Al0.21 alloy presented the best hydriding/dehydriding reversibility. The onset hydrogen desorption tempera- ture of the CeMg8.35Ni2.18Al0.21 hydride decreased remarkably owing to the phase transformation between the Cell2.51 and the CEH2.29.

Phase structure and electrochemical properties of non-stoichiometric La_(0.7)Ce_(0.3)(Ni_(3.65)Cu_(0.75)Mn_(0.35)Al_(0.15)(Fe_(0.43)B_(0.57))_(0.10))_x hydrogen storage alloys

Phase structure and electrochemical characteristics of Co-free La0.7Ce0.3（Ni3.65Cu0.75Mn0.35Al0.15（Fe0.43B0.57）0.10）x （0.90≤x≤1.10） alloys were investigated. When x was 0.90, the alloy was composed of LaNi5, La3Ni13B2 and Ce2Ni7 phases. The Ce2Ni7 phase disappeared, and the abundant of La3Ni13B2 phase decreased when x increased to 0.95. When x was 1.00 or higher the alloys consisted of LaNi5 phase. The lattice parameter a and the cell volume V of the LaNi5 phase decreased, and the c/a ratio of the LaNi5 phase increased with x value increasing. Maximum discharge capacity of the alloy electrodes first increased and then decreased with x value increasing from 0.90 to 1.10, and the highest value was obtained when x was 1.00. High-rate dischargeability at the discharge current density of 1200 mA/g increased from 50.7% （x= 0.90） to 64.1% （x=1.10）. Both the charge-transfer reaction at the electrode/electrolyte interface and the hydrogen diffusion in the alloy were responsible for the high-rate dischargeability. Cycling capacity retention rate at 100^th cycle （$10o） gradually increased from 77.3% （x= 0.90） to 84.6% （x= 1.10）, which resulted from the increase in Ni content and the c/a ratio of the LaNi5 phase with x value increasing.

Effect of Al_(82.8)Cu_(17)Fe_(0.2) alloy doping on structure and magnetic properties of SmCo5-based ribbons

This work tries to improve the magnetic properties by multi-element doping in the form of a ternary alloy.SmCo_(5+)χwt%Al-Cu-Fe(x=0-7)ribbons melt-spun at 40 m/s were produced by adding Al_(82.8)Cu_(17)Fe_(0.2)alloy into SmCo_(5) matrix,and their phases,microstructure,and magnetic properties were investigated.The results show that both x=0 and 3 ribbons form a cellular microstructure.Al-Cu-Fe addition reduces the content of the Sm_(2)(Co,M)_(7) cell wall,narrows its width,and forms the local disordered micro-regions and solute-segregation nanoclusters in the Sm(Co,M)_(5) grains.With x increasing to5,Al-Cu-Fe addition promotes the phase separation between and within grains of the SmCo_(5)-based alloy.The Al-Cu-Fe addition can simultaneously improve the coercivity and magnetization of the SmCo_(5)-based ribbons,in particular,the magnetization of the x=3 ribbons increases by 35%,while the coercivity of the x=5 ribbons increases by 3.9 times.Finally,the microstructure evolution models are built up,and the relationship between the microstructure and the magnetic properties is discussed.

Influence of magnesium content on structure and electrochemical properties of La_(1-x)Mg_xNi_(1.75)Co_(2.05) hydrogen storage alloys

La（1-x）MgxNi（1.75）Co（2.05）（x=0.07, 0.08, 0.10, 0.13, 0.15） alloys were prepared by high-frequency inductive method, and then their structure and electrochemical properties were investigated systematically. The XRD analysis revealed that the alloys consisted of LaNi5 phase and La4MgNi（19）（Ce5Co（19） ＋ Pr5Co（19）） phase, and the introduction of Mg could promote the formation of La4MgNi（19） phase. The observation of microstructure showed that all the alloys processed dendritic structure, which was refined with the increase of x value. The electrochemical measurements showed that all the alloys could be activated within 2 cycles, and with increasing x, the maximum discharge capacity obviously increased from 254.00 m Ah/g（x=0.07） to 351.51 mAh/g（x=0.15）, but the cycling stability（S（80）） decreased somehow from 78.4% to 73.9%. Meanwhile, the appropriate addition of Mg could improve the high-rate discharge capacity（HRD） of the alloy electrodes, which was mainly controlled by the electrochemical reaction rate on the surface of the alloys.

Microstructure and electrochemical characteristics of La_(0.7)Ce_(0.3)Ni_(3.75)Mn_(0.35)Al_(0.15)Cu_(0.75-x)(V_(0.81)Fe_(0.19))_x hydrogen storage alloys

Microstructure and electrochemical characteristics of La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-x（V0.81Fe0.19）x hydrogen storage alloys were investigated. XRD indicated that La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-x（V0.81Fe0.19）x alloys consisted of a single phase with CaCus-type structure, and the lattice parameter a and cell volume V increased with increasing x value. The maximum discharge capacity first increased from 319.0 （x=0） to 324.0 mAh/g （x=0.05）, and then decreased to 307.0 mAh/g （x=0.20）. The high-rate dischargeability at the discharge current density of 1200 mA/g first increased from 52.1% （x=0） to 59.1% （x=0.15）, and then decreased to 55.4% （x=0.20）. The hydrogen diffusion in the bulky alloy was responsible for the high-rate dischargeability. Cycling stability first increased with increasing x from 0 to 0.10 and then de- creased when x increased to 0.20, which was resulted fi＇om the synthesized effect of the improvement of the pulverization resistance and the decrease of corrosion resistance.

Study on structure and electrochemical properties of the (LaGdMg)Ni_(3.35-x)Co_xAl_(0.15)(x=0-2.0) hydrogen storage alloys

Hydrogen storage alloys(LaGdMg)Ni3.35-xCoxAl0.15(x=0,0.1,0.3,0.5,1.0,1.5,2.0) were prepared by induction melting followed by annealing treatment in argon atmosphere.The effects of partly replacing Ni by Co element in(LaGdMg)Ni3.35Al0.15 on the phase structure and electrochemical properties of(LaGdMg)Ni3.35-xCoxAl0.15 alloys were investigated.Structure analysis showed that the alloys consisted of Ce2Ni7-type(Gd2Co7-type),CaCu5-type,Pr5Co19-type,PuNi3-type phase structure.The addition of Co element obviously reduced the contents of CaCu5-type phase and increased the contents of Ce2Ni7-type phase.However,Pr5Co19-type and CaCu5-type phase obviously increased with the high content of Co.Rietveld analysis showed that the c-axis lattice parameters and cell volumes of the component phases increased with increasing Co content.The electrochemical measurements showed that as the Co content increased,the maximum discharge capacity and the cyclic stability of the annealed alloys both first increased then decreased.The(LaGdMg)Ni3.05Co0.3Al0.15 alloy electrode exhibited the maximum discharge capacity(392.92 mAh/g),and the(LaGdMg)Ni1.85Co1.0Al0.15 alloy electrode showed the best cyclic stability(S100=96.1%).

PHASE RELATIONSHIPS IN R－Fe PSEUDOBINARY SYSTEM (R＝Dy0．65Tb0．25Pr0．1)

The phase relationships of R-Fe pseudobinary system(R=Dy0.65Tb0.25Pr0.1) have been determined using optical microscopy,X-ray diffraction,EPMA and DTA techniques.This system contains one eutectic reaction and four peritectic reactions.The four intermetallic compounds are(Dy,Tb,Pr)Fe2,(Dy,Tb,Pr)Fe3,(Dy,Tb,Pr)6Fe23 and(Dy,Tb,Pr) 2Fe17 The homogeneity regions of these compounds shift towards rare earth-rich side of the stoichiometric composition except(Dy, Tb,Pr) 2Fe17.

Multiplex intermetallic phases in a gravity die-cast Mg-6.0Zn-1.5Nd-0.5Zr(wt%) alloy

Components and crystal structures of the intermetallic phases in a gravity die-cast Mg-6.0Zn-1.5Nd-0.5Zr(wt%)alloy were investigated using transmission electron microscopy.The results indicate that this alloy has multiple intermetallic phases and various inner faults.Totally,six eutectoid intermetallic phases,namely W(Mg Nd Zn_(3)),T(Mg_(39)Zn_(55)Nd_(6)),(Mg,Zr)Zn_(2),Z(Mg_(28)Zn_(65)Nd_(7)),H_(2)(Mg_(15)Zn_(70)Nd_(15)),and H1(Mg_(24)Zn_(64)Nd_(11)),were simultaneously observed at grain boundaries,and six precipitates(Z,Mg_(7)Zn_(3),T,Mg_(4)Zn_(7),β_(1)-Mg Zn_(2) and β_(2)-Mg Zn_(2))were found inα-Mg grains.Furthermore,faults like sub-grain boundaries,orientation domains(coherent with the same matching plane but with different orientations),stacking faults and twins were observed in the eutectoid intermetallic phases.Finally,some new orientation relationships between the known intermetallic phases were revealed.This paper can provide new insight into alloy design for Mg-Zn-RE(RE:rare earth)based alloys.

Effects of Different Processes on Phases and Service Performance of FeSiMg8RE5 Alloy

The difference of nodularizer in phase morphology and service performance by three processes was introduced.The three processes include directly pressing magnesium into molten alloy stirring by nitrogen gas and no stirring from 5 t arc furnace and melting magnesium in the intermediate frequency furnace.The microstructure patterns were observed by scanning electron microscope, and composition of phases was measured by energy dispersive spectrometer method.X-ray diffraction method was used to determine the phase structure of the nodularizer.The results show that spheroidizing reaction time and violent degree of nodularizers are influenced by grain size and distribution uniformity of siliconizing magnesium phase; spheroidizing reaction degree can be mitigated and spheroidizing time be increased by using N2 stirring in pressing magnesium from arc furnace.

A STUDY OF THE T_1' PHASE IN THE Al-2.6Li-1.3Cu ALLOY

ＡＳＴＵＤＹＯＦＴＨＥＴ１＇ＰＨＡＳＥＩＮＴＨＥＡｌ－２．６Ｌｉ－１．３ＣｕＡＬＬＯＹＣｕｉ，Ｙｕｅｘｉａｎ；Ｓｕｎ，Ｄｏｎｇｌｉ；Ｍａｏ，Ｊｉａｎｆｕ；Ｙａｎｇ，Ｄｅｚｈｕａｎｇ（ＨａｒｂｉｎＩｎｓｔｉｔｕｔｅｏｆＴｅｃｈｎｏｌｏｇｙ，Ｈａｒｂｉｎ...

MAGNETOSTRICTIVE BEHAVIOUR OF R(Fe1－xAlx)y ALLOYS(R＝Dy0．65Tb0．25Pr0．1)

The structure and magnetostriction of R(Fe_(1-x)Al_x)_y alloys(R=Dy_(0.65)Tb_(0.25)Pr_(0.1),x≤0.3,y=1.8 and 2) have been investigated using metallography, X-ray diffraction, electron probe micro- analysis(EPMA) and standard strain gauge techniques.It was found that the matrix of R(Fe_(1-x)Al_x)_2 alloys is cubic Laves phase(Dy,Tb,Pr)(Fe,Al)_2 and the second phase is PuNi3-type (Dy,Tb,Pr)(Fe,Al)_3 when x<0.15.The R(Fe_(1-x)Al_x)_(1.8) alloys contain trace of rare earth-rich phase.The magnetostriction of R(Fe_(1-x)Al_x)_y alloys decreases with increasing x in high magnetic fields; however, it exhibits a peak when x = 0.05 in low magnetic fields(H≤ 160 kA / m).The magnetostriction of R(Fe_(1-x)Al_x)_(1.8) alloys is higher than that of R(Fe_(1-x)Al_x)_2 alloys when x<0.15.

脉冲磁场对稀土AZ91D镁合金凝固组织及性能的影响

研究了脉冲磁场对稀土AZ91D镁合金凝固组织及力学性能的影响。研究表明:在AZ91D镁合金中加入适量稀土La有利于晶粒细化,形成新的稀土针状化合物Al_(2)La;在AZ91D-0.75La合金凝固过程中施加脉冲磁场处理后,针状化合物Al_(2)La长度更加短小,甚至趋于球化;同时,AZ91D-0.75La合金的凝固组织和力学性能得到进一步改善,当脉冲占空比为20%、频率为20 Hz时,合金的处理效果最好,晶粒尺寸从156.3μm下降至103.5μm,细化了33.78%,维氏硬度也从HV 53.8增加至HV 69.4。

Phase equilibria of long-period stacking ordered phase in the ternary Mg-Y-Al alloys

Phase equilibria focusing on the long-period stacking ordered(LPSO)phases have been experimentally in-vestigated in the Mg-Y-Al alloys.The microstructures of the eleven representative alloys annealed at 450,500 and 550°C were systematically investigated using X-ray diffraction(XRD),scanning electron mi-croscopy(SEM)and transmission electron microscopy(TEM).Two thermodynamically stable LPSO poly-types were identified,including 18R and 10H structures.Meanwhile,the transformation of 18R→10H was detected in Mg-9.0Y-1.7Al(at.%)alloy,while the coexistence of 18R and 10H was observed in Mg-14.2Y-12.8Al(at.%)alloy.It was found that the LPSO phases were non-stoichiometric compounds with ternary solubilities.The 18R can dissolve up to 7.21 at.%-8.37 at.%Al and 10.75 at.%-12.01 at.%Y,while the 10H can dissolve up to 9.35 at.%-10.37 at.%Al and 14.50 at.%-14.94 at.%Y.All of the experimental re-sults were used to construct the isothermal sections,which is conducive to the design of Mg-Y-Al alloys.

稀土贮氢合金的相结构研究

根据合金化原理，从合金相结构的角度，探讨合金优化时相结构对电极性能如放电容量和循环寿命等方面的影响。具有ｈＰ６－ＣａＣｕ５型结构的单相ＬａＮｉ５存在一个大的均相区，并为吸氢提供大量的四面体和八面体间隙位置。快凝下非化学计量ＡＢ５＋ｘ贮氢合金，由于过剩Ｂ原子的插入而产生各向异性变形晶体点阵也即ａ轴减小ｃ轴增加。经退火后变形晶体点阵得以弛予形成双相合金。面心立方ＮｉＣＯ３和六方的ＭｏＣＯ３相有利于电极综合性能的提高。对于富稀土混合稀土贮氢合金，ＭｍＮｉ（Ｍｍ：混合稀土）相在晶界择优沉淀，抗氧化能力降低；而贫稀土的合金ＡｌＮｉ３在晶界择优沉淀，大大地降低放电容量和循环寿命。原位Ｘ射线衍射方法是研究气相吸放氢等温过程及原位相结构点阵膨胀的有效方法。