Rare earth-based superlattice alloys have great potential for gaseous hydrogen storage,as well as successful application as nickel-metal hydride batteries anodes.In this work,Y substitution was carried out to adjust t...Rare earth-based superlattice alloys have great potential for gaseous hydrogen storage,as well as successful application as nickel-metal hydride batteries anodes.In this work,Y substitution was carried out to adjust the gaseous hydrogen storage properties of A_(2)B_(7)-type La_(0.7)Mg_(0.3)Ni_(3.5)alloys.The results indicate a multiphase structure in the alloys comprised of the main rhombohedral Gd_(2)Co_(7)and PuNi_(3)phases,with a small amount of CaCu_(5)phase.Moreover,the Y substitution results in higher abundance of the Gd_(2)Co_(7)phase.The alloy La_(0.42)Y_(0.28)Mg_(0.3)Ni_(3.5)exhibits a hydrogen storage cap acity of 1.55 wt%at 298 K and a desorption plateau pressure of 0.244 MPa.In addition,this alloy demonstrates a stable cycle life by a capacity retention of 94.2%after 50 cycles,with the main capacity degradation occurring during the initial 20 cycles.This work accentuates the potential of the La-Y-Mg-Ni-based superlattice alloys for applications in solid-state hydrogen storage.展开更多
A novel approach based on thermal diffusion was used to achieve controllable Mg content in A_(2)B_(7)-type La-Mg-Ni-based alloys.The formation mechanism of the A_(2)B_(7)-type phase as a result of the thermal diffusio...A novel approach based on thermal diffusion was used to achieve controllable Mg content in A_(2)B_(7)-type La-Mg-Ni-based alloys.The formation mechanism of the A_(2)B_(7)-type phase as a result of the thermal diffusion process and the effect of Mg content on hydrogen storage performance were investigated.X-ray diffraction(XRD)patterns and Rietveld refinement results showed that increased Mg transformed the LaNi_(5)phase in the La_(0.74)Sm_(0.03)Y_(0.23)Ni_(4.32)Al_(0.04)precursor alloy into a superlattice structure.Scanning electron microscopy(SEM)images showed that Mg was evenly distributed in the alloy bulk.Mg in the superlattice significantly inhibited the phase decomposition of the superlattice structure during the hydrogen absorption/desorption cycles.An A_(2)B_(7)-type La_(0.57)Sm_(0.02)Y_(0.18)Mg_(0.23)Ni_(3.38)Al_(0.03)alloy composed of Gd_(2)Co_(7)and Ce_(2)Ni_(7)phases was successfully synthesized.The pressure-composition isotherm profiles showed that the alloy had a hydrogen storage capacity as high as 1.73 wt%,with good cycling stability.After 50 cycles of hydrogen absorption/desorption,the alloy retained a hydrogen storage capacity of 1.45 wt%,with a capacity retention rate of up to 84.28%.The Mg thermal diffusion process thus provides a new approach for the controlled preparation of La-Mg-Ni-based alloys.展开更多
The effects of the Cr3C2 content and wheel speed on the amorphization behavior of the melt-spun SmCo7-x（Cr3C2）x （x=0.10-0.25） alloys were studied systematically by X-ray diffraction analysis （XRD）, differential ...The effects of the Cr3C2 content and wheel speed on the amorphization behavior of the melt-spun SmCo7-x（Cr3C2）x （x=0.10-0.25） alloys were studied systematically by X-ray diffraction analysis （XRD）, differential scanning calorimetry （DSC） and magnetic measurements. The ribbon melt-spun at lower wheel speed （20 m/s） has composite structure composed of mostly SmCo7 and a small amount of Sm2Co17R. The grain size of SmCo7 phase decreases with the increase of Cr3C2 content. With the increase of wheel speed, the XRD peaks become lower and accompanied with a broad increase in backgrounds, indicating a considerable decrease in the grain size of the SmCo7 phase. When the wheel speed increases to 40 m/s, SmCo7-x（Cr3C2）x alloys can be obtained in the amorphous state for 0.15≤x≤0.25 with intrinsic coercive Hci of 0.004-0.007 T. The DSC analysis reveals that SmCo7 phase firstly precipitates from the amorphous matrix at 650 °C, followed by the crystallization of Sm2Co17 phase at 770 °C.展开更多
In order to counteract the demagnetization caused by eddy current loss,widespread attention has been devoted to increasing the resistivity of permanent magnets.We prepared 2:17-type Sm Co magnets doped with different ...In order to counteract the demagnetization caused by eddy current loss,widespread attention has been devoted to increasing the resistivity of permanent magnets.We prepared 2:17-type Sm Co magnets doped with different ZrO_(2)contents and investigated the influence of the ZrO_(2)content on the magnetic properties and resistive anisotropism.The results showed that not only was the resistivity of the magnet improved,but,in addition,the coercivity of the magnet was significantly increased.The microstructure was studied with TEM,which showed that ZrO_(2)doping was able to cause a decrease in the lamellar phase density and the growth of cellular structures.The increased grain boundaries and Sm_(2)O_(3)phases were favorable to the improvement of resistivity.The decrease of the lamellar phases caused a narrowing of the resistive anisotropism.The additional Cu in the center of the cellular boundaries was the main reason for the enhancement of Hcj.However,an excessive amount caused an increase of the Zr_6(Fe Co)_(23)phase and a deterioration of the cellular structure,thereby leading to a decrease in coercivity.展开更多
In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six （x=0-0.2） electrode alloys were prep...In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six （x=0-0.2） electrode alloys were prepared by casting and annealing. The effects of adding Si on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated systematically. The results indicate that the as-cast and annealed alloys hold multiple structures, involving two major phases of （La, Mg）2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure as well as one residual phase LaNi3. The addition of Si results in a decrease in （La, Mg）2Ni7 phase and an increase in LaNi5 phase without changing the phase structure of the alloys. What is more, it brings on an obvious effect on electrochemical hydrogen storage characteristics of the alloys. The discharge capacities of the as-cast and annealed alloys decline with the increase of Si content, but their cycle stabilities clearly grow under the same condition. Furthermore, the measurements of the high rate discharge ability, the limiting current density, hydrogen diffusion coefficient as well as electrochemical impedance spectra all indicate that the electrochemical kinetic properties of the electrode alloys first increase and then decrease with the rising of Si content.展开更多
In order to improve the electrochemical cycle stability of the RE–Mg–Ni-based A2B7-type electrode alloys, a small amount of Si has been added into the alloys.The casting and annealing technologies were adopted to fa...In order to improve the electrochemical cycle stability of the RE–Mg–Ni-based A2B7-type electrode alloys, a small amount of Si has been added into the alloys.The casting and annealing technologies were adopted to fabricate the La0.8Mg0.2Ni3.3Co0.2Six(x = 0–0.2) electrode alloys. The impacts of the addition of Si and annealing treatment on the structures and electrochemical performances of the alloys were investigated systematically. The results obtained by XRD and SEM show that all the as-cast and annealed alloys are of a multiphase structure, involving two main phases(La, Mg)2Ni7and La Ni5 as well as a residual phase La Ni3. Both adding Si and the annealing treatment lead to an evident change in the phase abundance and cell parameters of(La, Mg)2Ni7and La Ni5 major phases of the alloy without altering its main phase component. Moreover, the annealing treatment has the composition of the alloy distributed more homogeneously overall and simultaneously causes the grain of the alloy to be coarsened obviously. The electrochemical measurements indicate that adding Si and the annealing treatment give a significant rise to the influence on the electrochemical performances of the alloys. In brief, the cycle stability of the as-cast and annealed alloys evidently increases with the rising of Si content, while their discharge capacities obviously decrease under the same circumstances. Furthermore, the electrochemical kineticproperties of the electrode alloys, including the high rate discharge ability, the limiting current density(IL), hydrogen diffusion coefficient(D), and the charge-transfer resistance, first augment and then decline with the rising of Si content. Similarly, it is found that the above-mentioned electrochemical properties first mount up and then go down with the rising annealing temperature.展开更多
Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))7.8(at%)sintered magnets with high remanence(B_(r)~1.15 T)were prepared using a traditional powder metallurgy method.Tunable magnetic properties,especially intrinsic coercivity(...Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))7.8(at%)sintered magnets with high remanence(B_(r)~1.15 T)were prepared using a traditional powder metallurgy method.Tunable magnetic properties,especially intrinsic coercivity(H_(cj)),were obtained through adjusting isothermal procedure parameters.H_(cj)of the magnets increases from 305 to 752 kA·m^(-1)with isothermal annealing time increasing from 3 to 20 h,while B_(r) of the magnets almost keeps constant.From the bright field transmission electron microscopy(TEM)images,it is found that:(1)there is dispersed precipitated phase with very small size in the magnet annealed for 3 h,while the magnets annealed for 20 h have distinct and intact cellular structure;(2)the number density of Z-phase in magnet annealed for 20 h is bigger than that for 3 h.Besides,the finer microstructures were studied with high-resolution transmission electron microscopy(HRTEM).展开更多
The melt-spun SmFe_(12)B_x(x = 0, 0.50, 0.75,1.00, 1.25 and 1.50) ribbons were prepared at 40 m·s^(-1),and their structure and magnetic properties were studied by powder X-ray diffraction(XRD), vibrating sample m...The melt-spun SmFe_(12)B_x(x = 0, 0.50, 0.75,1.00, 1.25 and 1.50) ribbons were prepared at 40 m·s^(-1),and their structure and magnetic properties were studied by powder X-ray diffraction(XRD), vibrating sample magnetometer(VSM) and transmission electron microscopy(TEM). XRD results indicate that SmFe_(12)B_x alloys with 0.50 ≤ x ≤ 1.00 are composed of single-phase TbCu_7-type structure. Moreover, it is found that the boron addition can inhibit the emergence of soft magnetic phase a-Fe and result in the increase in the axial ratio c/a. After annealing at 650 ℃ for 0.5 h, the metastable phase TbCu_7 initially decomposes into the stable phase Sm_2Fe_(14)B(Nd_2Fe_(14)B-type) and a-Fe. The value of magnetic moment per Fe atom increases slightly from 1.75 uB for boron-free sample to 1.80 uB for the x = 0.75 sample and then decreases again.In addition, the best magnetic properties of maximum energy product [(BH)_(max)] of 14.56 kJ·m^(-3), coercivity(H_(cj))of 172.6 kA·m^(-1) and remanence(B_r) of 0.45 T are obtained for the SmFe_(12)B_(1.00) alloy. Based on transmission electron microscopy(TEM) results, the average size of grains is around 197 nm for B-free sample and decreases to 95 nm for x = 1.00 sample, indicating that the addition of boron can refine grains.展开更多
The effects of different proportions of La and Y elements in the A-side on the structure and properties of A_(2)B_(7)-type La-Y-Ni hydrogen storage alloys were investigated.The(La,Y)_(2)Ni_(7)hydrogen storage alloys w...The effects of different proportions of La and Y elements in the A-side on the structure and properties of A_(2)B_(7)-type La-Y-Ni hydrogen storage alloys were investigated.The(La,Y)_(2)Ni_(7)hydrogen storage alloys with different La/Y ratios were prepared by sintering the Y_(2)Ni_(4)precursor and different AB_(5)-type precursors at 1298 K for 5 h and subsequently annealed for 20 h at 1248 K.All the alloys only contain Ce_(2)Ni_(7)(2H-type)and Gd_(2)Co_(7)(3R-type)phases with different mass ratios.As the La/Y ratio decreases,the cell volume of the two phases declines and the corresponding plateau pressure gradually increases.As the proportion of Y in the alloy increases,the hydrogen storage capacity increases gradually from 1.309 wt%(La/Y=1/1)to 1.713 wt%(La/Y=1/5)and the high-rate discharge(HRD1500)ability of the alloy electrodes increases gradually from 62.7%(La/Y=1/1)to 88.6%(La/Y=1/5).The hydrogen diffusion rate in the bulk of the alloy is the controlling step of hydriding/dehydriding kinetics.The Y ele ment can effectively inhibit the hydrogen-induced amorphous(HIA)of La-Y-Ni alloys,but the poor stability of the Y element in alkaline KOH aqueous solution leads to a decrease in the electrochemical cyclic stability with increasing Y content.展开更多
The casting and annealing technologies were applied to fabricate the La0.8Mg0.2Ni3.3Co0.2Six （x = 0-0.2） electrode alloys. The effects of Si content and annealing temperature on the structure and electrochemical per...The casting and annealing technologies were applied to fabricate the La0.8Mg0.2Ni3.3Co0.2Six （x = 0-0.2） electrode alloys. The effects of Si content and annealing temperature on the structure and electrochemical performances of the alloys were investigated systematically. The analyses of XRD and SEM show that all the alloys possess a multiphase structure, involving two main phases （La, Mg）2Ni7 and LaNi5 as well as a residual phase LaNi3. The addition of Si brings on an evident increase in the LaNi5 phase and a decrease in the （La, Mg）2Ni7 phase, without altering the main phase component of the alloy, which also makes the lattice constants and cell volumes of the alloy enlarged. Likewise, the annealing treatment engenders the same action on the lattice constants and cell volumes as adding Si. Simultaneously, it gives rise to the variation of the phase abundance and the coarsening of the alloy grains. The electrochemical measurements indicate that the addition of Si ameliorates the cycle stability of the as-cast and annealed alloys significantly, but impairs their discharge capacities clearly. Similarly, the annealing treatment makes a positive contribution to the cycle stability of the alloy evidently, and the discharge capacity of the alloy shows a maximum value with annealing temperature rising. Furthermore, the high rate discharge ability （HR） first augments and then declines with the rising of Si content and annealing temperature.展开更多
In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure ...In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure of the alloys were investigated in detail. XRD results showed that the alloys had multiphase structure composed of （La, Mg）2Ni7, LaNi5 and small amount of LaNi2 phases. The discharge capacity of the alloys first increased and then decreased with increasing Co content. At a discharge current density of 900 mA/g, the HRD of the alloy electrodes increased from 81.3% （x=0） to 89.2 % （x=0.2）, and then reduced to 87.8 % （x=0.6）. After 60 charge/discharge cycles, the capacity retention rate of the alloys enhanced from 52.67% to 61.32%, and the capacity decay rate of the alloys decreased from 2.60 to 2.05 mAh/g per cycle with increasing Co content. The obtained results by XPS and XRD showed that the fundamental reasons for the capacity decay of the La-Mg-Ni system （Ce2Ni7-type） alloy electrodes were corrosion and oxidation as well as passivation of Mg and Lain alkaline solution.展开更多
Investigation of alloy structure shows that La2-xMgxNi7 （x = 0.3 - 0.8） alloys are mainly com- posed of Ce/Ni7-type, Gd2Co7-type and PuNi3-type phase. The influence of Mg content in alloys on the phase structure is ...Investigation of alloy structure shows that La2-xMgxNi7 （x = 0.3 - 0.8） alloys are mainly com- posed of Ce/Ni7-type, Gd2Co7-type and PuNi3-type phase. The influence of Mg content in alloys on the phase structure is great, resulting in a linear decrease of the unit cell parameters of main phases and increase of hydrogen absorption/desorption plateau as Mg content increases. Electrochemical measurements show that as the Mg content increases, the discharge capacity of alloy electrodes first increases and then decreases. The cyclic stability presents a deteriorative trend. La1.4Mg0.6 Ni7 alloy electrode exhibits the maximum electrochemical discharge capacity （378 mAh·g^-1）, and the La1.6Mg0.4Ni7 alloy electrode shows the best cyclic stability （S270 = 81%）.展开更多
The compound Sm0.98Fe9.02-xGaxNδ（x=0, 0.25, 0.5, 0.75, 1） were prepared by melt-spun method and subsequent annealing and nitriding. The Rietveld analysis showed that the lattice expansion played an important role i...The compound Sm0.98Fe9.02-xGaxNδ（x=0, 0.25, 0.5, 0.75, 1） were prepared by melt-spun method and subsequent annealing and nitriding. The Rietveld analysis showed that the lattice expansion played an important role in improving the Curie temperature. An obvious development of the Curie temperature was obtained with the increased Ga content from x=0-1 （ΔTc=90 ℃）. The optimum coercivity of nitrides was obtained at x=0.25 with the value Hcj=652 kA/m （8.15 kOe） after annealing, which corresponded to a reasonable distribution of grain sizes of both TbCu7-type SmFe9Nδandα-Fe. However, an excess of Ga doping might lead to an ab-normal growth of α-Fe, which in turn deteriorated the magnetic properties. It was concluded that a moderate Ga content was very ef-fective in raising the coercivity and Curie temperament in the TbCu7-type Sm-Fe-N.展开更多
Nanocrystalline SmFe_（8.95-x）Ga_（0.26）Nb_xN_δ（x=0, 0.1, 0.2, 0.3） were prepared using rapid-quenching,annealing and nitriding. The magnetic properties and crystal structures were systematically studied under va...Nanocrystalline SmFe_（8.95-x）Ga_（0.26）Nb_xN_δ（x=0, 0.1, 0.2, 0.3） were prepared using rapid-quenching,annealing and nitriding. The magnetic properties and crystal structures were systematically studied under various wheel velocities to investigate the influence of Nb doping for the compounds. It is found that TbCu7-type structure is able to be obtained even though the wheel velocity is reduced to 20 m/s（x = 0.3）. An significant increase（△T_c=70 ℃） of the Curie temperature is obtained with Nb doping at x = 0.1 due to the lattice expansion revealed by Rietveld analysis. The optimum coercivity with the value H_（cj） of 810 kA/m is achieved at x = 0.2 in the nitrides, in which a reasonable distribution of grain sizes of both TbCu_7-type SmFe_9 N_δ and α-Fe can be found. However, an excess of Nb doping may lead to the increase of the weight fraction of α-Fe, which in turn deteriorates the magnetic properties.展开更多
The partial substitution of Zr for La has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni based A2B7-type electrode alloys. The melt spinning technology was used t...The partial substitution of Zr for La has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni based A2B7-type electrode alloys. The melt spinning technology was used to prepare the La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x=0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The impacts of the melt spinning and the substituting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were systemically investigated. The analysis of XRD and TEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning ameliorate the electrochemical cycle stability of the alloys dramatically. Furthermore, the high rate discharge ability (HRD) of the as-spun (10 m/s) alloys notably declines with growing the amount of Zr substitution, while it first augments and then falls for the (x=0.1) alloy with rising the spinning rate.展开更多
基金Project supported by the National Natural Science Foundation of China(52271214,51831009)。
文摘Rare earth-based superlattice alloys have great potential for gaseous hydrogen storage,as well as successful application as nickel-metal hydride batteries anodes.In this work,Y substitution was carried out to adjust the gaseous hydrogen storage properties of A_(2)B_(7)-type La_(0.7)Mg_(0.3)Ni_(3.5)alloys.The results indicate a multiphase structure in the alloys comprised of the main rhombohedral Gd_(2)Co_(7)and PuNi_(3)phases,with a small amount of CaCu_(5)phase.Moreover,the Y substitution results in higher abundance of the Gd_(2)Co_(7)phase.The alloy La_(0.42)Y_(0.28)Mg_(0.3)Ni_(3.5)exhibits a hydrogen storage cap acity of 1.55 wt%at 298 K and a desorption plateau pressure of 0.244 MPa.In addition,this alloy demonstrates a stable cycle life by a capacity retention of 94.2%after 50 cycles,with the main capacity degradation occurring during the initial 20 cycles.This work accentuates the potential of the La-Y-Mg-Ni-based superlattice alloys for applications in solid-state hydrogen storage.
基金financially supported by the National Key Research and Development Program of China(2022YFB3803804)the National Natural Science Foundation of China(Nos.51971197,52071281 and 52201282)+3 种基金Basic Innovation Research Project in Yanshan University(No.2022LGZD004)China Postdoctoral Science Foundation(2023M742945)Postdoctoral research project of Hebei Province(B2023003023)Subsidy for Hebei Key Laboratory of Applied Chemistry after Operation Performance(No.22567616H)。
文摘A novel approach based on thermal diffusion was used to achieve controllable Mg content in A_(2)B_(7)-type La-Mg-Ni-based alloys.The formation mechanism of the A_(2)B_(7)-type phase as a result of the thermal diffusion process and the effect of Mg content on hydrogen storage performance were investigated.X-ray diffraction(XRD)patterns and Rietveld refinement results showed that increased Mg transformed the LaNi_(5)phase in the La_(0.74)Sm_(0.03)Y_(0.23)Ni_(4.32)Al_(0.04)precursor alloy into a superlattice structure.Scanning electron microscopy(SEM)images showed that Mg was evenly distributed in the alloy bulk.Mg in the superlattice significantly inhibited the phase decomposition of the superlattice structure during the hydrogen absorption/desorption cycles.An A_(2)B_(7)-type La_(0.57)Sm_(0.02)Y_(0.18)Mg_(0.23)Ni_(3.38)Al_(0.03)alloy composed of Gd_(2)Co_(7)and Ce_(2)Ni_(7)phases was successfully synthesized.The pressure-composition isotherm profiles showed that the alloy had a hydrogen storage capacity as high as 1.73 wt%,with good cycling stability.After 50 cycles of hydrogen absorption/desorption,the alloy retained a hydrogen storage capacity of 1.45 wt%,with a capacity retention rate of up to 84.28%.The Mg thermal diffusion process thus provides a new approach for the controlled preparation of La-Mg-Ni-based alloys.
基金Project (51104188) supported by the National Natural Science Foundation for Young Scholars of China
文摘The effects of the Cr3C2 content and wheel speed on the amorphization behavior of the melt-spun SmCo7-x（Cr3C2）x （x=0.10-0.25） alloys were studied systematically by X-ray diffraction analysis （XRD）, differential scanning calorimetry （DSC） and magnetic measurements. The ribbon melt-spun at lower wheel speed （20 m/s） has composite structure composed of mostly SmCo7 and a small amount of Sm2Co17R. The grain size of SmCo7 phase decreases with the increase of Cr3C2 content. With the increase of wheel speed, the XRD peaks become lower and accompanied with a broad increase in backgrounds, indicating a considerable decrease in the grain size of the SmCo7 phase. When the wheel speed increases to 40 m/s, SmCo7-x（Cr3C2）x alloys can be obtained in the amorphous state for 0.15≤x≤0.25 with intrinsic coercive Hci of 0.004-0.007 T. The DSC analysis reveals that SmCo7 phase firstly precipitates from the amorphous matrix at 650 °C, followed by the crystallization of Sm2Co17 phase at 770 °C.
基金the National Natural Science Foundation of China(Grant No.51877094)Ningbo Science and Technology Project(Grant No.2014B11009)。
文摘In order to counteract the demagnetization caused by eddy current loss,widespread attention has been devoted to increasing the resistivity of permanent magnets.We prepared 2:17-type Sm Co magnets doped with different ZrO_(2)contents and investigated the influence of the ZrO_(2)content on the magnetic properties and resistive anisotropism.The results showed that not only was the resistivity of the magnet improved,but,in addition,the coercivity of the magnet was significantly increased.The microstructure was studied with TEM,which showed that ZrO_(2)doping was able to cause a decrease in the lamellar phase density and the growth of cellular structures.The increased grain boundaries and Sm_(2)O_(3)phases were favorable to the improvement of resistivity.The decrease of the lamellar phases caused a narrowing of the resistive anisotropism.The additional Cu in the center of the cellular boundaries was the main reason for the enhancement of Hcj.However,an excessive amount caused an increase of the Zr_6(Fe Co)_(23)phase and a deterioration of the cellular structure,thereby leading to a decrease in coercivity.
基金Projects(50961009,51161015)supported by the National Natural Science Foundation of ChinaProject(2011AA03A408)supported by the High-tech Research and Development Program of ChinaProjects(2011ZD10,2010ZD05)supported by the Natural Science Foundation of Inner Mongolia,China
文摘In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six （x=0-0.2） electrode alloys were prepared by casting and annealing. The effects of adding Si on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated systematically. The results indicate that the as-cast and annealed alloys hold multiple structures, involving two major phases of （La, Mg）2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure as well as one residual phase LaNi3. The addition of Si results in a decrease in （La, Mg）2Ni7 phase and an increase in LaNi5 phase without changing the phase structure of the alloys. What is more, it brings on an obvious effect on electrochemical hydrogen storage characteristics of the alloys. The discharge capacities of the as-cast and annealed alloys decline with the increase of Si content, but their cycle stabilities clearly grow under the same condition. Furthermore, the measurements of the high rate discharge ability, the limiting current density, hydrogen diffusion coefficient as well as electrochemical impedance spectra all indicate that the electrochemical kinetic properties of the electrode alloys first increase and then decrease with the rising of Si content.
基金financially supported by the National Natural Science Foundation of China (Nos. 50961009 and 51161015)the National High Technology Research and Development Program of China (No. 2011AA03A408)the National High Technology Research and Development Program of China (Nos. 2011ZD10 and 2010ZD05)
文摘In order to improve the electrochemical cycle stability of the RE–Mg–Ni-based A2B7-type electrode alloys, a small amount of Si has been added into the alloys.The casting and annealing technologies were adopted to fabricate the La0.8Mg0.2Ni3.3Co0.2Six(x = 0–0.2) electrode alloys. The impacts of the addition of Si and annealing treatment on the structures and electrochemical performances of the alloys were investigated systematically. The results obtained by XRD and SEM show that all the as-cast and annealed alloys are of a multiphase structure, involving two main phases(La, Mg)2Ni7and La Ni5 as well as a residual phase La Ni3. Both adding Si and the annealing treatment lead to an evident change in the phase abundance and cell parameters of(La, Mg)2Ni7and La Ni5 major phases of the alloy without altering its main phase component. Moreover, the annealing treatment has the composition of the alloy distributed more homogeneously overall and simultaneously causes the grain of the alloy to be coarsened obviously. The electrochemical measurements indicate that adding Si and the annealing treatment give a significant rise to the influence on the electrochemical performances of the alloys. In brief, the cycle stability of the as-cast and annealed alloys evidently increases with the rising of Si content, while their discharge capacities obviously decrease under the same circumstances. Furthermore, the electrochemical kineticproperties of the electrode alloys, including the high rate discharge ability, the limiting current density(IL), hydrogen diffusion coefficient(D), and the charge-transfer resistance, first augment and then decline with the rising of Si content. Similarly, it is found that the above-mentioned electrochemical properties first mount up and then go down with the rising annealing temperature.
基金the National Basic Research Program of China(No.2014CB643701)the National Natural Science Foundation of China(No.51171048)。
文摘Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))7.8(at%)sintered magnets with high remanence(B_(r)~1.15 T)were prepared using a traditional powder metallurgy method.Tunable magnetic properties,especially intrinsic coercivity(H_(cj)),were obtained through adjusting isothermal procedure parameters.H_(cj)of the magnets increases from 305 to 752 kA·m^(-1)with isothermal annealing time increasing from 3 to 20 h,while B_(r) of the magnets almost keeps constant.From the bright field transmission electron microscopy(TEM)images,it is found that:(1)there is dispersed precipitated phase with very small size in the magnet annealed for 3 h,while the magnets annealed for 20 h have distinct and intact cellular structure;(2)the number density of Z-phase in magnet annealed for 20 h is bigger than that for 3 h.Besides,the finer microstructures were studied with high-resolution transmission electron microscopy(HRTEM).
基金financially supported by the National Natural Science Foundation of China (No. 51401028)
文摘The melt-spun SmFe_(12)B_x(x = 0, 0.50, 0.75,1.00, 1.25 and 1.50) ribbons were prepared at 40 m·s^(-1),and their structure and magnetic properties were studied by powder X-ray diffraction(XRD), vibrating sample magnetometer(VSM) and transmission electron microscopy(TEM). XRD results indicate that SmFe_(12)B_x alloys with 0.50 ≤ x ≤ 1.00 are composed of single-phase TbCu_7-type structure. Moreover, it is found that the boron addition can inhibit the emergence of soft magnetic phase a-Fe and result in the increase in the axial ratio c/a. After annealing at 650 ℃ for 0.5 h, the metastable phase TbCu_7 initially decomposes into the stable phase Sm_2Fe_(14)B(Nd_2Fe_(14)B-type) and a-Fe. The value of magnetic moment per Fe atom increases slightly from 1.75 uB for boron-free sample to 1.80 uB for the x = 0.75 sample and then decreases again.In addition, the best magnetic properties of maximum energy product [(BH)_(max)] of 14.56 kJ·m^(-3), coercivity(H_(cj))of 172.6 kA·m^(-1) and remanence(B_r) of 0.45 T are obtained for the SmFe_(12)B_(1.00) alloy. Based on transmission electron microscopy(TEM) results, the average size of grains is around 197 nm for B-free sample and decreases to 95 nm for x = 1.00 sample, indicating that the addition of boron can refine grains.
基金Project supported by the National Natural Science Foundation of China(51961002)National Key Research and Development Projects of China(2018YFE124400)+2 种基金Natural Science Foundation of Inner Mongolia(2020MS05013,2018MS05016)Science and Technology Program of Inner Mongolia(2020B2156)Special Project of Achievement Transformation in Inner Mongolia(2019CG082)。
文摘The effects of different proportions of La and Y elements in the A-side on the structure and properties of A_(2)B_(7)-type La-Y-Ni hydrogen storage alloys were investigated.The(La,Y)_(2)Ni_(7)hydrogen storage alloys with different La/Y ratios were prepared by sintering the Y_(2)Ni_(4)precursor and different AB_(5)-type precursors at 1298 K for 5 h and subsequently annealed for 20 h at 1248 K.All the alloys only contain Ce_(2)Ni_(7)(2H-type)and Gd_(2)Co_(7)(3R-type)phases with different mass ratios.As the La/Y ratio decreases,the cell volume of the two phases declines and the corresponding plateau pressure gradually increases.As the proportion of Y in the alloy increases,the hydrogen storage capacity increases gradually from 1.309 wt%(La/Y=1/1)to 1.713 wt%(La/Y=1/5)and the high-rate discharge(HRD1500)ability of the alloy electrodes increases gradually from 62.7%(La/Y=1/1)to 88.6%(La/Y=1/5).The hydrogen diffusion rate in the bulk of the alloy is the controlling step of hydriding/dehydriding kinetics.The Y ele ment can effectively inhibit the hydrogen-induced amorphous(HIA)of La-Y-Ni alloys,but the poor stability of the Y element in alkaline KOH aqueous solution leads to a decrease in the electrochemical cyclic stability with increasing Y content.
基金Funded by National Natural Science Foundations of China(Nos.51161015 and 51371094)National 863 Plans Projects of China(No.2011AA03A408)
文摘The casting and annealing technologies were applied to fabricate the La0.8Mg0.2Ni3.3Co0.2Six （x = 0-0.2） electrode alloys. The effects of Si content and annealing temperature on the structure and electrochemical performances of the alloys were investigated systematically. The analyses of XRD and SEM show that all the alloys possess a multiphase structure, involving two main phases （La, Mg）2Ni7 and LaNi5 as well as a residual phase LaNi3. The addition of Si brings on an evident increase in the LaNi5 phase and a decrease in the （La, Mg）2Ni7 phase, without altering the main phase component of the alloy, which also makes the lattice constants and cell volumes of the alloy enlarged. Likewise, the annealing treatment engenders the same action on the lattice constants and cell volumes as adding Si. Simultaneously, it gives rise to the variation of the phase abundance and the coarsening of the alloy grains. The electrochemical measurements indicate that the addition of Si ameliorates the cycle stability of the as-cast and annealed alloys significantly, but impairs their discharge capacities clearly. Similarly, the annealing treatment makes a positive contribution to the cycle stability of the alloy evidently, and the discharge capacity of the alloy shows a maximum value with annealing temperature rising. Furthermore, the high rate discharge ability （HR） first augments and then declines with the rising of Si content and annealing temperature.
基金the National Natural Science Foundation of China (50701011)Natural Science Foundation of Inner Mongolia, China (200711020703)Science and Technology Planned Project of Inner Mongolia, China (20050205)
文摘In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure of the alloys were investigated in detail. XRD results showed that the alloys had multiphase structure composed of （La, Mg）2Ni7, LaNi5 and small amount of LaNi2 phases. The discharge capacity of the alloys first increased and then decreased with increasing Co content. At a discharge current density of 900 mA/g, the HRD of the alloy electrodes increased from 81.3% （x=0） to 89.2 % （x=0.2）, and then reduced to 87.8 % （x=0.6）. After 60 charge/discharge cycles, the capacity retention rate of the alloys enhanced from 52.67% to 61.32%, and the capacity decay rate of the alloys decreased from 2.60 to 2.05 mAh/g per cycle with increasing Co content. The obtained results by XPS and XRD showed that the fundamental reasons for the capacity decay of the La-Mg-Ni system （Ce2Ni7-type） alloy electrodes were corrosion and oxidation as well as passivation of Mg and Lain alkaline solution.
文摘Investigation of alloy structure shows that La2-xMgxNi7 （x = 0.3 - 0.8） alloys are mainly com- posed of Ce/Ni7-type, Gd2Co7-type and PuNi3-type phase. The influence of Mg content in alloys on the phase structure is great, resulting in a linear decrease of the unit cell parameters of main phases and increase of hydrogen absorption/desorption plateau as Mg content increases. Electrochemical measurements show that as the Mg content increases, the discharge capacity of alloy electrodes first increases and then decreases. The cyclic stability presents a deteriorative trend. La1.4Mg0.6 Ni7 alloy electrode exhibits the maximum electrochemical discharge capacity （378 mAh·g^-1）, and the La1.6Mg0.4Ni7 alloy electrode shows the best cyclic stability （S270 = 81%）.
基金supported by International Science and Technology Cooperation Project(2010 DFB53520)the National High Technology Research and Development Program of China(2011AA03A402)
文摘The compound Sm0.98Fe9.02-xGaxNδ（x=0, 0.25, 0.5, 0.75, 1） were prepared by melt-spun method and subsequent annealing and nitriding. The Rietveld analysis showed that the lattice expansion played an important role in improving the Curie temperature. An obvious development of the Curie temperature was obtained with the increased Ga content from x=0-1 （ΔTc=90 ℃）. The optimum coercivity of nitrides was obtained at x=0.25 with the value Hcj=652 kA/m （8.15 kOe） after annealing, which corresponded to a reasonable distribution of grain sizes of both TbCu7-type SmFe9Nδandα-Fe. However, an excess of Ga doping might lead to an ab-normal growth of α-Fe, which in turn deteriorated the magnetic properties. It was concluded that a moderate Ga content was very ef-fective in raising the coercivity and Curie temperament in the TbCu7-type Sm-Fe-N.
文摘Nanocrystalline SmFe_（8.95-x）Ga_（0.26）Nb_xN_δ（x=0, 0.1, 0.2, 0.3） were prepared using rapid-quenching,annealing and nitriding. The magnetic properties and crystal structures were systematically studied under various wheel velocities to investigate the influence of Nb doping for the compounds. It is found that TbCu7-type structure is able to be obtained even though the wheel velocity is reduced to 20 m/s（x = 0.3）. An significant increase（△T_c=70 ℃） of the Curie temperature is obtained with Nb doping at x = 0.1 due to the lattice expansion revealed by Rietveld analysis. The optimum coercivity with the value H_（cj） of 810 kA/m is achieved at x = 0.2 in the nitrides, in which a reasonable distribution of grain sizes of both TbCu_7-type SmFe_9 N_δ and α-Fe can be found. However, an excess of Nb doping may lead to the increase of the weight fraction of α-Fe, which in turn deteriorates the magnetic properties.
文摘The partial substitution of Zr for La has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni based A2B7-type electrode alloys. The melt spinning technology was used to prepare the La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x=0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The impacts of the melt spinning and the substituting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were systemically investigated. The analysis of XRD and TEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning ameliorate the electrochemical cycle stability of the alloys dramatically. Furthermore, the high rate discharge ability (HRD) of the as-spun (10 m/s) alloys notably declines with growing the amount of Zr substitution, while it first augments and then falls for the (x=0.1) alloy with rising the spinning rate.
