Investigation on the structures and electrochemical performances of La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.2) electrode alloys prepared by melt spinning

In order to improve the electrochemical cycle stability of the La–Mg–Ni system A₂B₇-type electrode alloys, La in the alloy was partially substituted by Zr and the melt-spinning technology was used for preparing La_0.75−xZr_xMg_0.25Ni_3.2Co_0.2Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM showed that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Zr for La leads to an obvious increase of the LaNi₅ phase in the alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. The results of the electrochemical measurement indicated that the substitution of Zr for La obviously decreased the discharge capacity of the as-cast and quenched alloys, but it significantly improved their cycle stability. The discharge capacity of the alloys (x ≤ 0.1) first increased and then decreased with the variety of the quenching rate. The cycle stability of the alloys monotonously rose with increasing quenching rate.     

复合储氢合金Mg1.8Zr0.2Ni- (1.2-x)Ni -xMgTi3结构和电化学性能研究

为改善Mg₂Ni储氢合金电化学性能,采用机械合金化法(Mechanical Alloying,MA),分别制备出改性合金Mg_1.8 Zr Ni以及MgTi₃,按一定比例和Ni混合球磨,制备出纳米晶或非晶化的Mg_1.8Zr_0.2Ni- (1.2-x)Ni -xMgTi₃复合储氢合金。研究结果表明,经部分取代改性和包覆修饰后的复合储氢合金,其表面和内部形成较多的纳米级褶皱、空隙层状和多相结构缺陷。随着MgTi₃含量增加,Mg_1.8Zr_0.2Ni- (1.2-x)Ni -xMgTi₃复合储氢合金初始放电比容量也逐渐增加,当MgTi₃含量为x=0.5时,合金初始放电比容量为973.3 mAh.g_-1。但MgTi3含量超过x=0.5时,其初始放电比容量又有所下降,研究表明添加MgTi₃却不利于复合储氢合金的循环稳定性和高倍率放电性能。通过对Mg_1.8Zr_0.2Ni- (1.0-x)Ni -xMgTi₃复合储氢合金进行线性极化、阳极极化和交流阻抗测试,进一步研究了系列合金电极的表面电化学反应、电荷转移过程、氢在合金中的扩散情况以及它们的电化学性能。     

Improvement in the electrochemical properties of ZrMn2 hydrides by substitution of elements

The hydrogen-storage properties and the electrochemical properties are investigated for the alloys ZrMn₂Ni_x, ZrMnNi_1+x, Zr_0.5Ti_0.5Mn_0.4V_0.6Ni_1−xFe_x and Zr_0.5Ti_0.5Mn_0.4V_0.6Ni_0.85M_0.15. The C14 Laves phase forms in all the alloys ZrMn₂Ni_x (x=0.0, 0.3, 0.6, 0.9 and 1.2). Among the alloys ZrMn₂Ni_x, ZrMn₂Ni_0.6 has the largest discharge capacity (29 mAh/g) and a relatively good cycling performance, and shows a relatively easy activation. The C14 Laves phase also forms in all the alloys ZrMnNi_1+x (x=0.0, 0.1, 0.2, 0.3 and 0.4). Among the alloys ZrMnNi_1+x, ZrMnNi_1.0 has the largest discharge capacity (42 mAh/g) and a relatively good cycling performance, and shows the easiest activation. Zr_0.5Ti_0.5Mn_0.4V_0.6Ni_1−xFe_x (x=0.00, 0.15, 0.30, 0.45 and 0.60) has the C14 Laves phase hexagonal structure. Their hydrogen storage capacities do not show significant differences. The discharge capacity just after activation decreases with an increase in the amount of the substituted Fe but the cycling performance is improved. The discharge capacity after activation of the alloy with x=0.00 is about 240 mAh/g at the current density 60 mA/g. Zr_0.5Ti_0.5Mn_0.4V_0.6Ni_0.85Fe_0.15 is the best composition with a relatively large discharge capacity and a good cycling performance. The increase in the discharge capacity of Zr_0.5Ti_0.5Mn_0.4V_0.6Ni_0.85Fe_0.15 with the increase in the current density (from 60 mA/g to 125 mA/g) is considered to result from the self-discharge property of the electrode. Zr_0.5Ti_0.5Mn_0.4V_0.6Ni_0.85M_0.15 (M=Fe, Co, Cu, Mo and Al) alloys also have the C14 Laves phase hexagonal structure. The alloys with M=Co and Fe have relatively larger hydrogen storage capacities. The discharge capacities just after activation are relatively large in the case of the alloys with M=Co and Fe. The Zr_0.5Ti_0.5Mn_0.4V_0.6Ni_0.85Co_0.15 alloy is best with a relatively large discharge capacity (257 mAh/g at the current density 250 mA/g for the 12^th cycle) and a good cycling performance. During activation form Ni-rich and Fe-rich regions on the surface of the Zr_0.5Ti_0.5Mn_0.4V_0.6 Ni_0.85Fe_0.15 alloy. They may act as the active sites for the electrochemical reaction. With the increase in the number of charge-discharge cycles for the Zr_0.5Ti_0.5Mn_0.4V_0.6Ni_0.85Fe_0.15 alloy, the quantities of the Zr and Fe dissolved in the electrolyte solution increase. This article is based on a presentation made in “The 2nd KIM-JIM Joint Symposium: Hydrogen Absorbing Materials”, held at Hanyang University, Seoul, Korea, October 27–28, 2000 under the auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Synthesis of HCP, FCC and BCC structure alloys in the Mg–Ti binary system by means of ball milling

Mg_xTi_100−x (35 ≤ x ≤ 80) alloys with hexagonal close packed (HCP), face centered cubic (FCC) and body centered cubic (BCC) structures were successfully synthesized by means of ball milling. Mg_xTi_100−x alloys with a BCC structure at x = 35 and 50 and with a HCP structure at x = 80 were synthesized by milling of Mg and Ti powder using stainless steel milling balls and pots. At x = 65, the BCC and HCP phases were synthesized. Mg_xTi_100−x alloys with a FCC structure were synthesized at x = 35 and 50 by milling using zirconia milling balls and pots. The FCC and HCP phases were synthesized at x = 65 and 80 using zirconia milling balls and pots. The crystal structure of Mg_xTi_100−x alloys synthesized by the ball milling method depended on the materials of milling balls and pots. That indicates that milling products are determined by the dynamic energy given by the milling setup. The lattice parameters of Mg_xTi_100−x in the HCP, FCC and BCC phases increased with increase of the Mg content, x.     

Microstructure and Mechanical Properties of AZ91 Alloys by Addition of Yttrium

Effects of yttrium (Y) on the microstructure and properties of as-cast Mg-Al-Zn (AZ91) alloys were studied. Y additions not only change the microstructure but also influence the mechanical properties of AZ91 alloy. AZ91 unmodified alloys under as-cast state indicate that eutectic phase Mg₁₇Al₁₂ is continuous and reticulated. Yttrium addition to AZ91 casting alloys has an important influence on the primary-phase and precipitation. When the Y content is 0.3 wt.%, no Y-containing compound was observed. When the Y content is 0.6 and 0.9 wt.%, Al₂Y phase formed in the alloy and the growth morphology of eutectic Mg₁₇Al₁₂ phase is modified. When the Y content is further increased to 1.2 wt.%, the Al₂Y phase becomes coarser and Mg₁₇Al₁₂ transforms into a cotton-shape structure. The results showed that Y can improve significantly as-cast microstructure of AZ91 alloys, refining Mg₁₇Al₁₂ phase and increasing in hardness and strength and decreasing in impact toughness and elongation.     

Peculiarities of ball-milling induced crystalline–amorphous transformation in Cu–Zr–Al–Ni–Ti alloys

An amorphization process in (Cu₄₉Zr_45−xAl_6+x)_100−y−zNi_yTi_z (x = 1, y, z = 0; 5; 10) induced by ball-milling is reported in the present work. The aim was investigation of the effect of Ni and Ti addition to Cu₄₉Zr₄₅Al₆ and Cu₄₉Zr₄₄Al₇ based alloys as well as type of initial phases on the amorphization processes. Also the milling time sufficient for obtaining fully amorphous state was determined. The entire milling process lasted 25 h. Drastic structural changes were observed in each alloy after first 5 h of milling. In most cases, after 15 h of milling the powders had fully amorphous structure according to XRD except for those ones, where TEM revealed a few nanosized crystalline particles in the amorphous matrix. In (Cu₄₉Zr₄₅Al₆)₈₀Ni₁₀Ti₁₀ alloy the amorphization process took place after 12 h of milling and the amorphous state was stable up to 25 h of milling. In the case of (Cu₄₉Zr₄₄Al₇)₈₀Ni₁₀Ti₁₀ alloy the powders have fully amorphous structure between 12 h and 15 h of milling.     

Influences of Ti substitution on the structure and electrochemical properties of Mg1-xTixNi（x=0,0.1, 0.2, and 0.3） hydrogen storage alloys

MgNi-based hydrogen storage alloys Mg_1−x Ti _x Ni (x = 0, 0.1, 0.2, and 0.3) were prepared by means of mechanical alloying. Mg in the alloy was partially substituted by Ti to improve the cycle stability of the alloys. The effects of the substitution of Ti for Mg on the microstructure and electrochemical performances of the alloys were investigated in detail. The results indicate that the substitution of Ti for Mg obviously decreases the discharge capacity, but it significantly improves their cycle stabilities. The microstructure of the alloys analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) shows that the alloys have a dominatingly amorphous structure. The substitution of Ti for Mg helps to improve the anti-oxidation/corrosion ability of the MgNi alloy but demolishes the electrochemical kinetics of hydrogenation/dehydrogenation. The Mg_0.9Ti_0.1Ni alloy electrode milled for 80 h exhibits the best integrative capability, which has the maximal discharge capacity of 331.66 mAh/g and the C ₃₀/C _max of 63.65%.     

Influences of the substitution of Fe for Ni on structures and electrochemical performances of the as-cast and quenched La0.7Mg0.3Co0.45Ni2.55−xFex (x = 0–0.4) electrode alloys

In order to improve the cycle stability of the La–Mg–Ni system PuNi₃-type hydrogen storage electrode alloys, Ni in the alloy was partially substituted by Fe. The La_0.7Mg_0.3Co_0.45Ni_2.55−xFe_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the substitution of Fe for Ni on the structures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results of the electrochemical measurement indicate that the substitution of Fe for Ni obviously decreases the discharge capacity, high rate discharge capability (HRD) and discharge potential of the as-cast and quenched alloys, but it significantly improves their cycle stabilities, and its positive impact on the cycle life of as-quenched alloy is much more significant than on that of the as-cast one. The microstructure of the alloys analyzed by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure which is composed of two major phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Fe for Ni helps the formation of a like amorphous structure in the as-quenched alloy. With the increase of Fe content, the grain sizes of the as-quenched alloys significantly reduce, and the lattice constants and cell volumes of the alloys obviously increase.     

An investigation on hydrogen storage kinetics of nanocrystalline and amorphous Mg2Ni1−xCox (x = 0-0.4) alloy prepared by melt spinning

In order to improve the hydrogen storage kinetics of the Mg₂Ni-type alloys, Ni in the alloy was partially substituted by element Co, and melt-spinning technology was used for the preparation of the Mg₂Ni_1−xCo_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and spun alloys are characterized by XRD, SEM and TEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-spun alloys is tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves are plotted by an electrochemical workstation. The results show that the substitution of Co for Ni notably enhances the glass forming ability of the Mg₂Ni-type alloy. Furthermore, the substitution of Co for Ni, instead of changing major phase Mg₂Ni, leads to forming secondary phases MgCo₂ and Mg. Both the melt spinning treatment and Co substitution significantly improve the hydrogen absorption and desorption kinetics. The high rate discharge ability, the hydrogen diffusion coefficient and the limiting current density of the alloys significantly increase with raising both the spinning rate and the amount of Co substitution.     

Structure and electrochemical properties of the Fe substituted Ti–V-based hydrogen storage alloys

To elucidate the effects of Fe on the Ti–V-based hydrogen storage electrode alloys, the Ti_0.8Zr_0.2V_2.7−xMn_0.5Cr_0.8Ni_1.0Fe_x (x = 0.0–0.5) alloys were prepared and their structures and electrochemical properties were systematically investigated. XRD results show that all the alloys consist of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with bcc structure. With increasing Fe content, the abundance of the C14 Laves phase gradually decreases from 43.4 wt% (x = 0.0) to 28.5 wt% (x = 0.5), on the contrary, that of the V-based solid solution phase monotonously increases from 56.6 wt% to 71.5 wt%. In addition, SEM observation finds that the grain size of the V-based solid solution phase is first gradually reduced and then enlarged with increasing x. Electrochemical investigations indicate that the substitution of Fe for V markedly improves the cycling stability and the high rate dischargeability of the alloy electrodes, but decreases the maximum discharge capacity and the activation performance. Further electrochemical impedance spectra, the linear polarization curve and the potentiostatic step discharge measurements reveal that the electrochemical kinetics of the alloy electrodes should be jointly controlled by the charge-transfer reaction rate on the alloy surface and the hydrogen diffusion rate in the bulk of the alloys. For the alloy electrodes with the lower Fe content (x = 0.0–0.2), the hydrogen diffusion in the bulk of the alloys should be the rate-determining step of its discharge process, and while x increases from 0.3 to 0.5, the charge-transfer reaction on the alloy surface becomes to the rate-determining step, which induces that the electrochemical kinetics of the alloy electrodes is firstly improved and then decreased with increasing Fe content.     

Effects of Sc,Zr and Ti on the microstructure and properties of Al alloys with high Mg content

The effects of trace Sc, Zr, and Ti on the microstructure and hardness of Al alloys with high Mg content (Al-6Mg, Al-8Mg, and Al-10Mg) were studied by optical microscope, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brinell hardness. The grain size of the as-cast alloys was refined by the addition of Sc and Zr, and it was further refined by the addition of Ti. With the same contents of Sc, Zr, and Ti, an increase in Mg content was beneficial to the refinement due to the solution of Mg into α-Al. The refined microstructures of the as-cast alloys were favorable for Brinell hardness. Addition of Sc, Zr, and Ti to the Al-10Mg alloy results in the improvement of peak hardness and it is about 45% higher than that of the Al-10Mg alloy, which is due to fine precipitations of Al₃(Sc_1−x Zr _x ), Al₃(Sc_1−x Ti _x ), and Al₃(Sc_1−x−y Zr _x Ti _y ).     

Effects of lutetium addition on formation,oxidation and tribological properties of a Zr-based bulk metallic glass

Enhancement of glass-forming ability (GFA) and surface properties are important for the application of Zr-based bulk metallic glasses (BMGs), and surface oxidation is an effective strategy for surface strengthening. In this paper, the effects of rare earth element Lu addition on GFA and oxidation properties of a Zr₅₀Ti₂Cu₃₈Al₁₀ bulk metallic glass were studied. The tribological properties of Lu-free and Lu-doping BMGs before and after oxidation were also investigated. It is found that 2 at.% Lu addition in this alloy significantly enhance the critical diameter (d_c) from 5 mm to 20 mm. The oxidation rate of 2 at.% Lu-doping alloy is higher than Lu-free alloy, indicating that the addition of Lu facilitates the formation of oxidized scale on the surface of Zr₅₀Ti₂Cu₃₈Al₁₀ alloy. Moreover, surface oxidation treatment remarkably improves the wear resistance of Zr₅₀Ti₂Cu₃₈Al₁₀ and (Zr_0.5Ti_0.02Cu_0.38Al_0.1)₉₈Lu₂. This study is beneficial for the improvement of surface properties and further application of Zr-based BMGs.     

Effects of Ga and Sn on the electrochemical behavior of Mg–6Al–1Zn as anode materials

The microstructure and electrochemical behavior of Mg–6Al–1Zn, Mg–6Al–1Zn–1Ga, Mg–6Al–1Zn–1Sn, and Mg–6Al–1Zn–0.5Sn–0.5Ga as anode materials in a 3.5 wt% NaCl solution are compared systematically. The results show that Sn alloying refines the second-phases of Mg–6Zn–1Al by promoting tiny granular Mg₁₇Al₁₂ phases containing Sn, and inspires their disperse distribution. However, the Ga results in the formation of semicontinuous reticular Ga containing Mg₁₇Al₁₂ phases. The comparison of discharge tests indicates that Mg–6Al–1Zn–1Sn has the highest discharge activity, and Mg–6Al–1Zn–1Ga displays the largest hydrogen evolution corrosion resistance in 3.5 wt% NaCl solution at 298 K. The synergy of Ga and Sn can shorten discharge activation time and promote low discharge potential. In addition, the utilization efficiencies of the alloys decrease as follows: Mg–6Al–1Zn–1Ga > Mg–6Al–1Zn–0.5Sn–0.5Ga > Mg–6Al–1Zn–1Sn > Mg–6Zn–1Al. This study illustrates that the Mg–6Al–1Zn–0.5Sn–0.5Ga alloy has acceptable utilization efficiency and desirable electrochemical activity, which implies that doping Ga and Sn obtains a balance between discharge activity and utilization efficiencies.     

Microstructure and remarkably improved hydrogen storage properties of Mg2Ni alloys doped with metal elements of Al,Mn and Ti

Mg₂Ni_0.7M_0.3 (M=Al, Mn and Ti) alloys were prepared by solid phase sintering process. The phases and microstructure of the alloys were systematically characterized by XRD, SEM and STEM. It was found that Mg₃MNi₂ intermetallic compounds formed in Mg₂Ni_0.7M_0.3 alloys and coexisted with Mg and Mg₂Ni, and that radius of M atoms closer to that of Mg atom was more beneficial to the formation of Mg₃MNi₂. The hydrogen storage properties and corrosion resistance of Mg₂Ni_0.7M_0.3 alloys were investigated through Sievert and Tafel methods. Mg₂Ni_0.7M_0.3 alloys exhibited remarkably improved hydrogen absorption and desorption properties. Significantly reduced apparent dehydriding activation energy values of ?46.12, ?59.16 and ?73.15 kJ/mol were achieved for Mg₂Ni_0.7Al_0.3, Mg₂Ni_0.7Mn_0.3 and Mg₂Ni_0.7Ti_0.3 alloys, respectively. The corrosion potential of Mg₂Ni_0.7M_0.3 alloys shifted to the positive position compared with Mg₂Ni alloy, e.g. there was a corrosion potential difference of 0.110 V between Mg₂Ni_0.7Al_0.3 alloy (?0.529 V) and Mg₂Ni (?0.639 V), showing improved anti-corrosion properties by the addition of Al, Mn and Ti.     

Hydrogen storage characteristics of Ti2Ni alloy synthesized by the electro-deoxidation technique

Ti₂Ni alloy was synthesized in the molten CaCl₂ electrolyte by the electro-deoxidation method at 900 °C and the electrochemical hydrogen storage characteristics of the synthesized alloy was observed. The X-ray diffraction peaks indicated that stoichiometric oxides in TiO₂–ZrO₂–NiO mixture reduced to Ti₃O₅, CaTiO₃, CaZrO₃, Ni and Ti₂O₃ within 5 h electro-deoxidation process. Extension of the electro-deoxidation time to 10 h caused formations of TiO and equilibrium Ti₂Ni phase. After 24 h electro-deoxidation the target alloy with the equilibrium Ti₂Ni phase structure and the maximum amount of the dissolved Zr in it was obtained. It was observed that the synthesized alloy had maximum discharge capacity of 200 mA h g⁻¹. Upon increase in the charge/discharge cycles, however, the discharge capacity decayed sharply. According to the gathered EIS data at various DODs, the rapid degradation in the electrode performance of Ti₂Ni alloy was attributed to the developed barrier oxide layer on the electrode surface.     

Effect of manganese on the microstructure of Mg–3Al alloy

The effect of manganese on the microstructure of Mg–3Al alloy, especially the nucleation efficiency of Al–Mn particles on primary Mg, has been investigated in this paper. Mg–0.72Mn was used to fabricate Mg–3Al–xMn (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys, and the grain sizes of these alloys fluctuate at 390 μm indicating addition of manganese does not evidently influence the grain size of Mg–3Al alloy. Through XRD, FESEM and TEM detection, it is found that Al_0.89Mn_1.11 compound is the dominant Al–Mn phase in Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, and distributes in primary Mg matrix and interdendritic regions with an angular blocky morphology. The number of Al_0.89Mn_1.11 increases gradually with increasing manganese content while the grain sizes of primary Mg are nearly the same in Mg–3Al, Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, indicating Al_0.89Mn_1.11 has low nucleation efficiency on primary Mg.     

Powder metallurgical processing of Ni–Ti–Zr alloys undergoing martensitic transformation: part I

Ni–Ti–Zr materials with Zr 12–25 at.% and Ni 42–50 at.% have been produced by powder metallurgy. Suitable temperatures for sintering in Ar-atmosphere Ni–Ti–Zr compacts are within the range 900–1000 °C. Sintering at temperatures above 1000 °C causes melting of the compacts with high Zr content. The presence of ZrC, ZrO₂, Zr₃O, TiO₂ and TiO of different modifications, complex oxides such as Ni₅TiO₇, Ti_0.5Zr_0.5O_0.2 and equilibrium phases after sintering at temperatures above 1000 °C in alloys with low Zr-content was derived from X-ray diffractometry. During sintering at temperatures below 1000 °C the phases belonging to the binary Ti–Ni and Ti–Zr systems were formed. Long-term sintering and slow furnace cooling allowed the precipitation of Ni₄Ti₃ and Ni₂Ti. The process of sintering is controlled by the diffusion of Ni in Ti and Zr particles during the early stages of sintering. Slow diffusion of Zr atoms in Ti₂Ni, Ti–Ni and diffusion of Ti atoms in Zr₂Ni, Ni–Zr controls the later stages of sintering.     

Effects of Al content on the corrosion properties of Mg–4Y–xAl alloys

The corrosion performances of Mg–4Y–xAl (x = 1, 2, 3, and 4 wt%) alloys in the 3.5% NaCl electrolyte solution are investigated by electrochemical tests, weight loss measurement and corrosion morphology observation. The results indicate that corrosion modes for the alloys are localized corrosion and the filiform type of attack. With Al concentration increasing from 1 to 4 wt%, the corrosion rate of Mg–4Y–xAl alloys decreases firstly and then increases, and WA42 alloy shows the best corrosion resistance. The addition of Al element to Mg–4Y alloys leads to the formation of Al₂Y and Al₁₁Y₃ intermetallic compounds and reduces the proportion of Mg₂₄Y₅ phase. Corrosion resistance of the Mg–4Y–xAl alloys mainly depends on the size and distribution of the second phases. Besides, the addition of excessive Al can greatly consumes the Y element in the matrix, thus leading to a less protective film on the alloys. The effect of the relative Volta potential changes between the second phases and α-Mg on corrosion resistance of Mg–4Y–xAl alloys is insignificant. The main corrosion products of the Mg–4Y–xAl alloys are Mg(OH)₂, Mg₃(OH)₅Cl·4H₂O, Mg_0.72Al_0.28(CO₃)_0.15(OH)_1.98(H₂O)_0.48, and Mg₄Al₂(OH)₁₂CO₃·3H₂O.     

Effects of amorphous Co–C on the structural and electrochemical characteristics of La0.8Mg0.2Ni0.8Mn0.1Co0.5Al0.1 hydrogen storage alloy

Amorphous Co–C powder prepared by ball milling was introduced to improve the performance of La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 hydrogen storage alloy. The structural and electrochemical properties of the as-prepared La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1–x wt.% Co–C composites were investigated systematically. Scanning electron microscopic images show La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 alloy was coated by Co–C particles. X-ray diffraction patterns suggest that the composite almost remained original phase structures of La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 and Co–C in both charge and discharge processes. The maximum discharge capacity of the composites reached 414 mAh g^?1 at a current density of 50 mA g^?1 at 298 K. The cyclic stability and the discharge capacities of the composite electrodes were noticeably improved in comparison with single La–Mg–Ni-based alloy due to increased corrosion resistance and the catalysis of the Co–C powder. Cyclic voltammogram and potentiodynamic polarization studies on the composite indicate that the electrochemical kinetics was improved and the corrosion resistance was increased. The cycling performance of the composite electrode at high current density is good as well.     

Electron irradiation induced nano-crystallization in Zr66.7Ni33.3 amorphous alloy and Zr60Al15Ni25 metallic glass

Electron irradiation induced phase transformation behavior of an amorphous phase in Zr_66.7Ni_33.3 alloy, and an amorphous phase or supercooled liquid in Zr₆₀Al₁₅Ni₂₅ alloy was investigated. The amorphous phase could not maintain the original glassy structure under electron irradiation at 298 K, and f.c.c.-solid solution precipitated under electron irradiation in both alloys. The precipitation of C16-Zr₂Ni, big-cube (metastable f.c.c.-based Zr₂Ni intermetallic compound), Zr₆Al₂Ni and Zr₅AlNi₄ crystalline phases from an amorphous phase was not observed during electron irradiation induced crystallization. The amorphous phase in Zr₆₀Al₁₅Ni₂₅ metallic glass shows the highest phase stability against electron irradiation induced crystallization among Zr_66.7Cu_33.3, Zr_66.7Ni_33.3, Zr₆₅Al_7.5Ni_27.5, Zr₆₀Al₁₅Ni₂₅ and Zr₆₅Al_7.5Ni₁₀Cu_17.5 alloys. In Zr₆₀Al₁₅Ni₂₅ metallic glass, electron irradiation promoted the precipitation of f.c.c.-solid solution and Zr₆Al₂Ni crystalline phases from the supercooled liquid.