Guo Shihai

Magnetic-Field-Induced Strains of Bonded Ni–Mn–Ga Melt-Spun Ribbons

Non-stoichiometric Ni50Mn27Ga23 polycrystalline ribbons are prepared by melt-spinning technique. The magnetic-field-induced strain (MFIS) of Ni–Mn–Ga bulk alloy prepared by bonding the melt-spun ribbons is obtained. The experimental results show that Ni50Mn27Ga23 bonded ribbons exhibit a typical thermal-elastic shape memory effect in the thickness direction. The martensitic transformation strain of bonded ribbons is an expansive strain of about 0.3% without the magnetic field and a contractive strain of about -0.46% at the magnetic field of 1 T. The field can not only enhance the value of the martensitic transformation strain of the bonded ribbons, but can also change the direction of the strain. The bonded ribbons alloy presents negative MFIS and obtains a larger value of the strain though influenced by the adhesive between the ribbons. Therefore, the preparation technique of the Ni–Mn–Ga bulk alloy by bonding melt-spun ribbons is helpful to get rid of the size restriction of the ribbon and to broaden the applications of the ribbons.

Study on Hydrogen in Mixed Gas Separated by Rare Earth Hydrogen Storage Alloys

AB5-type rare-earth nickel (RE-Ni) based hydrogen storage alloys and AB3-type La-Mg-Ni based hydrogen storage alloys were prepared by vacuum medium-frequency induction melting in argon atmosphere. Industrial offgas was simulated by the mixed gas including H2, N2 and CH4. The purity of hydrogen separated by rare-earth hydrogen storage alloys and anti-poison and anti-pulverization properties of the alloys in the process of hydrogen absorption and desorption were studied. The results show that AB5-type RE-Ni based hydrogen storage alloys are possessed of the single structure with CaCu5-type, and AB3-type La-Mg-Ni based hydrogen storage alloys are possessed of the multi-phase structure with (La, Mg) Ni3, LaNi5 and LaNi2 phase. The hydrogen storage alloys will be poisoned by impurity gas in the separation of hydrogen, resulting in lower speed rate of hydrogen absorption and lesser capacity of hydrogen absorption. The anti-pulverization property of La-Mg-Ni based alloys is better than that of LaNi5 alloy and its complex alloy. LaNi3.7Mn0.4Al0.3Fe0.4Co0.2 alloy is considered as better alloy to separate hydrogen from the mixed gas, considering the purity of separated hydrogen, anti-poison and anti-pulverization property of the alloy. The hydrogen purity of 90.7% can be achieved.

Electrochemical and Hydrogen Absorption/Desorption Properties of Nanocrystalline Mg2Ni-type Alloys Prepared by Melt Spinning

Abstract The nanocrystalline Mg2Ni-type alloys with the compositions of Mg20Ni10−xCux (x=0, 1, 2, 3, 4) were synthesized by melt spinning technique. The microstructures of the alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system, and their hydriding and dehydriding kinetics were measured by an automatically controlled Sieverts apparatus. The results show that all the as-spun alloys hold a typical nanocrystalline structure. The substitution of Cu for Ni improves the electrochemical hydrogen storage performances of the alloys significantly, involving both the discharge capacity and the electrochemical cycle stability. Furthermore, the hydrogen absorption capacity of the alloy first increases and then decreases with the rising of Cu content, but the hydrogen desorption capacity grows dramatically for the same reason.

Hydrogen Storage Behaviours of Nanocrystalline and Amorphous Mg20-xLaxNi10(x=0-6) Hydrogen Storage Alloys

Abstract Mg2Ni-type hydrogen storage alloys with nominal composition Mg20-xLaxNi10 (x = 0, 2, 4, 6) were prepared by melt spinning. The microstructures of the alloys were studied by XRD, SEM and HRTEM. It is found that no amorphous phase formed in the as-spun La-free alloy, but the as-spun alloys containing La mainly held a major amorphous phase. When La content x≤2, the major phase in the as-cast alloys is Mg2Ni phase, but with the further increase of La content, the major phase of the as-cast alloys changes into (La, Mg)Ni3+LaMg3 phases. The hydrogen absorption and desorption kinetics of the as-cast and spun alloys were measured using an automatically controlled Sieverts apparatus, indicating that the hydrogen absorption and desorption capacity and the kinetics of the x = 2 alloy clearly increase with rising of spinning rate, but a contrary result is obtained for x = 6 alloy. The electrochemical measurement shows that the discharge capacity of the x = 2 alloy grows with rising of spinning rate, but it is a completely contrary result for x = 6 alloy. The melt spinning significantly improves the cycle stability of the x = 2 and 6 alloys.

Influences of Substitution of Zr for La on Structures and Electrochemical Performances of A2B7-Type Electrode Alloys by Melt-Spinning

Abstract A 2 B 7 -type electrode alloys with a nominal composition of La 0.75- x Zr x Mg 0.25 Ni 3.2 Co 0.2 Al 0.1 ( x = 0, 0.05, 0.1, 0.15, 0.2) were prepared by casting and melt-spinning. The influences of the substitution of Zr for La on the structures as well as the electrochemical performances of the alloys were investigated. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La, Mg)Ni 3 and LaNi 5 as well as a residual phase LaNi 2 . The substitution of Zr for La leads to an obvious increase of the LaNi 5 phase in the alloys, and it also helps the formation of a like amorphous structure in the as-spun alloy. The results of the electrochemical measurements indicate that the substitution of Zr for La obviously decreases the discharge capacity of the as-cast and spun alloys, but significantly improves their cycle stability. With increasing the spinning rate, the discharge capacity of the alloys ( x =0.1) first increases and then decreases, while the cycle stability monotonously rises.

Enhanced Hydriding and Dehydriding Kinetics of as-Spun Nanocrystalline Mg2Ni-Type Alloy Substituting Ni with Cu

Abstract In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloy, Ni in the alloy was partially substituted by element Cu. The nanocrystalline Mg2Ni1-xCux (x=0, 0.1, 0.2, 0.3, 0.4) alloys were prepared by melt-spinning technology. The structures of the as-cast and spun alloys were analyzed by XRD, SEM and HRTEM. The hydriding and dehydriding kinetics of the alloys were measured by using an automatically controlled Sieverts apparatus. The results show that all the as-spun alloys hold a nanocrystalline structure. The substitution of Cu for Ni leads to form secondary phase Mg2Cu without changing of the major phase of Mg2Ni in the alloy, The hydrogen absorption capacity of the alloys first increases and then decreases with rising of Cu content, but the hydrogen desorption capacity of the alloys monotonously grows with increasing of Cu content. The melt spinning significantly improves the hydrogenation and dehydrogenation capacity and the kinetics of the alloys.

Improved Cycle Stability of La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1 (x=0-0.4) Electrode Alloys 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 Pr. The melt-spinning technology was used for preparing La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures of the as-cast and spun alloys were investigated by XRD, SEM and TEM. The results show that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The melt spinning leads to an obvious increase of the LaNi5 phase and a decrease of the (La, Mg)Ni3 phase in the alloys. The melt spinning significantly improves the cycle stability of the alloys. The capacity retaining rate at 100th charging and discharging cycle (S100) is enhanced from 65.32% to 73.97% for the x = 0 alloy and from 79.36% to 93.08% for the x = 0.4 alloy with increasing of spinning rate from 0 m/s (as-cast was defined as spinning rate of 0 m/s) to 20 m/s.

Enhanced Electrochemical Hydrogen Storage Characteristics of Nanocrystalline and Amorphous Mg20Ni10-xCox (x=0-4) Alloys by Melt Spinning

Abstract In order to improve the electrochemical hydrogen storage performances of the Mg 2 Ni-type alloys, Ni in the alloy was partially substituted by element Co. The nanocrystalline and amorphous Mg 20 Ni 10- x Co x ( x =0, 1, 2, 3, 4) alloys were prepared by melt-spinning technology. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The electrochemical hydrogen storage characteristics of the alloys were measured. The results show that the substitution of Co for Ni leads to the formation of secondary phase MgCo 2 without altering the major phase of Mg 2 Ni. No amorphous phase is detected in the as-spun alloy ( x =0), whereas the as-spun alloy ( x =4) holds a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni significantly increases the glass forming ability of the Mg 2 Ni-type alloy. The substitution of Co for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, including the discharge capacity and the cycle stability, for which the increased glass forming ability by Co substitution is mainly responsible.

Effects of Rapid Quenching on Structure and Hydrogen Storage Characteristics of Mg20Ni10-xMnx (x=0-4) Alloys

Abstract In order to improve the hydrogen storage characteristics of the Mg 2 Ni-type alloys, Ni in the alloy was partially substituted by Mn. Rapid quenching technology was used to prepare the Mg 20 Ni 10- x Mn x ( x =0, 1, 2, 3, 4) hydrogen storage alloys. The microstructures of the as-cast and quenched alloys were characterized by XRD and HRTEM. The hydriding and dehydriding kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical performances were tested by an automatic galvanostatic system. The results show that, as the quenching rate reaches to 20 m/s, an amorphous phase can be detected in the ( x =4) alloy, and the amorphization degree of the alloy visibly increases with the growing of the quenching rate. The rapid quenching improves the hydrogen absorption and desorption characteristics of the alloy dramatically. Additionally, it also enhances the electrochemical hydrogen storage performances greatly, including the discharge capacity and cycle stability of the alloys substituted by Mn.

Investigation of Electrochemical Hydrogen Storage Kinetics of Melt Spun Nanocrystalline and Amorphous Mg2Ni-type Alloy

Abstract The Mg 2 Ni-type Mg 2 Ni 1− x Co x ( x =0, 0.1, 0.2, 0.3, 0.4) alloys were prepared by melt-spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The electrochemical hydrogen storage kinetics of the as-spun alloy ribbons was tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys were calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves were plotted by an electrochemical workstation. The results show that the as-spun Co-free alloy exhibits a typical nanocrystalline structure, while the as-spun ( x =0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg 2 Ni-type alloy. The amorphization degree of the as-spun alloys substituted by Co visibly increases with the increase in the amount of Co replacement. The Co replacement for Ni notably improves the electrochemical hydrogen storage kinetics of the alloys. With a growth in the amount of Co replacement from 0 to 0.4, the high rate discharge ability of the as-spun (25 m/s) alloy increases from 65.3% to 75.3%, the hydrogen diffusion coefficient ( D ) from 2.22 to 3.34 cm 2 /s and the limiting current density I L from 247.8 to 712.4 mA/g, respectively.