Papers by Keyword: Melt-Spinning

Abstract: The poor electrochemical cycle stability of Re-Mg-Ni system A2B7-type electrode alloys has limited their practical application as the negative electrode materials of Ni-MH battery. In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.2) electrode alloys were fabricated by casting and melt-spinning. The microstructures and the electrochemical cycle stability and kinetics of the alloys were investigated. The structure characterized by XRD, SEM and HRTEM 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 as-spun Zr-free alloy displays an entire nanocrystalline structure, but a like amorphous structure is detected in the as-spun alloy substituted by Zr, suggesting that the substitution of Zr for La facilitates the formation of an amorphous structure. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning remarkably ameliorate electrochemical cycle stability of the alloys. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) and the potential-step measurements all indicate that both of the melt spinning and the Zr substitution bring on a notable decline of the electrochemical kinetics of the alloys.

Abstract: A novel approach to the functionalization of nanometer-sized graphene was presented in this work. Covalent bonding between the filler and matrix was formed, with minimal disruption to the sp² hybridization of the pristine graphene sheet. Functionalization proceeded by covalently bonding a 4-substituted benzoic acid monomer to the surface of expanded graphene, via ‘‘direct Friedel-Crafts” acylation in mild reaction medium of polyphosphoric acid (PPA)/phosphorous pentoxide. Polyamide 6 (PA6)-functionalized graphene (FG) composites were prepared by in situ polymerization of ε-caprolactam in the presence of nanometer-sized FG. Nanocomposite fiber with 0.1 wt.% content of nanometer-sized FG was prepared with a piston spinning machine and hot-roller drawing machine. The nanometer-sized FG performed homogeneous dispersion in the polymer matrix. The mechanical properties of the PA6-FG composites fiber was enhanced by adding FG in the polymer matrix. The new functionalization method paves the way to prepare graphene-based nanocomposites fiber simply, without disrupting the primary structures of nanometer-sized graphene.

Abstract: The melt-spinning technique is applied to the preparation of the nanocrystalline and amorphous Mg2Ni-type alloys with nominal compositions of Mg₂₀Ni_10-xMn_x (x=0, 1, 2, 3, 4). The microstructures of the as-cast and spun alloys were characterized by XRD and HRTEM. The electrochemical performances of the as-spun alloys are measured by an automatic galvanostatic system. The results show that the as-spun Mg₂₀Ni₁₀ alloy displays an entire nanocrystalline structure, whereas the as-spun Mg20Ni6Mn4 alloy exhibits a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg₂Ni-type alloy. And the amorphization degree of the as-spun alloys substituted by Mn increases with the growing of the spinning rate. The substitution of Mn for Ni and the melt spinning ameliorate electrochemical hydrogen storage characteristics of the alloys substantially. The electrochemical discharge capacity and cycle stability of the alloys are considerably enhanced by increasing the amount of Mn substitution and the spinning rate. The high rate discharge ability (HRD) of the alloys first augments and then falls with the growing of the Mn content and the spinning rate.

Abstract: The RE-Mg-Ni-based A2B7-type La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys were synthesized by melt spinning technology. The impacts of the melt spinning and the substitution of Pr for La on the microstructures and electrochemical characteristics of the alloys were investigated in detail. The results reveal that the as-cast and spun alloys have a multiphase structure, containing two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The melt spinning results in a notable grain refinement of the alloys without altering the phase structure of the alloys. The discharge capacity of the (x=0.1) alloy first mounts up and then falls with rising the spinning rate. And the as-spun (10 m/s) alloy yields the maximum discharge capacity with the variation of Pr content. Furthermore, the measurements of the electrochemical hydrogen storage kinetics reveal that the high rate discharge ability (HRD), the hydrogen diffusion coefficient (D) and the limiting current density (IL) of the alloys first increases then decreases with rising the spinning rate and the amount of Pr substitution.

Abstract: The partial substitution of M (M=Cu, Mn) for Ni has been performed in order to ameliorate the hydriding and dehydriding kinetics of Mg2Ni-type hydrogen storage alloys. The melt spinning technology was used to prepare the Mg20Ni10-xMx (M=Cu, Mn; x=0, 1, 2, 3, 4) alloys. The structures of the as-spun alloys were characterized by XRD and TEM. The hydriding and dehydriding kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The results show that the as-spun (M=Cu) alloys hold a typical nanocrystalline structure, whereas the as-spun (M=Mn) alloys display a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg2Ni-type alloy. Furthermore, Mn substitution results in the formation of the secondary phases MnNi and Mg instead of changing the major phase of Mg2Ni. The substitution of M (M=Cu, Mn) for Ni exerts an insignificant effect on the hydriding kinetics, but it ameliorates the hydrogen desorption kinetics of the alloys dramatically. The hydrogen desorption ratio ( ) is enhanced form 20.84% to 52.88% for the (M=Cu) alloy spun at 20 m/s, and from 20.84% to 53.87% for the (M=Mn) alloy spun at 20 m/s by increasing the M (M=Cu, Mn) content from 0 to 4.

Abstract: The poor electrochemical cycle stability of RE–Mg–Ni system A₂B₇-type electrode alloys have limited their practical application as the negative electrode materials of Ni–MH battery. In order to improve the electrochemical cycle stability of the La–Mg–Ni system A₂B₇-type electrode alloys, the partial substitution of Pr for La has been performed. The La_0.75−xPrxMg_0.25Ni_3.2Co_0.2Al_0.1 (x = 0–0.4) electrode alloys were fabricated by casting and melt-spinning. The microstructures and electrochemical cycle stability of the as-cast and spun alloys were investigated by XRD, SEM and HRTEM. The results show that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La, Mg)₂Ni₇ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Pr for La brings on a notable grain refinement of the as-cast alloys instead of altering the phase structure of the alloys. The electrochemical measurement indicates that the cycle stability of the alloy remarkably grows with increasing both Pr content and spinning rate. The substitution of Pr for La and the melt spinning significantly ameliorate electrochemical cycle stability of the alloys. The capacity retaining rate (S₁₀₀) of the as-spun (15 m/s) alloys at 100th charging/discharging cycle is enhanced from 72.38% to 90.33% by increasing Pr content from 0 to 0.4. And that of the Pr0.3 alloy is increased from 78.11% to 92.32% by growing spinning rate from 0 (as-cast was defined as the spinning rate of 0 m/s) to 20 m/s.

Abstract: Microstructure of rapidly solidified Al₉₁Mn₇Fe₂ (at.%) alloy was investigated using SEM and TEM techniques. Quasicrystalline particles of different shapes and sizes embedded in the aluminium matrix were observed. Quasilattice constant was calculated as 0.461 Å. Additionally orientation relationships between matrix and quasicrystals particles were found based on electron diffraction patterns and high resolution images, such that: five-fold axis lie along [011] or [001] axes of the α-Al crystallographic direction.

Abstract: The alloys Al-12 wt % Zn-3 wt % Mg-1.5 wt % Cu with addition of Zr were melt spun and then hot pressed under 600 MPa pressure at 380 °C. Refinement of the microstructure and reduction of the volume fraction of the η (MgZn2) phase was observed in melt spun ribbon, as compared to the mould cast alloys. Good quality samples without pores and cracks obtained by hot pressing were composed of grains of size 0.2-0.5 µm. The particles of the η phase enriched in Zn, Mg and Cu were homogenously distributed in the matrix, while a few nanometres large precipitates of magnesium oxide were located at grain boundaries. Plate like precipitates of metastable h¢ phase appear after ageing at 120 °C and lead to microhardness increase up to about 195 HV as compared to 145 HV in pressed sample. Hot pressed ribbons showed compression strength of about 450 MPa which increased up to 630 MPa after ageing.

Abstract: In order to improve the electrochemical cycle stability of the La–Mg–Ni system A₂B₇-type electrode alloys, the partial substitution of Zr for La has been performed. The La_0.75−xZr_xMg_0.25Ni_3.2Co_0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys were fabricated by casting and melt-spinning. The influences of both the substitution of Zr for La and the melt spinning on the structures and the electrochemical cycle stability of the alloys were investigated. The structure characterization of XRD, SEM and HRTEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)₂ Ni₇ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Zr for La results in an evident refinement of the grains of the alloys instead of changing the structures of two major phases. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning remarkably ameliorate electrochemical cycle stability of the alloys. The capacity retaining rate (R100) of the as-spun (5 m/s) alloys at 100th charging/discharging cycle is enhanced from 67.43% to 79.22% by increasing Zr content from 0 to 0.2. And that of the Zr0.1 alloy is increased from 73.21% to 82.07% by growing spinning rate from 0 (as-cast was defined as the spinning rate of 0 m/s) to 20 m/s.

Abstract: Mg2Ni-type Mg20Ni10-xMx (M=Cu, Co; x=0, 1, 2, 3, 4) electrode alloys with nanocrystalline and amorphous structure were synthesized by melt-spinning technique. The microstructures of the as-spun alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage properties of the experimental alloys were measured. The obtained results show that the as-spun (M=Cu) alloys hold an entire nanocrystalline structure, whereas the as-spun (M=Co) alloys display a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg2Ni-type alloy. Furthermore, such substitution results in the formation of secondary phases Mg2Cu and MgCo2 instead of changing the major phase of Mg2Ni. The substitution of M (M=Cu, Co) for Ni markedly improves the electrochemical performances of the alloys, involving the discharge capacity and the cycle stability as well as the high rate discharge ability.