Influence of rapid quenching on cyclic stability of La-Mg-Ni system (AB_3-type) electrode alloys

Aiming at the improvement of the cyclic stability of La-Mg-Ni system （PuNi3-type） hydrogen storage alloy, Ni in the alloy was partly substituted by Fe. The electrode alloys of La0.7Mg0.3Co0.45Ni255-xFex （x=0, 0.1, 0.2, 0.3, 0.4） were prepared by casting and rapid quenching. The influence of the quenching on cyclic stability as well as structure of the alloys was investigated in detail. The results of electrochemical measurement indicated that rapid quenching significantly improved cyclic stability. When the quenching rate rose from 0 （As-cast was defined as a quenching rate of 0 m/s） to 30 m/s, the cyclic life of Fe-free alloy （x=-0） increased from 81 to 105 cycles, and for alloy containing Fe（x=0.4）, it grew from 106 to 166 cycles at a current density of 600 mA/g. The results obtained by XRD, TEM and SEM revealed that the as-cast and quenched alloys had multiphase structures, including two major phases （La, Mg）Ni3 and LaNi5 as well as an imptLrity phase LaNi2. Rapid quenching helped the formation of an amorphous-like structure in Fe containing alloys.

Effects of rapid quenching on structure and cycle stability of La-Mg-Ni-Co type hydrogen storage alloy

In order to improve the cycle stability of La-Mg-Ni-Co type alloy electrode, rapid quenching technology was employed. The effects of rapid quenching on the microstructure and cycle stability of the alloy were investigated. The obtained results show that the La2Mg(Ni0.85Co0.15)9M0.1 (M=B, Cr) alloy electrodes are composed of (La, Mg)Ni3 phase, LaNi5 phase and a small amount of the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast MB alloy, and the Ni2B phase in the alloy nearly disappears after rapid quenching. Rapid quenching technology can slightly improve the cycling life of the alloy. When the quenching rate increases from 0 m·s-1 (As-cast is defined as quenching rate of 0 m·s-1) to 30 m·s-1, the cycle lives of the MB, MCr alloys enhance from 86 and 87 cycles to 106 and 119 cycles, respectively. On the other hand, the average capacity decay rates of the MB, MCr alloys decrease from 1.7172 and 1.7178 mAh·g-1·cycle-1 to 1.5751 and 1.3060 mAh·g-1·cycle-1 after 86 charge-discharges cycling, respectively.

Effect of Rapid Quenching on Microstructures and Electrochemical Performances of La_2Mg(Ni_(0.85)Co_(0.15))_9M_(0.1)(M=B, Cr) Hydrogen Storage Alloys

The La-Mg-Ni-system （PuNi3-type） La2Mg （Ni0.85 Co0.15 ）9M0.1 （ M = B, Cr） hydrogen storage etectrode alloys were prepared by casting and rapid quenching. The electrochemical performances and microstructures of the as-cast and quenched alloys were determined and measured. The effects of rapid quenching on the microstructures and electrochemical properties of the alloys were investigated in detail. The obtained results show that the alloys are composed of the （La, Mg） Ni3 phase （PuNi3-type structure） and the LaNi5 phase, as well as the small amount of the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloy containing boron, and the Ni2B phase in the alloy nearly disappears after rapid quenching. The relative amount of each phase in the alloys depends on the quenching rate. The rapid quenching technique can greatly improve the electrochemical performance of the alloy, and the effect of rapid quenching on the activation performances of the alloys is minor. Rapid quenching enhances the cycle stability of the alloy, and the cycle life of the alloy increases with the increase of the quenching rate.

Effect of rapid quenching on the microstructure and electrochemical characteristics of La_(0.6)Ce_(0.4)Ni_(3.6)Co_(0.65)Mn_(0.4)Al_(0.2)Ti_(0.05_(FeB)_(0.1) hydrogen storage alloy

In order to improve the cycling stability of AB5 type alloy electrodes,rapid quenching technology and new alloy composition design were employed.A hydrogen storage alloy with nominal composition La0.6Ce0.4Ni3.6Co0.65Mn0.4Al0.2Ti0.05（FeB）0.1 was prepared by vacuum magnetic levitation melting under high purity argon atmosphere,followed by rapid quenching at different cooling rates.XRD results show that all alloys exhibit the single-phase CaCu5-type structure.Electrochemical tests indicate that rapid quenching can slightly improve the cycling life of the alloy.Nevertheless,the high-rate dischargeability of the quenched alloys is lower than that of the as-cast alloy.

Structure and electrochemical properties of hypo-stoichiometric hydro-gen storage alloys prepared by twin-roller rapid quenching process

The stoichiometric alloy MlB5.0 and the hypo-stoichiometric alloy MlB4.85 were prepared by twin-roller rapid quenching process, and their structure and electrochemical properties were studied. The results of XRD show that both of the alloys have a typical single-phase hexagonal CaCus-type structure. The cell volume of the hylpo-stoichiometric alloy M1B4.85 is slightly larger than that of the stoichiometric alloy M1B5.0, although its lattice constant cla is smaller. Under 2 C discharging rate, i.e. 640 mA/g, the M1B4.85 has a discharge capacity of 320 mAh/g, which is higher than that of the M1Bs.o, 312 mAh/g. Nevertheless, the capacities of the M1B4.85 and the M1Bs.o decline 24.7% and 20.2% after 400 cycles, respectively. The relationship of electrochemical performances of the alloys with their structures is discussed.

Cycle Stabilities of La_(0.7)Mg_(0.3)Ni_(2.55-x)Co_(0.45)M_x (M=Fe, Cu, Al;x=0, 0.1) Electrode Alloys Prepared by Casting and Rapid Quenching

La-Mg-Ni system (PuNi3-type) hydrogen storage alloys La0.7Mg0.3Ni2.55-xCo0.45Mx (M=Fe, Cu, Al; x=0, 0.1) were prepared by casting and rapid quenching. Aiming to improve the cycle stabilities of the alloys, Ni in the alloy was partly substituted by Fe, Cu and Al. The effects of the substitution of Fe, Cu and Al for Ni and the rapid quenching on the microstructures and electrochemical properties of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM indicate that the element substitution has no influence on the phase compositions of the alloys, but it changes the phase abundances of the alloys. Particularly, the substitution of Al and Cu obviously increases the amount of the LaNi2 phase. The substitution of Al and Fe leads to a great refinement of the as-quenched alloy′s grains. The substitution of Al strongly restrains the formation of the amorphous in the as-quenched alloy, but the substitution of Fe and Cu is quite helpful for the formation of an amorphous phase. The effects of the substitution of Fe, Cu and Al on the cycle stabilities of the as-cast and quenched alloys are different. The positive impact of the substitution elements on the cycle stabilities of the as-cast alloys is ranked in proper order Al>Fe>Cu, and for as-quenched alloys, the order is Fe>Al>Cu. Rapid quenching engenders an unconscious influence on the phase composition, but it markedly enhances the cycle stabilities of the alloys.

Influence of rapid quenching on hydrogen storage characteristics of nanocrystalline Mg_2Ni-type alloys

Nanocrystalline Mg2Ni-type alloys with nominal compositions of Mg20Ni10–xCux(x=0,1,2,3,4,mass fraction,%) were synthesized by rapid quenching technique.The microstructures of the as-cast and quenched alloys were characterized by XRD,SEM and HRTEM.The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system.The hydriding and dehydriding kinetics of the alloys were measured using an automatically controlled Sieverts apparatus.The results show that all the as-quenched alloys hold the typical nanocrystalline structure and the rapid quenching does not change the major phase Mg2Ni.The rapid quenching significantly improves the electrochemical hydrogen storage capacity of the alloys,whereas it slightly impairs the cycling stability of the alloys.Additionally,the hydrogen absorption and desorption capacities of the alloys significantly increase with rising quenching rate.

Effect of Rapid Quenching on Electrochemical Properties of AB_5 and AB_(3.5)-Type Hydrogen Storage Alloys

Effect of rapid quenching on the electrochemical properties of AB5 and AB3.5-type hydrogen storage alloys was studied. The results indicated that the discharge capacities of the rapid quenching MmNi3.55Co0.75Mn0.4Al0.3 alloys decrease under 25 and -35 ℃ with the increase of the quenching rate. Comparatively, the decrease extent of the quenching alloys at -35 ℃ is lower than that at 25 ℃. The result on the study of the cycle life indicated that the quenching process was favorable to improve the cycle stabilities of the MmNi3.55Co0.75-Mn0.4Al0.3 alloys under 25 and -35 ℃. Whereas, the effect of the quenching process on the La0.7Mg0.3(Ni0.85Co0.15)3.5 alloy was different at 25 ℃ from at -35 ℃. Under 25 ℃, the cycle life of the alloy was obviously improved by the quenching process, however, the quenching process did not improve but decreased slightly the cycle life at -35 ℃.

Development of Rapidly Quenched Soft Magnetic Materials in China

Thediscovery ofthefirstFe-based ferrom agneticam orphousalloy in 1966 had m ade an im pacton conventionalm agnetic m aterialsbecause ofitsuniqueproperties. Since then, a num berof am orphousm agneticm aterialshavebeen successfully developed and used in aw ide variety ofapplica- tions. Abriefreview ofR& Dactivitieson am orphoussoftm agneticm aterialsin Chinaisgiven from the beginning to the presentin a som ew hatchronologicalorder, followed by a briefintroduction to their applicationson electric and electronicindustries. An analysis and aprospectofChinesem arket ofsuch am orphous m aterials are also presented.

Structural Characteristics of Rapidly Quenched Al-Si Alloys

The structure of rapldly quenched Al-Si alloys (1 and 4 wt-%Si) was systematically studied by optical and transmission electron microscopy (TEM ) as welI as X-ray djffractjon (XRD). ExperimentaIresults show that rapid solidification refines the grain size. extends the solid solubility of Si in Al and Introduces a high density ot defects which exist in the forms of vacancies, dislocations and dislocation loops. etc.. The decomposition process of the alloys was fol lowed by using differential scanning calorimeter (DSC) and the activation energy for precipitation of Si was obtained through Kissinger analysis. The precipitation behaviour of Supersaturated Si in both samples was further examined by TEM. It was found that Si mainly precipitated inside the grains in Al-1 wt-%Si alloy. while in Al-4 wt-%Si alloy. nearly all the Si precipitates distributed along the grain boundaries. This may be due to the structure difference between the alloys in as-quenched state

Characterizations of Skeletal Iron Catalysts Prepared from Rapidly and Naturally Quenched Fe-Al Alloys

Surface morphology, physical-chemical properties of skeletal iron catalysts prepared by leaching of the rapidly quenched(RQ) and naturally quenched(NQ) Fe-Al alloys with an aqueous solution of NaOH were characterized by using a series of techniques including XRD, BET, XPS, SEM, H_2 and CO-TPD. It was found that the RQ skeletal iron catalyst exhibits a smaller particle size, larger specific surface area and pore volume than the NQ one. The H_2 and CO-TPD experiments showed that the RQ skeletal iron exhibits stronger affinity for H_2 and milder affinity for CO compared with the NQ one. But the NQ skeletal catalyst shows a better thermal stability than the RQ catalyst.

Development of Rapidly Quenched Soft Magnetic Materials in China

The discovery of the first Fe-based ferromagnetic amorphous alloy in 1966 had made an impact on conventional magnetic materials because of its unique properties. Since then, a number of amorphous magnetic materials have been successfully developed and used in a wide variety of applications. A brief review of R & D activities on amorphous soft magnetic materials in China is given from the beginning to the present in a somewhat chronological order, followed by a brief introduction to their applications on electric and electronic industries. An analysis and a prospect of Chinese market of such amorphous materials are also presented.

Evolution of microstructure in semi-solid slurries of rheocast aluminum alloy

Semi-solid metal processing is being developed in die casting applications to give several cost benefits. To efficiently apply this emerging technology, it is important to understand the evolution of microstructure in semi-solid slurries for the control of the theological behavior in semi-solid state. An experimental apparatus was developed which can capture the grain structure at different times at early stages to understand how the semi-solid structure evolves. In this technique, semi-solid slurry was produced by injecting fine gas bubbles into the melt through a graphite diffuser during solidification. Then, a copper quenching mold was used to draw some semi-solid slurry into a thin channel. The semi-solid slurry was then rapidly frozen in the channel giving the microstructure of the slurry at the desired time. Samples of semi-solid 356 aluminum alloy were taken at different gas injection times of 1, 5, 10, 15, 20, 30, 35, 40, and 45 s. Analysis of the microstructure suggests that the fragmentation by remelting mechanism should be responsible for the formation of globular structure in this rheocasting process.

Study on Nanocrystalline Rare Earth Mg-Based System Hydrogen Storage Alloys with AB_3-Type

A sort of rare earth Mg-based system hydrogen storage alloys with AB3-type was prepared by double-roller rapid quenching method. The alloys were nanocrystalline multi-phase structures composed of LaNi3 phase and LaNi5 phase by X-ray diffraction and scanning electron microscopy analyses, and the suitable absorption/desorption plateau was revealed by the measurement of P-C-I curve. Electrochemical studies indicate that the alloys exhibit good electrochemical properties such as high capacity and stable cycle life, and the discharge capacity is 369 mAh·g-1 at 0.2 C (72 mA·g-1). after 460 cycles, the capacity decay was only 19.4% at 2 C (720 mA·g-1).

Gaseous and Electrochemical Hydrogen Storage Kinetics of As-quenched Nanocrystalline and Amorphous Mg_2Ni-type Alloys

The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox （x = 0, 0.1, 0.2, 0.3, 0.4） alloys were synthesized by melt quenching technology. The structures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The gaseous hydrogen storage kinetics of the alloys was measured using an automatically controlled Sieverts apparatus. The alloy electrodes were charged and discharged with a constant current density in order to investigate the electrochemical hydrogen storage kinetics of the alloys. The results demonstrate that the substitution of Co for Ni results in the formation of secondary phases MgCo2 and Mg instead of altering the major phase Mg2Ni. No amorphous phase is detected in the as-quenched Co- ffee alloy, however, a certain amount of amorphous phase is clearly found in the as-quenched alloys substituted by Co. Furthermore, both the rapid quenching and the Co substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys, for which the notable increase of the hydrogen diffusion coefficient （D） along with the limiting current density （IL） and the obvious decline of the electrochemical impedance generated by both the Co substitution and the rapid quenching are basically responsible.

Effects of substituting Ni with M (M=Cu, Al and Mn) on microstructures and electrochemical characteristics of La-Mg-Ni system (PuNi_3-type) electrode alloys

In order to improve the electrochemical cycle stability of La-Mg-Ni system (PuNi3-type) hydrogen storage alloy, Ni in the alloys was partially substituted by M (M=Cu, Al, Mn). A new La-Mg-Ni system electrode alloys La0.7Mg0.3Ni2.55-xCo0.45Mx (M=Cu, Al, Mn; x=0, 0.1) were prepared by casting and rapid quenching. The effects of element substitution and rapid quenching on the microstructures and electrochemical performances of the alloys were investigated. The results by XRD, SEM and TEM show that the alloys have a multiphase structure, including the (La, Mg)Ni3 phase, the LaNi5 phase and the LaNi2 phase. The rapid quenching and element substitution have an imperceptible influence on the phase compositions of the alloys, but both change the phase abundance of the alloys. The rapid quenching significantly improves the composition homogeneity of the alloys and markedly decreases the grain size of the alloys. The Cu substitution promotes the formation of an amorphous phase in the as-quenched alloy, and a reversal result by the Al substitution. The electrochemical measurement indicates that the element substitution decreases the discharge capacity of the alloys, whereas it obviously improves the cycle stability of the alloys. The positive influence of element substitution on the cycle life of the alloys is in sequence Al>Cu>Mn, and negative influence on the discharge capacity is in sequence Al>Mn>Cu. The rapid quenching significantly enhances the cycle stability of the alloys, but it leads to a different extent decrease of the discharge capacity of the alloys.

STUDY OF MECHANISM OF RQ EMBRITTLEMENT OF Fe_(73.5)Cu_1-Nb_3Si_(13.5)B_9 NANOCRYSTALLINE SOFT MAGNETIC ALLOY

Rapidly quenching embrittlement (RQE) sometimes appears in nanocrystalline soft magnetic alloy (FINEMET) during production process. As a re-sult of RQE the ductility of the as-quenched ribbon drops seriously. The mechanism of RQE has been elucidated in the recent works of current authors. R was believed that RQE is due to the structural relaxation but not related to α-Fe(Si) crystallization. In this paper, the high resolution TEM (HRTEM) method and image digital processing were applied to analyze the HRTEM images of two FINEMET rapidly quenched ribbons with different thicknesses in detail. In the thinner ductile sample, the ordering domains with the size of about 3nm are observed. In the thicker RQE sample, the metastable nanocrystalline domains with the size of 18nm are observed along with the structural relaxation. These domains seem to have Fe3B-like metastable phase struc-ture on nanometer scale. The result indicates that the local atomic ordering regions extend when RQE induced by structural relaxation occurs.

Magnetic properties optimization of nanocomposite Nd_9Fe_(85)B_6 magnets by controlling microstructure of as-quenched ribbons

To optimize the magnetic properties of nanocomposite Nd9Fe85B6 magnets, the as-quenched ribbons with different microstructures were prepared at six wheel velocities from 10 to 30 m s^-1through rapid quenching,followed by a series of annealing treatments at 550-800 °C for 5-10 min. It is found that both the large initial grains at low cooling rate and high content of amorphous phase at high cooling rate cause a-Fe grains coarsening, which leads to a decline in the strength of exchange coupling interaction and the deterioration of magnetic properties. In order to optimize the magnetic properties, the as-quenched ribbons should be chosen with relatively small initial grains as well as a small amount of amorphous phase. For nanocomposite Nd9Fe85B6 materials, the optimized magnetic properties of Hcj= 446 kA m^-1, Br= 0.86 T,（BH）max=80 kJ m^-3are obtained for ribbons prepared at 18 m s-1after annealing at 620 °C for 5 min.

Effect of Oxygen on Microstructure Evolution and Glass Formation of Zr-based Metallic Glasses

The effect of oxygen on the microstructure evolution and glass formation of Zr-based bulk metallic glasses（BMGs）was studied in detail.It was found that oxygen did not form oxides or dissolve in glass matrix,but induced the precipitation ofα-Zr which has the high affinity and solubility of oxygen in the Zr-based bulk metallic glass（ZrBMG）.With the precipitation ofα-Zr,the remaining melts contain much lower oxygen content and have strong glass formation,resulting in the formation ofα-Zr/BMG composite.The findings provide an important insight into the mechanism of the oxygen on glass formation,and give us a useful guideline to avoid the oxygen detrimental for designing new BMGs.