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Enhanced Hydrogen Storage Kinetics of Nanocrystalline and Amorphous Mg2Ni-type Alloy by Melt Spinning  [PDF]
Yang-Huan Zhang,Bao-Wei Li,Hui-Ping Ren,Xia Li,Yan Qi,Dong-Liang Zhao
Materials , 2011, DOI: 10.3390/ma4010274
Abstract: Mg 2Ni-type Mg 2Ni 1?xCo x (x = 0, 0.1, 0.2, 0.3, 0.4) alloys were fabricated by melt spinning technique. The structures of the as-spun alloys were characterized by X-ray diffraction (XRD) and transmission electron microscopy (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 was tested by an automatic galvanostatic system. The results show that the as-spun (x = 0.1) 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 notably intensifies the glass forming ability of the Mg 2Ni-type alloy. The melt spinning treatment notably improves the hydriding and dehydriding kinetics as well as the high rate discharge ability (HRD) of the alloys. With an increase in the spinning rate from 0 (as-cast is defined as spinning rate of 0 m/s) to 30 m/s, the hydrogen absorption saturation ratio ( ) of the (x = 0.4) alloy increases from 77.1 to 93.5%, the hydrogen desorption ratio ( ) from 54.5 to 70.2%, the hydrogen diffusion coefficient ( D) from 0.75 × 10 ? 11 to 3.88 × 10 ? 11 cm 2/s and the limiting current density IL from 150.9 to 887.4 mA/g.
Gaseous and Electrochemical Hydrogen Storage Properties of Nanocrystalline Mg2Ni-Type Alloys Prepared by Melt Spinning  [PDF]
Zhihong Ma, Bo Li, Huiping Ren, Zhonghui Hou, Guofang Zhang, Yanghuan Zhang
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.23018
Abstract: A partial substitution of Ni by Cu has been carried out in order to improve the hydrogen storage characteristics of the Mg2Ni-type alloys. The nanocrystalline Mg20Ni10-xCux (x = 0, 1, 2, 3, 4) alloys are synthesized by the melt-spinning technique. The structures of the as-cast and spun alloys have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). The electrochemical performances were evaluated by an automatic galvanostatic system. The hydrogen absorption and desorption kinetics of the alloys were determined by using an automatically controlled Sieverts apparatus. The results indicate that the substitution of Cu for Ni does not alter the major phase Mg2Ni. The Cu substitution significantly ameliorates the electrochemical hydrogen storage performances of alloys, involving both the discharge capacity and the cycle stability. The hydrogen absorption capacity of alloys has been observed to be first increase and then decrease with an increase in the Cu contents. However, the hydrogen desorption capacity of the alloys exhibit a monotonous growth with an increase in the Cu contents.
Hydriding and dehydriding kinetics of melt spun nanocrystalline Mg20Ni10-xCux (x = 0-4) alloys  [PDF]
Yang-Huan Zhang, Dong-Liang Zhao, Bao-Wei Li, Hui-Ping Ren, Shi-Hai Guo, Xin-Lin Wang
Natural Science (NS) , 2010, DOI: 10.4236/ns.2010.21003
Abstract: The nanocrystalline Mg2Ni-type electrode alloys with nominal 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 hydrogen absorption and desorption kinet-ics of the alloys were measured using an auto-matically controlled Sieverts apparatus. The re- sults show that all the as-spun alloys hold ty- pical nanocrystalline structure. The substitution of Cu for Ni does not change the major phase Mg2Ni but it leads to the formation of the sec-ondary phase Mg2Cu. The hydrogen absorption capacity of the alloys first increases and then decreases with rising Cu content, but the hy-drogen desorption capacity of the alloys mono- tonously grows with increasing Cu content. The melt spinning significantly improves the hydro- genation and dehydrogenation capacities and kinetics of the alloys.
Resistencia al picado de Aleaciones Nanocristalinas de Al90Fe7Nb3 y Al90 Fe7Zr3obtenidas por Solidificación Rápida y Extrusión Caliente Pitting Resistance of Al90Fe7Nb3 and Al90Fe7 Zr3 Nanocrystalline Alloys Obtained by Melt-Spinning and Hot Extrusion  [cached]
C. A. D. Rodrigues,C. S. Kiminami,W. J. Botta,G. Tremiliosi-Filho
Portugaliae Electrochimica Acta , 2009,
Abstract: Las aleaciones a base de aluminio con estructura amorfa y/o nanocristalinas tienen mejores propiedades mecanicas, cuando se comparan con las aleaciones convencionales. En su obtencion se pueden utilizar diferentes tecnicas, como la solidificacion rapida (melt-spinning), donde el material se obtiene en forma de cinta y la pulvimetalurgia, que partiendo de polvos atomizados u obtenidos por molienda, se pueden conseguir piezas con geometrias y formas variadas. A partir de polvos se pueden obtener muestras de mayor volumen (bulk) es decir, muestras de grandes dimensiones (en mm), mayores que las obtenidas por solidificacion rapida (<40 mm). Las aleaciones obtenidas a partir de polvo pueden ser consolidadas en caliente, siendo un desafio importante en este tipo de aleaciones, que se pueda conservar una microestructura fina. En este trabajo se realiza una evaluacion de la resistencia al picado en aleaciones nanocristalinas de Al90Fe7Nb3 y Al90Fe7Zr3, obtenidas a partir de polvos parcialmente amorfos, aleados mecanicamente y conformados mediante solidificacion rapida y extrusion caliente. La resistencia a la corrosion se evalua mediante ensayos electroquimicos, utilizando una disolucion al 0,9% de NaCl, a pH 7,0. Las curvas de polarizacion obtenidas indicaron que los mejores resultados de resistencia a la corrosion se dan en las muestras Al90Fe7Nb3 y Al90 Fe7Zr3 cuando estas se obtienen por solidificacion rapida Amorphous and/or nanocrystalline Al-based alloys have better mechanical properties when compared with crystalline conventional Al-alloys. Different techniques can be used to obtain amorphous Al-based alloys, usually in a ribbon form (from melt-spinning processing) or powders (from gas atomization or ball milling processing). To obtain bulk samples, that is, samples with dimensions typic ally much larger (mm scales) than the ones obtained from the above mentioned techniques (<40 mm), the ribbons or powders must be hot-consolidated. One of the most important challenges in the development of such alloys is to keep a refined microstructure after the necessary heating. The present work focuses the pitting resistance by electrochemical corrosion resistance test in solution 0.9 % NaCl and pH 7.0, for Al90Fe7Nb3 and Al90Fe7Zr3 nanocrystalline alloys, which were obtained by hot-extrusion of mechanically alloyed powders, and melt-spinning process. The results of the polarization curves indicated that the Al90Fe7Nb3 and Al90 Fe7Zr3 ribbons present better corrosion properties than the extruded alloys.
Analyses of the melt cooling rate in the melt-spinning process  [PDF]
B. Karpe,B. Kosec,M. Bizjak
Journal of Achievements in Materials and Manufacturing Engineering , 2012,
Abstract: Purpose: Rapid solidification (RS) of metallic melts is important for the development of the advance metallic materials, because enables the production of new alloys with superior properties according to conventionally treated alloys. In practice it turned out, that single roll melt spinning process has one of the highest melt cooling rates among all continuous casting processes. But, because very short solidification time and movement of the melt and substrate, melt cooling rate is very difficult to measure with confidence. Primary goal of our work was to determine the limits of cooling rate over the ribbon thickness and to outline, which property or typical feature of the process has the greatest influence on cooling rate of the melt. Design/methodology/approach: On the basis of developed mathematical model, a computer program was made and used for melt cooling rate calculation in the melt-spinning process.Findings: The calculations show that distance from the contact surface in relation to the thermal properties of the melt, chilling wheel material and contact resistance between metal melt and chilling wheel have the greatest influence on melt/ribbon cooling rate. In the case of continuous casting, significant “long term” surface temperature increase may take place, if the wheel is not internally cooled.Research limitations/implications: Influence of the melt physical properties, chill wheel material, contact resistance and cooling mode of the chill wheel on melt cooling rate are outlined.Practical implications: Practical limits of melt cooling rate over ribbon thickness are outlined and directions for the chill wheel cooling system design are indicated.Originality/value: Comparison between cooling rates calculated at various thermal resistance assumptions of particular constituents is outlined. New method for determining contact resistance through variable heat transfer coefficient is introduced which takes into account physical properties of the casting material, process parameters and contact time/length between metal melt/ribbon and substrate and enables cooling rate prediction before the experiment execution. In the case of continuous casting, heat balance of the melt-spinning process is calculated and influence of the chill wheel cooling mode on cooling rate of metallic ribbon is analyzed.
Magnesium-Nickel alloy for hydrogen storage produced by melt spinning followed by cold rolling
Leiva, Daniel Rodrigo;Costa, Hevlin Cristina de Almeida;Huot, Jacques;Pinheiro, Tiago Santos;Jorge Junior, Alberto Moreira;Ishikawa, Tomaz Toshimi;Botta Filho, Walter José;
Materials Research , 2012, DOI: 10.1590/S1516-14392012005000096
Abstract: severe plastic deformation routes (spd) have been shown to be attractive for short time preparation of magnesium alloys for hydrogen storage, generating refined microstructures and interesting hydrogen storage properties when compared to the same materials processed by high-energy ball milling (hebm), but with the benefit of higher air resistance. in this study, we present results of a new processing route for mg alloys for hydrogen storage: rapid solidification followed by cold work. a mg97ni3 alloy was processed by melt spinning (ms) and by extensive cold rolling (cr). submitting mg97ni3 ribbons between steel plates to cold rolling has shown to be a viable procedure, producing a thin cold welded foil, with little material waste. the as-processed material presents a high level of [002] fiber texture, a sub microcrystalline grain structure with a high density of defects, and also a fine dispersion of mg2ni nanoparticles. this refined microstructure allied to the developed texture resulted in enhanced activation and h-sorption kinetics properties.
REMARKABLE IMPROVEMENT OF THE COERCIVITY OF TbMn6Sn6 COMPOUND BY MELT-SPINNING PROCESS

Zhao Peng,Zhang Shao-ying,Zhang Hong-wei,Yan A-ru,Shen Bao-gen,

中国物理 B , 2001,
Abstract: The melt-spinning process has been carried out to improve the hard-magnetic properties of the TbMn6Sn6 compound. For the TbMn6Sn6 ribbons quenched at a rate of 40m/s and annealed at 545K for 30min, the highest coercivity of about 0.6T is achieved at room temperature, which is much higher than that of the TbMn6Sn6 ingot. Both the ingot and the ribbon coercivities will increase with decreasing temperature. For ribbons, a greater improvement of coercivity has been made at lower temperatures. Microstructural studies show the uniform nanocrystalline distribution in the TbMn6Sn6 ribbons and a small amount of Tb-rich phase in grain boundaries. The observed remarkable improvement of magnetic hardening in ribbons is believed to arise from the uniform nanoscale microstructure and the domain-wall pinning at the grain boundaries.
Modeling of heat transfer in the cooling wheel in the melt-spinning process  [PDF]
B. Karpe,B. Kosec,M. Bizjak
Journal of Achievements in Materials and Manufacturing Engineering , 2011,
Abstract: Purpose: In the case of continuous casting of metal ribbons with the melt-spinning process on the industrial scale, larger quantity of melt could lead to a slow excessive warming of the chilling wheel, which would further lead to solidification of a ribbon at non-uniform conditions and increased wearing of the wheel. Primary goal of our work was to determine to what extent the release of heat during contact of the melt/ribbon on the circumferential surface of the chilling wheel affect its surface temperature rise, and inversely how much elevated temperature of the chill wheel surface affects on metal ribbon cooling rate and its solidification velocity.Design/methodology/approach: On the basis of developed mathematical model, a computer program was made and used for analyses of heat transfer in the melt-spinning process.Findings: The calculations show that contact resistance between metal melt and chilling wheel has a great influence on melt/ribbon cooling and chill wheel heating rate, and must not be neglected in numerical calculations, even if its value is very low. In the case of continuous casting, significant “long term” surface temperature increase may take place, if the wheel is not internally cooled. But inner cooling is effective only if wheel casing thickness is properly chosen.Research limitations/implications: Influence of process parameters and chill wheel cooling mode on cooling and solidifying rate over ribbon thickness are outlined.Practical implications: Directions for the chill wheel cooling system design are indicated.Originality/value: New method for determining contact resistance through variable heat transfer coefficient is introduced which takes into account physical properties of the casting material, process parameters and contact time/length between metal melt/ribbon and substrate and enables cooling rate prediction before the experiment execution. In the case of continuous casting, heat balance of the melt-spinning process is calculated and influence of the chill wheel cooling mode on cooling rate of metallic ribbon is analyzed.
Simulation of Multifilament Semicrystalline Polymer Fiber Melt-Spinning
Young-Pyo Jeon,Christopher L. Cox
Journal of Engineered Fibers and Fabrics , 2009,
Abstract: The goal of this effort is to provide an accurate simulation of multifilament fiber melt spinning, applicable for a wide range of material and process conditions. For ease of use, the model should run on a standard laptop or desktop computer in reasonable time (one hour or less). Most melt spinning models simulate the formation of a single filament, with little or no attention given to multifilament effects. Available multifilament simulations are primarily limited to Newtonian constitutive models for the polymer flow. We present a multifilament simulation based on the flow-enhanced crystallization approach of Shrikhande et al. [J. Appl. Polym. Sci., 100, 2006, 3240-3254] combined with a variant on the multifilament quench model of Zhang, et al. [J. Macromol. Sci. Phys., 47, 2007, 793-806]. We demonstrate the versatility of this model by applying it to isotactic polypropylene and polyethylene terephthalate, under a variety of process conditions.
Microstructure of ZrNiSn-base Half-Heusler Thermoelectric Materials Prepared by Melt-spinning  [PDF]
YU Cui, ZHU Tie-Jun, XIAO Kai, JIN Ji, SHEN Jun-Jie, YANG Sheng-Hui, ZHAO Xin-Bing
无机材料学报 , 2010, DOI: 10.3724/sp.j.1077.2010.00569
Abstract: Thermoelectric materials Zr(Hf)NiSn(Sb) alloys were prepared by levitation melting followed by melt-spinning to refine the microstructure, and then consolidated by spark plasma sintering for the property measurements. XRD analysis showed that the half-Heusler phases were obtained. The microstructures of the melt spun thin ribbons were studied by the scanning electron microscope and transmission electron microscope. The thin ribbons were in the size of a few hundreds nanometers which didn't grow too much during the sintering process. Nanocrystals were found in the crystal grains. The carrier concentration increased for the melt-spinning samples compared with the levitation melting samples, indicating that the nanocrystals were metallic. The increasing boundary scattering after melt-spinning made the lattice thermal conductivity decrease.
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