Ni-based amorphous alloys

Ni based amorphous alloy containing Pd in low concentration seems to be a good candidate for hydrocarbon oxidation as both metals are active in oxidation reactions [8]. In the present work from the possible Ni-based metal alloys the Ni5oNb50 composition has been selected as we have good deal of experience in its preparation. We replaced part of Nb by Pd and used Pd2Ni5oNb4g amorphous alloy ribbons as starting material for the oxidation of xylene. The latter reaction has been selected as a model reaction for the oxidation of unbumt hydrocarbons in automobile exlraust gases. 

Initial studies on electrocatalysis for fuel cell application using amorphous alloys were related to the oxygen evolution reaction (OER) [131,132], Ni-based amorphous alloys have a significant contribution to the development of materials for application in fuel cells due to their high stability in alkaline medium, relative low overpotential, low cost, and high corrosion resistance. The synthesis of the alloys is relatively simple. The catalyst can be obtained via the mechanical alloy technique, where the metallic elements are placed in a planetary ball mill for several hours, at the desired ratio. An important observation is that the as-synthesized catalyst does not display significant catalytic activity as compared to the crystalline material. An acid treatment with HE or HF-HNO3 is required for activation of the material surface [133,134],... 

Yamaura S, Kim HY, Kimura H, Inoue A, Arata Y, Thermal stabilities and discharge capacities of melt-spun Mg-Ni-based amorphous alloys . Journal of Alloys and Compounds, 2002 339 230-235. 

Dolan, M., Dave, N., Morpeth, L. et al. (2009) Ni-based amorphous alloy membranes for hydrogen separation at 400°C. Journal of Membrane Science, 326, 549-555. 

Fig. 4..3-20a,b Magnetostriction Ag of FeCo-based and FeNi-based amorphous alloys depending on Co and Ni Content (a) (FeCo)8oB2o [3.18], (b) (FeNi)goB2o [3.12, 18]... 

It is shown in sect. 3.1 that Mg-based amorphous alloys are obtained in Mg-Ni—R and Mg-Cu-R and that glass formation is independent of the kind of R element. It is important to know the influence of the atomic size of R on the Vickers hardness (H ) of Mg-R-M amorphous alloys. Figure 75 shows the change in of the amorphous Mg65Cu2sRio alloys with the kind of R element, together with the data of their atomic radii (S.G. Kim 1992). Although exceptional values are observed only for Eu and Yb, which also have significantly different atomic sizes, there is a tendency for to increase from about 180 for R=La to about 310 for the R element with the smallest atomic radius. 

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

Fig. 3.67 Changes in corrosion rates of amorphous Fe-, Co- and Ni-base alloys measured in I N HCl at room temperature as a function of alloy chromium content "...

Similarly, a number of amorphous alloys based on Fe-Zr, Ni-Zr, Co-Zr, Ni-Nb, have not shown any increase in activity over that expected for the mechanical mixture of the crystalline components [571]. For Ni-Nb the overpotential has even increased. Only Cu-Ti alloys have shown apparent synergetic effects, but the results of Machida et al. [89] (cf. Fig. 32) should also be taken into account. Jorge et al. [152] have observed higher activity for the amorphous form of Cu-Ti alloys, but they have attributed it to the preferential dissolution of Ti in the amorphous sample under cathodic load, with formation of a relatively porous Cu layer. The same effect was obtained more rapidly by means of HF etching [89,152]. 

Amorphous metals can be prepared in a wide variety of stable and metastable compositions with all catalyti-cally relevant elements. This synthetic flexibility and the isotropic nature of the amorphous state with no defined surface orientations and no defect structure (as no long-range ordering exists) provoked the search for their application in catalysis [21]. The drastic effect of an average statistical mixture of a second metal component to a catalytically active base metal was illustrated in a model experiment of CO chemisorption on polycrystalline Ni which was alloyed by Zr as a crystalline phase and in the amorphous state. As CO... 

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