Amorphous alloys mechanism

Several materials have been investigated as cathode activators. Among the most studied systems we find CuTi, CuZr, NiTi, NiZr, FeCo, NiCo. A variety of methods are available to prepare amorphous alloys [562] and, as expected, the resulting activity is largely dependent on them. Normally, amorphous phases are obtained by rapidly quenching a melt. The material can thus be obtained in the form of ribbons, but mechanical alloying by compaction is also possible [572]. The metallic components are usually alloyed with non-metallic components such as B, Si and P which stabilize the metastable non-crystalline structures. Electrodeposition is thus also a viable preparation route [573, 574],... 

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]. 

In 1979, White [3.2] observed that, by milling elemental Nb and Sn powders, the distinct X-ray diffraction peaks of the elements disappeared and typical diffuse peaks of an amorphous pattern showed up. But these samples did not show the superconducting transition temperature of vapor-quenched amorphous Nb-Sn alloys. In 1983, Koch et al. reported on the Preparation of amorphous Ni60Nb40 by mechanical alloying [3.3]. After the detection of amorphization by solid-state reaction in evaporated multilayer films by Schwarz and Johnson [3.4] (see also Chap. 2), Schwarz et al. [3.5] proposed after investigating glass formation in Ni-Ti alloys, that amorphization by mechanical alloying is also based on the solid-state reaction process. Within the last couple... 

Whereas mechanical alloying of Nd-Fe-B permanent magnets developed from amorphization studies in the Fe-Zr-B system without involving any amorphiz-ation, it will be shown in this section that amorphization by mechanical alloying is essential in the formation of new Sm-Fe-X phases, which show a high potential as novel generation of permanent magnets [3.80]. 

Besides the mechanical alloying of elemental powders, ball-milling of an intermetallic compound can also lead to amorphization, as demonstrated for several alloys [3.18, 19, 130, 131] (for more details see Chap. 2). This cannot be explained by the above statements, since in this case no composition-induced destabilization provides the driving force for an interdiffusion reaction. Amorphization by milling starting from powders of crystalline intermetallics is attributed instead to the accumulation of lattice defects - mainly the creation of antiphase boundaries - which raise the free enthalpy of the faulted intermetallic above that of the amorphous alloy. Therefore, there exists some similarity with irradiation-induced amorphization [3.20]. 

It was previously shown that rapidly solidified Al-RE and Al-TM-RE alloys (RE is rare earth metal or yttrium, TM is transition metal) have amorphous structure in relatively wide range of compositions and alloying elements [1], Similarly to rare earth metals and Y, Sc belongs to the IIIB group of the Periodic Table of Elements, but we have found no data on the influence of Sc on the formation of amorphous structure in A1 alloys in the literature. On the other hand, Sc is known for a many-sided improving action on many crystalline A1 alloys [2], The aim of this work was to investigate the effect of Sc on the structure and mechanical properties (hardness) of rapidly solidified binary Al-Sc alloys as well as of Al-Ce-Sc and Al-Ni-Ce-Sc amorphous alloys. 

Hydrogen is an excellent candidate as an efficient and inexpensive energy carrier in the future because it is recyclable, nonpolluting, and available in practically unlimited supply. Since hydrogen can be produced by the electrolysis of water, the search for suitable electrodes is important. Because amorphous alloys possess high mechanical strength and superior corrosion resistance, as well as a defect-free homogeneous structure, they are attractive as electrode materials. 

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