Fe-Pt alloys

The magnetization of Pd-rich and Pt-rich Fe-Pd, Co-Pd, and Fe-Pt alloys indicate ferromagnetic Co-Co and Fe-Fe interactions typical of case (d), with definite contributions from the solvent atoms, especially from Pd (101,137,138,381). Crangle (138) tentatively concluded that jiFe = 2.8 and for c > 0.1, mp[Pg.330]

Fe/Pt alloys are an important class of materials in permanent magnetic applications because of their large uniaxial magnetocrystalline anisotropy [Xu 7 x 10 J/m j [170] and good chemical stability. As the magnetic stability of individual particles scales with the anisotropy constant, K, and the particle volume, V, small Fe/Pt... 

The tendency of monodisperse nanocrystals to arrange into ordered three-dimensional arrays extending to a few microns has been noticed [117]. Careful tuning of crystallization conditions have yielded crystallites of micrometer dimensions consisting of AU55 nanocrystals and Fe-Pt alloy nanocrystals (4.5 nm) [118, 119]. However, it was observed that the nanocrystal arrangement in all the above crystallites was polymorphous. It is believed that such crystallites, consisting of ordered nanocrystals, could prove to be the best candidates to study the collective properties of an ensemble of nanocrystals. 

Fe—Pt Alloys Because of the wide application on the information recording density of materials, these types of alloys are being studied a lot recently. 

The catalytic activity of Cu-Fe-Pt ternary alloy was investigated using an electrochemical mediod in a polymer electrolyte fuel cell by [2000Shi]. It was established that the electrode prepared using a Cu-Fe-Pt alloy catalyst showed higher cell performance dian unalloyed Pt. 

Brief detals of some studies of materials properties in Cu-Fe-Pt alloys are given in Table 3. 

Thermal Properties. Tables 3.1-212- 3.1-215,3.1-233, and 3.1-234 [1.217,217] provide selected data of thermal conductivity and thermal expansion. In the disordered state the Fe—Pt alloy system exhibits a negative thermal expansion coefficient at room temperature near FesPt (Invar effect) [1.281,282],... 

Colloids of alloys have been made by the chemical reduction of the appropriate salt mixture in the solution phase. Thus, Ag-Pd and Cu-Pd colloids of varying composition have been prepared by alcohol reduction of mixtures of silver nitrate or copper oxide with palladium oxide (Vasan and Rao 1995). Fe-Pt alloy nanocrystals have been made by thermal decomposition of the Fe and Pt acetylac-etonates in high-boiling organic solvents (Sun et al. 2000). Au-Ag alloy nanocrystals have been made by co-reduction of silver nitrate and chloroauric acid with sodium borohydride (Sandhyarani et al. 2000 He et al. 2002). 

Intermetallic compounds with a certain formula and crystal structure are thermodynamically more stable than the disordered solid solution with the same element ratio and exhibit different electrocatalytic activities and durabilities. Annealing can drive the transformation from disordered alloys to ordered intermetallic compounds. In the example of Fe-Pt-alloy BMNCs, Fe atoms and Pt atoms distribute randomly in face-center-cubic (FCC) Fe-Pt and in order in face-center-tetragonal (FCT) Fe-Pt. FCC Fe-Pt NCs could transform to FCT Fe-Pt during thermal treatment and the ORR activity and durability inaeased after this transformation [14]. A similar phenomenon was also found in surface-dealloyed Pt-Co alloy NCs as catalyst of ORR [15]. 

Fig. 6.10 (a) TEM and HRTEM images of Pt-Ag alloy nanowires formed by oriented coalescence of Pt-Ag crystallites along the [111] direction. Modified with permission from ref. [37]. (b, top) Scheme showing the reversed micelle formed by OM in the synthesis of Fe-Pt-aUoy nanowires and (b, bottom) TEM and HRTEM images of Fe-Pt-alloy nanowires. Modified with permission from ref. [32]... 

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