Nanocrystalline metals grain size

X-ray powder diffraction measurements have revealed that the metal powders obtained by the deoxygenation of metal oxides are generally nanocrystalline. The grain size of the nickel and cobalt powders was determined by TEM to range between 6 -10 nm and 1 - 5 nm. 

The electrodeposition of metals from ionic liquids is a novel method for the production of nanocrystalline metals and alloys, because the grain size can be adjusted by varying the electrochemical parameters such as over-potential, current density, pulse parameters, bath composition and temperature and the liquids themselves. Recently, for the first time, nanocrystalline electrodeposition of Al, Fe and Al-Mn alloy has been demonstrated. 

Nanocrystalline materials have received extensive attention since they show unique mechanical, electronic and chemical properties. As the particle size approaches the nanoscale, the number of atoms in the grain boundaries increases, leading to dramatic effects on the physical properties and on the catalytic activity of the bulk material. Nowadays, there is a wide variety of methods for the preparation of nanocrystalline metals such as thermal spraying, sputter deposition, vapor deposition and electrodeposition. The electrodeposition process is commercially attractive since it can be performed at room temperature and the experimental set-up is less demanding. Furthermore, the particle size can be adjusted over a wide range by controlling the experimental parameters such as overvoltage, current density, composition, and temperature (see Chapter 8). 

In ionic liquids the situation seems to be totally different. It was surprising to us that the electrodeposition of metals and semiconductors in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide delivers nanocrystalline deposits with grain sizes varying from 10 to 200 nm for the different materials, like Si, Al, Cu, Ag and In, investigated to date. It was quite surprising in the case of Al deposition that temperature did not play a tremendous role. Between 25 and 125 °C we always got nanocrystalline Al with similar grain sizes. Similar results were obtained if the deposition was performed in tri-hexyl- tetradecylphos-phonium bis (trifluoromethylsulfonyl) amide. Maybe liquids with saturated nonaromatic cations deliver preferentially nanomaterials this is an aspect which, in our opinion, deserves further fundamental studies. 

Figures 4(a) and 4(b) show the relationship between the average grain size and the coercivity in various Fe-based nanocrystalline soft magnetic alloys prepared by crystallization of amorphous precursors (For details, see Herzer [13], Yoshizawa [31], Muller and Mattem [32], Fujii et al. [33], and Suzuki et al. [34, 35]). As shown in Fig. 4(a), the coercivity Ha of the nanocrystalline Fe-Si-B-M-Cu (M = IVa to Via metal) alloys follows the predicted D6 dependence in a D range below LO ( 30 to 40 nm for this alloy system) although the plots deviate from the predicted D6 law in the range below H0 1 A/m where the effect of grain refinement on is overshadowed by magneto-elastic and annealing induced anisotropies. Hence, the experiments are better described by Hc [a2 + where a...

Eckert J. 1995. Relationships governing the grain size of nanocrystalline metals and alloys. Nanostructured Materials. 6(1-4) 413 16. 

Zhang Z, Zhou F, Lavemia EJ (2003) On the analysis of grain size in bulk nanocrystalline materials via X-ray diflraction. Metall Mater Trans A 34A(6) 1349-1355... 

HPT has been successfully applied for microstructure refinement in metals, alloys and not long ago in composites and in semiconductors [17,18], as well as consolidation of nanopowders [7], Among new developments in HPT processing we would like to emphasize also the observation of SPD-induced nanocrystallization in initially amorphous alloys producing nanocrystalline materials with a grain size of 10-15 nm [19],... 

Large-angle X-ray powder diffraction (XRD) has been one of the most versatile techniques utilized for the structural characterization of nanocrystalline metal powders. The modern improvements in electronics, computers, and X-ray sources have allowed XRD to become an indispensable tool for identily-ing nanocrystalline phases as well as crystal size and crystal strain. The comparison of the crystallite size obtained by the XRD difffactogram using the Scherrer formula with the grain size obtained from the TEM image allows us to establish if the nanoparticles have a mono- or polycrystalline nature. 

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