Nanostructured Ni—Cd powders.

Autor: Pugachev, V. M., Zaharov, Yu. A., Valnyukova, A. S., Dodonov, V. G., Datiy, K. A.
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Zdroj: Russian Chemical Bulletin; Jun2018, Vol. 67 Issue 6, p1018-1025, 8p
Abstrakt: Nanostructured powders of the Ni—Cd system containing 0-50 mol.% Cd obtained by co-reduction of metal salts from aqueous solutions by hydrazine were studied by X-ray diffraction, optical emission spectroscopy and electron microscopy. The reduction leads to formation of polycrystalline particles of 100-350 nm size, consisting of 10-20 nm crystallites. Phase composition of the powders is substantially different from that predicted by equilibrium on the phase diagram. Instead of a two-phase area consisting of Ni—NiCd intermetallide, other phase states are observed. If the system contains up to 6% Cd, the XRD data indicates the presence of a single-phase solid solution with a face centred cubic (fcc)-structure. The increase in the Cd content to ~40% is accompanied by formation of the NiCd5 intermetallide phase, along with a solid solution. In the 40-50% Cd content range, the main phases are NiCd5, as well as a fcc-phase containing up to 18% Cd and characterized by a strong broadening of the diffraction maxima caused by the presence of 2-3 nm crystallites. Furthermore, the system of such composition contains a previously unknown non-stoichiometric phase based on Ni3Cd, having a similar to Cu3Au structure. The results serve to clarify compositions of reduction products and the character of the structural-phase transformations of the intermediate hydroxides and metal products during the reduction process. Based on the obtained data, we proposed a formation scheme for the phases that are unconventional for the studied composition region of the Ni-Cd system. It has been concluded that the main factors determining formation of the reduction products are particle nanoscale dimensionality and occurrence of the reduction process far from equilibrium. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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