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Metals 2017, 7(2), 46; doi:10.3390/met7020046

Nanoporous Microtubes via Oxidation and Reduction of Cu–Ni Commercial Wires

Department of Chemistry and NIS, University of Turin, I-10125 Turin, Italy
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Academic Editor: Houshang Alamdari
Received: 9 December 2016 / Revised: 21 January 2017 / Accepted: 29 January 2017 / Published: 7 February 2017
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Abstract

Metallic porous microtubes were obtained from commercial wires (200–250 µm diameter) of Cu-65Ni-2Fe, Cu-44Ni-1Mn and Cu-23Ni, alloys (wt. %) by surface oxidation at 1173 K in air, removal of the unoxidized core by chemical etching, and reduction in annealing in the hydrogen atmosphere. Transversal sections of the partially oxidized wires show a porous layered structure, with an external shell of CuO (about 10 μm thick) and an inner layer of NiO (70–80 μm thick). In partially oxidized Cu-44Ni-1Mn and Cu-23Ni, Cu2O is dispersed in NiO because the maximum solubility of Cu in NiO is exceeded, whereas in Cu-65Ni-2Fe, a Cu2O shell is present between CuO and NiO layers. Chemical etching removed the unoxidized metallic core and Cu2O with formation of porous oxide microtubes. Porosity increases with Cu content because of the larger amount of Cu2O in the partially oxidized wire. After reduction, the transversal sections of the metallic porous microtubes show a series of f.c.c.-(Cu,Ni) solid solutions with different compositions, due to the segregation of CuO and NiO during oxidation caused by the different diffusion coefficients of Ni and Cu in the respective oxides. Pore formation occurs at each step of the process because of the Kirkendall effect, selective phase removal and volume contraction. View Full-Text
Keywords: Cu-Ni alloy; oxidation; etching; reduction; porous material; microtube Cu-Ni alloy; oxidation; etching; reduction; porous material; microtube
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Marano, E.F.; Castellero, A.; Baricco, M. Nanoporous Microtubes via Oxidation and Reduction of Cu–Ni Commercial Wires. Metals 2017, 7, 46.

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