Nanoporous microtubes obtained from a Cu-Ni metallic wire

Abstract

Nanoporous microtubes of a nickel-copper alloy were obtained from a Cu-44Ni-1Mn (wt.%) wire (200 µm diameter). A new synthesis method was established through three steps: 1) partial oxidation of the wire at 1173 K in air, 2) removal of the inner unoxidized core by chemical etching, 3) reduction in 10 bar hydrogen atmosphere. During oxidation, the segregation of Cu and Ni occured because of their different diffusion coefficients in the corresponding oxides. As a consequence, pores were formed by Kirkendall effect and due to selective chemical etching of the different oxides. Additional porosity formed because of volume contraction during reduction with hydrogen.The process allowed to obtain microtubes with tuneable wall thickness and inner pores around 180 ± 80 nm. The morphological features developed suggest improved capillarity properties for applications in MEMS.

Oxydation à haute température de l’alliage Cu₅₄Ni₄₅Mn₁ : analyse isotherme

“…La faible teneur du nickel dans la partie non oxydée du métal, s'explique selon Haugsrud (2001) par une oxydation interne du nickel à partir de l'oxygène issu de la dissociation du Cu2O. Cependant Marano et al (2016) affirment qu'en plus de la dissociation du Cu2O, il se produit à l'interface métal-oxyde la réaction de déplacement : Cu2O + Ni → 2Cu + NiO qui explique aussi la baisse du taux de nickel dans la phase métallique proche de l'interface métal-oxyde.…”

“…L'oxydation du cuivre et du nickel a fait l'objet de plusieurs études (Bertrand et al, 2001 ;Chevalier et al, 2005 ;Haugsrud, 2003). Compte tenu de leurs bonnes propriétés de résistance à l'oxydation, les alliages Cu-Ni ont fait l'objet de nombreux travaux ces dernières années (Marano et al, 2016 ;Jondo et al, 2008) afin de mieux appréhender les mécanismes mis en jeu et améliorer le comportement de ces alliages à l'oxydation. Les alliages Cu-Ni sont un des systèmes modèles pour l'étude des mécanismes d'oxydation à haute température (Haugsrud, 2000).…”

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

“…As shown in Ref. [23] for the Cu-44Ni sample, the broad crystallographic reflections of the Ni-rich f.c.c. solid solution can be successfully fitted by Rietveld refinement assuming the coexistence of various f.c.c.-(Cu-Ni) solid solutions with different lattice parameters, as a consequence of the continuous variation in composition along the cross section of the microtubes.…”

“…In Cu-44Ni and Cu-23Ni, the intermediate oxide layer shows a mixture of green and red pixels, indicating the coexistence of NiO and Cu2O in agreement with the corresponding XRD patterns. In the case of Cu-65Ni, Figure 4a, and Cu-44Ni, Figure 4b, between the intermediate oxide layer and the unoxidized metallic core, there is a thin red ring (Cu-rich), which has a metallic appearance when observed at the optical microscope [23]. The formation of this metallic copper layer occurs according to the reaction [29]: Figure 4a, and Cu-44Ni, Figure 4b, between the intermediate oxide layer and the unoxidized metallic core, there is a thin red ring (Cu-rich), which has a metallic appearance when observed at the optical microscope [23].…”

“…In a previous work, a simple method for the synthesis of a nanoporous metallic microtube starting from a commercial constantan (Cu-Ni alloy) wire was presented [23]. The processing route consists of the following three steps: (1) partial oxidation of the alloy; (2) chemical etching for the removal of the un-oxidized inner core; and (3) reduction of the oxides in hydrogen atmosphere.…”