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Nanoporous Microtubes Obtained from a Cu-Ni Metallic Wire
Emanuele Francesco Marano,Danilo Lussana,Alberto Castellero,Marcello Baricco 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.2
Nanoporous microtubes of a nickel-copper alloy were obtained from a Cu-44Ni-1Mn (wt%) commercial 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 occurred 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. After reduction, the microtube shows a composition gradient from the inner wall (almost pure nickel) to the outer wall (almost pure copper). 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.
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Hossein Asghari Shivaee,Alberto Castellero,Paola Rizzi,Paola Tiberto,Hamid-Reza Madaah-Hosseini,Marcello Baricco 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.4
In this study, the kinetics of nanocrystallization of amorphous Fe73.5Si13.5B9Nb3Cu1 (F1) and Fe77Si11B9Nb2.4Cu0.6(F2) alloys is investigated. The microstructure and magnetic properties of the nanocrystalline alloys are compared. The crystallization temperature of F2 alloy is shifted towards lower temperatures with respect to F1. Thus, the crystalline volume fraction and the crystalline grain size at specific annealing temperature for the F2 alloy are higher than for the F1 alloy, accounting for the higher coercive force of F2 alloy with respect to the one of F1 alloy. According to isoconversional methods, the activation energy for crystallization is variable as a function of transformed fraction because of the continuous changes in chemical composition during the transformation. Mean values of 350 and 290 kJ/mol are obtained for F1 and F2, respectively. Microstructural observations confirm that minor changes in chemical composition affect the kinetics and final microstructure of the nanocrystalline alloy, that determine the observed magnetic properties.
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