Study On The Dealloying Of Mg-Cu Based Alloys And The Formation Of Nanoporous Copper

In the present work, it has been found that nanoporous Cu can be fabricated through chemical or electrochemical dealloying of rapidly solidified Mg-Cu alloys. The experimental results of chemical dealloying of these Mg-Cu alloys show that nanoporous Cu can be obtained by the dealloying of the four Mg-Cu alloys (Mg67Cu33, Mg60Cu40, Mg50Cu50 and Mg4oCu6o) in a 5 wt.% HCl aqueous solution, except for the Mg33Cu67 alloy, which is composed of a single MgCu2 phase. Moreover, uniform, bicontinuous ligament-channel nanostructures can be obtained from whether the single-phase Mg-Cu alloy composed of Mg2Cu phase or the two-phase alloy composed of Mg2Cu and MgCu2 phase. However, the results of electrochemical dealloying performed in a 0.2 M NaCl aqueous solution show that all the Mg-Cu alloys can be dealloyed into nanoporous Cu. For a given Mg-Cu alloy, the ligament size of nanoporous Cu obtained by chemical dealloying is different from that fabricated by electrochemical dealloying. Besides, the electrochemical tests show that the electrochemical activities of the starting Mg-Cu alloys are related to both alloy composition and phase constitution. In addition, both the chemical and electrochemical dealloying results demonstrate that the dealloying mechanism of the Mg2Cu phase is quite different from that of the MgCu2 phase. In comparison, the dealloying of MgCu2 phase is more difficult and complicated than that of Mg2Cu phase. Furthermore, the less noble Mg2Cu phase shows a significant promoting effect on the dealloying of the more noble MgCu2 phase.A small amount of Pd elements added into the Mg50Cu50 alloy will greatly influence the phase constitution of the alloys. Both the rapidly solidified Mg50Cu45Pd5 and Mg50Cu40Pd10 alloys have been dealloyed in the 5 wt.% HC1 aqueous solution. The XRD and SEM results show that the Mg50Cu45Pd5 alloy can be completely dealloyed with forming a nanoporous Cu-Pd alloy. However, the TEM and HRTEM results show that the Mg50Cu40Pd10 alloy has been partially dealloyed into a composite structure with the undealloyed MgPd phase and newly formed nanoporous Cu-Pd alloy. The ligament size of nanoporous Cu-Pd alloy obtained from the Mg-Cu-Pd alloy is much smaller than that of nanoporous Cu fabricated through chemical dealloying of the Mg50Cu50 alloy, which has been verified by the SEM and TEM images. It is obvious that the phase constitution and microstructure of the as-dealloyed Mg50Cu45Pd5 and Mg50Cu40Pd10 alloys are quite different. In addition, the electro-catalytic experiments demonstrate that the as-dealloyed Mg-Cu-Pd alloys show superior catalytic activities towards electro-oxidation of methanol and ethanol.