Microstructure evolution of monolithic nanoporous copper from dual-phase Al 35 atom % Cu alloy

Before uniform nanoporous structure can be achieved through chemical dealloying of dual-phase Al-Cu alloy with 35 atom % Cu in a hydrochloric acid (HCl) or sodium hydroxide (NaOH) aqueous solution under free corrosion conditions, microstructure evolution of the alloy during dealloying process in each solution is investigated and their formation mechanism is discussed. The microstructure of as-dealloyed samples was characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and high-resolution transmission electron microscopy. The experimental results show that the alloy presents remarkably different microstructure evolution characteristics during dealloying process in the acidic/alkaline corrosive environment, which can be attributed to the difference between electrochemical activities of Al in two distinct phases of the alloy. Additionally, an evidently small pore size can be obtained in the as-dealloyed samples upon dealloying in the NaOH solution compared with relatively large one formed in the HCl solution, which mainly results from the lower surface diffusivity of Cu atoms along the alloy/solution interfaces in the alkaline solution.