Copper Surfaces with Bimodal Nanoporosity by Microstructural Length Scale Controlled Dealloying of a Hypereutectic Al-Cu
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https://doi.org/10.1007/s11837-020-04391-2 2020 The Minerals, Metals & Materials Society
SURFACE ENGINEERING: APPLICATIONS FOR ADVANCED MANUFACTURING
Copper Surfaces with Bimodal Nanoporosity by Microstructural Length Scale Controlled Dealloying of a Hypereutectic Al-Cu Alloy T. SONG1,2 1.—Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne, Australia. 2.—e-mail: [email protected]
Copper (Cu) surfaces with bimodal nanoporosity can be used for a variety of applications. This research shows that bimodal nanoporous Cu surfaces can be fabricated by dealloying of an as-cast hypereutectic alloy Al75Cu25 (at.%) alloy, which solidifies as pre-eutectic Al2Cu (micrometre-scaled) and eutectic lamella of a-Al/Al2Cu (nanoscaled). The bimodal nanoporous Cu surface is a result of a microstructural length scale controlled dealloying process: In the beginning, the micrometre-scaled Al2Cu acts as a cathode enabling the preferential dissolution of a-Al (anode) for larger pores to form. Afterwards, the nanosize effect of a-Al overrides the intrinsic difference in electrochemical potential allowing for subsequent simultaneous dealloying leading to finer pores. The assessment of the in situ Synchrotron XRD data of the formation of bimodal nanoporous Cu surfaces revealed a two-stage kinetic process, closely related to the formation of bimodal pores during the microstructural length scale controlled dealloying process. The underlying rationales and implications are discussed.
INTRODUCTION Dealloying is a unique low-cost flexible fabrication process for nanoporous metal surfaces for a variety of essential applications.1–3 For example, nanoporous metal (e.g. Cu,4 Sn5) surfaces made by dealloying have been well recognized as multifunctional electrode surfaces for lithium-ion batteries (LIBs).6,7 They are also effective heterogeneous catalyst materials benefiting from their high surface area, high density of low-coordinated sites on the ligament surface and unsupported character.8,9 Bimodal or hierarchical nanoporous metal surfaces can offer distinctive attributes (e.g. superhydrophobicity,10 effective transport properties,11 etc.) compared with nanoporous metal surfaces with one length scale of porosity. In this regard, the dealloying method has recently been used to fabricate such novel bimodal or hierarchical nanoporous metal surfaces, which have imparted enhanced or novel properties to the porous metals.12–14 For instance, a dealloying-fabricated hierarchical nanoporous Au (Received July 15, 2020; accepted September 14, 2020)
surface boosted the charge transport by > 100 times compared with single nanoporous Au.12 However, the capabilities of using dealloying to fabricate bimodal or hierarchical nanoporous metal surfaces remain largely unexplored. Phases with different compositions and dissimilar electrochemical properties can result in different dealloyed surface microstructures. Dealloying of a bespoke multi-phased precursor alloy thus meets one of the basic principles for producing a poro
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