Pattern formation during electrochemical and liquid metal dealloying
- PDF / 3,665,859 Bytes
- 8 Pages / 585 x 783 pts Page_size
- 99 Downloads / 198 Views
uction Dealloying, described by Sieradzki and Weissmüller in the Introductory article in this issue, can be generally defined as a materials-processing method, where one component is selectively dissolved from a multicomponent alloy.1,2 During dissolution, an interfacial pattern-forming instability can occur if the remaining component (or components) are mobile along the metal–liquid interface.3,4 Rather than maintaining a planar interface, the remaining components reorganize into a threedimensionally topologically complex morphology.5 The remaining nondissolved components have the morphology of an open, porous structure with a characteristic length scale on the order of 1 nm.3,6 Dealloying has thus been used to create nanoporous metals, but bicontinuous composite materials can also be made by infiltration and solidification of a liquid.7–9 Dealloying has, for most of its history, been studied in the context of electrochemistry, where it is an important process in corrosion as well as the facile fabrication of bulk quantities of nanostructured metals.10–12 One begins with a homogeneous, single-phase alloy and immerses it in an electrolyte solution, either under free corrosion or an applied potential. One of the components must dissolve in the electrolyte, and the other components must (with a few exceptions) remain unoxidized and mobile along the metal–electrolyte interface.2,4 As a consequence, most electrochemically dealloyable systems contain a relatively noble element such as gold, platinum,
or copper—forming nanoporous gold (np-Au), or nanoporous platinum (np-Pt)—which are extremely useful for catalysis, sensing, and as model systems to study the mechanics of nanotrusses.13–27 A transformative innovation, first reported by Harrison and Wagner 50 years ago, was recently rediscovered by Kato and Wada.7,28,29 This breakthrough was that the dissolution medium does not need to be electrochemical in nature. The only requirement is selective dissolution of one component. As an example to follow this concept, we forged a TiTa alloy and immersed it in a bath of molten Cu.8,9,30 This system is chosen such that Ta and Ti form a solid solution; Ti is highly soluble in molten copper (up to 70 at.% at 1100°C); and Ta is insoluble in solid and molten copper (up to 1500°C). Upon immersion, Ti dissolves from the alloy, leaving behind porous Ta surrounded by molten Cu. A fully dense metal–metal composite is formed upon cooling, and porous Ta can be extracted if the copper is subsequently etched out—although our preference is the bicontinuous metal nanocomposite due to its superior mechanical behavior. We refer to this type of dealloying as liquid metal dealloying (LMD) to contrast it with electrochemical dealloying (ECD). LMD is an important advance because it expands the set of dealloyable systems to include components from nearly the entire periodic table. Figure 1a illustrates all of the elements that have been fabricated using ECD and LMD,
Ian McCue, Texas A&M University, USA; [email protected] Alain Karma, Northeastern Univ
Data Loading...
