Nanoporous Metals by Alloy Corrosion: Formation and Mechanical Properties

Abstract

Nanoporous metals prepared by the corrosion of an alloy can take the form of monolithic, millimeter-sized bodies containing approximately 1015 nanoscale ligaments per cubic millimeter. The ligament size can reach down to the very limits of stability of nanoscale objects. The processes by which nanoporous metals are formed have continued to be fascinating, even though their study in relation to surface treatment, metal refinement, and failure mechanisms can be traced back to ancient times. In fact, the prospect of using alloy corrosion as a means of making nanomaterials for fundamental studies and functional applications has led to a revived interest in the process. The quite distinct mechanical properties of nanoporous metals are one of the focus points of this interest, as relevant studies probe the deformation behavior of crystals at the lower end of the size scale. Furthermore, the coupling of bulk stress and strain to the forces acting along the surface of nanoporous metals provide unique opportunities for controlling the mechanical behavior through external variables such as the electrical or chemical potentials.

Nanoporous Gold—Testing Macro-scale Samples to Probe Small-scale Mechanical Behavior

“…[38] For NPG, results obtained with several small-scale testing schemes suggest m ≈ −0.6, [5] yet tests on macroscopic samples [7] indicate the stronger size dependence m ≈ −1 (see also below). The Gibson-Ashby scaling relations implicitly require that the pore space is empty and so carries no load.…”

“…[5]) that the apparent local stiffness at the ligament scale may depend on L. Mameka et al, [34] considering the bending stiffness as the relevant parameter for the elastic response at the ligament level, present a simple argument for the impact of surface excess elasticity on the apparent Y loc . The dependence of the surface stress on tangential strain defines a surface excess elastic constant, and an intuitively accessible parameterization of this constant is via an apparent excess of material at the surface, in other words an apparent thickening of the ligaments by the radius increment τ .…”

“…Yet, studies of the mechanical behavior of NPG more often than not use the Gibson-Ashby laws to obtain benchmarks to which the actual findings can be compared. Several of these studies even either report or even presuppose agreement, [2,5,7,12,13,16] while others discuss corrections. [22,23,36,37] Thus, even though it is now widely realized that the Gibson-Ashby scaling relations are not designed for network structures such as NPG, these relations remain indispensable as a starting point for discussing scaling in that material.…”

“…Nanoporous metals, and specifically those made by dealloying, thus provide a materials base for exploring the simultaneous impact of porosity and of nanoscale structuring on mechanical behavior. [2][3][4][5] As the most extensively studied dealloying-made material, nanoporous gold (NPG) exhibits a perfectly conventional polycrystalline microstructure with tens or hundreds of micron grain size. The highly ordered crystal lattice of each grain is porous, and the prevalent microstructural feature is the uniformly interconnected *Corresponding author.…”

Capillary condensation in deformable mesopores: wetting versus nanomechanics

“…The broad variety of practical applications has spurred the development of many different mesoporous materials such as glasses and ceramics [8] or various carbon materials [9]. Very recently, even metallic systems have been synthesized [10]. A broad variety of adsorbates ranging from classical polar and nonpolar fluids [11,12] to quantum fluids [13] have been investigated.…”