Porous Metals Formed by Leaching Mn–Ni Alloys

Several Mn–Ni alloys having more than 50 at. % Mn were prepared, and their phase microstructures were examined using optical microscopy, electron microprobe analysis, and X-ray diffraction. These alloys were leached in concentrated acetic acid aqueous solutions. The resulting nanoporous materials were characterized using optical microscopy, element composition analysis, and liquid nitrogen physisorption. Three alloy compositions were studied in detail. The first alloy containing ∼57 at. % Mn was only leachable near the surface. The second alloy containing ∼86 at. % Mn was readily leachable in concentrated acetic acid aqueous solution. Butyronitrile hydrogen reaction was performed over the resulting porous catalyst. The third alloy containing ∼73 at. % Mn was strong, nonbrittle, and did not deteriorate over more than 25+ years of observation. When this alloy was leached in concentrated acetic acid aqueous solution for up to 7 days, a nanoporous brick-like microstructure was produced that is extremely strong, nonbrittle, and lightweight with a low overall density. This material should find uses in applications that require strong, lightweight materials. When leached for 14 days, enough of the manganese atoms were removed that the microstructure had transitioned to a powdery macroporous material.