Fractal structures of highly-porous metals and alloys at the nanoscale

• Highly-porous metals are obtained via low-temperature reduction of metal complexes.
• Open interconnected fractal porosity is observed in the resulting metals and alloys.
• Alloy composition is preserved throughout the reduction process of bimetallic systems.
• The metal complex reduction method to yield metals and alloys is extended and generalized.
• The resulting porous metals and alloys are crystalline and consist of nanocrystallites.

The fabrication of nanoporous alloys with uniform compositions has been a synthetic challenge in the last two decades. Fine nanoscale porosity in metals is usually obtained by destructive dealloying of bulk cast alloys, whereas nanoscale bimetallic alloys have been prepared by a rather sophisticated method, namely, the reduction of bimetallic ionic complexes. However, the physical properties of these alloys have not been fully elucidated and the generality of the methods remains limited. We show that chemical reduction of metal complexes at a low but constant temperature preserves alloy composition and produces a highly-porous metallic material (>90% porosity) with open interconnected fractal porosity extended down to a nanoscale. These porous metallic materials that consist of nanocrystallites can be obtained for a wide range of binary systems and pure metals (binary systems: Pt3Ru2, Co2Pt3, CoPt, Co2Pt, IrPt, Rh2Ru, Rh3Ru2, RhRu, Ir2Ru, IrRu; pure metals: Co, Ru, Rh, Pd, Ag, Ir, Pt). Geometrical analysis of several nanoporous metals and alloys suggests that the three-dimensional structure of these materials may be represented by a mathematical fractal model.

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