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

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.