Influence of processing conditions on structures of 3D ordered macroporousmetals prepared by colloidal crystal templating

This paper presents general methods of preparing three-dimensionally ordere d macroporous (3DOM) metals or alloys via templated precipitation and subse quent chemical conversion of metal salts (acetates, oxalates) within colloi dal crystals of poly(methyl methacrylate) (PMMA) or polystyrene (PS) sphere s. Three approaches are given to prepare 3DOM metallic Ni, Co, and Fe and t he alloy Ni1-xCox: (1) calcination of the metal oxalate/template composite in a nitrogen atmosphere, (2) formation of a 3DOM metal oxide followed by r eduction in hydrogen, and (3) direct reduction of the metal oxalate/templat e composite in hydrogen. The 3DOM products obtained by these routes differ in size of the grains that compose the wall skeletons, in surface areas, an d in compositions. Method 1 leads to very small grains and high surface are as but incomplete removal of carbon with graphitic layers surrounding metal grains. Method 2, as a two-step process, leads to relatively large metal g rains, smaller surface areas, and carbon-free products. Method 3 strikes a compromise in these properties, with intermediate surface areas and small ( <2%) amounts of remaining carbon. This paper presents synthetic details, di scusses effects of the template choice (PMMA vs PS), and compares structura l features of the macroporous metals and alloys, using the results of XRD, TGA, SEM, TEM, nitrogen adsorption data, and chemical analysis.