Porous metals have been under development for nearly a century, but commercial adoption remains limited. This development has followed two primary routes: liquid state or solid state processing. Liquid state foaming introduces porosity to a liquid or semi‐solid metal, and solid state foaming introduces porosity to a metal, which is fully solid. Either method may create pores by internal gas pressure or introducing metal around a template directly control porosity. Process optimization and commercial output has been primarily related to liquid state methods, as solid state processing is often more complex, diverse, and with lower throughput. Solid state methods, however, are often more versatile and offer greater control of pore characteristics. Ongoing advancements in solid state foaming have allowed for a wide array of metals and alloys to be made porous and the three‐dimensional structure to be precisely tailored. In general, solid state processing remains limited to niche applications, often with modest dimensions (cm scale). “Traditional” solid state processes are being further refined and extended, and continuing developments to reduce cost, increase output, and control pore characteristics are likely to produce important advancements in coming years. The extensive variability of pore quantity and morphology makes solid state processes suitable, and often preferable, for an assortment of functional and structural applications, with electrodes and biomedical devices being among the most popular in current research. Various techniques for introducing porosity, the way these methods are applied, important considerations, typical outcomes, and current applications are reviewed.

Carbon nanofibers were generated over bimetallic catalysts in an atmospheric pressure chemical vapor deposition (APCVD) reactor. Catalyst compositions of Fe 30 at%, Cu and Ni 30 at% and Cu were mechanically alloyed using high-energy ball milling over durations of 4,8,12,16, and 20 h. The catalyst powders were then used to produce carbon nanofibers in ethylene and hydrogen (4:1) at temperatures of 500, 550, and 600 °C. The microstructures of the catalysts were characterized as a function of milling time as well as at deposition temperature. The corresponding carbon deposition rates were assessed and are correlated to the microstructural features of each catalyst. The milling process directly determines the performance of each catalyst toward carbon deposition, and both catalysts performed comparably to those made by traditional co-precipitation methods. Considerations in miscible and immiscible nanostructured alloy systems are discussed.

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Mechanical alloying (MA) has been and continues to be thoroughly examined for creating structural materials, but the production of catalysts is relatively rare. This is especially true for catalysts used in the production of carbon nanofibers (CNFs), a versatile material for applications such as energy storage, catalyst support, advanced composites and others. The application of MA to create CNFs presents a valuable tool in reducing their cost and complexity, and thereby may increase their commercial potential. In this study, the effects of milling duration on CNF deposition are studied by the complementary methods of X-ray diffraction, compositional mapping, electron microscopy, particle size analysis and surface area analysis. These were used to determine microstructural and macroscale evolution of the catalyst powder and its effects on the kinetics and characteristics of carbon deposition using Ni and Ni 30 at % Cu. The results have important implications for low cost catalyst production and provide general guidance on the development of catalytic materials in miscible systems.

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