Hierarchical‐porous copper foams by a combination of sponge replication and freezing techniques

Abstract

Open-porous copper foams with additional strut porosity are manufactured by two different manufacturing routes. The first is based on the Schwarzwalder sponge replication technique. The second method is a combination of Schwartzwalder sponge replication and freezing technique in which an additional strut porosity is generated inside the struts of the sponge-replicated foams by freezing at 20 C for 24 h and subsequent sublimation. Thermal processing of both types of foams is conducted at 500 and 900 C for 6 h in a hydrogen-containing atmosphere to reduce copper oxides and to facilitate the sintering process of the copper powder particles. Despite significant shrinkage of both foam series after thermal processing, hollow struts and lamellar pores keep their shape and do not collapse. The influences of the additional lamellar pores and thermal processing temperature on the cellular structure, porosity, specific surface area, yield strength, absorbed energy, and thermal conductivity are studied. The additional strut porosity generated by the freezing step significantly increases the specific surface area of the copper foams by a factor of 2 in comparison to the sponge replicated foams.