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Metals 2012, 2(3), 265-273; doi:10.3390/met2030265
Article

Preparation and Characterization of Directionally Freeze-cast Copper Foams

1,2
 and
1,*
1 Department of Material Science and Engineering, Northwestern University, Evanston, IL 60208, USA 2 Institute for Applied Materials, Karlsruhe Institute of Technology, Karlsruhe 76131, Germany
* Author to whom correspondence should be addressed.
Received: 2 June 2012 / Revised: 9 July 2012 / Accepted: 30 July 2012 / Published: 9 August 2012
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Abstract

Because of their excellent thermal and electric conductivities, copper foams are ideally suited for applications such as heat exchangers, catalyst supports and EMI-shields. Here, we demonstrate the preparation of copper with ~80% aligned, elongated, interconnected pores via directional freeze casting, a well established processing technique for porous ceramics. First, an aqueous slurry of 40−80 nm cupric oxide powders was directionally solidified, resulting in a preform consisting of elongated, aligned dendrites of pure ice separated by interdendritic ice walls with high oxide powder content. Oxide rather than metallic nanometric particles are used, as the latter would oxidize rapidly and uncontrollably when suspended in the aqueous solution used during directional casting. The preforms were then freeze-dried to sublimate the ice and sintered in a hydrogen-bearing atmosphere to reduce the copper oxide to metallic copper particles and densify these copper particles. Microstructural analysis of the copper foams shows that three types of porosities are present: (i) aligned, elongated pores replicating the ice dendrites created during the freeze-casting process; (ii) micro-porosity in the partially sintered copper walls separating the elongated pores; and (iii) cracks in these copper walls, probably created because of shrinkage associated with the reduction of the oxide powders.
Keywords: porous materials; metallic foams; copper; copper oxide; freeze-casting; chemical reduction; sintering; oriented pores porous materials; metallic foams; copper; copper oxide; freeze-casting; chemical reduction; sintering; oriented pores
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Ramos, A.I.C.; Dunand, D.C. Preparation and Characterization of Directionally Freeze-cast Copper Foams. Metals 2012, 2, 265-273.

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