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In order to study laser-matter interactions on the Megajoule Laser facility, CEA needs to synthesize metallic foams with specific characteristics. The goal is to realize in a millimetric scale, metallic foam samples with a density lower than 10% of the bulk material and structured with a micrometric porosity (< 5 µm). To obtain these specific materials, CEA has developed an innovative process using the Contact Glow Discharge Electrolysis technique (CGDE) to grow metallic foam at a cathode surface. Under specific conditions and when a critical potential is applied, an uniform and stable gaseous envelop is formed around the immersed cathode in the ionic solution. Due to the high electrical field at the electrode surface, channels plasma are formed with the propagation of streamers between the cathode and the liquid surface. When the electrical arcs meet the liquid, metallic cations are reduced to form metallic strands with a bush-like shape. In these conditions, several metallic foams can be obtained (Au, Cu, Pt, Ag, alloys …) with a relative density of 0.5%. All strands of the foam are about 100 nm in diameter and are interconnected together to form porosity about 1 µm. This very fast process allows synthesizing 1 mm thick of foam in less than 10 seconds. This presentation explains the patented process offering a versatile technological way to synthesize microporous and ultra-light metal foams. A new phenomenomenological process is proposed to describe the different steps that take place from plasma formation to nano-foam growth. The structure (see picture below) of the foams (several m²/g, and ultra-low density ~ 0.5% relative density) could be used for many applications such as battery, fuel cells, hydrogen trapping, catalysis... Figure 1 |
