Figure 4From: Low-density nanoporous iron foams synthesized by sol-gel autocombustionPhotographs before and after combustion. (a) Photograph of the gel in a quartz tube before combustion. (b) Photograph of the porous iron foam after combustion. The volume expanded greatly compared with the corresponding gel before combustion. The color is silver gray, and the foam can be attracted by a magnet.Back to article page