Figure 4.

Photographs 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.

Hua et al. Nanoscale Research Letters 2012 7:129   doi:10.1186/1556-276X-7-129
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