Metal Foams May Be Effective for Fire and Heat Protection

Composite metal foams (CMFs) are already recognized for effective impact resistance and radiation shielding. Now, researchers have shown that CMFs may be better heat insulators and fire protection than the base metals from which they’re made.

Capitalizing on the fact that heat travels more slowly through air than through metal, researchers at North Carolina State University developed lightweight CMFs that may be effective in insulating against high heat. Their character gives them potential for use for storing and transporting hazardous materials, explosives and other heat sensitive materials, the research team says.

The metal foam consists of hollow spheres of carbon steel, stainless steel or titanium embedded in a metallic matrix made of alloys of aluminum, steel, or other metals.

Afsaneh Rabiei, professor of mechanical and aerospace engineering, described two technologies the research team developed for manufacturing the CMFs.

One is based on casting a low melting point matrix material, such as aluminum, around hollow spheres made of a material with a higher melting point, such as steel. This creates aluminum-steel CMFs, for example, Rabiei says.

The other technique is based on sintering, or baking, the matrix powder around prefabricated hollow spheres. “This creates CMFs such as steel-steel, which consist of steel hollow spheres in a steel matrix,” he says.

Rabiei says another advantage the research found is that CMFs expand at a fairly constant rate when exposed to high heat. This compares to a much more rapid expansion of conventional bulk metals and alloys such as stainless steel.