Researchers found that new composite metal foams (CMFs) have excellent thermal protection compared to plain metal, turning armor piercing bullet into dust.

North Carolina State University researchers studied lightweight CMFs and found that the air pockets inside the metal foams are effective heat blockers. This makes CMFs a promising tool for use in transport and storage of hazardous materials, explosives, nuclear elements, and other heat sensitive materials. It could also prove beneficial for space exploration.

Mechanical and aerospace engineering professor at NC State Afsaneh Rabiei shared that this property can be attributed to the hollow spheres in the CMFs, which is composed of stainless steel, carbon steel, or titanium implanted in a metallic matrix of aluminum, metallic alloys, and steel.

"The presence of air pockets inside CMF make it so effective at blocking heat, mainly because heat travels more slowly through air than through metal," said Rabiei.

The researchers employed two technologies in creating CMFs. One is by making a cast of low melting point matrix material using aluminum to surround the hollow spheres, which has a higher melting point like steel. Another technique is by having prefabricated hollow spheres covered with baked matrix powder, which creates a steel-steel CMF.

To prove the heat and fire protection capability of CMFs, the researchers subjected samples of 2.5-inch x 2.5-inch steel-steel CMF that have 0.75 inch thickness to an 800 degree Celsius (1,472 degrees Fahrenheit) fire for 30 minutes. The researchers monitored the material and measured the length of time to reach the other side of the sample. The stainless steel sample only took 4 minutes to breach the 800 degree mark but for the CMF, it took 8 minutes to reach the same temperature.

According to Rabiei, CMFs thermal conductivity could prevent accidents from leading to explosions.

The research also found that CMFs made up of stainless steel has an 80 percent less expansion at 200 degrees Celsius. The expansion during high heat exposure is constant compared to conventional bulk metals and alloys.

Researchers concluded that CMF has excellent thermal insulation, good flame retardant performance, and superior thermal stability when compared to conventional materials available in the market today.

In Rabiei's previous study published in the journal Radiation Physics and Chemistry, lightweight metal foams have previously been proven to efficiently block neutron radiation, gamma rays, and X-ray, which can pave the way for more studies that focus on nuclear safety, healthcare applications, and space exploration.



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