Scientists discovered that when it comes to bullet proof vests and protective gear, new composite metal foams (CMFs) can provided better thermal protection compared to regular metal, where these foams can transform a speeding bullet into dust. 

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In this new study, researchers from the North Carolina State University investigated the lightweight properties of CMFs and revealed that the air pockets that are found inside the metal foams are apparently also effective in blocking heat. CMFs can become the next generation protection tool for transporting and storing hazardous materials and weapons, including explosives and even nuclear substances, along with heat sensitive materials. This material can also become a useful tool for space missions. 

According to mechanical and aerospace engineering professor, Afsaneh Rabiei from the North Carolina State University, this material possesses a unique property that involves hollow spheres that are made of stainless and carbon steel, where titanium is implanted inside the core of the steel, aluminum and metal alloys.

Rabiei says that the presence of these air pockets inside the CMF material is apparently very effective in blocking heat since heat travels slowly through air compared to metal.

In order to create CMF technology, researchers utilized two techniques in producing this state of the art material. One method is to create a cast of low melting point matrix material with the aluminum to coat the aluminum spheres which had a higher melting point similar to steel. Another technique is to prefabricate hollow spheres that are coated in baked matrix powder that can create a steel to steel CMF.

In their experiments, the CMFs were tested for heat and fire protective capabilities using 2.5 inch by 2.5 inch steel to steel CMF that possesses 0.75 inch thickness where it was exposed to a flame with temperatures of 1,472 degrees Fahrenheit for a span of 30 minutes. Researchers then observed how the flame would pierce and melt through the CMF and steel samples on the other side. 

The results revealed that the stainless steel sample only went through four minutes to surpass the 800 degree mark, however, the CMF withstood the intense heat for twice as long at eight minutes, under the same conditions.

Rabiei says that this crucial thermal conductivity of the CMFs can lead to further prevention of explosions by accident. New findings also reveal that CMFs that ae composed of stainless steel which cannot expand by 80 percent more when exposed to 200 degrees Celsius. This constant expansion during high heat exposure in conventional bulk metals and alloys. 

This new study concludes that CMF materials possess excellent thermal insulation and can lessen the spread of heat throughout the material including efficient thermal stability as opposed to conventional materials that are commercially available today.

Apart from this, lightweight metal foams are also proven by Rabiei's prior research that they can also effectively block neutron radiation, gamma rays and X-rays that can lead to more preventive measures from radiation exposure in healthcare, military and space missions.