Study finds metal foam handles heat better than steel
by Staff Writers
Raleigh NC (SPX) Apr 01, 2016
A new study from North Carolina State University researchers finds that novel light-weight composite metal foams (CMFs) are significantly more effective at insulating against high heat than the conventional base metals and alloys that they're made of, such as steel. The finding means the CMF is especially promising for use in storing and transporting nuclear material, hazardous materials, explosives and other heat-sensitive materials, as well as for space exploration.
"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," says Afsaneh Rabiei, a professor of mechanical and aerospace engineering at NC State and corresponding author of a paper on the work.
The composite metal foam consists of metallic hollow spheres - made of materials such as carbon steel, stainless steel or titanium - embedded in a metallic matrix made of steel, aluminum or metallic alloys.
"We have developed two technologies for manufacturing CMFs," Rabiei says.
"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. 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."
In one test, researchers exposed samples of 2.5 inch by 2.5 inch steel-steel CMF that were 0.75 inches thick to a fire with an average flame temperature of 800 degrees Celsius for a period of 30 minutes on one side, and monitored the material to see how long it would take for the heat to reach the opposite side of the sample.
For a piece of bulk stainless steel with the same dimensions as the CMF sample, it took only four minutes to reach 800 degrees Celsius through the entire thickness of the sample. But it took eight minutes for the steel-steel CMF to reach the same temperature.
"We already knew the CMFs are light-weight materials with outstanding high-velocity impact resistance, and effective radiation shielding, now we know that it can withstand high heat," Rabiei says. "This difference in thermal conductivity means that the use of composite metal foams could help avoid circumstances where accidents can lead to explosions."
The researchers also found that the composite metal foam made entirely of stainless steel expands 80 percent less than bulk stainless steel at 200 degrees Celsius - and the differential increases at higher temperatures.
Another noteworthy advantage is that the composite metal foam expands at a fairly constant rate when exposed to high heat - whereas conventional bulk metals and alloys such as stainless steel expand more rapidly as temperature increases.
"Our findings suggest that CMF can offer extremely good thermal insulation, superior thermal stability, and excellent flame retardant performances as compared to commercially available materials such as stainless steel," Rabiei says.
The paper, "Experimental and computational studies on the thermal behavior and fire retardant properties of composite metal foams," is published in the International Journal of Thermal Sciences. Lead author of the paper is Shuo Chen, a former Ph.D. student at NC State. The paper was co-authored by Jacob Marx, a Ph.D. student at NC State.
North Carolina State University
Space Technology News - Applications and Research
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.