For more than a quarter century, the University of Nebraska has been doing pioneering engineering work using femtosecond lasers, and now a team led by College of Engineering professors is using those lasers to blaze new trails that reach far into outer space.
From the use of Nebraska Research Institute funds to purchase its first femtosecond laser in 1987, the College of Engineering and Electrical Engineering Professor Dennis Alexander have been on the leading edge of the use those ultrashort-pulsed lasers to perform laser-induced spectroscopy (LIBS) and to functionalize materials.
But only recently, through an interdisciplinary effort between two of the college’s departments, are UNL professors starting to heat up things in hopes of making life in outer space even cooler and more efficient.
The team – led by Alexander, Mechanical and Materials Engineering Professor George Gogos, MME Assistant Professor Sidy Ndao, EE Research Assistant Professor Troy Anderson and EE post-doctoral research assistant Craig Zuhlke – has secured a $563,131 NASA Nebraska EPSCoR (Experimental Program to Stimulate Competitive Research) grant and about $250,000 in other funding to create functionalized metallic surfaces that can be used to help with thermal management systems in space applications.
The group also includes MME Chair and Professor Jeff Shield, MME Professor Joe Turner and Assistant Professors Benjamin Terry and Lucia Fernandez-Ballester, EE Professor Ned Ianno, CSE Professor Jitender Deogun, 10 graduate students and eight undergraduate students.
“In general, we’ve been one of the world’s leaders in the use of femtosecond lasers for LIBS technology,” Alexander said, noting that technology is being used on Mars rovers to analyze soil samples. “A lot of people do not know that we were pioneering this type of work. Because of NRI funding, we were out on the forefront of femtosecond laser technology before many other institutions were.”
Immediately after its purchase, Alexander said, the primary use of the femtosecond laser was for creating nanoparticles and for LIBS research. Eventually, with the purchase of more lasers, a new path of study emerged: functionalization of metallic materials – basically, treating a surface with a laser to change the makeup of microstructures and nanostructures, thus giving the metal entirely different and, sometimes, desirable properties.
Some of these layers, Gogos said, are as small as one-fifth the diameter of a human hair.
“In these (functionalization) processes, we basically mimic what’s going on in nature, which creates almost all surfaces to have micro- and nanoscale surface features. But we can now functionalize metallic surfaces to have micro- and nanoscale surface features for specific functionality, just like nature does with many surfaces,” Alexander said.
“Before our way of functionalizing these surfaces, many researchers and industry would put coatings and polymers on things, but they’re not very permanent, especially at high temperatures. The coatings also break down under ultraviolet light. It’s not that many of these polymers that other people have made haven’t been wonderful, like Teflon on pans. But we all know Teflon comes off our cooking pans.
“The beauty of what we do, when we functionalize a metallic surface, the altered surface material is exactly the same as what you start out with. Because of that, the functionalized surfaces are much more permanent than polymer-type coatings that people have been applying.”
When the researchers functionalized stainless steel pans, they noticed that not only did water boil much more quickly than in an untreated pans, but also that more and smaller bubbles were created and that the bubbles rise through the water at a faster rate.
It was then that Alexander sought the help of an MME colleague who could help him conduct research on the heat-transfer properties associated with these new surfaces. It also led to the creation of the Center for Electro-Optics and Functionalized Surfaces (CEFS), of which Alexander is the director.
“That’s when we brought in Dr. Gogos,” Alexander said. “The idea was to quantify scientifically what is going on here. Just a visual observation is not scientific work. It’s great PR, but it’s not what we do. We have to have scientific data about how much enhancement we are getting in the heat transfer and why it’s occurring.”
Gogos said early collaborations included proposals for grants to explore the production of hydrogen and another for studying heat transfer, which led to a recent proposal for a grant to model the heat-transfer process on those surfaces.
Alexander and his research group had been performing research on the enhancement of bubble formation by the functionalization of stainless steel electrodes used in the production of hydrogen and oxygen in electrolysis. That research was funded by a private company and the Nebraska Center for Energy Science Research (NCESR). That led to NCESR grants for studying heat transfer and modeling laser-light material interactions that create the unique structures on stainless steel surfaces.
With the addition of MME assistant professor Ndao in 2012, the team has made “great strides in showing why these processes have increased boiling efficiency,” Alexander said, “and now we are well-recognized in the scientific community for manufacturing these surfaces, and the scientific reason is increased heat transfer.”
Dr. Ned Ianno collaborates with the research group to use atomic layer deposition (ALD) to incorporate atoms of different materials into the surface structure, thereby giving it a different chemistry and increasing the potential for creating electrolysis on that surface.
“You could put down platinum on a surface, and platinum is the best electrolysis electrode you can use to produce hydrogen and oxygen from water, but solid platinum is too expensive,” Alexander said. “By using this technique to coat a stainless steel electrode, we can functionalize it even further by putting it on an atomic layer of platinum and improving the stainless steel electrode to perform like a pure platinum one.”
The team’s expertise and experience, Gogos said, led to the NASA EPSCoR grant, which will allow for the better thermal management of NASA applications by using titanium and silicon carbide in the functionalization process to improve thermal heat management during space travel.
“Right now, there’s a limit of materials and what temperature you can use them, roughly 1,200 degrees Celsius (about 2,200 degrees Fahrenheit). By elevating that temperature – say to 1,500 Celsius (about 2,700 Fahrenheit) – you are going to have a system that will be more efficient,” Gogos said.
With an increase in temperatures at which these engines can operate, there is also an increased need for ways to reject that heat and transfer it to another place. The group is also researching processes to improve heat transfer to keep other equipment, such as electronic devices, from overheating.
“It’s expected that the surfaces would help in saving energy, having better engines and making more comfortable environments for astronauts in space,” Ndao said.
The first part of the thermal-management work, Ndao said, involves the use of microchannel technology and femtosecond laser fabricated functionalized micro- and nanostructures to create a two-phase flow heat transfer, in this case the use of a liquid in a closed loop to provide cooling.
Ndao and Gogos are also working to develop a novel heat-pipe technology by using functionalized metal to not only improve the integrity of the pipe itself, but to increase the wicking capability of the liquid that flows through the pipe and the pipe’s heat-transfer performance.
This new heat-pipe technology includes walls that have nanoparticles in them that Gogos said have been shown to have “super wicking capabilities” with a transfer of liquid from areas with lower temperatures through the pipe to an area with higher temperatures.
“Ultimately, our new heat-pipe technology would have the same use as other cooling technologies,” Ndao said. “But at the same time, it is less noisy, is monolithic, has no pump, and would be more efficient and compact.”
These materials also have other applications, including use in biomedical fields. In a collaborative test involving veterinary scientists, Alexander said, the CEFS team made surfaces that “pushed” cow’s blood away. That, he said, could be beneficial in vascular surgeries and in creating devices that don’t become contaminated easily.
This venture is just the latest connection between the CEFS and NASA. Corey Kruse, one of the group’s doctoral students, earlier this year received the prestigious NASA Space Technology Research Fellowship, the first one given in Nebraska. It includes $68,000 in annual funding and is renewable for up to three years.
The research performed by this group also has an impact on Nebraska industry where the team is collaborating with companies such as Hexagon Lincoln, Li-Cor, ConAgra, and Global Functionalized Surface Technologies (GFS) to solve specific problems and advance manufacturing technology.
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