The Elements of Innovation Discovered
The Elements of Innovation Discovered
Metal Tech News – January 3, 2024
Graduate students Evan Willing (left) and Tyler Dabney set up equipment to apply a coating via cold spray in Professor Kumar Sridharan's Cold Spray Laboratory.
From left to right: Engineer Jeremiah Kirch, postdoctoral researcher Mykola Ialovega, and assistant scientist Marcos Xavier Navarro-Gonzalez, who worked on the implementation of tantalum coatings as a plasma-facing material for the WHAM device, which is pictured in the background.
On the coattails of mankind's breakthrough in fusion technology, the University of Wisconsin-Madison is preemptively preparing a technology that could further stabilize the potential energy of a man-made micro-sun with a spray coating technology that could simultaneously maintain temperature integrity while also extracting the very fuel of a star – hydrogen.
"The fusion community is urgently looking for new manufacturing approaches to economically produce large plasma-facing components in fusion reactors," said Mykola lalovega, a postdoctoral researcher in nuclear engineering physics at UW-Madison and lead author of a paper published recently in the journal Physica Scripta. "Our technology shows considerable improvements over current approaches. With this research, we are the first to demonstrate the benefits of using cold spray coating technology for fusion applications."
Using a cold spray to layer a coating of tantalum, a metal known to withstand high temperatures, on stainless steel, the researchers tested their formula in extreme conditions to mimic similar conditions to that of a fusion reactor, and what they found was extremely promising.
Further, experimentation discovered that their material was exceptionally good at trapping hydrogen particles.
"We discovered that cold spray tantalum coating absorbs much more hydrogen than bulk tantalum because of the unique microstructure of the coating," said Kumar Sridharan, a professor of nuclear engineering and engineering physics and materials science and engineering.
Over the last decade, Sridharan's research group has been exploring cold spray technology for the nuclear energy community by implementing it through multiple applications related to existing fission reactors.
"The simplicity of the cold spray process makes it very practical for applications," he added.
Fission reactors, which basically split an atom and harness the ensuing explosive energy from that separation, differ from fusion devices, in which plasma – an ionized hydrogen gas – is heated to extremely high temperatures, and atomic particles essentially collide and fuse instead.
This fusion process produces excess energy, as in basic physics, no two objects can occupy the same space; therefore, the excess "mass," so to speak, is let off as energy. However, in existing models and calculations, some hydrogen ions are lost in the process.
"These hydrogen neutral particles cause power losses in the plasma, which makes it very challenging to sustain a hot plasma and have an effective small fusion reactor," said lalovega, who also works in the research group of Oliver Schmitz, a professor of nuclear engineering and engineering physics.
This loss is essentially what led the researchers to create a new surface for plasma-facing reactor walls –to capture the excess hydrogen particles.
In nature, tantalum is often found alongside its twin element, niobium. Though it is difficult to distinguish the nearly identical properties of these two elements, in the workplace, one of these critical twin metals typically dons a hard hat and work boots in the construction and energy industries, while you are more likely to find the other working in the high-tech sector.
"The leading use of niobium is in the production of high-strength steel alloys used in pipelines, transportation infrastructure, and structural applications," the United States Geological Survey penned in a 2018 report on the indispensable twins. "Electronic capacitors are the leading use of tantalum for high-end applications, including cell phones, computer hard drives, and such implantable medical devices as pacemakers."
Although niobium and tantalum generally take differing career paths, they have a common origin story due to the shared traits of these nearly identical metals.
"Niobium and tantalum are transition metals that are almost always found together in nature because they have very similar physical and chemical properties," the U.S. Geological Survey wrote in a 2018 paper on the twin metals.
Biologically inert, tantalum sets itself apart from its twin with an exceptional capacity to store and release energy, a property that sets its usage toward more technological ventures than mechanical.
Because tantalum is so good at storing and releasing energy, capacitors and resistors made with this transition metal can be exceptionally small. This is crucial in the shrinking of modern electronics, such as smartphones, hearing aids, personal computers, and automobile components.
Tantalum oxides are also used to make lighter-weight glass camera lenses that produce a brighter image.
To add to its resume of incredible properties, tantalum is also inherently good at absorbing hydrogen – and the UW-Madison team believed creating a tantalum coating using a cold spray would boost its hydrogen-trapping abilities even more.
Creating a cold spray coating is much like using a can of spray paint. Typically consisting of propelling particles of the material at high velocity onto a surface, upon impact, the particles flatten like clay and spread to coat the entire surface, all while preserving the nanoscale boundaries between the coated particles.
It was this boundary that the researchers found facilitated the trapping of hydrogen particles.
lalovega conducted experiments on the coated material at facilities at Aix Marseille University in France and Forschungszentrum Jülich GmbH in Germany.
During these experiments, he found that when he heated the material to a higher temperature, it expelled the trapped hydrogen particles without modifying the coatings – a process that essentially regenerates the material so it can be used once more.
"Another big benefit of the cold spray method is that it allows us to repair reactor components on site by applying a new coating," said lalovega. "Currently, damaged reactor components often need to be removed and replaced with a completely new part, which is costly and time consuming."
The researchers plan to use their new material in the Wisconsin HTS Axisymmetric Mirror (WHAM).
The experimental device is under construction near Madison, Wisconsin, and will serve as a prototype for a future next-generation fusion power plant that UW-Madison spinoff Realta Fusion aims to develop.
Housed in the Physical Sciences Laboratory, the WHAM experiment is a partnership between UW-Madison, Massachusetts Institute of Technology, and Commonwealth Fusion Systems.
"Creating a refractory metal composite with these features of well-controlled hydrogen handling combined with erosion resistance and general material resilience is a breakthrough for the design of plasma devices and fusion energy systems," said Schmitz. "The prospect of changing the alloy and including other refractory metals to enhance the composite for nuclear applications is particularly exciting."
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