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      in Environment

      MIT-led teams win National Science Foundation grants to research sustainable materials

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      Three MIT-led teams are among 16 nationwide to receive funding awards to address sustainable materials for global challenges through the National Science Foundation’s Convergence Accelerator program. Launched in 2019, the program targets solutions to especially compelling societal or scientific challenges at an accelerated pace, by incorporating a multidisciplinary research approach.

      “Solutions for today’s national-scale societal challenges are hard to solve within a single discipline. Instead, these challenges require convergence to merge ideas, approaches, and technologies from a wide range of diverse sectors, disciplines, and experts,” the NSF explains in its description of the Convergence Accelerator program. Phase 1 of the award involves planning to expand initial concepts, identify new team members, participate in an NSF development curriculum, and create an early prototype.

      Sustainable microchips

      One of the funded projects, “Building a Sustainable, Innovative Ecosystem for Microchip Manufacturing,” will be led by Anuradha Murthy Agarwal, a principal research scientist at the MIT Materials Research Laboratory. The aim of this project is to help transition the manufacturing of microchips to more sustainable processes that, for example, can reduce e-waste landfills by allowing repair of chips, or enable users to swap out a rogue chip in a motherboard rather than tossing out the entire laptop or cellphone.

      “Our goal is to help transition microchip manufacturing towards a sustainable industry,” says Agarwal. “We aim to do that by partnering with industry in a multimodal approach that prototypes technology designs to minimize energy consumption and waste generation, retrains the semiconductor workforce, and creates a roadmap for a new industrial ecology to mitigate materials-critical limitations and supply-chain constraints.”

      Agarwal’s co-principal investigators are Samuel Serna, an MIT visiting professor and assistant professor of physics at Bridgewater State University, and two MIT faculty affiliated with the Materials Research Laboratory: Juejun Hu, the John Elliott Professor of Materials Science and Engineering; and Lionel Kimerling, the Thomas Lord Professor of Materials Science and Engineering.

      The training component of the project will also create curricula for multiple audiences. “At Bridgewater State University, we will create a new undergraduate course on microchip manufacturing sustainability, and eventually adapt it for audiences from K-12, as well as incumbent employees,” says Serna.

      Sajan Saini and Erik Verlage of the MIT Department of Materials Science and Engineering (DMSE), and Randolph Kirchain from the MIT Materials Systems Laboratory, who have led MIT initiatives in virtual reality digital education, materials criticality, and roadmapping, are key contributors. The project also includes DMSE graduate students Drew Weninger and Luigi Ranno, and undergraduate Samuel Bechtold from Bridgewater State University’s Department of Physics.

      Sustainable topological materials

      Under the direction of Mingda Li, the Class of 1947 Career Development Professor and an Associate Professor of Nuclear Science and Engineering, the “Sustainable Topological Energy Materials (STEM) for Energy-efficient Applications” project will accelerate research in sustainable topological quantum materials.

      Topological materials are ones that retain a particular property through all external disturbances. Such materials could potentially be a boon for quantum computing, which has so far been plagued by instability, and would usher in a post-silicon era for microelectronics. Even better, says Li, topological materials can do their job without dissipating energy even at room temperatures.

      Topological materials can find a variety of applications in quantum computing, energy harvesting, and microelectronics. Despite their promise, and a few thousands of potential candidates, discovery and mass production of these materials has been challenging. Topology itself is not a measurable characteristic so researchers have to first develop ways to find hints of it. Synthesis of materials and related process optimization can take months, if not years, Li adds. Machine learning can accelerate the discovery and vetting stage.

      Given that a best-in-class topological quantum material has the potential to disrupt the semiconductor and computing industries, Li and team are paying special attention to the environmental sustainability of prospective materials. For example, some potential candidates include gold, lead, or cadmium, whose scarcity or toxicity does not lend itself to mass production and have been disqualified.

      Co-principal investigators on the project include Liang Fu, associate professor of physics at MIT; Tomas Palacios, professor of electrical engineering and computer science at MIT and director of the Microsystems Technology Laboratories; Susanne Stemmer of the University of California at Santa Barbara; and Qiong Ma of Boston College. The $750,000 one-year Phase 1 grant will focus on three priorities: building a topological materials database; identifying the most environmentally sustainable candidates for energy-efficient topological applications; and building the foundation for a Center for Sustainable Topological Energy Materials at MIT that will encourage industry-academia collaborations.

      At a time when the size of silicon-based electronic circuit boards is reaching its lower limit, the promise of topological materials whose conductivity increases with decreasing size is especially attractive, Li says. In addition, topological materials can harvest wasted heat: Imagine using your body heat to power your phone. “There are different types of application scenarios, and we can go much beyond the capabilities of existing materials,” Li says, “the possibilities of topological materials are endlessly exciting.”

      Socioresilient materials design

      Researchers in the MIT Department of Materials Science and Engineering (DMSE) have been awarded $750,000 in a cross-disciplinary project that aims to fundamentally redirect materials research and development toward more environmentally, socially, and economically sustainable and resilient materials. This “socioresilient materials design” will serve as the foundation for a new research and development framework that takes into account technical, environmental, and social factors from the beginning of the materials design and development process.

      Christine Ortiz, the Morris Cohen Professor of Materials Science and Engineering, and Ellan Spero PhD ’14, an instructor in DMSE, are leading this research effort, which includes Cornell University, the University of Swansea, Citrine Informatics, Station1, and 14 other organizations in academia, industry, venture capital, the social sector, government, and philanthropy.

      The team’s project, “Mind Over Matter: Socioresilient Materials Design,” emphasizes that circular design approaches, which aim to minimize waste and maximize the reuse, repair, and recycling of materials, are often insufficient to address negative repercussions for the planet and for human health and safety.

      Too often society understands the unintended negative consequences long after the materials that make up our homes and cities and systems have been in production and use for many years. Examples include disparate and negative public health impacts due to industrial scale manufacturing of materials, water and air contamination with harmful materials, and increased risk of fire in lower-income housing buildings due to flawed materials usage and design. Adverse climate events including drought, flood, extreme temperatures, and hurricanes have accelerated materials degradation, for example in critical infrastructure, leading to amplified environmental damage and social injustice. While classical materials design and selection approaches are insufficient to address these challenges, the new research project aims to do just that.

      “The imagination and technical expertise that goes into materials design is too often separated from the environmental and social realities of extraction, manufacturing, and end-of-life for materials,” says Ortiz. 

      Drawing on materials science and engineering, chemistry, and computer science, the project will develop a framework for materials design and development. It will incorporate powerful computational capabilities — artificial intelligence and machine learning with physics-based materials models — plus rigorous methodologies from the social sciences and the humanities to understand what impacts any new material put into production could have on society. More

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      in Environment

      Exploring the nanoworld of biogenic gems

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      A new research collaboration with The Bahrain Institute for Pearls and Gemstones (DANAT) will seek to develop advanced characterization tools for the analysis of the properties of pearls and to explore technologies to assign unique identifiers to individual pearls.

      The three-year project will be led by Admir Mašić, associate professor of civil and environmental engineering, in collaboration with Vladimir Bulović, the Fariborz Maseeh Chair in Emerging Technology and professor of electrical engineering and computer science.

      “Pearls are extremely complex and fascinating hierarchically ordered biological materials that are formed by a wide range of different species,” says Mašić. “Working with DANAT provides us a unique opportunity to apply our lab’s multi-scale materials characterization tools to identify potentially species-specific pearl fingerprints, while simultaneously addressing scientific research questions regarding the underlying biomineralization processes that could inform advances in sustainable building materials.”

      DANAT is a gemological laboratory specializing in the testing and study of natural pearls as a reflection of Bahrain’s pearling history and desire to protect and advance Bahrain’s pearling heritage. DANAT’s gemologists support clients and students through pearl, gemstone, and diamond identification services, as well as educational courses.

      Like many other precious gemstones, pearls have been human-made through scientific experimentation, says Noora Jamsheer, chief executive officer at DANAT. Over a century ago, cultured pearls entered markets as a competitive product to natural pearls, similar in appearance but different in value.

      “Gemological labs have been innovating scientific testing methods to differentiate between natural pearls and all other pearls that exist because of direct or indirect human intervention. Today the world knows natural pearls and cultured pearls. However, there are also pearls that fall in between these two categories,” says Jamsheer. “DANAT has the responsibility, as the leading gemological laboratory for pearl testing, to take the initiative necessary to ensure that testing methods keep pace with advances in the science of pearl cultivation.”

      Titled “Exploring the Nanoworld of Biogenic Gems,” the project will aim to improve the process of testing and identifying pearls by identifying morphological, micro-structural, optical, and chemical features sufficient to distinguish a pearl’s area of origin, method of growth, or both. MIT.nano, MIT’s open-access center for nanoscience and nanoengineering will be the organizational home for the project, where Mašić and his team will utilize the facility’s state-of-the-art characterization tools.

      In addition to discovering new methodologies for establishing a pearl’s origin, the project aims to utilize machine learning to automate pearl classification. Furthermore, researchers will investigate techniques to create a unique identifier associated with an individual pearl.

      The initial sponsored research project is expected to last three years, with potential for continued collaboration based on key findings or building upon the project’s success to open new avenues for research into the structure, properties, and growth of pearls. More

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      in Energy

      A new way to assess radiation damage in reactors

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      A new method could greatly reduce the time and expense needed for certain important safety checks in nuclear power reactors. The approach could save money and increase total power output in the short run, and it might increase plants’ safe operating lifetimes in the long run.

      One of the most effective ways to control greenhouse gas emissions, many analysts argue, is to prolong the lifetimes of existing nuclear power plants. But extending these plants beyond their originally permitted operating lifetimes requires monitoring the condition of many of their critical components to ensure that damage from heat and radiation has not led, and will not lead, to unsafe cracking or embrittlement.

      Today, testing of a reactor’s stainless steel components — which make up much of the plumbing systems that prevent heat buildup, as well as many other parts — requires removing test pieces, known as coupons, of the same kind of steel that are left adjacent to the actual components so they experience the same conditions. Or, it requires the removal of a tiny piece of the actual operating component. Both approaches are done during costly shutdowns of the reactor, prolonging these scheduled outages and costing millions of dollars per day.

      Now, researchers at MIT and elsewhere have come up with a new, inexpensive, hands-off test that can produce similar information about the condition of these reactor components, with far less time required during a shutdown. The findings are reported today in the journal Acta Materiala in a paper by MIT professor of nuclear science and engineering Michael Short; Saleem Al Dajani ’19 SM ’20, who did his master’s work at MIT on this project and is now a doctoral student at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia; and 13 others at MIT and other institutions.

      The test involves aiming laser beams at the stainless steel material, which generates surface acoustic waves (SAWs) on the surface. Another set of laser beams is then used to detect and measure the frequencies of these SAWs. Tests on material aged identically to nuclear power plants showed that the waves produced a distinctive double-peaked spectral signature when the material was degraded.

      Short and Al Dajani embarked on the process in 2018, looking for a more rapid way to detect a specific kind of degradation, called spinodal decomposition, that can take place in austenitic stainless steel, which is used for components such as the 2- to 3-foot wide pipes that carry coolant water to and from the reactor core. This process can lead to embrittlement, cracking, and potential failure in the event of an emergency.

      While spinodal decomposition is not the only type of degradation that can occur in reactor components, it is a primary concern for the lifetime and sustainability of nuclear reactors, Short says.

      “We were looking for a signal that can link material embrittlement with properties we can measure, that can be used to estimate lifetimes of structural materials,” Al Dajani says.

      They decided to try a technique Short and his students and collaborators had expanded upon, called transient grating spectroscopy, or TGS, on samples of reactor materials known to have experienced spinodal decomposition as a result of their reactor-like thermal aging history. The method uses laser beams to stimulate, and then measure, SAWs on a material. The idea was that the decomposition should slow down the rate of heat flow through the material, that slowdown would be detectable by the TGS method.

      However, it turns out there was no such slowdown. “We went in with a hypothesis about what we would see, and we were wrong,” Short says.

      That’s often the way things work out in science, he says. “You go in guns blazing, looking for a certain thing, for a great reason, and you turn out to be wrong. But if you look carefully, you find other patterns in the data that reveal what nature actually has to say.”

      Instead, what showed up in the data was that, while a material would usually produce a single frequency peak for the material’s SAWs, in the degraded samples there was a splitting into two peaks.

      “It was a very clear pattern in the data,” Short recalls. “We just didn’t expect it, but it was right there screaming at us in the measurements.”

      Cast austenitic stainless steels like those used in reactor components are what’s known as duplex steels, actually a mixture of two different crystal structures in the same material by design. But while one of the two types is quite impervious to spinodal decomposition, the other is quite vulnerable to it. When the material starts to degrade, the difference shows up in the different frequency responses of the material, which is what the team found in their data.

      That finding was a total surprise, though. “Some of my current and former students didn’t believe it was happening,” Short says. “We were unable to convince our own team this was happening, with the initial statistics we had.” So, they went back and carried out further tests, which continued to strengthen the significance of the results. They reached a point where the confidence level was 99.9 percent that spinodal decomposition was indeed coincident with the wave peak separation.

      “Our discussions with those who opposed our initial hypotheses ended up taking our work to the next level,” Al Dajani says.

      The tests they did used large lab-based lasers and optical systems, so the next step, which the researchers are hard at work on, is miniaturizing the whole system into something that can be an easily portable test kit to use to check reactor components on-site, reducing the length of shutdowns. “We’re making great strides, but we still have some way to go,” he says.

      But when they achieve that next step, he says, it could make a significant difference. “Every day that your nuclear plant goes down, for a typical gigawatt-scale reactor, you lose about $2 million a day in lost electricity,” Al Dajani says, “so shortening outages is a huge thing in the industry right now.”

      He adds that the team’s goal was to find ways to enable existing plants to operate longer: “Let them be down for less time and be as safe or safer than they are right now — not cutting corners, but using smart science to get us the same information with far less effort.” And that’s what this new technique seems to offer.

      Short hopes that this could help to enable the extension of power plant operating licenses for some additional decades without compromising safety, by enabling frequent, simple and inexpensive testing of the key components. Existing, large-scale plants “generate just shy of a billion dollars in carbon-free electricity per plant each year,” he says, whereas bringing a new plant online can take more than a decade. “To bridge that gap, keeping our current nukes online is the single biggest thing we can do to fight climate change.”

      The team included researchers at MIT, Idaho National Laboratory, Manchester University and Imperial College London in the UK, Oak Ridge National Laboratory, the Electric Power Research Institute, Northeastern University, the University of California at Berkeley, and KAUST. The work was supported by the International Design Center at MIT and the Singapore University of Technology and Design, the U.S. Nuclear Regulatory Commission, and the U.S. National Science Foundation. More

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      in Energy

      Mining for the clean energy transition

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      In a world powered increasingly by clean energy, drilling for oil and gas will gradually give way to digging for metals and minerals. Today, the “critical minerals” used to make electric cars, solar panels, wind turbines, and grid-scale battery storage are facing soaring demand — and some acute bottlenecks as miners race to catch up.

      According to a report from the International Energy Agency, by 2040, the worldwide demand for copper is expected to roughly double; demand for nickel and cobalt will grow at least sixfold; and the world’s hunger for lithium could reach 40 times what we use today.

      “Society is looking to the clean energy transition as a way to solve the environmental and social harms of climate change,” says Scott Odell, a visiting scientist at the MIT Environmental Solutions Initiative (ESI), where he helps run the ESI Mining, Environment, and Society Program, who is also a visiting assistant professor at George Washington University. “Yet mining the materials needed for that transition would also cause social and environmental impacts. So we need to look for ways to reduce our demand for minerals, while also improving current mining practices to minimize social and environmental impacts.”

      ESI recently hosted the inaugural MIT Conference on Mining, Environment, and Society to discuss how the clean energy transition may affect mining and the people and environments in mining areas. The conference convened representatives of mining companies, environmental and human rights groups, policymakers, and social and natural scientists to identify key concerns and possible collaborative solutions.

      “We can’t replace an abusive fossil fuel industry with an abusive mining industry that expands as we move through the energy transition,” said Jim Wormington, a senior researcher at Human Rights Watch, in a panel on the first day of the conference. “There’s a recognition from governments, civil society, and companies that this transition potentially has a really significant human rights and social cost, both in terms of emissions […] but also for communities and workers who are on the front lines of mining.”

      That focus on communities and workers was consistent throughout the three-day conference, as participants outlined the economic and social dimensions of standing up large numbers of new mines. Corporate mines can bring large influxes of government revenue and local investment, but the income is volatile and can leave policymakers and communities stranded when production declines or mineral prices fall. On the other hand, “artisanal” mining operations are an important source of critical minerals, but are hard to regulate and subject to abuses from brokers. And large reserves of minerals are found in conservation areas, regions with fragile ecosystems and experiencing water shortages that can be exacerbated by mining, in particular on Indigenous-controlled lands and other places where mine openings are deeply fraught.

      “One of the real triggers of conflict is a dissatisfaction with the current model of resource extraction,” said Jocelyn Fraser of the University of British Columbia in a panel discussion. “One that’s failed to support the long-term sustainable development of regions that host mining operations, and yet imposes significant local social and environmental impacts.”

      All these challenges point toward solutions in policy and in mining companies’ relationships with the communities where they work. Participants highlighted newer models of mining governance that can create better incentives for the ways mines operate — from full community ownership of mines to recognizing community rights to the benefits of mining to end-of-life planning for mines at the time they open.

      Many of the conference speakers also shared technological innovations that may help reduce mining challenges. Some operations are investing in desalination as alternative water sources in water-scarce regions; low-carbon alternatives are emerging to many of the fossil fuel-powered heavy machines that are mainstays of the industry; and work is being done to reclaim valuable minerals from mine tailings, helping to minimize both waste and the need to open new extraction sites.

      Increasingly, the mining industry itself is recognizing that reforms will allow it to thrive in a rapid clean-energy transition. “Decarbonization is really a profitability imperative,” said Kareemah Mohammed, managing director for sustainability services at the technology consultancy Accenture, on the conference’s second day. “It’s about securing a low-cost and steady supply of either minerals or metals, but it’s also doing so in an optimal way.”

      The three-day conference attracted over 350 attendees, from large mining companies, industry groups, consultancies, multilateral institutions, universities, nongovernmental organizations (NGOs), government, and more. It was held entirely virtually, a choice that helped make the conference not only truly international — participants joined from over 27 countries on six continents — but also accessible to members of nonprofits and professionals in the developing world.

      “Many people are concerned about the environmental and social challenges of supplying the clean energy revolution, and we’d heard repeatedly that there wasn’t a forum for government, industry, academia, NGOs, and communities to all sit at the same table and explore collaborative solutions,” says Christopher Noble, ESI’s director of corporate engagement. “Convening, and researching best practices, are roles that universities can play. The conversations at this conference have generated valuable ideas and consensus to pursue three parallel programs: best-in-class models for community engagement, improving ESG metrics and their use, and civil-society contributions to government/industry relations. We are developing these programs to keep the momentum going.”

      The MIT Conference on Mining, Environment, and Society was funded, in part, by Accenture, as part of the MIT/Accenture Convergence Initiative. Additional funding was provided by the Inter-American Development Bank. More

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      in Energy

      Engineers solve a mystery on the path to smaller, lighter batteries

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      A discovery by MIT researchers could finally unlock the door to the design of a new kind of rechargeable lithium battery that is more lightweight, compact, and safe than current versions, and that has been pursued by labs around the world for years.

      The key to this potential leap in battery technology is replacing the liquid electrolyte that sits between the positive and negative electrodes with a much thinner, lighter layer of solid ceramic material, and replacing one of the electrodes with solid lithium metal. This would greatly reduce the overall size and weight of the battery and remove the safety risk associated with liquid electrolytes, which are flammable. But that quest has been beset with one big problem: dendrites.

      Dendrites, whose name comes from the Latin for branches, are projections of metal that can build up on the lithium surface and penetrate into the solid electrolyte, eventually crossing from one electrode to the other and shorting out the battery cell. Researchers haven’t been able to agree on what gives rise to these metal filaments, nor has there been much progress on how to prevent them and thus make lightweight solid-state batteries a practical option.

      The new research, being published today in the journal Joule in a paper by MIT Professor Yet-Ming Chiang, graduate student Cole Fincher, and five others at MIT and Brown University, seems to resolve the question of what causes dendrite formation. It also shows how dendrites can be prevented from crossing through the electrolyte.

      Chiang says in the group’s earlier work, they made a “surprising and unexpected” finding, which was that the hard, solid electrolyte material used for a solid-state battery can be penetrated by lithium, which is a very soft metal, during the process of charging and discharging the battery, as ions of lithium move between the two sides.

      This shuttling back and forth of ions causes the volume of the electrodes to change. That inevitably causes stresses in the solid electrolyte, which has to remain fully in contact with both of the electrodes that it is sandwiched between. “To deposit this metal, there has to be an expansion of the volume because you’re adding new mass,” Chiang says. “So, there’s an increase in volume on the side of the cell where the lithium is being deposited. And if there are even microscopic flaws present, this will generate a pressure on those flaws that can cause cracking.”

      Those stresses, the team has now shown, cause the cracks that allow dendrites to form. The solution to the problem turns out to be more stress, applied in just the right direction and with the right amount of force.

      While previously, some researchers thought that dendrites formed by a purely electrochemical process, rather than a mechanical one, the team’s experiments demonstrate that it is mechanical stresses that cause the problem.

      The process of dendrite formation normally takes place deep within the opaque materials of the battery cell and cannot be observed directly, so Fincher developed a way of making thin cells using a transparent electrolyte, allowing the whole process to be directly seen and recorded. “You can see what happens when you put a compression on the system, and you can see whether or not the dendrites behave in a way that’s commensurate with a corrosion process or a fracture process,” he says.

      The team demonstrated that they could directly manipulate the growth of dendrites simply by applying and releasing pressure, causing the dendrites to zig and zag in perfect alignment with the direction of the force.

      Applying mechanical stresses to the solid electrolyte doesn’t eliminate the formation of dendrites, but it does control the direction of their growth. This means they can be directed to remain parallel to the two electrodes and prevented from ever crossing to the other side, and thus rendered harmless.

      In their tests, the researchers used pressure induced by bending the material, which was formed into a beam with a weight at one end. But they say that in practice, there could be many different ways of producing the needed stress. For example, the electrolyte could be made with two layers of material that have different amounts of thermal expansion, so that there is an inherent bending of the material, as is done in some thermostats.

      Another approach would be to “dope” the material with atoms that would become embedded in it, distorting it and leaving it in a permanently stressed state. This is the same method used to produce the super-hard glass used in the screens of smart phones and tablets, Chiang explains. And the amount of pressure needed is not extreme: The experiments showed that pressures of 150 to 200 megapascals were sufficient to stop the dendrites from crossing the electrolyte.

      The required pressure is “commensurate with stresses that are commonly induced in commercial film growth processes and many other manufacturing processes,” so should not be difficult to implement in practice, Fincher adds.

      In fact, a different kind of stress, called stack pressure, is often applied to battery cells, by essentially squishing the material in the direction perpendicular to the battery’s plates — somewhat like compressing a sandwich by putting a weight on top of it. It was thought that this might help prevent the layers from separating. But the experiments have now demonstrated that pressure in that direction actually exacerbates dendrite formation. “We showed that this type of stack pressure actually accelerates dendrite-induced failure,” Fincher says.

      What is needed instead is pressure along the plane of the plates, as if the sandwich were being squeezed from the sides. “What we have shown in this work is that when you apply a compressive force you can force the dendrites to travel in the direction of the compression,” Fincher says, and if that direction is along the plane of the plates, the dendrites “will never get to the other side.”

      That could finally make it practical to produce batteries using solid electrolyte and metallic lithium electrodes. Not only would these pack more energy into a given volume and weight, but they would eliminate the need for liquid electrolytes, which are flammable materials.

      Having demonstrated the basic principles involved, the team’s next step will be to try to apply these to the creation of a functional prototype battery, Chiang says, and then to figure out exactly what manufacturing processes would be needed to produce such batteries in quantity. Though they have filed for a patent, the researchers don’t plan to commercialize the system themselves, he says, as there are already companies working on the development of solid-state batteries. “I would say this is an understanding of failure modes in solid-state batteries that we believe the industry needs to be aware of and try to use in designing better products,” he says.

      The research team included Christos Athanasiou and Brian Sheldon at Brown University, and Colin Gilgenbach, Michael Wang, and W. Craig Carter at MIT. The work was supported by the U.S. National Science Foundation, the U.S. Department of Defense, the U.S. Defense Advanced Research Projects Agency, and the U.S. Department of Energy. More

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      in Energy

      With new heat treatment, 3D-printed metals can withstand extreme conditions

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      A new MIT-developed heat treatment transforms the microscopic structure of 3D-printed metals, making the materials stronger and more resilient in extreme thermal environments. The technique could make it possible to 3D print high-performance blades and vanes for power-generating gas turbines and jet engines, which would enable new designs with improved fuel consumption and energy efficiency.

      Today’s gas turbine blades are manufactured through conventional casting processes in which molten metal is poured into complex molds and directionally solidified. These components are made from some of the most heat-resistant metal alloys on Earth, as they are designed to rotate at high speeds in extremely hot gas, extracting work to generate electricity in power plants and thrust in jet engines.

      There is growing interest in manufacturing turbine blades through 3D-printing, which, in addition to its environmental and cost benefits, could allow manufacturers to quickly produce more intricate, energy-efficient blade geometries. But efforts to 3D-print turbine blades have yet to clear a big hurdle: creep.

      In metallurgy, creep refers to a metal’s tendency to permanently deform in the face of persistent mechanical stress and high temperatures. While researchers have explored printing turbine blades, they have found that the printing process produces fine grains on the order of tens to hundreds of microns in size — a microstructure that is especially vulnerable to creep.

      “In practice, this would mean a gas turbine would have a shorter life or less fuel efficiency,” says Zachary Cordero, the Boeing Career Development Professor in Aeronautics and Astronautics at MIT. “These are costly, undesirable outcomes.”

      Cordero and his colleagues found a way to improve the structure of 3D-printed alloys by adding an additional heat-treating step, which transforms the as-printed material’s fine grains into much larger “columnar” grains — a sturdier microstructure that should minimize the material’s creep potential, since the “columns” are aligned with the axis of greatest stress. The researchers say the method, outlined today in Additive Manufacturing, clears the way for industrial 3D-printing of gas turbine blades.

      “In the near future, we envision gas turbine manufacturers will print their blades and vanes at large-scale additive manufacturing plants, then post-process them using our heat treatment,” Cordero says. “3D-printing will enable new cooling architectures that can improve the thermal efficiency of a turbine, so that it produces the same amount of power while burning less fuel and ultimately emits less carbon dioxide.”

      Cordero’s co-authors on the study are lead author Dominic Peachey, Christopher Carter, and Andres Garcia-Jimenez at MIT, Anugrahaprada Mukundan and Marie-Agathe Charpagne of the University of Illinois at Urbana-Champaign, and Donovan Leonard of Oak Ridge National Laboratory.

      Triggering a transformation

      The team’s new method is a form of directional recrystallization — a heat treatment that passes a material through a hot zone at a precisely controlled speed to meld a material’s many microscopic grains into larger, sturdier, and more uniform crystals.

      Directional recrystallization was invented more than 80 years ago and has been applied to wrought materials. In their new study, the MIT team adapted directional recrystallization for 3D-printed superalloys.

      The team tested the method on 3D-printed nickel-based superalloys — metals that are typically cast and used in gas turbines. In a series of experiments, the researchers placed 3D-printed samples of rod-shaped superalloys in a room-temperature water bath placed just below an induction coil. They slowly drew each rod out of the water and through the coil at various speeds, dramatically heating the rods to temperatures varying between 1,200 and 1,245 degrees Celsius.

      They found that drawing the rods at a particular speed (2.5 millimeters per hour) and through a specific temperature (1,235 degrees Celsius) created a steep thermal gradient that triggered a transformation in the material’s printed, fine-grained microstructure.

      “The material starts as small grains with defects called dislocations, that are like a mangled spaghetti,” Cordero explains. “When you heat this material up, those defects can annihilate and reconfigure, and the grains are able to grow. We’re continuously elongating the grains by consuming the defective material and smaller grains — a process termed recrystallization.”

      Creep away

      After cooling the heat-treated rods, the researchers examined their microstructure using optical and electron microscopy, and found that the material’s printed microscopic grains were replaced with “columnar” grains, or long crystal-like regions that were significantly larger than the original grains.

      “We’ve completely transformed the structure,” says lead author Dominic Peachey. “We show we can increase the grain size by orders of magnitude, to massive columnar grains, which theoretically should lead to dramatic improvements in creep properties.”

      The team also showed they could manipulate the draw speed and temperature of the rod samples to tailor the material’s growing grains, creating regions of specific grain size and orientation. This level of control, Cordero says, can enable manufacturers to print turbine blades with site-specific microstructures that are resilient to specific operating conditions.

      Cordero plans to test the heat treatment on 3D-printed geometries that more closely resemble turbine blades. The team is also exploring ways to speed up the draw rate, as well as test a heat-treated structure’s resistance to creep. Then, they envision that the heat treatment could enable the practical application of 3D-printing to produce industrial-grade turbine blades, with more complex shapes and patterns.

      “New blade and vane geometries will enable more energy-efficient land-based gas turbines, as well as, eventually, aeroengines,” Cordero notes. “This could from a baseline perspective lead to lower carbon dioxide emissions, just through improved efficiency of these devices.”

      This research was supported, in part, by the U.S. Office of Naval Research. More

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      in Energy

      In nanotube science, is boron nitride the new carbon?

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      Engineers at MIT and the University of Tokyo have produced centimeter-scale structures, large enough for the eye to see, that are packed with hundreds of billions of hollow aligned fibers, or nanotubes, made from hexagonal boron nitride.

      Hexagonal boron nitride, or hBN, is a single-atom-thin material that has been coined “white graphene” for its transparent appearance and its similarity to carbon-based graphene in molecular structure and strength. It can also withstand higher temperatures than graphene, and is electrically insulating, rather than conductive. When hBN is rolled into nanometer-scale tubes, or nanotubes, its exceptional properties are significantly enhanced.

      The team’s results, published today in the journal ACS Nano, provide a route toward fabricating aligned boron nitride nanotubes (A-BNNTs) in bulk. The researchers plan to harness the technique to fabricate bulk-scale arrays of these nanotubes, which can then be combined with other materials to make stronger, more heat-resistant composites, for instance to shield space structures and hypersonic aircraft.

      As hBN is transparent and electrically insulating, the team also envisions incorporating the BNNTs into transparent windows and using them to electrically insulate sensors within electronic devices. The team is also investigating ways to weave the nanofibers into membranes for water filtration and for “blue energy” — a concept for renewable energy in which electricity is produced from the ionic filtering of salt water into fresh water.

      Brian Wardle, professor of aeronautics and astronautics at MIT, likens the team’s results to scientists’ decades-long, ongoing pursuit of manufacturing bulk-scale carbon nanotubes.

      “In 1991, a single carbon nanotube was identified as an interesting thing, but it’s been 30 years getting to bulk aligned carbon nanotubes, and the world’s not even fully there yet,” Wardle says. “With the work we’re doing, we’ve just short-circuited about 20 years in getting to bulk-scale versions of aligned boron nitride nanotubes.”

      Wardle is the senior author of the new study, which includes lead author and MIT research scientist Luiz Acauan, former MIT postdoc Haozhe Wang, and collaborators at the University of Tokyo.

      A vision, aligned

      Like graphene, hexagonal boron nitride has a molecular structure resembling chicken wire. In graphene, this chicken wire configuration is made entirely of carbon atoms, arranged in a repeating pattern of hexagons. For hBN, the hexagons are composed of alternating atoms of boron and nitrogen. In recent years, researchers have found that two-dimensional sheets of hBN exhibit exceptional properties of strength, stiffness, and resilience at high temperatures. When sheets of hBN are rolled into nanotube form, these properties are further enhanced, particularly when the nanotubes are aligned, like tiny trees in a densely packed forest.

      But finding ways to synthesize stable, high quality BNNTs has proven challenging. A handful of efforts to do so have produced low-quality, nonaligned fibers.

      “If you can align them, you have much better chance of harnessing BNNTs properties at the bulk scale to make actual physical devices, composites, and membranes,” Wardle says.

      In 2020, Rong Xiang and colleagues at the University of Tokyo found they could produce high-quality boron nitride nanotubes by first using a conventional approach of chemical vapor deposition to grow a forest of short, few micron-long carbon nanotubes. They then coated the carbon-based forest with “precursors” of boron and nitrogen gas, which when baked in an oven at high temperatures crystallized onto the carbon nanotubes to form high-quality nanotubes of hexagonal boron nitride with carbon nanotubes inside.

      Burning scaffolds

      In the new study, Wardle and Acauan have extend and scale Xiang’s approach, essentially removing the underlying carbon nanotubes and leaving the long boron nitride nanotubes to stand on their own. The team drew on the expertise of Wardle’s group, which has focused for years on fabricating high-quality aligned arrays of carbon nanotubes. With their current work, the researchers looked for ways to tweak the temperatures and pressures of the chemical vapor deposition process in order to remove the carbon nanotubes while leaving the boron nitride nanotubes intact.

      “The first few times we did it, it was completely ugly garbage,” Wardle recalls. “The tubes curled up into a ball, and they didn’t work.”

      Eventually, the team hit on a combination of temperatures, pressures, and precursors that did the trick. With this combination of processes, the researchers first reproduced the steps that Xiang took to synthesize the boron-nitride-coated carbon nanotubes. As hBN is resistant to higher temperatures than graphene, the team then cranked up the heat to burn away the underlying black carbon nanotube scaffold, while leaving the transparent, freestanding boron nitride nanotubes intact.
      By using carbon nanotubes as a scaffold, MIT engineers grow forests of “white graphene” that emerge (in MIT pattern) after burning away the black carbon scaffold. Courtesy of the researchersIn microscopic images, the team observed clear crystalline structures — evidence that the boron nitride nanotubes have a high quality. The structures were also dense: Within a square centimeter, the researchers were able to synthesize a forest of more than 100 billion aligned boron nitride nanotubes, that measured about a millimeter in height — large enough to be visible by eye. By nanotube engineering standards, these dimensions are considered to be “bulk” in scale.

      “We are now able to make these nanoscale fibers at bulk scale, which has never been shown before,” Acauan says.

      To demonstrate the flexibility of their technique, the team synthesized larger carbon-based structures, including a weave of carbon fibers, a mat of “fuzzy” carbon nanotubes, and sheets of randomly oriented carbon nanotubes known as “buckypaper.” They coated each carbon-based sample with boron and nitrogen precursors, then went through their process to burn away the underlying carbon. In each demonstration, they were left with a boron-nitride replica of the original black carbon scaffold.

      They also were able to “knock down” the forests of BNNTs, producing horizontally aligned fiber films that are a preferred configuration for incorporating into composite materials.

      “We are now working toward fibers to reinforce ceramic matrix composites, for hypersonic and space applications where there are very high temperatures, and for windows for devices that need to be optically transparent,” Wardle says. “You could make transparent materials that are reinforced with these very strong nanotubes.”

      This research was supported, in part, by Airbus, ANSYS, Boeing, Embraer, Lockheed Martin, Saab AB, and Teijin Carbon America through MIT’s Nano-Engineered Composite aerospace STructures (NECST) Consortium. More

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      in Energy

      Simplifying the production of lithium-ion batteries

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      When it comes to battery innovations, much attention gets paid to potential new chemistries and materials. Often overlooked is the importance of production processes for bringing down costs.

      Now the MIT spinout 24M Technologies has simplified lithium-ion battery production with a new design that requires fewer materials and fewer steps to manufacture each cell. The company says the design, which it calls “SemiSolid” for its use of gooey electrodes, reduces production costs by up to 40 percent. The approach also improves the batteries’ energy density, safety, and recyclability.

      Judging by industry interest, 24M is onto something. Since coming out of stealth mode in 2015, 24M has licensed its technology to multinational companies including Volkswagen, Fujifilm, Lucas TVS, Axxiva, and Freyr. Those last three companies are planning to build gigafactories (factories with gigawatt-scale annual production capacity) based on 24M’s technology in India, China, Norway, and the United States.

      “The SemiSolid platform has been proven at the scale of hundreds of megawatts being produced for residential energy-storage systems. Now we want to prove it at the gigawatt scale,” says 24M CEO Naoki Ota, whose team includes 24M co-founder, chief scientist, and MIT Professor Yet-Ming Chiang.

      Establishing large-scale production lines is only the first phase of 24M’s plan. Another key draw of its battery design is that it can work with different combinations of lithium-ion chemistries. That means 24M’s partners can incorporate better-performing materials down the line without substantially changing manufacturing processes.

      The kind of quick, large-scale production of next-generation batteries that 24M hopes to enable could have a dramatic impact on battery adoption across society — from the cost and performance of electric cars to the ability of renewable energy to replace fossil fuels.

      “This is a platform technology,” Ota says. “We’re not just a low-cost and high-reliability operator. That’s what we are today, but we can also be competitive with next-generation chemistry. We can use any chemistry in the market without customers changing their supply chains. Other startups are trying to address that issue tomorrow, not today. Our tech can address the issue today and tomorrow.”

      A simplified design

      Chiang, who is MIT’s Kyocera Professor of Materials Science and Engineering, got his first glimpse into large-scale battery production after co-founding another battery company, A123 Systems, in 2001. As that company was preparing to go public in the late 2000s, Chiang began wondering if he could design a battery that would be easier to manufacture.

      “I got this window into what battery manufacturing looked like, and what struck me was that even though we pulled it off, it was an incredibly complicated manufacturing process,” Chiang says. “It derived from magnetic tape manufacturing that was adapted to batteries in the late 1980s.”

      In his lab at MIT, where he’s been a professor since 1985, Chiang started from scratch with a new kind of device he called a “semi-solid flow battery” that pumps liquids carrying particle-based electrodes to and from tanks to store a charge.

      In 2010, Chiang partnered with W. Craig Carter, who is MIT’s POSCO Professor of Materials Science and Engineering, and the two professors supervised a student, Mihai Duduta ’11, who explored flow batteries for his undergraduate thesis. Within a month, Duduta had developed a prototype in Chiang’s lab, and 24M was born. (Duduta was the company’s first hire.)

      But even as 24M worked with MIT’s Technology Licensing Office (TLO) to commercialize research done in Chiang’s lab, people in the company including Duduta began rethinking the flow battery concept. An internal cost analysis by Carter, who consulted for 24M for several years, ultimately lead the researchers to change directions.

      That left the company with loads of the gooey slurry that made up the electrodes in their flow batteries. A few weeks after Carter’s cost analysis, Duduta, then a senior research scientist at 24M, decided to start using the slurry to assemble batteries by hand, mixing the gooey electrodes directly into the electrolyte. The idea caught on.

      The main components of batteries are the positive and negatively charged electrodes and the electrolyte material that allows ions to flow between them. Traditional lithium-ion batteries use solid electrodes separated from the electrolyte by layers of inert plastics and metals, which hold the electrodes in place.

      Stripping away the inert materials of traditional batteries and embracing the gooey electrode mix gives 24M’s design a number of advantages.

      For one, it eliminates the energy-intensive process of drying and solidifying the electrodes in traditional lithium-ion production. The company says it also reduces the need for more than 80 percent of the inactive materials in traditional batteries, including expensive ones like copper and aluminum. The design also requires no binder and features extra thick electrodes, improving the energy density of the batteries.

      “When you start a company, the smart thing to do is to revisit all of your assumptions  and ask what is the best way to accomplish your objectives, which in our case was simply-manufactured, low-cost batteries,” Chiang says. “We decided our real value was in making a lithium-ion suspension that was electrochemically active from the beginning, with electrolyte in it, and you just use the electrolyte as the processing solvent.”

      In 2017, 24M participated in the MIT Industrial Liaison Program’s STEX25 Startup Accelerator, in which Chiang and collaborators made critical industry connections that would help it secure early partnerships. 24M has also collaborated with MIT researchers on projects funded by the Department of Energy.

      Enabling the battery revolution

      Most of 24M’s partners are eyeing the rapidly growing electric vehicle (EV) market for their batteries, and the founders believe their technology will accelerate EV adoption. (Battery costs make up 30 to 40 percent of the price of EVs, according to the Institute for Energy Research).

      “Lithium-ion batteries have made huge improvements over the years, but even Elon Musk says we need some breakthrough technology,” Ota says, referring to the CEO of EV firm Tesla. “To make EVs more common, we need a production cost breakthrough; we can’t just rely on cost reduction through scaling because we already make a lot of batteries today.”

      24M is also working to prove out new battery chemistries that its partners could quickly incorporate into their gigafactories. In January of this year, 24M received a grant from the Department of Energy’s ARPA-E program to develop and scale a high-energy-density battery that uses a lithium metal anode and semi-solid cathode for use in electric aviation.

      That project is one of many around the world designed to validate new lithium-ion battery chemistries that could enable a long-sought battery revolution. As 24M continues to foster the creation of large scale, global production lines, the team believes it is well-positioned to turn lab innovations into ubiquitous, world-changing products.

      “This technology is a platform, and our vision is to be like Google’s Android [operating system], where other people can build things on our platform,” Ota says. “We want to do that but with hardware. That’s why we’re licensing the technology. Our partners can use the same production lines to get the benefits of new chemistries and approaches. This platform gives everyone more options.” More