MIT researchers team up with leaders from the metals and minerals industry to envision a more sustainable future.
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Assistant Professor of Materials Science and Engineering Elsa A. Olivetti [standing, right] shares a summary of a breakout session on disposal and recovery challenges for metals and minerals with participants in the Metals & Minerals for the Environment (MME) initiative’s first public Symposium on May 11 at MIT. Photo, Davide Ciceri.

Metals and minerals form the base of our society, with diverse applications infiltrating all corners of our lives, including agriculture, infrastructure, transportation and information technology. As populations grow, and demand for metals and minerals rises, enhancing the sustainability of the sector is a goal for many companies, communities and policymakers.

To contribute to this, on May 11-12, 2017, MIT launched the Metals & Minerals for the Environment (MME) initiative with its first public Symposium. MIT has long been home to research on myriad aspects of metals and minerals, and the MME Symposium serves to crystallize these efforts around the unique environmental and social challenges the sector faces.

Funded by the MIT Environmental Solutions Initiative, with additional support from the Industrial Liaison Program, the MME Symposium hosted industry professionals involved in sustainability, engineering, R&D, and other related topics. The event featured presentations from MIT faculty and industry experts, as well a glimpse into current research with a tour of MIT laboratories and a student-led poster session.

MME’s Principal Investigator, Assistant Professor of Metallurgy Antoine Allanore, introduced his research around metal extraction by electrolysis, which shows great promise for reducing greenhouse gas emissions and increasing productivity. Co-Principal Investigator T. Alan Hatton, the Ralph Landau Professor of Chemical Engineering, explained his innovations in carbon capture and waste separations, providing another angle for decreasing the industry’s environmental impacts.

Other speakers suggested additional angles for achieving sustainability goals, such as Maurice F. Strong Career Development Professor Matthew Amengual’s work on the impact of mining on local communities, and Professor of Biological Engineering Bevin P. Engelward’s research on the health impacts of metals. Assistant Professor of Materials Science and Engineering Elsa A. Olivetti discussed the potential for higher use of recycled materials and waste byproducts, while John F. Elliott Professor of Materials Chemistry Donald R. Sadoway showed the future of renewable energy battery storage, highly relevant for the remote locations of many mines. Vice President for Open Learning Sanjay Sarma closed out the Symposium, providing a vision of how the Internet of Things can be applied within the metals and minerals sector to monitor safety and increase efficiency.

“This Symposium provided a unique opportunity for MIT researchers to hear directly from the industry what their concerns are, where technologies might be deployed, and what is preventing industry from adopting some sustainability upgrades,” MME Program Manager Suzanne Greene says.

Allanore hopes that the event will culminate in a raised awareness of work at MIT that could be of immediate use to the industry, and of larger innovations under development that could serve as disruptive technologies to modernize the industry.

Learn more about the MME at metalsandminerals.mit.edu.

back to newsletterMay 22, 2017

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Participants in the Metals & Minerals for the Environment (MME) initiative’s first public Symposium on May 11 and 12 at MIT gathered for a group shot outside Fariborz Maseeh Hall. Photo, Davide Ciceri.

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Mechanical actuators developed by MIT team expand and contract as they let oxygen in and out.
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This diagram illustrates how the thin-film material bends from its normal flat state (center) as oxygen is taken up by its structure (right) or released (left). This behavior enables the film’s shape to be controlled remotely by changing its electric charge. Courtesy of the researchers

Carrying out maintenance tasks inside a nuclear plant puts severe strains on equipment, due to extreme temperatures that are hard for components to endure without degrading. Now, researchers at MIT and elsewhere have come up with a radically new way to make actuators that could be used in such extremely hot environments.

The system relies on oxide materials similar to those used in many of today’s rechargeable batteries, in that ions move in and out of the material during charging and discharging cycles. Whether the ions are lithium ions, in the case of lithium ion batteries, or oxygen ions, in the case of the oxide materials, their reversible motion causes the material to expand and contract.

Such expansion and contraction can be a major issue affecting the usable lifetime of a battery or fuel cell, as the repeated changes in volume can cause cracks to form, potentially leading to short-circuits or degraded performance. But for high-temperature actuators, these volume changes are a desired result rather than an unwelcome side effect.

The findings are described in a report appearing this week in the journal Nature Materials, by Jessica Swallow, an MIT graduate student; Krystyn Van Vliet, the Michael (1949) and Sonja Koerner Professor of Materials Science and Engineering; Harry Tuller, professor of materials science and engineering; and five others.“The most interesting thing about these materials is that they function at temperatures above 500 degrees Celsius,” Swallow explains.

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David L. Chandler | MIT News Office
May 8, 2017 

MIT Breathing Films 1 Swallow Web
"The most interesting thing about these materials is they function at temperatures above 500 degrees Celsius," says MIT graduate student Jessica Swallow, pictured with the equipment used for testing the new materials. Courtesy of the researchers

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Thursday, 18 May 2017 10:45

The tenured engineers of 2017

Twelve appointments in the School of Engineering.
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Top row, left to right: Yuriy Roman, Katharina Ribbeck, Ryan Williams, Bradley Olsen, Noelle Selin, and John Hart. Bottom row, left to right: Polina Anikeeva, Cullen Buie, Nuno Loureiro, Timothy Lu, Jessika Trancik, and Xuanhe Zhao.

The School of Engineering has announced that 12 members of its faculty have been granted tenure by MIT.

“This year’s newly tenured faculty in the School of Engineering are remarkable,” said Ian A. Waitz, dean of the School of Engineering. “The scale and breadth of their scholarship and the depth of their commitment to teaching demonstrate how strong we are as a community.”

This year’s newly tenured associate professors are:

Polina Anikeeva PhD ’09, the Class of 1942 Career Development Professor in the Department of Materials Science and Engineering, does research in bioelectronics, specifically the development of materials and devices that enable recording and manipulation of signaling processes within the nervous system.

Read more at the MIT News Office.

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School of Engineering
May 12, 2017

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Platform may be used to explore avenues for quantum computing.
MIT Graphene Semiconductors Web
MIT physicists have found that when a flake of graphene is sandwiched between superconductors, its electronic state changes dramatically, inheriting some of those materials’ superconducting qualities. Pictured is the experimental concept and device schematic.

In normal conductive materials such as silver and copper, electric current flows with varying degrees of resistance, in the form of individual electrons that ping-pong off defects, dissipating energy as they go. Superconductors, by contrast, are so named for their remarkable ability to conduct electricity without resistance, by means of electrons that pair up and move through a material as one, generating no friction.

Now MIT physicists have found that a flake of graphene, when brought in close proximity with two superconducting materials, can inherit some of those materials’ superconducting qualities. As graphene is sandwiched between superconductors, its electronic state changes dramatically, even at its center.

The researchers found that graphene’s electrons, formerly behaving as individual, scattering particles, instead pair up in “Andreev states” — a fundamental electronic configuration that allows a conventional, nonsuperconducting material to carry a “supercurrent,” an electric current that flows without dissipating energy. Their findings, published in Nature Physics, are the first investigation of Andreev states due to superconductivity’s “proximity effect” in a two-dimensional material such as graphene.

Down the road, the researchers’ graphene platform may be used to explore exotic particles, such as Majorana fermions, which are thought to arise from Andreev states and may be key particles for building powerful, error-proof quantum computers.

“There is a huge effort in the condensed physics community to look for exotic quantum electronic states,” says lead author Landry Bretheau, a postdoc in MIT’s Department of Physics. “In particular, new particles called Majorana fermions are predicted to emerge in graphene that is connected to superconducting electrodes and exposed to large magnetic fields. Our experiment is promising, as we are unifying some of these ingredients.”

Landry’s MIT co-authors are postdoc Joel I-Jan Wang, visiting student Riccardo Pisoni, and associate professor of physics Pablo Jarillo-Herrero, along with Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science, in Japan.

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Jennifer Chu | MIT News Office
May 4, 2017

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Desktop Metal thinks its machines will give designers and manufacturers a practical and affordable way to print metal parts.
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This steel propeller has just been printed. Between the propeller’s blades and the metal support is a thin line of ceramic, which will turn to sand during the sintering process, allowing the finished part to be easily separated from the support.

It’s less than two months before his company’s initial product launch, and CEO Ric Fulop is excitedly showing off rows of stripped-down 3-D printers, several bulky microwave furnaces, and assorted small metal objects on a table for display. Behind a closed door, a team of industrial designers sit around a shared work desk, each facing a large screen. The wall behind them is papered with various possible looks for the startup’s ambitious products: 3-D printers that can fabricate metal parts cheaply and quickly enough to make the technology practical for widespread use in product design and manufacturing.

The company, Desktop Metal, has raised nearly $100 million from leading venture capital firms and the venture units of such companies as General Electric, BMW, and Alphabet. The founders include four prominent MIT professors, including the head of the school’s department of materials science and Emanuel Sachs, who filed one of the original patents on 3-D printing in 1989. Still, despite all the money and expertise, there’s no guarantee the company will succeed in its goal of reinventing how we make metal parts—and thus transforming much of manufacturing.

As Fulop moves about the large, open workspace, his excitement and enthusiasm seem tempered by anxiety. The final commercial printers are not yet ready. Employees are busy tinkering with the machines, and fabricated test objects are scattered about. Progress is being made, but it’s also obvious that the clock is ticking. In a corner near the front door and entrance area, the floor is empty and taped off; soon the space needs to be filled with a mockup of the company’s planned booth for an upcoming trade show.

If it succeeds, Desktop Metal will help solve a daunting challenge that has eluded developers of 3-D printing for more than three decades, severely limiting the technology’s impact. Indeed, despite considerable fanfare and evangelical enthusiasts, 3-D printing has, in many ways, been a disappointment.

Hobbyists and self-proclaimed makers can use relatively inexpensive 3-D printers to make wonderfully complex and ingenious shapes out of plastics. And some designers and engineers have found those machines useful in mocking up potential products, but printing polymer parts has found little use on the production floor in anything but a few specialized products, such as customized hearing aids and dental implants.

Though it is possible to 3-D-print metals, doing so is difficult and pricey. Advanced manufacturing companies such as GE are using very expensive machines with specialized high-power lasers to make a few high-value parts (see “Additive Manufacturing” in our 10 Breakthrough Technologies list of 2013). But printing metals is limited to companies with millions to spend on the equipment, facilities to power the lasers, and highly trained technicians to run it all. And there is still no readily available option for those who want to print various iterations of a metal part during the process of product design and development.

The shortcomings of 3-D printing mean the vision that has long excited its advocates remains elusive. They would like to create a digital design, print out prototypes that they could test and refine, and then use the digital file of the optimized version to create a commercial product or part out of the same material whenever they hit “make” on a 3-D printer. Having an affordable and fast way to print metal parts would be an important step in making this vision a reality.

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The propeller after processing provides an example of a high-performance part that can be made with 3-D printing. Engineers can use the method to prototype and optimize different designs.

It would give designers more freedom, allowing them to create and test parts and devices with complex shapes that can’t be made easily with any other production method—say, an intricate aluminum lattice or a metal object with internal cavities. It could eventually enable engineers and materials scientists to create parts with new functions and properties by depositing various combinations of materials—for example, printing out a magnetic metal next to a nonmagnetic one. Beyond that, it would redefine the economics of mass production, because the cost of printing something would be the same regardless of how many items were produced. That would change how manufacturers think about the size of factories, the need for backup inventory (why keep many parts in stock if you can simply and quickly print one out?), and the process of tailoring manufacturing to specialized products.

This is why there has been a race to turn 3-D printing into a new way to produce parts. Longtime suppliers of 3-D printers, including Stratasys and 3D Systems, are introducing increasingly advanced machines that are fast enough for manufacturers to use. Last year, HP introduced a line of 3-D printers that the company says will allow manufacturers to prototype and make products with nylon, a widely used thermoplastic. And last fall, GE spent over a billion dollars on a pair of European companies specializing in 3-D-printing of metal parts.

But the real competition for Desktop Metal is probably not from the growing number of companies in 3-D printing. For one thing, the 3-D printers from HP, Stratasys (an investor in Desktop Metal), and 3D Systems mainly use various types of plastics, not the range of metals Fulop’s company wants to use in its printers. And GE’s high-end machines overlap little with Desktop Metal’s market ambitions. Instead, the real competitors for Desktop Metal are more likely to be established metal-processing technologies. Those include automated machining techniques—such as the method used to make the ultra-thin aluminum back casing of iPhones—and a rapidly growing practice called metal injection molding, a common way to mass-produce metal products.

In other words, rather than merely trying to outdo other 3-D printers, Desktop Metal will have the tough task of converting manufacturers away from production methods that are at the heart of their businesses. But the very existence of this large, established market is what makes the prospect so intriguing. Making metal parts, says Fulop, “is a trillion-dollar industry.” And even if 3-D printing wins only a small portion of it, he adds, it could still represent a multibillion-dollar opportunity.

Too hot to print

Look around. Metals are everywhere. But whereas 3-D printing has been widely used in making plastics, the technology’s use in making metal parts “has been narrowly confined,” says Chris Schuh, head of materials science and engineering at MIT and cofounder of Desktop Metal. “Metal processing is more of an art. It’s a very challenging space.”

Making metal objects using 3-D printing is difficult for several reasons. Most obvious is the high temperature required for processing metals. The most common way to print plastics involves heating polymers and squirting the material out the printer nozzle; the plastic then quickly hardens into the desired shape. The process is simple enough to be used in 3-D printers that sell for around $1,000. But building a 3-D printer that directly extrudes metals is not practical, given that aluminum melts at 660 °C, high-carbon steel at 1,370 °C, and titanium at 1,668 °C. Metal parts also have to go through several high-temperature processes to ensure the expected strength and other mechanical properties.

To make a 3-D printer fast enough to be used in manufacturing metal objects, Desktop Metal turned to a technology that dates back to the late 1980s. That’s when a team of MIT engineers led by company cofounder Sachs filed a patent for “three-dimensional printing techniques.” It described a process of putting down a thin layer of metal powder and then using ink-jet printing to deposit a liquid that selectively binds the powder together. The process, which is repeated for hundreds or thousands of layers to define a metal part, can make ones with nearly unlimited geometric complexity. In the most common application of the technology, the binder acts like a glue. However, it can also be used to locally deposit different materials in different locations.

The MIT researchers knew their printing method could be used to make metal and ceramic parts, says Sachs. But they also knew it was too slow to be practical, and the metal powders required for the process were far too expensive at the time. Sachs turned to other research interests, including an effort to improve the manufacturing of photovoltaics (see “Praying for an Energy Miracle”). In the next decades 3-D printing took off and captured the imagination of many product designers. Most famously, a cheap and easy-to-use 3-D printer from MakerBot was introduced in 2009, appealing to many self-styled inventors and tinkerers. But these affordable printers bumped up against the reality that they were limited to using a few cheap plastics. What’s more, though the machines can print complex shapes, the final product often isn’t as good as a plastic part made with conventional technology.

Meanwhile, researchers at industrial manufacturers like GE were busy advancing laser-based technologies invented in the late 1980s for printing metals. These machines use lasers—or, in some cases, high-power electron beams—to draw shapes in a layer of metal powder by melting the material. They repeat the process to build up a three-dimensional object out of the fused powders. The technique is impressive in its capabilities, but it’s slow and expensive. It is worthwhile only for extremely high-value parts that are too complex to make using other methods. Notably, GE’s new jet engine uses a series of sophisticated 3-D-printed fuel nozzles; they are lighter and far more durable because intricate cooling channels have been built into them.

The founders of Desktop Metal decided that to make 3-D metal printing more widely accessible, they would need to sell two different types of machines: a relatively inexpensive “desktop” model suitable for designers and engineers fabricating prototypes, and one that is fast and large enough for manufacturers. Luckily, several innovations have finally made Sachs’s original invention practical for mass production, including the development of very high-speed ink-jet printing for depositing the binder. Successively printing about 1,500 layers, each 50 micrometers thick and deposited in a few seconds, the production-scale printer can build up a 500-cubic-inch part in an hour. That’s about 100 times faster than a laser-based 3-D printer can make metal parts.

For its prototyping machine, Desktop Metal adopted a method from plastic-based 3-D printing. But instead of a softened polymer, it uses metal powders mixed with a flowable polymer binder. The formulation is extruded, using the printed binder to clump the metal powder into the intended shapes.

Key Players in 3-D printing

Stratasys Technology

Technology: One of the original 3-D-printing companies, Stratasys was founded by Scott Crumb, the inventor of fused deposition modeling, the most common way to print plastic parts.

Products: Sells machines that can print a variety of photopolymer and thermoplastic materials.

Carbon

Technology: This Silicon Valley startup has developed a novel photochemical process for fabricating parts out of various plastics, including polyurethane and epoxy.

Products: Introduced a modular system for manufacturers this spring.

HP

Technology: Its line of machines exploits the company’s long history with ink-jet printing through what it calls “multi jet fusion technology.” This uses multiple nozzles for high-speed and high-resolution printing.

Products: Introduced its first 3-D printers last year. The initial machines print nylon, but the company is looking to expand to other materials.

3D Systems

Technology: The first 3-D-printing company, 3D Systems was founded by Chuck Hull, the inventor of stereolithography, which uses light to form parts out of photopolymers. It now offers various types of 3-D printers, including some that print metal parts.

Products: Introduced the latest iteration of stereolithography last year.

However, whether the part is printed with the prototyping machine or the production model, the resulting object—part plastic binder and part metal—lacks the strength of a metal one. So it goes into a specially designed microwave oven for sintering, a process of using heat to make the material more dense, producing a part with the desired properties. In a series of carefully calibrated steps during the sintering process, the polymer is burned off, and then the metal is fused together at a temperature well below its melting point.

The sales pitch

According to the promises of its enthusiasts, 3-D printing will reduce the need for industrial manufacturers and empower local artisan producers (see “The Difference Between Makers and Manufacturers”). The reality is likely to be far different but nonetheless profound. Many sectors of industrial production increasingly use automation and advanced software, and 3-D printing enhances this ongoing move to digital manufacturing. In some ways, it is not unlike an automated machining process that works off a digital file to create a metal part. What’s different about 3-D printing is that it offers ways to make far more complex objects and removes many of the constraints that the production process puts on designers and engineers.

It could also inspire manufacturers to change their logistics and production strategies. For relatively small quantities of goods, 3-D printing could be cheaper, since it eliminates the costs associated with the tooling, casting, and molds required to churn out most metal and plastic objects. The time and money needed to set all that up is one reason why mass production is often required if a manufacturer is going to make money. Without that incentive to commit to mass-scale production, factories could shift production schedules and be more responsive to demand, moving even closer to just-in-time manufacturing. John Hart, a professor of mechanical engineering at MIT and cofounder of Desktop Metal, calls it customized mass production. Rather than having large facilities make a huge number of identical parts that have to be shipped across the world and warehoused, manufacturers might maintain scattered factories that make a diverse set of products, ramping up production as needed. “The implications in a decade or two are probably beyond our imagination,” Hart says. “I don’t really think we know what we will do with these technologies.”

For now, the challenge for Desktop Metal is to get its equipment in the hands of designers and engineers who are responsible for their companies’ next generation of products. This winter Fulop was preparing to showcase the company’s initial product, the prototyping machine, at a trade show in Pittsburgh in early May. (The production 3-D printer is scheduled to be available next year.) His task would be to convince attendees that spending $120,000 on Desktop Metal’s prototyping printer and sintering furnace is essential for the future of their companies.

It is a sales job that Fulop is well suited for. He has started more than a half-dozen companies, beginning with one that imported computer hardware and software that he founded when he was 16 and still living in his native Venezuela. He is probably best known for founding A123 Systems, a battery company that was one of the highest-flying startups in the late 2000s, culminating with a $371 million IPO in 2009. The company was based on a novel lithium-ion technology developed by Yet-Ming Chiang, an MIT professor who is also a cofounder of Desktop Metal. Like their current 3-D-printing startup, A123 hoped to apply materials science expertise to revolutionize a huge market.

It could also inspire manufacturers to change their logistics and production strategies.

Though A123 enjoyed rapid growth and a highly successful IPO, the company declared bankruptcy in 2012 (Fulop left in 2010). Ask Fulop the lesson from A123 and he says simply: “Batteries are a low-margin market.” Indeed, A123 struggled to compete in an increasingly crowded battery business, and it didn’t offer a radical enough performance improvement over established lithium-ion batteries to immediately win over a fledging hybrid-vehicles market (see “A123’s Technology Just Wasn’t Good Enough”).

The challenges faced by Desktop Metal will be very different. A huge market for metal parts already exists. And the startup believes its technology will, at least in the short run, have few direct competitors. Chiang points to the startup’s “really rich” patent portfolio. “It’s not just the materials; it’s the techniques, it’s the [sintering] furnace,” he says. “The harder the technology is, the higher the barrier to entry you build if you’re successful.”

In his office, Chiang has a wooden box containing a half-dozen swords, on loan from the Museum of Fine Arts in Boston, that were made in the 1970s using traditional Japanese techniques. Chiang uses the swords in teaching. The lesson: how the craftsmen used the secrets of metallurgy to turn iron ore into the final product—an ultra-sharp, slightly curved steel sword. Showing off the swords, Chiang points to some of their details, explaining the tricks their makers used, such as the quenching method used to create an extremely hard edge and a softer body. Back at his desk, his attention again on Desktop Metal, he’s equally enthusiastic as he describes the metal objects recently printed by the company and on display at its facilities. What’s exciting is “the idea that you can really make these parts,” Chiang says. “A few hours, and here’s a part that you couldn’t even make before.”

It won’t replace such century-old production techniques such as forging and metal casting, but 3-D printing could create new possibilities in manufacturing – and, just maybe, reimagine the art of metallurgy.

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Article courtesy of the MIT Technology Review.

David Rotman, Editor
MIT Technology Review

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Graduate student Cooper Rinzler and Assistant Professor of Metallurgy Antoine Allanore develop new formulas for analyzing molten semiconducting compounds.
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Graduate students Cooper Rinzler and Youyang Zhao and Assistant Professor of Metallurgy Antoine Allanore developed new formulas for predicting which molten compounds will be semiconducting and built a high-temperature thermoelectric device to produce electricity from molten semiconducting compounds that could reuse industrial waste heat. Photo, Denis Paiste, Materials Processing Center.

Despite decades of research on solid-state semiconductors that led to the digital transformation of society, much remains to be discovered about these materials when they are heated to their liquid state. Assistant Professor of Metallurgy Antoine Allanore and his lab group are discovering new analytical and experimental tools to understand these molten electronic materials.

Graduate students and postdocs in Assistant Professor of Metallurgy Antoine Allanore’s lab are untangling a web of complementary behaviors – electrochemical, thermodynamic, ionic and electronic – in molten industrial materials that may lead to better devices, processing and energy use.

That understanding has led to new routes for extracting metals like copper from molten compounds, and creating new thermoelectric devices that can transform waste heat from industries such as glass and steel making into electricity using molten compounds.

Framework for prediction

The change in free energy of a system with temperature is known as entropy and is a key thermodynamic property. Doctoral candidate Charles Cooper Rinzler and Allanore co-authored two papers that lay out a framework for quantifying the entropy [thermodynamics], chemical structure [configuration of atoms] and electronic behavior in liquid semiconducting compounds.

“What we’ve done in the collection of papers, I believe, is propose a way in which to look at, experimentally access and leverage these materials that allows us to characterize their properties and take advantage of their excellent properties and low cost,” says Rinzler, who defended his doctoral thesis this month and will receive his doctorate in June. A Fannie and John Hertz Foundation Fellow at MIT, Rinzler received his undergraduate education in physics and engineering at Harvard.

Working model

Graduate student Youyang Zhao, Rinzler and Allanore demonstrated a working molten tin sulfide thermoelectric device with potential applications in high-temperature reactors such as those of steel and glass making. “Tin sulfide is one example of a material for which we were able to employ new methods to determine key properties that were previously unknown,” Rinzler says. “It’s indicative of our ability to describe the general class of ordered liquids and shows that we can not only study these materials and determine their properties, but we can actually work practically with these systems that come at cost points that are very interesting for applications that are not addressed by the solid-state today.”

“We were interested in studying material systems like copper sulfide, as an example, because they are industrially relevant for extractive metallurgic processes, and they also have some potentially interesting properties for thermoelectric application,” Rinzler says. Producers of metals such as copper, zinc, nickel, and lead may extract them from hot liquid compounds that are also liquid semiconductors but they are not currently taking advantage of the electronic properties during processing.

The Allanore group’s combination of both theoretical analysis and experimental verification holds promise that these molten semiconductor systems can be integrated into high-temperature industrial furnaces to improve their operation and increase energy efficiency. The new predictive toolset means that researchers can screen candidate materials for devices in a fraction of the time it took for previous computational approaches. Molecular simulations for cadmium telluride, which remains a semiconductor when it is melted, took several years, Rinzler notes.

Transition point

The new formulas also allow researchers to pinpoint the compositions and temperatures at which certain compounds separate into their elements and can no longer mix [like oil and water], which is called their miscibility gap. The critical point of a miscibility gap defines the point where the liquid compound is no longer semiconducting but changes to metallic behavior, Rinzler says.

A key finding in Cooper’s analysis is that the entropy of electrons moving freely through these liquid semiconductors dominates their overall entropy of mixing and also is the moving force behind their ability to produce an electric current when the temperature difference between their hot side and cold side is large enough. This current is called thermopower. “We made the theoretical leap to say could there be a quantitative connection between that transport property [thermopower] and the entropy that we consider in thermodynamics, which is what drives the things like melting temperatures and miscibility gaps and all these features that we see in the phase diagram,” Cooper says.

The new theory allows researchers to evaluate this thermopower as a function of temperature from electrical signals, and translates these electronic measurements into thermodynamic data. Cooper validated his new formulas against experimental findings for both liquid and solid semiconductor compounds within 10 percent accuracy.

“We took a step back and looked at the thermodynamics [properties] of these systems, and we actually found that there was a really interesting correlation between thermodynamic properties and electronic properties,” Rinzler says. “For example, we could actually predict, based on looking at features of that phase diagram, whether the system was going to behave as a molten semiconductor or not. That led us down a line of questioning of why a connection between a thermodynamic property and an electronic property of the material may exist, which lead to this theoretical investigation of what could bridge that gap between the two.”

Matching experimental data

For processes as diverse as thermoelectric devices, metals extraction and energy storage, technologists need to know the entropy of metal-based compounds melted at high temperatures. They can now quantify how that entropy is transferred through a melt in terms of its electrical conductivity, thermopower, and electronic mobility, which are directly measurable. In a Philosophical Magazine paper last year, Rinzler and Allanore proposed that for semiconducting molten systems their electronic entropy of mixing is nearly equal to their total entropy of mixing. The formula they developed closely approximated experimentally reported data for a tellurium-thallium system.

In a second Philosophical Magazine paper this year, Rinzler and Allanore detailed how their earlier theoretical findings can predict whether a solid compound will be semiconducting or metallic when it is melted.

“It enables us to make quantitative predictions about whether systems will be semiconductors, over what range of temperature and composition they are going to be semiconductors, and it allows us to actually perform electronic measurements to generate thermodynamic data or perform thermodynamic measurements to generate electronic data,” Rinzler says. “So it basically allows us to now have a framework by which to predict key properties, to be able to practically leverage these systems, whereas before there was no prediction capability. There was only empirical investigation. You had to measure every property to know what it was. Now we have the ability to connect between thermodynamics and electronic properties to be able to actually make a prediction of what the material properties are going to be.”

While the molten tin sulfide thermoelectric device provides working proof of concept, Rinzler notes, “We’ve actually run a substantial number of experiments to confirm the electronic properties in other test cells as well, just not with a full device generating electricity like Youyang has done for tin sulfide.” 

This line of research can also provide feedback to lab mates exploring metals extraction from molten compounds. When you want to use a melt as a thermoelectric device, you want to see electronic behavior but when you are trying to separate out a metal you want to see ionic behavior but not electronic behavior.
“So by doing this work of understanding better in which conditions these molten materials are semiconductors, we also know in which conditions it is not a semiconductor, which is very helpful for new electrochemical techniques,” Allanore says.

This work was supported by the Fannie and John Hertz Foundation and the Air Force Office of Scientific Research [Grant number FA9550-15-1-0046].

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– Written by Denis Paiste, Materials Processing Center
May 22, 2017

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MIT researchers base high-temperature device to produce electricity from industrial waste heat on molten compound’s semiconducting properties.

Thermoelectric Test Cell

Thermoelectric Test Cell MPC Youyang Zhao Web

MIT researchers have demonstrated a liquid thermoelectric device with a molten compound of tin and sulfur that can efficiently convert waste heat to electricity, opening the way to affordably transforming waste heat to energy conversion at high temperatures. Graduate student Youyang Zhao built the thermoelectric test cell based on a concentric cylinder design similar to one used by the late Robert K. Williams, a long-time metal and ceramic division researcher at Oak Ridge National Laboratory in Tennessee, for studying thermal conductivity of molten sulfides. Ilustration, Youyang Zhao

Glass and steel makers produce large amounts of wasted heat energy at high temperatures, but solid-state thermoelectric devices that convert heat to electricity either don’t operate at high enough temperatures or cost so much that their use is limited to special applications such as spacecraft. MIT researchers have developed a liquid thermoelectric device with a molten compound of tin and sulfur that can efficiently convert waste heat to electricity, opening the way to affordably transforming waste heat to power at high temperatures.

Youyang Zhao, a graduate student in Assistant Professor of Metallurgy Antoine Allanore’s research group, built a thermoelectric test cell that operates in a liquid state at temperatures from 950 to 1,074 degrees Celsius [1,742 to 1,965 degrees Fahrenheit]. Commercial thermoelectric devices, based on materials such as solid-state bismuth telluride, operate at about 500 degrees Celsius, and a block of bismuth telluride costs in the neighborhood of 150 times more than tin sulfide per cubic meter [about 35 cubic feet].

Once melted, tin sulfide provides a consistent thermoelectric output over a wide temperature range up to 200 degrees above its melting point of 882 degrees Celsius, says Zhao, first author of an ECS Journal of Solid State Science and Technology paper, “Molten Semiconductors for High Temperature Thermoelectricity,” with Allanore and graduate student Charles Cooper Rinzler. Zhao found no significant performance drop as he cycled the device up to 1,074 degrees Celsius and back down to 950 degrees Celsius, and this over several hours.

“For me, I first heat up the sample to its melting point and then scan the temperature up to 200°C above melting and then scan back while doing multiple measurements during the heating up and the cooling down part. What we found is the property is fairly consistent,” Zhao says.

Materials for large-scale industrial operations

Zhao’s thermoelectric device operates in conditions that are relevant to industrial applications, while the material he used, tin sulfide, is appealing from a cost perspective, Allanore says. Thermoelectric devices work by sandwiching together materials that produce an electric voltage when there is a temperature difference between their hot and cool sides. In reverse, they can be used as cooling devices turning an electric current into a temperature drop. Such devices are used, for example, to heat and cool seats in luxury car models and to power on-board electronics on spacecraft on long journeys (using a nuclear energy source and with specialty devices that can operate at higher temperatures than commercial devices).

The environmental benefits that producing electricity from waste heat yields are unlikely to be a primary motivator for glass and steel makers to adopt this technology, Allanore suggests. These operations have to run their vats or kilns at temperatures of 1,000 degrees Celsius or higher to make their products, and they make their profits off those products. But reaching this high heat is a one-time cost. If thermoelectric management of that heat allows producers to operate hotter, which could increase productivity, or to extend the life of their equipment, then they will be more likely to adapt it, Allanore says. “We already know that in the steady state we have 1,000 degrees Celsius at that location,” he says. And that’s enough to melt the semiconducting materials in a liquid thermoelectric device.

“At the beginning we thought about how do we implement at large scale, on high temperature metallurgical furnaces, materials that could recover waste heat. That was our first idea. But then the second vision of this is to say, what can I do with that electricity? Because you’re not going to deploy that to make electricity, you’re going to deploy that because you have a true benefit to your production,” Allanore explains. Being able to manage heat at very high temperature thanks to electrically active materials like molten compounds is one benefit that is now a possibility.

These findings can have a large impact on metals producers who already handle hundreds of thousands of tons per year of copper sulfide, iron sulfide, and similar materials in their molten state, but who don’t currently take advantage of the materials’ semiconducting properties. “We know how to handle these things at very large scale,” Allanore says.

In 2013, Allanore and John F. Elliott Professor of Materials Chemistry Donald R. Sadoway developed an inexpensive alloy of chromium and iron to serve as the anode in producing steel through molten oxide electrolysis. The process produces metal of high purity and releases oxygen instead of carbon dioxide, which is a major contributor to the greenhouse gas effect. An MIT spinout company, Boston Electrometallurgical Corp., grew out of that work, which has demonstrated molten metal production at the scale of several hundreds pounds per day.

Pairing theory and experiment

The new work on thermoelectric devices under similarly high temperatures provides experimental confirmation of Allanore lab colleague Rinzler’s work explaining the theoretical basis for semiconducting behavior in metallic compounds in their hot, liquid state. Rinzler’s work lays out a predictive framework for quantifying the energy profile [thermodynamics], chemical structure [configuration of atoms] and electronic behavior in certain liquid semiconducting compounds, such as tin sulfide or copper sulfide.

“It’s not a simple matter of just saying what temperature range can you operate under? It’s what can you achieve under practical conditions of operation that matter for the application at hand and at what cost point of material and device,” Rinzler says.

“The beauty of something like this is we that can capture both, we can improve waste heat collection, which we may care about from an energy savings perspective, but industry is encouraged to use it because it actually benefits them in the context that they care about directly as well,” Rinzler says.

Measured on a dollar-per-watt basis, Allanore explains, molten tin sulfide devices could be important to industries that operate at high temperature. “The dollar per watt, when you have large surface area, is dictated by the cost of your material,” he says. Other advantages of the proposed system include the simplicity of handling tin and sulfur, the semiconducting mixture’s relatively high electrical conductivity and relatively low toxicity compared to compounds such as tellurium and thallium or lead and sulfur.

Zhao moved from concept to working device within a year, remarkable progress for scientific research, Allanore notes. “First, it’s Youyang, who is very good, and second it’s the liquid state ... that makes this type of fast demonstration possible,” he says. Zhao earned his B.S. in Materials Science and Engineering from Georgia Institute of Technology in 2013.

Rinzler Zhao Allanore v4 8445 DP Web
Graduate students Cooper Rinzler and Youyang Zhao and Assistant Professor of Metallurgy Antoine Allanore developed new formulas for predicting which molten compounds will be semiconducting and built a high-temperature thermoelectric device to produce electricity from molten semiconducting compounds that could reuse industrial waste heat. Photo, Denis Paiste, Materials Processing Center.

Self-healing system

“The liquid state is very forgiving of large temperature changes in a way the solid-state is not. If you think about a solid-state material that is going through such a range of temperature, you always have thermal expansion, mechanical problems, corrosion,” he says. These phenomena prevent many solid materials from being reversible in the sense that as the temperature goes up and down, the performance will remain the same. “This is again one of the features of the liquid state. We call it self-healing,” Allanore explains. “As long as you don’t change the chemical composition macroscopically, you just get the same material. From an engineering standpoint and adoption for large-scale application, this is a very important feature.”

“I think people are afraid of it, in a sense, because it seems dangerous to be hot and molten, but once you are molten and know what you are doing, it’s very forgiving,” Allanore says.

For their experimental device, the researchers adapted a concentric cylinder design similar to one used by the late Robert K. Williams, a long-time metal and ceramic division researcher at Oak Ridge National Laboratory in Tennessee, for a 1968 study of thermal conductivity in molten silver sulfide. “They proved convection is a really important factor in liquids,” Zhao says. “And for us, we are designing a device. We are not just talking about the properties of the material. We have to consider the cell geometry and design. When you put a novel material into a device, the overall property might be different from the material itself. So that means it is the overall liquid property, possibly with effect from convection, that dominates the performance of the device.”
Researchers compare different thermoelectric materials by determining their “figure of merit,” which is a measure of each material’s effectiveness at thermoelectric conversion. For many potentially useful compounds at high temperature, Allanore says, the thermoelectric figure of merit has never been investigated, so the new device also provides an experimental framework to evaluate this.

Role of convection

The thermoelectric figure of merit for a device is slightly different than that of the thermoelectric material it uses because of effects from natural convection as well as interference from the device itself. In the paper, Zhao says, “We reported the figure of merit of the device, not necessarily for the material, because we believe there is a contribution, or there is a performance degradation, from natural convection. In that sense, if we could minimize natural convection, the figure of merit for this device could go up.”

“That is the next step for our study,” Zhao says. “Currently I am trying to study what is the effect of natural convection on either [the] Seebeck coefficient [a measure of a material’s strength at converting heat to electricity] or electrical conductivity or thermal conductivity.”

The MIT researchers have filed a provisional patent application for certain aspects of their work.

Allanore hopes the work will broaden understanding of molten compounds. Unlike in solid materials where atoms are relatively fixed, he says, atoms in liquids vary in arrangement on a scale of several micrometers to several millimeters. [Think for example of the difference between the water molecules in a block of frozen ice versus those same molecules in a pot of boiling water.] “In a molten material, you have constant movement, and it’s a complexity that it is not present its solid state and is not described by existing models of the materials science we teach in class,” Allanore says. “We are comfortable that one day we will bridge the two and then it will be a full story that speaks not only about the electronic structure and property, but also what we call physical chemistry, which is viscosity, density, diffusivity – all these phenomena which are essentials to the liquid state.”

The work was supported by MITEI Seed Fund 2013 and the U.S. Air Force Office of Scientific Research (Grant number FA9550-15-1-0046).

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Written by Denis Paiste, Materials Processing Center
May 22, 2017

Related: Faculty Highlight: Antoine Allanore

 

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Tuesday, 16 May 2017 10:54

Newsletter, May 2017

MIT Materials News that Matters
May 2017
Materials Processing Center at MIT
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Email:mpc@mit.edu

Materials Day 

Symposium and Poster Session
October 11, 2017
Kresge Auditorium

Save the Date! 

2016 Summer Scholar Jennifer Coulter wins three fellowships

Rutgers senior chooses Department of Energy award to study computational physics at Harvard.

MPC-CMSE Summer Scholar Jennifer Coulter. Photo, Denis Paiste
Coulter.

Rutgers University physics major Jennifer Coulter struck academic gold three times this year, winning a National Science Foundation Graduate Research Fellowship, a National Defense Science and Engineering Graduate Fellowship and a Department of Energy Computational Science Graduate Fellowship.Coulter, a graduating senior, was honored with a prestigious Goldwater scholarship last year. At MIT, Coulter was a research assistant to Alfredo Alexander-Katz, an associate professor in the Department of Materials Science and Engineering. She modeled how spinning colloidal particles move through a fixed array of obstacles.

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Liquid tin-sulfur compound shows thermoelectric potential

MIT researchers base high-temperature device to produce electricity from industrial waste heat on molten compound's semiconducting properties.



Thermoelectric test cell

MIT researchers have developed a liquid thermoelectric device with a molten compound of tin and sulfur that can efficiently convert waste heat to electricity, opening the way to affordably transforming waste heat to power at high temperatures.

Youyang Zhao, a graduate student in Assistant Professor of Metallurgy Antoine Allanore's research group, built a thermoelectric test cell that operates in a liquid state at temperatures from 950 to 1,074 degrees Celsius [1,742 to 1,965 degrees Fahrenheit].

Read more.

Predicting high-temperature, liquid electronic properties


Graduate student Cooper Rinzler and Assistant Professor of Metallurgy Antoine Allanore develop new formulas for analyzing molten semiconducting compounds.

Graduate students Cooper Rinzler and Youyang Zhao and Assistant Professor of Metallurgy Antoine Allanore developed new formulas for predicting which molten compounds will be semiconducting and built a high-temperature thermoelectric test device.
Rinzler, Zhao and Allanore.

Despite decades of research on solid-state semiconductors, much remains to be discovered about these materials when they are heated to their liquid state. Assistant Professor of Metallurgy Antoine Allanore and his lab group are discovering new tools to understand these molten electronic materials.

Doctoral candidate Charles Cooper Rinzler and Allanore co-authored two papers that lay out a framework for quantifying the entropy [thermodynamics], chemical structure [configuration of atoms] and electronic behavior in liquid semiconducting compounds.

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Envisioning the future of metal and mineral production

MIT researchers team up with leaders from the metals and minerals industry to envision a more sustainable future.

Assistant Professor of Materials Science and Engineering Elsa A. Olivetti_ standing_ right_ shares a summary of a breakout session on disposal and recovery challenges with participants in the Metals _ Minerals for the Environment at MIT May 11_ 2017.  Photo_ Davide Ciceri.
Assistant Professor of Materials Science and Engineering Elsa A. Olivetti, standing, right, shares a summary of a breakout session on disposal and recovery challenges. Photo, Davide Ciceri.

Metals and minerals form the base of our society, with diverse applications infiltrating all corners of our lives, including agriculture, infrastructure, transportation and information technology. As populations grow, and demand for metals and minerals rises, enhancing the sustainability of the sector is a goal for many companies, communities and policymakers.

To contribute to this, on May 11-12, 2017, MIT launched the Metals & Minerals for the Environment (MME) initiative with its first public Symposium. MIT has long been home to research on myriad aspects of metals and minerals, and the MME Symposium serves to crystallize these efforts around the unique environmental and social challenges the sector faces.

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The 3-D printer that could finally change manufacturing

The propeller after processing provides an example of a high-performance part that can be made with 3-D printing. Engineers can use the method to prototype and optimize different designs.

Desktop Metal thinks its machines will give designers and manufacturers a practical and affordable way to print metal parts.

Desktop Metal, has raised nearly $100 million from leading venture capital firms and the venture units of such companies as General Electric, BMW, and Alphabet. The founders include four prominent MIT professors, including the head of the school's department of materials science and Emanuel Sachs, who filed one of the original patents on 3-D printing in 1989. Still, despite all the money and expertise, there's no guarantee the company will succeed in its goal of reinventing how we make metal parts - and thus transform much of manufacturing.

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In Other News

The most interesting thing about these materials is they function at temperatures above 500 degrees Celsius, says MIT graduate student Jessica Swallow, pictured with equipment used for testing new breathing materials. Courtesy of the researchers

High-temperature films  that breathe and bend

MIT team develops mechanical  actuators to expand, contract,  through oxygen exchange.
 

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Top row, left to right, Yuriy Roman, Katharina Ribbeck, Ryan Williams, Bradley Olsen, Noelle Selin, and John Hart. Bottom row, left to right, Polina Anikeeva, Cullen Buie, Nuno Loureiro, Timothy Lu, Jessika Trancik, and Xuanhe Zhao.

The tenured engineers  of 2017

12 remarkable members of the  School of Engineering faculty  are granted tenure by MIT.

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MIT physicists have found that when a flake of graphene is sandwiched between superconductors_ its electronic state changes dramatically_ inheriting some of their__ superconducting qualities. Pictured is the test concept and device schematic.

Graphene adopts exotic  electronic states

  A flake of graphene inherits  some qualities from nearby  superconducting materials.

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Upcoming Events  

MIT Sea Grant Program Open House, Building NW98, 12 Emily St., Cambridge, Mass., 2-4pm, Thurs., June 8, 2017.

MIT Commencement: Investiture of Doctoral Hoods, Johnson Athletics Center 10am, Thurs., June 8;  Commencement, Killian Court, 10am, Fri., June 9, 2017.

Koch Institute for Integrative Cancer Research Symposium: Convergence of Science and Engineering in Cancer Research,  W-16, Kresge Auditorium, 9am-4:45pm, Fri., June 16, 2017.

EurekaFest 2017, Museum of Science, Boston, Mass., 11am-4:30pm,  Saturday, June 17, 2017.

2017 AIM Photonics Summer Academy, Fundamentals of Integrated Photonics: Principles, Practice and Applications, 

Massachusetts Institute of Technology, Cambridge, Mass., July 24-28, 2017. Registration deadline Fri., June 30, 2017.

Materials Day Symposium and Poster Session, Kresge Auditorium, MIT Building W16, Oct.11, 2017. SAVE THE DATE.

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For more information, contact Mark Beals at 617-253-2129 or mbeals@mit.edu

About MPC


The goals of the Materials Processing Center are to unite the materials research community at MIT and to enhance Institute-industry interactions. Collaboration on research ventures, technology transfer, continuing education of industry personnel, and communication among industrial and governmental entities are our priorities. The MPC Industry Collegium is a major vehicle for this collaboration. The MPC sponsors seminars and workshops, as well as a summer internship for talented undergraduates from universities across the U.S. We encourage interdisciplinary research collaborations and provide funds management assistance to faculty.

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Materials researcher is working on the magnetic memory of the future.

MIT Geoffrey Beach A1 Brauer Web
“There are many thousands of combinations of materials and interfaces that we can create,” says associate professor Geoffrey Beach. “So with this wealth of material structures, rather than relying on the few materials that nature has given us, we can now design materials and their magnetic properties to exhibit the characteristics that we want.” Photo, M. Scott Brauer

Geoffrey Beach has been tinkering and building things most of his life, including some 50 model rockets that he built and launched while in high school in Oklahoma. But it wasn’t until his undergraduate studies in physics that he zeroed in on the topic that has dominated his research ever since: the study of magnetism and how to control it.

In his work, Beach combines the deep, theoretical understanding of a physicist with an engineer’s passion for building and refining the devices needed to carry out his investigations.

“In high school and college, I was always interested in physics,” says Beach, who is an associate professor in MIT’s Department of Materials Science and Engineering, where he earned tenure in 2015. He received his bachelor’s degree from Caltech, where his interest in magnetism first came into focus.

During those college years studying physics, “everyone there wanted to work on gravity,” he says. “I liked the theoretical aspect, but I’ve always been a very hands-on person. I always liked to build things, and I really like to see how things work.”

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David L. Chandler | MIT News Office
April 24, 2017

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Brittle electrodes handle expansion by going glassy, study shows.

MIT Battery Expansion 1 Web
These images, made by transmission electron microscopy, show the progression of the sodium-olivine electrode material, first in the original starting material in powdered form [a]; after sodium is inserted in different concentrations [b and c]; and after an amorphous, glassy structure forms in between tiny areas of microcrystalline structure [d and e]. Image courtesy of the researchers.

When you charge a battery, or when you use it, it’s not just electricity but also matter that moves around inside. Ions, which are atoms or molecules that have an electric charge, travel from one of the battery’s electrodes to the other, making the electrodes shrink and swell. In fact, it’s been a longstanding mystery why fairly brittle electrode materials don’t crack under the strain of these expansion and contraction cycles.

The answer may have finally been found. A team of researchers at MIT, the University of Southern Denmark, Rice University, and Argonne National Laboratory has determined that the secret is in the electrodes’ molecular structure. While the electrode materials are normally crystalline, with all their atoms neatly arranged in a regular, repetitive array, when they undergo the charging or discharging process, they are transformed into a disordered, glass-like phase that can accommodate the strain of the dimensional changes.

The new findings, which could affect future battery design and even lead to new kinds of actuators, are reported in the journal Nano Letters, in a paper by MIT professor of materials science and engineering Yet-Ming Chiang, graduate students Kai Xiang and Wenting Xing, and eight others.

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Read more at the MIT News Office.

David L. Chandler | MIT News Office
April 12, 2017

Published in Newsletter Articles
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