Thursday, July 9th, 2020

Time	Event
11:24a	To engineers’ surprise, radiation can slow corrosion of some materials Radiation nearly always degrades the materials exposed to it, hastening their deterioration and requiring replacement of key components in high-radiation environments such as nuclear reactors. But for certain alloys that could be used in fission or fusion reactors, the opposite turns out to be true: Researchers at MIT and in California have now found that instead of hastening the material’s degradation, radiation actually improves its resistance, potentially doubling the material’s useful lifetime. The finding could be a boon for some new, cutting-edge reactor designs, including molten-salt-cooled fission reactors, and new fusion reactors such as the ARC design being developed by MIT and Commonwealth Fusion Systems. The finding, which came as a surprise to nuclear scientists, is reported today in the journal Nature Communications, in a paper by MIT professor of nuclear science and engineering Michael Short, graduate student Weiyue Zhou, and five others at MIT and at the Lawrence Berkeley National Laboratory. Short says the finding was a bit of serendipity; in fact, the researchers were looking to quantify the opposite effect. Initially they wanted to determine how much radiation would increase the rate of corrosion in certain alloys of nickel and chromium that can be used as cladding for nuclear fuel assemblies. The experiments were difficult to carry out, because it’s impossible to measure temperatures directly at the interface between the molten salt, used as a coolant, and the metal alloy surface. Thus it was necessary to figure out the conditions indirectly by surrounding the material with a battery of sensors. Right from the start, though, the tests showed signs of the opposite effect — corrosion, the main cause of materials failure in the harsh environment of a reactor vessel, seemed to be reduced rather than accelerated when it was bathed in radiation, in this case a high flux of protons. “We repeated it dozens of times, with different conditions,” Short says, “and every time we got the same results” showing delayed corrosion. The kind of reactor environment the team simulated in their experiments involves the use of molten sodium, lithium, and potassium salt as a coolant for both the nuclear fuel rods in a fission reactor and the vacuum vessel surrounding a superhot, swirling plasma in a future fusion reactor. Where the hot molten salt is in contact with the metal, corrosion can take place rapidly, but with these nickel-chromium alloys they found that the corrosion took twice as long to develop when the material was bathed in radiation from a proton accelerator, producing a radiation environment similar to what would be found in the proposed reactors. Being able to more accurately predict the usable lifetime of critical reactor components could reduce the need for preemptive, early replacement of parts, Short says. Careful analysis of images of the affected alloy surfaces using transmission electron microscopy, after irradiating the metal in contact with molten salt at 650 degrees Celsius, (a typical operating temperature for salt in such reactors), helped to reveal the mechanism causing the unexpected effect. The radiation tends to create more tiny defects in the structure of the alloy, and these defects allow atoms of the metal to diffuse more easily, flowing in to quickly fill the voids that get created by the corrosive salt. In effect, the radiation damage promotes a sort of self-healing mechanism within the metal. There had been hints of such an effect a half-century ago, when experiments with an early experimental salt-cooled fission reactor showed lower than expected corrosion in its materials, but the reasons for that had remained a mystery until this new work, Short says. Even after this team’s initial experimental findings, Short says, “it took us a lot longer to make sense of it.” The discovery could be relevant for a variety of proposed new designs for reactors that could be safer and more efficient than existing designs, Short says. Several designs for salt-cooled fission reactors have been proposed, including one by a team led by Charles Forsberg, a principal research scientist in MIT’s Department of Nuclear Science and Engineering. The findings could also be useful for several proposed designs for new kinds of fusion reactors being actively pursued by startup companies, which hold the potential for providing electricity with no greenhouse gas emissions and far less radioactive waste. “It’s not particular to any one design,” Short says. “It helps everybody.” The research team included K. Woller, P. Stahle and G. Q. Zheng at MIT, and Y. Yang and A. M. Minor at Lawrence Berkeley National Laboratory. The work was supported by the Transatomic Power Corporation and the U.S. Department of Energy. (Comment on this)
11:33a	Engineers design a reusable, silicone rubber face mask Researchers at MIT and Brigham and Women’s Hospital have designed a new face mask that they believe could stop viral particles as effectively as N95 masks. Unlike N95 masks, the new masks were designed to be easily sterilized and used many times. As the number of new Covid-19 cases in the United States continues to rise, there is still an urgent need for N95 masks for health care workers and others. The new mask is made of durable silicone rubber and can be manufactured using injection molding, which is widely used in factories around the world. The mask also includes an N95 filter, but it requires much less N95 material than a traditional N95 mask.  “One of the key things we recognized early on was that in order to help meet the demand, we needed to really restrict ourselves to methods that could scale,” says Giovanni Traverso, an MIT assistant professor of mechanical engineering and a gastroenterologist at Brigham and Women’s Hospital. “We also wanted to maximize the reusability of the system, and we wanted systems that could be sterilized in many different ways.” The team is now working on a second version of the mask, based on feedback from health care workers, and is working to establish a company to support scaled-up production and seek approval from the FDA and the National Institute for Occupational Safety and Health (NIOSH). Traverso is the senior author of a paper describing the new masks, which appears today in the British Medical Journal Open. The lead authors of the study are James Byrne, a radiation oncologist at Brigham and Women’s Hospital and research affiliate at MIT’s Koch Institute for Integrative Cancer Research; Adam Wentworth, a research engineer at Brigham and Women’s Hospital and a research affiliate at the Koch Institute; Peter Chai, an emergency medicine physician at Brigham and Women’s Hospital; and Hen-Wei Huang, a research fellow at Brigham and Women’s Hospital and a postdoc at the Koch Institute. Easy sterilization The N95 masks that health care workers wear to protect against exposure to SARS-CoV-2 and other viruses are made from polypropylene fibers that are specially designed to filter out tiny viral particles. Ideally, a health care worker would switch to a new mask each time they see a different patient, but shortages of these masks have forced doctors and nurses to wear them for longer than they are meant to be worn. In recent months, many hospitals have begun sterilizing N95 masks with hydrogen peroxide vapor, which can be used up to 20 times on a single mask. However, this process requires specialized equipment that is not available everywhere, and even with this process, one mask can be worn for only a single day. The MIT/BWH team set out to design a mask that could be safely sterilized and reused many times. They decide on silicone rubber — the material that goes into silicone baking sheets, among other products — because it is so durable. Liquid silicone rubber can be easily molded into any shape using injection molding, a highly automated process that generates products rapidly. The masks are based on the shape of the 3M 1860 style of N95 masks, the type normally used at Brigham and Women’s Hospital. Most of the mask is made of silicone rubber, and there is also space for one or two N95 filters. Those filters are designed to be replaced after every use, while the rest of the mask can be sterilized and reused. “With this design, the filters can be popped in and then thrown away after use, and you’re throwing away a lot less material than an N95 mask,” Wentworth says. The researchers tested several different sterilization methods on the silicone masks, including running them through an autoclave (steam sterilizer), putting them in an oven, and soaking them in bleach and in isopropyl alcohol. They found that after sterilization, the silicone material was undamaged. Fit test To test the comfort and fit of the masks, the researchers recruited about 20 health care workers from the emergency department and an oncology clinic at Brigham and Women’s Hospital. They had each of the subjects perform the standard fit test that is required by the Occupational Safety and Health Administration (OSHA) for N95 masks. During this test, the subject puts the mask on and then performs a series of movements to see if the mask stays in place. A nebulized sugar solution is sprayed in the room, and if the subject can taste or smell it, it means the mask is not properly fitted. All 20 subjects passed the fit test, and they reported that they were able to successfully insert and remove the N95 filter. When asked their preference between the new mask, a typical N95 mask, and a standard surgical mask, most either said they had no preference or preferred the new silicone mask, Byrne says. They also gave the new mask high ratings for fit and breathability. The researchers are now working on a second version of the mask, which they hope to make more comfortable and durable. They also plan to do additional lab tests measuring the masks’ ability to filter viral particles. As many regions of the United States have seen a surge in Covid-19 cases over the past month, hospitals in those areas face the possibility of mask shortages. There is also a need for more masks in parts of the world that don’t have the equipment needed for hydrogen peroxide sterilization. “We know that Covid is really not going away until a vaccine is prevalent,” Byrne says. “I think there’s always going to be a need for masks, whether it be in the health care setting or in the general public.” The research was funded, in part, by the Prostate Cancer Foundation, the MIT Department of Mechanical Engineering, Brigham and Women’s Hospital, the National Institutes of Health, E-Ink Corporation, Gilead Sciences, Philips Biosensing, and the Hans and Mavis Lopater Psychosocial Foundation. (Comment on this)
3:25p	A new approach to carbon capture An essential component of any climate change mitigation plan is cutting carbon dioxide (CO2) emissions from human activities. Some power plants now have CO2 capture equipment that grabs CO2 out of their exhaust. But those systems are each the size of a chemical plant, cost hundreds of millions of dollars, require a lot of energy to run, and work only on exhaust streams that contain high concentrations of CO2. In short, they’re not a solution for airplanes, home heating systems, or automobiles. To make matters worse, capturing CO2 emissions from all anthropogenic sources may not solve the climate problem. “Even if all those emitters stopped tomorrow morning, we would still have to do something about the amount of CO2 in the air if we’re going to restore preindustrial atmospheric levels at a rate relevant to humanity,” says Sahag Voskian SM ’15, PhD ’19, co-founder and chief technology officer at Verdox, Inc. And developing a technology that can capture the CO2 in the air is a particularly hard problem, in part because the CO2 occurs in such low concentrations. The CO2 capture challenge A key problem with CO2 capture is finding a “sorbent” that will pick up CO2 in a stream of gas and then release it so the sorbent is clean and ready for reuse and the released CO2 stream can be utilized or sent to a sequestration site for long-term storage. Research has mainly focused on sorbent materials present as small particles whose surfaces contain “active sites” that capture CO2 — a process called adsorption. When the system temperature is lowered (or pressure increased), CO2 adheres to the particle surfaces. When the temperature is raised (or pressure reduced), the CO2 is released. But achieving those temperature or pressure “swings” takes considerable energy, in part because it requires treating the whole mixture, not just the CO2-bearing sorbent. In 2015, Voskian, then a PhD candidate in chemical engineering, and T. Alan Hatton, the Ralph Landau Professor of Chemical Engineering and co-director of the MIT Energy Initiative’s Low-Carbon Energy Center for Carbon Capture, Utilization, and Storage, began to take a closer look at the temperature- and pressure-swing approach. “We wondered if we could get by with using only a renewable resource — like renewably sourced electricity — rather than heat or pressure,” says Hatton. Using electricity to elicit the chemical reactions needed for CO2 capture and conversion had been studied for several decades, but Hatton and Voskian had a new idea about how to engineer a more efficient adsorption device. Their work focuses on a special class of molecules called quinones. When quinone molecules are forced to take on extra electrons — which means they’re negatively charged — they have a high chemical affinity for CO2 molecules and snag any that pass. When the extra electrons are removed from the quinone molecules, the quinone’s chemical affinity for CO2 instantly disappears, and the molecules release the captured CO2.  Others have investigated the use of quinones and an electrolyte in a variety of electrochemical devices. In most cases, the devices involve two electrodes — a negative one where the dissolved quinone is activated for CO2 capture, and a positive one where it’s deactivated for CO2 release. But moving the solution from one electrode to the other requires complex flow and pumping systems that are large and take up considerable space, limiting where the devices can be used.  As an alternative, Hatton and Voskian decided to use the quinone as a solid electrode and — by applying what Hatton calls “a small change in voltage” — vary the electrical charge of the electrode itself to activate and deactivate the quinone. In such a setup, there would be no need to pump fluids around or to raise and lower the temperature or pressure, and the CO2 would end up as an easy-to-separate attachment on the solid quinone electrode. They deemed their concept “electro-swing adsorption.” The electro-swing cell To put their concept into practice, the researchers designed the electrochemical cell shown in the two diagrams in Figure 1 in the slideshow above. To maximize exposure, they put two quinone electrodes on the outside of the cell, thereby doubling its geometric capacity for CO2 capture. To switch the quinone on and off, they needed a component that would supply electrons and then take them back. For that job, they used a single ferrocene electrode, sandwiched between the two quinone electrodes but isolated from them by electrolyte membrane separators to prevent short circuits. They connected both quinone electrodes to the ferrocene electrode using the circuit of wires at the top, with a power source along the way. A power source creates a voltage that causes electrons to flow from the ferrocene to the quinone through the wires. The quinone is now negatively charged. When CO2-containing air or exhaust is blown past these electrodes, the quinone will capture the CO2 molecules until all the active sites on its surface are filled up. During the discharge cycle, the direction of the voltage on the cell is reversed, and electrons flow from the quinone back to the ferrocene. The quinone is no longer negatively charged, so it has no chemical affinity for CO2. The CO2 molecules are released and swept out of the system by a stream of purge gas for subsequent use or disposal. The quinone is now regenerated and ready to capture more CO2. Two additional components are key to successful operation. First is an electrolyte, in this case a liquid salt, that moistens the cell with positive and negative ions (electrically charged particles). Since electrons only flow through the external wires, those charged ions must travel within the cell from one electrode to the other to close the circuit for continued operation. The second special ingredient is carbon nanotubes. In the electrodes, the quinone and ferrocene are both present as coatings on the surfaces of carbon nanotubes. Nanotubes are both strong and highly conductive, so they provide good support and serve as an efficient conduit for electrons traveling into and out of the quinone and ferrocene. To fabricate a cell, researchers first synthesize a quinone- or ferrocene-based polymer, specifically, polyanthraquinone or polyvinylferrocene. They then make an “ink” by combining the polymer with carbon nanotubes in a solvent. The polymer immediately wraps around the nanotubes, connecting with them on a fundamental level. To make the electrode, they use a non-woven carbon fiber mat as a substrate. They dip the mat into the ink, allow it to dry slowly, and then dip it again, repeating the procedure until they’ve built up a uniform coating of the composite on the substrate. The result of the process is a porous mesh that provides a large surface area of active sites and easy pathways for CO2 molecules to move in and out. Once the researchers have prepared the quinone and ferrocene electrodes, they assemble the electrochemical cell by laminating the pieces together in the correct order — the quinone electrode, the electrolyte separator, the ferrocene electrode, another separator, and the second quinone electrode. Finally, they moisten the assembled cell with their liquid salt electrolyte. Experimental results To test the behavior of their system, the researchers placed a single electrochemical cell inside a custom-made, sealed box and wired it for electricity input. They then cycled the voltage and measured the key responses and capabilities of the device. The simultaneous trends in charge density put into the cell and CO2 adsorption per mole of quinone showed that when the quinone electrode is negatively charged, the amount of CO2 adsorbed goes up. And when that charge is reversed, CO2 adsorption declines. For experiments under more realistic conditions, the researchers also fabricated full capture units — open-ended modules in which a few cells were lined up, one beside the other, with gaps between them where CO2-containing gases could travel, passing the quinone surfaces of adjacent cells. In both experimental systems, the researchers ran tests using inlet streams with CO2 concentrations ranging from 10 percent down to 0.6 percent. The former is typical of power plant exhaust, the latter closer to concentrations in ambient indoor air. Regardless of the concentration, the efficiency of capture was essentially constant at about 90 percent. (An efficiency of 100 percent would mean that one molecule of CO2 had been captured for every electron transferred — an outcome that Hatton calls “highly unlikely” because other parasitic processes could be going on simultaneously.) The system used about 1 gigajoule of energy per ton of CO2 captured. Other methods consume between 1 and 10 gigajoules per ton, depending on the CO2 concentration of the incoming gases. Finally, the system was exceptionally durable. Over more than 7,000 charge-discharge cycles, its CO2 capture capacity dropped by only 30 percent — a loss of capacity that can readily be overcome with further refinements in the electrode preparation, say the researchers.  The remarkable performance of their system stems from what Voskian calls the “binary nature of the affinity of quinone to CO2.” The quinone has either a high affinity or no affinity at all. “The result of that binary affinity is that our system should be equally effective at treating fossil fuel combustion flue gases and confined or ambient air,” he says.  Practical applications The experimental results confirm that the electro-swing device should be applicable in many situations. The device is compact and flexible; it operates at room temperature and normal air pressure; and it requires no large-scale, expensive ancillary equipment — only the direct current power source. Its simple design should enable “plug-and-play” installation in many processes, say the researchers. It could, for example, be retrofitted in sealed buildings to remove CO2. In most sealed buildings, ventilation systems bring in fresh outdoor air to dilute the CO2 concentration indoors. “But making frequent air exchanges with the outside requires a lot of energy to condition the incoming air,” says Hatton. “Removing the CO2 indoors would reduce the number of exchanges needed.” The result could be large energy savings. Similarly, the system could be used in confined spaces where air exchange is impossible — for example, in submarines, spacecraft, and aircraft — to ensure that occupants aren’t breathing too much CO2. The electro-swing system could also be teamed up with renewable sources, such as solar and wind farms, and even rooftop solar panels. Such sources sometimes generate more electricity than is needed on the power grid. Instead of shutting them off, the excess electricity could be used to run a CO2 capture plant. The researchers have also developed a concept for using their system at power plants and other facilities that generate a continuous flow of exhaust containing CO2. At such sites, pairs of units would work in parallel. “One is emptying the pure CO2 that it captured, while the other is capturing more CO2,” explains Voskian. “And then you swap them.” A system of valves would switch the airflow to the freshly emptied unit, while a purge gas would flow through the full unit, carrying the CO2 out into a separate chamber. The captured CO2 could be chemically processed into fuels or simply compressed and sent underground for long-term disposal. If the purge gas were also CO2, the result would be a steady stream of pure CO2 that soft-drink makers could use for carbonating drinks and farmers could use for feeding plants in greenhouses. Indeed, rather than burning fossil fuels to get CO2, such users could employ an electro-swing unit to generate their own CO2 while simultaneously removing CO2 from the air.  Costs and scale-up The researchers haven’t yet published a full technoeconomic analysis, but they project capital plus operating costs at $50 to $100 per ton of CO2 captured. That range is in line with costs using other, less-flexible carbon capture systems. Methods for fabricating the electro-swing cells are also manufacturing-friendly: The electrodes can be made using standard chemical processing methods and assembled using a roll-to-roll process similar to a printing press.  And the system can be scaled up as needed. According to Voskian, it should scale linearly: “If you need 10 times more capture capacity, you just manufacture 10 times more electrodes.” Together, he and Hatton, along with Brian M. Baynes PhD ’04, have formed a company called Verdox, and they’re planning to demonstrate that ease of scale-up by developing a pilot plant within the next few years. This research was supported by an MIT Energy Initiative (MITEI) Seed Fund grant and by Eni S.p.A. through MITEI. Sahag Voskian was an Eni-MIT Energy Fellow in 2016-17 and 2017-18. This article appears in the Spring 2020 issue of Energy Futures, the magazine of the MIT Energy Initiative.  (Comment on this)
4:10p	MIT research on seawater surface tension becomes international guideline The property of water that enables a bug to skim the surface of a pond or keeps a carefully placed paperclip floating on the top of a cup of water is known as surface tension. Understanding the surface tension of water is important in a wide range of applications including heat transfer, desalination, and oceanography. Although much is known about the surface tension of fresh water, very little has been known about the surface tension of seawater — until recently. In 2012, John Lienhard, the Abdul Latif Jameel Professor of Water and Mechanical Engineering, and then-graduate student Kishor Nayar SM ’14, PhD ’19 embarked on a research project to understand how the surface tension of seawater changes with temperature and salinity. Two years later, they published their findings in the Journal of Physical and Chemical Reference Data. This spring, the International Association for the Properties of Water and Steam (IAPWS) announced that they had deemed Lienhard and Nayar’s work an international guideline. According to the IAPWS, Lienhard and Nayar’s research “presents a correlation for the surface tension of seawater as a function of temperature and salinity.” The announcement of the guideline marked the completion of eight years of work with dozens of collaborators from MIT and across the globe. “This project grew out of my work in desalination. In desalination, you need to know about the surface tension of water because that affects how water travels through pores in a membrane,” explains Lienhard, a world leading expert in desalination — the process by which salt water is treated to become potable freshwater. Lienhard suggested Nayar take measurements of seawater’s surface tension and compare the results to the surface tension of pure water. As they would soon find out, getting reliable data from salt water would prove to be incredibly difficult.  “We had thought originally that these experiments would be pretty simple to do, that we'd be done in a month or two. But as we started looking into it, we realized it was a much harder problem to tackle,” says Lienhard. From the outset, Nayar hoped to get enough accurate data to inform a property standard. Doing so would require the uncertainty in the measurements to be less than 1 percent. “When you talk about property measurements, you need to be as accurate as possible,” explains Nayar. The first hurdle he had to surmount to achieve this level of accuracy was finding the appropriate instrumentation to make reliable measurements — something that turned out to be no easy feat. Measuring surface tension To measure the surface tension of water, Lienhard and Nayar teamed up with Gareth McKinley, professor of mechanical engineering, and then-graduate student Divya Panchanathan SM '15, PhD '18. They began with a device known as a Wilhelmy plate, which finds the surface tension by lowering a small platinum plate into a beaker of water then measuring the force the water exerts as the plate is raised. Nayar and Panchanathan struggled to measure the surface tension of salt water at higher temperatures. “The issue we kept finding was once the temperature was above 50 degrees Celsius, the water on the beaker evaporated faster than we could take the measurements,” Nayar says.  No instrument would allow them to get the data they needed — so Nayar turned to the MIT Hobby Shop. Using a lathe, he built a special lid for the beaker to keep vapor in. “The little lid Kishor built had accurately cut doors that allowed him to put a surface tension probe through the lid without letting water vapor get out,” explains Lienhard. After making progress on obtaining data, the team suffered a massive setback. They found that barely visible salt scales, which formed on their test beaker over time, had introduced errors to their measurements. To get the most accurate values, they decided to use fresh new beakers for every single test. As a result, Nayar had to repeat nine months of work just prior to his master’s thesis being due. Fortunately, since the main problem was identified and solved, experiments could be repeated much faster. Nayar was able to redo the experiments on time. The team measured surface tension in seawater ranging from room temperature to 90 degrees Celsius and salinity levels ranging from pure water to four times the salinity of ocean water. They found that surface tension decreases by roughly 20 percent as water goes from room temperature toward boiling. Meanwhile, as salinity increases, surface tension increases as well. The team had unlocked the mystery of seawater surface tension. “It was literally the most technically challenging thing I had ever done,” Nayar recalls. Their data had an average deviation of 0.19 percent, with a maximum deviation of just 0.6 percent — well within the 1 percent bound needed for a guideline. From master’s thesis to international guideline Three years after completing his master’s thesis, Nayar, by then a PhD student, attended an IAPWS meeting in Kyoto, Japan. The IAPWS is a nonprofit international organization responsible for releasing standards on the properties of water and steam. There, Nayar met with leaders in the field of water surface tension who had been struggling with the same issues Nayar had faced. These contacts introduced him to the long, rigorous process of declaring something an international guideline. The IAPWS had previously published standards on the properties of steam developed by the late Joseph Henry Keenan, professor and one-time department head of mechanical engineering at MIT. To join Keenan as authors of an IAPWS standard, the team’s data needed to be verified by measurements conducted by other researchers. After three years of working with the IAPWS, the team’s work was finally adopted as an international guideline. For Nayar, who graduated with his PhD last year and is now a senior industrial water/wastewater engineer at engineering consulting firm GHD, the guideline announcement made the long months collecting data well worth it. “It felt like something getting completed,” he recalls.  The findings that Nayar, Panchanathan, McKinley, and Lienhard reported back in 2014 are broadly applicable to a number of industries, according to Lienhard. “It’s certainly relevant for desalination work, but also for oceanographic problems such as capillary wave dynamics,” he explains. It also helps explain how small things — like a bug or a paperclip — can float on seawater. (Comment on this)

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