Materials Performance

AUG 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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6 AUGUST 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 8 UP FRONT Fast, Nondestructive Test for Two-Dimensional Materials In this test, red light is emitted from the edges where defects are located. Image courtesy of Penn State. Pennsylvania State University (Penn State) (University Park, Pennsylvania) researchers are using a fast, nondestructive optical method to analyze defects in two-dimen- sional materials. Their technique utilizes fluorescent microscopy, in which a laser of a specific wavelength is shined on a sample. Excited electrons, pushed to a higher energy level, emit photons of a longer wavelengths when they drop to a lower energy state. The longer wavelengths can be measured by spectroscopy, giving information about the defect type and location. The sample goes in a specimen holder with a 77 °K (–196 °C) temperature, where the electron-hole pairs producing the fluo- rescence are bound to the defect—emitting a stronger signal than in pristine areas. "For the first time, we have established a direct relationship between the optical response and the amount of atomic defects in two-dimensional materials," says researcher Victor Carozo. The team correlates results visually with a high-powered electron microscope known as transmission electron microscopy (TEM). Theoretical simulations are also used for validation. Without the optical method, the TEM imaging process would take much longer, researchers say, while also posing more risk of damaging the sample. The team identifies the semiconductor industry as one potential beneficiary. "In the semiconductor industry, defects are important because you can control properties through defects," says Mauricio Terrones, a Penn State professor and researcher. "This is known as defect engi- neering. Industry knows how to control defects and which types are good for devices." For more information, visit www.news. psu.edu. Real-Time Monitoring for Irradiated Materials The new method relies on optical probes, which use multiple sets of laser beams. Image courtesy of MIT. Massachusetts Institute of Technology (MIT) (Cambridge, Massachusetts) researchers developed a new method to enable the continuous monitoring of mate- rials exposed to high radiation. They believe this could eliminate the need for preventive replacement by allowing materials to remain in place longer. According to the team, findings show their technique, known as transient grating spectroscopy (TGS), can be performed quickly and with high sensitivity. Traditional practices requiring samples to be extracted and tested in outside devices can be time- consuming and expensive, the researchers explain, and they also do not provide infor- mation on how damage occurs over time. However, this method works without requiring any physical contact between the monitoring device and metals. Instead, it relies on optical probes, which use one set of laser beams to stimulate surface vibra- tions, and others to probe the properties of those vibrations by using the interference patterns of the beams. Those properties can reveal details of both the surface properties and bulk material. The new approach can also show changes in the thermal and mechanical properties that affect the material's response to temperature surges or vibra- tion. "What we're working toward is a real- time diagnostic system that works under radiation conditions," says Michael Short, an MIT professor and researcher. Compared to existing methods, which use multiple samples exposed over long periods, Short says the technique can pro- vide "more data from one sample, in one experiment, in less than 1% of the time." For more information, visit www.news. mit.edu. Self-Healing Technology Boosts Lithium-Ion Batteries Researchers at the University of Illinois (Champaign, Illinois) are applying self-heal- ing technology to lithium-ion batteries to make them more reliable. The group devel- oped a battery that utilizes a silicon nanoparticle composite material on the negatively charged side and uses a novel way to hold the composite together—often a problem in batteries with silicon. The negatively charged electrode, or anode, inside lithium-ion batteries is typi- cally made of a graphite particle composite. These batteries work well, but they can take a long time to power up. Over time, the charge does not last as long. Past research found that anodes made from nanosize sili- con particles are less likely to break down, but suffer from other problems. "You go through the charge-discharge cycle once, twice, three times, and eventu- ally you lose capacity because the silicon particles start to break away from the binder," says Scott White, an engineering professor who helped lead the study. To combat this problem, the group fur- ther refined the silicon anode by giving it the ability to fix itself on the fly. This self- healing happens through a reversible chem- ical bond at the interface between the sili- con nanoparticles and polymer binder. The researchers tested their new battery against one without the reversible chemical bonding and found that it retains 80% of its initial capacity, even after 400 cycles. It also has higher energy density, meaning it can store more electricity than a graphite-anode battery. Future studies will examine how this technology can work with solid-state batteries. For more information, visit www.news. illinois.edu. —Ben DuBose

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