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6 MARCH 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 3 UP FRONT —Ben DuBose Rapid Ceramic-Metal Processing Method for Superior Composites Ceramic metal composites, or cermets, are designed to enhance transportation and energy conversion technologies. Image courtesy of Texas A&M; University. Texas A&M; University (College Station, Texas) researchers have developed a tech- nology that enables ceramics and metals to be processed together into cermets with lit- tle to no reaction between constituent materials. Many ceramics and metals are unstable when combined at high temperatures and react with each other, leaving the final com- posite materials with undesirable proper- ties like brittleness or poor resistance to high temperatures. "This severely limits the number of new composite materials that can be developed for our growing needs," says Miladin Radovic, associate professor and head of Texas A&M;'s materials science and engineering department. To address this, Radovic, other faculty, and students developed a current-activated, pressure-assisted infiltration (CAPAI) method to combine ceramics and metals— creating stable, high-performance compos- ites after as little as 9 s. The method uses electric current to instantly heat the metal, and applied pressure to drive the molten metal into a ceramic foam. In their study, the researchers selected aluminum for its light weight, corrosion resistance, and popularity in automotive and aerospace industries, along with tita- nium aluminum carbide (Ti 2 AlC) ceramic foams for fracture toughness, and electrical and thermal conductivity. "The electric current and the pressure together provided simultaneous heating and pressure that actively drove the molten metals into the ceramic preform," Radovic says. "The fast and controllable heating rate, which was as high as 700 °C, offered an easy and efficient way to avoid reactions between ceramics and molten metal." Researchers found the resulting com- posite (Ti 3 AlC 3 /Al) was lightweight with competitive mechanical properties at ambi- ent and elevated temperatures. It is 10 times stronger at room temperatures and 14 times stronger at 400 °C than aluminum alloys. For more information, visit engineering. tamu.edu. Scientists Seek to Raise Concrete's Strength, Ductility Scientists simulated tobermorite to see how it uses dislocations to relieve stress when used in concrete. Photo courtesy of Rice University, Multiscale Materials Laboratory. Rice University (Houston, Texas) scientist Rouzbeh Shahsavari performed an atom- level computer analysis of tobermorite, a naturally occurring crystalline analog to the calcium-silicate-hydrate that comprises cement and holds concrete together. By understanding the structure, researchers hope to make concrete stronger, tougher, and better able to deform without cracking under stress. Tobermorite forms in layers, like paper stacks, that solidify into particles. These particles often have screw dislocations and shear defects that help relieve stress by allowing layers to slide past each other. Shahsavari's team built computer mod- els of tobermorite "super cells," with dislo- cations either perpendicular to or in paral- lel with layers in the material, and then applied shear force. They found that defect- free tobermorite deformed easily as water molecules caught between layers helped them glide past each other. But in particles with screw defects, the layers only glided so far before being locked into place by tooth- like core dislocations. That effectively passed the buck to the next layer, which glided until caught—relieving stress with- out cracking. "The defects can lead to dislocation jogs in certain orientations, which act as a bot- tleneck for gliding, thus increasing the yield strength and toughness," Shahsavari says. For more information, visit news.rice.edu. Three-Layer Nanoparticle Catalysts Boost Batteries Researchers at Singapore's government-led Agency for Science, Technology and Research (A*STAR) discovered that nanoparticles containing three different layers of material can boost the perfor- mance of zinc-air batteries. Historically, zinc-air batteries are cheap and long-lasting. But the sluggish reaction between the water-based electrolyte and oxygen limits the battery's voltage output and its performance at high current. In response, researchers developed a nanoparticle catalyst. The particles are 20 to 50 nm across, with a cobalt core encased by an inner shell of cobalt oxide (Co 3 O 4 ) and surrounded by an outer shell of pyrolyzed polydopamine (PPD)—a form of carbon "dotted" with nitrogen atoms. These nanoparticles coat a porous carbon support that acts as an electrode. Their structure helps prevent them from leaching cobalt or clumping together, and the protective outer shell boosts durability. These nanoparticles transform oxygen to hydroxide in a single step. Researchers suggest nitrogen atoms in the PPD shell help attract and make oxygen atoms more reactive on their way to catalytic sites in the cobalt oxide and PPD. Meanwhile, the cobalt core and PPD shell help electrons flow efficiently to the oxygen atoms. In con- trast, particles containing only cobalt and cobalt oxide, or only PPD, transformed oxy- gen in a two-step process that produced hydroperoxide, a corrosive intermediate. The researchers tested their electrode in a zinc-air battery and found that it pro- duced a current of 5 mA/cm 2 at 1.36 V for five days, outperforming an electrode that relied on a conventional platinum catalyst. For more information, visit research. a-star.edu.sg.