Materials Performance

AUG 2018

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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18 AUGUST 2018 W W W.MATERIALSPERFORMANCE.COM MATERIAL MATTERS H 2 O," the researchers write. "Therefore, water vapor directly inf luences the alloy oxidation processes in the early stages, which could affect the formation of a pro- tective oxide layer." The researchers also performed and analyzed in situ TEM experimental mea- surements of oxidation kinetics after the initial oxide layer had formed. The gen- eral process of the oxide grow th on Ni-Cr featured the sparse nucleation and grow th of oxide islands on the initial layer, they say. With subsequent oxida- tion, these oxide islands reached a few microns. By tracking these islands through two series of time-resolved TEM images, the researchers found that the measured oxidation rate in H 2 O showed wider scattering than in O 2 . "The more porous structure of the ini- tial oxide formed in H 2 O leads to a rela- tively large variation in oxide grow th rates," the researchers write. "However, the general trend is that the grow th rate of NiO islands in H 2 O is higher than that in pure O 2 ." Separately, the researchers also found that the oxidation of pure Ni in H 2 O also led to the formation of vacancy clusters, which did not happen in the case of oxida- tion in O 2 . In closing, the researchers explain that the Ni-Cr alloy was routinely shown to have an enhanced oxidation rate dur- ing the early oxidation stages in moist environments at elevated temperatures, adding that the water vapor-promoted oxidation largely stemmed from the incorporation of interstitial protons (H i ) derived from water disassociation. Researchers examined oxide growth on a nickel-chromium alloy when exposed to water, as shown here, and compared it to oxidation when exposed to oxygen. Photo courtesy of EMSL. "The dissolved proton in the oxide lowers vacancy forma- tion energ y, promotes vacancy clustering, and enhances cation and anion diffusion, all of which leads to an increased oxida- tion rate in water vapor and conse- quently a porous structure in the devel- oped oxides at an early stage," they say. The project was worked on by scien- tists from the EMSL, the Pacif ic North- west National Laboratory (Richland, Washington, USA), the Chinese Academy of Sciences (Beijing, China), and State University of New York at Binghamton (Binghamton, New York, USA). The work was supported by the materials sciences and engineering division of the U.S. Department of Energ y (Washington, DC, USA). Research was conducted at EMSL's facilities. Source: EMSL, www.emsl .pnl .gov. Reference 1 "Peering into the Mist: How Water Vapor Changes Metal at the Atomic Level," EMSL News, May 25, 2018, https://www.emsl.pnl. g o v / e m s l w e b / n e w s / p e e r i n g - m i s t - h o w - water -vapor -changes-metal-atomic-level ( June 22, 2018). —Ben DuBose Continued f rom page 17 AUTHORS WANTED NACE is looking for industry experts to write and edit NACE- published books and compilations. Contact Jean Broge +1 281-228-6455 THICKNESS MEASUREMENT OF PROTECTIVE COATINGS Coating Thickness Material Analysis Microhardness Material Testing (860)683-0781 Robust, fast and reliable For ships, bridges, off-shore plat- forms, pipelines and structures Measures in accordance with SSPC-PA2, IMO-PSPC and others From basic "readings only" to stats and detailed inspection plans Surface Profile Measurement Easy and affordable ▪ ▪ ▪ ▪ ▪ ▪ Accurate and precise measurement of coating thick- ness with the Fischer FMP Series

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