{"id":8232,"date":"2016-03-30T06:31:29","date_gmt":"2016-03-30T06:31:29","guid":{"rendered":"http:\/\/revoscience.com\/en\/?p=8232"},"modified":"2016-03-30T06:31:29","modified_gmt":"2016-03-30T06:31:29","slug":"how-to-make-metal-alloys-that-stand-up-to-hydrogen","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/how-to-make-metal-alloys-that-stand-up-to-hydrogen\/","title":{"rendered":"How to make metal alloys that stand up to hydrogen"},"content":{"rendered":"

New approach to preventing embrittlement could be useful in nuclear reactors.<\/em><\/strong><\/p>\n

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\"An<\/a>
An artist\u2019s rendering of nuclear fuel rods in front of a colorful computational valley predicted for alloying compositions.
Image: Mostafa Youssef and Lixin Sun<\/figcaption><\/figure>\n

CAMBRIDGE, MA<\/strong> — High-tech metal alloys are widely used in important materials such as the cladding that protects the fuel inside a nuclear reactor. But even the best alloys degrade over time, victims of a reactor\u2019s high temperatures, radiation, and hydrogen-rich environment. Now, a team of MIT researchers has found a way of greatly reducing the damaging effects these metals suffer from exposure to hydrogen.<\/span>
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The team\u2019s analysis focused on zirconium alloys, which are widely used in the nuclear industry, but the basic principles they found could apply to many metallic alloys used in other energy systems and infrastructure applications, the researchers say. The findings appear in the journal\u00a0<\/span>Physical Review Applied<\/em>, in a paper by MIT Associate Professor Bilge Yildiz, postdoc Mostafa Youssef, and graduate student Ming Yang.<\/span>
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Hydrogen, which is released when water molecules from a reactor\u2019s coolant break apart, can enter the metal and react with it. This leads to a reduction in the metal\u2019s ductility, or its ability to sustain a mechanical load before fracturing. That in turn can lead to premature cracking and failure. In nuclear power plants, \u201cthe mechanical integrity of that cladding is extremely important,\u201d Yildiz says, so finding ways to improve its longevity is a high priority.<\/span>
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But it turns out that the initial entry of the hydrogen atoms into the metal depends crucially on the characteristics of a layer that forms on the metal\u2019s surface.<\/span>
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A coating of zirconium oxide naturally forms on the surface of the zirconium in high-temperature water, and it acts as a kind of protective barrier. If carefully engineered, this layer of oxide could inhibit hydrogen from getting into the crystal structure of the metal. Or, under other conditions, it could emit the hydrogen in gas form.<\/span>
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[pullquote]The team\u2019s findings suggest two potential strategies, one aimed at minimizing hydrogen penetration and one at maximizing the ejection of hydrogen atoms that do get in.[\/pullquote]<\/p>\n

While researchers have been studying hydrogen embrittlement for decades, Yildiz says, \u201calmost all of the work has been on what happens to hydrogen inside the metal: What are the consequences, where does it go, how does it lead to embrittlement? And we learned a lot from those studies.\u201d But there had been very little work on how hydrogen gets inside in the first place, she says. How hydrogen can enter through this surface oxide layer, or how it can be discharged as a gas from that layer, has not been quantified.<\/span>
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\u201cIf we know how it enters or how it can be discharged or ejected from the surface, that gives us the ability to predict surface modifications that can reduce the rate of entry,\u201d Yildiz says. Her team has found that it\u2019s possible to do just that, improving the barrier\u2019s ability to block incoming hydrogen, potentially by as much as a thousandfold.<\/span>
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The hydrogen has to first dissolve in the oxide layer before penetrating into the bulk of the metal beneath. But the hydrogen\u2019s dissolution can be controlled by doping that layer \u2014 that is, by introducing atoms of another element or elements into it. The team found that the amount of hydrogen solubility in the oxide follows a valley-shaped curve, depending on the doping element\u2019s ability to introduce electrons into the oxide layer.<\/span>
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\u201cThere is a certain type of doping element that minimizes hydrogen\u2019s ability to penetrate, whereas other doping elements can introduce a maximum amount of electrons in the oxide, and facilitate the ejection of hydrogen gas right at the surface of the oxide,\u201d says Mostafa. So being able to predict the dopants that belong to each type is the essential trick to making an effective barrier.<\/span>
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The team\u2019s findings suggest two potential strategies, one aimed at minimizing hydrogen penetration and one at maximizing the ejection of hydrogen atoms that do get in.<\/span>
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The blocking strategy is \u201cto target the bottom of the valley\u201d by incorporating the right amount of an element, such as chromium, that produces this effect. The other strategy is based on different elements, including niobium, that propel hydrogen out of the oxide surface and protect the underlying zirconium alloy.<\/span>
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The doping could be accomplished by incorporating a small amount of the dopant metal into the initial zirconium alloy matrix, so that this in turn gets incorporated into the oxidation layer that naturally forms on the metal, the team says.<\/span>
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The team stresses that what they found is likely to be a general approach that can be applied to all kinds of alloys that form oxidation layers on their surfaces, as most do. Their approach could lead to improvements in longevity for alloys used in fossil fuel plants, bridges, pipelines, fuel cells, and many other applications.<\/span>
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\u201cAny place you have metals exposed to high temperatures and water,\u201d Yildiz says \u2014 for example on equipment used in oil and gas extraction \u2014 is a potential situation where this work might be applicable.<\/span>
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The work was supported by the Consortium for Advanced Simulation of Light Water Reactors, funded by the U.S. Department of Energy, and computational support was provided by the U.S. National Science Foundation.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

A team of MIT researchers has found a way of greatly reducing the damaging effects these metals suffer from exposure to hydrogen.<\/p>\n","protected":false},"author":6,"featured_media":8233,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-8232","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0-150x150.jpg",150,150,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0-300x200.jpg",300,200,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",600,400,false],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",600,400,false],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",540,360,false],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",95,63,false],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",639,426,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",96,64,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2016\/03\/MIT-Hydrogen-Crack_0.jpg",150,100,false]},"author_info":{"info":["Amrita Tuladhar"]},"category_info":"Research<\/a>","tag_info":"Research","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/8232","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=8232"}],"version-history":[{"count":0,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/8232\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/8233"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=8232"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=8232"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=8232"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}