Surprising discovery could change the way industry uses nickel

Surprising discovery could change the way industry uses nickel
SEM image of corroded nickel at the surface. Credit: Mengying Liu

Nickel is one of the most abundant elements on earth. It is hard, yet malleable, magnetic at room temperature, and a relatively good conductor of electricity and heat. Most notably, nickel is highly corrosion resistant, which provides for a variety of uses by industry.

However, a surprising discovery by a team of researchers at Texas A&M University has found that not only corrodes, but does so in a way that scientists least expected.

The team was led by Dr. Michael Demkowicz, associate professor and graduate director in the Department of Materials Science and Engineering, and director of the Center for Research Excellence on Dynamically Deformed Solids at Texas A&M University.

Their work was published in the American Physical Society's Physical Review Materials journal in an article titled "Preferential Corrosion of Coherent Twin Boundaries in Pure Nickel Under Cathodic Charging."

A surprising observation

Like a finished jigsaw puzzle, materials are made of interlocking pieces. Microscopically, nickel is made of aggregates of small, tightly packed crystals or grains.

Corrosion preferentially attacks the joints, or "boundaries," between these grains. This phenomenon, known as intergranular corrosion, is a localized type of decay that occurs at the microscopic level, targeting the breakdown of materials at the edges of each of these boundaries, rather than at the outer surface of the material. As such, it weakens the material from the inside-out.

Coherent twin boundaries are areas in which the material’s internal structure pattern forms a mirror image of itself along a shared border. Credit: Dharmesh Patel

Until now, scientists thought that one special type of boundary, known as a coherent twin boundary, was resistant to corrosion. Surprisingly, the team discovered that nearly all the corrosion in their experiments occurred precisely on these boundaries.

Coherent twin boundaries are areas in which the material's internal structure pattern forms a mirror image of itself along a shared border. They occur when crystal formations on either side of an atom-wide border line up without disorder or disarray. These types of boundaries naturally occur during crystallization, but can also be the result of mechanical or thermal influence.

"Pure nickel is mostly corrosion resistant. But when we charged it at the cathodic (passive and lowest energy) side, which is even less likely to corrode, we did, surprisingly, see visible corrosion trenches on coherent twin boundaries," said Mengying Liu, graduate student at the Department of Materials Science and Engineering at Texas A&M and first author on the paper. "This finding will help engineers predict where corrosion is most likely to begin. It may even lead to the production of metals that corrode less."

A better understanding

The team's research not only provides engineers with vital insight into materials often utilized in situations that require corrosion resistance, but also offers a new perspective regarding intergranular corrosion along coherent twin boundaries.

For years, researchers have operated on the assumption that coherent twin boundaries resist corrosion. They have even worked to create metals that have more of these boundaries in an effort to reduce corrosion.

"This finding takes decades of assumptions on metal corrosion and flips them on their head," said Demkowicz. "In an effort to reduce corrosion, people have been making metals that contain as many coherent twin boundaries as possible. Now that entire strategy will have to be reconsidered."

Demkowicz believes the scientific insight provided by this study may be even more important than its technological applications. "It turns out the reasoning that previously led us to believe coherent twin boundaries are corrosion resistant is flawed," he said. "This work provides clues on how to improve our fundamental understanding of metal ."


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More information: Mengying Liu et al, Preferential corrosion of coherent twin boundaries in pure nickel under cathodic charging, Physical Review Materials (2019). DOI: 10.1103/PhysRevMaterials.3.063606
Citation: Surprising discovery could change the way industry uses nickel (2019, August 6) retrieved 21 August 2019 from https://phys.org/news/2019-08-discovery-industry-nickel.html
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Aug 06, 2019
Why is Nickel so often used when it causes serious health problems?
I know it's cheap, but sensitization will affect a slowly increasing significant proportion of people.
Nickel is an important cause of allergic contact dermatitis (ACD) in the general population, both among children and adults, with a worldwide prevalence of around 8.6%. The prevalence among young females is even higher, around 17%. (https://www.ncbi....047925/)
I find old cupro nickel coinage very much less allergic - and pure Nickel I can tell within seconds.
Is there any way we could reduce these debilitating effects? - maybe plate cupronickel, or stainless - it seems OK if in solid solution with another metal.


Aug 06, 2019
Hi, #An, is there significant correlation between nickel-related ACD and zinc deficiency / poor uptake ?

Aug 07, 2019
Why is Nickel so often used when it causes serious health problems?


"Nickel is one of the most abundant elements on earth. It is hard, yet malleable, magnetic at room temperature, and a relatively good conductor of electricity and heat. Most notably, nickel is highly corrosion resistant, which provides for a variety of uses by industry."

Nickel is used by many enzymes; we need it in food. It is also excreted so that we have a good balance: "The average daily exposure does not pose a threat to human health. Most of the nickel absorbed every day by humans is removed by the kidneys and passed out of the body through urine or is eliminated through the gastrointestinal tract without being absorbed. Nickel is not a cumulative poison, but larger doses or chronic inhalation exposure may be toxic, even carcinogenic, and constitute an occupational hazard.[95]" [ https://en.wikipe...cal_role ]

So, not a problem. Your link does not work, but seriously: allergies?

Aug 07, 2019
- ctd -

That is like complaining that people like cats or nuts, despite that some people are allergic to those. Sure, we could wish allergies do not exist, and we can avoid allergens when necessary. But is it a "serious" problem, in proportion? (Some allergies, like nut allergy, can kill...)

Aug 07, 2019
Sorry, the link is a couple of characters too long: https://www.ncbi....3047925/
I think that an allergy rate of 8.6% is a serious concern and was asking how it could be reduced by carefull alloying, not an outright ban. The rate of allergy is not set at a particular figure, it increases due to sensitisation. Once an individual has become sensitized to nickel, it will be a life-long condition
The paper above concludes: Nickel is the most common sensitizing agent worldwide. Allergic contact dermatitis due to this metal represents great morbidity.

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