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Researchers discover that adding arsenic to magnesium imparts corrosion resistance; “stainless magnesium”

Researchers in Australia and Wales have discovered that alloying additions of arsenic to magnesium can impart significant corrosion resistance. Their discovery, reported in the journal Electrochemistry Communications, could have implications for light-weighting in the aerospace, automotive and electronics industries.

Weighing in at two thirds less than aluminium, magnesium is the lightest structural metal. It has many potential industrial applications, but uptake is severely restricted by its poor resistance to corrosion. Identification of methods to restrict magnesium corrosion is the first step in engineering such technology into functional alloys.

The researchers, led by Monash University’s Associate Professor Nick Birbilis, found that the addition of very low levels of arsenic to magnesium retards the corrosion reaction by effectively “poisoning” the reaction before it completes.

Once magnesium is available in a more stainless, or corrosion-resistant, form wider use will lead to significant weight and energy savings in transportation industries. It has been the subject of significant research efforts concentrating on developing light metals.

Associate Professor Birbilis, of the Monash Department of Materials Engineering, said the discovery would contribute to the birth of more stainless magnesium products by exploiting cathodic poisons.

In an era of light-weighting for energy and emissions reductions, there is a great demand for magnesium alloys in everything from portable electronics to air and land transportation. Magnesium products are rapidly evolving to meet the demands of industry, but presently are hindered by high corrosion rates. The arsenic effect we discovered is now being trialled as a functional additive to existing commercial alloys. Our breakthrough will help develop the next generation of magnesium products, which must be more stainless.

—Associate Professor Birbilis

Resources

  • N. Birbilis, G. Williams, K. Gusieva, A. Samaniego, M.A. Gibson, H.N. McMurray (2013) Poisoning the corrosion of magnesium, Electrochemistry Communications, Volume 34, September 2013, Pages 295-298, doi: 10.1016/j.elecom.2013.07.021

Comments

Engineer-Poet

If the arsenic can be limited to a thin surface coating (like nitriding) rather than being incorporated into the bulk, the total amount would be reduced immensely and the potential for contamination with it.

GreenPlease

Nitriding is a gaseous diffusion heat-treat. It might be easier/safer to incorporate it into the bulk metal especially if concentrations are sufficiently low and the As became bound to the Mg.

Davemart

Surely this is not much different to the age-old practise of doping steel with chromium?
I write under correction, as I am certainly no industrial chemist!

Predrag Raos

GreenPlease, arseniding could be probably effected from the gaseous phase too by using arsine (AsH3) as a source of the element.

GreenPlease

Just seems like alloying would be an easier process, plus, if there was surface wear, the corrosion protection would remain (vs. a surface treatment). Both are viable approaches I guess.

sd

Magnesium has a density about 2/3 that of aluminum not two thirds less than aluminum. 1.738 gm/cm-3 versus 2.700 g/cm-3. Also, if you are looking for light weight structures try beryllium at 1.85 gm/cm-3. It is stiffer than steel and is used for satellite components including optical mirrors but it does have some problems and is not easy to work with.

Mannstein

Machining beryllium definitely is a health problem.

sd

"Machining beryllium definitely is a health problem."

It has to be done in a controlled atmosphere and there are bad health consequences if you inhale beryllium dust. That is why I said that it is not easy to work with. It is used in special circumstances. I used to work for Draper Labs/MIT Instrumentation Lab back in the late 60's and the 70's. They designed machined beryllium parts for missile guidance systems. Apparently, there have also been some very expensive bicycle frames made from beryllium tubes. Carbon fiber may be better than steel but it is not as good as beryllium for stiffness to weight.

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