Electrically controlled metals

05 June 2011
Posted by Dave Ansell.

Materials tend to be either hard which means they are strong, but also very brittle and easy to crack, or soft and weaker but able to absorb energy. Although there are ways of getting the best of both worlds there is always a trade off.

Hai-Jun Jin from the Chinese Academy of Science and collegues may have come up with a way around this. They have taken an alloy of gold and silver and then dissolved out the silver. This produces a porous structure of gold with a network of holes a few tens of nm across. They then filled these holes with perchloric acid, a strong oxidant. But gold being unreactive it isn't oxidised, so it continues being the soft malleable material that it normally is.

But they then applied a voltage between the liquid and the gold, which forced a surface layer of gold oxide to form less than 1 atom thick on the huge surface area of the structure. This had the effect of making the material up to twice as stiff and strong, and then by removing the voltage it reverted to its original properties.

The material they made is unlikely to be commercialised as the change in properties was not huge, and it is made out of solid gold!  But if they can achieve larger effects with cheaper materials, it opens up the possibilities of making a material soft while you work it into shape, and then harden it for use. Or softening a damaged hard material to allow it to flow and repair the damage, then hardening it to be used again.


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