Swiss researchers create unscratchable gold

December 16, 2011 By Laure-Anne Pessina
Credit: 2011 Hublot

(PhysOrg.com) -- EPFL scientists have created 18-karat gold that's harder than tempered steel and virtually unscratchable.

By combining a gold alloy with , an extremely hard ceramic that’s used in bulletproof vests, a team of EPFL researchers has succeeded in making the world’s toughest 18-karat gold (75% gold). With a Vickers hardness number of 1000, it’s harder than most tempered steels (600 Vickers) and thus almost impossible to scratch, except with a diamond. This discovery is the result of a three-year collaboration between the Mechanical Metallurgy Laboratory in EPFL’s Institute of Materials, under the leadership of Professor Andreas Mortensen, and the Swiss watchmaking company Hublot.

The process for developing this material is relatively complicated. Powdered boron carbide is heated to almost 2000°C, where it forms a rigid, porous structure by a process called sintering. A liquid molten alloy of gold is infiltrated under very high pressure into the pores of this structure, and then solidified, yielding a pore-free composite material. The final material is thus made up of two kinds of crystals that are intimately interconnected in space, like two three-dimensional labyrinths. Because the molten gold used is a previously-made alloy based on 24-karat gold and aluminum (3%) for strength, the final gold is thus 3% aluminum, 75% gold and 22% boron carbide
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By definition, gold is very soft. Managing to harden it to this degree while still maintaining 18-karat purity was a real challenge for the EPFL scientists. They overcame the obstacle by taking the ceramic-metal composite approach. Composite materials are created by artificially combining several materials that conserve their individual characteristics even after they’re assembled. In this they are different from alloys, in which atoms mix together to form a new, homogeneous, material.

The EPFL researchers aren’t the first to play around with different materials in an effort to make more resistant gold. They are, however, the first to have attained this degree of hardness in 18-karat gold. The first watches made using this new will be presented in 2012 at BaselWorld, the world watch and jewelry show.

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Nanobanano
2.3 / 5 (9) Dec 16, 2011
Interesting.

Try it with platinum and silver?

Maybe the "Ancient Aliens" really were mining gold, lol...

From the "New Jerusalem" in the Bible...

"And the building of the wall of it was of jasper: and the city was pure gold, like unto clear glass.

and the street of the city was pure gold, as it were transparent glass."

Maybe it's some sort of nanotechnology involved?

Gold has recently been shown to change it's optical properties, including color, under different preparations of nanotechnology, involving different sized particles.

Could we make "pure Gold" transparent (yet strong enough and hard enough to be used as a "street",) by using the right shape of nanoparticle and the right lattice structuers?
tadchem
3.5 / 5 (2) Dec 16, 2011
Another step forward in composite materials...
The BC provides a skeleton for the Au-Al alloy because the BC lattice (a diamond-like lattice) is very open, and allows for interspersed atoms.
A step back from this would involve layering of alternate 2-D lattices. A step forward would involve interpenetrating 3-D lattices. One eventual outcome would be ultra-high density data storage in 'holographic' memory based on interpenetrating semiconductor lattices.
jselin
1 / 5 (1) Dec 16, 2011
@tadchem:

This is just old fashioned metal matrix composites... not some sort of atomic scale intercalation.
Nik_2213
1 / 5 (1) Dec 16, 2011
I'd be concerned that the aluminium content will react with salt sweat...
thuber
4 / 5 (1) Dec 16, 2011
This has great application in Space technology, as opposed to say just jewelry. More robust circuitry is important when you are traveling at astronomical speeds.
Isaacsname
not rated yet Dec 17, 2011
So they use high-pressure to force the gold to effuse into the BC ? Fascinating, if I understand correctly. They made a metal foam and forced another metal into it.

So...aside from scratch-proof watches,.....
Blakut
4 / 5 (1) Dec 19, 2011
Finally, a gold sword that's tougher than steel in all those RPG games makes sense!

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