Unscratchable Gold Is Harder Than Steel

No doubt, gold is a beautiful and popular precious metal. But it's also soft and tends to scratch easily. Making it more resilient requires mixing it with other metals, but that reduces its quality.

Now a research team from the EPFL in Switzerland, with support from Swiss watchmaker Hublot, have created a very hard high-quality gold. And recently, they unveiled the shiny result.

“What is radically new is being able to make something that is both extremely hard and 18-karat gold. The challenge was to stick with that boundary,” said Andreas Mortensen, a metallurgy professor at the EPFL in Switzerland who led the work. Metallurgy lecturer Ludger Weber, postdoc Reza Tavangar and materials engineer Senad Hasanovic collaborated with Mortensen to develop the new gold.

Others have been able to make hard gold in the past but they haven't been able to achieve the level of hardness required to meet the 18-karat standard, separating real gold from impure gold. Hublot filed for a patent on the new gold composite, Mortensen said. He called Hublot an adventurous company when it comes to designing with new materials.

To make the new gold, the EPFL team used boron carbide, a ceramic that’s one of the hardest materials in the world, along with diamonds. This material has numerous applications, including as a component in bulletproof vests.

First the ceramic was heated in an oven to more than 3,600 degrees Fahrenheit, producing a three-dimensional network almost like a scaffold, with just the right amount of pores. That network was then infiltrated with liquid gold, meaning the scientists pushed gold into the pores. Finally, the combination was solidified to form the composite material.

Mortensen said the new gold looks and feels distinctive. It’s harder to the touch than other gold, and has a darker hue. The material is so hard that no coating is needed to make it unscratchable. Although that’s an advantage to watch-wearers looking for durability, there is a trade-off because it’s slightly more fragile than pure gold that’s soft.

Since gold doesn’t oxidize, there could be other applications beyond jewelry, although the cost of the higher quality and its heft might limit the uses. Luxury goods conglomerate LMVH owns Hublot, so the unscratchable gold may end up being incorporated into other high-end products. Currently Hublot watches made with the new gold are being readied for a large jewelry show in Basel next year. The material still needs to undergo extensive testing, Mortensen added.

Read more at Discovery News