When it comes to gold, beauty and weight are two sides of the same coin. As nice as it looks in a watch or ring, pure gold would get too heavy for everyday wear, so it’s often lightened up with alloys. Now, by mixing it with plastic instead of other metals, researchers at ETH Zurich have created a new form of gold with as little as one-10th the usual weight, but retaining the same purity.
While 24-karat gold is entirely pure, that’s not entirely practical for jewelry. To make the precious metal lighter and more resistant to damage, it’s mixed with another metal, often copper, giving it a purity of 18 karats. Usually the ratio is 75 percent gold to 25 percent copper, giving it a density of about 15 grams per cubic centimeter.
But the new mixture weighs between one-fifth and one-10th of this, with a density of around 1.7 g/cm3. Rather than another metal, the gold is mixed with polymer latex and protein fibers, and dotted with air pockets. Importantly, it’s still 18-karat gold, making it just as pure as any other piece of jewelry with that rating. The resulting material looks exactly like gold, with all the luster you’d expect of this precious metal, only it's far lighter.
If this sounds familiar, that’s because the team has previously concocted gold foam, the lightest form of the stuff ever. But that form wasn’t stable enough to make jewelry or anything else with it, so the researchers instead developed a more useful new type of gold.
To make the new lightweight gold, the team starts by combining tiny gold platelets, the polymer latex, fibers, water and salt, creating a gel. Then the water is replaced with alcohol and the mix is placed in a pressure chamber full of CO2, turning the golden plastic into a light aerogel. After that, the gold can be heated to melt and shape it into whatever form is needed.
Along with being much lighter, the new type of gold has several other advantages over traditional forms. Properties like hardness can be easily tweaked at the beginning of the process by changing the composition. Even the color can be changed by swapping in different shaped nanoparticles, with spheres giving the material a violet hue.
It can also be easier to mold – normally gold melts at 1,064° C (1,943° F), but this version becomes soft enough to shape at just 105° C (221° F).
One thing the team may not have considered, though, is whether the public will accept plastic gold. Even if it looks the same and officially has the same purity, the fact that it feels like costume jewelry might be enough to put some people off. Lab-made diamonds are facing a similar quandary.
That said, there are plenty of applications for the new material outside of jewelry. The team says that this new form of gold will also be useful in making electronic devices, chemical catalysts and even radiation shielding.
The research was published in the journal Advanced Functional Materials, and the team shows off the plasticky nature of the new gold in the video below.
Source: ETH Zurich
