The New Gold

Lightweight gold with equivalent monetary value to its origin. The amazing possibilities of a recent invention by the ETH Zurich.

A composite of gold - polymers and air. A year ago, the very big news of lightweight 18-carat gold went around the world. Where does research stand today? A conversation with Prof. Dr. Raffaele Mezzenga from the ETH Zurich

About a year ago the headline could be read everywhere: "18-carat plastic nugget invented at ETH Zurich". What has happened in the meantime?
One year ago, we were capable of producing 2-3 nuggets per week, at most. In the meantime, we focused on making the technology more scalable in order to allow the production of volumes which are more relevant for real applications. We are now confident, that we will be able to produce any type of shape and any volume in a fully scalable and industrially-relevant way.

The publication also mentioned the weight of the nugget. Ordinary gold has a density of 15 g/cm3. Your light gold has a density of only 1.7 g/cm3, yet it has 18 carats. Why is that so?
The main point of our technology is replacing copper, silver or other heavy metals typically used to produce 18 carat gold alloys, with polymers and air! Polymers have a density of 1 g/cm3, air has virtually zero density. The result is a new type of 18K gold blend with a density ranging between 1 and 4 g/cm3, depending on whether voids are introduced or not in the final material.

You mention the jewelry and watch industry as possible areas of application, but also electronics. Have you received a lot of interest from these industries?
We have received an overwhelming interest from a number of different sectors, but most importantly, from the jewelry and watch industry. At the moment, we remain open and consider all possibilities and sectors, such as electronics, but also fine arts and other creative and innovative fields.

You also refer to a shielding property against radioactive radiation. Have other areas of potential applications emerged in the meantime?
Gold has a very high cross-section to electromagnetic and particle radiation. For these reasons it is a typical material one looks at with respect to cosmic radiation. Some discussion has been initiated within the aerospace sector to explore this possibility further.

Your lightweight gold can also change color depending on its composition and is processable just as conventional gold. So, is it a product suitable for industrial use or does it need further research?
We are still working on that, but yes, the color can be changed significantly towards pink and violet because we use a colloidal approach where different sizes of gold nanoparticles are used to promote absorption and different wavelengths, i.e. color appearance. No chemistry involved: only physics.

The processing of gold is often done under highly polluting processes. Does your process differ in this regard?
Yes, and this is perhaps one of the most innovative components of our work. As you mention, gold processing, particularly refinement of gold back to 24 carats, is a highly polluting process, involving very corrosive and harmful chemicals. The gold we have invented can be fully recycled back to 24 carats purity with one single environmentally friendly step. In this respect, we can certainly say that ours is not only the lightest gold ever produced, but also the only one which has a fully environmental friendly profile, thus holding a unique position within a very unique niche in the circular economy of gold.

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