An 18-carat gold nugget made of plastic

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PinkDiamond
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An 18-carat gold nugget made of plastic

Post by PinkDiamond »

This is another one that Steve found and sent to me, and it's fascinating. :shock:

Note that this article is from Phys.org, not the industry, so they incorrectly used carat, which is for gemstones, instead of karat which is for gold. We'll forgive them though because this is quite remarkable, and as far as I know this hasn't made it way to the industry quite yet since I've seen nothing about it in the trade news. You're hearing it here first, folks. :)

January 10, 2020
An 18-carat gold nugget made of plastic
by Peter Rüegg, ETH Zurich

Image
Looks amazingly similar to a real nugget: 18-carat gold with latex as the base material. Credit: ETH Zurich / Peter Rüegg

"ETH researchers have created an incredibly lightweight 18-carat gold, using a matrix of plastic in place of metallic alloy elements.

Lovers of gold watches and heavy jewellery will be thrilled. The objects of their desire may someday become much lighter, but without losing any of their glitter. Especially with watches, a small amount of weight can make all the difference. No one wants to wear a heavy watch on their wrist, even if it's made of real gold. After a time, it becomes uncomfortable and annoying.

Formerly a postdoc in the ETH lab headed by Raffaele Mezzenga, Professor of Food and Soft Materials, Leonie van 't Hag set to create a new form of gold that weighs about five to ten times less than traditional 18-carat gold. The conventional mixture is usually three-quarters gold and one-quarter copper, with a density of about 15 g/cm3.

That's not true for this new lightweight gold: its density is just 1.7 g/cm3. And nonetheless it is still 18-carat gold. How was this miraculous lightness achieved? Instead of a metal alloy element, van 't Hag, Mezzenga and colleagues used protein fibres and a polymer latex to form a matrix in which they embedded thin discs of gold nanocrystals. In addition, the lightweight gold contains countless tiny air pockets invisible to the eye. The researchers' study on this process has just been published in the journal Advanced Functional Materials.

Image
Gold nanoplatelets embedded in a latex matrix. Credit: Stephan Handschin/ScopeM/ETH Zurich

Here's how the researchers create the new lightweight gold: first, they add the ingredients to water and create a dispersion. After adding salt to turn the dispersion into a gel, next they replace the water in it with alcohol.

Then they place the alcohol gel into a pressure chamber, where high pressures and a supercritical CO2 atmosphere enables miscibility of the alcohol and the CO2 gas; when the pressure is released, everything turns it into a homogeneous gossamer-like aerogel. Heat can be further applied afterwards to anneal the plastic polymers, thus transforming the material and compacting into the final desired shape, yet preserving the 18 carat composition.

Properties of a plastic workpiece

"This gold has the material properties of a plastic," Mezzenga says. If a piece of it falls onto a hard surface, it sounds like plastic. But it glimmers like metallic gold, and can be polished and worked into the desired form.


Credit: ETH Zurich

The researchers can even adjust the hardness of the material by changing the composition of the gold. They can also replace the latex in the matrix with other plastics, such as polypropylene. Since polypropylene liquifies at some specific temperature, "plastic gold" made with it can mimic the gold melting process, yet at much lower temperatures. Furthermore, the shape of the gold nanoparticle can change the material's colour: "nanoplatelets" produce gold's typical shimmer, while spherical nanoparticles of gold lend the material a violet hue.

"As a general rule, our approach lets us create almost any kind of gold we choose, in line with the desired properties," Mezzenga says.

Gold for watchmaking and electronics

Mezzenga points out that, while the plastic gold will be in particular demand in the manufacture of watches and jewellery, it is also suitable for ... "

https://phys.org/news/2020-01-carat-gol ... y-nwletter
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Re: An 18-carat gold nugget made of plastic

Post by rocks2dust »

Yes, that is interesting. I wonder if this might also lead to gold metal clays that don't shrink as much and cost less?
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Re: An 18-carat gold nugget made of plastic

Post by SwordfishMining »

I was wondering if it was made with a ceramic sponge, then the gold would smear polish over into a "solid layer" when buffing. Works a job on the opal buyers, we will see how the gold buyers take to it. It is 18ct by wt not by volume and like the 1kt might be more properly called gold flavored.
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Re: An 18-carat gold nugget made of plastic

Post by PinkDiamond »

SwordfishMining wrote:It is 18ct by wt not by volume and like the 1kt might be more properly called gold flavored.


For sure it could be called 'gold flavored', but that's the whole idea; that the volume is less so the metal is lightweight instead of the normal weight of gold. Personally, I like the weight and feel of gold, and I would think this could be damaged quite easily, and even deform and break, so I doubt I would favor it for anything other than possibly large earrings, since the weight of gold pulls on and can expand piercings in earlobes as this article from JCK on this new alloy correctly points out.

That said, it will be interesting to see how designers and the trade react to it, and whether the public will take to it or not. Here's JCK's take on it. :)

New Alloy Creates 18k Gold That’s 10 Times Lighter
January 24, 2020 by Rob Bates

Image

"Scientists have developed a new alloy they say produces 18k gold that is five to 10 times lighter than the standard product.

The new alloy, created by researchers at Swiss university ETH Zurich, is made from protein fibers and a polymer latex instead of metals like copper. The resulting gold weighs 1.7 grams per cubic centimeter; standard 18k gold weighs 15 grams per cubic centimeter.

Raffaele Mezzenga, professor of food and soft materials at ETH, believes the jewelry industry will embrace the new lightweight metal.

“Gold is a beautiful material but its density is high,” he tells JCK. “This will essentially have a density similar to aluminum but physical properties similar to plastic.

“It’s a matter of trade off between properties,” he adds. “If you want to go for something that is light and durable, this is a way to go. Traditional gold is 10 times more dense. It depends on what you want to do.”

He notes that some people find gold products too heavy.

“Gold earrings are often too heavy and uncomfortable; they pull on the ears. The same with necklaces. This will let you have a similar volume of gold. It will just be 10 times lighter.

But does the new alloy have the exact same durability as traditional 18k gold? Mezzenga can’t say for sure.

“My naive answer would be no,” he says. “Gold is gold. It’s perpetual. Plastics are long term but I wouldn’t compare the durability of plastic that of gold.”

He says that the new gold will be immediately identifiable by jewelers, who will feel its lighter weight.

The researchers can even vary the hardness of the gold by changing its content.

Mezzenga says the material can still be melted down for its gold content, but it will melt at a lower temperature as standard gold.

The team of researchers had previously created what they called the lightest gold in the world—a metal so lightweight it could float on cappuccino froth. But that proved too ... "

https://www.jckonline.com/editorial-art ... -18k-gold/
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