Manufacturing Bits: Jan. 13

Plastic gold
ETH Zurich has developed an 18-carat gold nugget based on plastic.

Instead of traditional metallic alloy elements, ETH’s gold nugget consists of a matrix of plastic. Weighing five to ten times less than traditional gold, ETH’s plastic gold can be used in watches, jewelry, radiation shielding, catalysis and electronics.

Gold is a chemical element used in a plethora of applications, but the material is relatively heavy.

To develop plastic gold, researchers from ETH used protein fibers and a polymer of latex to form a matrix. Then, they embedded gold nanocrystal discs. The resulting material also consists of tiny air pockets.

In the process flow, the materials are subjected to water. Then, salt is added to create an aerogel. The water is replaced 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,” according to ETH. “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.”

In some cases, a gold alloy consists of three-quarters gold and one-quarter copper with a density of about 15 g/cm3. ETH’s plastic gold is 1.7 g/cm3, but it is still 18-carat.

“This gold has the material properties of a plastic,” said Raffaele Mezzenga, a professor at ETH. “As a general rule, our approach lets us create almost any kind of gold we choose, in line with the desired properties.”

Atomic gold pyramids
KU Leuven has gained some new insights in the properties of atomic gold clusters. In select conditions, they take the shape of a pyramid.

Most elements organize themselves by forming shells around one central atom, but gold is a different story, according to KU Leuven.

Researchers from KU Leuven have demonstrated that freestanding clusters of 20 gold atoms take on a tetrahedral or pyramidal shape. The structure involves a ground plane of 10 atoms. On top of the ground plane, there are triangles of 6 and 3 atoms, topped by a single atom.

For some time, the research community has studied the properties of few-atom gold clusters. These structures have some interesting chemical and electronic properties. Potential applications include carbon capture, catalysis, fuel cells and optics.

In the lab, KU Leuven devised a way to make few-atom gold clusters. Sodium chloride or salt layers were grown on a gold substrate using a vapor deposition technique in a chamber.

Then, 20 gold cluster ions were produced using cluster-beam deposition. The ions were produced in a proprietary magnetron sputtering system.

The resulting structure was a 20-gold atom cluster on an ultrathin salt film. The cluster maintained its pyramid structure. It had a large high occupied molecular orbital–lowest unoccupied molecular orbital gap of around 1.8 electron volts, according to researchers.

“Part of the sputtered atoms grow together to small particles of a few up to a few tens of atoms, due to a process comparable with condensation of water molecules to droplets,” said Zhe Li, the main author of the paper, who is at the Harbin Institute of Technology. “We selected a beam of clusters consisting of exactly twenty gold atoms. We landed these species with one of the triangular facets onto a substrate covered with a very thin layer of kitchen salt (NaCl), precisely three atom layers thick.”

Gold outlook
In a video, an executive from BMG Group presented an outlook for gold as well as the economy. “Gold had a good year in 2019, rising about 18%. Since 2000, gold has averaged 11% annually in the major currencies, with 9.7% in USD and 8.8% in Canadian,” said Nick Barisheff, president and chief executive of the firm.