Two researchers at ETH in Switzerland have succeeded in producing the world’s lightest form of gold. Made of foam, the gold is light enough to rest atop cappuccino foam without sinking.
Created by Dr. Mezzenga and Dr. Gustav Nyström, the gold is made of 80% 20-karat gold, and nano-metre wide strands of milk protein. The volume is 98% air, making it lighter than water. It is virtually identical in appearance to conventional gold, and even has a metallic shine.
The scientists built the material by first heating milk proteins to produce amyloid fibrils. Then the amyloid fibrils were combined with a gold salt solution. The gold salt and amyloid fibrils interlocked to form the basic structure. At the same time, the gold particles crystallised, creating smaller particles and eventually a gel-like gold fibre network.
The scientists were then tasked with drying the material without destroying it—which proved to be quite the obstacle. In a process similar to the one used to decaffeinate coffee, carbon dioxide was used to dry the gold network as air would have been too damaging.
That’s when they made a fascinating discovery.
"The optical properties of gold depend strongly on the size and shape of the gold particles," said Nyström.
"Therefore we can even change the colour of the material. When we change the reaction conditions in order that the gold doesn't crystallise into microparticles but rather smaller nanoparticles, it results in a dark-red gold."
Even the shine of the gold can be manipulated.
The material is also fit for technological application. When atmospheric pressure is increased the aerogel, the compressing of gold particles allows the material to become conductive. When the pressure is relaxed, the aerogel becomes insulative.
Airspace firms have already contacted Mezzenga about using the product in future technologies. While Mezzenga concedes that “Aerospace is a very promising market,” he argues that it may be too early for him to determine an exact price for his product. His estimate, however, is sure to appeal to the many technology industries which rely upon gold.
“If you would work out a price there is only the material content. I could say it’s probably 1,000 times less expensive than normal gold because it’s 1,000 times less dense,” Mezzenga.