Cup of coffee with a nugget on top? Thursday, 26 November 2015

Swiss scientists have created a nugget of 20 carat cold so light it can float on the froth of  cappuccino.

Professor Raffaele Mezzenga from ETH Zurich says the nugget is a three-dimensional mesh of gold consisting mostly of pores, making it the lightest gold nugget ever created.

"The so-called aerogel is a thousand times lighter than conventional gold alloys. It is lighter than water and almost as light as air," he said.

His team created the material by heating milk proteins to produce nanometre-fine protein fibres, called amyloid fibrils, which they then placed in a solution of gold salt. The protein fibres interlaced themselves into a basic structure along which the gold simultaneously crystallised into small particles. This resulted in a gel-like gold fibre network.

Mezzenga said the new gold form can hardly be differentiated from conventional gold with the naked eye – the aerogel even has a metallic shine. But in contrast to its conventional form, it is soft and malleable by hand.

It consists of 98 parts air and only two parts of solid material. Of this solid material, more than four-fifths are gold and less than one-fifth is milk protein fibrils. This corresponds to around 20 carat gold.

The new material could be used in many of the applications where gold is currently being used, says Mezzenga. One he highlighted was chemical catalysis. Because the highly porous material has a huge surface, chemical reactions that depend on the presence of gold can be run in a very efficient manner. The material could also be used in applications where light is absorbed or reflected or even pressure sensors.

"At normal atmospheric pressure the individual gold particles in the material do not touch, and the gold aerogel does not conduct electricity," he said.

"But when the pressure is increased, the material gets compressed and the particles begin to touch, making the material conductive."

 

Photo: Gustav Nyström and Raffaele Mezzenga  / ETH Zurich