Deakin University researchers have solved a 100-year-old mystery of the mechanism behind an important geological phenomenon, which could help in the development of next-generation nanomaterials.
‘Pressure solution’, which takes place during the formation of sedimentary rocks such as sandstone, was first observed by geologists in 1908, however the actual mechanism behind this process has never been properly understood. This includes the curious effect of clays that accelerate the dissolution of certain minerals close to them.
However, new research completed at Deakin’s Institute for Frontier Materials, recently published in the Journal of the American Chemical Society, shows that the silica dissolution reaction is fundamentally an electro-chemical reaction, opening opportunities for manipulation in safe and energy efficient ways.
This fundamental research discovery changes the understanding of the mineral dissolution reaction and unlocks potential applications, including in the mining industry and in the development of important nanotechnology, such as photonic crystals, nanopores, and nanofluidic channels.
There is typically not much you can do to manipulate the rate of a dissolution reaction other than increase the temperature or use harsh acids or bases,” senior researcher Dr Wren Greene said.
“However, we discovered that just by pressing a second surface against the dissolving surface and vibrating the pressure, we are able to speed up the dissolution of silica by more than 600,000 times.
“Because the pressure solution effect only occurs where the two materials contact each other, the effect is very localised and can be used to create nanomaterials, without expending a lot of energy or using harmful chemicals.”
IFM PhD student Kilian Fraysse, who made the discovery, said the rate enhancing mechanism depended upon the effect that the pressure oscillations had on the electric fields at the silica surface, which regulate how quickly dissolved silica molecules can be transported away from the surface.
“The second surface combined with the pressure effectively catalyses the dissolution of the silica,” Mr Fraysse said.
“While geologists always imagined pressure solution to be a rather slow process, we show that under the right conditions, it can happen very, very quickly.”
His team has shown for the first time how pressure solution can be used for nano-printing on glass by selectively etching the glass underneath a pattern. This etching is done in pure water without the need for any chemicals or expensive equipment.
Mr Fraysse recently inscribed the world’s smallest Australian flag (pictured below) into glass measuring about two microns by four microns – half the width of the average human hair.
Australian flag etched into fused silica using the frequency enhanced pressure solution effect. The red fields are etched to a depth of 50 nanometres. The white fields are etched to 0.5 nanometres (1-2 atomic layers). Total fabrication time was less than five minutes.
