Tag Archives: Fabio Bergamin

‘No kiln’ ceramics

Sometimes it’s hard to believe what one reads and this piece about ceramics made without kilns  (for me) fits into that category (from a Feb. 28, 2017 ETH Zurich [English: Swiss Federal Institute of Technology in Zurich] [German: Eidgenössische Technische Hochschule Zürich]) press release (also on EurekAlert) by Fabio Bergamin),

The manufacture of cement, bricks, bathroom tiles and porcelain crockery normally requires a great deal of heat: a kiln is used to fire the ceramic materials at temperatures well in excess of 1,000°C. Now, material scientists from ETH Zurich have developed what seems at first glance to be an astonishingly simple method of manufacture that works at room temperature. The scientists used a calcium carbonate nanopowder as the starting material and instead of firing it, they added a small amount of water and then compacted it.

“The manufacturing process is based on the geological process of rock formation,” explains Florian Bouville, a postdoc in the group of André Studart, Professor of Complex Materials. Sedimentary rock is formed from sediment that is compressed over millions of years through the pressure exerted by overlying deposits. This process turns calcium carbonate sediment into limestone with the help of the surrounding water. As the ETH researchers used calcium carbonate with an extremely fine particle size (nanoparticles) as the starting material, their compacting process took only an hour. “Our work is the first evidence that a piece of ceramic material can be manufactured at room temperature in such a short amount of time and with relatively low pressures,” says ETH professor Studart.

Stronger than concrete

As tests have shown, the new material can withstand about ten times as much force as concrete before it breaks, and is as stiff as stone or concrete. In other words, it is just as hard to deform.

So far, the scientists have produced material samples of about the size of a one-franc piece using a conventional hydraulic press such as those normally used in industry. “The challenge is to generate a sufficiently high pressure for the compacting process. Larger workpieces require a correspondingly greater force,” says Bouville. According to the scientists, ceramic pieces the size of small bathroom tiles should theoretically be feasible.

Energy-efficient and environmentally benign

“For a long time, material scientists have been searching for a way to produce ceramic materials under mild conditions, as the firing process requires a large amount of energy,” says Studart. The new room-temperature method – which experts refer to as cold sintering — is much more energy-efficient and also enables the production of composite materials containing, for example, plastic.

The technique is also of interest with a view to a future CO2-neutral society. Specifically, the carbonate nanoparticles could conceivably be produced using CO2 captured from the atmosphere or from waste gases from thermal power stations. In this scenario, the captured CO2 is allowed to react with a suitable rock in powder form to produce carbonate, which could then be used to manufacture ceramics at room temperature. The climate-damaging CO2 would thus be stored in ceramic products in the long term. These would constitute a CO2 sink and could help thermal power stations to operate on a carbon-neutral basis.

According to the scientists, in the long term, the new approach of cold sintering even has the potential to lead to more environmentally friendly substitutes for cement-based materials. However, great research efforts are needed to reach this goal. Cement production is not only energy-intensive, but it also generates large amounts of CO2 – unlike potential cold-sintered replacement materials.

Here’s a link to and a citation for the paper,

Geologically-inspired strong bulk ceramics made with water at room temperature by Florian Bouville & André R. Studart. Nature Communications 8, Article number: 14655 (2017) doi:10.1038/ncomms14655 Published online: 06 March 2017

This paper is open access.

Florian Bouville’s work in ceramics was last mentioned here in a March 25, 2014 posting.

Nanowalls (like waffles) for touchscreens

ETH Zurich has announced a new technique for creating transparent electrodes in a Jan. 6, 2016 news item on ScienceDaily,

Transparent electrodes have been manufactured for use in touchscreens using a novel nanoprinting process. The new electrodes are some of the most transparent and conductive that have ever been developed.

From smartphones to the operating interfaces of ticket machines and cash dispensers, every touchscreen we use requires transparent electrodes: The devices’ glass surface is coated with a barely visible pattern made of conductive material. It is because of this that the devices recognise whether and where exactly a finger is touching the surface.

Here’s an image illustrating the new electrodes,

With a special mode of electrohydrodynamic ink-jet printing scientists can create a grid of ultra fine gold walls. (Visualisations: Ben Newton / Digit Works)

With a special mode of electrohydrodynamic ink-jet printing scientists can create a grid of ultra fine gold walls. (Visualisations: Ben Newton / Digit Works)

I think these electrodes resemble waffles,

[downloaded from https://github.com/jhermann/Stack-O-Waffles] Credit: jherman

[downloaded from https://github.com/jhermann/Stack-O-Waffles] Credit: jherman

Getting back to the electrodes themselves, a Jan. 6, 2016 ETH Zurich press release (also on EurekAlert*)by Fabio Bergamin, which originated the news item, provides more details,

Researchers under the direction of Dimos Poulikakos, Professor of Thermodynamics, have now used 3D print technology to create a new type of transparent electrode, which takes the form of a grid made of gold or silver “nanowalls” on a glass surface. The walls are so thin that they can hardly be seen with the naked eye. It is the first time that scientists have created nanowalls like these using 3D printing. The new electrodes have a higher conductivity and are more transparent than those made of indium tin oxide, the standard material used in smartphones and tablets today. This is a clear advantage: The more transparent the electrodes, the better the screen quality. And the more conductive they are, the more quickly and precisely the touchscreen will work.

Third dimension

“Indium tin oxide is used because the material has a relatively high degree of transparency and the production of thin layers has been well researched, but it is only moderately conductive,” says Patrik Rohner, a PhD student in Poulikakos’ team. In order to produce more conductive electrodes, the ETH researchers opted for gold and silver, which conduct electricity much better. But because these metals are not transparent, the scientists had to make use of the third dimension. ETH professor Poulikakos explains: “If you want to achieve both high conductivity and transparency in wires made from these metals, you have a conflict of objectives. As the cross-sectional area of gold and silver wires grows, the conductivity increases, but the grid’s transparency decreases.”

The solution was to use metal walls only 80 to 500 nanometres thick, which are almost invisible when viewed from above. Because they are two to four times taller than they are wide, the cross-sectional area, and thus the conductivity, is sufficiently high.

Ink-jet printer with tiny print head

The researchers produced these tiny metal walls using a printing process known as Nanodrip, which Poulikakos and his colleagues developed three years ago. Its basic principle is a process called electrohydrodynamic ink-jet printing. In this process scientists use inks made from metal nanoparticles in a solvent; an electrical field draws ultra-small droplets of the metallic ink out of a glass capillary. The solvent evaporates quickly, allowing a three-dimensional structure to be built up drop by drop.

What is special about the Nanodrip process is that the droplets that come out of the glass capillary are about ten times smaller than the aperture itself. This allows for much smaller structures to be printed. “Imagine a water drop hanging from a tap that is turned off. And now imagine that another tiny droplet is hanging from this drop – we are only printing the tiny droplet,” Poulikakos explains. The researchers managed to create this special form of droplet by perfectly balancing the composition of metallic ink and the electromagnetic field used.

Cost-efficient production

The next big challenge will now be to upscale the method and develop the print process further so that it can be implemented on an industrial scale. To achieve this, the scientists are working with colleagues from ETH spin-off company Scrona.

Here’s a link to and a citation for the paper,

Electrohydrodynamic NanoDrip Printing of High Aspect Ratio Metal Grid Transparent Electrodes by Julian Schneider, Patrick Rohner, Deepankur Thureja, Martin Schmid, Patrick Galliker, Dimos Poulikalos. Advanced Functional Materials DOI: 10.1002/adfm.201503705 First published: 15 December 2015

This paper is behind a paywall.

*'(also on EurekAlert)’ added on Jan. 7, 2016.