Tag Archives: André R. Studart

‘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.

Bend it, twist it, roll it—composites inspired by nature

Researchers at ETH (Swiss Federal Institute of Technology) Zurich have developed a new composite material with bioinspired microstructures, from the Apr. 16, 2013 news item on Nanowerk,

Plant components that bend, roll or twist in response to external stimuli such as temperature or moisture are fairly commonplace in nature and often play a role in the dispersal of seeds. Pine cones, for instance, close their scales when wet and open them again once they have dried out. André Studart, a professor of complex materials at ETH Zurich’s Department of Materials, and his group have now applied the knowledge of how these movements come about to produce synthetically a composite material with comparable properties …

The Apr. 16, 2013 ETH Zurich news article by Maja Schaffner, which originated the news item, goes on to describe how the pine cone comes by its abilities,

Studart and co-workers knew from the literature how pine cone scales work: two firmly connected layers lying on top of each other inside a scale are responsible for the movement. Although the two layers consist of the same swellable material, they expand in different ways under the influence of water because of the rigid fibres enclosed in the layers. In each of the layers, these are specifically aligned, thus determining the direction of expansion. Therefore, when wet only one of the two layers expands in the longitudinal direction of the scale and bends on the other side.

The scientists then devised an artificial means of achieving the pine cone’s ability to swell in two orientations (from the article),

Inspired by nature, the scientists began to produce a similar moving material in the lab by adding ultrafine aluminium oxide platelets as the rigid component to gelatine – the swellable base material – and pouring it into square moulds. The surface of the aluminium oxide platelets is pre-coated with iron oxide nanoparticles to make them magnetic. This enabled the researchers to align the platelets in the desired direction using a very weak rotating magnetic field. On the cooled and hardened first layer, they poured a second one with the same composition, differing only in the direction of the rigid elements.

The scientists cut this double-layered material into strips. Depending on the direction in which these strips were cut compared to the direction of the rigid elements in the gelatine pieces, the strips bent or twisted differently under the influence of moisture: some coiled lengthwise like a pig’s tail, others turned loosely or very tightly on their own axis to form a helix reminiscent of spiral pastries. “Meanwhile, we can programme the way in which a strip should take shape fairly accurately,” explains Studart.

The researchers also produced longer strips that behave differently in different sections – curl in the first section, for instance, then bend in one direction and the other in the final section. Or they created strips that expanded differently length and breadthwise in different sections in water. And they also made strips from another polymer that responded to both temperature and moisture – with rotations in different directions.

However, Studart was most interested in rotational movements (from the article),

“Bending movements,” he says, “are relatively straightforward.” Metallic bilayer compounds that bend upon temperature changes are widely used in thermostats, for instance. The new method, however, is largely material-independent, which means that any material that responds to external stimuli – and, according to Studart, there are quite a few – can potentially be rendered self-shaping. “Even the solid component is freely selectable and can be made magnetically responsive through the iron-oxide coating,” he says.

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

Self-shaping composites with programmable bioinspired microstructures by Randall M. Erb, Jonathan S. Sander, Roman Grisch, & André R. Studart. Nature Communications 4, Article number: 1712 doi:10.1038/ncomms2666 Published 16 April 2013

This article is behind a paywall.

According to Schaffner’s article, Studart believes this work could have applications in the field of medical devices and for self-shaping ceramic devices.