Tag Archives: Florian Bouville

‘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.

One tough mother, imitating mother-of-pearl for stronger ceramics

I love mother-of-pearl or nacre as it’s also known,

The iridescent nacre inside a Nautilus shell cut in half. The chambers are clearly visible and arranged in a logarithmic spiral. Photo taken by me -- Chris 73 | Talk 12:40, 5 May 2004 (UTC)

The iridescent nacre inside a Nautilus shell cut in half. The chambers are clearly visible and arranged in a logarithmic spiral.
Photo taken by me — Chris 73 | Talk 12:40, 5 May 2004 (UTC)

We had a mother-of-pearl-covered shell when I was a child, one I loved to hold but ours had a blue-black sheen. Enough of this trip down memory lane, it turns out that nacre has inspired a new type of stronger ceramic material from scientists at the Centre national de la recherche scientifique (CNRS) as a March 24, 2014 news item on ScienceDaily notes,

Whether traditional or derived from high technology, ceramics all have the same flaw: they are fragile. Yet this characteristic may soon be a thing of the past: a team of researchers led by the Laboratoire de Synthèse et Fonctionnalisation des Céramiques (CNRS/Saint-Gobain), in collaboration with the Laboratoire de Géologie de Lyon: Terre, Planètes et Environnement (CNRS/ENS de Lyon/Université Claude Bernard Lyon 1) and the Laboratoire Matériaux: Ingénierie et Science (CNRS/INSA Lyon/Université Claude Bernard Lyon 1), has recently presented a new ceramic material inspired by mother-of-pearl from the small single-shelled marine mollusk abalone.

This material, almost ten times stronger than a conventional ceramic, is the result of an innovative manufacturing process that includes a freezing step. This method appears to be compatible with large-scale industrialization and should not be much more expensive than the techniques already in use.

The CNRS March 21,2014 press release, which originated the news item, describes the properties of nacre which excited the scientists and the way in which they mimicked those properties in a synthetic material,

Toughness, i.e. the ability of a material containing a crack to resist fracture, is considered to be the Achilles heel of ceramics. To compensate for their intrinsic fragilit y, these are sometimes combined with tougher materials such as metals or polymers — generally leading to varying degrees of limitations. For example, polymers cannot resist temperatures above 300°C, which restricts their use in motors or ovens.

A material similar to ceramic, although extremely tough, is found in nature. Mother-of-pearl, which covers the shells of abalone and some bivalves, is 95% composed of calcium carbonate (aragonite), an intrinsically fragile material that is nonetheless very tough. Mother-of-pearl can be seen as a stack of small bricks, welded together with mortar composed of proteins. Its toughness is due to its complex, hierarchical structure where cracks must follow a tortuous path to propagate. It is this structure that inspired the researchers.

As a base ingredient, the team from the Laboratoire de Synthèse et Fonctionnalisation des Céramiques (CNRS/Saint-Gobain) used a common ceramic powder, alumina, in the form of microscopic platelets. To obtain the layered mother-of-pearl structure, they suspended this powder in water. The colloidal suspension (1) was then cooled to obtain controlled ice crystal growth, caus ing alumina to self-assemble in the form of stacks of platelets. The final material was subsequently obtained from a high temperature densification step.

This artificial mother-of-pearl is ten times tougher than a conventional alumina ceramic. This is because a crack has to move round the alumina “bricks” one by one to propagate. This zigzag pathway prevents it from crossing the material easily.

One of the advantages of the process is that it is not exclusive to alumina. Any ceramic powder, as long as it is in the form of platelets, can self-assemble via the same process, which could easily be used on an industrial scale. This bio-inspired material’s toughness for equivalent density could make it possible to produce smaller, lighter parts with no significant increase in costs. This invention could become a material of choice for applications subjected to severe constraints in fields ranging from energy to armor plating.

For those who like their communiqué de presse en français,

Les céramiques, qu’elles soient traditionnelles ou de haute technologie, présentent toutes un défaut : leur fragilité. Ce côté cassant pourrait bientôt disparaître : une équipe de chercheurs, menée par le Laboratoire de synthèse et fonctionnalisation des céramiques (CNRS/Saint-Gobain), en collaboration avec le Laboratoire de géologie de Lyon : Terre, planètes et environnement (CNRS/ENS de Lyon/Université Claude Bernard Lyon 1) et le laboratoire Matériaux : ingénierie et science (CNRS/INSA Lyon/Université Claude Bernard Lyon 1) vient de présenter un nouveau matériau céramique inspiré de la nacre des ormeaux, petits mollusques marins à coquille unique. Ce matériau, près de dix fois plus tenace qu’une céramique classique, est issu d’un procédé de fabrication innovant qui passe par une étape de congélation. Cette méthode semble compatible avec une industrialisation à échelle plus importante, à priori sans surcoût notable par rapport à celles déjà employées. Conservant ses propriétés à des températures d’au moins 600°C, cette nacre artificielle pourrait trouver une foule d’applications dans l’industrie et permettre d’alléger ou de réduire en taille des éléments céramiques des moteurs ou des dispositifs de génération d’énergie. Ces travaux sont publiés le 23 mars 2014 sur le site internet de la revue Nature Materials.

La ténacité, capacité d’un matériau à résister à la rupture en présence d’une fissure, est considérée comme le talon d’Achille des céramiques. Pour pallier leur fragilité intrinsèque, celles-ci sont parfois combinées à d’autres matériaux plus tenaces, métalliques ou polymères. L’adjonction de tels matériaux s’accompagne généralement de limitations plus ou moins sévères. Par exemple, les polymères ne résistent pas à des températures supérieures à 300°C, ce qui limite leur utilisation dans les moteurs ou les fours.

Dans la nature, il existe un matériau proche de la céramique qui est extrêmement tenace : la nacre qui recouvre la coquille des ormeaux et autres bivalves. La nacre est composée à 95 % d’un matériau intrinsèquement fragile, le carbonate de calcium (l’aragonite). Pourtant, sa ténacité est forte. La nacre peut être vue comme un empilement de briques de petite taille, soudées entre elles par un mortier composé de protéines. Sa ténacité tient à sa structure complexe et hiérarchique. La propagation de fissures dans ce type d’architecture est rendue difficile par le chemin tortueux que celles-ci doivent parcourir pour se propager. C’est cette structure qui a inspiré les chercheurs.

Comme ingrédient de base, l’équipe du Laboratoire de synthèse et fonctionnalisation des céramiques (CNRS/Saint-Gobain) a pris une poudre céramique courante, l’alumine, qui se présente sous la forme de plaquettes microscopiques. Pour obtenir la structure lamellée de la nacre, ils ont mis cette poudre en suspension dans de l’eau. Cette suspension colloïdale (1) a été refroidie de manière à obtenir une croissance contrôlée de cristaux de glace. Ceci conduit à un auto-assemblage de l’alumine sous forme d’un empilement de plaquettes. Finalement, le matériau final a été obtenu grâce à une étape de densification à haute température.

Cette nacre artificielle est dix fois plus tenace qu’une céramique classique composée d’alumine. Ceci est dû au fait qu’une fissure, pour se propager, doit contourner une à une les « briques » d’alumine. Ce chemin en zigzag l’empêche de traverser facilement le volume du matériau.

L’un des avantages du procédé est qu’il n’est pas exclusif à l’alumine. N’importe quelle poudre céramique, pour peu qu’elle se présente sous la forme de plaquettes, peut subir le même processus d’auto-assemblage. De plus, l’industrialisation de ce procédé ne devrait pas présenter de difficultés. L’obtention de pièces composées avec ce matériau bio-inspiré ne devrait pas entraîner de grands surcoûts. Sa forte ténacité pour une densité équivalente pourrait permettre de fabriquer des pièces plus petites et légères. Il pourrait devenir un matériau de choix pour les applications soumises à des contraintes sévères dans des domaines allant de l’énergie au blindage.

Here’s a link to and a citation for the research paper which was published in English,

Strong, tough and stiff bioinspired ceramics from brittle constituents by Florian Bouville, Eric Maire, Sylvain Meille, Bertrand Van de Moortèle, Adam J. Stevenson, & Sylvain Deville. Nature Material (2014) doi:10.1038/nmat3915 Published online 23 March 2014

This paper is behind a paywall.