Tag Archives: ceramics

Cannibalisitic nanostructures

I think this form of ‘cannibalism’ could also be described as a form of ‘self-assembly’. That said, here is an August 31, 2018 news item on ScienceDaily announcing ‘cannibalistic’ materials,

Scientists at the [US] Department of Energy’s [DOE] Oak Ridge National Laboratory [ORNL] induced a two-dimensional material to cannibalize itself for atomic “building blocks” from which stable structures formed.

The findings, reported in Nature Communications, provide insights that may improve design of 2D materials for fast-charging energy-storage and electronic devices.

An August 31, 2018 DOE/Oak Ridge National Laboratory news release (also on EurekAlert), which originated the news item, provides more detail (Note: Links have been removed),

“Under our experimental conditions, titanium and carbon atoms can spontaneously form an atomically thin layer of 2D transition-metal carbide, which was never observed before,” said Xiahan Sang of ORNL.

He and ORNL’s Raymond Unocic led a team that performed in situ experiments using state-of-the-art scanning transmission electron microscopy (STEM), combined with theory-based simulations, to reveal the mechanism’s atomistic details.

“This study is about determining the atomic-level mechanisms and kinetics that are responsible for forming new structures of a 2D transition-metal carbide such that new synthesis methods can be realized for this class of materials,” Unocic added.

The starting material was a 2D ceramic called a MXene (pronounced “max een”). Unlike most ceramics, MXenes are good electrical conductors because they are made from alternating atomic layers of carbon or nitrogen sandwiched within transition metals like titanium.

The research was a project of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, a DOE Energy Frontier Research Center that explores fluid–solid interface reactions that have consequences for energy transport in everyday applications. Scientists conducted experiments to synthesize and characterize advanced materials and performed theory and simulation work to explain observed structural and functional properties of the materials. New knowledge from FIRST projects provides guideposts for future studies.

The high-quality material used in these experiments was synthesized by Drexel University scientists, in the form of five-ply single-crystal monolayer flakes of MXene. The flakes were taken from a parent crystal called “MAX,” which contains a transition metal denoted by “M”; an element such as aluminum or silicon, denoted by “A”; and either a carbon or nitrogen atom, denoted by “X.” The researchers used an acidic solution to etch out the monoatomic aluminum layers, exfoliate the material and delaminate it into individual monolayers of a titanium carbide MXene (Ti3C2).

The ORNL scientists suspended a large MXene flake on a heating chip with holes drilled in it so no support material, or substrate, interfered with the flake. Under vacuum, the suspended flake was exposed to heat and irradiated with an electron beam to clean the MXene surface and fully expose the layer of titanium atoms.

MXenes are typically inert because their surfaces are covered with protective functional groups—oxygen, hydrogen and fluorine atoms that remain after acid exfoliation. After protective groups are removed, the remaining material activates. Atomic-scale defects—“vacancies” created when titanium atoms are removed during etching—are exposed on the outer ply of the monolayer. “These atomic vacancies are good initiation sites,” Sang said. “It’s favorable for titanium and carbon atoms to move from defective sites to the surface.” In an area with a defect, a pore may form when atoms migrate.

“Once those functional groups are gone, now you’re left with a bare titanium layer (and underneath, alternating carbon, titanium, carbon, titanium) that’s free to reconstruct and form new structures on top of existing structures,” Sang said.

High-resolution STEM imaging proved that atoms moved from one part of the material to another to build structures. Because the material feeds on itself, the growth mechanism is cannibalistic.

“The growth mechanism is completely supported by density functional theory and reactive molecular dynamics simulations, thus opening up future possibilities to use these theory tools to determine the experimental parameters required for synthesizing specific defect structures,” said Adri van Duin of Penn State [Pennsylvania State University].

Most of the time, only one additional layer [of carbon and titanium] grew on a surface. The material changed as atoms built new layers. Ti3C2 turned into Ti4C3, for example.

“These materials are efficient at ionic transport, which lends itself well to battery and supercapacitor applications,” Unocic said. “How does ionic transport change when we add more layers to nanometer-thin MXene sheets?” This question may spur future studies.

“Because MXenes containing molybdenum, niobium, vanadium, tantalum, hafnium, chromium and other metals are available, there are opportunities to make a variety of new structures containing more than three or four metal atoms in cross-section (the current limit for MXenes produced from MAX phases),” Yury Gogotsi of Drexel University added. “Those materials may show different useful properties and create an array of 2D building blocks for advancing technology.”

At ORNL’s Center for Nanophase Materials Sciences (CNMS), Yu Xie, Weiwei Sun and Paul Kent performed first-principles theory calculations to explain why these materials grew layer by layer instead of forming alternate structures, such as squares. Xufan Li and Kai Xiao helped understand the growth mechanism, which minimizes surface energy to stabilize atomic configurations. Penn State scientists conducted large-scale dynamical reactive force field simulations showing how atoms rearranged on surfaces, confirming defect structures and their evolution as observed in experiments.

The researchers hope the new knowledge will help others grow advanced materials and generate useful nanoscale structures.

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

In situ atomistic insight into the growth mechanisms of single layer 2D transition metal carbides by Xiahan Sang, Yu Xie, Dundar E. Yilmaz, Roghayyeh Lotfi, Mohamed Alhabeb, Alireza Ostadhossein, Babak Anasori, Weiwei Sun, Xufan Li, Kai Xiao, Paul R. C. Kent, Adri C. T. van Duin, Yury Gogotsi, & Raymond R. Unocic. Nature Communicationsvolume 9, Article number: 2266 (2018) DOI: https://doi.org/10.1038/s41467-018-04610-0 Published 11 June 2018

This paper is open access.

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.

New thinking applied to nail polish

According to a Dec. 15, 2012 news item on Nanowerk, a nanotechnology-enabled nail polish has received a provisional patent,

Nano Labs Corp. announced it has been awarded a provisional patent number61,735,705 for its original nano nail polish and lacquer, the third advanced nanotechnology product the Company has introduced in as many months.

“We’ve brought new thinking to a whole new product,” said Dr. Victor Castano, CEO of Innovation at Nano Labs. “The nano lacquer – or nail polish – is a nanohybrid compound, which is a rather new concept. In the past, bringing different chemical mixtures together could be problematic. … With the nail polish, we’ve taken ceramics – which provide excellent hardness and high scratch and chip resistance – and mixed them with polymer and metallic nano particles. The result is a material that is flexible but strong, non-toxic, and eco-friendly. Not to mention it can hold a great range of colours and sheen.”

Nano Labs promotes the nail polish as twice as durable conventional products. It dries to a very hard state, and resists shock, cracking, scratching, and chipping. It offers superior ease of application, quick drying film formation, and high coverage and adhesion, with bright, vivid colours and high gloss. It also offers the flexibility of a wide spectrum of colour – introduced at the nano level – with pigments including gold, silver, titanium, and other metals and oxides with a wide range of tones. Its elasticity allows for easy and effective application to nail curves without cracking. Nano Labs has also removed toxic solvents from the nail polish equation thanks to material that quickly evaporates, with no toxicity.

Nano Labs noticed that existing products produce a physical adhesion to the natural or plastic nail. The new nano nail polish produces a chemical adhesion which is about a 1,000 times stronger and requires significantly less coverage. Therefore you are getting a better color, coat, and longer-lasting finish.

The removal of the nail polish also required a new way of thinking. How to create a solution to remove the nano nail polish that wasn’t harsh on the nails or the person as traditional cleaners. While conventional nail polish removers will remove the nano nail polish, Dr. Castano and his team created a non-toxic, solvent which removes the nano nail polish without the traditional harsh effects and toxicity of conventional cleaners.

There are no more technical details in the news item or on the company (Nano Labs) website. In fact, the company website  doesn’t yet (as of Dec. 17, 2012 1000 hours PST) have a posted news release about this development. According to the news item on Nanowerk,

At the request of a major American manufacturer and distributor the company has completed its nano-technological lacquer research and filed patent applications (File Number – 61,735,705). Further disclosure will be made upon completion of the pending licensing agreement with the 3rd parties. [emphasis mine]

“The nano nail polish is a very important example of Nano Labs in action and the importance of our patents.” explains Mr. Bernardo Camacho, President of Nano Labs, “Without going into the technical data and formulas, there is a very narrow range of chemical properties, compositions, phase separations, and segregations that need to applied to create these types of products correctly. The only way to put these items together is in this narrow band, which is complicated, and is protected in our patent. [emphasis mine] We look forward to introducing the product to the global marketplace with partners in the cosmetic industry.”

The emphasis on the narrow band within which this nail polish innovation can occur and the company’s soon-to-be patent protection seems at odds with the company philosophy as stated by Dr. Castano,

“Our philosophy of green chemistry and using friendly organics allows us to focus on sustainable products that are less toxic and harmful to customers who are trending more and more toward healthier, environmentally sound consumer options,” Dr. Castano said.

The issue isn’t the patent so much as what appears to be an attempt by the company to ‘own’ all innovation in a niche they have defined in their patent. If the focus is “healthier, environmentally sound consumer options,” then surely, the company wants a patent that allows them to profit from their innovation while spurring more ‘green options’.

One final note, Nano Labs is a very young company having been founded in Oct. 2012.