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Basic science




Published on September 6th, 2011 | By: Eileen De Guire

SEM image of Ti3C2 synthesized by exfoliation of Ti3AlC2 with hydrofluoric acid. Credit: Babak Anasori, Drexel University Graphene, a two-dimensional sheet of carbon, has been the subject of much research since it was discovered in 2004. Its basic properties are fairly well documented, and papers are appearing about possible applications, for example, as supercapacitor electrodes …

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SEM image of Ti3C2 synthesized by exfoliation of Ti3AlC2 with hydrofluoric acid. Credit: Babak Anasori, Drexel University

Graphene, a two-dimensional sheet of carbon, has been the subject of much research since it was discovered in 2004. Its basic properties are fairly well documented, and papers are appearing about possible applications, for example, as supercapacitor electrodes or composite reinforcement. Some novel ideas are emerging as a recent paper on graphene-based artificial muscles illustrates.

Graphene is interesting stuff, but its range of properties is limited by its super-simple chemistry. In multilayer form, weak van der Waals bonding between layers is a limiting factor, too.

However, if two-dimensional materials with more complex chemistries could be made, the door would be opened to tune properties and engineer materials for specific applications.

Well, count among the door-openers Drexel University professors and ACerS Fellows Yury Gogotsi and Michel Barsoum, who describe a process for synthesizing such materials in a new paper, “Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2,” in Advanced Materials (doi: 10:1002/adma.201102306).

As their paper states, “Complex, layered structures that contain more than one element may offer new properties because they provide a larger number of compositional variables that can be tuned for achieving specific properties.”

Barsoum was among the first to work on the so-called MAX phases, which are layered ternary carbides or nitrides. MAX refers to the material’s chemistry: “M” is an early transition metal (Ti, Ta, etc.), “A” is an A-group metal (Al, In, Si, etc.) and “X” is carbon or nitrogen. So far, more than 60 MAX compounds have been identified.

The layered morphology gives them some interesting physical properties that can be metal-like or ceramic-like, but their structure and chemistry also make them good precursor materials for carbide-derived carbons, which are nanostructured porous materials. CDCs are synthesized by removing the “M” and “A” with hydrofluoric acid, and we wrote about some of their anomalous supercapicitance properties in an earlier post.

Wondering whether a hybrid MAX-CDC material could be synthesized, the Drexel team began experimenting with selective removal of “A” elements. MX compounds are chemically stable, and the “A” elements tend to be weakly bonded and are more reactive.

The process was surprisingly simple: They synthesized Ti3AlC2 by first ball milling, and then immersing the resultant powders in a concentrated HF solution at room temperature; next, they rinsed and centrifuged the material. Finally, they used cold pressing to align flakes. They characterized the flakes with XRD, SEM and TEM, and determined the chemistries with X-ray energy dispersive spectrometry in the TEM.

By removing the aluminum (“A” element), they discovered they had formed a new two-dimensional material with the composition Ti3C2. Because its morphology is similar to graphene, the team refers to this class of materials as “MXene.” They report having formed nanosheets (a few layers thick) and conical scrolls.

Gogotsi says they have demonstrated the ability to synthesize MX compounds through exfoliation on a wide range of MAX compounds, including carbo-nitrides. According to the paper they already have “solid evidence for the exfoliation of Ta4AlC3 into Ta4C3 flakes,” but offered no information on the material properties of these latter two compounds.

Given that the MAX compounds comprise a well-defined family of materials, they seem to be good candidates for the Materials Genome Initiative concept. Gogotsi confirmed that they are. “These materials are a perfect case for computational materials engineering. It’s a much better and more efficient way to go after the structures of this family of materials.”

In a NanoWerk article, Gogotsi says, “We are talking about a large family of 2D metal carbides and nitrides, so exploring different structures to find the optimum chemistry for each application is the next step in our work,” plus property characterization and controlling the surface chemistries.

The potential applications of MXene materials is wide. Ab initio simulations predict that they will have large elastic moduli. By varying their surface chemistries (for example, in the paper, the surfaces are terminated by hydroxl and/or fluorine groups) interfaces and bandgaps can be tuned. The large surface areas and layered structure make these materials interesting candidates for Li-ion battery electrodes, pseudocapacitors, polymer composite fillers and other energy and electronic devices.

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Basic science




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Other materials stories that may be of interest
Published on September 2nd, 2011 | By: pwray@ceramics.org

Check ’em out: NIST: Iron ‘veins’ are secret of promising new hydrogen storage material With plutonium-238 supplies running low, the race is on to find new power sources for spacecraft Construction of US’s first large-scale industrial carbon capture and storage facility begins Dynamic windows improve efficiency, human experience in buildings India’s government plans to step …

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Ceramic Tech Today




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Two approaches for using nanowires, including core–shell structures, to improve photovoltaics
Published on September 2nd, 2011 | By: pwray@ceramics.org

Schematic shows how to make core/shell nanowire solar cell starting from left with a CdS nanowire (green) that is dipped in CuCl where cation exchange reaction creates a Cu2S shell coating (brown). Metal contacts are then deposited on the CdS core and Cu2S shell. Credit: Yang et. al. By sheer coincidence, I received information about …

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ACerS news




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Materials Football Game of the Week: University of California, Davis at Arizona State University
Published on September 1st, 2011 | By: Eileen De Guire

The GameUniversity of California, Davis at Arizona State UniversitySept. 1, 7:00 p.m., PT; Tempe, Ariz. The last time these teams met was 71 years ago in September 1940, a contest ASU won. UC Davis is a Division 1-FCS (Football Championship Subdivision) in the Great West Conference, and ASU is a Division 1-FBS (Football Bowl Subdivision) …

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Business




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White House: 45 companies pledge to double engineering internships next year
Published on August 31st, 2011 | By: pwray@ceramics.org

Credit: American Society for Engineering Education/SMART. This should be welcome news (via the DOE): This afternoon, the President’s Council on Jobs and Competitiveness along with the Business Council, Business Roundtable, US Chamber of Commerce, National Association of Manufacturers and the American Chemistry Council announced that 45 businesses (including many big names) have committed doubling the …

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Ceramic Tech Today




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Feynman’s life grist for new graphic novel
Published on August 31st, 2011 | By: pwray@ceramics.org

A new graphic biography about physicist Richard Feynman has just been published. I don’t have particular “heroes,” but I have always wished I could emulate Feynman’s wisdom, wit and mellow attitude about the physical world. So, I have been looking forward to the completion of this work by writer Jim Ottaviani and illustrator Leland Myrick. The …

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Biomaterials




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The beer brewer’s kin: The genealogy of lager beer microbes
Published on August 31st, 2011 | By: Eileen De Guire

Octoberfest in Germany. Credit: senator86; Wikepedia, Creative Commons license It’s September, which means Octoberfest season is almost here. Ever wonder what really makes those delicious brews? I just came across this fun piece of science about the domestication of yeast microbes, those friendly little beasts that make lager beers for us. The domestication of plants …

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Business




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ARPA-E awards $15.5M to leverage $108M for five clean tech innovators; says rare-earth innovations awards coming
Published on August 31st, 2011 | By: pwray@ceramics.org

Transphorm, one of the companies that will be receiving ARPA-E and private investment funding, uses gallium nitride transistors to tackle the current level of power conversion losses (10%). Credit: Energy Information Administration. ARPA-E announced a new round of seed awards, $1.5–$6 million each, which the agency says will unlock a total investment of $100 million …

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Business




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Ceramics and glass business news of the week
Published on August 31st, 2011 | By: pwray@ceramics.org

Here’s what we are hearing: PPG to form fiber glass joint venture with Harsha in India PPG Industries announced that it has signed a letter of intent with Harsha Exito Engineering Private Limited (India) to establish a 50-50 joint venture for the manufacture and sale of fiber glass reinforcement products. “We are encouraged by the …

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ACerS news




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October book releases from ACerS-Wiley
Published on August 30th, 2011 | By: Eileen De Guire

Check out three great, new authored books being released in October. ACerS members receive a 20% discount by simply entering “ceram” in the promotion code box at check-out. Advanced Structural Ceramics Bikramjit Basu and Kantesh Balani 512 pages US $149.95 Advanced Structural Ceramics covers the area of advanced ceramic composites broadly, with introductory chapters to …

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