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Caltech - Ceramics don't have to be brittle

DCN Corp® - this sequence shows how Greer Laboratory 3D ceramic nano-lattices can recover after being compressed by more than 50%. Clockwise, from left to right, an Alumina (Al2O3) nano-lattice before compression, during compression, fully compressed, and recovered following compression. Credit - Lucas Meza/CaltechImagine in the future how a balloon could float without using any lighter-than-air gas.  Alternatively it could have all of its air sucked out while maintaining its filled space. Such an example, could help ease the world's current shortage of Helium (He), which can only be made if a new material existed that was strong enough to sustain that pressure generated by forcing out all that air while still being lightweight and flexible...

Caltech researchers - including Dr Julie Greer, a Professor of Materials Science and Mechanics in the Division of Engineering and Applied Science - are on the path to developing a material (as described above) and many others that possess unheard-of combinations of properties. For instance, they may be able to create a material that is thermally insulating, but also lightweight, or at the same time strong, lightweight and non-breakable.

Greer's team have developed a process for constructing new structural materials, by smartly taking advantage of the unusual properties that solids can have at the nanometer scale. In a paper published in September 2012 of the journal Science, the Caltech researchers explain how they employed the method of produce a ceramic, that contains about 99.9% air yet is incredibly strong, and can recover its original shape after being smashed by more than 50%.

Greer stated - "ceramics have always been thought to be heavy and brittle," - and - "we're showing that in fact, they don't have to be either. This very clearly demonstrates that if you use the concept of the nanoscale to create structures and then use those nanostructures like LEGO to construct larger materials, you can obtain nearly any set of properties you want.  You can create materials by design."

The researchers used a direct laser writing method dubbed two-photon lithography to "write" a 3D pattern in a polymer by allowing a laser beam to cross-link and harden the ploymer wherever it is focused. The parts of the polymer that were exposed to the laser remain intact while the rest is dissolved away, revealing a 3D scaffold.  Such a structure can then be coated with a thin layer of just about any kind of material. In addition, the researchers employed another method to etch out the polymer from within the structure, leaving behind a hollow architecture.

In the group's latest work, Greer et al. used the technique, above, to produce what they call a 3D nano-lattice, which formed a repeating nanoscale pattern. After the patterning step, they coated the polymer scaffold with a ceramic called Alumina - Aluminum Oxide (Al2O3) - producing hollow-tube alumina structures with walls ranging in thickness from 5-60 nm and tubes from 450-1,380 nm in diameter.

In their next phase of research, Greer's team wanted to test the mechanical properties of the various nano-lattices they created. They employed two different devices for poking and prodding materials on the nanoscale, whereby they squished, stretched and otherwise tried to deform the samples to understand how they held-up.

Findings revealed that the Alumina structures with a wall thickness of 50 nm and a tube diameter of about 1 micron shattered when compressed. This was not surprising given that ceramics are brittle.  However, compressing lattices with a lower ratio of wall thickness to tube diameter, whereby the wall thickness is about 10 nm, produced a very different result. Greer continued on to state - "you deform it, and all of sudden, it springs back," - and - "in some cases, we were able to deform these samples by as much as 85%, and they could still recover."

To understand the above statement, consideration has to be made with regard to most brittle materials, such as ceramics, Silicon (Si) and glass shatter, because ultimately they are filled with flaws. The more prefect the material, the less the likelihood of finding a weak spot where it could fail. Therefore, the researchers hypothesised, when reducing the structures down to the point where individual walls are only 10 nm thick, both the number of flaws and the size of any flaws are kept to a minimum, making the whole structure much less likely to fail.

Concluding Greer states - "one of the benefits of using nano-lattices is that you significantly improve the quality of the material because you're using such small dimensions," - and - "it's basically as close to an ideal material as you can get, and you get the added benefit of needing only a very small amount of material in making them."

Going forward, the Greer laboratory, is now pursuing various ways of scaling-up the production of the meta-materials. Original article available here

In summary, the above research clearly highlights how nano coating can be employed on a laser etched 3D scaffold. As stated previously, DCN Corp believes it can provide a strong "solution enabling" platform. Therefore, if you and/or your colleagues are interested - please ensure to contact the company as soon as practicably possible.