Perhaps the best known example of the additive process is the Hewlett-Packard 3-D printer, or as it is now called: Designjet 3D. Announced in January of 2010 to considerable hoopla, it’s just now coming to market at the popular price of about $17,000 (which is actually a lot cheaper than heavy-duty commercial versions of similar technology). It uses a thermoplastic (ABS) as the construction material and as controlled by a computer with Computer Assisted Design (CAD) software, it can create objects by spraying layer after layer of the plastic to build up a complete shape. Its immediate use is for prototyping designs. The idea sounds neat, if somewhat like science fiction. However, the fact is additive layer manufacturing (ALM or often just AM) has many forms and is slowly but surely becoming a factor in the world of commercial manufacturing.

The reasons for the rise in popularity start with economics: There is much less waste. On average, about 26 times less waste of material than standard manufacturing. This is related to a second big reason for popularity: The high degree of control over the process. By constructing things layer by layer to very exact specifications, components can be built that are impossible with traditional methods. This leads to a third reason for popularity: Designers and engineers are freer to use their imagination. After all, additive layer manufacturing’s first tasks were to make prototypes. AM is very good at making one-of-a-kind pieces, for example, artificial hip joints for specific people. All this control and freedom does have a drawback, AM processes are not very robust, that is the precision required is difficult to maintain. The mechanics are finicky and difficult to calibrate. The hard part for using AM on commercial quantity production for standard metallic or plastic components is the need to make it less delicate.

With nanotechnology, however, working with extreme precision at very small scale is the name of the game. Nanomanufacturing is already built on the foundation of very complex and ‘delicate’ machinery – marrying it with additive layer manufacturing at its present level of sophistication seems like a natural fit.

Researchers are working at combining high-performance polymers (such as polyether ether ketone, or PEEK) with carbon nanotubes. The hope is to develop AM ‘printing’ techniques that combine growing carbon nanotubes within the material in aligned formation. In short, the goal is to embed the carbon nanotube structures to perform electronic functions such as sensing and communications. Most AM techniques involve the spraying or deposition of very fine-grain particles, which are then burned or manipulated with high-powered lasers, so it’s no surprise AM companies are working with makers of nanoparticles to experiment with improved composite construction, or to add electrical properties.

The combination of additive manufacturing and nanotechnology falls into the domain of ‘emerging technologies.’ There is a perceived need to provide manufacturing techniques for some kinds of nanotechnology that are between the self-assembly envisioned at the molecular level and the traditional techniques applied to micron (or larger) scale materials. As far back as 2004 (practically ancient history in the nanotech business), a conference on Advanced Technology and the Future of American Technology came to the conclusion:

Highly miniaturized, functional, and efficient electronics devices, and precise and selective biomolecular materials are part of this future. At the same time, it is not yet well known how to manufacture nanomaterials and how to integrate nano- and large-scale manufacturing. Advancing these developments depends on the ability to foster multidisciplinary interconnections between researchers in a range of scientific and engineering disciplines, business managers, policy makers, and educators.

[Source: Georgia Tech]

What is called for could be the use of nanoparticles within the composites of additive manufacturing.

For more background on additive manufacturing, I’d recommend The rise of additive manufacturing at the Engineer (UK).

There are many labs working on growing carbon nanotubes (tiny tubes sized less than 1/100,000th of a human hair) on some kind of substrate (a film, or skin, or layer). The idea is to use the many electrical and chemical properties of nanotubes over larger areas, with the substrate acting as fabric to hold things together. These days there are many industries using metal composites because they are light weight but comparatively strong, however it has been difficult for these composites to retain the electrical properties of the original metal. This is something that carbon nanotubes grown on individual carbon fibers can address – a fabric with the lightweight composition but the electrical characteristics of metals. That is, if the fabric can be manufactured in quantities and sizes that are useful for commercial products.

That’s where most of the seven years went for the University of Dayton team – scaling – in developing the processes that allow for uniform, reliable growth of nanotubes on carbon fibers that can then be made into wide fabrics. Their research continually developed manufacturing techniques that improved from individual fibers, to carbon fiber yarn, and finally to engineered textiles. A prototype production plant was built in Dayton, Ohio where 12 inch (30 cm) wide fuzzy fabric was produced in lengths up to 500 feet (152 m). Now, with additional grants from the state of Ohio, the U.S. military and private industry a new full production plant will be built to produce fabric 60 inches (1.5 m) wide.

Fuzzy fabric can easily be incorporated into resin products that can be tailored for electrical and thermal conductivity, with applications in chemical and biological sensing, energy storage and conversion, and thermal management – among many other things. One of the first large-scale uses of fuzzy fiber will be in UAVs (Unmanned Aerial Vehicles, a.k.a. drones) where the conductive ‘skin’ of fuzzy fiber can serve for the plane’s power, sensor, and communications, thereby cutting weight.

You’ll notice the involvement of government, in this case the military, in the funding and application of fuzzy fiber. That’s quite typical. Though there is often a potential for large-scale application in many nanotechnologies, the road to large-scale production is tricky – and expensive. For one thing, the unusual and beneficial properties exhibited by materials at the nano-scale, and usually tested in the laboratory at that same scale, often behave differently when aggregated into larger pieces. There’s a risk in trying to move nanotechnology from lab to factory, a risk that sometimes only government is willing to shoulder.

Lafdi called the material “game-changing” because of its ability to be produced in continuous sheets to desired sizes like other fabrics. “Everybody is growing carbon nanotubes on substrates,” Lafdi said. “We’re the only people who are producing them on a large-scale and continuous process, and not just in batches. This means we can produce the material at a low cost, and it also means we can produce pieces big enough to cover an aircraft.”

[Source: University of Dayton]

The ability to print the RFID ‘device’ into the packaging is a big advantage. It’s a three step process to print one-bit tags, which include antenna, electrodes, and dielectric layers on plastic foil (thin film media). These tags are passive; they don’t transmit information unless energized by radio waves at the correct frequency. Because they don’t need a power supply, their lifetime is almost unlimited.

Before this becomes commercial, the nano-RFID will need to be the size of standard bar codes and the range of transmission must increase. The research team is also working on increasing the tag’s digital capacity to 16 bits for more detailed information, and the ability to print the tags on paper

The technology reported in the March issue of the journal IEEE Transactions on Electron Devices is based on a carbon-nanotube-infused ink for ink-jet printers first developed in the Rice lab of James Tour, the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. The ink is used to make thin-film transistors, a key element in radio-frequency identification (RFID) tags that can be printed on paper or plastic.

“Right now, the emitter has to be pretty close to the tags, but it’s getting farther all the time,” Tour said. “The practical distance to have it ring up all the items in your shopping cart is a meter. But the ultimate would be to signal and get immediate response back from every item in your store – what’s on the shelves, their dates, everything.

“At 300 meters, you’re set – you have real-time information on every item in a warehouse. If something falls behind a shelf, you know about it. If a product is about to expire, you know to move it to the front – or to the bargain bin.”

[Source: EurekAlert]

Whether it’s silkworm silk (the textile silk) or spider silk (that stuff of horror movies), silk is a natural protein fiber. The fiber is put together something like a stack of pancakes, the analogy carrying as far as being soft and flexible. What has puzzled scientists for some time is that the bonds holding the stack together (technically, beta-sheets of a fibroin protein) are simple hydrogen bonds, which are not known for their strength.

The MIT researchers used computer models to probe the structures of silk, principally the beta-sheets of fibroin, for their failure mechanism – the point where the bonds break. They found that unlike many other very strong substances, for example ceramics, the hydrogen bonds of silk fail slowly and unevenly, not all breaking at once like ceramics. This gives silk considerable elasticity – it bend (or stretches) before it breaks. This accounts for some of the strength.

Looking at the silk material in greater depth, the researchers observed the tiny (nano-scale) beta-sheet crystals (the fibroin is formed into crystalline shape) and that these crystals were in alternating alignment from sheet to sheet. In a sense, the alternating shapes of the crystals are ‘interlocking’ and allow for more hydrogen bonds – there’s more strength in numbers. The result is a silk thread, a ‘column’ or stack of crystalline sheets, that can actually support the hydrogen bonding as the material stretches or bends. The hydrogen bonds work together, reinforcing each other against outside forces. This is what gives silk such extensibility and strength. Think of the strands of spider silk stretched across more than a meter of space and able to withstand strong winds and fierce struggles as spider engulfs prey.

One of the more important findings of the MIT study was the critical relationship between the size of the beta-sheet crystals and the properties of the silk. With a size of about 3 nanometers (3 billionths of a meter), the silk is ultra-strong and ductile. Make those crystals just above 5 nanometers and the silk becomes weak and brittle. As is often shown to be the case, materials behave differently at very small sizes, particularly at the nanoscale.

There are plenty of implications for this study, not the least of which is a better understanding of fibers, hydrogen bonding crystalline structures, and tensile strength. Markus Buehler, Associate Professor at MIT’s Department of Civil and Environmental Engineering and leader of the research team, puts it this way:

He notes that the findings could be applied to a broader class of biological materials, such as wood or plant fibers, and bio-inspired materials, such as novel fibers, yarns and fabrics or tissue replacement materials, to produce a variety of useful materials out of simple, commonplace elements. For example, he and his team are looking at the possibility of synthesizing materials that have a similar structure to silk, but using molecules that have inherently greater strength, such as carbon nanotubes.

The long-term impact of this research, Buehler says, will be the development of a new material design paradigm that enables the creation of highly functional materials out of abundant, inexpensive materials. This would be a departure from the current approach, where strong bonds, expensive constituents, and energy intensive processing (at high temperatures) are used to obtain high-performance materials.

[Source: EurekAlert]

The researchers considered the drawbacks of making boron nitride nanotubes – requiring special instrumentation, dangerous chemistry, and temperatures of over 1,500 degrees Celsius. They decided that what was needed was a little help, which in nanochemistry (as elsewhere) means catalysts. In this case it meant using substrates (the base material) made of simple catalysts magnesium oxide, iron or nickel. This worked with the same temperature (about 1100 degrees Centigrade) and instrumentation used for making carbon nanotubes.

One of the interesting developments after the boron nitride nanotubes could be made in quantity was the discovery that…

These transparent nanotube sheets have another interesting property: they shed water like a duck’s back, a quality known as the lotus effect. “Water just slides away,” says Yoke Khin Yap, associate professor of physics.”Anything coated with it would not only be stain resistant, it would be protected from anything water-soluble.” This superhydrophobicity holds at all pH levels, so anything coated with it would be protected from even the strongest acids and alkalis.

[Source: Nanotechnology Today]

The immediate next steps are various testing trials, both of applications and manufacturing techniques. Someday, probably within a couple of years, boron nitride nanotubes will be looking for commercial applications.

Pint grew his carbon nanotubes using the chemical vapor deposition (CVD) technique, which starts with a layer of catalytic metal nanoparticles. The size of these particles helps determine the size of the carbon nanotubes. The layer of catalyst (a substrate) is heated to 700C and two gasses are introduced, one is a process gas (ammonia, nitrogen, or hydrogen) and the other a carbon containing gas (acetylene, ethylene, ethanol, or methane). From these gases, carbon nanotubes grow at the sites of the metal catalyst. Typically the catalyst metal stays attached to the tips of the growing nanotubes, or remains at the base. However, Pint found that by etching the nanotubes with a mixture of hydrogen gas and water vapor, the bonds of the metal catalyst are loosened. When the nanotubes are ‘stamped’ (pressed onto another surface), they adhere to the new surface, leaving behind the catalyst.

The nanotubes stick to a surface thanks to something called the Van der Waals forces. Named after the Dutch scientist Johannes van der Waals, these forces are the attraction or repulsion between molecules, or within a molecule, at the quantum level. This relatively weak bond is different than chemical bonds created by shared ions, or bonds created by electron sharing covalence. Weak though they may be, Van der Waals forces have interesting effects, for example, the gecko (a lizard) can climb glass windows because it has millions of microscopic hairs on its feet, which generate a Van der Waals bond with surfaces it climbs. Similarly with carbon nanotubes, they ‘adhere’ to surfaces with Van der Waals forces.

Pint’s work with the CVD technique has led to the research paper on the use of metallic nanoparticles of controlled size for the carbon nanotube catalyst. The discovery of a technique for making nanotubes adhere to surfaces has led to the ability to easily create patterns – rows, crosses – of nanotubes. This is a key property in nanotube manufacturing processes and should be readily scalable for commercial purposes.

Pint is primary author of the research paper, which also details a way to quickly and easily determine the range of diameters in a batch of nanotubes grown through chemical vapor deposition (CVD). Common spectroscopic techniques are poor at seeing tubes bigger than two nanometers in diameter – or most of the nanotubes in the CVD “supergrowth” process.

“This is important since all of the properties of the nanotubes – electrical, thermal and mechanical – change with diameter,” he said. “The best thing is that nearly every university has an FTIR (Fourier transform infrared) spectrometer sitting around that can do these measurements, and that should make the process of synthesis and application development from carbon nanotubes much more precise.”

[Source: EurekAlert]

From the standpoint of the ongoing (or is it onrushing?) advance of practical applications for nanotechnology, really interesting indeed.

Carbon nanotubes and boron nitride nanotubes can both be rolled into sheets, but carbon nanotubes can be metallic or semiconducting (electrically active), boron nitride nanotubes are electrical insulators. They are also more stable under heat and chemical action. These properties will guide the many potential uses of boron nitride nanoyarn.

Researchers at NASA’s Langley Research Center, the Department of Energy’s Thomas Jefferson National Accelerator Facility and the National Institute of Aerospace created a new technique to synthesize high-quality boron-nitride nanotubes (BNNTs). They are highly crystalline and have a small diameter. They also structurally contain few walls and are very long. Boron nitride is the white material found in clown make-up and face powder.

“Before, labs could make really good nanotubes that are short or really crummy ones that are long. We’ve developed a technique that makes really good ones that are really long,” said Mike Smith, a staff scientist at NASA’s Langley Research Center.

The synthesis technique, called the pressurized vapor/condenser (PVC) method, was developed with Jefferson Lab’s Free-Electron Laser and later perfected using a commercial welding laser. In this technique, the laser beam strikes a target inside a chamber filled with nitrogen gas. The beam vaporizes the target, forming a plume of boron gas. A condenser, a cooled metal wire, is inserted into the boron plume. The condenser cools the boron vapor as it passes by, causing liquid boron droplets to form. These droplets combine with the nitrogen to self-assemble into BNNTs.
…
The researchers say the next step is to test the properties of the new boron-nitride nanotubes to determine the best potential uses for the new material. They are also attempting to improve and scale up the production process.

“Theory says these nanotubes have energy applications, medical applications and, obviously, aerospace applications.”

[Source: Jefferson Lab (U.S. DOE)]

“Plastics is a $300 billion U.S. industry because of the massive throughput that’s possible with fluid processing,” said Rice’s Matteo Pasquali, a paper co-author and professor in chemical and biomolecular engineering and in chemistry. “The reason grocery stores use plastic bags instead of paper and the reason polyester shirts are cheaper than cotton is that polymers can be melted or dissolved and processed as fluids by the train-car load. Processing nanotubes as fluids opens up all of the fluid-processing technology that has been developed for polymers.”
…
“The current research shows that we have a true solvent for nanotubes — chlorosulfonic acid — which is what we set out to find when we started this project nine years ago.”
…
But a final breakthrough remains before the true potential of high-quality carbon nanotubes can be realized. That’s because HiPco and all other methods of making high-end, “single-walled” nanotubes generate a hodgepodge of nanotubes with different diameters, lengths and molecular structures. Scientists worldwide are scrambling to find a process that will generate just one kind of nanotube in bulk, like the best-conducting metallic varieties, for instance.

“One good thing about the process that we have right now is that if anybody could give us one gram of pure metallic nanotubes, we could give them one gram of fiber within a few days,” Pasquali said.

[Source: Nanotechnology Today]