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Nano Materials: Why Size Will Matter
Nano materials will change the way engineers design mechanical parts, but progress will be slow
Doug Smock, Contributing Editor -- Design News, January 8, 2007
Two automotive OEMs are developing aluminum engine blocks that use less than 5 lb of nanosteel coatings on key components to reduce heat transfer and improve wear resistance. That's one example of how nano materials will become an important new weapon in a design engineer's materials' arsenal.
But the hype machine on nano often gets out of control, making ultra tiny look like the best thing since sliced silicon. The venture capital money is pouring in and the market research firms are churning out forecasts with almost unbelievable numbers. The PR factories are working overtime and states like Pennsylvania and New York are racing to provide economic development seed money. The federal Nanotechnology Initiative will pump $1.3 billion into nano development in 2007.
Is There Real, Meaningful Future Potential Behind Today's Headlines?
First, a look at nano. Technically, it's a unit of size in the International System of Units indicating a factor of 10–9. A nanometer is 1 billionth of a meter. It's reported that Albert Einstein wrote in a doctoral thesis that the size of a sugar molecule is 1 nm. When applied to materials, the definition of nano is often determined by the supplier. Here's one from PPG Industries, one of the leaders in commercial nano applications: Nanoparticles are those materials with at least one dimension less than 100 nm.
Some research engineers say nano is just a buzzword. Development work in the area dates back to the 1950s, at least, when it was called atomic engineering.
Adding to the confusion, nano increasingly is used to indicate anything really small. Witness the formation of a special interest group at the Society of Plastics Engineers called Nano/Micro Molding. That's odd because micro molding is the creation of very tiny parts whereas molding with nano today may refer to the production of parts, often quite large, with a barrier material that incorporates nano-sized additives. Another factor: nano refers to developments in almost every major field of science, and sometimes to the creation of nano-sized materials built up from the atomic stage and sometimes to materials that are reduced in size.
When the focus is placed squarely on designers engineering mechanical products, there are specific developments of significance on the real-world horizon.
Enhancing Aluminum
NanoSteel, the company behind the work on the aluminum engine blocks, is a case in point. Based in Providence, RI, the 5-year-old company sells patented nano-structured materials that can be applied via thermal spraying, welding and laser cladding. Specific improvements are sought in wear, erosion, high temperature oxidation and corrosion.
“We design our own steel-based, glass-forming alloys,” says Dr. Daniel James Branagan, chief technical officer of NanoSteel. Branagan developed a specialized ability to control complex multicomponent metallurgical transformations on a nanoscale level while researching hard magnetic materials in 1996. The research was initially funded by the Idaho National Engineering Laboratory (INEEL) and later by the Defense Advanced Research Projects Agency (DARPA). In 2002, Military Commercial Technologies (MILCOM) licensed this work and formed NanoSteel.
One newly commercialized application for nano metals is a coating for aluminum chutes used to move concrete from a mixing truck to a specific site. “Steel chutes weigh about 80 lb,” says Branagan. “Moving that chute involves a lot of wear- and-tear for the workers.” An aluminum chute with the new nano coating weighs less than 20 lb. “That's an example of a NanoSteel coating enabling a new use for a material,” he adds.
The same idea applies to the engine blocks under study, where 2 or 3 lb of steel coating is applied to aluminum, which would allow significant weight savings in future vehicles. Cost of the NanoSteel is typically $30 to $35 a pound. In a new application for drills used for oil exploration, NanoSteel developed a custom formulation in about six months. Another target is thermal spray coating for plastic composites.
If you look at nano from a different perspective, it really isn't all that new in the steel industry.
“Although nano technology is being touted as a new breakthrough, and indeed for some products and materials it really is, the use of super-fine nanostructures is and has been employed to manufacture steel for many years and we continue using these recipes and procedures to create better, lighter, stronger and more cost-effective materials' solutions for our customers,” says Michael Simko, technical manager, coated products, U.S. Steel Research and Technology Center, Monroeville, PA. “(Our) steel structures are created in situ via composition control and thermo-mechanical processing techniques. Theories about adding particulate to steels in the liquid form and solidifying them in place has been speculated about. But there have not been commercial applications using this approach to our knowledge and certainly not yet a processing route used by U.S. Steel.”
Plastics Impact
Most of the action in structural materials is in plastic composites. New applications get plenty of attention, but their penetration will be slowed by high costs and extensive development time. Nano first appeared on the plastics scene at the National Plastics Exposition in Chicago in 2000, when two companies touted the technology. At the NPE held last year, there were still only a handful of companies showing nano.
One of the newer players is Nycoa, the Nylon Corp. of America, based in Manchester, NH. A nylon 6-based nanocomposite made by Nycoa through in situ polymerization is used to make a single-layer blow-molded fuel tank for a riding lawn mower. Nanoclays dispersed throughout the nylon make the structure up to 98 percent less permeable to fuel vapors than a polyethylene structure with no barrier. Nycoa also says the nano nylon is 55 percent tougher than traditional super-tough nylons. The part is being molded by Confer Plastics of Tonawanda, NY, partly in reaction to tougher vapor standards established by California Air Resources Board TP-901 requirements.
Specialty compounder RTP of Winona, MN, also announced last year expanded nano capabilities, including a competing nylon 6 product to meet tougher fuel vapor standards. “The nanocomposites perform exceptionally well in these fuel tank applications due to large aspect ratio layers creating an extremely tortuous path for diffusion,” says Sam Dahman, product development engineer at RTP.
From a design engineering perspective, one of the big advantages of nanocomposites is the ability to save weight and improve properties compared to glass-filled materials, says Suresh Shah, senior technical fellow at Delphi Automotive Systems, Troy, MI.
“You can get the same stiffness with significantly less loading (5 percent) with nanocomposites,” says Shah. “You reduce the weight as a result. You also don't have to worry about how the fibers will orient … More uniform properties and less warpage (with nanocomposites) give design engineers more freedom.” A side benefit is a thinner part, and reduced cycle time. Aesthetics are also improved, because glass fibers are sometimes visible on the surface of a part. The Future: Two-Shot
Shah cautions, however, that because of the increased costs with nano, they will only be used where they are truly needed, particularly in the cost-conscious mood in Detroit. One example where nano fits is a two-shot body side molding where an inner layer of nano polypropylene composite provides stiffness and an outer layer provides optimum aesthetics and weatherability.
General Motors announced more than a dozen applications of nanocomposites, such as a van step assist, Impala side moldings, and Hummer H2 trim and panels. Early problems included painting issues and surface defects, caused in part by reagglomeration of nanoparticles. New surface treatments and processing technologies resolved early problems with nanocomposites, according to suppliers. The developmental nanocomposites at GM were thermoplastic olefin-based. The materials supplier for the initial GM parts was Basell Polyolefins of Elkton, MD.
GM is a good example of the problems that will face nano. New applications were pushed by the R&D engineers, but commercial officers balked at increased costs. The nanoclays cost about $3/lb and are used in loadings of 3-4 percent. The competitor is talc, which costs 30 cents/lb and is used at loadings of 10-15 percent. Another issue: Widespread replacement with nanocomposites may have required extensive re-tooling because of differences in shrinkage rates. Yet one more caveat about nanocomposites is reduced impact strength. “There is a lot of development work going on to improve impact strength with elastomers,” says Shah.
Leading U.S.-based suppliers of clay-based nano materials for plastic composites are Southern Clay, Gonzalez, TX, and Nanocor, Arlington Heights, IL.
Major investigations involving nano are still under way in Detroit, with specialty compounder PolyOne of Cleveland, OH, a major player.
In Europe, major cable manufacturers are rapidly switching to nano-filled composites of ethylene vinyl acetate/polyethylene to improve flame retardance. European regulations ban use of heavy metals previously used in cable jacketing. Replacements, such as aluminum trihydroxides (ATH), require loadings of 60 to 65 percent. As a result, mechanical properties are compromised and the compounds are difficult to process. “You can reduce about 15-20 percent (of the ATH) by adding 3 to 5 percent of the nanoclay,” says Stefan Richter, technical manager for Süd-Chemie, the leading European supplier of nanoclay products for plastic composites.
“In many cases, the combination of conventional flame retardants and nano-sized particles leads to synergistic effects,” says the Fraunhofer Institute of Bremen, Germany, which has been studying nanocomposites since 1997. “These combinations increase flame retardance significantly compared to a standalone usage of the components.”
Carbon Nanotubes
Meanwhile, developments in carbon nanotubes may affect plastics design in coming years. Carbon nanotubes are cylindrical carbon molecules that are strong, possess unique electrical properties and are efficient heat conductors. They belong to the fullerene structural family, which includes spherically shaped buckyballs. Diameters of carbon nanotubes typically run from less than 1 nm up to 50 nm. Lengths range from 100 to 1,000 times their diameter. They occur in nature in uncontrolled environments and are typically manufactured from carbon sources using high-tech processes, such as catalytic carbon vapor deposition.
One of the players is Nanocyl, which was formed in Belgium in 2002 based on university research. Nanocyl recently established a U.S. presence through a collaboration agreement with Boston-based Vantage Resin Systems, led by Andrew Rich. Initial targets in the U.S. are thermoplastic applications that require electrical conductivity or mechanical strength. Other opportunities include long-life batteries and mobile fuel cells.
Cost will be a factor. Carbon nanotubes will be priced at about $130/lb for orders of 1 to 5 tons per year, says Rich. “As for the effect on the polymer price, it depends on what you are putting the nanotubes into,” he adds. “Nanotubes in HDPE (high-density polyethylene) would make the 50 cent per pound raw material go over $5/lb. However, in something like a higher priced engineering polymer which starts out at $25-$45/lb and uses a lower loading, the impact on price can be less than 10 percent.”
Nanocyl is ramping up manufacturing, and expects to have the capacity to make 35 tons this year.
Exploding Fluids
Other important developments are on the horizon. For example, Five Star Technologies of Cleveland, OH, is using a proprietary hydrodynamic cavitation process to reduce the size of metallic and other particulates for use in thermoset or ceramic systems used for electronic packaging applications. Nano-sized silver is highly loaded in epoxy to make electrically conductive adhesives.
The size-reducing process does not damage the dispersion material, which is suspended in a prepolymer of the final matrix compound. “The fluid becomes stretched so much that vapor bubbles form in it,” says Timothy E. Fahey, vice president, business development. “And then when those vapor bubbles collapse, there is a burst of energy like a shock wave that hits the material and causes the particles to slam into each other.” That aspect is important for future plastic composites. “If you process carbon nanofibers conventionally, they come out like a hairball,” says Fahey. “If you process them in high-pressure equipment, you can damage their aspect ratio and destroy their ability to do the reinforcement that a mechanical engineer would be looking at,” adds Fahey. The hydrostatic cavitation process (which only works for thermosets) unbundles the carbon fibers without any damage to the aspect ratio, according to Fahey.
But like the other nano projects, development time will be significant. And cost will be an important factor.
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Nano Materials: Why Size Will Matter
Nano materials will change the way engineers design mechanical parts, but progress will be slow
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