The Genie in the Bottle: Nano-Science, Nano-Technology (Part II)

Part II: Article written and submitted by Dr. Hisham Abdel-Aal and featured in the May 2007 issue of Southern Metal Finishing.

How can such a technology impact metal and surface finishing?
A powerful promise of Nanotechnology is the potential to manipulate the very building blocks of matter.  This ability, when mastered, would allow the customization of materials.  That is, it will enable the so called “synthesizes of application driven materials” or the material on demand concept.  So, by manipulating the arrangement of atoms, molecules, and the strength or order of bonding, at least in principle, one can induce desirable changes in a material, or better yet, design a custom tailored substance.  Such a concept is not new, it is applied for instance in polymers where the change of the position of the molecules in a chain may create a new polymer with desirable properties.  Nanotechnology induces such an effect through miniaturization.  The common consensus is that the properties of materials at the nano scale differ from those of the bulk material.  This is an effect that we encounter in daily life when objects become smaller and hard to break, for example.
By reducing the size of the particles that make a material, desirable properties may be induced.  Such an approach is already applied in coatings by embedding nano-particles to change properties, or by deposition of very thin coatings to alter behavior.  Take for an example Titanium Nitride coatings that are applied to tool inserts, or diamond like carbon layers that are applied to high end computer hard disks.
In the strict sense of metal finishing the potential lies in producing powder coatings that employ nano-particles to induce a desired behavior.  For example, adding nano-particles to enhance scratch resistance, corrosion resistance, and protect from harmful light waves to protect paints.     
               
The Science and the science fiction
Nano-coatings have already been applied to a diverse but specialized array of objects, from parts for nuclear steam generators and barrels of field artillery to expensive golf clubs.
Air Canada recently announced it will experiment next year with a commercial jet stripped entirely of its traditional paint job, and instead protected with a nano-coating. The weight reduction will be about 350 pounds, and the resulting savings in fuel could total more than $25,000 per year. Other such cost-saving experiments and applications are expected to follow.
Under a microscope, even the smoothest, crystalline coatings--such as polished chrome--show irregular gaps between the crystals. Over time, this causes these materials to weaken, crack and creep, especially when the structure is under stress. Nanotechnology offers a potential solution: reordering the gaps into a uniform pattern, or by reducing crystal size. Naturally, the impact of the weaknesses caused by the gaps depends on the application.  For a chrome automobile bumper, gaps are probably immaterial. Automotive chrome coatings usually outlast the life of a typically driven car. However, in applications where both strength and weight are of primary importance, crystalline and molecular weakness may pose a detrimental influence on the surface of the metal and its strength.  The irregular gaps can be exploited by outside forces such as water, temperature, and ultra-violet light from the sun. Air pressure, weight, and g-forces will also stress coatings and can lead to metal failure. This can have disastrous effects in landing gear applications, for example. The Canadian air force uses nanotechnology to plate and coat landing gear for Canada’s fighter jets, and other aircraft, to improve the strength of these structures which experience extreme stress during take-offs and landings.

Nanotechnology in metal plating and coating can also reduce friction on the striking surfaces of golf clubs, thus creating a larger “sweet spot” and reducing club weight. For example, PowerMetal Technologies (Carlsbad, Calif.) offers high-end nano-coated woods and drivers; the super-thin face coatings on these clubs help move some of the weight to the dense portion of the club, thus inhibiting longer, more accurate shots. Some of PowerMetal’s coated clubs are being used on the PGA tour, and the firm said it is also working on nano-coated baseball bats, skis, and super-lightweight high-performance bicycle components.

Nanotechnology offers an effective way to address environmental issues. Nano cobalt-phosphorus, for instance, is compatible with most existing electroplating equipment and positioned as an effective replacement for hexavalent chromium. Nano crystalline material is considered stronger and more durable than hex chrome. Electroplated nano-aluminum coatings offer potential as a cadmium replacement and are environmentally safe.
Nano-coatings are not cheap to apply to date, and the expertise required to develop and use the technology is highly specialized and therefore expensive. However, costs are coming down; already there are undergoing efforts to reduce processing expenses of nano-coating golf clubs and other sporting equipment, bringing these items into a relatively affordable range. In addition, where cost is secondary to certain other factors, such as strength and safety, nano-coating technology is growing from a niche into a category within the metal finishing industry.
Nanotechnology is used by finishers of mechanical, optical and analytical equipment, biomaterials and drug packaging, electronics and computer-chip manufacturers, and in automotive applications such as antireflection coatings, in addition to the applications mentioned earlier.
There are two approaches to manipulate grain boundaries in various materials: the “top down” approach, which is trademarked under the name Grain Boundary Engineering (GBE), works down from the surface into the inside of a material. The “bottom up” approach, called Nanoplate, improves coating strength through electroplating.
The approaches were developed with the help of Professor Uwe Erb, of the Department of Materials Science and Engineering at the University of Toronto, who specializes in nanomaterials. The GBE process is designed to control disorderly gaps between the crystals in crystalline materials. The Nanoplate process reduces grain size to create a larger overall grain surface area. According to Erb’s research, in conventional plating, unavoidable impurities in metal alloys spread throughout a coating, migrating naturally to grain boundaries and precipitating there, causing weaknesses that stress and other factors can exploit.

By comparison, nano-coatings the size of the grains is much, much smaller, and their number is increased exponentially. The result is that impurities are super-diffused, through the so called “homogenization by segregation.” A coating with nano-grain size is stronger and more resistant to stress and corrosion cracking. GBE process can be applied to bulk metals as a surface treatment to pre-finished and semi-finished metals, or a “heating and beating” system.  The finished or semi-finished surface is exposed to shot-peening (“beating”), then induction-heated to create a kind of coating from the substrate layers of the original surface. Research has shown that as much as 70% of this “coating” is orderly, grain-boundary material, or an ideal nano-coating. For pre- and semi-finished metals, weldability, corrosion resistance, sulfidation resistance, fatigue resistance, and resistance to high-temperature creep are all improved. Tests on Allow 800, which is particularly vulnerable to intergranular corrosion, show a corrosion reduction rate from 2.2 to 0.22 mm per year.
It is worth mentioning that there are many ideas that are produced on a laboratory scale or just as a computer simulated product.  An example is the so called “smart coating concept” where, instead of nano-particles, a coating will be made entirely of programmable nano-machines (robots).  A designer, in principle, can program these nano-entities to increase bonding, reduce grain sizes, increase stiffness or even change the color of the surface.  Naturally, a parallel break through in production at a commercial scale needs to take place.  This, however, belongs to an entirely different article.

Further Reading
1.  For a comparative view of commonly known items and nano-sized entities, see www.nano.gov/html/facts/The_scale_of_things.html.

2.   For the text of Feynman’s address, see http://www.zyvex.com/nanotech/feynman.html.

3. For congressional addresses on this topic delivered by leaders in the field of nanoscale science and technology, see addresses delivered by:
- Eugene Wong, assistant director of Engineering of the National Science Foundation(www.house.gov/science/wong_062299.htm);   
- Richard Smalley, Nobel Laureate and Professor of Chemistry at Rice University  (www.house.gov/science/smalley_062299.htm), and
- Ralph Merkle, Research Scientist (Xerox) and Senior Research Associate, Institute for Molecular Manufacturing (www.house.gov/science/merkle_062299.htm).

4. For an address delivered by Dr. M.C. Rocco (Senior Advisor for Nanotechnology at the National Science Foundation) at the Euro Nano Forum, December 10, 2003, see:
http://www.nsf.gov/home/crssprgm/nano/nni031210roco@euronanoforum.pdf

Dr. Abdel-Aal is an assistant professor in the Department of Engineering at the University of Wisconsin-Platteville. He acquired his PhD in Tribology from the University of North Carolina in Charlotte. He actively engages in research projects, as well as teaching.
You can visit his website at:
http://www.uwplatt.edu/~abdelaah/












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