The Science of Small Grows BIG

Article From: Products Finishing, , from Products Finishing

Posted on: 8/1/2005

Nanotechnology is everywhere. It is even making advancements in the finishing market...

Nanotechnology encompasses a broad range of industries from plating to cosmetics to optical to the military. Basically, nanotechnology is a "catch-al" description of activities at the level of atoms and molecules that have applications in the real world.1 Nanocrystalline metals (nickel, cobalt, palladium, copper and some of their alloys, for example) can provide an extremely thin coating that is more wear resistant than normal plated finishes. Also, the fine-grained structure of the nanocrystalline metals can affect beneficially the magnetic, hardness, optical and corrosion resistance and other properties of the finish, according to scientists.

There are several ways to develop nanocrystalline finishes, including: vapor phase processing, inert gas condensation, mechanical alloying or high-energy ball milling, chemical synthesis and electroplating. There are two methodologies for building nanocrystalline structures. The two technologies are considered "bottom up" and "top down."

The "top-down" method means that nanoscale structures are developed using machining and etching techniques. The "bottom-up" method refers to building organic and inorganic structures atom by atom or molecule by molecule. According to the Institute of Nanotechnology, most of the technology used today is still in the "top-down" stage.

Optimizing property-specific grain size when building nanocrystalline finishes is important to producing extremely dense coatings without any unnecessary porosity, since many properties attributed to nanostructures are due to the residual porosity of the material.2

Properties of nanocrystalline deposits fall into two categories: one set of properties is dependent on grain size; the other set of properties is independent of grain size. Various physical effects are achieved by engineering the surfaces and layers of the nanocrystalline material as it is applied. In electroplating, this is often achieved by suspending in solution second-phase nanocrystalline particles, which are then codeposited in a specific method to achieve certain effects.

Present finishing applications for nanocrystalline coatings include multilayer protective coatings as well as extremely hard and/or wear-resistant coatings. In the automotive finishing industry, plastic nanocomposites are used for the step assists on General Motors Safari and Astro Vans. The material is scratch-resistant, lightweight and rustproof. This provides for greater fuel savings and a longer life for the automobile. In 2001, Toyota began using a nanocomposite in bumpers. These bumpers were 60% lighter and twice as resistant to denting and marring. Metal nanocrystals are also used in car bumpers to increase strength. Scientists have shown that the nanocrystals of various metals are 100 to 300% harder than the same materials in bulk form.

Corrosion Resistance

Nanocrystalline nickel finishes exhibit higher general corrosion resistance than polycrystalline nickel. The finish corrodes more uniformly with fewer localized corrosion sites, particularly along grain boundaries. Using ASTM B-117 salt-spray test, it was determined that the microstructure of electroplated nickel has little effect on corrosion performance. On mild steel, both the nanocrystalline and polycrystalline coating provide the same corrosion protection.3

Electroplated nanocrystalline finishes could be used as chromium replacements in various applications to lower weight and provide greater corrosion protection, such as landing gear in airplanes and engine parts for automotive applications.
In the military, for instance, nanocrystalline organic finishes could enable jeeps, tanks and other vehicles to detect corrosion and scratches and "heal themselves," or even change color on the battlefield for instant camouflage. These organic coatings could also be used by the automotive industry.

Wear Resistance/Hardness

Electroplated nanocrystalline finishes have greater wear resistance than traditional plated finishes. In testing, Vickers hardness increased significantly in nickel plated finishes when the grain size was reduced. Most nanocrystalline deposits also exceed the wear resistance of hard chromium. Because weight is also reduced with nanocrystalline deposits, this property is significant for the automotive, aerospace and military industries. It allows platers to provide finishes that stand up to wear and tear, but also help the product (engines, turbines, anything with bearings, etc.) to last longer.

Imparting hardness and wear resistance during the nanocrystalline plating process is possible using codeposition. During this process, the second nanoparticulate is maintained in suspension in the plating solution and uniformly plated with the original nanocrystalline metal. This allows the plater to incorporate specific functions into the finish. This may include coatings for products in the electronics market that require good magnetic properties and excellent hardness, wear and corrosion resistance.

In Production

Aerospace. Currently in production are multi functional nanocrystalline coatings for aerospace applications that can provide corrosion protection using environmentally safe materials. These coatings sense corrosion and mechanical damage of aircraft skin and initiate responses to repair it. Because these coatings also improve fatigue resistance, are lightweight, strong and thermally stable they can be used in turbines and landing gear.

Electronics. The electronics market continues to make products smaller and smaller. Because of this, nanocrystalline finishes play an important role. Using electroplating, bulk material, foils and coatings of any shape can be produced. Often the electroplating process can be combined with electroforming and reel-to-reel plating. The ability to control finish properties, such as magnetics and wear resistance are also important to this industry, and nanocrystalline coatings provide a way to achieve the properties and still maintain "small" products.

Hard Chromium Applications. Electroplated nanocrystalline metals and alloys may also be used as a replacement for hard chromium. In addition to greater corrosion resistance, nanocrystalline finishes also have higher ductility and improved fatigue performance due to the absence of microcracking. Nanocrystalline metal and alloy plating also feature high current efficiency, which can relieve hydrogen embrittlement concerns.

More breakthroughs and advancements in nanotechnology are expected in the future. An article in February 13, 2005, Business Week, predicts that within eight years the health care industry will have portable labs capable of analyzing diabetes to HIV. The article also contends that the health care industry will have implantable health monitors or nano agents able to kill cancer. Within three years there should be lighter tennis rackets, fabric that doesn't stain and golf balls that will help straighten out your drives, all due to nanotechnology.

Instead of everything getting bigger and faster, it is becoming smaller and stronger, including finishes. While the metal still will cover, the structure of the metal will be different. Since the atoms can be manipulated, it will allow for tighter coatings that are more wear resistant, corrosion resistant and lighter, because the finish is thinner.

There are two good websites for information on nanotechnology: www.azonano.com and www.nano.org.uk, the web site for the Institute of Nanotechnology.

  1. Institute of Nanotechnology, "Nanotechnology - What is It?", www.nano.org.uk/nano.htm
  2. G. Polumbo, F. Gonzalez, K.Tomantschger, U.Erb and K.T. Aust, Plating and Surface Finishing, Vol. 90, No. 2, February 2003, pages 36-43.
  3. G. Polumbo, F. Gonzalez, K.Tomantschger, U.Erb and K.T. Aust, Plating and Surface Finishing, Vol. 90, No. 2, February 2003, pages 36-43.

 




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