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Graphene as a lubricant Posted on 12 Jan 11:52

Graphene Is an excellent lubricant.

Sometimes, all it takes is an extremely small amount of material to make a big difference. Scientists at Argonne National Laboratory have recently discovered that they could substitute one-atom-thick graphene layers for oil-based lubricants on sliding steel surfaces, enabling a dramatic reduction in the amount of wear and friction.

New studies led by Argonne materials scientists Anirudha Sumant and Ali Erdemir showed that graphene is able to drastically reduce the wear rate and the (COF) of steel. The marked reductions in frictionand wear are attributed to the low shear and highly protective nature of graphene, which also prevented oxidation of the steel surfaces when present at sliding contact interfaces.

Stainless steel ball bearings form an integral part of many moving mechanical machines, ranging from table fans to giant wind turbines.

"Reducing energy and materials losses in these moving mechanical systems due to friction and wear remains one of the greatest engineering challenges of our time," Sumant said.

Current lubricants reduce friction and wear either through the use of environmentally unfriendly additives, or in some cases, solid lubricants such as molybdenum disulfide or boric acid. The oil-based lubricants need to be consistently reapplied, producing additional waste. The cost of applying solid lubricant coatings is rather high and due to finite thickness, they do not last very long and must also be expensively reapplied.

On the other hand, coatings made of graphene flakes are not harmful to the environment and can last a considerable length of time due to the flakes' ability to reorient themselves during initial wear cycles, providing a low COF during sliding.

Sumant and Erdemir estimated that the reduced loss of energy to friction offered by new materials would yield a potential energy savings of 2.46 billion kilowatt-hours per year, equivalent to 420,000 barrels of oil.

"Applying or reapplying the graphene coating does not require any additional processing steps other than just sprinkling a small amount of solution on the surface of interest, making this process simple, cost-effective, and environmentally friendly," said Diana Berman, a postdoctoral researcher at Argonne's Center for Nanoscale Materials (CNM).

"It is interesting to see how a one-atom-thick material affects the properties at a larger scale," Sumant said. "I believe that graphene has potential as a solid lubricant in the automotive industry and, once fully developed, it could have positive impacts on many mechanical applications that could lead to a tremendous savings of energy."

Sumant is associated with Argonne's CNM, while Erdemir works for Argonne's Energy Systems Division. Funding came from Argonne's Laboratory-Directed Research and Development office.

The team recently published their findings in two consecutive papers in the high impact journal Carbon.

Provided by: Argonne National Laboratory
April 26, 2013 by Jared Sagoff, Argonne National Laboratory

Better, Stronger & Cleaner Steel Posted on 12 Jan 11:49

We cook in stainless steel skillets, ride steel subway cars over steel rails to our offices in steel-framed building. Steel screws hold together broken bones, steel braces straighten crooked teeth and steel scalpels remove tumors. Most of the goods we consume are delivered by ships and trucks built of steel.

While various grades of steel that have been developed over the past 50 years, steel surfaces have remained largely unchanged. The steel of today is still vulnerable to the corrosive effects of water and salt and abrasive materials. Steel surgical tools still carry microorganisms that cause deadly infections.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have demonstrated a way to make steel stronger, safer and more durable. Their new surface coating, made from rough nano-porous tungsten oxide, is supposedly the most durable anti-fouling and anti-corrosive material to date. They claim it is capable of repelling any kind of liquid even after sustaining severe abuse.

The new material joins the portfolio of other non-stick, anti-fouling materials developed in the lab of Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science and core faculty member of the Wyss Institute for Biologically Inspired Engineering at Harvard University. Aizenberg's team developed “Slippery Liquid-Infused Porous Surfaces” in 2011 and since then they have demonstrated a broad range of applications for the super-slick coating, known as “SLIPS”. The new SLIPS-enhanced steel is described in the scientific peer-reviewed publication Nature Communications.

"Our slippery steel is several orders of magnitude more durable than any anti-fouling material that has been developed before," said Aizenberg. "So far, these two concepts of mechanical durability and anti-fouling were at odds with each other. We need surfaces to be textured and porous to impart fouling resistance but rough nano-structured coatings are intrinsically weaker than their bulk analogs.

This research shows that careful surface engineering allows the design of a material capable of performing multiple functions, without performance degradation.

The material could have far-ranging applications and avenues for commercialization, including non-fouling medical tools and devices, such as implants and scalpels, nozzles for 3D printing and, potentially, larger-scale applications for buildings and marine vessels.

Snake skin-like surfaces reduce friction up to 40% Posted on 12 Jan 11:48

Friction reduction breakthrough is no snake oil — Snakeskin. Credit: Jessica Paterson / Flickr 2009 - used under CC BY 2.0 license

Snake skin inspired surfaces smash records, providing an astonishing 40% friction reduction in tests of high performance materials.

These new surfaces could improve the reliability of mechanical components in machines such as high performance cars and add grist to the mill of engineers designing a new generation of space exploration robots.

A paper discussing this finding is published today in the Bioinspiration & Biomimetics journal.

The skin of many snakes and lizards has been studied by biologists and has long been known to provide friction reduction to the animal as it moves. It is also resistant to wear, particularly in environments that are dry and dusty or sandy.

Dr Greiner and his team used a laser to etch the surface of a steel pin so that it closely resembled the texture of snake skin. They then tested the friction created when the pin moved against another surface.

In dry conditions, i.e. with no oil or other lubricant, the scale-like surface created far less friction—40% less—than its smooth counterpart.

Lead researcher, Dr Christian Greiner said "If we'd managed just a 1% reduction in friction, our engineering colleagues would have been delighted; 40% really is a leap forward and everyone is very excited!"

Applications are likely to be in mechanical devices that are made to a micro or nano scale. Familiar examples include the sensors in car anti-lock braking systems, computer hard disk drives, and the component called an accelerometer, which means your mobile phone can tell if it is in portrait or landscape mode, and your activity band can count your steps as you move.

"Our new surface texture will mainly come into its own when engineers are really looking to push the envelope," Dr Greiner said.

The snake skin surface could be used in very high end automotive engineering, such as Formula 1 racing cars; in highly sensitive scientific equipment, including sensors installed in synchrotrons such as the Diamond Light Source in the UK or the Large Hadron Collider in Switzerland; and anywhere the engineering challenge is to further miniaturise moving parts.

There is interest in snake skin inspired materials from the robotics sector, too, which is designing robots, inspired by snakes, which could aid exploration of very dusty environments on earth or even in space. This raises a new challenge for Dr Greiner's team—to make a material that decreases friction in only one direction.

Anyone who has felt a snake's skin will know that the scales all lie in the same direction and are articulated to aid the snake in its forward motion, whilst resisting backwards motion. The steel pins tested in this research mimic only the overall surface texture of snake skin and reduce friction in at least two directions.

Dr Greiner has made some progress with polymers that even more closely mimic snake skin to reduce friction in only one direction. It is, he says, early days and this later work is not yet scheduled for publication.

The only caution is that this new surface doesn't work well in an environment where oil or another lubricant is present. In fact, the snake skin effect created three times more friction, with lubricant, than an equivalent smooth surface.

"This wasn't a huge surprise," Dr Greiner explained, "since we were looking to nature for inspiration and the species we mimicked - the royal python and a lizard called a sandfish skink—live in very dry environments and don't secrete oils or other liquids onto their skin."

More information: 'Bio-inspired scale-like surface textures and their tribological properties' Bioinspiration Biomimetics 10 044001. iopscience.iop.org/1748-3190/10/3/044001.