A piece of steel (left) coated with a thin layer of the super-slippery material just 2 to 3 micrometers thick – such coatings provide a kind of eternal lubrication to reduce friction and save energy (Image: US DoE Ames Lab)
A superhard substance that is more slippery than Teflon could protect mechanical parts from wear and tear, and boost energy efficiency by reducing friction.
The “ceramic alloy” is created by combining a metal alloy of boron, aluminium and magnesium (AlMgB14) with titanium boride (TiB2). It is the hardest material after diamond and cubic boron nitride.
BAM, as the material is called, was discovered at the US Department of Energy Ames Laboratory in Iowa in 1999, during attempts to develop a substance to generate electricity when heated.
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Eternal lubricant
BAM didn’t do that, but was found to have other desirable characteristics. “Its hardness was discovered by accident. We had a terrible time cutting it, grinding it, or polishing it,” says Alan Russell, a materials scientist at Iowa State University in Ames.
Those chance findings have now developed into a $3-million programme at the Ames Lab to develop the BAM into a kind of eternal lubricant, a coating for moving parts to boost energy efficiency and longevity by reducing friction.
BAM is much slipperier than Teflon, with a coefficient of friction of .02 compared to .05. Lubricated steel has a friction coefficient of 0.16.
One way to exploit this slipperiness is to coat the rotor blades in everyday pumps used in everything from heating systems to aircraft, says Russel. A slick BAM coating of just 2 microns (see image, top right) could reduce friction between the blades and their housing, meaning less power is needed to produce the same pumping power.
Mystery material
Bruce Cook, lead investigator on the Ames Lab project, estimates that merely coating rotors with the material could save US industry alone 330 trillion kilojoules (9 billion kilowatt hours) every year by 2030 – about $179 million a year.
BAM is also potentially attractive as a hard coating for drill bits and other cutting tools. Diamond is commonly used for this, and is harder, but it reacts chemically with steel and so degrades relatively quickly when used to cut the metal.
By contrast, BAM is cheaper and does not degrade when used with steel.
The exact reason for the new material’s characteristics is still unclear, Russell told New Scientist. Most superhard materials, such as diamond, have a simple, regular and symmetrical crystalline structure. But BAM is complex, unsymmetrical, and its lattice contains gaps, none of which would be expected in a hard material.
Its slipperiness is also not entirely understood. Although Russell says the best theory is that the boron interacts with oxygen to make tiny amounts of boron oxide on its surface. They would attract water molecules from the air, to make a slippery coating.
“It’s almost as if it’s a self-lubricating surface. You don’t need to add oil or other lubricants. It’s inherently slippery,” he says.
