Nano-boric acid
makes motor oil more slippery
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ARGONNE, Ill. (Aug. 3, 2007) — One key to saving the environment, improving
our economy
and reducing our dependence on foreign oil might just be sitting in your
mother's medicine cabinet.
Scientists at the U.S. Department of Energy's Argonne National Laboratory
have begun to combine infinitesimal particles of boric acid — known primarily
as a mild antiseptic and eye cleanser — with traditional motor oils in order
to improve their lubricity and by doing so increase energy efficiency.
Ali Erdemir,
senior scientist in Argonne's Energy
Systems Division, has spent nearly 20
years investigating the lubricious properties of boric acid. In 1991, he received
an R&D
100 award — widely considered the "Oscar of technology" — for
showing that microscopic particles of boric acid could dramatically reduce
friction between automobile engine parts. Metals covered with a boric acid
film exhibited coefficients of friction lower than that of Teflon, making
Erdemir's films the slickest solids in existence at that time.
"Ali was looking at large, micron-sized, particles," said George Fenske, who
works alongside Erdemir at Argonne. "He was just sprinkling boric acid onto
surfaces."
But driven by a conviction that he could fashion boric acid into an even better
lubricant, Erdemir continued to chase the ultimate frontier: a perfectly frictionless
material. Glimpsing the potential of nanotechnology, Erdemir went smaller — 10
times smaller — and was astonished by the behavior of much thinner boric acid
films. "If you can produce or manufacture boric acid at the nanoscale, its
properties become even more fantastic," he said.
Reducing the size of the particles to as tiny as 50 nanometers in diameter — less
than one-thousandth the width of a human hair — solved a number of old problems
and opened up a number of new possibilities, Erdemir said. In previous tests,
his team had combined the larger boric acid particles with pure poly-alpha-olefin,
the principal ingredient in many synthetic motor oils. While these larger particles
dramatically improved the lubricity of the pure oil, within a few weeks gravity
had started to separate the mixture. By using smaller particles, Erdemir created
a stable suspension of boric acid in the motor oil.
In laboratory tests, these new boric acid suspensions have reduced by as much
as two-thirds the energy lost through friction as heat. The implications for
fuel economy are not hard to imagine, Erdemir said. "You're easily talking
about a four or five percent reduction in fuel consumption," he said. "In
a given day, we consume so many millions of barrels of oil, and if you can
reduce that number by even one percent, that will have a huge economic impact."
Argonne is currently in talks with
materials and lubricant
manufacturers
to bring boric acid technology to market, Erdemir said. While these new additives
need to pass a battery of environmental and safety tests, they will probably
be available within two years.
In his first experiments with boric acid, Erdemir demonstrated that the compound
not only proved an effective lubricant but was also every industrial technologist's
dream: It came from naturally abundant minerals, was cheap to manufacture,
and posed no health hazards or environmental threats.
Boric acid owes its lubricious properties to its unique natural structure.
The compound consists of a stack of crystallized layers in which the atoms
tightly adhere to each other. However, these layers stack themselves relatively
far apart, so that the intermolecular bonds — called van der Waals forces — are
comparatively weak. When stressed, the compound's layers smear and slide over
one another easily, like a strewn deck of playing cards. The strong bonding
within each layer prevents direct contact between sliding parts, lowering friction
and minimizing wear.
Until recently, most of Erdemir's work in boric acid lubrication had been
restricted to motor oils, principally because of the relative bulk of the larger
particles. The move to the nanoscale, however, has opened up other possible
uses of the chemical. Through a simple chemical reaction, nano-boric acid can
be transformed into a liquid relative of boric acid that has shown potential
to increase fuel lubricity.
Using this liquid analog of solid boric acid as a fuel additive on a large
scale could greatly benefit the environment, both because it would help to
increase fuel efficiency and because it would replace existing fuel lubricants
that are potentially harmful to the environment, Erdemir said.
By themselves, most fuels — especially
diesels — contain
some sulfur and other special chemical additives to boost lubricity. When burned,
however, some of these additives along with sulfur may cause harmful emissions
and acid rain. However, the lack of a suitable alternative complicates efforts
to cut sulfur content.
The substitution of liquid boric acid for sulfur-containing additives preserves
the health of the car as well as that of the environment. Sulfur exhaust gradually
coats the surface of a car's catalytic converter, the part that helps to reduce
the toxicity of a car's emissions. Eventually, the converter becomes so choked
with sulfur that it is no longer able to process any more exhaust.
Even though he has just begun to unleash the potential of boric acid, Erdemir
believes that nanoscale synthetic compounds may prove to be even more effective
lubricants. "The next step is to use the basic knowledge that we have
gained out of this particular compound to come up with more exotic compounds
that will work even better," he said. — Jared Sagoff
For more information, please
contact Steve McGregor (630/252-5580 or media@anl.gov)
at Argonne.
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