|The crystalline structure of boric acid. Boron atoms are shown as blue spheres, oxygen as pink, and hydrogen as brown. Molecular forces that bind the layers in the lattice enable them to slide over one another with very low friction. Click to enlarge.|
Scientists at the US Department of Energy’s Argonne National Laboratory have begun to nanoparticles 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.
In laboratory tests, these new boric acid suspensions have reduced by as much as two-thirds the energy lost through friction as heat. This could result in a four or five percent reduction in fuel consumption, according to Ali Erdemir, senior scientist in Argonne’s Energy Systems Division.
Erdemir received an R&D 100 award in 1991 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.
Reducing the size of the particles to as tiny as 50 nanometers in diameter solved a number of old problems and opened up a number of new possibilities. 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.
If you can produce or manufacture boric acid at the nanoscale, its properties become even more fantastic.—Ali Erdemir
Argonne is currently in talks with materials and lubricant manufacturers to bring boric acid technology to market. While these new additives need to pass a battery of environmental and safety tests, they will probably be available within two years.
Boric acid comes from naturally abundant minerals, is cheap to manufacture, and poses no known health hazards or environmental threats.
|The microscopic layered structure of the compound. Click to enlarge.|
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 (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 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 benefit the environment, both because it would help to increase fuel efficiency and because it would replace existing fuel lubricants—such as sulfur. 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, as well as eventually compromising catalytic devices in the vehicle.
Erdemir believes that nanoscale synthetic compounds may prove to be even more effective lubricants than nanoscale boric acid.
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.—Ali Erdemir