REHOVOT, Israel June 19, 1997 A material discovered at the Weizmann Institute of Science has shown superior properties as a machine lubricant in tests simulating industrial conditions. When compared with the best existing lubricants, the material reduced friction between moving metal parts to less than half, and also cut wear on parts by up to six times. These findings are reported in the June 19 issue of Nature.
Using the new material as a lubricant would significantly increase the lifespan and efficiency of machinery from power tools and motor vehicles to airplanes and satellites.
"Lubricants reduce friction, and reduced friction means that machinery parts work more efficiently, so that cars, for example, would use less gasoline," says Prof. Reshef Tenne of the Institute's Materials and Interfaces Department, who headed the research team.
"In fact, growing environmental awareness is increasing pressure to improve the lubricants used in all machinery as a way of raising energy efficiency."
Friction between moving metal parts is the main cause of reduced efficiency in all machines, and also causes wear-and-tear on parts. Lubricants aim to combat this, but even high-performance lubricants, which mix solid and liquid ingredients, tend to stick to metal parts and eventually rub off, slowing down the workings and causing wear. Tenne and team have now produced a material made of molecules that adhere and rub off far less than the best existing lubricants.
"Existing lubricants contain crystallites, which are shaped like flat platelets and have chemically reactive edges. In working conditions, they stick to machinery parts and undergo chemical reactions that lead them to decompose and rub off," says Tenne.
"In contrast, our molecules are round and inert, so they just roll against each other and against the machinery parts, and don't stick to anything, like Teflon."
Tenne's team was made up of Ph.D. students Yshai Feldmann and Moshe Homyonfer, Dr. Sidney Cohen of the Institute's Chemical Services Unit, and Dr. Lev Rapoport and other researchers from the Center for Technological Education in Holon.
Inorganic "buckyballs"
In the mid-1980's, scientists made the revolutionary discovery that in certain conditions carbon atoms will cluster together to form a stable, hollow sphere that remarkably resembles a soccer ball. These round carbon molecules, which won their discoverers the 1996 Nobel Prize in Chemistry, were named fullerenes after R. Buckminster Fuller, the architect famous for designing domes with a soccer ball structure. Initially it was thought that fullerenes, or "buckyballs" as they are sometimes known, could be formed only by carbon, or possibly by other carbon-containing molecules. But in 1992, Weizmann Institute scientists led by Tenne and colleagues discovered that a synthetic inorganic molecule, tungsten disulfide, also forms fullerene-like balls in certain conditions. This finding opened a new field of research in materials science.
Outperforming existing lubricants
Tenne soon realized that the tungsten disulfide fullerene-like molecule shows properties that make it particularly suitable for use as a lubricant. Its round shape means it does not adhere to other substances, and it is larger than the carbon fullerene, enabling it to maintain a significant distance between two moving metal parts. In addition, it is made up of many layers of balls, rather like an onion, so that if the top layer wears away, those underneath continue to maintain a lubricating action.
In the study now being published in Nature, Tenne's team synthesized tungsten disulfide fullerene-like molecules of a relatively uniform shape and size, each molecule measuring about one millionth of a centimeter across. The researchers showed that in conditions similar to those prevailing in industry, the molecule significantly outperformed all existing solid lubricants, including normal tungsten disulfide and molybdenum disulfide.
The Institute's technology transfer arm, Yeda Research and Development Co. Ltd., has already filed patent applications for the new material, and industrial companies worldwide are expressing interest.
Tenne's team is now developing ways to produce commercial quantities of the tungsten disulfide fullerene-like molecule.
"The material works very well in the laboratory, and our challenge now is to synthesize it in large quantities for testing in the field," Tenne says.
Illustration: A high-resolution electron microscope image of a tungsten disulfide molecule is available.
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Journal
Nature