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Posted: Oct 04, 2010

Success in reduction of frictional force using the piezoelectric effect

(Nanowerk News) Dr. Masahiro Goto of the Micro-nano Materials Engineering Group, Materials Reliability Center of the National Institute for Materials Science, in joint work with Dr. Masahiro Tosa, Group Leader, and Dr. Akira Kasahara, both of the same group, discovered that zinc oxide coatings possess low frictional characteristics under all environments in the atmosphere, vacuum, and oil when their crystal orientation is skillfully controlled. This research also revealed that such coatings have a mysterious property, unlike that under normally conditions, in which the friction coefficient decreases as the load increases in oil.
With global environmental and energy problems becoming increasingly serious, generation of electric power using natural energy is now considered a high priority. Similarly, the development of energy saving technologies is also expected. One key energy saving measure is technologies which reduce friction in materials. Drive systems are an essential part of all types of transportation equipment, such as aircraft, ships, and automobiles, and friction causes energy loss in these systems. Moreover, in recent years, drive environments have become more diverse, including high temperature and humidity, vacuums, and oil. Thus, the development of low friction materials which are capable of reducing frictional force, while also withstanding the changes in these environment, is necessary and indispensible.
In this research, we succeeded in accurately controlling the crystal orientation of zinc oxide using an independently developed combinatorial sputter coating system (COSCOS).1) When friction tests were performed with these coating films under various environments, we ascertained that the materials possess low friction coefficients under all environments when the crystal orientation is properly controlled. We also discovered a phenomenon in which the piezoelectric effect2) of zinc oxide functions due to pressure applied from an indenter, generating a repulsion force. As a result, the friction coefficient of the material decreases as increasing of the load in oil.
This result is a basic technology which makes it possible to realize reductions in frictional force by the load resulting from gravity, without supplying any kinds of energy such as application of a magnetic field, electric field, or the like. Therefore, in the future, it is expected that energy savings can be realized by utilizing this technology in the drive parts of various devices.
This research result was obtained in "Reduction of Frictional Force Utilizing Piezo Effect and Development of Low Friction Coatings" under the Ministry of Education, Culture, Sports, Science and Technology Grants-in-Aid for Scientific Research (KAKENHI) program, Basic Research A (21246030).
Source: National Institute for Materials Science
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