Japanese researchers say they have discovered a way to manipulate zinc oxide coatings to maintain their low-friction characteristics and even reduce friction in any environment—a finding that holds significant potential for energy savings in transportation.
Zinc oxide coatings “possess low frictional characteristics under all environments in the atmosphere, vacuum, and oil when their crystal orientation is skillfully controlled,” according to materials engineering researchers at Japan’s National Institute for Materials Science.
Not only that, but the research “also revealed that such coatings have a mysterious property, unlike that under normal conditions, in which the friction coefficient decreases as the load increases in oil.”
The discovery holds significant potential as an energy-saving technology in ships, aircraft, automobiles and other forms of transportation, the team said.
“One key energy-saving measure is technologies which reduce friction in materials,” they said. “Drive systems are an essential part of all types of transportation equipment, … 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.”
Materials that can reduce frictional force while withstanding environmental changes are “necessary and indispensible,” the scientists said.
The research employed what is known as the Piezoelectric Effect, in which a mechanical stressor (usually, stretching or squeezing) is applied to a substance to produce an electrical charge.
In this case, the scientists said, “we succeeded in accurately controlling the crystal orientation of zinc oxide using an independently developed combinatorial sputter coating system (COSCOS).”
After performing friction tests with the coating films in 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 Effect 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.”
The result is a basic technology that “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,” the researchers said.
“Therefore, in the future, it is expected that energy savings can be realized by utilizing this technology in the drive parts of various devices.”
The research, “Reduction of Frictional Force Utilizing Piezo Effect and Development of Low Friction Coatings,” was supported by the Ministry of Education, Culture, Sports, Science and Technology Grants-in-Aid for Scientific Research program.