1. Introduction
Ever since superlubricity (SL, e.g., mo0.010) was first observed
during water lubricated sliding tests of ceramics, there has been an
increasing interest in their tribological behavior due to the remarkable
scientific, technological and environmental importance of this finding.
In the mid 80's, Tomizawa and Fischer measured friction
coefficients lower than 0.01 during water lubricated sliding tests
using a pin and disc of silicon nitride [1]. The very low friction
values were attributed to the formation of a highly polished surface
obtained due to the wear of the rubbing components, which
provide the means to reach hydrodynamic load carrying capacity.
Later on, Tomizawa and Fischer observed a similar phenomenon
during water lubricated sliding tests using a pin and disc of Silicon
Carbide [2].
In 2000, Xu and Kato [3] justified the very low friction
coefficient of ceramic sliding pairs (SiC–SiC and Si3N4–Si3N4) to
the occurrence of tribochemical reactions during the rubbing
process. They also stated that the charged particles of colloidal
silica contribute to reduce the friction coefficient at mixed lubrication
regime due to the formation of an electric double layer that is
an auxiliary mechanism to increase the separation between the
sliding surfaces.
1. IntroductionEver since superlubricity (SL, e.g., mo0.010) was first observedduring water lubricated sliding tests of ceramics, there has been anincreasing interest in their tribological behavior due to the remarkablescientific, technological and environmental importance of this finding.In the mid 80's, Tomizawa and Fischer measured frictioncoefficients lower than 0.01 during water lubricated sliding testsusing a pin and disc of silicon nitride [1]. The very low frictionvalues were attributed to the formation of a highly polished surfaceobtained due to the wear of the rubbing components, whichprovide the means to reach hydrodynamic load carrying capacity.Later on, Tomizawa and Fischer observed a similar phenomenonduring water lubricated sliding tests using a pin and disc of SiliconCarbide [2].In 2000, Xu and Kato [3] justified the very low frictioncoefficient of ceramic sliding pairs (SiC–SiC and Si3N4–Si3N4) tothe occurrence of tribochemical reactions during the rubbingprocess. They also stated that the charged particles of colloidalsilica contribute to reduce the friction coefficient at mixed lubricationregime due to the formation of an electric double layer that isan auxiliary mechanism to increase the separation between thesliding surfaces.
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