Thermally Stimulated Electron Emission from Scratched Metal Surfaces
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Thermally Stimulated Electron Emission from Scratched Metal Surfaces Keiji Nakayama and Hitoshi Matamura National Institute of Advanced Industrial Science and Technology, Namiki 1-2-1 Tsukuba, 305-8564, Japan ABSTRACT In order to have a knowledge on electron emission from wearing metal surfaces under frictional heating, we investigated thermally stimulated electron emission (TSEE) phenomena together with thermoelectronic emission for 14 kinds of scratched metal surfaces, Al, Ti, V, Cr, Fe, Co, Ni, Cu, Mo, W, Pd, Pt, Ag and Au. The scratched metal surfaces in ambient air were thermally stimulated in a constant heating rate ranged from 1.3 to 4.4 °C/s from room temperature to 700 °C in a residual gas pressure of 10-4 Pa in a vacuum chamber. During the stimulation, a channeling type secondary electron multiplier detected the electrons emitted from the scratched metal surfaces. The TSEE glow curves and the integrated electron emission intensities over tested temperature range for the metals are presented and the emission mechanisms are discussed.
INTRODUCTION Tribochemical reactions, which take place at and near the sliding contact, govern the chemical reactions of lubricant fluids under frictional contact leading to the formation of effective lubricating films or shortening the life of lubricant. As the tribochemical reactions are often observed even at extremely low frictional temperature rise, it has been believed that some unknown high energetic or electron emission phenomena are generated to cause the tribochemical reactions. On the other hand, electron emission has been observed from wearing solid surfaces at room temperature. Metals emit electrons [1], while insulators and semiconductors emit not only electrons but also positive ions and even photons during sliding [2]. The electron emission from wearing metals has been attributed to the chemi-emission mechanism due to the interaction between the fresh worn metal surface and the surrounding gas molecules [1]. While triboemission of electrons, ions and photons from insulators have been attributed to the emission of these particles from the tribomicroplasma generated in a gap of sliding contact due to discharging of the ambient gas with the intense electric fields caused by tribocharging [3]. The
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tribomicroplasma must be the high energetic state to cause the tribochemical reaction. These two kinds of electrons are emitted from the sliding contact in the dark at room temperature. As surface temperature is elevated by friction, the electrons at the surfaces must be stimulated with the temperature rise to emit electrons.
Two kinds of electron emission
phenomena are observed when solids are heated. One of them is, thermoelectronic emission (TEE) and the other one is thermally stimulated electron emission (TSEE), in which electrons are emitted in much lower temperatures than those in thermoelectrons [4]. However, the mechanism of the TSEE is not clear. The TSEE or both TSEE and TEE must take place at and near the sliding contact by frictional te
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