SURFACE AND TRIBOLOGICAL CHEMISTRY OF WATER AND CARBON DIOXIDE ON COPPER SURFACES

OCTAVIO JAVIER FURLONG; ZHENJUN LI; FENG GAO; WILFRED T. TYSOE

TRIBOLOGY LETTERS

SPRINGER/PLENUM PUBLISHERS

Año: 2008 vol. 31 p. 167 - 176

1023-8883

The tribological chemistry of carbon dioxide and water vapor is studied on copper surfaces at high pressures, with a view to understand the gas-phase lubrication of copper–copper sliding contacts. The adsorption and film formation properties are studied on vapor-deposited copper films in an ultrahigh vacuum chamber using a quartz crystal microbalance. The nature of the reactively formed film is studied after reaction by ex situ X-ray photoelectron spectroscopy (XPS). Carbon dioxide adsorbs reversibly on copper, while water vapor adsorbs both reversibly and irreversibly, where XPS reveals that the irreversibly formed film consists of a mixture of cuprous oxide/hydroxide. Measuring the thickness of the cuprous oxide/hydroxide film as a function of water vapor pressure and temperature reveals that its thickness varies between about 6 and 14 Å and is proportional to the total amount of water adsorbed on the surface. This results in a cuprous oxide/hydroxide film that is thinner at higher temperatures. Measurements of the friction coefficient as a function of temperature and pressure in the presence of water vapor shows that it correlates with film thickness, reaching a limiting value of ~0.35 for thicker films.