Chemisorption and Tribochemical Reaction Mechanisms of HFC-134a on Nascent Ceramic Surfaces

Abstract

Chemisorption and tribochemical reaction of HFC-134a on the nascent surfaces of Al2O3, SiO2, AlN, and Si3N4 ceramics were studied using an adsorption test apparatus with a quadrupole mass spectrometer in a high vacuum at room temperature. The chemisorption of HFC-134a and the desorption of the tribochemical product of trifluoroethylene were observed during the rubbing processes of these ceramics. It has been found that the adsorption rate and the adsorption activity of HFC-134a on the nitride ceramics were higher than that on the oxide ceramics. Dehydrofluorination of the adsorbed HFC-134a molecules occurred on the nascent ceramic surfaces and the olefin of CF2CHF formed as a product. The yield of CF2CHF on the oxides was higher than that on the nitrides at the same condition and was proportional to the adsorption rate. By XPS analysis, Al−F or Si−F bonding was also found on the worn surface of these ceramics. A possible mechanism for the chemisorption and the tribochemical reaction of HFC-134a on the nas...