The surface decomposition and extreme-pressure tribological properties of highly chlorinated methanes and ethanes on ferrous surfaces

Autor: L. Huezo, W. S. Millman, Wilfred T. Tysoe, P.V. Kotvis
Rok vydání: 1991
Předmět:
Zdroj: Wear. 147:401-419
ISSN: 0043-1648
DOI: 10.1016/0043-1648(91)90195-z
Popis: Two distinct types of extreme pressure lubricant additive behavior using chlorinated hydrocarbons have been identified using a pin and v-block apparatus. The first, which has been observed previously (and referred to as Type I) and exhibited by 1,4-dichloro-butane, CHCl3, and CH2Cl2, shows an initial increase of seizure load as a function of additive concentration, but reaches a plateau at higher concentrations. In contrast, the seizure load continues to increase with concentration when CCl4 is used as an additive. This behavior is designated Type II. Both C2Cl6 and C2HCl5 exhibit both types of behavior, being Type I at lower concentrations, converting to Type II at higher concentrations. The rate of film growth on an iron foil measured with a microbalance is shown to be significantly faster for a Type II additive (CCl4) and a Type I additive (CH2Cl2, CHCl3). CCl4 is also shown to grow according to an essentially linear rate law with an activation energy of about 38 kJ mol−1. Two possible seizure mechanisms are postulated. First, seizure is considered to occur when film removal by abrasion exceeds the growth rate, thereby leading to complete removal of the protective film. Secondly, measurements of the temperature close to the interface indicate that seizure can occur at some critical temperature Tc. Measurements of the seizure load as a function of bath temperature corroborate this view and Tc appears to be about 950 K. X-ray photoelectron spectroscopy analysis of the films formed by CH2Cl2 decomposition shows substantial carbon depletion in the film at higher growth temperatures. Surface analysis of chemisorbed carbon and chlorine formed by CCl4 decomposition shows that carbon is removed from the surface in this temperature range. FeCl2 also thermally decomposes and melts at about 950 K and provides a possible alternative explanation for the onset of seizure at Tc.
Databáze: OpenAIRE
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