Perfluoropolyalkylether Lubricants under Boundary Conditions: Iron Catalysis of Lubricant Degradation

摘要

Perfluoropolyalkylether (PFPE) oils and oil-based greases exhibit significant degradation under boundary lubrication conditions. In the absence of significant concentrations of oxygen, as in the case of spacecraft orbital environments, the degradation mechanism consists of two steps: (1) the initial reaction of the PFPE molecules with freshly exposed iron to form the Lewis acid, FeF3, followed by (2) the reaction of the FeF3 with unreacted PFPE molecules, which results in the''leavage of the etherate linkages. The result is an autocatalytic degradation that takes place at temperatures below the onset of thermal decomposition. This mechanistic hypothesis is supported by the following experimental results: (1) The reaction of PFPE with FeF3 has been shown to give rise to fluorinated-ketone and acid fluoride ether-cleavage products that are more reactive than the parent PFPE molecules and have lower molecular weights and thus poorer lubricating ability. (2) FeFX compounds are formed in the wear tracks of wear-test components under boundary lubrication conditions. Keywords: Lubricant degradation, Lubricants, Perfluoropolyalkylether, Infra red spectroscopy, Lewis acids.