High Temperature Reaction of Aryl Phosphate Esters on an Iron Film

Abstract

The reaction between vaporous aryl phosphate esters and iron is known to yield a lubricious product film at high temperatures. The rate law exhibited in the growth of this film is consistent with a diffusion controlled process. In this work the actual movement of elements during this growth process was characterized using composite metal foil samples consisting of a 1,000 Å iron film deposited on a platinum substrate. The interface between the platinum and iron served as a reference datum against which the movement of the elements was measured. Iron was found to be the solitary mobile element in the product growth process. A Boltzman-Matano analysis was applied to the iron concentration-depth profile of the product to assess the diffusivity of the iron during the product growth. In this case the diffusivity of iron was found to be greater than its self diffusivity but less than its diffusivity in magnetite. The data suggests that the diffusivity of iron across the iron/product interface is the rate controlling step in the product growth process.

KEY WORDS:

• Vapor Phase Lubrication
• Phosphate Esters
• Auger Electron Spectroscopy (AES)
• Surface Films
• Coatings