ABSTRACT
The inhibition of corrosion in the petroleum production industry is both economically important and technically challenging. Organic monolayer corrosion inhibitors have been used effectively to reduce corrosion rates of carbon steels in production and refining environments. These molecules typically include a heteroatom site that attaches the molecule to the surface and a hydrocarbon portion of the molecule that serves to form a protective barrier. The actual mode of interaction with the surface, thermal stability, and decomposition pathways for these inhibitor molecules are not well understood. Surface science methods can be used to examine the thermal stability and decomposition pathways of these monolayer inhibitors, using well-characterized model substrates and model inhibitor molecules. A combination of vibrational spectroscopy, thermal desorption spectroscopy, and electron spectroscopic methods has been used to examine the interactions of model corrosion inhibitor molecules with well-characterized iron surfaces. Alkanethiol decomposition has been studied for a series of normal and substituted thiol molecules. Decomposition via βhydride elimination limits the thermal stability of the normal alkanethiols. Methyl substitution at the β-site improves thermal stability and leads to possible oligomerization on the surface. Oligomerization is also observed in studies of thiophene decomposition, leading to improved corrosion inhibition for this overlayer. Redox active inhibitors such as polyaniline have been examined, as have phosphorous containing inhibitors whose action may involve structural modification of the corroding surface. These studies indicate the importance of understanding kinetic pathways for decomposition and thermodynamic and structural stability of the organic corrosion inhibitor monolayer.
