Adsorption at the Metal-Hydrocarbon Interface
Authors: Fort Tomlinson , Bardasz Ewa A. , Ambwani Durga S. 
Published: December 2007

This paper was prepared for the Oilfield Chemistry Symposium of the Society of Petroleum Engineers of AIME, to be held in Denver, Colo., May 24–25, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

A study was made of the adsorption, from hydrocarbon solution, of a number of long chain polar-nonpolar molecules onto the surface of mercury. Work with mercury, a liquid metal, avoids the problems of surface cleanliness, heterogeneity and nonequilibrium character which have plagued the many studies of adsorption onto solid surfaces. The molecular, thermodynamic and kinetic aspects of adsorption of these typical lubricant additives is discussed. Points of interest include the effects of solute and solvent type and concentration, and the temperature, on both the nature of the adsorption process and the character of the adsorbed films. Special attention is paid to solvent structuring in the vicinity of the metal-hydrocarbon interface.

Introduction

Adsorption from hydrocarbon solutions onto metal surfaces has been a subject of inquiry for more than fifty years. Aside from its basic scientific interest, adsorption at this interface is of prime importance in practical problems of boundary lubrication, practical problems of boundary lubrication, corrosion inhibition, adhesion, and heterogeneous catalysis. Much interesting and useful information has been obtained and many technical variety of adsorption systems. However, quantitative information about adsorption from hydrocarbon solution onto well-defined metal surfaces is still lacking. The reasons are that metal surfaces are highly energetic and are, consequently, usually coated with a film of oxide and/or other contaminant, and that metal surfaces are typically rough, polycrystalline and of nonequilibrium configuration. polycrystalline and of nonequilibrium configuration. Accurate information about the thermodynamics and kinetics of adsorption, and about the molecular nature, of films deposited from solution onto well-characterized metal surfaces does not so far exist.

If the desired data are ever to be obtained, the effects on adsorption of the chemical as opposed to the physical influences of the metal surface must be separated and studied one at a time. Many of the physical factors which have complicated prior work (metal surface roughness, crystal structure and nonequilibrium nature) are associated exclusively with solid surfaces, and can be completely circumvented by studying adsorption at the surfaces of liquid metals. Liquid surfaces are smooth, have no complicating crystal structure, and are always strain free. Furthermore, the purity of liquid surfaces may be assessed through measurement of interfacial tension.