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The load-carrying properties of a range of dialkyl phosphites have been examined under antiwear (AW) and antiscuff conditions using the four-ball machine. Adsorption/reaction of these compounds with iron surfaces has also been carried out. The results showed that both the load-carrying and adsorption/reaction properties of these dialkyl phosphites are markedly affected by the chain length and structure of the alkyl group. A mechanism of action of dialkyl phosphites is proposed which not only provides an explanation for both sets of observations but also highlights the difference in load-carrying action of dialkyl phosphites compared to the corresponding phosphates. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Atlanta, Georgia, October 16–18, 1973

Polyisobutenyl (PIB) succinimides are widely used as low/medium temperature detergent/dispersant additives in lubricants. To elucidate their mechanism of action, soluibility, micelle formation, adsorption, zeta potential, sedimentation and detergency studies have been carried out on a range of PIB succinimides in non-aqueous media. The results showed that the performance of PIB succinimides in various tests was dependent both on the molecular weight of the PIB and on the chemical structures of the amine used to make the succinimide. It was also concluded that these additives function by a steric stabilization mechanism and not by either electrostatic repulsion or micellar solubilization.

The surface topography and the nature of the surface layer of wear scars obtained with Bi(III), Pb(II), Cd(II), Ni(ll), and Zn(II) di-(4-methylpentyl-2) dithiophosphates, using the four-ball machine, have been studied using an electron probe microanalysis (EPMA) technique. The results show that the nature of the dithiophosphate markedly affects the surface topography, element content, and distribution of the wear scar in both the extreme pressure and mixed lubrication or antiwear regions. The implication of these EPMA results on the load-carrying mechanism of metal dialkyl dithiophosphates is discussed.

A range of diester disulphides was synthesised and their extreme-pressure and antiwear properties assessed using the Four-Ball machine. The diester disulphides had better antiwear properties, and poorer extreme-pressure properties than the corresponding unsubstituted disulphides. Dialkoxy substituted disulphides had similar extreme-pressure and antiwear properties to unsubstituted disulphides. Maximum antiwear protection at low additive concentration, followed by subsequent increase in wear with increasing concentration, was obtained for diester disulphides [-S(-CH 2 ) n COOC 2 H 5 ] 2 where n = 1, 2 and 3, but not when n = 5, 10. Explanations for these results are given and these are supported by heats of adsorption and electron probe microanalysis studies. It is suggested that the prime requirement for improving the antiwear properties of organo-sulphur compounds is the presence of strongly adsorbing groups at both ends of the molecule. These results also highlight the fact that the load-carrying properties of additives for one application can be improved only at the expense of its possible use in other fields.

The lubrication regions covered by the terms anti-wear (a.w) and extreme pressure (e.p.) are defined. The functions of a wide range of these load-carrying additives are presented together with the current thoughts on their mechanisms of action. The general additive types, namely; organo-sulphur (e.g. disulphides), organo-phosphorus (e.g. metal diaklyl dithiophosphates, phosphates, etc) and organo-chloro (e.g. chlorinated paraffins) are discussed and broadly classified as a.w. or e.p. additives. The effect of base oil structure on additive performance is shown to be important. Typical applications requiring a.w. and e.p. additives are given.

A review is presented of the work carried out by the author and his colleagues at the British Petroleum Research Centre on the load-carrying action of organo-sulphur compounds. This review shows how a hypothesis for the mechanism of load-carrying action of organo-sulphur compounds in both the antiwear and extreme-pressure regions was developed. The application of electron probe microanalysis techniques to studies of surface films in the lubricated contacts is also presented.

The load-carrying properties of a range of dialkyl phosphates and their alkylamine salts were assessed using the four-ball machine. The antiwear and extreme-pressure properties of these additives were found to be markedly dependent on the structure of both the acid phosphate and the amine. Similar trends were not observed for the dithiophosphate analogues. Possible explanations for these results are presented.

The liquid phase adsorption and reaction of a range of organo-sulfur compounds with ground iron powder were studied in the temperature range 25–170 C. The reactivity of organic disulfides was found to increase along the series: Monosulfides and mercaptans were found to be less reactive than the corresponding disulfides. A mechanism of reaction of these organo-sulfur compounds with the metal surface has been derived. This mechanism has confirmed the authors' earlier proposed mechanism of load-carrying action of organo-sulfur compounds as extreme pressure (EP) additives, but has resulted in a modification of the authors' proposed mechanism of antiwear (AW) action of these additives. This study has also indicated the temperature at which organo-disulfides function as EP additives. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE International Lubrication Conference held in New York City, October 9–12, 1972