Overbased Calcium Sulphonate Research Articles

Effect of lubricant additives on the tribological behavior of aluminum alloy against steel

Abstract This study aims to understand the impact of various lubricant additives on the friction- and wear behavior of aluminum alloys against steel. Employing the aluminum alloy Al 6061 and the steel AISI E 52100 as representatives, we studied the effects of the main additives typically found in fully formulated lubricants individually by formulating model lubricants consisting of base oil and just one additive at a time. The additives we studied include sulfurized olefin, complex alkyl phosphate amine, alkyl phosphite, overbased calcium sulphonate, zinc dithiophosphate (ZDP), and calcium sulfonate detergents. For each model lubricant, as well as for the base oil and the fully formulated oil, we performed ball-on-disc experiments with aluminum alloy balls on steel discs. We obtained the friction coefficient, determined the wear volume of the aluminum alloy, and analyzed the composition of the wear surface. We found that all additives except calcium sulfonate detergents promote the formation of aluminum oxide. Among all individually tested additives, zinc dithiophosphate provides the best wear resistance, while sulfurized olefin provides the lowest friction. The lowest friction combined with the second lowest wear rate was actually observed for a fully formulated oil (containing an optimized mixture of several additives).

Influence of water on the tribological properties of zinc dialkyl-dithiophosphate and over-based calcium sulphonate additives in wet clutch contacts

Usually the wet clutch lubricant properties vary with different formulations of base oil types and additives. The aim of this paper was to evaluate the effect of water on the performance of additives in ATF. Simplified lubricants, ZDDP and over-based Ca-sulfonates detergent additives in an API Group I mineral base oil, were employed to compare with the commercial fully-formulated automatic transmission fluid (DEXRON®VI) during water-contamination. A full-scale wet clutch test rig was used to evaluate the frictional response due to water contamination of the lubricants. Fourier Transform Infrared Spectroscopy was utilized to evaluate the variation in the solubility of these polar organic additives in the water phase and Karl-Fischer titration was utilized to evaluate the post-test water content for different formulations.

Lubrication of aluminium–silicon surfaces with ZDDP and detergents

A review of the lubrication of aluminium–silicon (Al-Si) substrates by zinc dialkyldithiophosphate (ZDDP) and detergent engine oil additives is presented. Greater attention has been paid to understand the interactions of ZDDP, rather than detergents, with the aforementioned non-ferrous substrates. Zinc dialkyldithiophosphate generates tribofilms on both aluminium and silicon regions of aluminium–silicon alloys. However, film formation is believed to occur on silicon grains within the alloy, and those layers observed on aluminium regions are material transfer or the product of ZDDP thermal decomposition. There were many similarities in terms of film thickness, reduced elastic modulus, tribochemistry and topography of ZDDP derived tribofilms on both ferrous and Al–Si substrates. Calcium carbonate based films were observed on silicon grains when the aluminium alloys were lubricated with overbased calcium sulphonate, the tribochemistry and topography of which were similar to layers formed on ferrous substrates. When lubricated with either fully formulated oil or lubricants containing both detergent and ZDDP, the subsequently generated films were of varying chemistry, but often contained zinc or calcium phosphate compounds. The antiwear characteristics of ZDDP and calcium sulphonate tribofilms on ferrous and aluminium–silicon substrates are discussed, with the mechanical and film thickness data for such layers presented.

Investigation of the interactions between a novel, organic anti-wear additive, ZDDP and overbased calcium sulphonate

The use of zinc dialkyldithiophosphate (ZDDP) in automotive lubricants is being questioned due to its detrimental effect to the efficiency of catalytic converters. In an effort to determine an effective replacement, a novel, organic anti-wear additive (OAW) was tested to examine its tribological properties and interactions with ZDDP and a deposit control additive (DCA), overbased calcium sulphonate (OBCS). Tribological tests were performed that found OAW to be beneficial to the anti-wear performance of the lubricant, through synergism with OBCS. Surface analysis techniques were employed to analyse the subsequent tribofilms that were found to be composed of CaCO 3 and Ca polyphosphates.

Friction Characteristics and Topography of Tribofilms from Anti-Wear Additives Applied to Metal V-Belt Type CVT Fluids

This study has investigated potential links between tribological performance and the morphology of tribofilms formed from anti-wear additives with application to metal V-belt pushing type continuously variable transmission fluids (B-CVTFs). The influence of metal–metal tribological properties of anti-wear additives was evaluated using a ball on plate tribometer, enabling friction and lubricant film formation to be monitored during reciprocating tests. Contact mode atomic force microscopy was utilised to investigate the nature of tribofilms at the nanometre scale. As a result, an additive formulation composed of hydrogen phosphite and over-based calcium sulphonate in a hydro-cracked mineral Group II base oil demonstrated a synergism with 8% higher friction coefficient and more stable film formation than the individual additive cases, providing a positive outcome for a B-CVTF. Tribofilm species produced by a chemical reaction between hydrogen phosphite and over-based calcium sulphonate were densely deposited on the wear scar to form a rougher surface, which may explain the higher friction observed.

Boundary lubrication film formation from phosphorus antiwear additives with application to metal V-belt type continuously variable transmission lubricants

This study has focused on the application of sulphur-free phosphorus antiwear additives in metal V-belt pushing type continuously variable transmission fluids to achieve higher friction coefficient plus excellent antiwear performance between the metal—metal contacting surfaces. The metal—metal tribological characteristics of phosphorus compounds were experimentally investigated using a reciprocating ball on plate tribometer, enabling film formation to be monitored during reciprocating sliding tests by an electric resistance method. As a result, sample with acid phosphate possessing C8 alkyl chain gave 20 per cent higher friction coefficient between metal contacting interfaces than C18 alkyl acid phosphate. Notably, an additive formulation composed of C8 acid phosphate with shorter alkyl chain, amine compound, and over-based calcium sulphonate demonstrated a synergism with 9 per cent higher friction and better antiwear performance than acid phosphate alone, which would give a positive outcome in the belt and pulley system of the continuously variable transmission. From surface analysis such as optical interferometry and X-ray photoelectron spectroscopy, it is hypothesized that the variation of tribofilm species produced by a chemical reaction between these additives plays a role in reducing corrosive wear and inhibiting the entrainment of lubricant into interfaces, resulting in higher friction. Moreover, the post-test rubbing tracks still possessed a longitudinally oriented surface pattern, which seemed to contribute to a reduced fluid film effect, giving a higher friction coefficient during rubbing tests.

Film Forming and Friction Properties of Overbased Calcium Sulphonate Detergents

The film-forming and friction properties of overbased calcium sulphonate (OBCaSu) detergents in rolling–sliding, thin film, lubricated contact have been investigated. All of the commercial detergents studied form thick, solid-like, calcium carbonate films on the rubbed surfaces, of thickness 100–150 nm. The films have a pad-like structure, interspersed by deep valleys in which practically no film is present. These films have the effect of increasing friction in intermediate speed conditions, an effect which is believed to occur because the pad structure of the film inhibits fluid entrainment and thus postpones the formation of an EHD film to higher entrainment speeds. Large differences were noted between the boundary friction coefficients of the various detergents tested. Two of them gave very low boundary friction coefficients, in the range 0.06–0.08, while the other two gave considerably higher friction. These differences are believed to originate from differences in the structures of the alkyl chains in the sulphonate detergent molecules. The films formed by OBCaSu detergents can be removed very effectively by treatment with EDTA solution and this shows that the films are effective in preventing wear.

Friction characteristics between metal contacting surfaces from antiwear additives with application to metal V-belt type continuously variable transmission lubricants

This study has focused on the application of lubricating oil additives in metal V-belt pushing type continuously variable transmission fluids (B-CVTFs) achieve higher friction coefficient and more stable lubricant film formation between the metal-metal contacting surfaces. The metal-metal tribological characteristics of various kinds of antiwear additives and a detergent were experimentally investigated using a ball on plate reciprocating tribometer (Plint TE77), which enables lubricant film formation to be monitored during a rubbing test. Zinc-dithio phosphates (ZnDTPs), a significant difference in instantaneous film formation was observed between primary and secondary type ZnDTP at the moment of increasing step load, due to the variation of the antiwear activity of different ZnDTPs. ZnDTPs in the presence of over-based calcium sulphonate detergent demonstrated slightly less tribofilm formationcompared with ZnDTP alone due to the competition for the rubbing surface. Very interestingly, in the case of phosphonic ester with calcium sulphonate, synergism was observed with more stable film formation and 8 per cent higher friction coefficient than without calcium sulphonate, a positive outcome for a B-CVTF. From surface analysis, it is hypothesized that the tribofilms species composed of iron phosphate, calcium phosphate, and calcium carbonate were generated by the reaction between phosphonic ester and calcium sulphonate, and that the resulting tribofilm plays a dual role in preventingwear and inhibiting the entrainment of lubricant into the interface, resulting in higher friction.

Lubricating properties of thixotropic systems based on overbased calcium sulphonate

AbstractThe lubricating properties of model systems based on overbased calcium sulphonate have been studied by simulating various kinematic, temperature, and load‐speed conditions of friction machines as well as by investigating the physical chemistry of friction surfaces. It is found that overbased sulphonate complex grease shows good antifriction, antiwear, and extreme‐pressure properties. A synergistic action of calcium tetraborate with overbased sulphonate has been shown. It is found that calcium 12‐hydroxystearate, however, has little effect on lubricating properties, but it improves the thixotropic characteristics of a system.

Study of deposit and friction films of overbased calcium sulphonate by PM‐IRRAS spectroscopy

AbstractThis paper deals with the study of deposit and friction films of overbased calcium sulphonate diluted in mineral oil, on metal surfaces.The technique used for this work is Infrared Reflection Absorption Spectroscopy by Fourier Transform and Polarisation Modulation (PM‐IRRAS or PM FTIR). The spectra obtained from this method contain only information on the absorption occurring in the immediate neighbourhood (⩽40 nm) of the metallic substrate and allow the average orientation for molecules adsorbed on metals to be deduced.This study shows that the adsorption of overbased calcium sulphonate on a steel surface leads to a preferential orientation of the sulphonate chains perpendicular to the surface and to a preferential orientation of the carbonate, the c axis being perpendicular to the surface. During friction, the sulphonate chains are ejected from the contact zone. We observed that the boundary film consists mainly of calcium carbonate, which crystallises into calcite.

Spectroscopic studies and electronic properties of heat treated calcium sulphonate

Overbased calcium sulphonate and its derivatives have been characterised by means of thermogravimetric analysis, X-ray and IR spectroscopy. The study was carried out after thermal treatment up to 900°C. Different phases appeared, showing a transition from an amorphous system to a crystallised medium. Electrical measurements showed electron behaviour for compounds obtained at low temperatures. ESR experiments produced classical results connected with the decomposition of organic chains.

Study of microstructural transformation of overbased calcium sulphonates during friction

AbstractColloidal dispersions of calcium carbonate stabilised by calcium alkylaryl sulphonates are detergent additives used in lubricant oils, and have particular effects on wear processes. In the present work, such additives were investigated using Small Angle X‐ray Scattering technique (SAXS). Different scattering intensity simulation and curve‐fitting programs were used to determine the size of the overbased calcium sulphonate particles and to characterise the interactions between them. In the additive oil (11 wt% CaCO3), the overbased calcium sulphonates appear as polydispersed micelles having an average calcium carbonate core radius of 2.0 nm. Moreover, an attractive potential between the micelles of less than kT has been observed. In order to investigate the effect of friction constraints on the additive, friction tests were performed on a rotative tribometer. Under specific conditions, there was a decrease in friction force arising from the formation of a viscous deposit. According to the differentanalyses, the viscous deposit contained more polydisperse particles, which did not have the same structure as those contained in the original additive. These particles consisted mainly of calcium carbonate. Some sulphonate chains were expelled from the friction zone. Moreover, the particles contained in the deposit interact with a potential on the order of 10 kT. Wide Angle X‐ray Scattering (WAXS) confirmed the presence of highly crystalline calcite. Moreover, the effects of pressure and the presence of water were studied. The pressure contributes neither to an increase in particle size nor to a crystallisation phenomenon. However, the presence of water in the additive oil alters the interactions between the micelles. The potential observed is 8.2 kT and suggests that the water is a responsible parameter for the agglomeration of micelles consisting of the viscous deposit.

The effects of engine oil additives on valve train wear

AbstractPreventing valve train wear in automotive engines is one of the most important properties of an engine oil. However, the influence of engine oil additives on valve train wear has not been sufficiently clarified.In this investigation, the antiwear performance of additives (such as ashless dispersants, metallic detergents and zinc dithiophosphate ‐ ZDTP) and the influence of the interaction of the additives were evaluated.Secondly, metallic detergents were considered. An overbased calcium sulphonate and an overbased phenate were found to have good anti‐scuffing performance when evaluated in engine tests and in Falex wear tests. However, from the results of four‐ball tests, these additives did not appear to have many extreme pressure properties. From surface analyses, it was determined that a calcium carbonate film was formed on the sliding surface of the Falex test piece, and this film provided good protection against wear.Finally, the interaction of ZDTP, succinimides and calcium detergents and their influence on valve train wear were studied. The decomosition temperature of ZDTP increased with certain additives. including the succinimide. As a result, scuffing was more prone, at temperatures below those increased temperatures. Also, changes in additive concentration on the sliding surface, due to competitive adsorption, altered the antiwear performance of the oil.

Infrared spectrophotometric determination of the alkalinity of overbased petroleum sulphonates

A simple, rapid and selective infrared spectrophotometric method was used to determine the alkalinity of the overbased calcium sulphonate additives. The intensities of the absorbance of the bands at 865 and 1180 cm–1, assigned to the δCO32– and νas SO vibrations, respectively, in the same spectrum of the overbased sulphonate sample were measured. The absorbance ratio method was applied as the path length was not known.