Hard-core RMs

The use of carbonate-benzenesulfonate hard-core RM additive drastically changes the build-up mechanisms and the resulting structure of the antiwear surface film. Considering these results, the main difference between the antiwear action of the ZDDP molecules and the hard-core RMs is clear. In the case of... 

ZDDP, the antiwear film formation requires that a chemical reaction occurs between the additive and the metallic surface. In the case of hard-core RMs, the mineral material CaC03 is directly introduced in the sliding contact and undergoes small physicochemical changes during the film build-up. Consequently no chemical reaction with the substrate surfaces is required. 

A multifunctional additive of carbonate-detergents RMs retarded the decomposition of ZDDP in the ISOT test (Yamada et al., 1992). Mixtures of ZDDP plus carbonate-detergents RMs additive have been reported to have synergistic effects on detergency, see Chapter 3.3 on tribochemical interactions of hard-core RMs and ZDDP (Inoue, 1993 Ramakumar et al., 1994 Willermet, 1995a and 1995b Yin et al., 1997)... 

The acid deactivation mechanism in hydrocarbon media is supplementary to the neutralizing action of carbonate-surfactant hard-core RMs. Traces of strong sulfur, nitrogen or halogen acids are scavenged by neutral detergents, with the... 

The oil analyses have shown that the TBN values of lubricating oils deplete completely while at the same time, the corrosion rate can be considerably reduced. The relationship between the solubilization of large quantities of acid, total base number (TBN), and total acid number (TAN) values with the rate of corrosion is still unresolved. TAN values are not a good prediction of corrosion, and the source of extra TBN is much more important in the neutralization of corrosive acids than the simple numerical value of TBN. The effect of hard-core RMs shows poor correlation between used oil sample TAN values and the potential for bearing corrosion (Denison, 1944 Kreuz, 1970). Where corrosion rates are reduced by treatment with hard-core reverse micelle detergent, and no significant reduction in TAN has occurred, corrosion protection must have occurred by a... 

Corrosivity of used oils. The classical determination of TBN and TAN involves a titrimetric procedure, whereby the oil sample is dissolved in a particular solvent system and neutralized by strong acid or strong base (ASTM D664 or 2896), equivalent to (IP 171 or 276). TBN and TAN values do not correlate with corrosivity and the titrimetric analysis has a very limited ability to differentiate between acids of varying strengths. A quantitative differential infrared spectroscopy technique used to monitor the neutralization reaction is more meaningful, since the technique applies to reactions in hydrocarbon solvents. The classical reaction between corrosive acids and hard-core RMs results in formation of the metal salt of the acid and carbonic acid ... 

The corrosive activity on copper/lead bearings for typical carboxylic acids, such as decanoic, lauric, palmitic, stearic, and oleic acids, as 1 % w/w solutions in a lubricating oil base stock with excess of hard-core RMs, measured by infrared spectroscopy, supports the observation for the corrosive activity of used lubricating oils. An increase in total acidic number (TAN) is generally either an indication of contamination with acidic combustion products or the result of oil oxidation. Corrosion of bearing metals by used lubricating oils requires the presence of both acids and peroxides and probably takes place by a two-step mechanism. In the first step, the peroxide reacts with the metal to form a metal... 

The shape and size of micellar particles can be determined using transmission electron microscopy (TEM) and photo-correlation spectroscopy (PCS). The size distribution of the hard-core RMs measured by PCS was confirmed by TEM technique the hard-core RMs micelles of carbonate-sulfonate had mean particle sizes between 10 and 20 nm while the neutral sulfonate formed micelles with a diameter of 2 nm (Chinas-Castilio and Spikes, 2000). 

Table 3.6. Typical hard-core RMs of sulfonate and phenate, sizes and variation in detergent content (Marsh, 1987)...

The term hard-core RMs is used to describe dispersions containing an excess of colloidal carbonate over that required to neutralize the sulfonic acid. The excess is found in calcium carbonate trapped in a micellar structure. The total base number (TBN) of the additive so obtained is 368 mg KOH/g of oil. The crude additive consisted of 33 wt% CaC03 (Delfort et al., 1995 Giasson et al., 1992). Some typical results of the core particle with the overall diameter and the detergent layer thickness are shown in Table 3.6 (Marsh, 1987). 

Hard-core RMs of carbonate-alkylaryl sulfonates (OCABS) are prepared by reaction of carbon dioxide with calcium or magnesium oxide (or hydroxide) in the presence of a surfactant (Delfort et al., 1995 Mansot et al., 1993a). Because of their alkaline reservoir they are able to neutralize the acidic by-products resulting from oxidation of oil and from fuel combustion products (blow-by). 

With the selection of proper water content and reaction temperature, a new type of hard-core RMs sulfonates which contained an ultrafine calcium borate as an alkaline component was prepared. Since both reactants, calcium hydroxide and boric acid, are oil insoluble, water is necessary as a reaction medium in the presence of neutral calcium sulfonates. When water content was less than 5% of the sulfonates used, the rate of the reaction was too low and unreacted materials were present in significant quantity as coarse particles. With the water content... 

From this test, antiwear and extreme-pressure data were determined, such as welding load, load wear index and wear scar diameter under a load of 40 decanewtons (daN), 60 daN and 80 daN, respectively. First, evaluations were performed on the three original nonmodified hard-core RMs, then evaluations were performed on the sulfur-functionalized ones. Four-ball test data (results only for one concentration 10 wt% additive) are summarized in Table 3.9 (Delfort et al., 1995 and 1999) for ... 

Modified hard-core RMs by phosphosulfurized compound. Improved extreme-pressure and antiwear properties have also been obtained with the introduction of some chemical species, such as sulfur, phosphorus or boron derivatives, into the colloidal core (Delfort et al., 1998 Inoue, 1993 Inoue and Nose, 1987). Welding loads, load wear index and wear scar diameter at 5 wt% of a CaC03 core surrounded by a calcium alkylaryl-sulfonate surfactant shell, and modified by phosphosulfurized calcium carbonate core were evaluated for calcium dialkyl dithiophosphate (CaDTP) and calcium trithiophosphate (CaTTP) with the four-ball extreme-pressure test (ASTM D2783 standard method). Both modified products exhibit improved extreme-pressure performances (welding load and load wear index), while their antiwear properties (wear scar diameter) compared to those of the original micellar substrate remain at least at the same level. 

The retardation of the decomposition of ZDDP by hard-core RMs can be properly explained in terms of neutralization of the sulfur acids into inactive species. Micellar sulfonate and salicylate, having borate as the alkaline micellar hard-core, shows better retardation effect on the decomposition of ZDDP than carbonate-sulfonate (salicylate) hard-core RMs. The neutral (normal) phenates, but not sulfonates and salicylates, also retards the decomposition of ZDDP, as does the hard-core micellar phenate. Phenates are much stronger bases than salicylates and sulfonates ... 

A combination of ZDDP and hard-core RMs leads to a synergistic effect of metallic detergents on the degradation of ZDDP. These phenomena are observed in many tests and can be explained in terms of (a) the acid neutralization property of hard-core RMs that leads to the prevention of decomposition of ZDDP (in the valve train wear test and the thin film oxygen uptake test), (b) the competitive adsorption of detergents that reduce the effective concentration of ZDDP on the metal surface (in the four-ball test), (c) the formation of mixed films on the metal surface, formed through the decomposition of ZDDP in the presence of hard-core RM s (the coefficient of friction in the Falex wear test). 

Surface processes under rubbing conditions Soft-core RMs Hard-core RMs... 

It was proven that the carbonate-sulfonate hard-core RMs, but not the calcium carbonate powder, has an effect on acid neutralization and performance. The effective diameter of the micelles is 5 to 10 nm, and it is known that the smaller the size of the micelle, the greater its ability to neutralize acids. In order to develop high performance calcium carbonate in RMs, it is important to understand... 

Comparative friction tests under boundary conditions suggest three types of interactions between ZDDP and carbonate-sulfonate RMs in the oil phase (Kapsa et al., 1981) (a) chemical interactions between ZDDP and hard-core RMs of carbonate-sulfonate lead to an effective ZDDP concentration decrease (b) the detergent effect due to the presence of calcium sulfonate molecules prevents materials from agglomeration during running (c) the specific role of the hard-core reverse micelles. 

Table 3.13. The effect of ZDDP, dispersant and carbonate-phenate hard-core RMs on the tribofilm formation in paraffinic oil (Willermet et al., 1995a)...

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