Dispersant + ZDDP

A) Strong intermolecular interactions dispersant-ZDDP. In hydrocarbon formulations, polyisobutyleneamine succinimide (PIBS) as a class has been found to form complexes with ZDDP (Ganc and Nigarajan, 1991 Harrison et al., 1992 Inoue and H. Watanabe, 1981 and 1983 Kulp et al., 1992 Ramakumar et al.,... 

Dispersant-ZDDP interactions at surfaces. The dispersant reduces the amount of ZDDP available for tribofilm formation by forming complexes to increase wear in 4-ball and valve train tests. The borated PIBS dispersants may participate in the formation of a borate component in the antiwear film. PIBS dispersants adversely affect the antiwear activity of ZDDP. The stronger the complexation, the greater the adverse effect on wear. It may well be that this effect is due largely to keeping ZDDP in suspension and away from the surface (Rounds, 1978 Shiomi et al., 1992 Shirahama and Hirata, 1989 Willermet, 1998). 

Mixtures of metallic detergents, such as phenates, sulfonates, phosphonates, and salicylates with ashless dispersants such as succinimides and benzylamine, together with zinc dialkyldithiophosphate (ZDDP), can lead to new effects. The possible interactions between these main additives used in lubricating formulations when dissolved/dispersed in hydrocarbon media are shown in Fig. 2.8 together with an indication of the intensity of those respective interactions. 

Fig. 2.9. Intermolecular interaction between dispersants (succinimides) and zinc dialkyldithiophosphates (ZDDPs)...

In XANES spectra of tribofilms, both the phosphorus and sulfur signals are very weak compared to ZDDP used alone. For all the concentrations (1%, 2%, 5%) of dispersant PIBS used, antiwear polyphosphate films were formed and unreacted ZDDP was not present in the film. These results imply that antiwear films are much thinner than either tribofilm generated by ZDDP alone or ZDDP with the detergent. This confirms that the PIBS dispersants compete for ZDDP adsorption on the surface (Yin, 1997b). 

Detergent-dispersant interactions at surfaces. In 4-ball wear tests, an ashless dispersant was found to have an adverse effect on ZDDP-sulfonate-carbonate hardcore RM additives. A high molecular weight Schiff base had the worst effect, followed by a bis-PIBS m-PIBS had the least adverse effect. Interactions among additives affects valve train wear. One of the effects is that a succinimide together with other additives increases the decomposition temperature of ZDDP (Ramakamur, 1994 Shirahama and Hirata, 1989). 

Acidic conditions accelerate ZDDP decomposition and basic barium sulfonate detergents increase the rate of the ZDDP thermal decomposition reaction pathway. ZDDPs have been reported to form complexes with amines and succinimide dispersants (Gallopoulos, 1964 Heilweil, 1969 Rounds, 1976). 

Case (B) was ZDDP + polyisobutylene succinimide dispersant, and a hard-core micellar carbonate-phenate RMs, [Ca] = 890 ppm. 

The effect of ZDDP, dispersant and carbonate-phenate RMs on the tribofilm composition is given in Table 3.13. 

B ZDDP + polyisobutylene succinimide dispersant + calcium carbonate-phenate [Ca] = 890 ppm Composed of inorganic, low molecular weight amorphous short chain ortho-(P043 ) and pyro- (P2074 ) phosphates ( 20% of zinc was replaced by calcium in phosphate tribofilm)... 

The tribofilms formed from a ZDDP were composed of long chain phosphates with zinc as a cation but with a mixture of a ZDDP + detergent and ZDDP + dispersant, only short-chain phosphates with zinc and calcium as cations are formed in the presence of a sulfide (Barcroft and Park, 1986 Willermet et al., 1995a). 

The engine oil containing ZDDP and carbonate-detergents RMs formed orthophosphate and pyrophosphate tribofilms. In the presence of detergent and dispersant only short-chain phosphates were observed (Willermet et al., 1991, 1992 and 1997 Yin et al., 1997b). 

The ZDDP additive is used rarely as the sole additive in oil formulations. The finished engine oil contains other additives to improve dispersancy, detergency... 

The antiwear mechanism of ZDDP in the presence of dispersants has been studied and it has been concluded that ZDDP forms an association complex with an amino group of a succinic type dispersant, and this complexation has been proved to be antagonistic to antiwear action (Gallopolous and Murphy, 1991 Rounds, 1986 Shiomi et al., 1986 Willermet et al. 1995b). The solubilization of ZDDP helps the adsorption of ZDDP on the surface, thus improving the antiwear performance of the additives (Forbes et al., 1970b). RMs would decrease the... 

Table 4. 5. The chemical nature of the tribofilm generated on steel surfaces using ZDDPs in the presence of detergents and dispersants (30 min wear machine). Results based on interpretation of phosphorus and sulfur L-edge tribofilm XANES spectra (Yin et al., 1997b)...

Chemical parameters What is meant by chemical parameters in oil formulation Which of the following is a chemical parameter adsorption, detergent, dispersant, concentration, ZDDP, or surface roughness ... 

X-ray spectroscopy On the basis of interpretation of phosphorus and sulfur L-edge tribofilm XANES spectra in Table 4.4 and 4.5, what is the chemical nature of antiwear tribofilm and composition of the following pairs (a) ZDDP + detergent, (b) ZDDP + dispersant ... 

Polar additives in oil formulation What type of interactions can you predict in the engine oil two-component system ZDDP + dispersant (a) in the hydrocarbon formulation, and (b) on the surface Consider the stronger the complexation, the greater adverse effect on wear. 

The ZDDP deterioration By reference to Table 6.10 and the case study 2 Evaluation of ZDDPs , in field tests of 56 passenger car vehicles (taxi cabs) and laboratory analysis of lubricating data were included viscosity, TBN, TAN, ZDDP (active), dispersants, oil consumption rate, engine deposits, camshaft and valve lifter wear. Which of the major ZDDPs and ZDDPs mixtures provide the best antiwear and antioxidant performance ... 

Exhaust gas recirculation will be deployed increasingly to reduce emissions of nitrous oxides. The consequence for the lubricant is that the higher soot loadings, which result, cause unacceptable increases in viscosity and increased wear (Bovington and Castle, 2001). The viscosity increase results from the agglomeration of soot particles in the lubricant and can be minimized by the use of dispersants. If increased levels of dispersant are deployed this can pose problems with wear since solubilization of ZDDP by dispersants (Korcek et al., 2000) influences adversely the formation of protective films. Inadequately solubilized soot will cause serious erosion of tribofilm and cause enhanced wear. 

Four-Ball Machine later to study the interaction between molybdenum disulphide and several anti-wear and extreme-pressure additives and detergent/dispersant additives in a mineral oil. Unfortunately these results are difficult to compare directly with those of Thorp because he only reported wear scar diameters at two load levels. He found that at high load (lOOON) with 1 % of molybdenum disulphide, the combination with a ZDDP gave a wear scar diameter higher than either additive separately, and comparable to that of the base oil, and he described this as an antagonistic effect between the two additives. 

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