ZDDPs active

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 ... 

The antioxidant nature of ZDDP has often been considered to be antagonistic to its antiwear performance. The most probable reason that can be given for this is the depletion of active ZDDP in the antioxidant action. In the case of diesel engines, special types of interaction are reported. Incomplete combustion of diesel fuel coupled with oil particulates in diesel engines lead to the formation of thick... 

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). 

An active intermediate, MoDDP, provides more efficient radical trapping (antioxidant activity) than either ZDDP or MoDTC (Johnson et al., 1997b). 

Active" ZDDP. Differential Infrared Spectroscopy (DIR) was used to determine the concentration of ZDDP in the used oil samples by measuring the absorbance of the P-O-C band at 1,000 cm 1. The ZDDP concentrations of the used oil samples were generally less than 0.05 mass percent (as zinc), which is substantially less than the nominal 0.12 mass percent in the fresh oils. There was no correlation between camshaft and lifter valve wear and amount of ZDDP remaining in the used oil. This result supports other observations that the decomposition of ZDDP results in other compounds which may also exhibit some antiwear properties. 

Lubricating-oil consumption in modem engines is generally very low (0.1 liters per 1,(XX) km), and their contribution to catalyst deactivation is small. However, with the requirement for extended catalyst durability and extended drain periods for oils, there is considerable interest about the effect of the oil additives on catalyst life. The chief component of the oil that affects catalyst durability is phosphorus, which is usually present in the form of zinc dialkyl-dithiophosphate (ZDDP). Both combusted and uncombusted forms of ZDDP can reach the catalyst, resulting in different effects on activity depending on the temperature of operation. The level of phosphorus in the oil and the amount of alkaline earth metals present (such as calcium) can dictate the extent to which phosphorus can be deposited on the catalyst. However, studies have shown quite clearly that well-formulated lubricants and well-designed catalysts ensure that the antiwear properties of the oils are maintained and that catalyst-equipped vehicles meet the emission standards required [15,16]. 

The model for film formation described above suggests that interactions between basestock and film-forming additives, which retard their adsorption, will have a detrimental influence on wear and friction. For instance, highly napthenic basestocks are good solvents for polar species whilst paraffinic basestocks are relatively poor solvents for polar species and will therefore enhance film-forming activity. Clear evidence of this effect has been shown for molybdenum chemistries [7] and for ZDDPs [8, 9]. 

It was also shown that PIBSA/PAM-type dispersants were able to convert basic (more thermally stable) ZDDP to normal (more active) forms [52]. Thus dispersants in general are expected to be beneficial for wear protection and it has been demonstrated that succinimide dispersants can partially remove films formed by ZDDP under rubbing conditions [53]. It is not known whether or not the dispersant used was borated, which may influence this phenomenon significantly. 

The principal problem, which is compounded by the above, is that the most cost-effective source of anti-wear film formation and the most effective peroxide decomposing agent has, since the 1940s, been ZDDPs which contain both sulphur and phosphorus as the active elements. 

Fully developed films in ZDDP containing oil have a layered structure and contain much less C at the outer edge than equivalent film formed in lubricants containing no ZDDP where detergent films are activated. 

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