Antioxidants ashless

Indeed, in the work of Fitzgerald and Wilson (55), the introduction of tributyl phosphate into the oil gave a rather steep deterioration of hydrocarbon activity. A similar sharp deterioration was also noted when an unidentified ashless antioxidant additive by itself was employed. The conclusion reached by the authors is that the presence of phosphatebinding metals, mainly Zn and Ca, is responsible for the inhibition of the poisoning influence of phosphorus from engine oils. 

Antioxidant technology To indicate the oxidation and thermal stability of a variety of ZnDTP-containing and ashless anti-wear hydraulic fluids, TOST and Cincinnati Milacron data - both relevant tests for this type of fluid - have been compiled and summarised. Table 4.9, from both published [80, 81] and in-house results. The data show that oxidation resistance and thermal stability of the premium fluids, both ashless and stabilised ZnDTP, are comparable and clearly outperform the normal-grade fluids. The normal ashless grade at 0.4-0.5% additives is superior to the normal ZnDTP-based grade, especially for thermal stability, which may be due to the use of thermally unstable secondary ZnDTPs. 

To boost the oxidation stability of fluids formulated with stabilised ZnDTPs, in most cases, zinc di-2-ethylhexyldithiophosphate, phenolic or aminic antioxidants are often added in combination. In a similar manner to the ashless antioxidants, the response pattern of the ZnDTPs used in these fluids is strongly influenced by the degree of raffination of the base stock [82]. 

Ashless antioxidants Lack of quality reliability claimed for passenger car engine oils in the United States led to the introduction of ILSAC GF-1 (API SH) for 1994 model year vehicles and the adoption of the American Chemistry Council Product Approval Code of Practice which addresses quality assurance issues. A similar system was adopted later in Europe. With the application of the ACC Code of Practice, the commonly used concentration of alkylated diphenylamine antioxidants in the oil was increased in order to pass Sequence HIE viscosity control requirements [106]. When the Sequence HIE, of 64 h test duration, was replaced by the Sequence IIIF, of 80 h duration, with ILSAC GF-3 (API SL) for 2001 model year vehicles, the trend to use higher concentrations of ashless antioxidants continued. 

In Europe, the decrease in engine oil phosphorus, sulphur and ash levels (SAPS) with the introduction of ACEA Cl, C2, C3 and E6 specifications in 2004, driven by emissions system compatibility, is also responsible for significant increases in the level of ashless antioxidants at the expense of ZDDP, which generally contributes all of the phosphorus, most of the sulphur and some of the ash to most engine oil formulations. Table 4.13 describes the current specified levels of SAPS by ACEA, with ILSAC GF-4 limits added for reference. 

Presently, there is a strong demand for environmentally acceptable fluids. As biolubes , they need to satisfy biodegradation and bioaccumulation standards, which mineral oil-based fluids cannot achieve. Therefore, the use of synthetic and natural esters for many industrial applications will develop [119]. Not only the base fluids but also the antioxidants used in them will have to fulfil certain specifications for aquatic toxicity, biodegradation and bioaccumulation. Because the antioxidant response of these new fluids is different from mineral oil-based lubricants, new classes of ashless bio-antioxidants may need to be developed. 

Roby, S.H., Supp, J.A., Bamer, D.E. and Hoyne, C.H.(1989) SAlE Paper 892108. Mazzamaro, G. (July/August 2001) Fubricants World, Ashless Antioxidants Enhance Tomorrow s Engine Oils . 

ZDDP functioning as an antioxidant can be replaced by ashless antioxidant components, such as hindered phenols and amines. Whilst effective, they are more expensive than ZDDP and can also compromise elastomer compatibility. Additionally, depending on the level of ashless antioxidant in the formulation, then-use may mean that product material safety labelling is more alarming to the end consumer. 

The studies carried out showed (Fig.l) that the presence of the additive P-1 did not have significant effect on the duration of the induction period of oxidation of the experimental samples. The positive effect observed after the fourth hour of operation was that the intensity of the oxidation processes decreased and the accumulation of acidic products in the exhausted lubricants was almost constant. This resulted from the exhaustion of the easily oxidizable hydrocarbons and, probably, the antioxidative effect of some of the products obtained. Positive effect on the antioxidative protection of the hydrocarbons in the lubricants studied had also the chemiadsorption properties of the ashless PSA participating in the composition of P-1 towards the metal surfaces. When adsorbed on the metal surface, they could impede the catalytic effect they have on the oxidation of the petroleum products. 

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