This paper reviews the use of copper deactivators and iron corrosion inhibitors in lubricating oils. The auto‐oxidation process is described in terms of initiation and chain propagation, branching and termination, and the primary and secondary oxidation inhibitors are described. Copper deactivators and corrosion inhibitors nature and action are discussed, and the paper also examines the applications for these additives.
The use of ashless antioxidants to increase the useful working life of synthetic fluids, such as polyalphaolefins, polyalkylene glycols and carboxylic acids, is discussed, and some general guidelines are proposed. The application of ashless antioxidants in controlling the oxidative degradation of several dtfferent types of biodegradable vegetable oil is illustrated. The action of the naturally occurring antioxidant, vitamin E, in some of these fluids has been examined and some preliminary results are reported.
Engines can be damaged in many ways: the principal oil‐related problems are due to deposit formation and viscosity increase. A first step in minimising the consequences of oil degradation is to reduce the formation of sludge and deposits. This can be accomplished by the judicious use of metal‐free (ashless) anti‐oxidants. Detergent/dispersant additives play a critical role in extending lubricant life by cleaning up deposits and keeping them in solution, and by neutralising acids formed during the combustion process. Several different types of antioxidants that can successfully eliminate precursors that lead to deposit formation and viscosity increase in oils in both gasoline and diesel engines have been identified. A novel, ashless, multifunctional additive that confers thermo‐oxidative stability and friction modification to engine lubricants is described here.
The long-term thermo-oxidative stability of lubricants and greases is a prerequisite to meet today's 'stay in grade' and extended drain interval requirements. To achiezie this goal, there is a need for a better understanding of thermo-oxidative lubricant degradation and of how antioxidants can affect this process. In this paper a tuio-stage degradation model is discussed. Primary degradation leads to the formation of very reactive species such as radicals and peroxides. These are the precursors for generating secondary degradation products, such as oligomers, sludge, or deposits. By applying the theory of reaction kinetics and the Arrhenius law, quantitative correlations may be derived between oxidation induction time (OIT) and temperature, and between OIT and antioxidant treat level. Pressurised differential scanning calorimetry (PDSC) data confirm these theoreticalfindings and demonstrate the benefit of the addition of aininic antioxidants i n comparison with high-molecular-weight hindered phenolic antioxidants.
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