Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/520842
42 | May- June 2015 | www.machinerylubrication.com Polycondensation and Polymerization Leading to… Formation of Organic Acids and High Molecular Weight Polymeric Products Inert Byproducts Termination Stage of Oxidation (Further Undesirable Reactions) Termination Stage of Oxidation (Desirable Stabilization of Free Radicals) Wear Metals Nitro-oxides UV Light High Temperatures Oxygen Lubricant High Temperatures Oxygen Lubricant (Hydrocarbon Base Oil + Additives) Oxygenated Compounds (Aldehydes, Ketones, Alcohols, Water) Reactions with Antioxidants (Phenolic/Aromatic Amines, Phosphates, etc.) Initiation Stage of Oxidation Propagation Stage of Oxidation Free Radicals (Alkyl Radicals, Hydroperoxide Radicals, etc.) Lubricant High Temperatures Oxygen Sludge Corrosion by Acids and Water Increased Oil Viscosity Varnish Deposits (Hydrocarbon B (a) (b) (h) (i) (j) (l) (n) (o) (p) (k) (m) (c) (d) (e) (f) (g) the base oil and additives fi ght against the oxidation process and are eventually subjected to degradation. During the initiation stage (b), the hydrocarbon molecules react with various catalysts, leading to the formation of free radicals. Once this has occurred, further initiations of the oxidation sequence may continue as the existing free radicals progress to the propagation stage. Wear metals (c) have the potential to cause or accelerate oxidation reactions by means of metal ions in copper, cobalt, chromium, iron and other transition metals. Thus, not only does oxidation have the ability to create wear debris, but wear debris can cycle back to promote further oxidation. Nitro-oxides (d) such as nitrogen dioxide, nitric oxide and nitrous oxide are another form of pro-oxidants that catalyze the oxidation reaction. Ultraviolet radiation (e) in the form of sunlight can also initiate oxidation reactions. This is frequently observed and can often explain the discoloration of unused oil. Elevated temperatures (f ) promote and sometimes are required for certain stages of oxidation to occur. When in combination with wear metals or oxygen, the effects may be multiplied. If temperatures are Oil Oxidation Stages