is the chemical combination of a substance with oxygen. All petroleum products are subject to oxidation, with resultant degradation of their composition and performance. The process is accelerated by heat, light, metal catalysts (e.g., copper), and the presence of water, acids, or solid contaminants. The first reaction products of oxidation are organic peroxides. Continued oxidation catalyzed by peroxides, forms alcohols, aldehydes, ketones, and organic acids, which can be further oxidized to form high-molecular-weight, oil-insoluble polymers; these settle out as sludges, varnishes, and gums that can impair equipment operation. The organic acids formed from oxidation are corrosive to metals. Oxidation resistance of a product can be improved by careful selection of basestocks (paraffins have greater oxidation resistance than naphthenes), special refining methods, and addition of oxidation inhibitors. Also, oxidation can be minimized by good maintenance of oil and equipment to prevent contamination and excessive heat.

Lubricating oil in engines and other components will combine with available oxygen under certain conditions to form a wide variety of harmful by-products.  Heat, pressure, and catalyst materials accelerate the oxidation process.  By-products of oxidation form lacquer deposits, corrode metal parts and thicken oil beyond its ability to lubricate.  Most lubricants contain additives which inhibit or retard the oxidation process.

Differential infrared analysis offers the only direct means of measuring the level of oxidation in used oil.  Note: A new oil reference is required for accurate measurement of oxidation.  Results are reported on an absorbance scale.

Oxidation CAUSE

• Overheating
• Extended oil drain
• Improper oil type/inhibitor additives
•  Combustion by-products/blow-by

Oxidation EFFECT

• Shortened equipment life
• Lacquer deposits
• Oil filter plugging
• Increased oil viscosity
• Corrosion of metal parts
• Increased operating expense
• Increased overall wear
• Decreased engine performance

Oxidation SOLUTION

• Use oil with oxidation inhibitor additives
• Shorten oil drain intervals
• Check operating temperatures
• Check fuel quality
• Evaluate equipment use vs. design
• Evaluate operating conditions

 

Also see engine deposits, gum in gasoline, oxidation stability.