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http://www.machinerylubrication.com/Read/28966/oil-oxidation-stability
polyalphaolefins (PAO), have inherently better oxidation stability than do mineral oils. This improved oxidation stability accounts for the slightly higher operating temperatures that these synthetic oils can accommodate.
BUT
There is a little controversy concerning the oxidation stability of natural mineral base oils as determined by the refining method. There is one school of thought that suggests that hydrotreated base stocks have superior oxidation resistance and thermal stability than does solvent-refined base oil.
This is based on the misconception that since hydrotreating removes all of the potentially undesirable compounds, the base oil tends to automatically reduce deposit-forming tendencies and thereby will better resist oxidation. However, removing all of the compounds considered undesirable can in fact be detrimental.
Solvent refining results in the production of base oils, which retain some sulfur compounds that are natural antioxidants. These base oils retain a natural ability to prevent oxidation, while hydrotreated base oils must be further fortified with antioxidants in order to maintain thermal and oxidation stability. Once the antioxidants are weakened or depleted, oxidation of some hydrotreated oils can occur very rapidly.
Severely hydrotreated base oils also have poor solubility characteristics. Without proper formulation, additives may not remain suspended, and some additive drop out could occur.
polyalphaolefins (PAO), have inherently better oxidation stability than do mineral oils. This improved oxidation stability accounts for the slightly higher operating temperatures that these synthetic oils can accommodate.
BUT
There is a little controversy concerning the oxidation stability of natural mineral base oils as determined by the refining method. There is one school of thought that suggests that hydrotreated base stocks have superior oxidation resistance and thermal stability than does solvent-refined base oil.
This is based on the misconception that since hydrotreating removes all of the potentially undesirable compounds, the base oil tends to automatically reduce deposit-forming tendencies and thereby will better resist oxidation. However, removing all of the compounds considered undesirable can in fact be detrimental.
Solvent refining results in the production of base oils, which retain some sulfur compounds that are natural antioxidants. These base oils retain a natural ability to prevent oxidation, while hydrotreated base oils must be further fortified with antioxidants in order to maintain thermal and oxidation stability. Once the antioxidants are weakened or depleted, oxidation of some hydrotreated oils can occur very rapidly.
Severely hydrotreated base oils also have poor solubility characteristics. Without proper formulation, additives may not remain suspended, and some additive drop out could occur.
