Cj. Lee et Ee. Klaus, EVALUATION OF DEPOSIT FORMING TENDENCY OF MINERAL AND SYNTHETIC BASE OILS USING THE PENN STATE MICROOXIDATION TEST, Lubrication engineering, 49(6), 1993, pp. 441-445
Deposit formation in the Penn State microoxidation test is the combine
d result of the lubricant oxidation and the secondary oxidation-conden
sation polymerization reactions to form high molecular weight products
. Results of this test have been previously shown to give excellent co
rrelation with the results from Sequence IIID engine tests and heavy-d
uty diesel engine tests. In the current study, the Penn State test was
used to evaluate a series of mineral and synthetic base oils with and
without oxidation inhibitors. The oils selected for this study cover
the range of viscosity and volatility typically used in formulating SA
E 5W-30 to 15W-40 crankcase lubricants. The experiments were designed
to show the relative contributions of volatility, thermal stability, o
xidative stability, type of refining, and type of oxidation inhibitor
on the process of deposit formation in a thin lubricating film on a ho
t ferrous surface. This study shows that the influence of volatility,
base stock refining, and inhibitor effectiveness on deposit formation
of mineral oil and synthetic base oils can be determined by using the
Penn State microoxidation test. Generally, data show that for the same
oxidation stability, volatility of the base stock plays an important
role in controlling deposit formation. The evaluation of two oxidation
inhibitors with different inhibiting mechanisms shows that the additi
ve response as a function of base oil refining may be significantly di
fferent. It is concluded that the addition of relatively high concentr
ations of copper as an additive, 2000 ppm Cu, can significantly reduce
the deposit formation tendencies of all the base oils considered in t
his study.