Lubricant Additives

266 Lubricant Additives: Chemistry and Applications

organosulfur compounds on the load-carrying properties of lubricating oils indicates that this is due
to their ability to form sulfi de fi lms that are more easily sheared than the metallic junctions under
EP conditions [36].
Therefore, active sulfur has a signifi cant infl uence on the AW performance. Higher sulfur activ-
ity results in faster formation of the metal sulfi de and higher wear. This performance is visualized
in Chart 9.3. The chart shows the four-ball wear scar (DIN 51350 Part 3) of sulfurized products with
various activities.

9.4.1.1.4 Copper Corrosion
ASTM D-130 [37] is a common method to determine the copper corrosion of additives. This copper
corrosion does not necessarily refl ect the activity of a sulfurized product, because very often yellow
metal deactivators are used to mask the active sulfur.
The degree of copper corrosion depends on the amount of active sulfur and the presence of yel-
low metal deactivators. Inactive sulfurized products will show a long-term inactivity toward yellow
metals, whereas active sulfur, masked with yellow metal deactivators, will react with the yellow
metal as soon as the deactivator is consumed/reacted.
Therefore, the only statement that can be made is that a product will not stain copper under the
given test parameters. This method is not suitable to determine the activity that is of major relevance
for the performance of a sulfurized product (see Section 9.4.1.1.3).

0

10

20

30

40

50

60

70

80

90

50 70 90 110 130 150

Temperature (°C)

Active sulfur (% of total sulfur).

A

B

C

D

E

Type Total Sulfur Active Sulfur at 149°C

A Olefin 40 36

B Olefin 20 5

C Triglyceride 10 0.5

D Triglyceride 18 10.5

E Olefin/ Triglyceride 15 4.5

CHART 9.2 Active sulfur of various sulfurized products.