Lubricant Additives

Sulfur Carriers 273

olefi ns in particular are known to reduce friction effi ciently in engines. They provide not only AW
and antifriction but also antioxidation properties. However, they cannot substitute the multifunc-
tional zincdialkyldithiophosphates in this application.
Besides crankcase applications, the use of sulfurized products in automotive gear lubricants
is far more important. Since the middle of the twentieth century, almost every gear lubricant for
automotive applications has been formulated with SIB.
The advantages of SIB are its high sulfur content, oxidation stability, and low corrosivity, but
the very distinct odor and the low lubricity are its disadvantages.
Sulfurized esters and triglycerides are used in special transmission fl uids to adjust the stick–slip
properties. These sulfur carriers are also used in other lubricants in the automotive area such as
wheel bearing or CVJ grease.

9.5.4 SYNERGIES/COMPATIBILITY WITH OTHER ADDITIVES

Sulfurized products are compatible with most of the additives used in lubricants. Only strong acids
and bases must be avoided in combination with sulfur carriers.

9.5.4.1 Zinc Dialkyldithiophosphates

ZnDTPs are used in combination with sulfurized products in various applications. Besides their
primary functions as AW and AOs, there is a well-known synergistic effect in regard to stabiliza-
tion and improvement of copper corrosion of sulfur carriers. This behavior is demonstrated in the
ASTM D-130 copper corrosion test (Table 9.5).
In addition, ZnDTP can have a very positive effect on the odor of sulfur carriers.

TABLE 9.4

Sulfur Carriers for Agricultural Applications

Sulfur Carrier Type Application

Ester, inactive Gear greases (NLGI class 000), cotton picker

spindle lubricants

Triglyceride, inactive Gear lubricants, hydraulic fl uids, greases for

bearing lubrication, chassis lubricants

Triglyceride, medium-active Gear lubricants, chain saw, and bar saw lubricants

Olefi n, inactive Gear greases (NLGI class 000), cotton picker

spindle lubricants

Triglyceride/olefi n, inactive Gear lubricants, hydraulic fl uids, greases for

bearing lubrication, chassis lubricants

TABLE 9.5

Synergistic Effect of ZnDTP on Copper Corrosion (ASTM DISO)

Type Total Sulfur Active Sulfur

Treatment

Level (%)

Cu Corrosion

3 h at 100°C

Cu Corrosion

(+1.5% ZnDTPa)

3 h at 100°C

Triglyceride 18 10.5 5 4c 3b

Ester 17 8.5 5 3b 1b

Triglyceride 15 5 5 3a 1b

a Thermally stabilized zinc dialkyldithiophosphate based on 2-ethylhexyl alcohol.