Lubricant Additives

Ashless Phosphorus-Containing Lubricating Oil Additives 97

the greater was the likelihood of desorption. Furthermore, good AW performance depended on high
phosphate and amine adsorption and retention of the phosphate moiety on the surface.
The conversion of a dialkyl acid phosphite to an amine phosphate and the use of the mixed
product as a multifunctional AW/EP additive, antioxidant, and corrosion inhibitor with improved
metal passivation properties were claimed in 1997 [118].
An amine salt and TCP were studied as AW agents for different synthetic esters by Weller and
Perez [119] and compared with a sulfurized hydrocarbon. The neutral ester (TCP) generally showed
an increasing amount of wear up to 1% addition before reducing at higher levels. The amine salt,
however, rapidly reduced wear to very low levels. Friction coeffi cients were also consistently lower
with the amine salt.
Kristen [120] reported the effect of additive interaction between amine phosphates and a phos-
phorothionate. The additives were evaluated under FZG gear test conditions (DIN 51354). The
results showed that the additives respond differently in nonpolar and polar base stocks, specifi cally
a polyalphaolefi n and a synthetic ester (Figures 3.16 and 3.17). In the synthetic hydrocarbon base, a
level of 0.75% amine phosphate and 0.25% phosphorothionate (or perhaps 0.5% of each) provided a
borderline FZG 12 load stage pass/fail. In comparison, 0.75% of amine phosphate ester and 1% of
phosphorothionate were required to achieve the same level of performance in the ester. Monitoring
the response of additive combinations reveals not only the most cost-effective mixtures but also any
antagonisms between additives, as were found here in the ester base at higher additive levels. Such
information is invaluable to formulators when trying to meet specifi cation requirements and ensur-
ing that the performance level is consistently above the minimum limit.
Amine salts, for example, triethanolamine salts of alkyl and arylpolyethyleneoxy acid phos-
phates, are widely used in metalworking applications. Some of these products are not only
commercially available but are also produced in situ when the pH of the product is adjusted by the
addition of base to ensure the product is alkaline in use. This is to avoid corrosion and minimize
skin irritation.

0 0.5 1.0 1.5 2.0

0 0.5 1.0 1.5

Additive concentration (%)

TPPT (%)

12

10

8

6

4

>12

Amine phosphate

TPPT

FZG load stage failure

Amine phosphate (%)

1.0

0.5

0

1.5

11

12 load stage

>12

FIGURE 3.16 FZG performance of an amine phosphate and TPPT separately and in mixtures in an ISO VG
32 polyalphaolefi n. (From Kristen, U., Additive für Schmierstoffe, Expert Verlag, Renningen-Malmshaim,
German, 1994. With permission.)