Lubricant Additives

90 Lubricant Additives: Chemistry and Applications

An additional application where interest has been expressed in alkyl phosphates is metalworking.
Owing to a desire on environmental grounds to move away from chlorine, mixtures of neutral phos-
phates and sulfur-containing additives have been promoted as alternatives [103–106]. As concerns
exist about the possible release of phenolic materials into the environment, the alkyl phosphates
are, perhaps, best suited for this application and are able to provide similar or better performance to
the chlorparaffi ns when used together with sulfur carriers. Table 3.10 summarizes the drill life and
other AW/EP performance in a neat oil for both neutral isopropylphenyl phosphate and neutral alkyl
phosphate in combination with a sulfurized olefi n when compared with a chlorparaffi n.
In an extension to this work, drill life test data were obtained on tri-isobutyl and tributoxy-
ethyl phosphate in comparison with a commercially available acid phosphate (oleyl acid phos-
phate). Each phosphate was evaluated at the same phosphorus level in the presence of a sulfur
carrier (a 4:1 mixture of a sulfurized fatty acid ester with 26% total sulfur and a dialkyl polysulfi de
with 40% total sulfur content), and all additives were dissolved in a neat paraffi nic mineral oil of

P OO

O

P

O

O

O

O

O

P OO

O

P

O

O

O

O

O

Resorcinol tetraphenyl bisphosphate

Isopropylidene di-p-phenylene tetraphenyl bisphosphate

FIGURE 3.12 Structures of high-molecular-weight phosphate esters.

TABLE 3.9

The Effect of High-Molecular-Weight AW Additives on the Coking, Wear and

Magnesium Corrosivity of Ester-Based Gas Turbine Oil Formulations

AW Additive

Deposit Formationa

(mg) Wearb (mm)

Magnesium

Corrosivityc

Blank—no additive 89 0.655 High

TCP 98 0.40 High

Tris-C 9 –C 10 alkylphenyl

phosphorodithioate

103 0.505 Pass

TBPP 94 0.54 Pass

Resorcinol tetraphenyl phosphate Not determined 0.425 Fail

Note: Additives used at 1% addition in the ester base.

a Fluid held at 300°C for 3 h: method described in paper by Gschwender et al., Lubrication Engineering,

pp. 20–25, May 2000.

b ASTM D 4172-88. Four-ball wear test for 1 h at 40 kg, 600 rpm, and 75°C.

c 20 mL sample held for 48 h at 232°C with 1 1/h, air fl ow.

Source: Gschwender, L., Private Communication, August 2001. With permission.