Lubricant Additives

Ashless Phosphorus-Containing Lubricating Oil Additives 101

of the phosphites against the corresponding acid phosphate revealed that the phosphites had better
load-carrying but inferior AW behavior (see Table 3.15). The authors suggest that the activity of the
phosphites is due to an initial hydrolysis to produce the following intermediate either in solution or
on the metal surface:

HO O

P

RO H

This reacts with the iron surface to give an iron salt that was thought to be responsible for the
AW properties of the product. Under much more extreme conditions as are found with scuffi ng,

TABLE 3.14

Antioxidant Synergism between Hindered Aryl Phosphites and a Hindered Phenol

Oxidation Stability

Base

Stock Antioxidant

% Viscosity

Change

Total Acid

Number Increase

1 Hindered phenol (0.5%) 357 11.5

Hindered phosphite A (0.5%) 438 12.2

Hindered phenol (0.1%) + phosphite A (0.4%) 8.7 0.01

Hindered phenol (0.17%) + phosphite A (0.33%) 9.4 0.06

2 Hindered phenol (0.5%) 712 14.2

Hindered phosphite B (0.5%) 452 10.6

Hindered phenol (0.1%) + phosphite B (0.4%) 8.1 0.05

Hindered phenol (0.17%) + phosphite B (0.33%) 8.7 0.03

Note: Hindered phenol is tetrakis-(methylene-3,5-ditert-butyl-4-hydroxy hydrocinnamate) methane; Phosphite

A is tri-(2,4-ditert-butylphenyl) phosphite; Phosphite B is bis-(2,4-ditert-butylphenyl) pentaerythritol

diphosphite. Test conditions: IP 48 (modifi ed), 200°C for 24 h, air at 15 1/h in an ISO VG 32 mineral oil.

Source: U.S. Patent 4,652,385, Petro-Canada Inc., 1987.

Ethyl

n-Butyl

2-Ethylhexyl

Lauryl

Cyclohexyl Stearyl

Compounds blended

at 4 mmol/100 g

liquid paraffin

2 4 6 8 10 12 14 16 18

0.2

0.3

0.4

0.5

0.6

0.7

Carbon chain length

Wear scar diameter (mm)

FIGURE 3.19 Effect of chain length on the four-ball AW performance of dialkyl phosphites. (From Forbes,
E.S., Battersby, J., ASLE Trans., 17(4), 263–270, 1974. With permission.)