Lubricant Additives

102 Lubricant Additives: Chemistry and Applications

the aforementioned salt was thought to decompose further to give the phosphorus-rich layer of the
following type:

OH

P

OO

The authors postulated the load-carrying mechanism of phosphites given in Figure 3.21.

3.5.5.1 Amine Salts of Acid Phosphites

In 1975, Barber [152] investigated the four-ball test performance of several long-chain amine salts of
short-chain acid phosphites, which were found to be very active. Unfortunately, he did not investigate

Ethyl

n-butyl

2-Ethylhexyl

Lauryl

Stearyl

Cyclohexyl

Compounds blended

at 4 mmol/100 g

liquid paraffin

2 4 6 8 10 12 14 16 18

100

120

140

160

150

130

110

210

200

190

180

170

220

Carbon chain length

Initial seizure load (kg)

FIGURE 3.20 Effect of chain length on the initial seizure loads of dialkyl phosphites. (From Forbes, E.S.,
Battersby, J., ASLE Trans., 17(4), 263–270, 1974. With permission.)

TABLE 3.15

Comparison of the Load-Carrying Properties of Dialkyl Phosphates

and Dialkyl Phosphites at 4 mmol/100 g Base Oil

Initial Seizure

Load (kg)

Wear Scar Diameter

(60 min) mm

Diethyl phosphite 225 0.70

Diethyl phosphate 160 0.43

Dibutyl phosphite 155 0.64

Dibutyl phosphate 85 0.42

Di-2-ethylhexyl phosphite 125 0.36

Di-2-ethylhexyl phosphate 80 0.29

Dilauryl phosphite 130 0.32

Dilauryl phosphate 80 0.35

Source: Forbes, E.S., Battersby, J., ASLE Trans., 17(4), 263–270, 1974. With permission.