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.