Lubricant Additives

96 Lubricant Additives: Chemistry and Applications

A further study of the mechanism of amine phosphates by Forbes and Upsdell appeared in
1973 [117]. Adsorption/reaction studies of dibutyl and di-2-ethylhexyl phosphates with either n-
octylamine or cyclohexylamine and iron powder showed that both the amine and the acid phosphate
were adsorbed onto the metal surface and that the rate and extent of their adsorption/desorption
varied with chemical structure. The higher the solubility of the iron–phosphate complex formed,

3.5

3.0

2.5

2.0

1.5

pK

of acidA

Four-ball wear scar diameter (mm)

0.3 0.4 0.5 0.6 0.65

2

5

3

4

6

1

1: n-butyl di-n-octylphosphinate

2: Di-n-butyl hexylphosphonate

3: Di-n-butyl phenylphosphonate

4: Tri-n-butyl phosphate

5: Diethyl benzyl phosphonate

6: Diethyl o-nitrophenylphosphonate

x

x

x

x

x

x

FIGURE 3.15 Effect of acid strength on AW performance. (From Forbes, E.S., Silver, H.B., J. Inst. Pet.
56(548), 90–98, 1970. With permission.)

TABLE 3.13

Four-Ball Test Results of Various Amine Dibutyl Phosphates in Diisooctyl Sebacate

EP Test AW Test

(BuO) 2 PO 2 NR^1 R^2 R^3 R^4 MHL (kg) WL (kg) ISL (kg) 30 min

WSD (mm)

after 45 min 60 min

nC 4 H 9 NH 2 40.5 130 125 0.38 0.38 0.36

nC 6 H 11 NH 2 40.0 130 115 0.37 0.38 0.39

PhNH 2 43.6 140 120 0.37 0.38 0.39

[nC 4 H 9 ]NH 2 34.8 140 100 0.26 0.27 0.33

[nC 4 H 9 ] 3 NH 37.8 150 110 0.37 0.38 0.42

[nC 4 H 9 ] 4 N 54.4 150 150 0.25 0.25 0.26

[CH 3 ] 2 [nC 8 H 17 ] 2 N 56.1 165 165 0.30 0.35 0.40

None 18.6 120 55 0.57 0.61 0.64

TCP 19.8 110 60 0.31 0.33 0.35

Note: % additive = 4 milliatoms of P/100 g of fl uid. (MHL, Mean Hertz Load; WL, Weld Load; ISL, Incipient Sei-

zure Load; WSD, Wear Scar Diameter.)

Source: Forbes, E.S., Silver, H.B., J. Inst. Pet., 56(548), 90–98, 1970. With permission.