Lubricant Additives

Ashless Phosphorus-Containing Lubricating Oil Additives 95

been made on the nature of surface fi lm deposited on the metal, but the adsorption mechanism
indicated previously is probably still valid.

3.5.3.3 Amine Salts of Acid Phosphates

One amine phosphate that appeared in the patent literature as early as 1934 as a corrosion inhibitor
for aqueous systems (and is still occasionally used) is triethanolamine phosphate [114]. Formed by
the neutralization of phosphoric acid with triethanolamine, this product was widely used as a cor-
rosion inhibitor for automotive antifreeze formulations for many years [115].
In 1970, Forbes and Silver [116] reported on their work investigating the effect of chemical
structure on the load-carrying properties of different phosphorus compounds. In this case, the
structures under review were di-n-butylphosphoramidates, amine salts of di-n-butyl phosphate, and
derivatives of dialkylphosphinic and alkylphosphonic acids. The results indicated that the phos-
phoramidates were more effective load-carrying additives than the neutral phosphates, TBP and
TCP, but less active than the amine salts of di-n-butyl phosphate. The evaluation of the series
of dialkylphosphinic and alkylphosphonic acid esters indicated that the AW performance related
directly to the strength of the acid from which they had been produced (Figure 3.15), suggesting that
adsorption through the polarity of the ester group was an important step in the process.
In addition to the work carried out in hydrocarbon base stocks, some testing was also performed
in a synthetic ester. This fl uid enabled a comparison to be made of tetra-alkylammonium salts of
dibutylphosphate (otherwise insoluble in mineral oil), which displayed the best AW/EP properties
of all the amine phosphates tested (Table 3.13). The authors suggested that this was probably due to
the stability of the ions.

TABLE 3.12

Phosphate Ester Surfactant Ranking on Steel in a Water-Based System as a Function

of Structure

Alcohol

Phosphate

EO Units

Pin-on-Vee

Block

Rankings of

Sample

Four-Ball

Wear

Tapping

Torque

Total of

Rankings

Overall

Rating

HLB

Number

C9–16 5.5 4 1 4 9 1 13

C18 4 6 4 2 12 2 12

Nonylphenol 4 10 2 1 13 3 11

C13 10 2 9 5 16 4 14

C12 6 1 12 7 20 5 12

C8–10 6 8 7 6 21 6 11.5

C12 12 5 8 12 25 7 15

C13 6 9 6 10 25 8 11.5

C12 9 7 5 14 26 9 14

Nonylphenol 6 14 3 9 26 10 8

Phenol 6 12 13 3 28 11 15.4

Dinonylphenol 5 3 14 11 28 12 9

Nonylphenol 9.5 11 11 8 30 13 13

C13 4 13 10 15 38 14 9.7

butanediol 6 15 15 13 43 15 —