Lubricant Additives

106 Lubricant Additives: Chemistry and Applications

• Low toxicity


• Biodegradable (many but not all products)


• Compatible with most other types of additives (particularly the neutral esters)


• Soluble in a wide range of base stocks, both mineral oil and synthetic, and able to assist the
  solvency of other additives

Although the physical properties of phosphorus-containing additives are not critical, the values for
the most widely used types of phosphate ester AW additives are given in Table 3.17, with TiBP as
an example of an alkyl phosphate, TCP as a natural phosphate, and ISO 32 grades of both types of
synthetic ester.
The major suppliers of phosphorus-containing lubricant additives are listed in Table 3.18, and
their current oil industry applications are summarized in Table 3.19. Undoubtedly, the most impor-
tant applications for the neutral aryl phosphates are hydraulic, turbine, and general circulatory oils,
whereas almost the entire market for the ethoxylated alkyl and aryl acid phosphates is to be found
in metalworking. The acid phosphates, acid phosphites, and amine salts of these acidic materials are
used in a mixture of metalworking, gear oils, hydraulic oils, etc., as indicated in Table 3.19.
The selection of an AW/EP additive depends on the specifi c requirements for the application;
for example, whether both AW and EP performance is needed and what levels are required. When
this has been ascertained, secondary considerations may be the level of stability required (oxida-
tive or hydrolytic), potential interaction with other components of the formulation, and the effect on
surface-active properties such as foaming. Table 3.20 attempts to identify the additives that should

TABLE 3.16

A Breakdown of the Market for Ashless Phosphorus-

Containing AW/EP Additives

Product Market Size (t)

Alkyl phosphates 100

Aryl phosphates 6000

Acid phosphates, ethoxylated alkyl and aryl phosphates,

and amine salts of acid phosphates

3000

Phosphites, acid phosphites, dialkyl alkyl phosphonates,

and amine salts of acidic products

1000

TABLE 3.17

Typical Physical Properties of the Most Widely Used Grades of Phosphorus-Based

AW Additives

Property Unit TiBP TCP IPP/32 TBPP/32

Viscosity at 40°C cSt 2.9 25.0 32.3 33

Viscosity at 0°C cSt 10.0 1000 990 1500

Specifi c gravity 20/20°C 0.965 1.140 1.153 1.170

Pour point °C <– 90 – 28 – 27 – 26

Acid number mg KOH/g 0.06 0.05 0.05 0.06

Water content % 0.01 0.06 0.05 0.05

Phosphorus level % 11.7 8.3 8.0 8.1

Flash point °C 155 240 245 255