Lubricant Additives

Ashless Antiwear and Extreme-Pressure Additives 231

N

O N

O R 5

S

R 3

R 4

R 1

R 2

N

N

S

H

H

R 3

R 4

R 1

R 2

N

N

S

H

R 3

R 4

R 1

R 2

H

+

O O

O O

R (^5) R
5
STRUCTURE J, TIDZ
N
X
N
R 2
S
R 1
R 3
H
N
O
N
H
S
R 1
N
O
N
SH
R 1
STRUCTURE K, TDZL STRUCTURE L, ODZ
8.2.5 PHOSPHORUS–NITROGEN ADDITIVES
Phosphorus–nitrogen additives are used to provide protection against moderate to high pressure,
metal-to-metal contacts in boundary lubrication, and EHL. Ashless phosphorus–nitrogen additives
are used as dual functional antiwear/antirust additives extensively, and those that are most com-
monly available in the marketplace are based on chemistries of amine dithiophosphates, amine
thiophosphates, amine phosphates, and phosphoramides.
8.2.5.1 Amine Phosphates
Amine phosphates are by far the most important phosphorus–nitrogen-containing additives used
in lubricants. In fact, they are multifunctional additives possessing very good antirust properties as
well as antiwear/EP properties.
8.2.5.1.1 Chemistry and Manufacture
Amine phosphates are produced by treating acid phosphates with alkyl or aryl amines. Under various
conditions, neutral, overbased, and underbased amine phosphates can be synthesized. If mixed mono-
and dialkyl acid phosphates are used as starting materials, mixed mono and dialkyl amine phosphates
are produced. The fi nal additives usually possess high total acid number (TAN) and high total base
number (TBN), although reaction adducts are considered fairly neutral. It is known that a complete neu-
tralization of both phosphoric acid groups in monoalkyl acid phosphates with amines cannot be easily
achieved, and therefore, under normal conditions, a partially neutralized amine phosphate is formed.
(RO) 2 P(=O)(OH) + R′NH 2 ⇒ (RO) 2 P(=O)O∙NH 3 R′ (8.34)
(RO)P(=O)(OH) 2 + R′NH 2 ⇒ (RO)P(=O)(OH)O∙NH 3 R′ (8.35)
8.2.5.1.2 Applications and Performance Characteristics
Amine phosphates are extensively used in industrial oils, greases, and automotive gear oils.
They offer very good rust protection as demonstrated in various bench rust tests (ASTM D665 and
CRC L-33). They also show very good antiwear/EP characteristics (Four-Ball Wear and Four-Ball