TECHNOLOGY
FEATURE
FORMULATIONS
The basics of
oil additives
By James Wakiru
James Wakiru is
a lubricants and
lubrication specialist
and has been involved
in lubricants market
development activities
for the past 12 years
O
il additives are chemical compounds that
improve the lubricant performance of base oil
or base stock. By utilizing the same base stock,
many different oils can be manufactured, each
with its distinctive properties. Additives comprise
up to 5% by weight of some oils. Additives basically
extend and/or reduce the rate at which undesirable changes take
place while others improve properties already present in the base
oil. Essentially, only the American Petroleum Institute (API) Service
SA motor oils have no additives, and they are therefore incapable of
protecting modern engines. The choice of additives is determined by the
application, e.g. the oil for a diesel engine with direct injection in a pickup
truck (API Service CJ-4) has different additives than the oil used in a small
gasoline-powered outboard motor on a boat (2-cycle engine oil).
Types of additives
Lubricants additives can be categorized by the
functions they undertake. This is done under
four main functions as follows:
I)
16
Controlling chemical
breakdown
Detergents additives are used to clean
and neutralize oil impurities which
would normally cause deposits (oil
sludge) on vital engine parts. If left to
accumulate these deposits cause piston
ring sticking and rapid wear as well as
blockage of oil flow passages. Detergents
additives serve to delay the formation
of deposits and reduce the rate at which
they accumulate. One main reason why
frequent oil is necessary is to remove
the contaminants from the oil before
the oil’s capacity to neutralize and hold
them is exceeded.
The measure of an oil’s ability to
neutralize these acidic by-products of
combustion is called the Total Base
Number (TBN). It is a measure of an oils
reserve alkalinity. The higher the TBN,
the better an oil’s ability to neutralize
acids. A TBN of 7 is typical for an average
quality gasoline engine petroleum oil.
Diesel oils have higher TBN values due
to the increased acidic by-products of
combustion created by the diesel fuel
combustion process. These values
can range from 8-11 up to 12-14 for
premium quality diesel oils.
Corrosion or rust inhibiting additives
retard the oxidation of metal inside
an engine. A corrosion inhibitor is a
chemical compound that, when added
to a liquid or gas, decreases the corrosion
rates of a material, typically a metal or
an alloy. There are two common mechanisms for inhibiting corrosion; one
involves formation of a coating, often
a passivation layer, which prevents
access of the corrosive substance to the
metal; the other is to actually neutralize
the acids so that the corrosive potency
is reduced to a level where it cannot
do any internal damage. Common
additives for these purposes include
Zinc, Phosphorus and Zinc Diethyl
Dithiophosphate (ZDDP), Calcium and
Barium.
Antioxidant additives retard the degradation of the oil by oxidation. Oxidation
results in increase of oil viscosity,
formation of acids, resins, lacquers and
varnish on internal parts, and especially
on pistons and piston rings. The effect of
varnish, resins and lacquers on pistons
and piston rings can cause a decrease
in the amount of heat transfer between
the piston and cylinder as well as stuck
piston rings, leading to severe engine
damage over a period of time.
If the temperatures continue to increase
to extremes, then these deposits will
continue to oxidize into very hard
carbon type materials.
When this hard carbon material meets
with combustion residues and water,
sludge is formed. Sludge can do further
damage such as plug and block critical
oil passageways and oil pump pick-up
screens.
II) For viscosity
Viscosity index improvers are additives
that keep the viscosity at acceptable
levels, which provide stable oil film even
at increased temperatures. They combat
the tendency of the oil to become thin
at high temperature. The advantage of
using less viscous oil with a VI improver
is that it will have improved low
temperature fluidity as well as being
Lubezine Magazine | January-March 2012