Metal Soap Greases - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 61

thickeners are based on 12-hydroxy stearic acid like their lithium counterpart and re-
sulting grease offers excellent mechanical property [9].
Alluminum soap Greases
Alluminum soap greases are special purpose lubricants. These greases are made a
process called double decomposition. The alluminum soap is prepared by the action
of water soluble alkaline soap on a solution of alluminum sulfate or chloride. The pre-
cipitated alluminum soap is washed free of impurities and dried. It is then dissolved in
mineral oil and thickened to the required nature. Due to the tri-valency of alluminum,
three forms of alluminum stearate are possible. Grease making alluminum stearates
are usually mixtures, with the mono or di stearates dominating, although pure forms of
the mono, di, and tri stearates are available.
Their particular advantage is that they are very sticky making them perfect for
applications requiring surface lubrication. Alluminum soaps of unsaturated acids such
as oleic have poor gelling properties and tend to form soft, unstable greases. Allumi-
num stearate provided tacky substance suitable for the chassis but the complete lack
of stability since they are sensitive to shear excluded its use in rolling elements. They
have signi¿ cant texture changes with the temperature. They can be used only in low
temperatures below 76°C because they tend to soften rapidly. They have excellent
water resistance but very poor mechanical stability.
6.4.3 Mixed Soap Greases
These greases are made with two or more metallic soap in combination to produce a
lubricant that contains some of the desired properties of both. The most successful of
these has been 16% sodium soap combined with 2% calcium soap with highly inhib-
ited oil base plus additives. This has been very effective in packing for the socalled pre
lubricated antifriction bearing [19].
Greases based on mixed soaps are classi¿ ed into a separate subgroup of soap greas-
es. They contain a thickener that is a mixture of soaps differing by the cation such as
calcium-sodium, lithium-potassium, lithium-calcium, and so on soaps. Greases with
such mixed soaps are as well called calcium-sodium (CaNa), lithium-calcium (LiCa),
lithium-lead (LiPb),and so on greases, that soap cation whose share in the thickener
is greater being the ¿ rst indicated one. However, when carrying out various technical
and economical analyses of grease production and application and selecting the grease
production method, such greases are included in the group of the predominant soap
cation [5].
Other combinations have been used, such as alluminum-sodium, calcium-zinc,
lithium-calcium-sodium, and lithium-sodium, however, most of these have been de-
veloped for highly specialized use, and some are still in the experimental stage [5].
6.4.4 Complex Soap Greases
Sodium Complex Grease
The primary intent of mixed base greases is to secure a very short fiber structure, ap-
proaching as closely as possible a smooth and buttery texture while retaining the high
melting point properties of the soda base. In most instances, soda soap predominates in