Chemistry Reference
In-Depth Information
the mixture and the resultant greases accordingly have properties substantially similar
to straight soda lubricants [8].
Lithium Complex Soap Grease
Lithium complex grease performance is like that of lithium greases except dropping
points is about 50°C higher. Lithium complex is a misnomer used to describe high
dropping point greases. Because lithium is monovalent (meaning it can only react
with one acid per ions), it cannot form a traditional soap where two or more acids
reacted with one basic ion. However there are several components that can be used
to enhance the molecular interactions of the soap molecules and increase the drop-
ping point enough to call the resulting grease a “lithium complex”. The most common
method is by forming a lithium salt of a dibasic acid (usually azelaic or sebacic)
in situ
with lithium 12-hydroxy stearate soap. Lithium complex greases provide good low
temperature performance and excellent high temperature life performance in tapered
roller bearings. It is the most popular of the complex greases and has wide spread ap-
plication [20].
Barium Complex Grease
Barium complexes were one of the first multipurpose greases. They are made by re-
acting barium hydroxide in a crystalline form with a fatty acid, complexing the soap
with stabilizing substances and then blending with the desired amount of oil. Textures
can vary from buttery to fibrous depending on the complexing agent used. The fibrous
is the most common. The dropping points range from 193-251°C, and is fairly stable
to shear and working. They are water resistant act as fair rust preventatives. They are
not very pumpable at cool temperatures, but can be made so by adjusting the base oil.
Barium complex is fairly good multipurpose grease, but is expensive and difficult to
manufacture. These greases work very well in wheel bearings, water pumps, chassis,
and universal joints. They also work well as an outside gear lubricant because of the
water resistance and have excellent adhesive properties [21].
Calcium Complex Grease
Calcium complex grease has unusually high heat resistance making it of considerable
value in extreme pressure applications. The dropping point of this type of grease is
260
o
C or even higher. This means that this type of lubricant will maintain its stability
while running continuously at high temperatures. However, this type of grease has
not replaced lithium soap greases because they are not as mechanically stable [21].
Calcium complexes should not be considered as multipurpose greases. They are very
useful, but should be considered carefully beforehand [17].
Alluminum Complex Grease
The soap used for alluminum complex grease is alluminum benzoyl stearoyl hydrox-
ide. These greases provide a wider range of applications than multipurpose types. They
are made from two dissimilar acids reacted with alluminum isopropoxide to form a
complex soap molecule, or this soap is formed by reacting alluminum isopropylate
with stearic acid, benzoic acid and water. They have high dropping points, excellent
water resistance, good shear stability and good pump ability depending on the mineral
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