Admixtures
Admixtures also aid dispersion by modifying the properties of the dispersant itself
that are responsible for the problem. Admixtures are added in larger quantities,
typically 1g/l. A list of commonly used admixtures is given below:
Sodium Hexametaphosphate
Sodium Pyrophosphate
Trisodium Phosphate
Ammonia
Sodium Oxalate
Calgon
Calcium Chloride
As these are solid materials dissolved into the dispersant the solution should be
filtered after preparation to remove impurities.
Slurries
The act of mixing up a small quantity of concentrated sample, dispersant and
additives before it is added to the instrument tank is known as preparing a slurry.
Once the particles have been successfully dispersed into a slurry, then the sample
may be added to the instrument without any further additions of surfactants etc.
to the instrument dispersion unit. The problem of the sample settling out within
the beaker can be solved by using a pipette to continually stir the sample. At the
same time as stirring you can continually fill and empty the pipette. Use the
pipette to add the sample to the dispersion tank.
The use of ultrasonics
In addition to the processes above ultrasonics can be applied to help the
dispersion whether or not it contains a surfactant.
When mixing the sample in the suspension medium, a visual inspection will often
indicate whether ultrasonics are necessary. If there are large agglomerates of
particles which sink to the bottom of the beaker, then try applying two minutes of
CHAPTER 9
Getting Started
Page 9.6
MAN 0101
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