2. Dispersion Methods
In dispersion methods, colloidal particles are
obtained by breaking large particles of a
substance in the presence of a dispersion
medium. Since the solsformed are unstable,
they are stabilized by adding mechanical
energy input.
Dispersion method in the preparation of
colloids can be done by crushing the large
suspension’s particles into small in size.
3. Dispersion Method
In these methods, the bigger particles of a
substances are broken down to form smaller
particles of colloidal dimensions thus
obtained are stabilized by the addition of
certain stabilizing agents. Some important
dispersion methods are as follows:
4. I. Mechanical Dispersion
Method
In this method, the dispersion of the coarse
material (whose colloidal solution is to be
prepared) is carried out in a machine called
colloid mill.
Colloid mill - It consists of two heavy steel
discs separated by a little gap. The gap may
be adjusted according to the particle size
desired. The two discs rotate at high speed
(about 8000 revolutions per minute) in the
opposite direction.
5. I. Mechanical Dispersion
Method
A suspension of the substance in water is
introduced into the mill. The coarse particles
present in the suspension are grinded to the
particles of colloidal dimensions and get
dispersed in water to form a sol. Finer
dispersion can be obtained by adding an inert
diluents which prevents the colloidal particles
to grow in size.
6. I. Mechanical Dispersion
Method
Mechanical dispersion is also called direct
dispersion. It is a method of making a colloid
by crushing or milling a given solid and the
powder produced is dispersed into a given
dispersing medium.
Examples : Making of sulphur sol with the use
of glucose as diluents.
8. II.Electrical Dispersion
Method
Also known as “Bredig arch method “
Is a method of preparing colloids, especially
metallic sols. In this method, two metallic
wires functioning as electrodes are immersed
into water, then on both ends of wires is given
a strong enough electric current to be
evaporated and then it is dispersed into water
to form a metallic sol.
9. II.Electrical Dispersion
Method
In this method, an electric are is struck between
the two electrodes of the metal (whose colloidal
solution is to be prepared) immersed in the
dispersion medium (say water).
The dispersion medium is cooled by surrounding
it with a freezing mixture. High temperature of
the arc vaporizes some of the metal. The vapour
condenses to the particles of colloidal size on
cooling. The colloidal particles thus formed get
dispersed in the medium to form a sol. of the
metal.
10. II.Electrical Dispersion
Method
This method is used for the preparation of
sols metals such as gold, silver, platinum etc.
Electtrical Dispersion Method
11. III. Peptization Dispersion
The process of converting aprecipitate into a
colloidalsol by shaking it with thedispersion
medium, in thepresence of a small amountof
electrolyte
Electrolyte = Peptizing agent
This method is used to convert a freshly
prepared precipitate into a colloidal sol
12. III. Peptization dispersion
In this method, a freshly prepared precipitate
of the substance is made to pass into the
colloidal state by the addition of a suitable
electrolyte. The process of dispersing a
freshly prepared precipitate into colloidal
form by using a suitable electrolyte is called
peptization. The electrolyte added is called
peptizing agent.
13. III.Peptization Dispersion
In peptization, the larger particles is
dispersed into smaller particles in a colloidal
size by adding a particular electrolyte which
acts as a dispersing agent.
For example, sediment of Al(OH)3 will change
into a colloid by adding a solution of AlCl3 ;
NiS will charge into sol when it is added into
H2S; and sediment of AgCl will charge into a
colloid by adding a solution of ammonia.
14. IV.Homogenization
Homogenization is a process for preparing
something to become homogeneous. In this
preparation, a particular emulsifier is usually
added to emulsify the fat particles in milk or
cream so that the milk or cream form a stable
colloid. In this process, skim milk powder is
often used and it is conducted in a
homogenization device.
15. Summary of Dispersion Method
Dispersion method - larger particles of a substance
(suspensions) are broken into smaller particles. The
following methods are employed.
There are 4 ways using dispersion method :
1. Mechanical Dispersion Method - the substance is
first ground to coarse particles.
2. Electical Dispersion Method - is used to prepare
sols of platinum, silver, copper or gold.
3. Peptization Dispersion - The process of converting
a freshly prepared precipitate into colloidal form by
the addition of suitable electrolyte
4. Homogenization - is any of several processes used
to make a chemical mixture the same throughout.
