The reasons for the coagulation:
- By boiling:
On boiling the sols dispersed phase particle aggregates together and neutralized leading to the formation of a precipitate. Eg: By boiling starch sol at high temperature, starch particle, are coagulated converting into a suspension.
- By prolonged electrophoresis:
Displacement of sol particle towards the electrode of opposite charge is known as electrophoresis. If this process is continued for large time, sol particle of the same charge combines and neutralize to form a precipitate.
- By persistent electrodialysis:
Removal of soluble ionic imparity by using semi-permeable membrane is known as Dialysis. This process is very slow, to faster the process electric plate are suspended into the dispersion medium such as water, so that the ionic impurities move towards the opposite plate in the electrodialysis. If this process is continued for a longer time all the ionic impurities are accommodated at a point and sol discharged due to neutralisation leading to the formation of the precipitate by coagulation.
- By the addition of another lyophitic sol of opposite charge:
Sols are charged the charge of sols due to personation adsorption of S ion on the surface of sol particle. In these type of sols a positive sol is coagulated by adding another negative sol is equal amounts while a negative sol or coagulated by adding another positive sol is equal amount, in this process the charges of sol particle are neutralized by the addition of particle of opposite charge leading to coagulation.
- By the addition of electrolyte in large amounts:
Small amount of electrolyte is added for the formation of sol by peptization. When same electrolyte is added in large amounts, these provide ions of opposite charge in large concentration to form a precipitate or coagulation of the neutralization of sol particle by the ions produced by the electrolyte. The coagulating or flocculate capacitor of electrolyte is determined by Hardy Schulze law.