8.10 Preparation and purification of colloids

1) Low solubility

2) Low concentration

3) Stabilizing reagent

Basic requirement:

1) preparation

dispersion method

condensation methodThe intrinsical diameter of colloids is 10-9 ~ 10-7 m.

Condensation method: by building up the particles from

single molecules.

Dispersion method: by disintegrating down the bulk

material to the colloidal particles.

condensation method / aggregation method

Chemical condensation:

1) reduction: AgNO3 + tannin + K2CO3

2) oxidation: H2S + SO2

3) hydrolysis: FeCl3 + boiling water

4) precipitation equilibria: AgNO3 + KI; NaSiO3+HCl

Physical condensation:

1) exchange of solvent: sulfur/alcohol sulfur / water

2) condensation of vapor: hydrosol of Hg, Na sol in benzene

Dispersion methods:

colloid millCoarse dispersion

1) colloid mill: mechanical dispersion 2) arc method: 3) ultrasonic method: 4) peptization method:

Bredig’s arc method

Ultrasonic generator

Piezoelectric device

Fe(OH)3 precipitation Newly formed can be peptized by FeCl3 solution and form Fe(OH)3 sol.

2) purification

(1) Dialysis and electrodialysis

Parchment membrane

Dialysing membrane

2) ultrafiltration

Hemodialysis