8.10 Preparation and purification of colloids

1)Low solubility 2)Low concentration 3)Stabilizing reagent Basic requirement:

1) preparation dispersion method condensation method The intrinsical diameter of colloids is ~ 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: AgNO 3 + tannin + K 2 CO 3 2) oxidation: H 2 S + SO 2 3) hydrolysis: FeCl 3 + boiling water 4) precipitation equilibria: AgNO 3 + KI; NaSiO 3 +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 mill Coarse 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 FeCl 3 solution and form Fe(OH) 3 sol.

2) purification (1) Dialysis and electrodialysis Parchment membrane Dialysing membrane 2) ultrafiltration

Hemodialysis