Advanced Electronic Ceramics I (2004)

Gouy-Chapmann theory

Advanced Electronic Ceramics I (2004)

Gouy-Chapmann theory

Advanced Electronic Ceramics I (2004)

Gouy-Chapmann theory

Advanced Electronic Ceramics I (2004)

Gouy-Chapmann theory

Advanced Electronic Ceramics I (2004)

Gouy-Chapmann theory

Advanced Electronic Ceramics I (2004)

Comparison

G-C between (37) and (62)

Advanced Electronic Ceramics I (2004)

Schultz-Hardy rule

♦ critical concentration of electrolyte required to flocculate the colloid: the valence of the opposite-charge ion plays the principal role on colloid stability

- the flocculation concentration for monovalent counter ionis 100 times higher than divalent ion,and is 1000 times higher than trivalent ion.

⇒ The effect on the screening of the surface charge is related tothe counter-ion valence

M ∝ Z-6

M : critical flocculation concentration (CFC)Z ; valence of the counter ion26= 64, 36=729

(ex) the use of Al or Fe ion to cause the flocculation the particleswith negative zeta potential in water treatment plants

Advanced Electronic Ceramics I (2004)

Critical Flocculation Concentration

6.9X10-4 M of divalent cation is needed to flocculate the negative As2S3 sols.6.3X10-4 M of divalent anion is required to flocculate the positive Al2O3 sols

Advanced Electronic Ceramics I (2004)

(Motivation)Does every monovalent ion give the same effect upon the flocculation?

(ex.)1. In order to flocculate the Ag2S3 solution (negative colloid)- 0.058 M Li+ ion or 0.051 M Na+ concentrations is required.2. In order to flocculate the AgI solution (negative colloid)- 0.165 M Li+ ion or 0.140 M Na+ concentrations is required.⇒ Na+ is more effective than Li+ in inducing flocculation

The effectiveness in inducing flocculationFor monovalent cationsCs+ > Rb+ > NH4

+ > K+ > Na+ > Li+

Critical Flocculation Concentration

Advanced Electronic Ceramics I (2004)

Stern adsorption

♦ Stern correction for EDL model

1. The adsorption of potential-determining ion at surface⇒ determine ψ0

ψ0 = (2.303RT/F) ln (C/Czp)

2. Diffuse double layer in Debye-Hückel and Gouy-Chapmann approximation indifferent ions as point charge (with no volume)

⇒ acceptable for the bulk region of dilute solution⇒ but situation becomes different at high concentration. Saturation

would occur at the inner edge of the diffuse part of double layer.

⇒ the model considering specific adsorption effect is required.

Advanced Electronic Ceramics I (2004)

Stern layer

♦ Stern layer : the layer of specific adsorption

♦ In general specific adsorption of an ion is enhanced by large size (large polarizability)

(Problem) introduce the parameterswhich is hard to measure

δ : the thickness of Stern layer, K : constant related with surface

adsorption