Aem Lect10
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Transcript of Aem Lect10
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