Gouy-Chapmann theory




Advanced Electronic Ceramics I (2004)




                                        Gouy-Chapmann t...
Gouy-Chapmann theory




Advanced Electronic Ceramics I (2004)




                                        Gouy-Chapmann t...
Gouy-Chapmann theory




Advanced Electronic Ceramics I (2004)




                                          Comparison


...
Schultz-Hardy rule

       ♦ critical concentration of electrolyte required to flocculate the colloid
         : the valen...
Critical Flocculation Concentration
      (Motivation)
      Does every monovalent ion give the same effect upon the flocc...
Stern layer
      ♦ Stern layer : the layer of specific adsorption

                                          ♦ In general...
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Aem Lect10

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Aem Lect10

  1. 1. Gouy-Chapmann theory Advanced Electronic Ceramics I (2004) Gouy-Chapmann theory Advanced Electronic Ceramics I (2004)
  2. 2. Gouy-Chapmann theory Advanced Electronic Ceramics I (2004) Gouy-Chapmann theory Advanced Electronic Ceramics I (2004)
  3. 3. Gouy-Chapmann theory Advanced Electronic Ceramics I (2004) Comparison G-C between (37) and (62) Advanced Electronic Ceramics I (2004)
  4. 4. 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 ion is 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 to the counter-ion valence M ∝ Z-6 M : critical flocculation concentration (CFC) Z ; valence of the counter ion 26= 64, 36=729 (ex) the use of Al or Fe ion to cause the flocculation the particles with 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)
  5. 5. Critical Flocculation Concentration (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 flocculation For monovalent cations Cs+ > Rb+ > NH4+ > K+ > Na+ > Li+ 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)
  6. 6. 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 parameters which is hard to measure δ : the thickness of Stern layer, K : constant related with surface adsorption Advanced Electronic Ceramics I (2004)

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