Presence or Absence of CIP

Raw titration curves need a correction according to Equation 2.12, which is applicable only for sets of charging curves with a CIP. Therefore, the presence or absence of a CIP is essential. CIPs are usually observed for metal oxides, and sets of charging curves without a CIP are typical of silica (see Section 2.6.3) and clay minerals (see Section 2.6.6). 

FIGURE 2.9 A set of charging curves at three electrolyte concentrations (Cj Cj C3) that merge at low pH. 

The charging curves of aluminum (hydr)oxides reported in [112] merge at pH 6-8 (no clear CIP), and they behave nearly as expected outside that pH range. The charging curves of goethite in [537] showed a CIP in the presence of NaNOj and NaCI, but in the presence of Li salts there was no clear CIP. Other sets of charging curves without a clear CIP are reported in [160,588-590]. 

The charging curves obtained in a 0.005-0.06 M electrolyte in [319] had a CIP, but the charging curve obtained in a 0.3 M electrolyte failed to have a CIP with other curves. The charging curves of ZnO obtained at the lowest ionic strengths in [549] had a CIP, but the charging curves obtained in an electrolyte over 0.1 M did not cross the other curves at that point. 

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