Some Thermodynamic Aspects of Interactions on Oxide Surfaces

6 Some Thermodynamic Aspects of Interactions on Oxide Surfaces 

Uniformity of the electrical double layer on oxides plot of -gj vs -ApH master curves for rutile, ruthenium dioxide and hematite. The concentration of KNO3 is indicated. 

Similar information as in Fig. 3.4 is given in Fig. 3.17 which plots surface charge (due to protonation or deprotonation vs -ApH (= pH - pHpzc) for three oxides. Within a certain band width these curves coincide. 

This pH-congruence can be explained (Lyklema, 1987) by inferring that the process of charge formation is independent of the nature of the oxide hence it must be determined by the solution side of the double layer. On the other hand, the specific part, determined by the surface side, is determined by the chemical nature and is reflected only by the pHpzc. 

Temperature congruence for the double layer on rutile in the presence of the indicated concentrations of KN03. Between 5 and 50° C all data coincide within the band width. 

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