Relaxation of the silver/silver iodide electrode in aqueous solution

The aim of this study is to detect and characterize relaxation processes on silver/silver iodide electrodes in aqueous electrolyte solution. The information obtained is to be used for an estimation of the consequences of similar processes on colloidal AgI particles during encounter.
In chapter 1 a general introduction is given. It is explained how electrode kinetic data can be used to obtain insight in the dynamic aspects of the stability of the lyophobic colloids.
Some fundamental properties of the Ag/AgI film electrode which are important in the interpretation of the relaxation measurements are described in chapter 2. The preparation of the electrode, the silver layer and the AgI film is described. The specific resistance of the AgI film was obtained from measurement of the electrode resistance and the thickness of the AgI film. An estimation of the roughness factor of the AgI surface is made using electron micrographs and results of other investigators who worked with the same type of electrodes.
In chapter 3 the relaxation behaviour of the Ag/AgI electrode in 0.1 M KNO ₃ solution is described. The used pulse technique, the experimental set-up and the method of analysis are treated. It is shown that there are two relaxation processes: a fast one on the Psec scale and a slower one on the wee scale. They are probably connected with charge transfer processes in the Ag/AgI and AgI/ electrolyte solution interface respectively. The standard exchange current density and the transfer coefficient for the slow relaxation of both the Ag ⁺ and the I ^- reaction are calculated. The double layer capacitances are also obtained and their values agree with the results of other studies.
Relaxation measurements in various KNO ₃ concentrations ' and various types of inert electrolyte are reported in chapter 4. One of the main conclusions is that the slow relaxation is not influenced by the concentration and nature of the inert electrolyte.
In chapter 5 an attempt is made to interpret the results obtained with the electrodes in terms of relaxation processes occurring at interacting AgI sol particles. It is indicated that some of the possible relaxation processes are fast as compared with the process of encountering of two colloid particles.
Diffuse double layer relaxation in the aqueous solution and migration of interstitial silver ions in the solid are examples of such fast processes. On the other hand, the transfer of potential determining ions (silver or iodide ions) through the Stem layer is a rather slow process with a time constant which is lower than the particle encountering time by a factor of about ten. Thus, in the case of silver iodide sols, exchange of charge between particle and solution will not occur. However, redistribution of charge in the region of short distance between the interacting particles is possible via the fast relaxation processes. Thus, the silver iodide colloid appears to be intermediate between the constant charge case and the constant potential case.