SOME INTERPHASE CHARACTERISTICS OF THE SYSTEM AL-OXIDE LAYER-ELECTROLYTE

Interphase characteristics of the system Al/oxide layer/electrolyte were investigated by the impedance method and by determining the contact angle. Solutions of borate, of tartrate and of their mixtures were used as the electrolyte. From Cole-Cole diagrams plotted from the results of electrical measurements, we can conclude that in some cases in the system there are relaxations the occurence of which depends on the pH and the composition of the solution. Relaxations are most pronounced in borate solutions with pH values in the range 5.5-6.0. In the frequency range investigated the semi-circle in the Cole-Cole diagram becomes progressively less well formed with increasing pH and with the addition of tartrate. The contact angle was measured at the phase boundary oxidized aluminium/solution/paraffin oil. The contact angle varies with solution pH and has its maximum value at pH 6.8. The addition of tartrate to borate solutions decreases the contact angle over the entire pH range investigated. The results are discussed in relation to the relaxation of dipoles of water at the interphase boundary oxidized aluminium/solution, in relation to the influence of surface charge, which varies with pH, as well as in relation to the influence of other species in the solution. © 1979.