CHARACTERIZATION OF ALUMINUM SURFACE TREATMENTS BY MEANS OF GAS-ADSORPTION MEASUREMENTS

Adsorption measurements were used to determine the specific surface ar ea of a.c. electrolytically grained aluminium and the porosity distrib ution diagram of porous anodized aluminium. Alternating current electr olytic graining of aluminium is used to increase the specific surface area for the preparation of litho sheets or capacitor foil. The specif ic surface area S (calculated by the BET procedure from the nitrogen a dsorption isotherm) was studied as a function of the graining frequenc y between 0. 1 and 1 000 Hz. The results were related to the graining morphology by comparing them with scanning electron microscopy microgr aphs. It is concluded that in contrast to the more common surface inve stigation techniques the method can be used to measure quantitatively the gain in surface area after such a treatment as a.c. electrolytic g raining. In the second part of the paper the pore size distribution di agrams are calculated from the adsorption isotherm for porous sulphuri c acid films. It is shown that the dominant pore diameter corresponds rather well to the pore diameter observed in transmission electron mic roscopy sectional views. This means that the adsorption method can be applied to study the porosity of the aluminum oxide films. The method was then used to study the influence of the pretreatment on the porous oxide film morphology.