Controlling the thickness of electrochemically produced porous alumina membranes: the role of the current density during the anodization

A study of the thickness growth rate of anodized porous alumina membranes (PAMs) and its connection to the current density during the anodization process is presented. Several samples of PAMs were prepared in a hydrate solution of 0.3 M oxalic acid, under applied voltages of 40 and 50 V with varying solution temperatures in a purpose-built electrochemical cell. The thickness of the PAMs produced under these conditions was measured using cross section images taken by scanning electron microscopy (SEM). From these measurements, a linear expression between the growth rate of PAMs and the current density during the anodization is deduced, giving an efficiency value of 53 and 65 % for applied voltages 40 and 50 V, respectively. In steady state conditions, i.e., after the stabilization of the anodization current, this linear dependence is very conveniently transformed into linear dependence of thickness versus total anodization time, providing thus a simple method for controlling the thickness of the produced membranes. Finally, from the Arrhenius-type plot of the thickness growth rate versus temperature and the anodization current density vs temperature a mean value of 48.5 kJ mol−1 for the aluminum oxide formation activation energy E a is deduced.