Effect of Aluminum Anode Temperature on Growth Rate and Structure of Nanoporous Anodic Alumina

In the present study, we investigated the effect of an anode temperature on current transient process during porous anodic alumina growth and morphology of the anodic layers. Alumina films were formed in a 0.4 M oxalic acid at a constant voltage mode and electrolyte temperature. The temperature of the Al anode was controlled by thermoelectric Peltier element and varied in the range of 5 °C–60 °C. Surface morphology of both sides of anodic films and their cross-sections were analyzed by scanning electron microscopy (SEM) with subsequent statistical analysis of the SEM images by ImageJ software. It was found that when anode temperature was increased from 5 °С to 50 °С the pores diameter and interpore distance has not changed, but the porous structure became more ordered. According to these results, the rate of chemical dissolution of the barrier layer and pore walls did not depend on the anode temperature. At the anode temperature of 60 °С, pores diameter has increased 1.7 times and there was a distortion of the ordering of porous cells. It was concluded that the temperature difference between the aluminum substrate and electrolyte is an important parameter affecting the formation of ordered structure of nanoporous anodic alumina.