Study on the structure and composition of anodic oxide films of aluminum

The structure and composition of the porous anodic oxide films of aluminum (abbreviated AOFAl) formed in oxalic acid (I) and sulfuric acid (II) solutions, respectively, have been investigated by TEM, IR and TGA. The results show that the porous anodic oxide films consist of a large number of hexagonal cells with an irregularly round pore in the center of each cell wich penetrates vertically from surface to botton, while a barrier layer under the film directly contacts with an aluminum substrate in a scallop shape. The content of Al-2(C2O4)(3) and Al-2(SO4)(3) in AOFAl (I) and (II) are similar to 4.9 wt % and similar to 14.2 wt %, respectively; similar to 3.5 wt % water of crystallization of Al-2(SO4)(3),xH(2)O which can be evolved at rather low temperature (similar to 85 degrees C) enriches between the cells and under the barrier layer of AOFAl (II); after irradiation by the electron beam of TEM the water of crystallization is removed and voids are formed.