Porous anodic layers were grown on aluminium alloys under different an
odizing conditions. Positron annihilation energy spectra were measured
as a function of the positron energy. Ortho-positronium formation in
the porous layer was detected. ?he positron characteristics could be c
orrelated to known parameters of the layers. This demonstrates that th
e positron annihilation method is a particularly useful technique to c
haracterise the anodic layers.