Determination of density and elastic constants of a thin phosphoric acid-anodized oxide film by acoustic microscopy

Quantitative acoustic measurements have been carried out on phosphoric acid -anodized (PAA) aluminum. This process creates a porous oxide layer which v aried from 1 to 22 mu m thick in the different specimens used here. The ela stic properties of the PAA oxide layer were determined by measurements of t he dispersion curves in the complex plane [speed of the surface acoustic wa ve (SAW) and its attenuation] alone. This was possible because two modes we re observed on samples with thicker oxide layers. It has also been shown th at the dependence of the attenuation on the oxide layer thickness around th e cutoff can be used for the determination of the density of the layer; The shape of the attenuation curve measured by the acoustic microscope near th e cutoff was smoother than predicted by the theory, and this phenomenon has been discussed. (C) 1999 Acoustical Society of America. [S0001-4966(99)043 11-8].