The purpose of this investigation is to evaluate the effects that relatively minor changes in phosphoric acid anodizing (PAA) parameters (voltage, temperature, time) have on oxide morphology and the subsequent penetration of an applied adhesive-primer into the porous oxide. This preliminary study examines two cases, one in which industry-standard PAA parameters have been followed, and a second in which the PAA parameters are slightly above industry limits.

Baseline PAA parameters have been developed in the aerospace industry from extensive empirical testing in order to maximize adhesive bond strength and durability in the presence aggressive environments. It has been noted that for effective mechanical strength of structurally bonded elements, penetration of the adhesive primer into the porous oxide formed by an anodizing pre-treatment is critical. Verifying primer penetration is somewhat problematic due to the high spatial resolution required to both structurally and chemically characterize an oxide film on the order of one micron in thickness.