Non-nickel-based sealing of anodic porous aluminum oxide in NaAlO2

A fast and non-toxic sealing method based on the use of NaAlO2 solution is investigated in detail. AlO2 sealing is carried out using NaAlO2 as the sealant, which is neutralized with H2SO4 and optimized to pH 7. Temperature, sealing time, pH is optimized in terms of chemical/mechanical properties, measured by Vickers hardness test, Tafel analysis, and sealing quality test based on ASTM-B680. The Vickers hardness, corrosion resistance, and sealing properties of the samples obtained by the proposed sealing method are found to be superior compared to those of the samples prepared by the conventional sealing methods. XPS data show a high intensity of boehmite (AlOOH) peaks in the sample obtained by the NaAlO2-based sealing, similar to the case of the sample obtained by hydrothermal sealing. During the NaAlO2 sealing process, a hard and dense layer of boehmite, which is formed from the dissipated AlO2− present in the sealant solution and the dissolved anodic oxide, is deposited within the pores of the anodic alumina in a short time; this leads to enhanced chemical/mechanical properties of the anodic porous alumina sample sealed using NaAlO2.