ИСТИНА

Here we present approach to prepare porous alumina films with highly ordered structure in corundum (α-Al2O3) form. AAO films were obtained by Al anodizing in 0.3 M sulfuric acid at 25 V. As-prepared anodic alumina represents honeycomb-like porous structure with interpore distance of 64 nm, pore diameter of ca. 18 nm (porosity of ~ 7%), and thickness of 50 µm. Two crystallization processes at 956 and 1193 °C were revealed by simultaneous thermal analysis (STA). Based on STA data, thermal treatment sequence with a heating rate of 1 °C/min around the transition temperatures, final annealing at 1200 °C for 4 h and slow cooling down to room temperature was proposed. Resulted AAO films are flat, warp/crack-free and, according to X-ray diffraction data, consist of α-Al2O3 phase without any low-temperature alumina polymorphs. According to electron back-scattering diffraction (EBSD), AAO films after crystallization into corundum consist of porous single-crystalline grains with average size of about 10 µm without any texture preferences. Slight increase in pore diameter up to 25 nm (porosity ~ 14%) due to volume shrinkage was observed.