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The nanoporosity investigation of porous anodic alumina (PAA) remains topical and is important in understanding the forming mechanism of the unique porous structure of anodic alumina films. On the other hand, only several works have been published about the nanoporosity of PAA, and comprehensive information of the subject is difficult to obtain. In this context, this paper presents results obtained by small-angle x-ray scattering (SAXS) of porous oxide films formed by anodization of aluminium and aluminium alloy (Al-0.5wt/% Mg) in an aqueous solution of oxalic acid (3%C2H2O4). SAXS from the anodic alumina films is caused mainly by nano-sized pores (nanopores), which are present in the bulk oxide. X-ray study of oxide films 60-100 µm thick was conducted using Cu-radiation at the k-range of 0.09 to 1.45 nm-1. It is concluded that in the porous alumina formed in oxalic electrolyte, in addition to main, regularly arranged pores, there also exist nanopores of three size fractions according to their mean values of Guinier radii R1 ~ 20 nm, R2 ~8 nm and R3~2 nm. It was shown that nanopores of R3 – fraction are structural, attributed to all kinds of anodic alumina. Nanopores of R1 – and R2 – fractions arise probably due to microinhomogeneties in oxide films of different origins; for example, pores which exist in the surface layer of porous alumina. It was shown that the nanopores of large size fractions (R1 and R2) have near to cylindrical form and the R3 – fraction is of spherical form. For the oxides formed by anodization of Al alloy with Mg (0.5 wt.), a pronounced increase (about 20%) in the ratio of the nanopore fraction with minimum radius (R3) was found. It is considered that the decline in the contribution of nanopores fractions of R1 and R2 is due to the reduction of compressive stress in the alumina formed by anodization of the magnium-containing alloy. |