Porous anodic alumina (PAA) membranes with highly ordered hexagonal cells and a novel pore structure have been fabricated by two-step hard anodization in a H(2)SO(4)-Al(2)(SO(4))(3)-H(2)O system at 40 and 50 V, giving average cell diameters of 77 and 96 nm, respectively. There are several tiny pores embedded in each big shallow pore on the top of the membranes, and there is only one pore in one cell at their bottom. The cells on both sides of the membranes present almost the same periodic arrangement. In order to explore the formation of the novel pore structure, PAA membranes fabricated at different current densities (30-200 mA cm(-2)) are obtained by maintaining a constant voltage at 40 V. The experimental results show that the interpore distance is not only dependent on the anodization voltage, but is also influenced by the current density, which means that the pore structure of PAA membranes fabricated by hard anodization can be accurately designed and controlled by adjusting the anodization voltage and current density simultaneously.

The relative biological value (RBV) for rats of the iron from 7 elemental iron powders (produced by electrolysis, reduction with hydrogen (H2), carbon monoxide (CO), and desiccated ammonia (NH3), and carbonyl process) were compared with the in vitro solubility of the iron powders in 0.2% HC1 (w/v, ca 0.05/V) for periods of 5 to 90 min. The values obtained for per cent solubility in 10 min were within the fiducial limits of the individual RBVs of 6 iron samples; the exception was one preparation of carbonyl iron whose solubility, but not RBV, was as high as that of electrolytic iron. These data indicate that dissolution rates were good predictors of bioavailability of some types of elemental iron powders. There was good agreement between specific surface areas and particle size distributions of discrete fractions containing fine particles of comparable sizes (7—10 μm) of electrolytic, H2- and CO-reduced iron, and whole preparations of carbonyl iron, but these measurements were not satisfactory criteria for predicting bioavailability. SLOWPOKE neutron activation analysis of the iron powders showed that the carbonyl iron samples contained the lowest concentrations of elements producing short- and long-lived radioisotopes (24Na, 27Mg, 49Ca, 38Cl, 28A1, 66Cu, 56Mn, 52V, 101Mo, 51Cr, 122Sb, and 60Co) with the exception that the Mo content of one preparation was ca 2 times higher than in the other iron samples. Electrolytic iron contained higher levels of Na, Ca, Al, Cu, Mn, V, Sb, and Co than carbonyl iron. H2-, CO-, and NH3-reduced iron samples contained the highest levels of impurities, notably Na, Mg, Ca, CI, Al, Cu, Mn, V, and Cr.