Composition and structure of iron oxidation surface layers produced in weak acidic solutions

Remarkable influence of surface composition and structure of oxidized iron layer on orange I decomposition mechanisms

“…This band changes shape and is shifted to lower frequency from a position at 923 cm −1 after 15 min to 904 cm −1 after 45 min of reaction. Very similar reflection spectra of iron were reported recently after interaction of iron with water at the same pH [22]. The broad band at around 900 cm −1 is assigned to the formation of Fe(OH) 2 , and the observed changes in the recorded spectra with reaction time most probably result from variations in the degree of iron hydroxide polymerization.…”

“…4B) and those without orange performed in similar conditions [22] shows that in both cases lepidocrocite is the only detected surface product. Moreover, the amount of lepidocrocite found on iron is about 15 times higher after 15 min in the case of orange reduction compared to experiments without orange, and 50% higher after 45 min.…”

“…At pH 3 and 30 • C the types and amounts of surface products (i.e., mixture of FeO and Fe(OH) 2 ), formed on the iron surface are almost exactly the same with orange ( Fig. 4A) and without orange [22].…”

“…The amount of lepidocrocite increases with reaction time forming a very thick surface layer. The quantitative evaluation, based on infrared spectroscopic data and the spectral simulation, was carried out as reported recently [22] and indicates that lepidocrocite is produced during orange I decomposition reactions. This oxy-hydroxide covers the iron surface with a 30-nm layer after 15 min, a 1-µm layer after 45 min, and 2.7-µm-high patches covering 40% of the surface with a 0.9-µm layer on the rest of the surface after 3 h.…”

“…Our previous studies [22] show that the iron surface is always covered by a layer of iron oxides and hydroxides or oxyhydroxides even at acidic pH. At pH 3, the iron surface is covered by a thin layer of polymeric Fe(OH) 2 mixed with FeO, whereas at pH 5 total oxidized iron is cumulated on the iron surface in the form of lepidocrocite (γ -FeOOH).…”