Masaichi Nagayama

Spectrophotometric determination of iron(II) with 1,10-phenanthroline in the presence of large amounts of iron(III)

A study was made to establish proper conditions for the selective determination of Fe(II) by the 1,10-phenanthroline method in the presence of large amounts of Fe(III). It was shown that fe(III) is effectively masked by fluoride. The pH of the solution to be masked should be below 2.5 in order to prevent acceleration by the fluoride of aerial oxidation of Fe(II).

The effect of ferric hydroxide on the oxygenation of ferrous ions in neutral solutions

The oxygenation of Fe2+ ions in neutral solutions is accelerated by the reaction product, Fe(III) hydroxide, and by the addition of Fe(III) hydroxide. The reaction proceeds along two paths; one is the homogeneous reaction occurring in the solution and the other is the heterogeneous one taking place on the Fe(III) hydroxide. At constant pH and O2 concentration, the rate is expressed by −d[Fe2+]dt=(k+k′[Fe(III)]) [Fe2+]. The rate constant k for the homogeneous reaction is equal to ko [O2] [OH−]2 and k′ for the heterogeneous reaction is determined by ks,o [O2]K[H+]; ko and ks,o being the real rate constants for the two reactions and K being the equilibrium constant for the adsorption of Fe2+ on Fe(III) hydroxide. The catalytic effect of Fe(III) hydroxide for the oxygenation is discussed in detail.

Effect of anions on the oxygenation of ferrous ion in neutral solutions

Abstract The rate of oxygenation of ferrous ion was measured in neutral and slightly acidic solutions containing various anions. The reaction proceeded according to − d ( Fe II d t = κ( Fe II ) (O 2 ) (OH − ) 2 in solutions of ClO 4 − , NO 3 − , Cl − , H 3 SiO 4 − , Br − , I − and SO 4 2− , the rate constant, κ, decreasing in the order of anions as arranged above. Anions such as F − and H 2 PO 4 − were found to accelerate the reaction remarkably. The rate equations obtained were − d ( Fe II d t = κ F ( Fe II ) (O 2 ) (OH − ) (F − ) 2 and − d ( Fe II d t = κ P ( Fe II ) (O 2 (OH − ) (H 2 PO 4 − ) n , The value of n was 1 or 2 depending upon the concentration of the anion. The role of the respective anions in the oxygenation was explained by assuming that the complex of the anion with ferrous ion constitutes the reacting species. The type of rate equation was shown to be determined by the competition of the complex with FeOH + for O 2 OH − , the dissociated species of hydrated oxygen.

The determination of the porosity of anodic oxide films on aluminium by the pore-filling method

Abstract The validity of the pore-filling method proposed by Dekker and Middelhoek to measure pore-filling was performed in an aqueous solution of boric acid-borate (pH = 7.4, 20°C) by applying a constant anodic current of 0.5 mA/cm 2 . It was found that the borate-glycol solution adopted by Middlehoek is not suitable because of anodic decomposition of glycol. The transport numbers for Al 3+ and O 2− ions moving across the barrier layer were estimated to be 0.40 and 0.60, respectively. Using these values, the porosity of films anodically formed in a H 2 C 2 O 4 solution was determined. The time-variation in the porosity during chemical etching of a porous oxide was followed by this method. The results obtained were always consistent with those estimated by electron microscopy. In addition to the porosity, the thickness of the porous oxide up to 5000 A could be determined by the pore-filling method.

Distribution of Anions and Protons in Oxide Films Formed Anodically on Aluminum in a Phosphate Solution

Pure Al foil specimens were galvanostatically anodized in a neutral phosphate solution , and the thickness and composition profile of the formed oxide films were examined as functions of the anode potential and current density (c.d.). Analysis of the films was made by chemical sectioning with a solution, combined with (i) electron microscopy, (ii) x‐ray photoelectron spectroscopy, (iii) capacitance measurements, (iv) dc polarization measurements, and (v) solution analysis. The films were found to consist of two parts, an outer part containing and OH−ions, and an inner part consisting of pure alumina. The outer part dissolved in the solution at a rate faster than that of the inner part, and thus the two parts were clearly distinguished by following the time variations in the reciprocal of capacitance during the chemical sectioning. For films formed with a constant c.d., the thickness ratio of the two parts, , and the phosphate concentration in the outer part do not change with the anode potential or the total film thickness. With increasing c.d., the two values tend to increase. The mechanism controlling the anion and proton distribution in the oxide film is discussed.

Composition of barrier type oxide films anodically formed on aluminium in a neutral borate solution

Abstract 99.99% Al specimens were anodically oxidized in a boric acid-borate solution (pH = 7.4, 20°C) by applying a constant potential of 50 V( vs sce ). The oxide films formed were compact and had a thickness of about 76 nm. The distributions of Al(III), O(II), and B(III) ions in the films were determined by X-ray photoelectron spectroscopy and chemical analysis combined with chemical sectioning of the films in a sulfuric acid solution. It was ascertained that the film consists of two parts: the average composition of the outer part is AlO 1.36 (OH) 0.28 (B 2 O 3 ) 0.07 , and that of the inner part is AlO 1.5 (B 2 O 3 ) 0.027 . The outer part is slightly hydrated, and in sulfuric acid solutions it dissolves more rapidly than the inner part. Borate ions are distributed throughout the films with an average concentration of 5.8 wt% as B 2 O 3 .

The hydration of barrier oxide films on aluminium and its inhibition by chromate and phosphate ions

Abstract Compact oxide films were formed on aluminium in a neutral borate solution (pH 7.4, 20°C) by applying a constant potential of 50 V (SCE), and then immersed in distilled water, a 0.001 mol dm−3 chromate solution (pH 7.0), or a 0.001 mol dm−3 phosphate solution (pH 7.0). Changes in the composition profile of the oxide caused by the immersion were examined by X-ray photo-electron spectroscopy (XPS) combined with a film sectioning technique. After a 72 h immersion in distilled water, the OH− content in the outer part of the film increased to about three times as that before immersion, and the film sustained only 30 V instead of the initial 50 V. As the profile of BO2− ions remained unchanged, the deterioration of the film is exclusively due to hydration of the oxide caused by the penetration of water molecules or OH− ions into the oxide lattice. It was found that the hydration is strongly inhibited by chromate and phosphate. XPS and chemical analysis showed that CrO42− and PO43− ions adsorb on the oxide surface to form a mono- or bi-layer, hindering the penetration of water molecules. The inhibiting behaviour, stabilizing oxide films, is important in explaining the function of these anions as corrosion inhibitors for metals in near neutral solutions.

X-ray photoelectron spectra of hexavalent iron

Abstract Binding energies of Fe 3 p and Fe 2 p electrons for K 2 FeO 4 were measured and compared with those for γ-FeOOH, α-Fe 2 O 3 , and for metallic iron.

Dissolution of porous anodic oxide films onAl in (COOH)2 solutions

Abstract The dissolution of porous anodic oxide films formed on Al has been studied in (COOH) 2 solutions of different concentrations and temperatures. The rate of dissolution from the pore-walls v (cm/min) and that from the bottoms of pores v b (cm/min) were separately determined by measurement of the amount of dissolved Al ions in the solution and by electronmicroscopic examination of the film. It was demonstrated that the dissolution at the pore-base is enhanced by the applied electrical field across the barrier layer whereas the rate of dissolution from the pore-walls does not change at all even when the current is interrupted. The rate v is increased with the rise of solution temperature, the apparent energy of activation of the process being about 16 kcal/mole. An attempt has been made to explain the significance of the limiting thickness beyond which no further growth of the film is possible.

Effect of organic inhibitors on the polarization characteristics of mild steel in acid solution

Abstract The effect of inhibitors on the corrosion of iron in hydrochloric and sulphuric acids has been studied by a technique involving rapid polarization of the corroding metal. Tafel lines for the anodic and cathodic process have been obtained which can be used to interpret the mechanism of inhibitor action.