Katsuya Inouye

The effect of copper(II) on the formation of γ-FeOOH

Abstract Various γ-FeOOH samples have been synthesized by air oxidation of FeSO 4 solution with or without addition of Cu(II) (0–46 at.%Cu/Fe) and examined by X-ray diffraction, electron-microscopic observation, BET surface area determination, infra red absorption, DTA and chemical analyses. A destructive action of doped Cu(II) ions on the crystal formation was apparently recognized and discussed based on the crystallographic structure. The possible mechanism of crystallization of γ-FeOOH appears to differ between pure and Cu-doped γ-FeOOH, particularly one containing nearly 50%Cu.

The role of copper (II) in the oxidation of ferrous hydroxide colloid with special reference to the corrosion of iron in an SO2-containing environment

The properties of oxidation products of ferrous hydroxide colloid, precipitated with or without the presence of copper (II) ion, have been examined from the viewpoint that the degree of compactness, i.e., the secondary structure, of the products may be affected by copper doped in a certain range of content. The sedimentation volume of the colloid oxidized with a limited amount of air showed particular variations with the CuFe ratio; a remarkable minimum exists in the range of approximately 1% to 3% CuFe. The dimensions of primary colloidal particles composed of Fe(OH)2 and Fe3O4 minute crystals, revealed by X-ray diffraction and electron-microscopic observations, were apparently larger in the above region of copper content than in other regions where the colloids were more amorphous. The oxidized colloids were then dried to form layers of model corrosion products, and the permeability and diffusion of gases through the oxide layers showed that the oxides are compact in the low range of CuFe ratios. The mechanism of the effect of copper on the oxidation of Fe(OH)2 colloid and on the formation of a particular secondary structure is discussed.

Micropore filling of NO, SO2, NH3, and CO2 onα-FeOOH dispersed activated carbon fibers

Adsorption isotherms of NO, SO2, NH3, and CO2 onα-FeOOH dispersed activated carbon fibers at 303 K were examined to determine the role of surface modification in micropore filling. The parameters on micropore structures were obtained from both nitrogen adsorption at 77 K and benzene adsorption at 303 K; both isotherms were of BDDTI type and gave the same micropore volume. The preoxidation conditions of ACF, prior to the deposition ofα-FeOOH against the NO adsorptivity were examined. The dispersion ofα-FeOOH on ACF was effective in enhancement of micropore filling, irrespective of the adsorbate molecule. We determined the degree of volume filling for each gas by the use of a DR plot. The modified DR plot for an NO gas, of which the critical temperature was much lower than 303 K, was proposed. The degree of volume filling for various gases was correlated with the deviation of each boiling point from 303 K and with the van der Waalsa constant.

Electrical conductivity as a defect property of γ-FeOOH

The electrical conductivity of γ-FeOOH, pretreated under 10–3 Pa for 14 h at different temperatures (100–140°C), was determined over the temperature range from –170 to 140°C and at various frequencies (d.c., 200 Hz-10 MHz). The electrical conductivity increased remarkably as the pretreatment temperature was raised. The activation energy for conduction decreased with increases in the pretreatment temperature and with increasing frequency. The conductivity was also decreased considerably by exposing crystals to oxygen. The results are discussed in the framework of small polaron theory with respect to the formation of iron(II) caused by dehydration.

The mechanism of chemisorption of SO2 on iron (III) hydroxide oxides

Abstract Changes in electrical conductivity of synthetic α-, β- and γ-FeOOH crystals caused by reacting with SO 2 of 0.1–50 Torr at 30 and 50°C have been examined. The conductivity decrease of FeOOH observed after the exposure to 0.1–0.3 Torr SO 2 was followed by the conductivity increase at higher SO 2 pressure than 1 Torr. The equilibrium electrical conductivity of γ-FeOOH increased remarkably with the SO 2 pressure. For α- and β-FeOOH, no increase of conductivity with the SO 2 pressure was noticed. The mechanism of the conductivity changes fy SO 2 adsorption is discussed in relation to the surface structure of FeOOH. A possible correlation between the changes in electrical properties of FeOOH and the acceleration of atmospheric corrosion of steel by SO 2 is suggested.

Dynamic NO adsorption characteristics of iron-treated activated carbon fibers

Abstract The breakthrough curve for NO adsorption on the activated carbon fibers treated in iron salt solutions was determined. They can adsorb much more NO than granular activated carbon by a factor of more than 10 from a flowing 300 ppm NO-N 2 mixed gas at 100°C and 20 ml min −1 ; the most effective one of the iron-treated carbon fibers of 0.2 g is able to reduce the NO concentration from 300 ppm to 30 ppm. These adsorbents can adsorb the same amount of NO from even a 300 ppm NO-500 ppm SO 2 -10% CO 2 -10% H 2 O-1% O 2 -N 2 mixed gas.

The Adsorption of NO and SO2on Synthetic Jarosites

Potassium-, sodium-, rubidium-, ammoniumand hydronium jarosites have been synthesized to investigate the adsorption activity for mainly NO and S02 as typical atmospheric pollutants. The static measurements of the equilibrium adsorption were done at 303 K by the gravimetric method, and the selective adsorbability of NO from a simulated flue gas at 373 K by the flow-gasmethod. The results indicate that jarosites in general are promising as adsorbents for NO in particular. It has to be recognized, however, that the adsorption rate ofNO on jarosite is low and that the effective surface area is to be increased. The rate ofadsorption ofNO on jarosite derivatives appears to be influenced by the inter-lamellar spacing. The adsorbability of S02 on jarosites is not distinctive among other adsorbents. The properties ofjarosite have been discussed in the light of its crystallographic structure and the state of agglomeration.

Adsorption Activity of NO on Iron Oxide-Dispersed Porous Materials

Iron oxide-dispersed activated carbon fibers (ACF), granular activated carbons, zeolites, and silica gels have been prepared in order to develop good adsorbents for NO. The adsorption isotherms of NO on these samples have been measured at 303 K over an NO pressure range up to 80 kPa. The iron oxide-dispersed ACF samples (α- and β-ACF), obtained under the synthetic conditions employed for the preparation of α-FeOOH and β-FeOOH respectively, show very high adsorption activity for NO; their adsorption rates and capacities are much greater than those for untreated activated carbons, zeolites and silica gels. Furthermore, α- and β-ACF are effective in adsorbing NO from a 5 ppm NO/N2 gas mixture, reducing the concentration from 5 ppm to less than 1 ppm at 303 K after just one circulation with a flow velocity of 200 ml/min.

Fast chemisorption of NO and SO2 on FeOOH crystals

Abstract The electrical conductivity changes of α-, β- and γ-FeOOH by adsorption of NO and SO 2 during 1 ms-1 min were determined. The conductivity change consists of fast and slow processes which are presumably caused by fast chemisorption on the oxygen vacancies and by slow one on the surface anions. The rate constants of fast and slow chemisorption were determined from the conductivity changes. The correlations of the rate constants with the compression pressure of specimen, adsorption temperature and original electrical conductivity are given. The order of magnitude of the fast chemisorption rate constants of the three polymorphs is related to the difference in the surface structure.

Ferromagnetic Iron Oxides from Synthetic β ‐ FeOOH by Vacuum Thermal Decomposition

Le β-FeOOH synthetique est deshydrate a 300-500°C. Les proprietes magnetiques des produits obtenus sont mesurees. On montre que ce sont des oxydes de la serie Fe 3 O 4 contenant diverses quantites de Fe 2+ et avec une certaine quantite de α-Fe 2 O 3