Rust Compounds Research Articles

Influence of Cr(III) on the formation and transformation of corrosion products of steel in marine environments

A fundamental approach is used to better understand the influence of Cr on the resistance of low alloy steel to marine corrosion. It focuses on the formation and transformation of corrosion products of steel in seawater-like electrolytes. Fe(OH)2 precipitates are then prepared by mixing a solution of NaCl, Na2SO4·10H2O, FeCl2·4H2O or FeCl2·4H2O + CrCl3·6H2O (so that Cr = 8% and Fe = 92%), with a solution of NaOH. The initial concentration ratio of reactants, Q=frac{2[{{{rm{Fe}}}}^{2+}]+3[{{{rm{Cr}}}}^{3+}]}{[{{{rm{OH}}}}^{-}]}, is set at Q = 0.88, 1, and 1.136. In a first approach, the obtained aqueous suspension is stirred, at a controlled temperature of 25 ± 0.5 °C, to be oxidized by air. The resulting oxidation product is characterized by XRD and Raman spectroscopy. In a second approach, the Fe(OH)2 precipitates are aged one week in suspension in anoxic conditions, filtered, mixed as a wet paste with glycerol and set as a thin compact layer on the sample holder of a X-ray diffraction system. The oxidation process of Fe(OH)2 is then monitored in situ during the acquisition of the X-ray diffractogram. The obtained results demonstrate that Cr(III) hinders the formation of green rust compounds, hence hindering the formation of γ-FeOOH, i.e., the main oxidation product of green rust compounds. The other oxidation pathways of Fe(OH)2, which lead to Fe3O4 or α-FeOOH, are thus favored. Nevertheless, Cr(III) favors mainly the solid state transformation pathway of Fe(OH)2, thus promoting α-FeOOH via the formation of poorly ordered Fe(III) oxyhydroxides, namely feroxyhyte and ferrihydrite.

Cleaning iron rust compounds from cotton textiles: application to Qing Dynasty armor

A composite structure consisting of cotton fabric and iron sheet was widely used in Qing Dynasty armor. Due to iron sheet corroding easily, the surfaces of cotton fabric were covered with numerous rust compounds, which has a significant negative impact on the relics. In this paper, by taking Qing Dynasty armor relics as the research object, the cleaning process was reported for cotton fabrics stained with corrosion products. Using an orthogonal experiment, rust stained model samples were used to explore a specialized and efficient cleaning process. Results show that the cleaning reagents, including ascorbic acid (mass fraction 10.0 g/L), ethylenediaminetetraacetic acid disodium salt (EDTA-2Na, mass fraction 10.0 g/L), and the surfactant composed of 70% rhamnolipid and 30% alkyl glycoside (mass fraction 8.0 g/L), could fully exert a synergistic effect. After treatment, the color difference (ΔE) value between the cleaned sample and the unstained sample is only 3.81. A series of comprehensive experimental results demonstrate that the cleaning procedure is effective and safe. There are almost no rust compounds and cleaning reagent residues, and no damage to cotton fiber. The reported wet cleaning process, aided by soft bristle brush, achieved good cleaning results, indicating that the process can be used to clean rust stain pollutants in Qing dynasty cotton armor.

Fortification performance of polyurethane coating in outdoor historical ironworks

BackgroundIronworks in the tomb of Suleiman Pasha Al-Faransawi (located in the old Cairo, Egypt) were exposed in the open-air are susceptible to various corrosion factors, which be contingent on the environmental conditions wherein the artifacts are displayed and the existence of a protective layer or not. Examinations and analysis were conducted to identify the structure and type of the alloys used in making the decorative ironworks, to identify the manufacturing technique and decoration, and to study the nature of rust compounds. This has been achieved by using metallographic microscopy, X-ray diffraction, and a carbon–sulfur analyzer. Many protection approaches have been worked such as varnishes, waxes, and oils, but they have had many disadvantages. The aim of this paper is to assess the competence of polyurethane coating by using electrochemical measurements (electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization) in the fortification of ironworks exposed in the outdoor environment.ResultsThe results confirmed that the decorative ironworks were manufactured from wrought and gray cast iron. The main corrosion products identified by XRD are goethite, akageneite, and maghemite. Lead oxide hydrate refers to old lead paints (red primer) which have been applied to protect the ironworks. Quartz and calcite are the products of heavy dust particles that covered the surface.ConclusionThe data proved that the polyurethane is acting as a good protective coating for the decorative ironworks exposed in an uncontrolled environment. The 2% is considered as the recommended dose for this polymer for the minimum corrosion rate of the ironworks.

Influence of Mg2+ Ions on the Formation of Green Rust Compounds in Simulated Marine Environments

Green rust compounds (GR), i.e., Fe(II-III) layered double hydroxides, are important transient compounds resulting from the corrosion of steel in seawater. The sulfated variety, GR(SO42−), was reported as one of the main components of the corrosion product layer, while the chloride variety, GR(Cl−), was more rarely observed. The carbonate variety, GR(CO32−), is favored by an increase in pH and forms preferentially in the cathodic areas of the metal surface. Since Mg(II) is abundant in seawater, it may have a strong influence on the formation of GR compounds, in particular as it can be incorporated in the hydroxide sheets of the GR crystal structure. In the present work, the influence of Mg2+ on the precipitation reaction of GR(SO42−) was investigated. For that purpose, Mg2+ was substituted, partially or entirely, for Fe2+. The GR was then prepared by mixing a solution of FeCl3·6H2O, Na2SO4·10H2O, NaCl, FeCl2·4H2O and/or MgCl2·4H2O with a solution of NaOH. The precipitation of the GR was followed or not by a 1-week aging period. The obtained precipitate was characterized by X-ray diffraction. It was observed that Mg(II) favored the formation of chloride green rust GR(Cl−) and magnetite Fe3O4 at the detriment of GR(SO42−). The proportion of GR(Cl−) and Fe3O4 increased with the Mg(II):Fe(II) substitution ratio. Without Fe(II), the precipitation reaction led to iowaite, i.e., the Mg(II)-Fe(III) compound structurally similar to GR(Cl−). It is forwarded that the presence of Mg2+ cations in the hydroxide sheets of the GR crystal structure is detrimental for the stability of the crystal structure of GR(SO42−) and favors the formation of other mixed valence Fe(II,III) compounds.

Electrochemical behavior of thick rust layers on steel artefact: Mechanism of corrosion inhibition

The electrochemical behavior of aged corrosion layers (CL) on artefact was studied, in corrosive reference water without and with non-toxic corrosion inhibitors such as decanoate ions and flavonoids compounds, constituting the condensed tannins, such as catechin. Electrochemical impedance spectroscopy measurements on the metal/CL system and voltammetric studies of FeOOH phases on carbon paste electrode show that the corrosion inhibition mechanism is mainly based on the blocking of the dissolution of FeOOH-type phase and the decrease of the diffusion of ionic species in the pores network of CL. Indeed, the formation of iron decanoate, revealed by X-ray diffraction and microscopic observation, inhibits the electrochemical activity of FeOOH-type phases and blocks the electrochemical dissolution of FeOOH into Fe2+ cations. On the other hand, the catechin compound modifies the surface of rust compounds into a blue-black compound, but this modification has a poor influence on the electrochemical activity of FeOOH-type compounds.

Evolution of the Rust Layers Formed on Carbon and Weathering Steels in Environment Containing Chloride Ions

To clarify the correlation between alloy elements and growth pattern of the rust layers, the rusting evolution of the carbon and weathering steels was investigated by using the gold markers method. The corrosion experiments were carried out in a simulated environment containing chloride ions. The results indicate that Ni, Cu, Cr and Mo elements in the weathering steel suppress the rust crystallization and impede the rust layer growth to an internal development, and the suppression function benefits the formation of a protective rust layer. Moreover, γ-FeOOH is mainly located in the outer rust layer, while β-FeOOH is mainly located in the inner rust layer, and the distribution of the rust compounds in the rust layer is closely related to the growth pattern of the rust layer.

An Experimental Study to Evaluate the Effect of Different Concentrations of Iron Rust Compounds on the Growth and Morphology of some Wood Degrading Fungi

An Experimental Study to Evaluate the Effect of Different Concentrations of Iron Rust Compounds on the Growth and Morphology of some Wood Degrading Fungi

Determination of standard Gibbs free energy of formation of green rusts and its application to the Fe(II–III) hydroxy-oxalate

The oxalate green rust GR(C2O42−) is obtained by oxidation of aerated aqueous suspensions of Fe(OH)2 precipitated from Fe(II) oxalate and NaOH solutions. The standard Gibbs free energy of formation of GR(C2O42−) is determined from redox potential measurements. The influence of O2/H2O redox couple is carefully studied and its impact on previous determinations of Gibbs free energy of various green rust compounds, namely GR(SO42−), GR(Cl−) and GR(CO32−), is discussed. Moreover, the ΔG°f values of GRs are given for hydrated compounds. The competitive formation of GR(C2O42−) and GR(SO42−) is studied similarly via the oxidation of Fe(OH)2 in aqueous media containing both C2O42− and SO42− anions. In the experimental conditions considered here, GR(C2O42−) forms preferentially, even when the sulphate ions are predominating in the solution. This indicates that oxalate ions may be preferred to sulphate for the building of a GR structure.

Role of sulphate ions on the formation of calcareous deposits on steel in artificial seawater; the formation of Green Rust compounds during cathodic protection

Cathodic protection of steel in seawater could be optimized by taking into account the calcareous deposits forming on the steel surface. The aim of this work was to study the influence of sulphate ions on the kinetics and mechanisms of formation of these deposits. The experiments were performed at 20 °C, with an applied potential of −1.0 V/saturated calomel electrode (SCE), in artificial seawater-like solutions with various SO 4 2− concentrations. The deposition was monitored by chronoamperometry and electrochemical impedance spectroscopy (EIS). Micro-Raman analyses were performed in situ in a specific electrochemical cell to identify the solids forming on the steel surface. It could be demonstrated that sulphate ions had an important effect on the formation of both Ca(II)- and Mg(II)-containing phases. In the solution enriched with sulphate ions, the deposition of CaCO 3 was almost totally inhibited. Experiments performed in Ca 2+-free solutions demonstrated that the Mg-based deposit was, in contrast, favoured by the increase of the sulphate concentration. In situ Raman spectra of the solid forming at the early stages of the cathodic protection proved to be characteristic of Green Rusts (GRs). This compound was favoured by the presence of Ca 2+ and/or Mg 2+ cations, and is more likely a GR-like M(II)-Fe(III) hydroxysulphate, with M = Fe, Mg and Ca.

XPS study of Fe(II)Fe(III) (oxy)hydroxycarbonate green rust compounds

AbstractThe oxidation behaviour of Fe(II)Fe(III) hydroxysalt green rust (GR) compounds was investigated using XPS. Stoichiometric GR(CO32−), i.e. Fe(II)4Fe(III)2(OH)12CO33H2O was prepared by co‐precipitating Fe(II) and Fe(III) ions in carbonate‐containing solution under an inert atmosphere. Fast oxidation of stoichiometric GR(CO32−) by hydrogen peroxide in aqueous medium resulted in GR(CO32−)* of various composition, i.e. Fe(II)6(1−x)Fe(III)6xO12H2(7−3x)CO3 with 1/3 ≤ x ≤1, where x is the Fe(III) molar fraction [Fe(III)]/[Fe(total)] of positively charged hydroxide sheets. The Fe(2p3/2) spectra of GRs of various composition were well fitted using Gupta and Sen multiplet peaks and additional broad satellite and surface features. The oxidation of Fe(II) in the GR structure is accompanied by deprotonation of hydroxyl groups as evidenced by the O(1s) spectra. The deprotonation of the hydroxyl groups compensated for the presence of excess positive charge that resulted from the oxidation of Fe(II) in the GR structure. In addition, the fully ferric GR(CO32−)* at x = 1 was coated on a sand substrate and the quality of the GR coating was investigated by XPS imaging. Copyright © 2008 John Wiley & Sons, Ltd.

Heterotrophic/autotrophic denitrification (HAD) of drinking water: prospective use for permeable reactive barrier

This work aims to explore the use of an innovative denitrification process developed by our group for groundwater remediation. This process is coupling heterotrophic-autotrophic denitrification processes (HAD) supported by cotton and zero-valent iron (ZVI). In the experimental part, the effect of two amounts of ZVI (150 and 300 g), two nitrate (100 and 220 mg/l) and phosphate (3 and 6 mg/l) inlet concentrations on nitrate removal performance is investigated in two parallel continuous fed plug-flow reactors. The possible in-situ application of the proposed system in permeable reactive barriers (PRB) is further discussed. The HAD showed higher volumetric nitrate removal ratio (VNR) than the cotton supported heterotrophic denitrification one, and VNR increased with the amount of ZVI packed in the reactors. Ammonium production by the reductive action of iron was kept on acceptable level adjusting the contact time between water and ZVI. Iron release from ZVI decreased with time to negligible value (<0.5 mg/l) thanks to the formation of iron green rust compounds (GR). The HAD seems to be adequate for PRB systems, because both cellulose-based material and ZVI have been used in reactive trench for site remediation. Moreover, the proposed process could have the function for removal of nitrate and priority pollutants, such as chlorinated ethenes, simultaneously.

Synthesis and characterisation of the Fe(II–III) hydroxy-formate green rust

A new methodology was envisioned in order to prepare green rust compounds build on organic anions that could intervene in microbiologically influenced corrosion processes of iron and steel. The formate ion was chosen as an example. The formation of rust was simulated by the oxidation of aqueous suspensions of Fe(OH)2 precipitated from Fe(II) lactate and sodium hydroxide, in the presence of sodium formate to promote the formation of the corresponding green rust. The evolution of the precipitate with time was followed by transmission Mossbauer spectroscopy at 15 K. It was observed that the initial hydroxide was transformed into a new GR compound. Its spectrum is composed of three quadrupole doublets, D 1 (δ=1.28 mm s−1, Δ=2.75 mm s−1) and D 2 (δ=1.28 mm s−1, Δ=2.48 mm s−1) that correspond to Fe(II) and D 3 (δ=0.49 mm s−1, Δ=0.37 mm s−1) that corresponds to Fe(III). The relative area of D 3, close to the proportion of Fe(III) in the GR, was found at 28.5±1.5% (∼2/7). Raman spectroscopy confirmed that the intermediate compound was a Fe(II–III) hydroxy-formate, GR(HCOO−).

In situ micro-Raman spectroscopy to investigate pitting corrosion product of 1024 mild steel in phosphate and bicarbonate solutions containing chloride and sulfate ions

The nature of the corrosion products generated by localized attack on 1024 mild steel have been investigated in the presence of chloride and/or sulfate ions in bicarbonate and phosphate aqueous solutions. A spectroelectrochemical cell was used for in situ measurements of the Raman spectra of the corrosion products generated during pitting. These products were identified as the so-called green rust compounds. The assignment of the hydroxyl groups in green rust is confirmed by isotopic substitution. The composition of the green rust generated in bicarbonate or phosphate solution containing chloride and/or sulfate ions has been determined. A correlation between the green rust composition and the electrochemical behaviour after the initiation of pitting has been noted and discussed.

Preparation and E h --pH diagrams of Fe(II)--Fe(III) green rust compounds; hyperfine interaction characteristics and stoichiometry of hydroxy-chloride, -sulphate and -carbonate

Fe(II)--Fe(III) hydroxy-chloride, -sulphate and -carbonate were prepared by oxidation of a ferrous hydroxide precipitate in anion-containing aqueous solutions. The compounds are characterized by monitoring the redox potential Eh and the pH of stochiometric suspension vs time with the appropriate concentration ratios. X-ray diffraction allows us to characterize the crystal structure by distinguishing “green rust one” (GR1) from “green rust two” (GR2). Since green rusts (GRs) are of a pyroaurite-sjogrenite-like structure, i.e., consisting of intercalated foreign anions and water molecules in the interlayers between the brucite-like layers of Fe(OH)2, their chemical formulae can be determined from the Mossbauer spectra. Three quadrupole doublets are observed: D1 and D2 correspond to a ferrous state with isomershift IS of about 1.27 mm s-1 and quadrupole splittings QS of about 2.85 and 2.60 mm s-1, respectively, whereas D3 corresponds to a ferric state with IS and QS of about 0.4 mm s-1. The hyperfine parameters of these doublets are similar from one green rust to another but their intensity ratios vary considerably. Finally, Eh and pH equilibrium diagrams of the Fe species in the presence of chloride, sulphate and carbonate anions contained within the water solution are drawn and the thermodynamic conditions of existence and degrees of oxidation of green rusts are discussed.

The anionic species competition in iron aqueous corrosion: Role of various green rust compounds

In the presence of various anions such as Cl −, SO 4 2− or CO 3 2−, aqueous suspensions of ferrous hydroxide Fe(OH) 2 usually oxidise into ferric oxyhydroxides via an intermediate Fe(II)Fe(III) hydroxy-salt designated as Green Rust (GR), e.g. GR1(Cl −), GR2(SO 4 2−) or GR1(CO 3 2−). First, the competition between SO 4 2− and CO 3 2− was studied by oxidising Fe(OH) 2 in the simultaneous presence of both anions. It appears that GR1(CO 3 2−) forms preferentially and GR2(SO 4 2−) is clearly observed only when the amount of carbonate anions is not sufficient to transform all the initial ferrous hydroxide. Then a mixture of both GRs is obtained. This confirms the affinity that pyroaurite-type layered hydroxides such as GRs exhibit for CO 3 2− anions, amongst any other type. This statement is supported by a theoretical approach based on the thermodynamic constants previously determined for GRs. Secondly, the possibility that a GR compound can oxidise into another one was definitively established. When SO 4 2− or CO 3 2− are provided, GR1(Cl −), owning an average oxidation number for Fe of + 2.25, oxidises into GR2(SO 4 2−) or GR1(CO 3 2−), compounds owning a larger oxidation number for Fe of + 2.33. The indirect oxidation process via a GR compound always takes place rather than a direct process into ferric oxyhydroxides.

Abiotic Nitrate Reduction to Ammonium: Key Role of Green Rust

Leaching of nitrate from soils and sediments can be reduced in anoxic environments due to denitrification to N2O/N2 or reduction of nitrate to ammonium. While microbial dissimilatory reduction of nitrate to ammonia is well known, it is shown here that this conversion can also proceed at appreciable rates in abiotic systems in the presence of green rust compounds [FeII4FeIII2(OH)12SO4·yH2O]. In the reaction nitrate is stoichiometrically reduced to ammonium, and magnetite (Fe3O4) is the sole Fe-containing product. At a constant pH of approximately 8.25 and 25 °C, the rate expression is given as: d[NH4+]/dt = k[Fe(II)]GR[NO3-],where k = 4.93 × 10-5 ± 0.39 × 10-5 L mol-1 s-1. In anoxic soils and sediments, this reaction may also lead to a nitrate to ammonium reduction, at rates of similar magnitude or even higher than microbial reduction rates. Hence green rust should be considered a possible important reductant for nitrate reduction to ammonium in subsoils, sediments, or aquifers where microbially mediated reduction rates are small.