Initial Corrosion Product Research Articles

Corrosion product formation on Zn55Al coated steel upon exposure in a marine atmosphere

The formation of corrosion products on Zn55Al coated steel has been investigated upon field exposures in a marine environment. The corrosion products consisted mainly of zinc aluminium hydroxy carbonate, Zn 0.71Al 0.29(OH) 2(CO 3) 0.145· xH 2O, zinc chloro sulfate (NaZn 4(SO 4)Cl(OH) 6·6H 2O), zinc hydroxy chloride, Zn 5(OH) 8Cl 2·H 2O and zinc hydroxy carbonate, Zn 5(OH) 6(CO 3) 2 were the first three phases were formed initially while zinc hydroxy carbonate Zn 5(OH) 6(CO 3) 2 was formed after prolonged exposure in more corrosive conditions. The initial corrosion product formation was due to selective corrosion of the zinc rich interdendritic areas of the coating resulting in a mixture of zinc and zinc aluminium corrosion products.

Synthesis and Structures of Pb3O2(CH3COO)2·0.5H2O and Pb2O(HCOO)2: Two Corrosion Products Revisited

Reactions of carboxylic acids with lead play an important role in the atmospheric corrosion of lead and lead-tin alloys. This is of particular concern for the preservation of lead-based cultural objects, including historic lead-tin alloy organ pipes. Two initial corrosion products, Pb(3)O(2)(CH(3)COO)(2)·0.5H(2)O (1) and Pb(2)O(HCOO)(2) (2), had been identified through powder diffraction fingerprints in the Powder Diffraction File, but their structures had never been determined. We have crystallized both compounds using hydrothermal solution conditions, and structures were determined using laboratory and synchrotron single-crystal X-ray diffraction data. Compound 1 crystallizes in P1, and 2 in Cccm. These compounds may be viewed as inorganic-organic networks containing single and double chains of edge-sharing Pb(4)O tetrahedra and have structural similarities to inorganic basic lead compounds. Bond valence sum analysis has been applied to the hemidirected lead coordination environments in each compound. Atmospheric exposure experiments contribute to understanding of the potential for conversion of these short-term corrosion products to hydrocerussite, Pb(3)(CO(3))(2)(OH)(2), previously identified as a long-term corrosion product on lead-rich objects. Each compound was also characterized by elemental analysis, thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), and Raman spectroscopy.

A Mechanism for the Atmospheric Corrosion of Copper Determined by Voltammetry with a Strongly Alkaline Electrolyte

A recently developed voltammetric technique using a strongly alkaline electrolyte was successfully applied to clarify a corrosion mechanism of copper under atmospheric conditions. In contrast to conventional potentiometric methods with neutral or weak alkaline electrolytes (e.g., 0.1 M KCl), the developed method could give qualitative and quantitative information about the corrosion products of copper, including oxides (i.e., and CuO) and hydroxide . In the presence of water under such atmospheric conditions, was the initial corrosion product formed on a copper surface. However, the surface layer did not grow much but dehydrated to become a layer of CuO. The thus-formed CuO layer grew until it became several molecules thick . For further progress of corrosion, an inner layer was generated by the proportionation reaction between the CuO layer and the base metal Cu. The inner layer grew for the subsequent oxidation until the thickness reached a certain value . For further oxidation, the top CuO layer grew again preferentially over the inner layer.

Influence of carbon content and microstructure on corrosion behaviour of low alloy steels in a Cl − containing environment

Corrosion behaviour of low alloy steels (A and B) with different carbon content was studied by a salt fog test and an outdoor test. A commercial weathering steel 09CuPCrNi was used for comparison. The corrosion resistance of steels A and B with homogeneous microstructures was better than that of the commercial weathering steel 09CuPCrNi in the salt fog test. Steel A with an ultra-low-carbon content had far less weathering resistance than the other steels in the outdoor test. Selective corrosion of large pearlite produces stress in initial corrosion product films. Uniform corrosion product films with few cracks tend to form on homogeneous microstructures such as ferrite and bainite, and this is advantageous for the formation of a compact rust layer in the initial stage of atmospheric corrosion. However, uniform microstructures will result in over even interfaces between rust layers and bases, which will lead to frequent peeling of rust layers from bases because stress is induced by large temperature fluctuations and wet-dry alternations. Protection of the rust layer on a low alloy steel is dependent on the rust density and the bonding performance of the rust-base rather than the proportion of the rust phase in the initial stage of atmospheric corrosion. These results indicate that homogenous microstructures, proper amounts of carbon content and fine carbon-rich phases that are produced by appropriate processes are beneficial for the corrosion resistance of steels.

Conversion electron Mössbauer spectroscopy study of growth and nature of corrosion products on mild steel exposed to different environments

In this study, conversion electron Mossbauer spectroscopy (CEMS) has been utilized for identifying the nature of initial corrosion products formed on the surface of steel under different environments and measurement of relative thickness of corrosion products formed. CEMS studies on mild steel exposed under different environments, viz. mild steel sprayed with (1) distilled water (2) 3% NaCl and (3) mild steel exposed to SO2 were carried out. The initial stable product of corrosion is found to be γ-FeOOH, which will transform into other oxyhydroxides and oxides, depending on environments. The mechanisms for the corrosion processes occurring under different conditions are also discussed.

Atmospheric corrosion of mild steel in Oman

A systematic study has been made of the initial corrosion products which form on mild steel capons exposed near the coastal region of Oman and at some industrial areas. The phases and compositions of the products formed at different periods of exposure were examined by using Mossbauer spectroscopy (295 and 78 K) and X-ray diffraction (XRD) techniques. The results show that lepidocorcite and maghemite are early corrosion products and goethite starts to form after 2 months of metal exposure to the atmosphere. Akaganeite is an early corrosion product but it forms in marine environments only, which reflects the role of chlorine effect in the atmosphere. The 12 months coupons showed the presence of goethite, lepidocorcite and maghemite, but no akaganeite being seen in the products of one of the studied areas.

1-エチル-3-メチルイミダゾリウムブロミドを用いて作製したZn-Mg合金めっきの耐食性

The corrosion resistance of Zn-Mg alloy plated steel prepared by the electrodeposition from 1-ethyl-3-methylimidazolium bromide (EMIB) based ionic liquid was investigated in 5mass% NaCl aqueous solution at 35oC. The first red rust generation time of Zn-Mg alloy plated steel containing more than 2.5mol% of Mg was about 20 weeks independently of the Mg content. The corrosion resistance of Zn-Mg alloy plated steel was about 20 times higher than that of Zn plated steel. The excellent corrosion resistance of the Zn-Mg alloy plating is due to the fact that the fine and insulating initial corrosion product ZnCl2•4Zn(OH)2•H2O is formed on the Zn-Mg alloy plating and Mg suppresses the cathodic reaction of corrosion and the formation of ZnO, which causes the corrosion of plating and steel. As a result, the effect of sacrificial protection of the Zn-Mg alloy for steel continues for a long time, and the corrosion resistance is improved.

Atmospheric corrosion of copper and the colour, structure and composition of natural patinas on copper

This paper describes the results of atmospheric corrosion testing and of an examination of patina samples from Brisbane, Denmark, Sweden, France, USA and Austria. The aim was threefold: (1) to determine the structure of natural patinas and to relate their structure to their appearance in service and to the atmospheric corrosion of copper; (2) to understand why a brown rust coloured layer forms on the surface of some copper patinas; (3) to understand why some patinas are still black in colour despite being of significant age. During the atmospheric corrosion of copper, a two-layer patina forms on the copper surface. Cuprite is the initial corrosion product and cuprite is always the patina layer in contact with the copper. The growth laws describing patina formation indicate that the decreasing corrosion rate with increasing exposure time is due to the protective nature of the cuprite layer. The green patinas were typically characterised by an outer layer of brochantite, which forms as individual crystals on the surface of the cuprite layer, probably by a precipitation reaction from an aqueous surface layer on the cuprite layer. Natural patinas come in a variety of colours. The colour is controlled by the amount of the patina and its chemical composition. Thin patinas containing predominantly cuprite were black. If the patina was sufficiently thick, and the [Fe]/[Cu] ratio was low, then the patina was green, whereas if the [Fe]/[Cu] ratio was approximately 10 at%, then the patina is rust brown in colour. The iron was in solid solution in the brochantite, which might be designated as a (copper/iron) hydroxysulphate. In the brown patinas examined, the iron was distributed predominately in the outermost part of the patina.

Comparative atmospheric corrosion of primary and cold rolled copper in Australia

Atmospheric corrosion tests, according to ASTM G50, have been carried out in Queensland, Australia, at three different sites representing three different environmental conditions. A range of materials including primary copper (electrosheet) and electrolytic tough pitch (traditional cold rolled) copper have been exposed. Data is available for five exposure periods over a three year time span. X-Ray Diffraction has been used to determine the composition of the corrosion products. Corrosion rates have been determined for each material at each of the exposure sites and are compared with corrosion rates obtained from other long term atmospheric corrosion test programs. Primary copper sheet (electrosheet) behaves like traditionally produced cold rolled copper (C11000) sheet but with an increased corrosion rate. This difference between the rolled copper samples and the primary copper samples is probably due to a combination of factors related to the difference in crystallographic texture of the underlying copper, the morphology and texture of the cuprite layer, the surface roughness of the sheets, and the differences in mass. These factors combine together to provide an increased oxidation rate and TOW for the electrosheet material and which is significantly higher at the more “tropical” sites. For a sulfate environment (Urban) the initial corrosion product is cuprite with posnjakite and brochantite also occurring at longer exposures. Posnjakite is either “washed away” or converted to brochantite during further exposure. The amount of brochantite increases with exposure time and forms the blue-green patina layer. For a chloride environment (Marine) the initial corrosion product is cuprite with atacamite also occurring at longer exposures.

Use of ion implantation to study the corrosion of an austenitic steel in an oxidizing/sulphidizing atmosphere

AbstractThe beneficial effect of the addition by ion implantation of cerium on the corrosion behaviour of a 32Ni‐20Cr austenitic steel in a mixed oxidizing/sulphidizing environment, at 700 °C has been studied. Emphasis was placed on the initial stages of the corrosion process using a wide range of surface analytical techniques. Comparison is made with unimplanted material and also with xenon‐ and chromium‐implanted steel. The latter had no significant effect. In contrast Ce ion implantation improved the corrosion behaviour, which is probably due to a change in the nucleation stage of corrosion, leading to an improved quality of the oxide layer forming under the initial corrosion products. Factors which might contribute to this are discussed.

Effects of Recrystallization on Time Variant Sorption of Radionuclides onto Steel Corrosion Products

ABSTRACTCorrosion products resulting from the oxidation of steel containers and iron-containing waste can alter the local geochemical environment in radioactive waste disposal vaults and trenches. In addition, corrosion products can enhance the retention of radionuclides by providing a highly sorptive media. Initial hydrous corrosion products are poorly crystalline with large surface area, high sorption capacity, and large Kds. Over time, corrosion products recrystallize by step-wise dehydration to phases with significantly smaller surface areas. The decreased surface area results in decreased sorption and the potential for remobilization of previously sorbed radionuclides. The impact of time-dependent variation in sorption on radionuclide transport is a complex function of the rate of recrystallization and the radionuclide half-life.A mathematical model has been developed, which coupling mass transport with corrosion product recrystallization and equilibrium sorption of radionuclides. The model is applied release of radionuclides with a range of half-lives (year to 100,000s of years) from radioactive waste disposal facilities to illustrate the significance of corrosion product recrystallization on release.

The corrosion of uraninite under oxidizing conditions

Abstract Uraninite is the most common uranium mineral, which, because of chemical and structural similarities to synthetic UO 2, is a useful natural analogue for UO 2 in spent fuel. Uraninite, however, contains “impurities” such as Pb, Ca, Si, U 6+, Th, Zr, and lanthanides. These affect the thermodynamic properties of uraninite, the rate of uraninite alteration, and the composition of the corrosion products. Uraninite can contain a significant amount of radiogenic Pb, and the Pb-uranyl oxide hydrates (Pb-UOH) are the most common corrosion products formed by the oxidative alteration of Pb-bearing uraninites. Incongruent alteration of the Pb-UOHs in natural waters produces increasingly Pb-enriched uranyl phases, effectively reducing the amount of U lost from the corrosion rind. This is not true of other uranyl oxide hydrates, such as schoepite, UO 3 · H 2O, or becquerelite, CaU 6O 19 · 11H 2O, which can dissolve completely under similar geochemical conditions. The most common end product of Pb-UOH alteration is curite. Curite may provide surface nucleation sites for certain uranyl phosphates, thereby enhancing their formation. Uranyl phosphates are generally less soluble than other uranyl phases. In the absence of Pb, schoepite and becquerelite are the common initial corrosion products. The reaction path for the alteration of Pb-free uraninite results in the formation of uranyl silicates, which are generally more soluble than the uranyl phosphates. Thus, the long-term oxidation behavior for ancient, Pb-bearing uraninite is different from young, Pb-free uraninite. Because the presence of Pb effectively reduces the mobility of uranium in oxidizing waters, the concentration of uranium in ground waters associated with oxidized uranium ore deposits will depend in part on the age of the primary uraninite.

Alteration of Natural Uranyl Oxide Hydrates in Si-Rich Groundwaters: Implications For Uranium Solubility

ABSTRACTThe uranyl oxide hydrates are common initial corrosion products of uraninite (nominally U02+x) during weathering. In the presence of dissolved silica these early-formed phases alter to uranyl silicates (most commonly soddyite, U2SiO8-2H2O, and uranophane, CaU2Si2O11·6H2O). Uraninite, however, usually contains radiogenic Pb, and the earlyformed Pb-poor uranyl oxide hydrates alter incongruously to uranyl silicates plus Pb-enriched uranyl oxide hydrates such as curite. Similar to dissolved silica, radiogenic Pb may also serve to limit the mobility of U in nature by fixing U in solid phases. Curite may also play an important role in the formation of uranyl phosphates, which are significantly less soluble than the uranyl silicates, and control U solubility in many groundwaters associated with altered U ore.

Effect of surface preparation of corrosion of mild steel in 1.0M hydrochloric acid

Chemical states of iron compounds produced on a steel surface, which was exposed to H2S(0.86 vol%)-N2(99.14 vol%) environment, were analysed and the variation of iron sulfides formed with the advance of corrosion was experimentally clarified. In the environment, FeS1−x (mackinawite) was formed as an initial corrosion product and it transformed to Fe3)S4 (greigite). Further FeS1−x, formed at the initial stage of corrosion, was oxidised to γ-FeOOH in the water-saturated air. The production of FeS1−x was faster in the H2 S(0.86 vol%)-O2(20.0 vol%)-N2(79.14 vol%) environment (relative humidity 100%).

Chemical state analysis of corrosion products on a steel in H 2S-N 2 and H 2S-O 2-N 2 environment by means of conversion electron Mössbauer spectrometry

Chemical states of iron compounds produced on a steel surface, which was exposed to H 2S(0.86 vol%)-N 2(99.14 vol%) environment, were analysed and the variation of iron sulfides formed with the advance of corrosion was experimentally clarified. In the environment, FeS 1− x (mackinawite) was formed as an initial corrosion product and it transformed to Fe 3)S 4 (greigite). Further FeS 1− x , formed at the initial stage of corrosion, was oxidised to γ-FeOOH in the water-saturated air. The production of FeS 1− x was faster in the H 2 S(0.86 vol%)-O 2(20.0 vol%)-N 2(79.14 vol%) environment (relative humidity 100%).

Microstructural study of initial corrosion product of aluminium-brass alloy after exposure to natural seawater

The study made direct use of analytical scanning transmission electron microscopy, to examine the morphology, crystalline structure and chemical composition of the corrosion product formed in the very first stage of exposure of an aluminium-brass alloy to a natural seawater environment. The technique uniquely allowed a recording of the microstructural changes taking place while the corrosion product was undergoing dehydration directly after its removal from the wet corrosive environment. Two forms of corrosion products were observed; fibre and film type. It was found that the products were liable to develop a crystalline structure with progressive drying. The chemical composition of the products depended strongly on exposure time to seawater environment. It is believed that the fibrous nature of the corrosion product arises from the extrusion of an initially formed gel through a semi-permeable membrane.

Corrosion of Copper and Brass: Non-Stoichiometric Mixed-Valence Oxides

During the course of studies of the corrosive effects of specific dissolved ions on copper and brass, persistent indications were found that the initial corrosion products did not conform to the simple cuprous and cupric oxides. Visual examination showed corrosion to be highly inhomogeneous, ranging from red to black or blue-black, with the red product commonly in sweeping, feather- like patches or spots. Reflection electron diffraction patterns did not show a simple correspondence: black = CuO and red = CU2O. Many black samples gave diffraction patterns for the red copper oxide, CU2O, although some had CuO patterns. Many of the CU2O patterns contained extra peaks, and preferred orientation was especially common in the brass samples (Figures 1 and 2, Table 1).

Dissolution of iron during the initial corrosion of carbon steel in aqueous H2S solutions

The dissolution of iron from carbon steel in aqueous H2S solutions has been studied as a function of time and temperature at 0.1 MPa H2S pressure using the rotating disc technique. The iron sulfide film formed on the disc surface has been identified by X-ray diffraction analysis. The solubility and dissolution rate of synthesized mackinawite, FeS(1−x), have also been determined to help establish the mechanism of release of iron from carbon steel corroding in aqueous H2S solutions.The rate data have been analysed by an equation for a joint chemical and transport controlled process. At 22 °C and 0.1 MPa H2S, the maximum rate of release of Fe2+, obtained by extrapolating the data to infinite rotation speed, is 7.4 ± 0.5 μmol/m2s. This is similar to the dissolution rate determined for synthesized mackinawite powders, but is 20 times faster than the rate of dissolution for troilite and more than 1000 times faster than the dissolution rates for pyrrhotite and pyrite. Thus, troilite and iron sulfide phases that form subsequently are not major contributors to Fe2+ release during the corrosion of carbon steel.At 22 °C the diffusion coefficient for the FeSH+ ion is (1.4 ± 0.2) × 10−9 m2/s and the activation energy of the diffusion process is 25 ± 7 kJ/mol. The chemical reaction occurring at the surface has an activation energy of 77 ± 14 kJ/mol.It is concluded that the release of iron from corroding carbon steel is governed by the dissolution rate of mackinawite, the initial corrosion product. This dissolution is controlled by the chemical reaction between mackinawite and H+ and by the transport of the complexed FeSH+ from the interface to the bulk solution.

Iron Sulfides Formed from Aqueous Solution at Low Temperatures and Atmospheric Pressure

Several different iron sulfides have been synthesized from aqueous sulfide solutions at low temperatures (20°-90° C.) and atmospheric pressure and identified by means of X-ray diffraction and/or chemical analysis. These are tetragonal FeS, pyrite, marcasite, a magnetic cubic iron sulfide of the spinel structure type, pyrrhotite, and an X-ray amorphous precipitated iron sulfide of composition approximating FeS. The nature of the resulting iron sulfide depends upon many factors, the most important of which are pH, temperature, the presence of specific oxidizing agents, and the type of iron source material used as a reactant. Tetragonal FeS was formed over a wide range of conditions and was the iron sulfide most commonly encountered in this study. It results from the reaction of hydrogen sulfide with fine-grained goethite under conditions simulating those in natural marine sediments. The substance described as hydrotroilite in many sedimentary occurrences is believed to be, at least in part, poorly crystallized tetragonal FeS. Tetragonal FeS has been found in the sediments of the Mystic River, Boston, Massachusetts, and in an iron sulfide concretion from the sediments of the Black Sea. The initial corrosion product of metallic iron in , which has been called kansite, is tetragonal FeS. The material originally denoted as melnikovite by Doss (1912) is believed to have been a mixture of phases containing one or more of several known magnetic iron sulfides. The substance called melnikovite by Volkov (1961) from the Black Sea concretion is shown to be the magnetic cubic iron sulfide synthesized in the present study.

Tetragonal Iron Sulfide

Studies of synthetic iron sulfides formed from aqueous solution at 25°C and atmospheric pressure have revealed the existence of a new phase, tetragonal FeS. This phase is formed as the initial corrosion product of metallic iron or steel in solutions of hydrogen sulfide. It has been discovered as an iron corrosion product in the sediments of the Mystic River at Boston, Massachusetts.