Characterization of Delhi iron pillar rust by X-ray diffraction, Fourier transform infrared spectroscopy and Mössbauer spectroscopy

Rust samples obtained from the region just below the decorative bell capital of the Delhi iron pillar (DIP) have been analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Mössbauer spectroscopy. The identification of iron hydrogen phosphate hydrate in the crystalline form by XRD was unambiguous. Very weak diffraction from the oxyhydroxides/oxides of iron was observed indicating that these phases are most likely to be present in the amorphous form in the rust. The present XRD analysis of rust obtained from an inaccessible area of the DIP has also been compared with earlier analyses of DIP rust obtained from regions accessible to the public. FTIR indicated that the constituents of the scale were γ-, α-, δ-FeOOH, Fe_3−xO₄ and phosphate, and that the scale was hydrated. The unambiguous identification of the iron oxides/oxyhydroxides in the FTIR spectrum implied that they are present in the amorphous state, as XRD did not reveal these phases. The FTIR results have also been compared with earlier FTIR spectroscopic results of atmospheric rust formation. Mössbauer spectroscopy indicated that the rusts contained γ-FeOOH, superparamagnetic α-FeOOH, δ-FeOOH and magnetite, all in the amorphous form. The Mössbauer spectrum also confirmed that iron in the crystalline iron hydrogen phosphate hydrate, whose presence was confirmed by XRD, was in the ferric state indicating that it was a stable end corrosion product.     

Corrosion resistance of the Dhar iron pillar

The corrosion resistance of the 950-year old Dhar iron pillar has been addressed. The microstructure of a Dhar pillar iron sample exhibited characteristics typical of ancient Indian iron. Intergranular cracking indicated P segregation to the grain boundaries. The potentiodynamic polarization behaviour of the Dhar pillar iron and mild steel, evaluated in solutions of pH 1 and 7.6, indicate that the pillar iron is inferior to mild steel under complete immersion conditions. However, the excellent atmospheric corrosion resistance of the phosphoric Dhar pillar iron is due to the formation of a protective passive film on the surface. Rust analysis revealed the presence of crystalline magnetite (Fe_3−xO₄), α-Fe₂O₃ (hematite), goethite (α-FeOOH), lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH) and phosphates, and amorphous δ-FeOOH phases. The rust cross-section revealed a layered structure at some locations.     

The atmospheric corrosion of iron as studied by Mössbauer spectroscopy

The composition of the rust on the surface of steel panels was determined after atmospheric exposure times of 2 weeks, 2 months and 6 months. The initial product is γ-FeOOH which converts in time to a mixture of α-FeOOH and γ-Fe₂O₃. Steel exposed for times of the order of 25 years is covered with corrosion product consisting largely of γ-Fe₂O₃. The similarity between the composition of the corrosion products and precipitates formed from FeSO₄ solution under mildly acidic conditions at 90°C suggests that the dominant anion in these atmospheric corrosion experiments is sulfate.     

Oxidation behavior of NixFe1−x(OH)2 in Cl-containing solution

The addition of Ni leads to the formation of protective rust layer on steel and subsequently high corrosion resistance of steel in Cl⁻-containing environment. α-FeOOH, β-FeOOH, γ-FeOOH and Fe₃O₄ are formed mainly on steels exposed to Cl⁻-containing atmosphere. It is expected that systematic investigation of the effect of Ni(II) on the formation process of each oxide in solution should lead to elucidation of the role of Ni in the formation of anticorrosive oxide layer. This study reports the oxidation behavior of Ni_xFe_1−x(OH)₂ in Cl⁻-containing solution at two different pH regions (condition I under which solution pH is allowed to decrease and condition II under which solution pH is maintained at 8) where γ-FeOOH and Fe₃O₄ are predominantly formed, respectively, upon the oxidation of Fe(OH)₂. In the presence of Ni(II) in the starting solution, the formation of Ni(II) doped β-FeOOH with very low crystalline was facilitated and the formation of γ-FeOOH was suppressed with increasing Ni(II) content and with increasing oxidation rate of Fe(II). Ni(II) was found to have Fe₃O₄-suppressing effect under condition II.     

Phasenumwandlungen in Korrosionsschichten auf Eisen: Mößbauerspektroskopische Untersuchungen

Phase transformations in corrosion layers on iron: Mössbauer spectroscopic studies The corrosion of steel surfaces was studied by Mössbauer spectroscopic phase analysis in scattering and transmission geometry. In atmospheres of low corrosivity, long exposure times result mainly in the relatively stable β-phases among the possible iron corrosion products. An increase in corrosivity by addition of hydrochloric acid leads to a pronounced formation of β-FeOOH, whereas the α-phases are absent. The influence of different coatings on the phase composition was also studied. The formation and transformation of the different iron containing phases in rust can be understood in terms of a stability diagram. Furthermore, the effect of so-called “rust transformers” was studied. None of these products showed the desired effect of phase transformations towards the formation of protective compounds such as Fe₃O⁴. In some cases it was found that the rust transformers even caused a destruction of an already existing protective layer.     

Röntgenamorphe Phasen im Rost

X-ray amorphous phases in rust The sum of the crystalline phases found during a quantitative X-ray analysis of rust is always below 100%. An attempt was therefore made to identify amorphous phases in several characteristic Of different types Of rust; to this end a combination was used of quantitative phase analysis by X-rays and chemical extraction. Rust from industrial, forest and lake environments does not contain amorphous components. The crystalline deficit found during phase analysis is due to lattice distorsions in the crystalline Phase α-FeOOH, γ-FeOOH and Fe₃O₄; the distorsions are greatest in the α-phase and smallest in Fe₃O₄. Rust from water ducts and maritime environments sometimes contains X-ray amorphous components. It is possible, however, that these components are formed only by the treatment Of rust samples in the air and that rust of this type does not contain any amorphous phase in its original environment.     

Taxonomy for protective ability of rust layer using its composition formed on weathering steel bridge

For a quantitative evaluation of the protectiveness of a rust layer formed on a weathering steel bridge, the relationship between the corrosion rate of the bridge and the composition of the rust layers formed on the girders was first investigated. These corrosion rates were clearly classified by the protective ability index (PAI) of α/γ^∗ and (β + s)/γ^∗, where α, γ^∗, β and s are the mass ratio of crystalline α-FeOOH, the total of γ-FeOOH, β-FeOOH and the spinel-type iron oxide (mainly Fe₃O₄), β-FeOOH and spinel-type iron oxide, analyzed by XRD, respectively. The inequality of the former index α/γ^∗ > 1 expressed the protectiveness criterion of the rust layer, while that of the latter index, (β + s)/γ^∗< 0.5 or > 0.5, classified the corrosion rate of the non-protective rust layer. The PAI is useful for a quantitative evaluation of the protectiveness of a rust layer formed on a weathering steel bridge and is an important item for the corrosion assessment of the bridge.     

Localized corrosion behavior of a zirconium-based bulk metallic glass relative to its crystalline state

To date, few detailed corrosion studies of the new bulk metallic glasses (BMGs) have been presented. In the present work, the aqueous electrochemical corrosion properties of BMG-11, 52.5Zr–17.9Cu–14.6Ni–5.0Ti–10.0Al (atomic percent), were investigated. Cyclic-anodic-polarization tests were conducted on amorphous and crystalline specimens in a 0.6 M NaCl solution (simulated seawater) and on amorphous specimens in a 0.05 M Na₂SO₄ solution (simulated moisture condensation, as related to ongoing fatigue experiments in humid air), all at room temperature. In the NaCl solution, both amorphous and crystalline materials were found to exhibit passive behavior with low corrosion rates (15 μm/year or less). However, susceptibilities to pitting corrosion were observed. The amorphous material was found to be more resistant to the onset of pitting corrosion under natural corrosion conditions. In the 0.05 M Na₂SO₄ solution, the amorphous BMG-11 was found to exhibit passive behavior with a very low corrosion rate (0.4 μm/year), and to be immune to pitting corrosion. Furthermore, when the protective passive film was removed by scratching with a diamond stylus, it was found to quickly reform. This result suggested that a corrosion influence on the fatigue properties of BMG-11 in humid air would be minimal.     

Cu、Mn的协同作用对低合金钢在模拟海洋大气环境中腐蚀的影响

    用增重法、扫描电镜、X射线衍射、电子探针和X射线光电子能谱等手段研究了在模拟海洋大气干湿交替环境下16Mn钢和Cu-Mn耐候钢的腐蚀行为及Cu、Mn共添加对低合金钢腐蚀行为的影响.结果表明：Cu-Mn耐候钢的腐蚀速率低于16Mn钢,其锈层更致密;两种钢的铁锈均由Fe₃O₄,α-FeOOH,β-FeOOH,γ-FeOOH和大量无定形相组成;添加Cu使Fe₃O₄含量增加,添加Mn使γ-FeOOH含量减少;Cu在Cu-Mn耐候钢锈层中以CuFeO₂存在;Mn在两种钢锈蚀初期以MnO存在,后期为Mn₃O₄.Cu、Mn的协同作用使Cu-Mn耐候钢抗大气腐蚀性能优于16Mn钢.     

海水飞溅区Ni-Cu-P钢的锈层和耐点蚀性能研究

在海水飞溅区对实验室冶炼的Ni-Cu-P钢、含Cu低合金钢和碳钢进行660 d的挂片实验,评价Ni-Cu-P钢的耐蚀性能;采用Fourier变换红外(FTIR)光谱、电感耦合等离子体原子发射光谱(ICP-AES)、电子探针(EPMA)、SEM和EDAX等技术,分析3种钢表面的锈层特征.结果表明,Ni-Cu-P钢表现出比...     

Role of oxide films in stress corrosion cracking of mild steel in nitrate solutions

Time to failure of iron with varying carbon content was determined during stress corrosion at 75°C in various nitrate solutions. Ability of these solutions to passivate iron was estimated. It has been suggested that the high rate of the intergranular stress corrosion cracking of mild steel is connected with the formation of the passive γ-Fe₂O₃ film and its sensitivity to the depassivating action of steel constituents such as carbon, segregated at grain boundaries. It is thought that the Fe₃O₄ film also protects the grain boundaries.     

Influence of Rust Layers on the Corrosion Behavior of Ultra-High Strength Steel 300M Subjected to Wet–Dry cyclic Environment with Chloride and Low Humidity

The influence of rust layers on the corrosion behavior of ultra-high strength steel 300 M subjected to a simulated coastal atmosphere was investigated by corrosion weight loss, surface analysis techniques, and electrochemical methods.The results exhibit the presence of a large proportion of c-Fe OOH and a-Fe OOH and a small amount of Fe3O4 in the outer rust layer. During the wet–dry cyclic process, the bonding performance and the density of outer rust layer deteriorate with the thickness of outer rust. The inner rust layer plays a main role on protectiveness, which can be attributed to the formation of an ultra-dense and adherent rust film with major constituent of a-Fe OOH and a-Fe2O3 on the steel.     

Phasenumwandlungen im Rost

Phase conversions in rust The principal components of rust are lepidocrocite (γ-FeOOH), göthite (α-FeOOH) and magnetite (Fe₃O₄). The first crystal phase, possibly via (FeOH)₂, is lepidocrocite. This may later be transformed into göthite and magnetite. The paper describes pseudo-morphoses of gothite and magnetite after lepidocrocite. Magnetite, which at higher temperatures is formed directly on the iron, grows epitactically and forms a protective layer which prevents further corrosion. In contrast, magnetite transformed from lepidocrocite cannot be expected to have such an effect. The necessary adhesion and freedom from pores is conditioned by the epitaxy of a protective layer.     

Structure of titanium-doped goethite rust

To investigate the influence of titanium addition on the formation and structure of goethite (α-FeOOH) rust which is one of main corrosion products of weathering steel, the artificially synthesized α-FeOOH rusts were prepared by hydrolysis of aqueous solutions of Fe(III) containing Ti(IV) at different atomic ratios (Ti/Fe) in the range 0-0.1. The obtained rusts particles were observed by TEM. Characterization by XRD, N₂ absorption, Mössbauer spectroscopy was also done. TEM observation revealed that the α-FeOOH rust particle size increased with the increase of Ti/Fe, and that Ti-enriched poorly crystalline particles were formed around the rust particles. XRD confirmed that the crystallite size increased with the increase of Ti/Fe, while the XRD peaks decreased in intensity. Specific surface area obtained by N₂ absorption increased with the increase of Ti/Fe. It is deduced from the obtained results that the addition of Ti(IV) increases the crystallite size of α-FeOOH, and produces double domain particles consisting of the particle core and a porous poorly crystalline shell. It is thought that such unique rust structure produced by titanium addition contributes to the protective properties of rust layer of the weathering steel.     

Field sludge characterization obtained from inner of pipelines

Physicochemical characterization of sludge obtained from refined hydrocarbons transmission pipeline was carried out through Mössbauer spectroscopy and X-ray diffraction. The Mössbauer and X-ray patterns indicate the presence of corrosion products composed of different iron oxide and sulfide phases. Hematite (α-Fe₂O₃), magnetite (Fe₃O₄), maghemite (γ-Fe₂O₃), magnetic and superparamagnetic goethite (α-FeOOH), pyrrhotite (Fe_1−xS), akaganeite (β-FeOOH), and lepidocrocite (γ-FeOOH) were identified as corrosion products in samples obtained from pipeline transporting Magna and Premium gasoline. For diesel transmission pipeline, hematite, magnetite, and magnetic goethite were identified. Corrosion products follow a simple reaction mechanism of steel dissolution in aerated aqueous media at a near-neutral pH. Chemical composition of the corrosion products depends on H₂O and sulfur inherent in fluids (traces). These results can be useful for decision-making with regard to pipeline corrosion control.     

Composition and protective ability of rust layer formed on weathering steel exposed to various environments

The compositional change of rust (corrosion products) layer formed on weathering steel exposed to atmosphere with different amount of air-borne sea salt particles in Japan have been investigated by the X-ray diffraction method. The mass ratio (α/γ) of crystalline α-FeOOH to γ-FeOOH, in the rust layer formed on the weathering steel exposed in an industrial environment, increases with an increase in exposure duration. The α/γ is closely related to the corrosion rate in environments when the amount of air-borne salt is less than 0.2 mg NaCl/dm²/day (2.31 × 10⁻⁷ g NaCl/m²/s). However this is not the case in seaside environments with a higher amount of air-borne salts. The mass ratio (α/γ^∗) of crystalline α-FeOOH to the total mass of γ-FeOOH, β-FeOOH and Fe₃O₄, in the rust layer formed on the weathering steel is related to the corrosion rate even in seaside environments certainly more than 0.2 mg/dm²/day (2.31 × 10⁻⁷ g/m²/s) of air-borne salt particles. When the α/γ^∗ is more than 1, a higher corrosion rate more than 0.01 mm/year (3.17 × 10⁻¹³ m/s) is not observed. The α/γ^∗ is a protective ability index of rust formed on weathering steel.     

The reductive dissolution of γ-FeOOH in corrosion scales formed on cast iron in near-neutral waters

Corrosion scales which form on cast iron in oxygenated, near-neutral waters at 50°C contain green rust, Fe₂O₄ and γ-FeOOH. Upon de-oxygenation of the water, γ-FeOOH → Fe₃O₄ occurs by dissolution-precipitation as a cathodic reaction in the corrosion cell. Mechanisms of corrosion reactions are postulated in which it is proposed that the amount of γ-FeOOH is controlled by a balance between its rate of precipitation and its rate of reductive dissolution. The mechanism explains the eventual predominance of Fe₃O₄ in scales formed in oxygenated waters and the absence of γ-FeOOH from scales formed in waters with [O₂] < ～ 1 ppm.     

Vorkommen,Entstehung und Phasenumwandlung von β-FeOOH in Rost

Occurrence, formation and phase transformation of β-FeOOH in rust A prerequisite to the formation of β-FeOOH is the presence of chloride or fluoride ions. These may take the form of corresponding acids, or of their salts. β-FeOOH is formed in the presence even of minute quantities of chloride, e. g. also under conditions of pitting corrosion, when FeCl₂, - 4 H₂O is formed. If the chloride input ceases, the hitherto unaffected surfaces will be affected by the normal α or γ-FeOOH, as the chloride ions are then fixed in the β-FeOOH lattice. β-FeOOH remains stable at low _PH values only; at higher _PH values, it is transformed into the α-modification or hematite. In contact with metallic iron, β-FeOOH has the effect of accelerating the corrosion rate, probably because of the continued liberation of chloride ions.     

低碳贝氏体钢在青岛曝晒一年的锈层力学性能和抗热震性能研究

研究了低碳贝氏体钢在青岛曝晒一年后表面锈层的相组成、形貌、力学性能以及抗热震性能.结果表明:锈层由α-FeOOH、β-FeOOH、γ-FeOOH、Fe3O4以及非晶相组成;锈层的表面和截面形貌显示锈层较为致密,合金元素Cr和Cu在锈层中接近钢基体处有明显的富集现象;锈层的弹性模量和硬度随距锈层/钢基体界面的距离增大而降低;锈层/钢基体的结合强度和抗热震能力均高于锈层本身.     

Corrosion resistance and mechanical properties of low-alloy steels under atmospheric conditions

The corrosion resistance and mechanical strength of four newly developed low-alloy steels (LAS) were compared with a carbon steel (SS400) and a weathering steel (Acr-Ten A) using a laboratory-accelerated test that involved cyclic wet/dry conditions in a chloride environment (5 wt.% NaCl). The new LAS were designated 1605A, 1605B, 1604A, and 1604B. After 72 cycles of cyclic corrosion tests, the susceptibility of the steels to corrosion could be listed in the following order based on their weight loss (from high to low): SS400 > Acr-Ten A > 1604B ? 1604A > 1605B ? 1605A. The change in mechanical properties by corrosion was the least for SS400, Acr-Ten A was second, and effects of corrosion on the mechanical properties of the other four low-alloy steels were similar. Finally, the characteristics of the rust layers on each LAS sample were observed by SEM, and analyzed by FTIR and EPMA. The results indicated that most of the rust layers on the test steels were composed of a loose outer rust layer and a dense inner rust layer. The outer rust layer of each steel was composed of α-FeOOH, γ-FeOOH, magnetite (Fe₃O₄), H₂O, and amorphous ferric oxyhydroxide (FeO_x(OH)_3−2x, x=0-1), while the inner rust layer was composed mainly of Fe₃O₄ with a little α-FeOOH. In addition, it was apparent that the copper and chromium alloying additions were enriched, respectively, at the rust-layer/substrate interface and in the rust layers. Finally, combining the results of the accelerated tests and the rust layer analysis showed that low-alloy steels, such as 1605A and 1605B, have better weathering steel properties than Acr-Ten A for use in the humid and salty weather.