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.     

Ex-situ and in-situ X-ray diffractions of corrosion products freshly formed on the surface of an iron-silicon alloy

Ex-situ X-ray diffraction measurements of a small amount of samples extracted from wet corrosion products freshly formed on a pure iron and iron-2 mass% silicon surfaces have been conducted using synchrotron radiation for clarifying the formation process of corrosion products. The results showed that γ-FeOOH was formed on the outer side of wet corrosion products formed on the surface of the pure iron by sodium chloride solution, while γ-FeOOH, α-FeOOH, Fe₃O₄, and green rusts were formed on the inner side. On the other hand, in comparison to the case of the pure iron, a significant formation of β-FeOOH was observed in the iron-silicon alloy. Influences of silicon alloying on corrosion products formed by aqueous solution containing sulfate ions were also observed. Furthermore, in-situ diffraction measurements by a conventional X-ray source were conducted for analyzing corrosion products formed on the pure iron and iron-silicon alloy surfaces by cyclic exposure to wet and dry atmospheres. The results obtained by the in-situ diffraction and ex-situ diffraction measurements on the corrosion products were consistent.     

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.     

Influence of manganese on iron oxyhydroxides and oxides formed in aqueous solution

Structural analysis techniques such as X-ray diffraction and anomalous X-ray scattering were used for characterizing the influence of manganese on iron oxyhydroxides and oxides formed from green rust (GR) in an aqueous solution. The results showed that the formation of Fe₃O₄ was enhanced by the addition of manganese ions during the conversion of GR2 to α-FeOOH and Fe₃O₄. The results obtained from anomalous X-ray scattering showed that manganese was present both in α-FeOOH and Fe₃O₄ particles. The incorporation of manganese in α-FeOOH appears to induce the distortion of the atomic-scale structure of α-FeOOH particles formed in an aqueous solution.     

Effects of DBU, morpholine, and DMA on corrosion of low carbon steel exposed to steam

Effects of morpholine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and dimethylamine (DMA) on oxidation kinetics and oxide phase formation/transformation of AISI 1018 steel at 120 °C were evaluated. Low carbon steel samples were exposed to steam in an autoclave containing amine added aqueous solution at pH of 9.5 for 1, 2, 4, 6, 8, and 12 h. Control samples exposed to plain steam and amines showed the highest and lowest weight loss respectively. Fourier Transform Infrared Spectrophotometry (FTIR) showed that DBU containing steam favored formation of magnetite (Fe₃O₄) while steam with DMA formed more α and γ-FeOOH. Transformation of magnetite to hematite (α-Fe₂O₃) was fastest for morpholine. Analysis of oxides morphology was done utilizing Scanning Electron Microscopy (SEM). Oxides formed in plain or DMA containing steam exhibited acicular particles of goethite/hematite (α-FeOOH/α-Fe₂O₃) compared to DBU containing steam that showed equiaxed particles of magnetite/maghemite (Fe₃O₄/γ-Fe₂O₃). Morpholine containing steam promoted agglomeration of thin sharp platelets into coarse flakes of hematite.     

Characterization of the rust formed on weathering steel exposed to Qinghai salt lake atmosphere

The product formed on weathering steel exposed to salt lake atmosphere for 12 months was investigated by X-ray diffraction (XRD), infrared transmission spectroscopy (IRS), scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and electrochemical techniques. The rust was mainly composed of β-FeOOH, Fe₈(O,OH)₁₆Cl_1.3 and a little γ-FeOOH. Amorphous δ-FeOOH was only on skyward surface. The rust layer suppressed anodic reaction and facilitated the cathodic reaction. The very small value of rust resistance R_r in this work indicated that the rust had poor protective ability. Cl element was rich in the whole rust layer and played an important role in accelerating the corrosion of weathering steel in salt lake atmosphere.     

In-depth distribution of rusts on a plain carbon steel and weathering steels exposed to coastal-industrial atmosphere for 17 years

In-depth distribution of rusts on two weathering steels and a plain carbon steel exposed to atmosphere for 17 years under a bridge at a coastal + industrial region in Japan were studied. In the rust layer on all specimens, α-FeOOH, β-FeOOH, γ-FeOOH, Fe₃O₄ and so-called amorphous rust were found. Within rust layers, there were thick parts and thin parts, which were finely and complicatedly distributed on steels. Among these rust species, α-FeOOH was dominant on all specimens. α-FeOOH appeared almost homogeneously through the rust layer. Its concentration was higher on weathering steels than on plain carbon steel. β-FeOOH was found mainly at thick parts and was scarce at thin parts of rust layers. Concentration of α-FeOOH was higher and that of γ-FeOOH was lower on weathering steels than on plain carbon steel. Amorphous rust was located at the bottom of the rust layer irrespective of steel types. Concentration of magnetite was negatively correlated with concentration of β-FeOOH.     

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.     

Corrosion mechanisms of steel concrete moulds in contact with a demoulding agent studied by EIS and XPS

The behaviour of E24 mild steel was studied by XPS analysis and electrochemical impedance spectroscopy (EIS) in a filtered solution of cement (pH 13), and an alkyl N-aminodiphosphonate aqueous solution called Aquadem^® (7?pH?13). XPS results showed that the corrosion products developed in both media consisted of Fe₂O₃, covered by a very thin layer of goethite. The thickness of this oxide layer was estimated to be 3 nm. XPS analysis also demonstrated the adsorption of Aquadem^® on the outer layer of FeOOH for pH lower than the zero charge pH of goethite (7.55). From XPS and EIS results, physical models of the E24 steel/electrolyte interface are proposed as a function of pH. For 11?pH?13, the steel is covered by a passive film, while for pH?10, pitting corrosion takes place. At pH 7, an additional mass transport phenomenon must be taken into account. The fitting procedure provided values for several physical parameters (electrolyte resistance, passive film resistance), from which the film capacitance and the dielectric constant of the oxide layer were calculated.     

Iron oxide hollow spheres: Microwave–hydrothermal ionic liquid preparation,formation mechanism,crystal phase and morphology control and properties

This paper reports on the microwave–hydrothermal ionic liquid method for the synthesis of a variety of iron oxide nanostructures such as α-FeOOH hollow spheres, β-FeOOH architectures and α-Fe₂O₃ nanoparticles. The formation mechanism for α-FeOOH hollow spheres is discussed. The effects of the reaction parameters on the morphology and crystal phase of the final product are studied. The relationship between the morphology and crystal phase of the product is discussed. A general thermal transformation strategy is designed to prepare α-Fe₂O₃ hollow spheres using α-FeOOH hollow spheres as the precursor and template. By thermal treatment of the as-prepared α-FeOOH hollow spheres, α-Fe₂O₃ hollow spheres showing good photocatalytic activity are obtained. And by autocatalysis of the adsorbed available Fe(II) on the α-FeOOH surfaces, Fe₃O₄ hollow spheres are also obtained.     

Physiochemical characterization of five iron tubercles from a single drinking water distribution system: Possible new insights on their formation and growth

Physiochemical data were obtained for five iron tubercles from a single drinking water distribution system (DS). Texturally, there were two groups based on internal morphology: one with a core of soft brownish material marbled with veins of a hard black material, the other has a core consisting mostly of the hard, black material. Three iron mineral phases occur, α-FeOOH, γ-FeOOH, or Fe₃O₄. All three coexist in each tubercle but in widely varying proportions. These iron pipe tubercles exhibit a greater diversity within a single DS than previously thought. Because the chemical conditions for the formation of each material is different, water quality parameters may not be the main control of tubercle formation and growth.     

Corrosion behavior of steel under wet and dry cycles containing Cr ion

The corrosion behavior of mild steel has been investigated during the wet and dry cyclic transitions containing Cr³⁺ ion added as sulfate in order to gain a better understanding of the influence of Cr on the atmospheric corrosion of steels. The corrosion rate during drying is greatly suppressed by the existence of Cr³⁺ ion in the electrolyte covered with the surface. Lower corrosion rates are observed during drying even if the surface have been polarized to negative potentials below −200 mV_SHE during the wet corrosion conditions in which the surface-covered electrolyte contains Cr³⁺ ion. This corrosion behavior is identical to the case of Cr-containing steel for the wet and dry cyclic transitions without the addition of Cr³⁺ ion. The composition of rust layer after the wet and dry cyclic transitions is composed of α-FeOOH, γ-FeOOH and Fe_3−δO₄ for both cases of non-Cr³⁺ and Cr³⁺-containing condition, and no significant difference in the mass fraction of the above rust substances between two conditions is observed by means of Mössbauer spectroscopy. The only difference in the rust layer is that the rust formed under the wet and dry cyclic transitions containing Cr³⁺ ion contains a certain amount of Cr near the steel/rust interface. Those results suggest that the role of Cr during the wet and dry cyclic transitions is the inhibition of the rust reduction and the formation of Fe²⁺-state intermediate by the existence of Cr in the rust layer. This can lead to the inhibition of the oxygen reduction during drying.     

Electrochemical behaviour and structure of rust formed on Si- and Al-bearing steel after atmospheric exposure

The corrosion resistance of Si- and Al-bearing steel was estimated by atmospheric exposure test, and the structure of the rust was examined by EPMA (electroprobe X-ray microanalysis) and TEM (transmission electron microscopy) analysis. Moreover, the electrochemical behaviour of rust was investigated by EIS (electrochemical impedance spectroscopy).The Si- and Al-bearing steel exhibited excellent corrosion resistance in the exposure test as compared with carbon steel (SM). EPMA and TEM analysis showed that Si and Al mainly existed in nanoscale iron complex oxides in the inner rust formed on this steel. The Al K spectrum of the rust exhibited a peak that was the same as that of Al₂O₃ in the EPMA and TEM-EELS (electron energy loss spectroscopy) analysis. This result suggests that Al was present in the complex oxides as Al³⁺. In the same way, Si was identified as being in an intermediate state in the complex oxides of the inner rust.EIS measurement of the exposure test samples revealed much higher rust resistance (R_rust) and corrosion reaction resistance (R_t) of Si- and Al-bearing steel compared to that of SM. Finally, it was found that nanoscale complex iron oxides formed in the inner rust of Si- and Al-bearing steel, resulting in increased R_rust and R_t, and corrosion suppression.     

Corrosion assessment of nitric acid grade austenitic stainless steels

The corrosion resistance of three indigenous nitric acid grade (NAG) type 304L stainless steel (SS), designated as 304L1, 304L2 and 304L3 and two commercial NAG SS designated as Uranus-16 similar to 304L composition and Uranus-65 similar to type 310L SS were carried out in nitric acid media. Electrochemical measurements and surface film analysis were performed to evaluate the corrosion resistance and passive film property in 6 N and 11.5 N HNO₃ media. The results in 6 N HNO₃ show that the indigenous NAG 304L SS and Uranus-65 alloy exhibited similar and higher corrosion resistance with lower passive current density compared to Uranus-16 alloy. In higher concentration of 11.5 N HNO₃, transpassive potential of all the NAG SS shows a similar range, except for Uranus-16 alloy. Optical micrographs of all the NAG SS revealed changes in microstructure after polarization in 6 N and 11.5 N HNO₃ with corrosion attacks at the grain boundaries. Frequency response of the AC impedance of all the NAG SS showed a single semicircle arc. Higher polarization resistance (R_P) and lower capacitance value (CPE-T) revealing higher film stability for indigenous NAG type 304L SS and Uranus-65 alloy. Uranus-16 alloy exhibited the lowest R_P value in both the nitric acid concentration. Auger electron spectroscopy (AES) study in 6 N and 11.5 N HNO₃ revealed that the passive films were mainly composed of Cr₂O₃ and Fe₂O₃ for all the alloys. The corrosion resistance of different NAG SS to HNO₃ corrosion and its relation to compositional variations of the NAG alloys are discussed in this paper.     

The corrosion resistance of ultra-low carbon bainitic steel

The corrosion resistance of ultra-low carbon bainitic (ULCB) steel was compared with a weathering steel 09CuPCrNi through accelerated corrosion tests. The results indicated that the corrosion resistance was almost the same for ULCB and 09CuPCrNi based on the weight loss. It can be seen that the grain refinement did not deteriorate corrosion resistance property. The homogeneous microstructure, lower carbon content and random distributing ∑3 boundary could effectively increase the corrosion resistance of the ULCB steel. The characteristics of the rust layers indicated that the inner rust layer contained nanocrystalline Fe_3−xO₄ particles, while copper and chromium alloying additions were enriched at the rust layer and substrate interface in ULCB steel. These factors played important roles in forming a compact protective rust layer.     

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 zinc compounds on the formation, morphology, and adsorption characteristics of β-FeOOH rusts

To simulate the corrosion of galvanized steel in marine zone, β-FeOOH was prepared by aging the FeCl₃ solutions containing ZnCl₂ and zinc rusts such as ZnO and zinc hydroxychloride (Zn₅(OH)₈Cl₂·H₂O:ZHC). Adding ZnCl₂, ZnO, and ZHC inhibited the crystallization and particle growth of β-FeOOH and the inhibitory effect was in order of ZHC ≈ ZnO > ZnCl₂. The adsorption of H₂O and CO₂ was suppressed by adding ZnCl₂, ZnO, and ZHC. These results imply that the rust formed on galvanized steel in marine environment is more compact, amorphous, and hydrophobic in nature which may lead to improve the corrosion resistance.     

Effect of Dy2O3 intergranular addition on thermal stability and corrosion resistance of Nd–Fe–B magnets

Sintered Nd–Fe–B magnets with and without Dy₂O₃ were prepared by powder blending method. The temperature-dependent magnetic properties, thermal stability, microstructure and corrosion resistance of sintered magnets were investigated. The temperature-dependent magnetic properties revealed that with intergranular addition of Dy₂O₃, the reversible temperature coefficients β and α in the range of 293–373 K were both lowered, indicating that the thermal stability was effectively improved. This was also verified by the decreased irreversible flux loss (h_irr) and the increased maximum operating temperature (MOT). Moreover, the electrochemical and accelerated corrosion results clearly evidenced that the corrosion resistance of Nd–Fe–B magnet was also modified by addition of Dy₂O₃. Furthermore, the related mechanisms on improved thermal stability and corrosion resistance were systematically discussed.     

XPS analysis of the passive film formed on austenitic stainless steel coated with conductive polymer

Improvement of the passivation behavior of Type 304 austenitic stainless steel (SS) by coating with conductive polymers (CPs), like polyaniline (PANI) and poly(o-phenylenediamine) (PoPD), followed by exposure in an acid solution has been demonstrated. The passive films formed on SSs (after peeling off the polymer layer) are compared with those formed during anodic polarization under the same exposure condition. The passive films beneath the CPs are thicker and less hydrated than those formed on uncoated stainless steel. The polymer layer enhances the enrichment of chromium and nickel in the entire passive oxide, forming a more protective film than that formed during anodic polarization. The elemental distribution within the passive film is different in the two modes of passivation. The type of the polymer influences on the composition of the passive film. The best passivation is obtained by PoPD, with the passive film resulting in significant resistance of the SS to pitting corrosion in the 3% NaCl solution. The oxide film of this steel is characterized, in its inner and outer layers, by the highest ratio of Cr(OH)₃/Cr₂O₃ and the lowest content of iron species.     

Substitutional adsorption isotherms and corrosion inhibitive properties of some oxadiazol-triazole derivative in acidic solution

A newly synthesized oxadiazol-triazole derivative (TOMP), was investigated as corrosion inhibitor of mild steel in 0.5 M H₂SO₄ solution using weight loss measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. Results obtained revealed that TOMP is effective corrosion inhibitor for mild steel in sulphuric acid and its efficiency attains more than 97.6% at 298 K. The number of water molecules (X) replaced by a molecule of organic adsorbate was determined from the substitutional adsorption isotherms applied to the data obtained from the weight loss experiments performed on mild steel specimen in acidic solution in the 298-333 K range.