Structure and properties of Ti(IV)-doped zinc hydroxychloride rusts formed at various temperatures

To simulate the atmospheric corrosion of steels galvanized with Ti–Zn alloys under different atmospheric temperatures, Ti(IV)-doped zinc hydroxychloride (Zn₅(OH)₈Cl₂·H₂O: ZHC) was prepared at various aging temperatures of 6–120 °C. Adding the Ti(IV) inhibited the crystallization and particle growth of ZHC, showing a minimum at 50 °C. Higher aging temperature promoted the formation of TiO₂ nano-particles. Elevating the aging temperature suppressed the adsorption of H₂O and CO₂ on Ti(IV)-doped ZHC. These results suggest that the alloying Ti in galvanized steel forms compact zinc rust layer at various atmospheric temperatures in marine environment, which would lead to the enhancement of corrosion resistance.     

Influence of anions on the formation and structure of artificial zinc rusts

To simulate the atmospheric corrosion of steels galvanized with Zn under different conditions, artificial zinc rusts of basic zinc salt (BZS) were prepared by hydrolyzing ZnO particles in aqueous solutions including ZnCl₂, ZnSO₄ and Zn(NO₃)₂. In ZnCl₂–ZnSO₄, ZnSO₄–Zn(NO₃)₂ and ZnCl₂–Zn(NO₃)₂–ZnSO₄ systems, zinc hydroxysulfate (Zn₄(OH)₆(SO₄)·nH₂O) was formed while zinc hydroxychloride (Zn₅(OH)₈Cl₂·H₂O) was generated in ZnCl₂–Zn(NO₃)₂ system. Zinc hydroxynitrate (Zn₅(OH)₈(NO₃)₂·2H₂O) was yielded in only Zn(NO₃)₂ system. All the formed artificial zinc rusts were hexagonal plate particles. These results suggest that SO_x is the most effective corrosive gas on the formation of BZS rusts on galvanized steel.     

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.     

Influence of metal ions on the formation of artificial zinc rusts

The artificial rust particles were prepared from ZnCl₂ solutions dissolving Al(III), Fe(III), Fe(II), Ni(II), Co(II) and Mg(II) at different atomic ratios from 0 to 0.3 in metal/Zn. With increasing metal/Zn the crystal phases of the products turned following as ZnO → a mixture of ZnO and Zn₅(OH)₈Cl₂ · H₂O (ZHC) → ZHC. Al(III) most facilitated the formation of ZHC but Mg(II) and Fe(III) produced no ZHC. The morphology of the formed particles varied following as agglomerate → fine → rod → sheet → irregular with the increase of metal/Zn. The sheet and irregularly shaped particles were identified as ZHC and the other particles as ZnO.     

Structure and composition of artificially synthesized rusts of Zn-Fe and Zn-Ti alloys

The artificial rusts of Zn-Fe and Zn-Ti alloys were synthesized from aqueous solutions of mixed metal chloride, sulphate, and nitrate such as ZnCl₂-FeCl₂, ZnSO₄-Ti(SO₄)₂, Zn(NO₃)₂-Fe(NO₃)₃, and so forth, and were characterized by a variety of techniques. Rust particles with different compositions and morphology were formed, strongly depending on the types of anions and metal ions. Sheet particles of basic zinc chloride (simonkolleite) were generated in the ZnCl₂-FeCl₂ system and the plate particles of basic zinc sulphate were formed in sulphate systems. These sheet or plate particles and the nanoparticles produced in Zn-Ti systems are expected to form compact rust layers by preferred orientation and dense packing, respectively, and contribute to a high corrosion resistance of Zn alloys.     

Air permeability of the artificially synthesized Zn-Al-Mg alloy rusts

The rust particles of Zn-Al-Mg alloys were synthesized from aqueous solutions dissolving ZnCl₂, AlCl₃, and MgCl₂ at different atomic ratios of the metal ions. The crystal phase and particle morphology of the products depended on the composition of the starting solutions. The compactness of the layers of the products was estimated by measuring their air permeability. The layer of mixed metal hydroxide chloride formed at Zn:Al:Mg = 1:1:1 showed a highest compactness, that was ascribed to the preferred orientation of the fine plate particles. The addition of Mg(II) made plate particles smaller to give more compact layers.     

Influence of N ion implantation on the corrosion and nano-structure of Ti samples

Nitrogen ions of 30 keV with different fluxes ranging from 5 × 10¹⁶ to 8 × 10¹⁷ ions/cm² were implanted in Ti foil of 1.8 mm thickness. X-ray diffraction (XRD) was used to obtain the structural characteristics, while atomic force microscope (AFM) was employed to obtain the surface morphology of the samples. The potentiodynamic method was employed to obtain corrosion resistance of the samples in NaCl (3.5%) solution. Titanium nitride formation was enhanced with increasing the nitrogen ion flux, while grain size and surface roughness of the samples were also increased. Optimum corrosion resistance was obtained for 5 × 10¹⁶ (N⁺ ions/cm²).     

Influence of silicon on local structure and morphology of γ-FeOOH and α-FeOOH particles

The extended X-ray absorption fine structure (EXAFS) method was used for investigating the local structures of lepidocrocite and goethite with and without silicon. The structure and morphology of these particles were investigated using X-ray diffraction and transmission electron microscopy, respectively. The bonding structure was examined by Fourier transform infrared spectroscopy (FT-IR). When silicon species was added, the structure and morphology changed while the linkage of FeO₆ octahedral units was distorted. The FT-IR spectra revealed the formation of the Fe-O-Si bond in particles containing silicate ions, and the characteristic bond affects the local structure and morphology of the particles.     

Atomic-scale structure and morphology of ferric oxyhydroxides formed by corrosion of iron in various aqueous media

Fine particles of corrosion products consisting of one kind of ferric oxyhydroxide, either γ-FeOOH (lepidocrocite) or α-FeOOH (goethite), were directly prepared by dipping pure iron into aqueous solutions containing sodium chloride, sodium sulfate, or their mixed salts with sodium bicarbonate. Quantitative X-ray structural analysis using an in-house X-ray diffraction apparatus has been used for characterizing the atomic-scale structure of these ferric oxyhydroxide particles. The morphology of the γ-FeOOH and α-FeOOH particles was observed by transmission electron microscopy (TEM), and their bonding structures were analyzed using Fourier transform infrared spectroscopy (FT-IR). The realistic atomic-scale structures in the γ-FeOOH and α-FeOOH particles were estimated by fitting the interference functions with the help of the reverse Monte Carlo (RMC) simulation technique. The results showed that the linkages of fundamental FeO₆ octahedral units in the particles were deviated from the ideal crystal structure. The structural deviation is believed to be due to the incorporation of foreign anions during the formation of these particles in the aqueous solutions. The resultant atomic-scale structures in the γ-FeOOH and α-FeOOH particles were correlated with their morphology and bonding structure.     

Influence of silicon species on the transformation of green rust I(Cl) in aqueous solution by oxidation

X-ray diffraction (XRD) and solution analysis were used for characterizing the influence of different silicon species on oxidation of green rust (GRI(Cl⁻)) suspension. While addition of silicon to metallic iron enhanced the formation of β-FeOOH, GRI(Cl⁻) in aqueous solution oxidized into lepidocrocite and oxidation was delayed in presence of silica and silicate species as noticed from potential, pH, and dissolved oxygen (DO) measurements. Transmission electron micrographs showed that the particle size of lepidocrocite was reduced due to silicate addition. The influence of silicate was attributed to its adsorption on GRI(Cl⁻) and lepidocrocite particles as confirmed from ICP-AES analysis of supernatant solution.     

Influence of phosphate species on green rust I transformation and local structure and morphology of γ-FeOOH

To clarify the role of phosphate in the formation of corrosion products, the transformation of GRI(Cl⁻) with the addition of phosphate was characterized through XRD, TEM, and solution analysis. Electrochemical analysis showed that the transformation of GRI(Cl⁻) was delayed and the size of the final products, i.e., γ-FeOOH was reduced in the phosphate added case. X-ray absorption spectroscopy indicated that the neighboring Fe–Fe coordination number of FeO₆ octahedral unit in γ-FeOOH was decreased. These effects of phosphate are attributed to its adsorption on GRI(Cl⁻) and nucleated γ-FeOOH that prevented particle growth during oxidation process.     

X-ray micro- fluorescence, diffraction and absorption spectroscopy for local structure investigation of a radioactive zinc ferrite deposit

X-ray micro- fluorescence (μXRF), diffraction (μXRD) and absorption spectroscopy (μXAS) techniques have been used to investigate the micro-crystalline and chemical structure of a radioactive zinc ferrite corrosion deposit phase formed on a zirconium dioxide substrate. Micro- fluorescence provides structural information based on the elemental distribution analysis, μXRD allows the determination of lattice parameters of crystalline compounds while μXAS yields data related to the atomic environment, such as coordination number and the distances to the nearest neighbours. The μXAS and the μXRD results are compared including a discussion of precision and accuracy of both techniques.     

Influence of chromium on the local structure and morphology of ferric oxyhydroxides

The extended X-ray absorption fine structure (EXAFS) method and transmission electron microscopy (TEM) have been used for characterizing the local structure and morphology of ferric oxyhydroxides, α-FeOOH and γ-FeOOH, with and without chromium. These ferric oxyhydroxide powders were prepared from aqueous solutions containing iron and chromium ions. Radial structural functions for iron obtained by Fe K edge EXAFS spectra showed that the linkage of structural units formed by FeO₆ octahedra in γ-FeOOH is distorted by chromium addition, while such distortion in α-FeOOH is not clearly detected. On the other hand, Cr K edge EXAFS spectra showed that the local structure around chromium does not necessarily correspond to the local structure around of iron, which is observed by Fe K edge EXAFS spectra. This suggests that the structural units containing iron and chromium are heterogeneously distributed in these ferric oxyhydroxides. The local structural information was discussed coupled with morphological features of these ferric oxyhydroxides observed by TEM.     

Influence of peening on the corrosion properties of AISI 304 stainless steel

The effects of peening treatment on the microstructure and corrosion behavior of AISI 304SS were investigated. Shot and ultrasonic peening were performed on the austenitic stainless steel, and peened specimens were compared in terms of microstructure, surface roughness and corrosion resistance. Nano-sized grains, multi-directional mechanical twins and strain-induced martensite were formed on the surfaces, and the volume fraction of strain-induced martensite in the ultrasonically peened specimen was higher than that of the shot-peened specimen. The ultrasonically peened specimen which had smoother surface and contained more strain-induced martensite showed superior general and localized corrosion resistance to the as-received and shot-peened specimens.     

Influence of silicate ions on the formation of goethite from green rust in aqueous solution

We investigated the influence of silicate ions on the formation of goethite converted from hydroxysulphate green rust, which was synthesized by neutralizing mixted solution of Fe₂(SO₄)₃ and FeSO₄ with NaOH solution, by O₂ in an aqueous solution. The pH and oxidation-reduction potential of the suspension and the Fe and Si concentrations in supernatant solutions were analyzed. X-ray diffraction results for the solid particles formed during the conversion were consistent with the results of the solution analyses. The results indicated that silicate ions suppressed the conversion from green rust to α-FeOOH and distorted the linkages of FeO₆ octahedral units in the α-FeOOH structure.     

Study of the electrochemical behaviour of nanocrystalline zinc by statistical methods

Pulse electrodeposition was used to synthesize nanocrystalline (NC) zinc coatings from citric acid bath. The electrochemical behaviour of the NC zinc coatings was investigated by using potentiostatic and potentiodynamic polarization methods in 0.5 mol/L NaCl (pH = 12) solution and compared with that of cast zinc. Pitting corrosion behaviour was characterized by pitting potential, induction time and stable pit growth rate which were analyzed according to statistical method. The results showed that nanocrystallization increased the sensitivity of E_pit refer to potential sweep velocity, changed the type of the pit generation from B1 (parallel) to B2 (series), accelerated the pitting initiation process and inhibited the stable pit growth process of NC zinc.     

An investigation on the role of texture and surface morphology in the corrosion resistance of zinc electrodeposits

It has been shown in the literature that texture plays a major role in the corrosion resistance of zinc electrodeposits. This is because the grain dissolution rate depends on its orientation. In this research, the corrosion behavior of zinc electrodeposited coatings was investigated. It was observed that the corrosion resistance of zinc electrodeposits is related to the crystallographic planes exposed to aggressive solution, and not only the planes of texture components. The findings highlight the role of surface morphology of the coatings in exchange current density of water reduction and its subsequent effect on corrosion resistance.     

Effects of titanium carbide (TiC) and anodizing voltages on discoloration resistance of colored-titanium sheets

Discoloration resistance of anodized titanium sheets was investigated by accelerated discoloration tests and atmospheric exposure tests. Anodized oxide layers were analyzed by various surface analytical methods. TiC beneath the titanium oxide layer accelerated discoloration in cases where thinner oxide layers existed. Increase of their thickness improved resistance even though TiC existed. On the other hand, in case of reducing TiC, the specimen with the thinnest oxide layer showed the most resistant to discoloration. The top-surface region of the oxide layer is considered to play an important role in discoloration resistance.     

Influence of anions on the formation of β-FeOOH rusts

The artificial β-FeOOH rusts were synthesized by oxidation of FeCl₂ solutions and hydrolysis of FeCl₃ solutions. Various Na salts such as sulfate, biphosphate, nitrate, and silicate were added to the starting solutions at different anion/Fe molar ratios of 0-0.05. The XRD patterns of the products showed only the diffraction peaks of β-FeOOH. The crystallinity of the products was noticeably reduced by adding and but slightly influenced by adding . The addition of markedly crystallized the products by the hydrolysis of FeCl₃. The N₂ adsorption revealed that the products with were porous particles assembled by β-FeOOH subcrystals. and strongly coordinating to Fe(III) markedly lowered the crystallinity of the products and remained in the formed particles.     

Interface characteristics and corrosion behaviour of oriented bulk Fe2B alloy in liquid zinc

The interface characteristics and corrosion behaviour of oriented Fe₂B in liquid zinc have been investigated. The results indicate that Fe₂B with preferential growth direction parallel to corrosion interface displays better corrosion resistance to liquid zinc. The Fe₂B/FeB phase transition occurs due to gradient of chemical potential in solid Fe₂B–liuqid zinc system. The liquid zinc corrosion is competition process of dissolution, Fe₂B/FeB transition and fracture–spalling. The fracture–spalling dominates corrosion process when preferred direction of Fe₂B is perpendicular to corrosion interface while Fe₂B/FeB transition plays a role in liquid zinc corrosion as preferred direction of Fe₂B is parallel to corrosion interface.