The effect of ionic peneration on semiconducting behaviour of temporarily protective oil coating on the surface of AISI 304 stainless steel

In this paper, the semiconducting behaviour of temporarily protective oil coatings on the surface of naked and prepassivated AISI 304 stainless steel immersed in 3% aqueous NaCl solution was studied by utilizing potential‐capacitance methode, Mott‐Schottky analysis and impedance analysis. It was pointed out that the temporarily protective oil coating behaves as a semiconductor during its degradation. The ionic penetration and the substrate greatly affect the conduction behaviour of the oil coating. On the surface of naked AISI 304 stainless steel, the oil coating behaves as a n‐type semiconductor. With increasing immersion time, the donor density of the space charge layer in the temporarily protective oil coating increases from 10¹⁹ to 10²⁵ m^?3. However, on the surface of the prepassivated substrate the space charge layer in the oil coating is significantly affected by the oxide on the steel electrode. In this case immersion time does not influence the density of charge carriers in the oil coating (10²¹ m^?3). Impedance analysis also verify above results.     

Surface treatment of Cf/Al composites with immersion in aqueous solution containing Ce ions for corrosion barrier

In this study, Ce‐rich coating is investigated as corrosion inhibitor of carbon fibers reinforcement aluminum matrix (Cf/Al) composites. The coatings are obtained by immersion in aqueous solution containing Ce(NO₃)₃ onto composite surface, whereas the Ce‐rich coating process produces a coating with highly heterogeneous nature of the surface, but micro‐cracked layer with “dry‐mud” morphology. The coatings were composed of Ce‐rich nano‐particles, Ce‐rich particles with a sphere‐like morphology, which are agglomerated particles with diameter 4 ～ 8 nm and piled up for this coating. TEM observation for Ce conversion coating of the corresponding ring‐like SAED patterns could not be matched to any of the previously reported structures of cerium compounds. Results of high‐resolution XPS spectra of Ce3d obtained for Ce conversion coating show that the Ce3d spectra has several components with binding energies characteristic of Ce³⁺ and Ce⁴⁺. The Ce‐rich coating process produces effective corrosion protecting of Cf/Al composites, which is verified by electrochemical measurement results. The R_t values of coated sample are higher than those of uncoated sample, this confirms the better corrosion resistance of coating obtained after immersion treatment for Cf/Al composites.     

Protection of passivated iron against corrosion in a 0.1 M NaNO3 solution by coverage with an ultrathin polymer coating of carboxylate SAM

An ultrathin, ordered and two-dimensional polymer coating was prepared on passivated iron by modification of 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻ self-assembled monolayer (SAM) with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. Protection of passivated iron against passive film breakdown and corrosion of iron was examined by monitoring of the open-circuit potential and repeated polarization measurements in an aerated 0.1 M NaNO₃ solution during immersion for many hours. Passive film breakdown on the polymer-coated electrode in the solution was not observed during immersion for 480 h, whereas that of the passivated one occurred at 18.1 h, indicating protection of the passive film from breakdown by coverage with the polymer coating. The protective efficiencies of the passive film covered with the coating were extremely high, around 99.9% in the initial region of the immersion time up to 72 h and more than 98.3% thereafter, indicating prominent cooperative suppression of iron corrosion in 0.1 M NaNO₃ by coverage with the passive film and polymer coating. The polymer-coated surface was characterized by contact angle measurement and electron-probe microanalysis.     

Microstructural characteristics and corrosion property of non‐chromate surface treatments on AZ91D magnesium alloy

Chromate conversion coatings can be successfully used for corrosion protection of magnesium alloys. However, the environmental laws have imposed severe restrictions on chromate use in many countries. In this study, a novel protective environmental‐functionally gradient coating was formed on AZ91D magnesium alloy by non‐chromate surface treatments, which consisted of pre‐etching followed by cerium‐based chemical conversion before applying the sol–gel CeO₂ film. It was determined by the analysis of X‐ray diffraction that the gradient coating was mainly composed of CeO₂. The calculation, based on the Scherrer formula, further revealed the formation of nanocrystalline structure in the coating. Scanning electron microscopy (SEM) observations showed that the coating was homogeneous and compact, no obvious cracked structure occurred. According to the immersion tests, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) tests, the corrosion resistance of AZ91D magnesium alloy was found to be greatly improved by means of this novel environmental‐functionally gradient coating.     

The long-term corrosion performance and adhesion properties of 7B04 aluminum alloy/anodic film/epoxy primer system in acidic NaCl solution

The deterioration process and corrosion protective effect of 7B04 aluminum alloy/anodic film/epoxy primer system in acidic NaCl solution for 3024 h were investigated by optical/electron microscopes, electrochemical impedance spectroscopy (EIS), scanning Kelvin probe (SKP), and pull-off adhesion test. The results showed that the protective system of anodic film and epoxy primer can protect aluminum alloy from pitting corrosion after immersion for 2352 h. According to the response characteristics of EIS and SKP, different stages of the failure process could be identified. During the first 100 h of immersion, the water transport in the coating followed Fickian law, and the water diffusion coefficient was 2.03 × 10^?11 cm²/s, which demonstrated that the coating has good impermeability. Anodizing and coating treatment improved the open circuit potential and impedance of 7B04 aluminum alloy and made the distribution of Volta potential more uniform. The decreasing rate of wet adhesion strength was first fast and then slow, which was similar to the variation rule of coating resistance. The anodic film enhanced the adhesion between epoxy primer and substrate so that the failure nature of the adhesion test was mainly the cohesive failure of the epoxy primer.     

Fuzzy cluster analysis constructed by numeric genetic algorithm (NGA) and its use in the evaluation of heterogeneity of temporarily protective oil coating

A fuzzy cluster analysis based on a numeric genetic algorithm (NGA) was applied for the study of the inhomogeneity of temporarily protective oil coating. Three different types of film behaviour can be assigned to the investigated temporarily protective coating: corrosive, protective and unstable. It is suggested that utilizing this method could evaluate the heterogeneity of temporarily protective oil coating more efficiently, precisely and more comprehensively.     

The inhibition effect of two commercial compounds on interface steel/natural softened water

The protection against the corrosion of the carbon steel in aqueous environment by commercial inhibitors, based of nitrite and alkanolamine, has been studied by electrochemical impedance spectroscopy (EIS) and several analytic methods. An inhibitor’s efficiency has been determined with the two compounds on polished surface in presence of softened water. The results show that the two inhibitors act by the formation of protective layer on interface steel/electrolyte but the efficiency is more important in the case of the nitrite compound thanks to the formation of film with thickness estimated by Atomic force microscopy (AFM) at 0.8 μm after 102 days of immersion. In the case of the nitrites, the inhibitor film is a porous layer, weak conductor and presents a considerable increase of the charge transfer resistance with time. This is a result of an interest protection of the surface against corrosion. The low frequencies limit (L _LF) reaches about 150 kOhm cm² after 59 days of immersion. In the case of the alkanolamine, XPS (X-Rray Spectroscopy) show that the film formed is richer of Fe ions but is offered a considerable protection of the interface, its thickness is about 0.26 μm and L _LF reaches about 35.5 kOhm cm² after 61 days of immersion. The influence of surface state is discussed in this paper, in fact on raw surface steel, no inhibitor efficiency is observed. A few protections are given with a crude surface in contact with water softened in presence of the nitrite compound.     

银纳米线透明电极的成膜及后处理综述

银纳米线是一种有较大应用潜力的新一代透明导电电极材料。总结了利用银纳米线制备透明电极常用的旋涂、喷涂和棒涂法3种主要液相成膜工艺,对成膜工艺对膜性能的影响以及其应用潜力进行了分析;介绍了加热、加压和引入介质3类后处理方法,阐述了不同后处理方法对银纳米线透明电极综合性能的影响。     

Cold-Sprayed Al Coating for Corrosion Protection of Sintered NdFeB

A protective Al coating was achieved on the sintered NdFeB magnet by cold spray. The sprayed Al particles generate plastic deformation and hang together. The thickness of the coating is about 170 μm. The corrosion currents of Al coating and NdFeB without immersion tested by potentiodynamic polarization in 3.5 wt.% NaCl solutions are 1.350 × 10^?6 and 4.361 × 10^?6 A/cm², respectively. X-ray photoelectron spectrometry results confirm that the oxide film is Al₂O₃ and the corrosion process can be derived into two different stages. The Al coating can provide long-term protection for NdFeB effectively.     

Protection of passivated iron from corrosion in 0.1 M KClO4 with and without Cl by coverage with a two-dimensional polymer film of carboxylate ion self-assembled monolayer

A film of two-dimensional polymer was prepared on an iron electrode passivated in a borate buffer solution at pH 8.49, derivatized with 16-hydroxyhexadecanoate ion and then modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. The protective ability of the polymer film adsorbed on passivated iron was examined by polarization measurement in oxygenated 0.1 M KClO₄ solutions with and without 1 × 10⁻⁴ and 1 × 10⁻³ M of Cl⁻. The values of the open-circuit potential, E_oc were monitored with the immersion time, t in these solutions. The E_oc value of the passivated electrode in 0.1 M KClO₄ was maintained high, more than −0.2 V/SCE in the initial region of t up to 10 h, indicating the presence of a passive film on the electrode. Thereafter, E_oc decreased to −0.4 V/SCE abruptly, exhibiting breakdown of the passive film. The value of the passivated electrode covered with the polymer film remained almost constant around −0.04 V/SCE during immersion for 45 h. The protective efficiency, P (%) of the polymer film on passivated iron was extremely high, more than 99.9% unless the passive film was broken down, indicating complete protection of iron against corrosion. The times for breakdown on the passivated electrode and polymer-coated one diminished with an increase in the concentration of Cl⁻. The polymer-coated surface was analyzed by electron-probe microanalysis after immersion in 0.1 M KClO₄ for 24 h.     

Impedance spectroscopy of undoped,doped and overoxidized polypyrrole films

The frequency response of polypyrrole thin films was studied in the presence of NO₃⁻, F⁻, Cl⁻ and Br⁻ in the potential region of interest for the study of the insulator—conductor transition. The impedance spectra have been interpreted using the Randles equivalent circuit modified with a constant phase element (CPE), using nonlinear least-squares fitting of the parameters of the circuit to experimental data. The results show that the distribution of relaxation times widens with oxidation of the polymer, indicating the presence of domains with different electrical properties, consistent with hopping of charge carriers in the oxidized state. It is also shown that in F⁻ solution and at moderate potentials, overoxidation leads to irreversible degradation of the electroactive properties, affecting the electronic conductivity and diffusion coefficients of ionic species within the film.     

Comparative study on corrosion protection properties of electroless Ni‐P‐ZrO2 and Ni‐P coatings on AZ91D magnesium alloy

Electroless Ni‐P‐ZrO₂ and Ni‐P coatings on AZ91D magnesium alloy were prepared, and their corrosion protection properties were compared in this paper. The potentiodynamic curves and electrochemical impedance spectroscopy (EIS) of the coated magnesium alloy in 3.5% NaCl solution showed that the corrosion performance of Ni‐P‐ZrO₂ composite coating was superior to that of Ni‐P coating. The same conclusion was obtained with salt spray and immersion tests. The corrosion morphologies of two kinds of coatings with various immersion time intervals in 3.5% NaCl solution indicated that most corrosion products concentrated on the nodules boundaries of Ni‐P coating and blocked corrosion pit was the main corrosion form. For the Ni‐P‐ZrO₂ coating, tortuous nodules boundaries were not the weak sites of the coating and corrosion initiated from the nickel phosphor alloy around the nanometer powders. Open corrosion pits occurred on the composite coating surface, and the coating was corroded gradually. Thus, the Ni‐P‐ZrO₂ coating exhibited better corrosion protection property to magnesium alloy substrate than Ni‐P coating.     

An ultrathin polymer coating of carboxylate self-assembled monolayer adsorbed on passivated iron to prevent iron corrosion in 0.1 M Na2SO4

For preparing an ultrathin two-dimensional polymer coating adsorbed on passivated iron, a 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻ self-assembled monolayer (SAM) was modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. Protection of passivated iron against passive film breakdown and corrosion of iron was investigated by monitoring of the open-circuit potential and repeated polarization measurements in an aerated 0.1 M Na₂SO₄ solution during immersion for many hours. The time required for passive film breakdown of the polymer-coated electrode was markedly higher in this solution than that of the passivated one, indicating protection of the passive film from breakdown by coverage with the polymer coating. The protective efficiencies of the passive film covered with the coating were extremely high, more than 99.9% in 0.1 M Na₂SO₄ before the passive film was broken down, showing prominent cooperative suppression of iron corrosion in the solution by coverage with the passive film and polymer coating. The polymer-coated surface was characterized by contact angle measurement and electron-probe microanalysis (EPMA). Prevention of passive film breakdown and iron corrosion for the polymer-coated electrode healed in 0.1 M NaNO₃ was also examined in 0.1 M Na₂SO₄.     

Effect of organic additives on the performance of titanium-based conversion coatings

The performance on aluminium-manganese alloy 3003 of hexafluorotitanic acid (H₂TiF₆) conversion treatments incorporating either poly(acrylic acid) (PAA) or tannic acid (TA) has been studied and compared with coatings without organic additions and coatings containing only the two organic compounds. Polarisation curves were first used to assess the performance, and elucidate protective mechanisms in NaCl solutions. It is shown that for short immersion times, the addition of the organic components gives pitting potentials (defined here as the potential at which the pitting current passes 0.01 mA cm⁻²) higher than for H₂TiF₆ alone, with pitting currents increasing more slowly as the scan continued. However, after longer immersion, whereas the H₂TiF₆ based coatings without inhibitor shows steadily increasing pitting potentials, improvement with inhibitors was less marked, so that after three days the uninhibited coating showed the highest pitting potential. Pitting inhibition for the combined systems (defined here as the degree of separation between corrosion potential and pitting potential) is limited, and after longer immersion times is usually worse than H₂TiF₆ alone, and sometimes worse than bare alloy. Corrosion currents fall markedly with time for most samples, but the TA- and PAA-containing coatings also show strong inhibition when first exposed. To investigate the separate protective effects of the inorganic Ti-containing film and the organic additives, AC impedance spectra were measured for coatings of PAA or TA without the inorganic component and compared with spectra for coatings of H₂TiF₆ alone [Surf. Eng. 15 (1999) 407]. All three coatings show polarisation resistances increasing significantly over time, indicating falling corrosion rates.     

Effect of oil in multiphase flow on corrosion product film in large horizontal pipeline

The properties of corrosion product film formed on carbon steel pipelines under saltwater‐oil‐CO₂ multiphase flow are examined by AC impedance methods. Experiments are performed in a 101.6 cm I.D., 10 m long pipeline. Experimental results show that there are two reactions on the steel surface in saltwater‐oil mixture. One is charge transfer, and the other is diffusion. By calculation of charge transfer resistance, R_t, and Warburg impedance coefficient, σ, it is found that, R_t in saltwater‐oil mixture is much higher than that in saltwater. In saltwater‐oil mixture, R_t and σ increase with immersion time. It is suggested that the porous corrosion film occurs on the surface of the steel, and that the film becomes compact when the immersion time increases. The longer the exposure time, the more compact the film, resulting in that the corrosion rate becomes lower.     

防锈油膜在5% Na2SO4溶液中的半导体导电行为

采用电位—电容法及Mott-Schottky分析技术研究了自腐蚀电位条件下防锈油膜在5% Na2SO4溶液中失效过程的导电机制转变行为.防锈油膜在5% Na2SO4溶液中的失效过程存在半导体导电特征，随着浸泡时间的延长，防锈油膜从浸泡初期的p型半导体转变为n型半导体，转变过程中，防锈油膜中出现两个空间电荷过渡层.随着浸泡时间的延长，防锈油膜中的空间电荷层厚度皆逐渐减小，载流子密度则逐渐增加，并且计算了不同转变时期防锈油膜中的电子给体（ND）和电子受体（NA）密度大小.     

Investigation of adsorption and corrosion inhibition effect of 1,1’-thiocarbonyldiimidazole on mild steel in hydrochloric acid solution

The adsorption and inhibition effect of 1,1′-thiocarbonyldiimidazole (TCDI) on the corrosion of mild steel (MS) in 0.5 M HCl solution was studied in both short and long immersion time (120 h) with the help of electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. For long-time tests, the hydrogen gas evolution (VH₂-t) and the change of open circuit potential with immersion time (E _ocp-t) were also utilized in addition to the former two techniques. The surface morphology of MS after its exposure to 0.5 M HCl solution with and without 1.0 × 10⁻² M TCDI was examined by scanning electron microscopy (SEM). It was demonstrated that the inhibition efficiency of studied inhibitor is concentration depended and increased with TCDI concentration. The higher value of inhibition efficiency was obtained after longer immersion time merely on the basis of strong increase of corrosion rate of mild steel in the blank solution. The high inhibition efficiency was discussed in terms of adsorption of inhibitor molecules and protective film formation on the mild steel surface which was substantiated by SEM micrographs. The adsorption of TCDI on MS was found to obey Langmuir adsorption isotherm.     

Preparation of polyaniline–TiO2 composite and its comparative corrosion protection performance with polyaniline

Due to strict environmental regulations on the usage of chromate in the coating industries, search for effective inhibitive pigment in replacing those chromate pigments has become necessary. In recent years it has been shown that electrically conducting polymers such as polyaniline (PANI) incorporated coatings are able to protect steel due to their passivating ability similar to that of chromates. This work presents the comparative corrosion protection performance of the coatings containing polyaniline and polyaniline–TiO₂ composite (PTC) on steel in acrylic binder. The PANI and PTC were prepared by chemical oxidative method of aniline by ammonium persulfate. The polymers were characterized by FTIR, XRD and SEM. The corrosion protection performance of the coatings containing PANI and PTC on steel was evaluated by immersion test in 3% NaCl for 60 days and salt fog test for 35 days. The performance of the coatings in both the tests was investigated by open circuit potential measurements and EIS technique. It has been found that the open circuit potential values of PTC containing coating are more nobler by 50–200 mV in comparison to that of coatings with PANI. Besides, the resistance values of the coating containing PTC were more than 10⁷ Ω cm² in the 3% NaCl immersion test after 60 days and 10⁹ Ω cm² in the salt fog test of 35 days which were two orders high in comparison to that of PANI containing coatings. The better performance of PTC containing coatings may be due to uniform distribution of polyaniline which can form uniform passive film on the iron surface.     

Self-healing coatings of inorganic particles using a pH-sensitive organic agent

A self-healing corrosion protective coating was developed using TiO₂ particles and casein as pH-sensitive organic agents that is also environmentally friendly materials. A film structured of TiO₂ particles was formed on a substrate (magnesium alloy) by dip-coating followed by immersion in a casein solution. Casein was inserted and fixed in the particle film by changing the pH of the casein solution. The polarization resistance of the scratched specimen prepared by changing the pH of the solution from 12 to 5 increased with testing time, and a deposited film consisting of TiO₂ particles and casein was observed after the test.     

Long-term anticorrosion behaviour of polyaniline on mild Steel

Anticorrosion performances of polyaniline emeraldine base/epoxy resin (EB/ER) coating on mild steel in 3.5% NaCl solutions of various pH values were investigated by electrochemical impedance spectroscopy (EIS) for 150 days. In neutral solution (pH 6.1), EB/ER coating offered very efficient corrosion protection with respect to pure ER coating, especially when EB content was 5-10%. The impedance at 0.1 Hz of the coating increased in the first 1-40 immersion days and then remained constant above 10⁹ Ω·cm² until 150 days, which in combination with the observation of a Fe₂O₃/Fe₃O₄ passive film formed on steel confirmed that the protection of EB was mainly anodic. In acidic or basic solution (pH 1 or 13), EB/ER coating also performed much better than pure ER coating. However, these media weakened the corrosion resistance due to breakdown of the passive film or deterioration of the ER binder.