Electrochemical study of corrosion inhibition of steel reinforcement in alkaline solutions containing phosphates based components

The aim of this study is to investigate the viability of use of sodium phosphate (Na₃PO₄: SP), tetrasodium pyrophosphate (Na₄P₂O₇: TSPP) and hydroxyethylidene-diphosphonic acid (C₂H₈O₇P₂: HEDP) as a non-toxic corrosion inhibitors of steel bars in alkaline media which simulate the electrolyte in the concrete pores. The effectiveness of these phosphate compounds as corrosion inhibitors was investigated by measuring the corrosion potentials, the polarization curves, the corrosion current densities, and the electrochemical impedance spectroscopy of steel bars immersed for 30 days in saturated Ca(OH)₂ solutions with and without chlorides. At the completion of the tests, the mass losses were determined in order to verify the reliability of the electrochemical results. The results showed that phosphate compounds form a protective layer on the steel surface when immersed in alkaline solution without chlorides. In the presence of chloride ions, the SP acts as an anodic inhibitor and reduces the corrosion activity on steel. The HEDP shows lower efficiency, probably due to the decrease of the pH and to the high [Cl⁻]/[inh] ratio used. Results obtained by electrochemical and gravimetric methods are in quite reasonable agreement.     

Corrosion behaviour of sol–gel coatings doped with cerium salts on 2024-T3 aluminum alloy

The corrosion behaviour of the sol–gel coatings doped with cerium chloride or cerium nitrate on 2024-T3 aluminum alloy was investigated by using electrochemical impedance spectroscopy (EIS) and immersion tests. The sol–gel matrix was obtained through hydrolysis, condensation of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetramethoxysilane (TMOS), using diethylentriamine as curing agent. The results indicated that cerium nitrate with concentration of 1 × 10⁻³ mol L⁻¹ in the silane solution was excellent on self-healing for the sol–gel coating, while cerium chloride had no obvious effect. This result suggested that the introduction of Cl⁻ promoted the under-film pitting of 2024-T3 substrate. It was found that Ce(OH)₃ and Ce(OH)₂²⁺ simultaneously existed in the silane solution by X-ray diffraction (XRD) analysis. Ce(OH)₂²⁺ transformed to CeO₂ due to high-temperature curing of sol–gel matrix demonstrated by X-ray photoelectron spectroscopy (XPS) analysis. Therefore, it can be considered that Ce(OH)₃ and CeO₂ played inhibition roles in the corrosion process of the sol–gel coatings.     

Effect of zinc phosphate chemical conversion coating on corrosion behaviour of mild steel in alkaline medium: protection of rebars in reinforced concrete

We outline the ability of zinc phosphate coatings, obtained by chemical conversion, to protect mild steel rebars against localized corrosion, generated by chloride ions in alkaline media. The corrosion resistance of coated steel, in comparison with uncoated rebars and coated and uncoated steel rebars embedded in mortar, were evaluated by open-circuit potential, potentiodynamic polarization, cronoamperometry and electrochemical impedance spectroscopy. The coated surfaces were characterized by x-ray diffraction and scanning electron microscopy. First, coated mild steel rebars were studied in an alkaline solution with and without chloride simulating a concrete pore solution. The results showed that the slow dissolution of the coating generates hydroxyapatite Ca₁₀(PO₄)₆(OH)₂. After a long immersion, the coating became dense and provided an effective corrosion resistance compared with the mild steel rebar. Secondly, the coated and uncoated steel rebars embedded in mortar and immersed in chloride solution showed no corrosion or deterioration of the coated steel. Corrosion rate is considerably lowered by this phosphate coating.     

Short-term corrosion behavior of galvanized coatings in natural waters of the Greek territory

The corrosion behavior of hot-dip galvanized steel immersed in domestic and seawater was investigated after an exposure period up to 10 days. The examination of the coatings was accomplished with optical microscopy, scanning electron microscopy and X-ray diffraction. From this investigation it was deduced that the corrosion process in domestic water is slow and mainly proceeds through pitting corrosion, while the corrosion phenomena in seawater are more intense. The main mechanisms in this environment are pitting and intergranular corrosion. In both waters the Cl⁻ and the O²⁻ ions diffuse in the coating up to the Fe/Zn interface. Especially in seawater the Cl⁻ ions seem to be very aggressive.     

Effect of zinc phosphate chemical conversion coating on corrosion behaviour of mild steel in alkaline medium: protection of rebars in reinforced concrete

Abstract

We outline the ability of zinc phosphate coatings, obtained by chemical conversion, to protect mild steel rebars against localized corrosion, generated by chloride ions in alkaline media. The corrosion resistance of coated steel, in comparison with uncoated rebars and coated and uncoated steel rebars embedded in mortar, were evaluated by open-circuit potential, potentiodynamic polarization, cronoamperometry and electrochemical impedance spectroscopy. The coated surfaces were characterized by x-ray diffraction and scanning electron microscopy. First, coated mild steel rebars were studied in an alkaline solution with and without chloride simulating a concrete pore solution. The results showed that the slow dissolution of the coating generates hydroxyapatite Ca₁₀(PO₄)₆(OH)₂. After a long immersion, the coating became dense and provided an effective corrosion resistance compared with the mild steel rebar. Secondly, the coated and uncoated steel rebars embedded in mortar and immersed in chloride solution showed no corrosion or deterioration of the coated steel. Corrosion rate is considerably lowered by this phosphate coating.     

镀锌层上单宁酸钝化膜的耐腐蚀性能

为提高镀锌板的耐蚀性,以硝酸、氟化铵、氧氯化锆为辅助成分,配制了单宁酸钝化液,并用其对镀锌板进行钝化处理。通过浸泡试验确定了最佳钝化工艺,通过扫描电镜（SEM）、Tafel曲线和交流阻抗谱研究了不同条件制备的钝化膜的形貌、耐蚀性。结果表明：镀锌层经1mol／L氢氧化钾溶液于65℃活化30s后再在含10g／L氧氯化锆的钝...     

Electrochemical characteristics of pipeline-steel with planar-defect epoxy-coating in simulated solutions of Ku'erle soil

An X70 pipeline steel and a low-carbon steel with different types of coating defects were studied using corrosion tests in Ku’erle simulated soil solution containing 0.6000 mol/L Cl⁻. Electrochemical characteristics of the X70 pipeline steel with planar-defect epoxy-coating in simulated solutions of Ku’erle soil were tested. The results show that in 0.6000 mol/L Cl⁻ simulated solution, for low-carbon steel with coating defects (the area ratio is 4.91%), at free corrosion potential and with immersion time, the corrosion with disbond was more severe than that with a break or with break and disbond. In Ku’erle soil simulated solution, when the coating defect area ratio was increased gradually (0.39% → 1.57% → 6.28%), the corrosion of the X70 steel under coating with break was promoted gradually, and the influence of immersion time on the corrosion decreased. The influence of the immersion time on the corrosion was weakened when the defect area ratio increased to a certain degree.     

Growth of calcium phosphate on surface-modified cotton

A study of the growth of amorphous calcium phosphate on surface-modified cotton fibres by a combination of scanning electron microscopy/electron diffraction X-ray analysis, micro-FTIR and X-ray photoelectron spectroscopy is reported. Cotton fibres phosphorylated by the urea/phosphorous acid method and then soaked in saturated Ca(OH)₂ for approximately one week were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5×SBF for as little as 1 day. Ca(OH)₂ soaking of the fibres is found to produce highly crystalline clusters lodged in the fibres which were confirmed by micro-FTIR to be calcium phosphite monohydrate (CaHPO₃·H₂O). In contrast, phosphorylated fibres not subjected to the Ca(OH)₂ treatment did not exhibit calcium phosphate growth upon immersion in 1.5×SBF solution. Soaking of the Ca(OH)₂-treated fibres with time in the 1.5×SBF solution produced progressively thicker layers of calcium phosphate on the fibres as confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. In general, calcium phosphate coatings formed over 1 1–5 day period soaking in 1.5×SBF solution appeared to consist of agglomerations of a large number of small spherical particles, while coatings formed after 17 days of soaking were distinctly chunky, thick and non-uniform in appearance. Micro-FTIR indicated that CaHPO₃·H₂O clusters were still present in cotton samples even after 4 days of soaking, while after 17 days, only the infrared spectrum typical of calcium phosphate was observed. EDX-measured Ca:P ratios of the coatings, although variable, suggested amorphous calcium phosphate. The mechanism of formation of the coating is believed to involve dissolution of the CaHPO₃.H₂O clusters upon introduction of the Ca(OH)₂-treated phosphorylated cotton into the 1.5×SBF solution which elevates the Ca²⁺ ion concentration in the vicinity of the fibres so stimulating calcium phosphate formation. It is postulated that phosphite groups chemically bound to the cotton fibre surface or a calcium phosphite coating on the fibres act as nucleation sites for calcium phosphate growth in 1.5×SBF solution.     

Corrosion kinetics and patina evolution of galvanized steel in a simulated coastal-industrial atmosphere

The corrosion kinetics and patina (corrosion products) layer evolution of galvanized steel submitted to wet/dry cyclic corrosion test in a simulated coastal-industrial atmosphere was investigated. The results show that zinc coating has a greater corrosion rate during the initial period and a lower corrosion rate during the subsequent period, and the patina composition and structure can greatly affect the corrosion kinetics evolution of zinc coating. Moreover, Zn₅(OH)₆(CO₃)₂ and Zn₄(OH)₆SO₄ are identified as the main stable composition and exhibit an increasing relative amount; while Zn₁₂(OH)₁₅Cl₃(SO₄)₃ cannot stably exist and diminish in the patina layer as the corrosion develops.     

Effect of four coating structures on corrosion kinetic of galvanized reinforcement in concrete

In the present work is described the effect of the characteristics of the galvanized coating on corrosion rate of reinforcing bars embedded in a concrete without additives and in another with 2% CaCl₂ in terms of cement weight. To this end, the following materials were subjected to the action of a moisture saturated atmosphere for a period of400 days: an annealed-galvanized coating; another one obtained by dipping in a molten Zn bath with0.025% Al and some others produced at450 and430°C in an ordinary bath. The attack evolution vs time was controlled by measuring the polarization resistance. The electrochemical determinations were gravimetrically verified and supplemented by a metallographic examination of tests coatings. In the absence of chlorides, the attack is fully tolerated. Chlorides radically change the corrosion behaviour of galvanized steel and increase the attack by a factor of2.8 in the most favourable case, but in these conditions, coatings with thick, homogeneous η layer outperform the usual ones, and specially the annealed ones.     

含H2S的NaCl溶液中溶解氧对PH13-8Mo钢腐蚀性能的影响

为研究新型马氏体沉淀硬化不锈钢PH13-8Mo在含饱和H_2S的NaCl溶液中的腐蚀行为,利用极化曲线、电化学阻抗谱等电化学测试和浸泡实验相结合的方法,通过扫描电子显微镜(SEM)和X射线光电子能谱分析技术(XPS),观察了该高强钢在含H_2S的除氧和不除氧的NaCl溶液中的腐蚀形貌,并对其腐蚀产物的成分进行了分析.结果表明:在除氧的NaCl溶液中,阳极极化曲线的形状发生了明显的变化,电化学阻抗谱的容抗弧的幅值也较未除氧的溶液中变小;在除氧的NaCl溶液中浸泡7 d后,由于H_2S水解后的S~(2-)或HS~-离子侵入到钝化膜的内部,并与钝化膜或金属基体发生反应,使得试样表面发生全面腐蚀,腐蚀产物主要为Fe、Cr、Ni、Mo的氧化物和硫化物;而在未除氧的NaCl溶液中浸泡后,试样表面仅发生局部腐蚀.     

Studies on the presence of copper in the galvanized coating on weathering steel and the adherence characteristic of the protective copper complex formed on galvanized weathering steel

Following the hot-dip process for zinc coating on weathering steel, the galvanizing bath was found to have picked up copper. The galvanizing bath was observed to pick up Cu from the weathering steel at an average rate of 1.83×10^–3% s^–1m^–2 at 452±2C. EDAX/SEM studies exhibited a concentration gradient of copper to exist across the thickness of the galvanized coating on weathering steel. XRD studies revealed the formation of a protective copper complex, {Cu[(OH)₂Cu]₃}SO₄, on galvanized coating containing 0.739% Cu, when exposed in marine and industrial atmospheres. The adherence characteristic of the copper complex to the galvanized coating was found to be very satisfactory.     

Resistance of concrete and mortar against combined attack of chloride and sodium sulphate

Marine environments are typically aggressive to concrete structures, since sea water contains high concentrations of chlorides and sulphates. To improve predictions of concrete durability within such environments, it is important to understand the attack mechanisms of these ions in combination.In this research, the reciprocal influence of Cl⁻ and SO₄²⁻ was investigated for four mixtures, namely with Ordinary Portland Cement, High Sulphate Resistant cement, and with Blast-Furnace Slag (50% and 70% cement replacement). Chloride penetration depths and diffusion coefficients were measured to investigate the influence of SO₄²⁻ on Cl⁻ attack. Besides, length and mass change measurements were performed to examine the influence of Cl⁻ on SO₄²⁻ attack. Since the formation of ettringite, gypsum and Friedel’s salt plays an important role, XRD-analyses were done additionally.It can be concluded that chloride penetration increases when the sulphate content increases at short immersion periods, except for HSR concrete. Concerning the sulphate attack, the presence of chlorides has a mitigating effect.     

陕西土壤模拟液中3种典型接地金属材料的腐蚀行为

为了弄清3种典型接地金属材料(H62黄铜、Q235钢、镀锌钢)在陕西土壤中的腐蚀情况,采用失重法(外加电流浸泡)、电化学测试、扫描电镜(SEM)和X射线衍射(XRD)研究了其在陕西中部土壤模拟液中的腐蚀行为和电化学规律。结果表明:在有外加电流的模拟液中浸泡,随浸泡时间延长,Q235钢腐蚀速率逐渐变慢,镀锌钢表面镀锌层腐蚀较快,H62黄铜的腐蚀速率变化不大;Q235钢、镀锌钢、H62黄铜的腐蚀产物分别主要为α-FeOOH、β-FeOOH、Fe3O4,ZnO、Zn(OH)2、FeOOH、Zn5(CO3)2(OH)6和Cu2O、CuO、CuCl2;在含相同NaCl浓度的模拟液中,H62黄铜的耐腐蚀性能最好,镀锌钢的次之,Q235钢的最差。     

镀锌钢板蒸镀镁层的耐腐蚀机理

采用真空蒸镀技术在镀锌钢板上蒸镀镁,制得了蒸镀镁层,将其在5%NaCl溶液中浸泡,运用XRD,SEM和电化学方法等对其腐蚀产物进行了分析.对2种材料的的腐蚀行为进行了研究,探讨了其耐腐蚀机理.结果表明:镀锌钢板蒸镀镁层是以MgZn2和Mg2Zn11.金属间化合物的形式存在;其腐蚀产物是以致密且具有良好绝缘性的ZnCl2·4Zn(OH)2·H2O和致密的Zn4CO3(OH)6·H2O为主体,而纯锌镀层的腐蚀产物是以疏松且具有N型半导体性质的ZnO为主体;蒸镀镁层的形成可以抑制Zn(OH)2向ZnO的转化,能促进Zn(OH)2向ZnCl2·4Zn(OH)2·H2O和Zn4CO3(OH)6·H2O的转化,后二者能够牢固地覆盖在基体表面,从而延缓了锌的腐蚀进程;在宏观上表现为镀锌钢板蒸镀镁层腐蚀产物相对于纯锌镀层更加致密,在电化学行为上表现为镀锌钢板蒸镀镬层具有更小的腐蚀电流和更高的极化电阻.     

Role of the medium in the character of delayed fracture of high-nitrogen steels

Halide ions efficiently accelerate corrosion processes under stresses due to adsorption of Hal-ions on high-nitrogen chromium-manganese steels and increase in the degree of filling of the surface (in the process of the change Cl⁻→Br⁻) with hydroxyhalide intermediates (FeHalOH)²⁻, (FeHalOH)⁻, and Cu₂(OH)₃Cl. Fracture of specimens made of 18Mn-18Cr steel in water at room temperature in the process of tests for long-term strength occurs according to a toughness mechanism due to the initiation, growth, and coalescence of micropores. In saturated NaCl and KBr solutions, fracture has a slight effect on the mechanism of initiation and coalescence of micropores. In a CuCl₂ saturated solution, a certain part of the surface is covered by products of corrosion, while the other part is covered by large pores. At the bottom of the pores, chaotically oriented micropores and inclusions are observed. Karpenko Physicomechanical Institute. Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 1, pp. 102–104, January–February, 2000.     

Study of vanadium-based chemical conversion coating on the corrosion resistance of magnesium alloy

In this study, magnesium alloy (AZ61) was immersed in vanadium containing bath with various conditions, such as the vanadium concentration, immersion time and bath temperature. The results indicate that increase of both vanadium concentration and immersion time produces a thicker conversion layer. However, when immersion time is too long, it will worsen the corrosion resistance due to the increasing of the crack density. The experimental parameter of bath temperature has no significant effect on corrosion resistance. Our results demonstrated that the better corrosion resistance coating can be obtained when the samples are submitted to an immersion in the conversion bath containing NaVO₃ with concentration of 30 g l⁻¹ for 10 min at 80 °C. The presented conversion treatment has its potential to replace the chrome-based conversion coating treatment.     

Studies on the corrosion behavior of cerium-implanted zircaloy-4 with GAXRD

In order to study the influence of cerium ion implantation on the aqueous corrosion behavior of zircaloy-4, specimens were implanted by cerium ions with a fluence range from 1×10¹⁶ to 1×10¹⁷ ions/cm² at maximum 150°C, using MEVVA source at an extracted voltage of 40 kV. The valence and elements penetration distribution of the surface layer were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES) respectively. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the cerium ion implantation in the oxide films. Three-sweep potentiodynamic polarization measurement was employed to value the aqueous corrosion resistance of zircaloy-4 in a 1 N H₂SO₄ solution. It was found that a significant improvement in the aqueous corrosion behavior of zircaloy-4 implanted with cerium ions compared with that of the as-received zircaloy-4. The improvement effect will declined with raising the implantation fluence. The bigger is the fluence, the less is the improvement. Finally, the mechanism of the corrosion behavior of the cerium-implanted zircaloy-4 is discussed.     

Protection of reinforcement steel corrosion by phenylphosphonic acid pre-treatment PART II: Tests in mortar medium

A pre-treatment of steel reinforcement in mortar by a 72 h immersion in 0.1 M phenyl-phosphonic acid (C₆H₅P(O)(OH)₂; PPA) was investigated. Then effectiveness of this procedure for protection against the corrosion of steel bars embedded in pre- or post-addition of sodium chloride mortar was evaluated by electrochemical impedance spectroscopy, visual inspection, SEM, and EDS analyses.The results showed that for non-treated steel reinforcement, the charge transfer resistance (R_t) decreases considerably with time indicating a very advanced state of corrosion after 54 months corrosion test. In contrast, for pre-treated steel rebar, this resistance remains high reflecting the effectiveness of the pre-treatment method against corrosion. The corrosion rate evaluated from the charge transfer resistance at 54 months corrosion in chloride containing medium was 0.5 μm year⁻¹.     

Nanotechnology-associated coatings for aircrafts

Polymeric epoxy-based composites are modified with nanopowders of silicon oxide (∼ 100 nm). By the method of spraying, these composites are applied to specimens of 2024-T3 aluminum alloy preliminary treated with molybdate solutions to get conversion layers. Three types of polymeric coatings are considered: reference, treated by silica, and with additional polyurethane coatings. The aim of modification of polymeric coatings is to absorb and/or block unwanted ions/molecules (Cl⁻, O₂, OH⁻, H₂O, etc.) and improve the protective properties of the films. The tests carried out by the method of electrochemical impedance spectroscopy, in a salt-fog chamber, and by immersion in a 0.5 M NaCl solution reveal high anticorrosion characteristics of the coating. New coatings are promising for the corrosion protection in the aircraft industry. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 3, pp. 103–108, May–June, 2007.