Corrosion behavior of Zn and Ni coated carbon steels in 3% NaCl

Corrosion behavior of electrolytic coated carbon steel in 3% NaCl solution was investigated using potentiodynamic polarization, lineer polarization resistance, chronoamperometry, open circuit potential as a function of time and impedance (EIS) measurements. Zn and Ni coated carbon steel surfaces immersed into 3% NaCl solution during 1, 5 and 10 days were characterized using scanning electron microscope (SEM). According to the experimental results, nickel coated carbon steel corrosion resistance was higher than that of Zn coating. Accordingly, the corrosion rate of nickel coated carbon steel decreased by 89.6% compared to the zinc coating.     

Characterization of Electroless Ni-P Deposits on Surface of AZ91D Magnesium Alloy

Characterization of electroless nickel deposits on magnesium alloys was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and electrochemical potentiodynamic polarization analysis.The result of XRD showed that the electroless nickel deposits on magnesium alloys were composed mostly of amorphous Ni-P and partially of microcrystalline nickel.The phosphorus content in the Ni-P deposits was 10.8%by the calculation of EDS.SEM micrographs showed that morphology of electroless nickel deposits on magnesium alloys was a typical cellular structure,and the growth of cellular structure was influenced by surface condition of substrate.Zinc layer between substrate and electroless nickel deposits was not found by the results of SEM and EDS,which indicated that the zinc layer on the surface of magnesium alloy was very thin,and the zinc would dissolved while being immersed in electroless nickel plating solution.The thin zinc layer was almost dissolved completely before Ni-P plating.The result of electrochemical potentiodynamic polarization analysis showed that the corrosion potential Ecorr of electroless nickel deposits in 3.5%NaCl solution was about-0.53 V,which was 1 V higher than that of magnesium alloys substrate.And corrosion current density of Ni-P deposits in 3.5%NaCl solution was much smaller than that of magnesium alloys substrate at the same potential value,which indicated that corrosion resistance of electroless Ni-P deposits was excellent.Discoloration time of concentrated nitric acid test for electroless nickel deposits on magnesium alloys was 445 s,which also indicated excellent corrosion resistance.     

Effects of Cathodic Potential, Bicarbonate, and Chloride Ions on SCC of X70 Pipeline Steel

This is an investigation on the stress corrosion cracking (SCC) behavior of X70 pipeline steel in high pH carbonate-bicarbonate solutions with different concentrations of bicarbonate and chloride ions and at cathodic potential of ?1100 mV versus saturated calomel electrode (SCE) using slow strain rate testing. Electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy were used to investigate the electrochemical behavior of X70 pipeline steel in solutions with different concentrations. X70 pipeline steel fracture surface morphology in these different solutions was also studied by scanning electron microscopy (SEM). The results suggested that the susceptibility to SCC for X70 pipeline steel decreased in the most dilute carbonate-bicarbonate solution in the absence of the chloride ion. Also, at potential of ?1100 mV versus SCE, all fracture surfaces showed semi-brittle behavior with transgranular cracks.     

Inhibition of Mild Steel Corrosion Using l-Histidine and Synergistic Surfactants Additives

The corrosion inhibition behavior of nitrogen-containing amino acid l-Histidine (LHS) on mild steel in 0.1 M H₂SO₄ solution in the temperature range of 30-60 °C was studied by weight loss measurements, and potentiodynamic polarization measurements. The effect of the addition of very small concentration of surfactants, sodium dodecyl sulfate (SDS), and cetyltrimethyl ammonium bromide (CTAB), respectively on the corrosion inhibition behavior of LHS was also studied. The surface morphology of the corroded steel samples was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). LHS significantly reduces the corrosion rates of mild steel, with the maximum inhibition efficiency (IE) being 71.09% at 30 °C in the presence of 500 ppm of LHS. The IE of LHS is synergistically increased in the presence of SDS and CTAB. The SEM and AFM photographs show a clearly different surface morphology in the presence of additives. LHS alone and in combination with surfactants obeys Langmuir adsorption isotherm from the fit of the experimental data of all concentration and temperature studied. The calculated thermodynamic parameters for adsorption reveal strong interaction between the inhibitors and the mild steel surface, and suggest physical adsorption. The results obtained by potentiodynamic polarization measurements are consistent with the results of the weight loss measurement. LHS acts more anodic than cathodic inhibitor.     

Corrosion of AISI 304 stainless steel induced by thermophilic sulfate reducing bacteria (SRB) from a geothermal power unit

Corrosion behavior of AISI 304 stainless steel induced by two strains of thermophilic sulfate reducing bacteria (SRB) was analyzed. Inoculated bacteria were isolated from the surface condenser's tubes of “Los Azufres”, a geothermal electric field located in the State of Michoacan in Central Mexico. Anaerobic corrosion tests were carried out for two months in Czapek's medium at 50°C and 90°C inoculated with strains. The examination in scanning electron microscope (SEM) was accomplished to determine the type of corrosion, morphology, and preferential attacked zones. Measuring the corrosion potential and determining of anodic potentiodynamic polarization curves after two months of exposure in anaerobic conditions carried out an electrochemical study.     

冷喷涂铬锆铜涂层在海水中的耐蚀性能

采用冷喷涂技术在普通碳钢基体上制备了厚度为300μm的铬锆铜涂层,用扫描电子显微镜(SEM)观察涂层的组织形貌。用开路电位（OCP）、电化学阻抗谱和动电位极化曲线等电化学方法研究冷喷涂铬锆铜涂层在天然海水中的耐蚀性能。研究表明,铬锆铜涂层组织致密,在海水环境中,涂层表面形成一层致密的腐蚀产物膜,能有效阻止腐蚀介质向涂层内部渗透,对基体起到良好的保护作用。     

Comparative study of protective magnesium deposit behaviour obtained by continuous and pulsed currents from methylmagnesium chloride solution

Pulsed and continuous (or direct) currents were used for the electrodeposition of magnesium from methylmagnesium chloride solution. The analytical characterization of the magnesium coating was performed by scanning electron spectroscopy (SEM) and the X-ray diffraction (XRD). The electrochemical behaviour of the steel substrate coated by magnesium was assessed by electrochemical impedance spectroscopy and potentiodynamic polarization curves. The deposits morphology was quite different; it changed from smooth and irregular with cracks for the deposit obtained by continuous current (cc), to granulate with an average grain diameter of about 3 µm for the deposit obtained by pulsed current (pc). The electrochemical results showed that the protection of the steel substrate against corrosion was better with the magnesium deposit obtained by pulsed electrodeposition process.     

空蚀对20SiMn在3%NaCl溶液中的电化学腐蚀行为的影响

利用带电化学测试系统的磁致伸缩空蚀试验机研究了 20SiMn低合金钢在3%NaCl水溶液中的电化学腐蚀行为，通过空蚀和静态条件下的自腐蚀电位变化以及交流阻抗谱和动电位极化曲线的比较，分析了空蚀加速20SiMn低合金钢电化学腐蚀的机理.结果表明，空蚀使20SiMn低合金钢的自腐蚀电位正移200 mV，并显著降低电荷转移电阻和线性极化电阻，使电化学腐蚀速率增大约54倍；随着空蚀的进行，电荷转移电阻和线性极化电阻减小，空蚀3 h后逐渐趋于稳定.     

316L不锈钢焊接头耐蚀性能研究

分别采用扫描电镜(SEM)、X射线衍射(XRD)、动电位极化技术及零内阻安培表方法研究爆炸焊接316L不锈钢接头的显微组织形貌、物相、点蚀及电偶腐蚀行为。结果表明,316L不锈钢侧焊缝金属存在严重的组织形变和金属间化合物相,且相对于基体试样,316L不锈钢侧焊缝和熔合区产生了更多的δ铁素体相,这些因素导致焊接后的316L不锈钢耐点蚀和电偶腐蚀性能降低。     

0Cr18Ni9不锈钢表面纳米化对耐蚀性的影响

对0Cr18Ni9不锈钢采用超音速微粒轰击(Supersonic Fine Particles Bombarding,SFPB)进行表面纳米化处理,利用X射线衍射仪和透射电镜对试样表面形成的纳米品组织进行了检验.对试样表面进行了点蚀试验和动电位极化曲线测试,用扫描电镜对点蚀试样表面形貌进行了观察与分析.结果表明,超音速微粒轰击使试样表面层形成平均尺寸约20 nm的纳米晶组织,表面纳米化可以明显改善0Cr18Ni9不锈钢样品在3.5%NaCl溶液中的动电位极化特性,大大提高其抗氯离子腐蚀性能.     

缓蚀剂对2024铝合金在海水中缝隙腐蚀行为的影响

通过缝隙腐蚀浸泡实验考察了钼酸铵((NH4)6Mo7O24)和氯化铈(CeCl3)对2024铝合金在海水中缝隙腐蚀行为的影响,采用扫描电子显微镜(SEM)及能谱EDAX对腐蚀试样表面形貌进行了观察,并分析了试样表面膜成分;结合动电位极化和交流阻抗对其抗缝隙腐蚀机理进行了讨论.结果表明:钼酸铵不能有效地抑制2024铝合金在海水中的缝隙腐蚀,虽然钼酸铵可以在缝隙外表面形成保护膜,但缝隙内的腐蚀却更为严重;而在含氯化铈的海水中,由于Ce3+的还原性降低了缝隙内外氧的浓度差,有效抑制了缝隙腐蚀的发生.     

Electrochemical deposition of nanocrystalline zinc on steel substrate from acid zincate bath

Nanocrystalline zinc coatings were deposited from acid zincate bath containing newly synthesized condensation product. The effect of bath constituents, pH, temperature and current density on the deposit nature were investigated through Hull cell experiments. Current efficiency, throwing power, cathodic polarization and corrosion behavior in 3.5 wt.% NaCl were studied under optimum concentration of additives. Salt spray test and electrochemical measurements showed that nanocrystalline zinc coatings have better corrosion resistance than the zinc coatings deposited from a simple acid zincate bath without additive. The surface morphology and thickness (cross section) of the zinc deposits were studied by scanning electron microscopy (SEM). The preferred orientation and average grain size of the zinc electrodeposit were obtained by X-ray diffraction analysis. The particle size was also characterized by TEM analysis. Energy X-ray diffraction (EDX) and FT-IR spectral analysis were carried out to determine the inclusion of addition agent in the deposit. The experimental results indicated that the addition of condensation product of thiamine hydrochloride (THC) and furfural (FFL) leads to a more uniform nanocrystalline deposition with the grain sizes varying from 20-22 nm.     

Study on Phosphating by Ultrasonic Wave at Room Temperature for Sintered NdFeB Magnet

The corrosion behavior of a NdFeB magnet obtained at room temperature,with and without ultrasonic were investigated.The corrosion resistance was investigated by corrosion immersion tests in 3 wt%neutral NaCl solutions,potentiodynamic polarization tests and electrochemical impedance spectroscopy(EIS).The morphology of the conversion coatings on NdFeB surface were analyzed by scanning electron microscopy(SEM).And the forming mechanism of coatings was studied by potential-time curves.The tests of corrosion resistances show that the combination of phosphating treatment with ultrasonic will further improve the corrosion resistance of the NdFeB.The SEM also confirms that phosphating coating under ultrasonic is more homogeneous and compact.     

Electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment

The electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment was investigated by potentiodynamic polarization technique, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results show that uniform corrosion occurs on 300M steel during the electrochemical measurements because no anodic passivation phenomenon is observed on polarization curves within the measurement range. The tests also show that 300M steel is highly susceptible to chloride containing solution, which is characterized by corrosion current density increasing with the addition of chlorides, and corrosion potential shifting towards positive direction and corrosion resistance decreasing, positively suggesting that chloride ions speed up the corrosion rate of 300M steel. Meanwhile corrosion products on the 300M steel surface formed during the salt spray test are too loose and porous to effectively slow down the corrosion rate. Additionally, a schematic structure of uniform corrosion mechanism can explain that 300M steel has better property of stress corrosion cracking (SCC) resistance than stainless steels.     

酸性介质中氮杂环类缓蚀剂在碳钢上的吸附行为

合成了一种新型含氮杂环有机物:2-(4-叔丁基-苯甲基硫)-5-(1,2,4-三氮唑)-甲基-(1,3,4-噁二唑)(TBTO),通过交流阻抗、动电位极化、失重实验研究了其在酸性介质中的缓蚀效率,并用扫描电镜方法分析了碳钢表面的腐蚀形貌变化.结果表明:TBTO在0.5mol/L H2SO4中对Q235钢的缓蚀作用高达96.2%,能同时抑制碳钢腐蚀的阴、阳极反应过程;化合物在碳钢表面上的吸附行为服从Langmuir吸附等温式.同时用量子化学中的从头算方法对缓蚀剂的分子结构与缓蚀性能的关系进行了研究.     

利用随机方法研究纳米化对纯锌点蚀行为的影响

选择柠檬酸型镀液,用脉冲电镀法成功制备纳米锌镀层;并用电化学法和随机法等研究纳米化对纯锌点蚀行为的影响.结果表明：纳米锌和铸态锌的点蚀击破电位均服从正态分布;纳米化增加了纯锌点蚀击破电位对电位扫描速度的敏感性,使纯锌的点蚀产生类型由B1（parallel）型转为B2（series）型,并能抑制纯锌的点蚀生长.     

TiO2纳米阵列超疏水膜的制备及耐腐蚀性能

采用阳极氧化法在纯钛表面制备TiO2纳米管阵列,使用六甲基二硅胺烷对TiO2纳米管阵列进行低表面能处理,得到超疏水表面．用接触角测量仪测定表面疏水性,采用SEM、EDS技术研究改性前后试样表面的形貌和元素组成,并利用极化曲线和电化学阻抗谱法研究了超疏水膜的耐腐蚀性能．结果表明,TiO2纳米管阵列经改性后超疏水效果明显,...     

4种铸造镁合金在SBF溶液中的腐蚀行为研究

比较了ZK60、AM60、AZ31和AZ91D等4种铸造镁合金在SBF模拟体液中浸泡72 h的腐蚀性能。利用SEM观察了镁合金腐蚀后的显微形貌,根据失重法计算了镁合金的腐蚀速率,采用极化曲线和电化学阻抗方法进一步评价了镁合金的耐蚀性。研究表明,AZ91D合金腐蚀速率最低,并且呈均匀腐蚀。AZ31合金耐蚀性最差,且点蚀严重,AM60和ZK60合金的耐蚀性相近。     

A comparison between the corrosion behavior of nanostructured copper thin films deposited on oxidized silicon and copper sheet in alkaline media

Copper thin films were deposited on oxidized silicon at a substrate temperature of 70 °C and 150 °C using EB-PVD technique. The morphology and crystal orientation of the deposited film were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Corrosion behavior of films was studied through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, immersion test, and cathodic chronopotentiography. Additionally, the crystalline structure of corroded samples immediately after polarization was examined by XRD. Corrosion current density for copper deposits was higher than copper sheet by polarization tests, while the data obtained by the EIS technique emphasized higher corrosion current density for copper sheet. However there was a conflict between polarization and EIS data, the other results obtained by immersion and cathodic chronopotentiography tests proved that the corrosion resistance of copper deposits was higher than copper sheet in the same alkaline media, which can be attributed to chemical composition and higher thickness of the passive layer formed on copper deposits. On the other hand, breakdown potential (E_bp) for copper sheet was about 0.3 V_SCE, while a distinct E_bp was not found for copper deposits. This was a sign of higher stability of the passive layer formed on copper deposits. The XRD patterns of samples immediately after polarization showed a higher content of Cu(OH)₂ on copper deposits in comparison with copper sheet. The stable morphology formed on the surface of copper after polarization was monoclinic CuO, which is assumed to have a significant effect on copper protection in alkaline media. This morphology was more compact on copper deposits in comparison with copper sheet. This was due to higher ability of deposits to react with hydroxyl ions.     

N-Aminorhodanine as an effective corrosion inhibitor for mild steel in 0.5 M H2SO4

The corrosion inhibition effect of N-aminorhodanine (N-AR) on mild steel (MS) in 0.5 M H₂SO₄ was studied in both short and long immersion duration using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), chronoamperometry and hydrogen gas evolution. The surface morphology of MS was examined with scanning electron microscopy (SEM) in absence and presence inhibitor. The inhibitor adsorption process on MS surfaces obeys the Langmuir adsorption isotherm. The results show that NAR is a good inhibitor for MS in the acidic medium. The inhibition efficiency obtained from potentiodynamic polarization, EIS and LPR up to 98% is determined.