Study of surface irregularity on corrosion of steel in alkaline media

In this study, the effects of the surface condition of rebar on its cathodic current efficiency were investigated. The cathodic current efficiencies for rebar with different surface conditions were determined from cyclic polarization experiments. The results showed that cathodic faradaic current increased with surface irregularity. Surface condition of steel in alkaline solution also had an effect on double-layer capacitance.     

功能梯度Ni-P合金镀层在酸性和碱性介质中的电化学腐蚀行为

通过电镀法制备了功能梯度N i-P合金镀层。SEM形貌照片显示,梯度层截面致密、无明显的宏观界面;400℃热处理前后梯度层中P含量分布曲线表明,从界面到镀层表面,P含量逐渐降低,呈现明显的梯度变化。在质量分数分别为10%的盐酸和氢氧化钠介质中的动电位极化曲线和电化学交流阻抗谱分析、含氯酸性介质中的腐蚀前后的表面形貌照片表明,与硬铬镀层相比,经过400℃热处理后的梯度N i-P合金镀层的腐蚀电位提高了600 mV以上,腐蚀电流分别降低了2个和1个数量级,阻抗值亦明显提高,而且,其腐蚀前无裂纹,腐蚀后仅发生轻微的点蚀现象。梯度N i-P合金镀层较硬铬镀层表现出更优异的耐蚀性能。     

Membraneless laminar flow-based micro fuel cells operating in alkaline, acidic, and acidic/alkaline media

The lack of a polymer electrolyte membrane (PEM, e.g. Nafion) in membraneless, laminar flow-based micro fuel cells (LF-FCs) eliminates several PEM-related issues such as fuel crossover, cathode flooding, and anode dry-out, as we reported previously. This paper explores the media flexibility of LF-FCs by working in acidic and alkaline media, as well under “mixed-media” conditions in which the anode is in acidic media while the cathode is in alkali, or vice versa. Operating a fuel cell under alkaline conditions has positive effects on the reaction kinetics, both at the anode and cathode, while the cell performance under “mixed-media” conditions offers an opportunity to increase the maximum achievable open cell potential (OCP). The lack of media-related constraints and the simplicity of the LF-FC design allow for these experiments to be performed consecutively in a single LF-FC without changing the system, except for altering the composition/pH of the fuel and oxidant stream. The performance of LF-FCs operated with different media is described and compared.     

The influence of different surface conditions in the corrosion process of carbon steel in alkaline sour media

Different electrochemical methodologies were established to induce general corrosion and blistering on homogeneous and heterogeneous carbon steel surfaces similar to the corrosion damage in a catalytic oil refinery plant. In one case, the film porosity and the iron sulphide stoichiometry were modified and in other case, the surface conditions were changed with sulphur films and microblisters. Additionally, we studied the influence of 1018 carbon steel surface conditions on the corrosion process in a medium simulating the average composition of sour waters in catalytic plants of PEMEX Mexico (0.1 M (NH₄)₂S, 10 ppm CN^– as NaCN, pH 8.8). Using the impedance spectra, from 10 kHz to 0.01 Hz, it was possible to qualitatively identify the carbon steel surface condition in an alkaline sour environment and to suggest the same corrosion process steps for this system, despite different surface conditions: charge transfer resistance of steel oxidation in the metal/corrosion product film interface and Fe²⁺ ion and H° diffusion through the corrosion product film. Finally, scanning electron microscopy of a freshly polished surface showed the formation of a homogeneous film immediately after introducing the carbon steel into the sour media. The other surface changes depended on the induced corrosion process and corroborated the electrochemical impedance predictions.     

Imidazoline hydrolysis in alkaline and acidic media—A review

The literature was reviewed for information on imidazoline hydrolysis. Conflicts involving structures and mechanisms of hydrolysis have been found. Researchers also disagree as to the role of water and whether a protonated form of the imidazoline exists. However, there is agreement that the rate of hydrolysis is dependent on pH and temperature.     

Influence of laser surface hardening on the corrosion resistance of martensitic stainless steel

Martensitic high nitrogen stainless steels offer a combination of wear-, corrosion- and fatigue properties. But for some applications a higher surface hardness is required. A laser hardening with rapid heating (without smelting) and cooling (quenching) rates can improve the surface hardness with compressive residual stresses in the near surface layer. Yet, some cases of pitting corrosion in chloride media are reported.In this study, the influence of process parameters, composition of the atmosphere and the overlapping ratio, has been investigated. With complementary surface analytical methods and electrochemical techniques the relation between surface structure and composition and corrosion behavior in chloride media has been studied.It has been shown that, during the laser treatment the surface must be shielded with argon in order to avoid the formation of a porous layer of iron oxides, which is dramatically detrimental to the corrosion resistance.After the laser treatment a mixture of martensite and retained austenite is obtained, depending on the surface temperature and overlapping ratio. With a surface temperature of 1200 °C and a minimal overlapping ratio (10%), a thin surface layer of retained austenite, wherein nitrides are dissolved, improves the corrosion resistance. The hardness increases with the amount of distorted martensite and reaches a maximum at 1000 °C.     

Corrosion resistance of nickel steel and nickel alloys in aggressive media

The corrosion resistance of austenitic steel and nickel alloys is studied in the most aggressive media within the chemical shops of coke plants: in the stock solutions of the sulfate department and in sulfuric-acid solutions used for the purification of crude benzene. In the study, the most dangerous ions, activating corrosion in 10X17H13M2T steel, are CNS^? ions, which are capable of destroying the passive layers on chromium-nickel-molybdenum steel in the stock solutions of the sulfate department. Research shows that sulfuric-acid solutions used for the purification of crude benzene are very aggressive in relation to high-alloy steel, titanium, zirconium, and copper. Possible structural materials for use in contact with such solutions include the nickel alloys ХН63МБ, ХН65МВНУ, and Hastelloy C-276.     

化学镀镍磷合金镀层碱性无铬钝化膜的耐蚀性研究

为了解决六价铬钝化工艺的毒性问题,采用碱性无铬钝化工艺对A3钢上化学镀Ni–P合金镀层进行钝化处理,在镀层表面获得了抗氧化性与耐蚀性良好的钼酸盐钝化膜。研究了钝化液组分(包括碳酸钠和钼酸钠)的质量浓度以及钝化温度对镀层耐硝酸点滴腐蚀时间的影响,获得了最佳的钝化工艺:NaOH 10 g/L,Na2CO3 4.0 g/L,钼酸钠40.0 g/L,复合添加剂(四硼酸钠与亚硝酸钠组成的复合缓冲体系)5 g/L,温度60°C,时间15 min。通过扫描电镜(SEM)和电化学测试,对比研究了钝化前、后Ni–P合金镀层的表面形貌及耐蚀性能,采用X射线光电子能谱仪(XPS)分析了最佳工艺得到的钝化膜的组成。经最佳钝化工艺处理得到的钝化膜无色透明,由Ni、P、O、Mo等元素组成。钝化后,Ni–P合金镀层在3.5%Na Cl溶液(p H=6.8)中的电荷转移电阻由钝化前的11.6 k?·cm2增大至448.2 k?·cm2,耐硝酸点滴腐蚀时间提高了60倍以上,耐蚀性明显提高。     

A general model of the anodic behaviour of nickel in acidic media

An experimental study of the anodic behaviour of nickel in acidic media is carried out by steady state polarization curves and faradaïc impedance measurements as a function of various parameters related to the electrolyte: pH, concentration and the nature of the anions. We propose several models of the electrode reaction path based on heterogenous chemical kinetic concepts. By a convenient numerical fitting method, we calculate a set of kinetic parameters which are afterwards put into the theoretical equations for dc and the impedance. By this procedure we are able to choose a general model accounting for the behaviour of nickel in a wide range of experimental conditions: active dissolution, passivity, secondary passivity and the oxidation of OH^? to molecular oxygen.     

Comparison of wool bleaching with hydrogen peroxide in alkaline and acidic media

A merino wool top was bleached in both alkaline and acidic media, varying the hydrogen peroxide concentration in the bleaching bath. For the same peroxide concentration, bleaching in an alkaline medium leads to a whiter and more chemically attacked wool than bleaching in an acidic medium. For the same chemical attack, wool bleached in an alkaline medium is whiter than for bleaching in an acidic medium.     

A nickel molybdenite cathode for the hydrogen evolution reaction in alkaline media

The characteristics and mechanism of the hydrogen evolution reaction on a nickel sulphide electrode incorporating molybdenite particles are described. At 25°C the overpotential for the reaction is 300 mV lower than that of the mild steel cathodes used in unipolar electrolysers. The material shows good stability under long term operation.     

Influence of 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole on corrosion inhibition of mild steel in acidic media

An example of a new class of corrosion inhibitors, namely, 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole (DAPT) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ at 30 °C was investigated by various corrosion monitoring techniques. A preliminary screening of the inhibition efficiency was carried out using weight loss measurements. At constant acid concentration, inhibitor efficiency increases with concentration of DAPT and is found to be more efficient in 0.5 M H₂SO₄ than in 1 M HCl. Potentiostatic polarization studies showed that DAPT is a mixed-type inhibitor. The effect of temperature on the corrosion behaviour of mild steel in 1 M HCl with addition of DAPT was studied in the temperature range from 25 to 60 °C. Its was shown that adsorption is consistent with the Langmuir isotherm for 30 °C. The negative free energy of adsorption in the presence of DAPT suggests chemisorption of thiadiazole molecules on the steel surface.     

Electrochemical corrosion of solid and liquid phase sintered silicon carbide in acidic and alkaline environments

Solid and liquid phase sintered silicon carbide (SiC) ceramics are used in aggressive environments, e.g. as seals and linings in chemical plant equipments. There exist data concerning corrosion of solid phase sintered SiC (SSiC), but there are only few data concerning their electrochemical corrosion behaviour. The corrosion of liquid phase sintered SiC ceramics (LPS SiC) containing yttria aluminium oxide grain boundary phases has been investigated by standard methods that have shown the decisive influence of the oxide grain boundary on the corrosion stability of these materials. But no electrochemical investigations are known. In this study therefore, potentiodynamic polarisation measurements have been used to determine the corrosion mechanisms of SSiC and LPS SiC ceramics at room temperature in acidic and alkaline environments. The investigation has shown a pronounced electrochemical corrosion in acids and alkaline solutions for both types of materials. In HCl and HNO₃ pseudo-passivity features due to the formation of a thin layer of SiO₂ on the surface were observed, whereas in NaOH soluble silicate ions were observed resulting in more pronounced corrosion. Microstructural observations of initial and corroded samples revealed that the residual carbon found in the microstructure of SSiC did not dissolve preferentially. The corrosion current densities of the LPS SiC materials were caused by the dissolution of SiC and not by the corrosion of the oxide grain boundary phase. The corrosion current densities of the LPS SiC materials investigated were lower than those of the SSiC materials.     

Leaching of sulphur and calcium from sulphur-infiltrated concrete by alkaline and neutral aqueous media

It has been found that calcium and sulphur are leached by alkaline or neutral aqueous media from sulphur-infiltrated concrete. From chemical examinations and Raman spectroscopy it has been shown that sulphur in the leachate is present as polysulphide anions. It is postulated that homonuclear polymeric anions of sulphur are formed in the presence of moisture when molten sulphur infiltrates concrete. The soluble calcium polysulphides so formed can then be leached by water.     

微裂纹镍和镍封防腐能力的比较

介绍了提高工件防腐能力2种主要工艺:镍封和微裂纹镍工艺。实验结果证明,这2种工艺都比双镍层有更好的防腐性能。分析了镍封和微裂纹镍的防腐机理,区别在于腐蚀开始后电子的流向:镍封/光镍层,电子从光镍层流向镍封层;微裂纹镍/光镍层,电子从微裂纹镍层流向光镍层。综合分析得出,镍封比微裂纹镍有更好的防腐能力。     

Effect of surface roughness on the corrosion resistance of ceramics

Glass and Ceramics -     

Effect of ball milling on the corrosion resistance of magnesium in aqueous media

The influence of the high-energy ball milling on the corrosion behavior of magnesium in aqueous media has been investigated through electrochemical experiments complemented by morphological, structural, chemical and surface analyses. The milling duration was varied from 0 to 40 h. Polarization curves show that the milling procedure improves the magnesium corrosion resistance in passive conditions (KOH solution) and in more active corrosion conditions (borate solution). This is illustrated by the corrosion potential which becomes nobler with milling. The variation of the polarization resistance and related corrosion current with milling time is also an indication of the improvement of the Mg corrosion resistance due to the milling. Moreover, the passive current is significantly lower for milled Mg. The Mg crystallite size is reduced from >100 to 34 nm after 10 h of milling and does not decrease significantly with further milling. The iron contamination of the Mg powder due to the erosion of the milling tools is very low (0.09 wt.% after 40 h of milling). In contrast, a significant oxygen contamination occurs during milling (2.6 wt.% after 40 h of milling). XPS and AES data indicate MgO enrichment in the bulk of the milled Mg without significant MgO increase at the powder surface. The corrosion improvement was attributed to the increase through the milling process of the density of surface defects and grain boundaries susceptible to increase the number of nucleation sites for Mg hydroxylation in aqueous media, leading to the rapid formation of a dense and protective Mg(OH)₂ layer.     

Influence of molecular weight of poly(ortho‐ethoxyaniline) on the corrosion inhibition efficiency of mild steel in acidic media

The present work revealed that the chemical polymerization of ortho‐ethoxyaniline yields two types of polymers not only with different spectroscopic properties but also with different molecular weights: (1) a green form, which corresponds to the high molecular weight fraction of the polymer with a molecular weight of 800,000 g mol^?1 based on the polystyrene calibration. It is mainly composed of quinoid and benzoid structures, which is an indication of a half‐oxidized polymer (emeraldine). This form of the polymer is insoluble in water‐miscible solvents like ethanol and methanol and thus cannot be tested in terms of corrosion inhibition efficiency; (2) a red form, which corresponds to the low molecular weight fraction of the polymer with a molecular weight of 44,000 g mol^?1. It is composed mostly of quinoid structures and exhibits an oxidation state similar to that of the completely oxidized polymer (pernigraniline). In our case, the polymer fraction, which is soluble in alcohol, was first tested as a corrosion inhibitor for mild steel in acidic media, not only at conventional molecular weight (44,000 g mol^?1) but also at different molecular weights. These different molecular weights of the polymer were obtained by adding varying amounts of neutral salt to the synthesis environment. Next, the effect of the molecular weight of the red form of the polymer on the corrosion inhibition efficiency of mild steel in hydrochloric acid solutions was investigated. The obtained results showed that the adsorption of the polymer alcoholic form obeys a Temkin adsorption isotherm with no significant change as function of inhibition efficiencies for a series of molecular weights ranging from13,000 to 124,000 g mol^?1. The effect of temperature on the corrosion behavior of mild steel in 1M HCl with addition of 100 ppm of the alcoholic form of poly(ortho‐ethoxyaniline) was studied in the temperature range 25–60°C. The associated activation corrosion energy was determined. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1275–1284, 2004     

Investigation of corrosion inhibitory effect of hydroxyl propyl alginate on mild steel in acidic media

The anti‐corrosion effect of hydroxyl propyl alginate (HPA) on mild steel in 1M HCl has been studied by chemical (weight loss) and electrochemical (polarization and electrochemical impedance spectroscopy) methods. From all the three methods, it is inferred that there is an increase in inhibition efficiency with increase in concentration of the inhibitor. Polarization studies revealed the mixed mode of inhibition by HPA. The mode of adsorption is physical in nature. The adsorption of HPA on mild steel followed Frumkin adsorption isotherm. The thermodynamic and kinetic parameters have been calculated and discussed. Surface morphological studies have been carried out with Scanning electron microscopy (SEM) and Atomic force microscopy (AFM). Fourier transform infrared spectroscopy (FTIR) is utilized to characterize the adsorbed film. SEM and AFM methods confirm the presence of inhibitor on the surface of the metal. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43004.