CORROSION BEHAVIOR OF X70 PIPELINE STEEL IN SIMULATED KUERLE SOIL SOLUTION WITH CO2

采用动电位扫描、交流阻抗电化学方法和慢应变速率拉伸实验(SSRT)研究了CO2对X70管线钢在库尔勒土壤模拟溶液中应力腐蚀开裂(SCC)行为的影响, 并利用扫描电镜分析了不同CO2分压下的断面形貌. 结果表明: CO2能够与腐蚀膜FeCO3反应, 生成可溶性Fe的络合物 Fe(CO3)2 2-, 加速X70管线钢腐蚀; CO2与H2O形成H2CO3和HCO3-, 为阴极反应提供H+. X70管线钢在含 CO2溶液中的SCC机理为氢脆--阳极溶解协同机理, 且随CO2 分压的增加, 氢脆作用增大.     

外加电位对316L不锈钢在硼酸溶液中应力腐蚀行为的影响

采用慢应变速率拉伸 (SSRT) 实验,结合不同扫描速率下的动电位极化曲线,对316L不锈钢在动电位极化曲线不同区下的应力腐蚀开裂 (SCC) 敏感性以及腐蚀机理进行了研究。通过断口的SEM形貌进一步分析了316L不锈钢在硼酸溶液中的应力腐蚀开裂机理。结果表明,在近中性硼酸溶液环境下,外加电位对应力腐蚀开裂敏感性具有一定影响;当外加电位处于钝化区和过钝化区时,其SCC机制是由阳极溶解控制,且随着电位的升高其SCC敏感性增大;外加电位为-600 mV时,开裂机制为氢致开裂,此时316L不锈钢有最大SCC敏感性。     

X70管线钢在含CO2库尔勒土壤模拟溶液中的腐蚀行为

采用动电位扫描、交流阻抗电化学方法和慢应变速率拉伸实验（SSRT）研究了CO2对X70管线钢在库尔勒土壤模拟溶液中应力腐蚀开裂（SCC）行为的影响,并利用扫描电镜分析了不同CO2分压下的断面形貌．结果表明：CO2能够与腐蚀膜FeCO3反应,生成可溶性Fe的络合物Fe（CO3）2^2-,加速X70管线钢腐蚀;CO2与H2O形成H2CO3和HCO3^-,为阴极反应提供H^＋．X70管线钢在含CO2溶液中的SCC机理为氢脆一阳极溶解协同机理,且随CO2分压的增加,氢脆作用增大．     

外加电位对X80管线钢在鹰潭土壤模拟溶液中应力腐蚀行为的影响

采用电化学动电位极化技术、慢应变速率拉伸(SSRT)实验和SEM对X80管线钢在鹰潭土壤模拟溶液中的应力腐蚀行为进行了研究.结果表明:X80管线钢在酸性土壤环境中具有较高的SCC敏感性,其断口模式为穿晶SCC;SCC机制随外加电位的不同而改变,在外加电位高于-930 mV时,其SCC机制由阳极溶解和氢致腐蚀两种电极过程控制,呈现阳极溶解和氢脆复合机制;当电位低于该电位时,其SCC为氢脆机制.随着外加阴极电位的降低,X80管线钢的SCC敏感性不断增大;与X70钢相比,氢脆作用在X80管线钢SCC过程中发挥了更重要的作用.     

800合金的碱性应力腐蚀破裂 I.外加电位的影响

采用恒电位C形环SCC试验方法,研究800合金在含0.3％SiO_2和0.3％Na_2S_2O_3的沸腾50％NaOH溶液中的SCC行为,并结合极化曲线测试及表面膜俄歇电子能谱(AES)分析结果进行了讨论。结果表明,在约-0.30V(SCE)以上的较高电位钝化区,800合金对碱性SCC非常敏感,而在约-0.45V(SCE)以下电位,SCC敏感性大大降低。这与较高电位下生成严重贫铬的Ni和Fe的氧化膜,而较低电位下生成由Cr、Fe、Ni的氧化物共同组成的表面膜密切相关。     

热浓碱中的电化学测试及其在SCC研究中的应用

通过对高镍合金800、690及其主要合金元素Ni、Cr、Fe在沸腾碱溶液中阳极极化曲线的测试,获得800、690合金的活化一钝化性能及其与主要合金元素电化学行为的相关性信息.对800合金在不同电位下生成的表面膜进行AES表面分析的结果与合金及纯金属电化学测试结果也有很好的对应关系.采用恒电位下定变形SCC试验,研究了在沸腾50%NaOH溶液中,添加有害杂质SiO_2、Na_2S_2O_3以及外加电位对合金碱性SCC敏感性的影响,讨论了SCC性能与电化学行为及表面膜组成之间的关系.结果表明,合金及纯金属元素的电化学测试是研究合金SCC敏感性及其机理的有用的辅助手段.     

外加电位对X70管线钢在库尔勒土壤模拟溶液中应力腐蚀开裂敏感性的影响

采用慢应变速率拉仲试验(SSRT)研究了不同外加电位下X70管线钢在库尔勒土壤模拟溶液中的应力腐蚀开裂(SCC)行为,并用扫描电镜分析了不同电位下的断面形貌.结果表明,X70管线钢在库尔勒土壤模拟溶液中具有SCC敏感性;在Ecorr附近施加弱极化时,应力腐蚀开裂敏感性增加;施加强阳极电位时,发生强烈阳极溶解,导致阳极溶解断裂;施加强阴极电位时,析氢过程加强,导致氢致应力腐蚀断裂.     

外加电位对X80钢在南雄土壤模拟溶液中应力腐蚀行为的影响

采用动电位极化技术、慢应变速率拉伸(SSRT)试验和SEM形貌分析等方法,研究了外加电位对X80钢在南雄土壤模拟溶液中的应力腐蚀破裂(SCC)行为的影响。结果表明,在不同外加电位下,X80钢在土壤模拟溶液中呈现出不同的SCC敏感性。在-550mV(SCE,下同)阳极电位下,X80钢的阳极溶解抑制了其SCC的发生;在自腐蚀电位Ecorr(约-720mV)下,X80钢SCC行为呈现出受阳极溶解和氢脆混合控制的机制;在-850mV阴极电位下,阴极保护抑制了X80钢SCC的发生;而在-1 000mV和-1 150mV阴极电位下,氢脆在X80钢SCC过程中占重要作用。     

库尔勒土壤模拟溶液中X80钢焊接接头的应力腐蚀开裂行为

利用动电位扫描技术和慢应变速率拉伸试验(SSRT)以及扫描电子显微镜(SEM)研究了库尔勒土壤模拟溶液中不同外加阴极电位下X80管线钢焊接接头的应力腐蚀开裂(SCC)行为。结果表明:阴极电位对X80钢焊接接头处的SCC敏感性影响较为明显。拉伸试样全部断裂在焊缝或热影响区。在Ecorr下,金属表面裂纹萌生于点蚀坑,试样开裂为阳极溶解机制。当外加电位为-800 m V至-900 m V时,金属处于阴极保护电位区,此时金属的SCC敏感性较低,其开裂机制为阳极溶解和氢致开裂混合机制。当外加电位小于等于-950 m V时,外加电位越低,材料的SCC敏感性越大,此时金属SCC行为表现为氢脆机制。     

X70管线钢在CO32-/HCO3-溶液中的电化学行为研究

采用动电位扫描技术研究了X70管线钢在CO32-/HCO3-溶液中的电化学行为.通过分析X70管线钢在Na2CO3/NaHCO3溶液中的极化曲线，讨论了HCO3-的浓度对阳极极化行为的影响.采用快扫描与慢扫描得到的结果，分别利用Parkins边界条件和应力腐蚀破裂（SCC）参数Pi，预测出X70管线钢在1 mol/L NaHCO3+0.5mol/L Na2CO3溶液中的SCC敏感性电位区间，两种方法得到的结果基本一致.     

Anodic Dissolution of Nickel from the Individual and NiZn Intermetallic Phases in Acidic Sulfate Solutions. II. NiZn Intermetallic Compound

Comparative investigation of the anodic behavior of nickel in its own phase and in NiZn intermetallic compound in acidic sulfate solutions showed that the kinetics of anodic process is the same in both cases, but the partial anodic curve and the passivation potentials of nickel in NiZn phase are shifted in the negative direction by 140 mV. The passivation current is larger, and the dissolution rate of nickel from NiZn phase at the cathodic polarization is higher. The peculiarity of the behavior of nickel in NiZn phase is related to the activity of surface nickel atoms and the increase in the number of active sites of anodic dissolution. It is shown that introducing an electrochemically negative metal into an alloy can, under certain conditions, facilitate the passivation of the latter irrespective of the passivability of the former.     

The electrochemical behaviour of 18Cr-8Ni stainless steel in hot concentrated aqueous magnesium chloride solution

The electrochemical behaviour of 18-8 stainless steel in concentrated aqueous magnesium chloride solution (bp 154°C) at 140°C has been examined.“Active” anodic dissolution of material carrying the original air-formed oxide film begins below ?250 mV(she). As the potential is raised, passivation slowly sets in, possibly through the selective dissolution of iron and chromium. Active dissolution begins again at ?170 mV(she) and increases up to ca. ?130 mV, when passivation by oxide-film formation begins; this is substantially complete between ?120 and ?110 mV(she). Breakdown of the “oxide” passivity by chloride ion begins at ?110 mV(she) and major pitting with large anodic c.d. is observed at ca. ?80 mV(she) and above. These values, obtained by slow potentiodynamic scan (2·5 mV/min) in the positive direction, are confirmed by potentiostatic current/time observations.The very large variation of anodic dissolution rate over a very small potential range is noted as being significant in the mechanism of stress-corrosion crack propagation in these alloys exposed to chloride-containing environments.     

Relation between individual properties of alloy components and anodic behavior of multicomponent alloys in acidic environments: I. Active dissolution and passivation of Fe-Cr alloys in sulfuric acid solutions

The active dissolution and passivation of Fe-Cr alloys are analyzed with the use of concepts of the appearance, operation, and blockade of active dissolution sites on the actual metal surface. General regularities of the effect of chromium on the rate of the anodic process at the change in the alloy composition and electrode potential are considered. The less noble, but easily passivable chromium component provides a dual effect on the anodic behavior of the binary alloys; it stimulates the anodic reaction at the low content in the alloy and suppresses the process at the high content. The principally different electrochemical properties of the alloy components result in the step-by-step passivation of the alloy with an increase in the potential, which is reflected by regular breaks in perfect anodic curves.     

Grundsätzliche Probleme der Korrosion von Legierungen

Fundamental problems of the corrosion of alloys Phenomenological equations are given for the steady state dissolution of alloys and their composition at the surface. The slow component with the smallest rate constant essentially determines the steady state dissolution rate and is enriched in the alloy surface. The phenomenological equations are compared to experimental results both for active and passive alloys. In ideal cases, phenomenological rate constants are independent of composition. Rate constants of pure slow components being much smaller than rate constants of pure fast components are enhanced by alloying with the fast component. Thus, corrosion protection by alloying often is much less efficient than predicted by the ideal case. Deviations from the ideal case can be understood, if dissolution proceeds at kinks in steps on low index planes of a crystalline alloy, or from equivalent sites in glassy metal alloys. Thus, the dissolution rates depend on the rate constants for dissolution from a kink and on the surface concentration of kinks. The surface concentration of kinks is determined by processes parallel to the dissolution from kinks, e. g. by dissolution of atoms from densely packed steps or by 2-dimensional nucleation in low index planes. The probability of such processes grows with the electrode potential and the concentration of a fast component. The resulting increase of the surface concentration of kinks occupied mainly by the slow component enhances its phenomenological rate constant. Steady states are approached at room temperature much slower than expected from diffusion coefficients of solid alloys extrapolated from high temperatures. Consequently, at room temperature changes of composition penetrate deeply into the bulk. The apparent increase of the interdiffusion coefficients is due to vacancy injection connected to the processes of kink generation. Selective corrosion and passivation often are accompanied by large surface stresses which may result in plastic deformation or fracture.     

Passivity of polycrystalline NiMnGa alloys for magnetic shape memory applications

The corrosion and passivation behaviour of bulk polycrystalline martensite Ni₅₀Mn₃₀Ga₂₀ and austenite Ni₄₈Mn₃₀Ga₂₂ alloys was compared in electrolytes with different pH values. Linear anodic and cyclic potentiodynamic polarisation methods and anodic current transient measurements have been conducted for the alloys and their constituents to analyze free corrosion, anodic dissolution and passive layer formation processes. Electrochemically treated alloy surfaces were characterized with scanning electron microscopy (SEM) and angle-resolved x-ray photoelectron spectroscopy (XPS). The electrochemical response of both alloys is in principal similar and is dominated by the Ni oxidation. In acidic solutions (pH 0.5 and 5) a slightly higher reactivity is detectable for the martensitic alloy which is mainly attributed to enhanced dissolution processes at the multiple twin boundaries. In weakly acidic to strongly alkaline solutions (pH 5-11) both alloys exhibit a low corrosion rate and a stable anodic passivity. While air-formed films comprise NiOOH, Ga₂O₃ and MnO₂, passive films formed in near neutral media (pH 5-8.4) are composed of Ni(OH)₂, NiOOH and Ga₂O₃ in the outer region and of NiO, MnO₂ and MnO in the metal-near region.     

XPS法研究高温弱酸性介质中化学镀Ni—Cu—P非晶态合金的腐蚀行为

利用ＸＰＳ法研究了化学镀Ｎｉ－Ｃｕ－Ｐ非晶态合金在１４０℃、ＰＨ＝５．０、ＣＯ２饮和Ｎａ２ＳＯ４溶液中片于不同电位下的表面膜组成。结果表明,处于不同电位下的Ｎｉ－Ｃｕ－Ｐ合金表面膜中皆有富Ｐ和富Ｃｕ现象发生,是膜中Ｎｉ选择性溶解的结果。Ｈ２ＰＯ２＾－和ＨＰＯ３＾２－吸附层的存在是合金发生钝化的原因。     

Effects of an applied magnetic field on the dissolution and passivation of iron in sulphuric acid

The effects of an applied magnetic field (MF) on the electrochemical state, anodic dissolution and passivation of iron in sulphuric acid solution were studied by potentiodynamic scanning polarisation measurements, potentiostatic polarisation measurements and scanning electron microscopy observation. The magnetic field reduced the fractional surface film coverage on the electrode by enhancing the film dissolution process. This made the electrode prone to active dissolution. With increasing applied potentials the magnetic field accelerated the anodic dissolution at relatively low potentials, changed the oscillation or passivation to permanent active dissolution at intermediate potentials, and maintained the passive state at high potentials. Potentials for the onset of passivation moved in the noble direction when the magnetic field was imposed. An electrode kinetics formulation for the effects of the magnetic field on the dissolution and passivation is proposed. In the presence of a magnetic field and at specific anodic potentials, scalloping occurred due to accelerated localized dissolution. The scalloping areas were on both sides of the electrode and oriented parallel to the direction of the earth’s gravitation field. The ratios of the scalloping area caused by a 0.4 T magnetic field on the whole electrode surface were 0.69 (at 200 mV), 0.66 (at 350 mV) and 0.75 (at 400 mV), respectively. In contrast, uniform electrode surfaces were observed at these anodic potentials in the absence of the magnetic field. Uneven dissolution of iron in the presence of a magnetic field was related to the relative configuration between the magnetic field direction and the electrode surface and also to the special concentration gradient of reactive species at the electrode circumferential area.     

化学镀Ni—Cr—P合金镀层在NaCli溶液中的耐蚀性

用电化学方法研究了化学镀Ｎｉ－Ｃｒ－Ｐ合金镀层在３．５％ＮａＣｌ溶液中的耐蚀性,结果表明Ｎｉ－Ｃｒ－Ｐ镀层与Ｎｉ－Ｐ镀层的阳极极化曲线形状相似,自腐蚀电位正移１５０ｍＶ以上,自腐蚀电流降低近３倍,在钝化区的阳极是约１个数量级,镀层的耐蚀性提高。     

Synergistic Effect of Mo,W, Mn and Cr on the Passivation Behavior of a Fe-Based Amorphous Alloy Coating

In this work, the electrochemical behaviors of SAM2 X5 Fe-based amorphous alloy coating and hard chromium coating were comparatively studied in 3.5 wt% Na Cl solution. In comparison with the hard chromium coating, the SAM2 X5 coating exhibited a wider and stable passive region with lower passive current density in the potentiodynamic polarization and showed a considerably lower current density at different anodic potentials in the potentiostatic polarization. In order to understand the passivation mechanism of the Fe-based amorphous coating, the components of the passive films formed at various polarization potentials were examined by X-ray photoelectron spectroscopy. The synergistic effect of Mo, W, Mn and Cr in the passive films was systemically analyzed. It has been revealed that Mo and W facilitate the formation of compact and stable Cr_2O_3 passive film at lower potentials, and the substantial enrichment of Mn in the passive film enhances the passivation ability at relatively higher potentials. The deep understanding of the passivation characteristics in multicomponent alloy systems could provide a guide for the design of corrosion-resistant amorphous alloy coatings for engineering applications.     

The anodic behavior of amorphous Ni-19P alloys in different amorphous states

An amorphous Ni-19P alloy prepared by rapid quenching of white heat melt showed a higher anodic dissolution current density in 1 N HCl in comparison with the same amorphous alloy prepared by rapid quenching of red heat melt. After structural relaxation these two specimens showed the same anodic polarization curve which is located between the polarization curves of as-quenched two specimens. The thermograms of these two as-quenched specimens were different from each other, showing that the difference in the amorphous states is due to the difference in structural relaxation during preparation. The difference in anodic behavior between these two as-quenched specimens seems due to the difference in the amounts of quenched-in defects. The higher current density of the relaxed specimen in comparison with the as-quenched specimen prepared by rapid quenching of the red heat melt has been interpreted in terms of introduction of chemical heterogeneity as a result of rearrangement and regroupings of atoms in the alloy during structural relaxation. The steady state current density was fairly low in the low potential region without showing a difference between two as-quenched specimens and then increased with increasing polarization potential. The difference in the quality of as-quenched alloy specimens seemed to be masked by the formation of phosphorus-covered alloy surfaces during anodic polarization at potentials lower than about 200 mV(SCE), because of a negligibly small dissolution rate constant of phosphorus in comparison with that of nickel.