Improving the corrosion performance of Cr-C amorphous coatings on steel substrate by modifying the steel surface preparation

Cr-C coating was electrodeposited on copper and steel substrates, using a trivalent chromium bath containing formic acid. Coatings produced had an amorphous cracked structure with a homogeneous granular morphology. The coated copper specimen showed passivation behaviour, but, the coated steel specimens revealed an active anodic behaviour. Evaluation of coatings produced on the steel substrate subjected to various surface preparations including mechanically polished, electropolished and anodically etched, showed a crack-free coating on the preanodically etched surface. Also, this coating had the lowest porosity, which provided the best protection and thus led to the lowest dissolution of the steel substrate.     

Electrocrystallization nucleation and growth of NiFe alloys on brass substrate

The electrocrystalliztion nucleation and growth process of Ni-Fe alloy was studied using cyclic voltammetry and chronoamperometry. The results show that, in the case of high deposition overpotential, the nucleation/growth process of Ni-Fe binary alloy is 3-D instantaneous, and the growth rate of the previously formed nuclei increases with overpotential. However, at low overpotential, no distinguished nucleation current can be observed. Meanwhile, the discrepancy between the experimental non-dimensional variables（I/Im）^2 and those calculated from the theoretical model was elucidated in the light of the molecular orbital theorem.     

The composition and morphology of oxide films formed on type 304 stainless steel in lithiated high temperature water

The morphology and composition of oxide films formed on type 304 stainless steel surfaces exposed to 300°C water at pH 10 have been examined. Emphasis was placed on characterizing the initial stages of oxidation. A correlation was found between oxide film thickness and average crystallite size. The outer, crystalline, part of the oxide was found to be Fe-rich; the inner, amorphous, layer was Cr-rich. Increases in film thickness were found to occur via thickening of the Cr-rich layer. It was also found that chemically pickled surfaces, which were Cr-rich relative to mechanically polished surfaces, were less susceptible to crystallite deposition than the polished surfaces.     

Ni-Co/ZrO2复合共沉积过程的电结晶行为

为了研究Ni-Co-ZrO_2复合镀层电结晶初期的共沉积行为,在酸性氨基磺酸盐体系中采用阴极扫描伏安和计时电流等电化学测试方法,通过电化学反应动力学参数计算揭示Ni-Co-ZrO_2复合镀层成核机理。结果表明:Ni-Co合金镀液中ZrO_2纳米粒子的添加使共沉积电位正移,降低了阴极极化度。Ni-Co合金和Ni-Co-ZrO_2复合镀层的形核/生长过程符合受扩散控制的Scharifker-Hill瞬时成核模型,在低负电位下,Ni-Co-ZrO_2复合镀层成核弛豫时间减少,成核速率更高,电极表面吸附的ZrO_2纳米粒子促进了基质金属的成核及生长;高负电位下,复合镀层体系的峰值电流略低于合金体系,且成核速率降低,ZrO_2纳米粒子在电极表面表现出空间位阻效应,抑制了基质金属的电结晶过程。     

The role of different surface damages in corrosion process in alkaline sour media

By applying different electrochemical methodologies to 1018 carbon steel/different electrolytic media interfaces, surfaces with generalised and blistered damages, commonly present in the oil refinery catalytic plants, were obtained. Afterwards, a freshly polished carbon steel surface as well as the damaged surfaces were characterised by electrochemical impedance spectroscopy and scanning electronic microscopy (SEM). The SEM results reveal that the damaged surfaces present films with different physical properties.In spite of the surface modification, the corrosion mechanism of these interfaces in a medium simulating catalytic plants condensates of the refineries in Mexico (0.1 M (NH₄)₂S, 0.4 mM NaCN (10 ppm CN⁻), pH=8.8) turned out to be the same. It was also found that the corrosion process presents the following steps: charge transfer resistance of steel oxidation in the metal/corrosion product film interface and the diffusion processes of Fe²⁺ and H^o ions through the corrosion product film. It was demonstrated that when there was no damage on the surface (freshly polished surface), a homogeneous film was formed instantaneously upon introducing carbon steel into the sour media. The corrosion process in this film occurs in three stages. On the surface with generalised corrosion the three stages are favoured, particularly that of atomic hydrogen process (inducing blistering). Meanwhile, the blistered surface presents a higher charge resistance of steel oxidation and the Fe²⁺ and atomic hydrogen diffusions through the corrosion products are slower than those presented on the other surface states.     

Kinetics of the nucleation and growth of nickel particles in α-alanine-containing electrolytes

Kinetics of the nucleation and growth of nickel particles in an α-alanine-containing solution is studied with the use of voltammetry and chronoammetry. The electrochemical crystallization of nickel on a copper electrode is found to proceed according to the instantaneous nucleation mechanism. The main kinetic characteristics of the nucleation process are calculated. Partial curves of the metal deposition and hydrogen evolution are constructed.     

Electrochemical behavior of electroplated Zn-P alloy

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STUDY OF THE INFLUENCE OF pH ON THE ELECTROCRYSTALLIZATION OF ZINC

1. IntroductionElectrodeposition ofalloys is w idely used in the production of new m aterials possessing specificchem ical,physicalproperties,such asnanocrystalline m agnetic thin film sand functionalm ultilayers[1-5].In com parison to otherdeposition tec…     

加热状态下的45钢内裂纹表面迁移

采用钻孔压缩法在45钢试样内部预制内裂纹,并对裂纹试样进行900℃、1000℃、1200℃加热,观察裂纹表面的组织变化。结果表明,45钢内裂纹试样加热时,裂纹表面普遍存在铁素体晶粒形核与长大,从而使裂纹表面向裂纹中心方向迁移,裂纹表面迁移有分段现象。原子扩散是物质补给方式,铁素体晶粒形核长大是内裂纹表面迁移方式。原子扩散是裂纹愈合的基本要素,为内裂纹表面迁移提供物质来源,但是铁素体晶粒形核长大能够使原子扩散速度加快,而裂纹表面无新晶粒形核长大的裂纹愈合现象,相比之下,存在铁素体晶粒形核长大现象的裂纹愈合行为中,裂纹表面迁移更迅速。     

Electropolishing effects on corrosion behavior of 304 stainless steel in high temperature, hydrogenated water

The corrosion rate of electropolished 304 stainless steel surfaces (UNS S30400) is found to be lower by more than a factor of three relative to that determined previously for machined surfaces in mildly alkaline, hydrogenated water at 260 °C. This favorable result is attributed to significant changes in nanocrystallinity of the corrosion oxide layer caused by the removal of surface microstrain, which had been imparted during the machining process. In the absence of microstrain, a low-porosity, protective, corrosion layer forms that is composed of extremely small and uniformly-sized spinel oxide crystals. Application of scanning electron microscopy (FEG-SEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS) in conjunction with ion milling and target factor analyses, found the corrosion layer to consist of micrometer-size crystals of a ferrite-based spinel oxide (non-protective) over-laying nanometer-size crystals of a chromite-based spinel oxide (protective). Composition of both phases is unchanged from that previously observed on corroded, machined surfaces and is representative of solvus phases in the immiscible Fe(Fe_1−nCr_n)₂O₄ spinel binary. The smaller size (10 vs. 26 nm) and greater surface density (∼10,000 vs. 835 μm⁻²) of the chromite-based crystals relative to those formed on machined (i.e., cold-worked) surfaces, however, is consistent with the absence of preferred high energy nucleation sites on strain-free surfaces. Therefore, electropolishing, which removes surface microstrain induced by cold-working, represents a preferred reference surface condition.     

Nickel co-deposition with SiC particles at initial stage

The cyclic voltammetry and chronoamperometry were used to study the influence of SiC particles on the nucleation and growth of nickel deposition on copper matrix from acid sulphate solution. The surface morphology of Ni-SiC co-deposition at initial stage was observed with scanning electron microscope（SEM）. The results show that the nickel co-deposition with SiC particles may begin at -700 mV （vs SCE） under the experimental conditions, and the nucleation/growth mechanism of Ni-SiC co-deposition tends Seharifker--Hill with three-dimension model. In the case of low over-potential of -710--740 mV, the nucleation process of Ni-SiC co-deposition may follow the progressive nucleation mechanism of Scharifker--Hill. During higher over-potential of-770--800 mV, it trends to follow a 3D instantaneous nucleation/growth mechanism. With the increase of over-potential, the relaxation time tin, corresponding to the peak current Im of Ni-SiC co-deposition decreases regularly and is shortened apparently, compared with that of pure Ni deposition. The observation with SEM confirms that SiC particles can be considered as favorable sites for nickel nucleating. When certain amount of SiC particles are adsorbed （or cover） on cathode surface, especially under the condition of high overpotential, they may represent an external inhibition of the nickel electron deposition.     

内蒙古发现大型富钛矿床

采用循环伏安法和计时电流法研究了700℃时LiF-NaF-KF-K2TiF6熔盐中Ti（Ⅳ）在铂电极上阴极电化学还原机理以及电结晶过程。结果表明：Ti（Ⅳ）的电化学还原机理为三步骤电荷传递反应：Ti（Ⅳ）＋e→Ti（Ⅲ）；Ti（Ⅲ）＋2e→Ti（Ⅰ）；Ti（Ⅰ）＋e→Ti（0），且阴极过程可逆：电结晶过程为瞬时形核。     

1,2,4-三氮唑和苯并三氮唑对316L不锈钢化学机械抛光的影响

为探究1,2,4-三氮唑(TAZ)和苯并三氮唑(BTA)对316L不锈钢化学机械抛光(CMP)的影响及作用机理,在酸性条件下使用TAZ或BTA为缓蚀剂化学机械抛光316L不锈钢,用白光干涉仪观测316L不锈钢抛光后的表面质量,用红外光谱仪表征缓蚀剂的结构,用接触角测量仪检测抛光表面钝化膜的疏水性能,并用电化学工作站分析...     

Nucleation/growth mechanism of electrocrystallization for As–Sb alloy in hydrochloric acid system

The initial electrocrystallization of As–Sb alloy on glass carbon (GC) electrode in hydrochloric acid system was studied via cyclic voltammetry (CV) and chronoamperometry measurements. Current transients were presented in dimensionless formation, which showed that the initial nucleation/growth process of As–Sb alloy followed three-dimensional nucleation model with diffusion-controlled growth. Relevant nucleation parameters were calculated by analyzing related current transients. Particular attention was paid to the effect of Sb(III) concentration on the nucleation process during the co-electrodeposition. The quantitative results showed that Sb(III) played a positive effect on enhancing the nucleation rate of As–Sb alloy, leading to the evolution of alloy surface morphology from grain structure to compact layer structure.     

SCC initiation for X65 pipeline steel in the “high” pH carbonate/bicarbonate solution

The initiation of stress corrosion cracking (SCC) was studied using scanning electron microscope observations of linearly increasing stress test specimens. SCC initiation from the following surfaces was studied: (i) initiation from the commercial pipe surface covered by the Zn coating, (ii) initiation from a mechanically polished surface with a deformed layer, and (iii) initiation from an electro-polished surface. SCC initiation involved different features for these surfaces as follows. (i) For the Zn coated commercial pipe surface, a crack in the Zn coating led to the dissolution of the deformed layer and when the deformed layer was penetrated, intergranular SCC initiation became possible. (ii) For a mechanically polished surface with a deformed layer, cracks in the surface oxide concentrated the anodic dissolution to such an extent that there was transgranular SCC in the deformed layer. SCC was intergranular when the deformed layer had been penetrated. Transgranular stress corrosion cracks were stopped at ferrite grain boundaries (GBs) oriented perpendicular to the SCC propagation direction. (iii) For an electro-polished surface, the surface oxide film was cracked at many locations, but intergranular SCC only propagated into the steel when the oxide crack corresponded to a GB. An oxide crack away from a GB is expected to be healed. The observed SCC initiation mechanism was not associated with simple preferential chemical attack of the ferrite GBs.     

Effects of 3-Thiothiol-1-propane-sulphonic acid sodium salt and Sulphuric Acid on the Initial Stages of Copper Electrodeposition

Initial stages of copper electrodeposition on a glassy carbon electrode from acid sulphate solutions are studied using cyclic voltammetry and chronoamperometry. The electrolyte consisted of 0.05 mol dm³ copper sulphate and 1.4 ～ 1.8 mol dm ³ sulphuric acid containing 2 × 10² g dm ³ 3-thiothiol-l-propane-sulphonic acid sodium salt (NaO₃S (CH₂)₃ SSH). The results show that the additive produces an initial inhibition of copper deposition, probably related to the adsorption whereas sulphuric acid promotes copper electrodeposition. The initial deposition kinetics corresponds to a model including instantaneous nucleation and diffusion controlled growth. Addition of 3-thiothiol-l-propane-sulphonic acid sodium salt and sulphuric acid does not change the initial nucleation of copper electrocrystallisation but it increases the nucleation rate and the number density of nuclei at the surface.     

The Link Between the Corrosion and calcium carbonate scaling susceptibilities of heat transfer surfaces

The nucleation of CaCO₃ scales on copper, graphite, aluminium and mild steel heat transfer surfaces at surface temperatures 54–56°C, from turbulent solutions (Re 22,000) of bulk temperature 30 °C, has been studied using thermal resistance and corrosion potential measurements and scanning electron microscopy. The rate of CaCO₃ scale nucleation and growth decreases in the order mild steel > aluminium > copper and graphite. Scale nucleation apparently proceeds from the very outset, throughout an apparent thermal induction period, the end of which appears to be associated with the development of nuclei into aragonite clusters. The differing scaling susceptibilities of the materials are directly related to their corrosion susceptibilities. Studies on aluminium highlight the importance of the nature and integrity of surface oxide films in determining scaling susceptibility. Under the conditions examined, scales consist primarily of aragonite, with small amounts of calcite and vaterite. Mild steel surfaces apparently favour growth of “flower” vaterite.     

Electrochemical Nucleation of Titanium on Platinum

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在NaHCO3-NaCI体系中阴离子对低碳钢点蚀的抑制作用

采用动电位和恒电位技术研究了低碳钢在NaHCO3-NaCl体系中的点蚀电位和再钝化电位的分布以及5种阴离子对它们的影响.结果表明,点蚀电位和再钝化电位均服从正态分布;在5种阴离子中,NO2-和MoO2-4能够抑制点蚀的发生和发展,而SO2-4、NO-3在低浓度时降低点蚀电位和再钝化电位,促进点蚀的发生,在高浓度时能够破坏自钝化;Cr2O2-7能显著抑制点蚀的发生,然而点蚀一旦产生后它却能加速点蚀的发展.     

在NaHCO_3-NaCl体系中阴离子对低碳钢点蚀的抑制作用

采用动电位和恒电位技术研究了低碳钢在NaHCO3 -NaCl体系中的点蚀电位和再钝化电位的分布以及 5种阴离子对它们的影响 .结果表明 ,点蚀电位和再钝化电位均服从正态分布 ;在 5种阴离子中 ,NO-2 和MoO2 -4 能够抑制点蚀的发生和发展 ,而SO2 -4 、NO-3 在低浓度时降低点蚀电位和再钝化电位 ,促进点蚀的发生 ,在高浓度时能够破坏自钝化 ;Cr2 O2 -7能显著抑制点蚀的发生 ,然而点蚀一旦产生后它却能加速点蚀的发展