Localized corrosion of carbon steel in a CO2-saturated oilfield formation water

In this work, corrosion and localized corrosion behavior of X65 pipeline steel were studied in a simulated, CO₂-saturated oilfield formation water by various electrochemical measurement techniques, including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, galvanic current and localized EIS (LEIS). The morphology and composition of the formed corrosion scale were characterized by scanning electron microscopy and energy-dispersive X-ray analysis. A conceptual model was developed to illustrate the occurrence of localized corrosion of the steel under scale. Both galvanic current and LEIS measurements showed that a galvanic effect existed between the bare steel and the scale-covered region. The scale-covered region served as cathode and the bare steel site as the anode. The big cathode vs. small anode geometry accelerated the local corrosion reaction. At an elevated temperature, a compact, crystalline scale was formed on the steel surface, enhancing the galvanic effect. Moreover, the stability of the scale was increased with time, and localized corrosion of the steel under scale experienced mechanistic changes with time.     

Marine microbial fuel cell: Use of stainless steel electrodes as anode and cathode materials

Numerous biocorrosion studies have stated that biofilms formed in aerobic seawater induce an efficient catalysis of the oxygen reduction on stainless steels. This property was implemented here for the first time in a marine microbial fuel cell (MFC). A prototype was designed with a stainless steel anode embedded in marine sediments coupled to a stainless steel cathode in the overlying seawater. Recording current/potential curves during the progress of the experiment confirmed that the cathode progressively acquired effective catalytic properties. The maximal power density produced of 4 mW m⁻² was lower than those reported previously with marine MFC using graphite electrodes. Decoupling anode and cathode showed that the cathode suffered practical problems related to implementation in the sea, which may found easy technical solutions. A laboratory fuel cell based on the same principle demonstrated that the biofilm-covered stainless steel cathode was able to supply current density up to 140 mA m⁻² at +0.05 V versus Ag/AgCl. The power density of 23 mW m⁻² was in this case limited by the anode. These first tests presented the biofilm-covered stainless steel cathodes as very promising candidates to be implemented in marine MFC. The suitability of stainless steel as anode has to be further investigated.     

Influence of salt content on clay electro-dewatering with copper and stainless steel anodes

Abstract

The electro-dewatering technique is an effective method to reinforce soft clay. Electro-dewatering experiments were conducted to assess the impact of salt content on electro-dewatering behaviors and effects with copper and stainless steel anodes. The changes in the current, accumulated drainage volume, and electro-osmotic flow velocity reflect the “catch point” phenomenon between the copper anode and the stainless steel anode. Moreover, the higher the salt content was, the earlier the appearance of the “catch point,” which means that the effect of the copper anode was better in the early stages and then worse in the following stages than that of the stainless steel anode. Based on photographs of anode surface, SEM-EDS (Scanning electron microscopy-Energy dispersive spectrometry) and XRD (X-ray diffraction) results, we found that the copper anode surface produced green product, which observably decreased the conductivity of the copper anode and then reduced the effective electrical potential gradient. On the other hand, there were no added elements on the stainless steel anode surface after the electro-dewatering experiments, and the conductivity of the stainless steel anode was similar to its initial status. The above two points led to the appearance of the“catch point” phenomenon. The pH value of the stainless steel anode was lower than that of copper anode, and the concentration of Cl^? had the opposite relationship. Because the effective electrical potential gradient of the stainless steel anode was higher than that of the copper anode after the “catch point,” the water content of the stainless steel anode was lower than that of the copper anode.     

Measurement of anode potentials at high current densities by the current interruption method for metals used in aviation technology

An electochemical flow-through cell and a current-interruption technique were used to investigate the potential of anodes made from mild steel, nickel, and four Ni-Cr-Fe alloys at high current densities (from 1 up to 100 A cm^–2) in NaCl solutions for a Reynolds number of 7370. A plot of the anode potential against logarithm of current density yielded a Tafel line over a broad range of current densities. The plateau on the anode potential against current density curve was attributed to salt film formation. This explanation was confirmed by visual observation of the anode surface.     

High Rate Anodic Dissolution of 100Cr6 Steel in Aqueous NaNO 3 Solution

The high rate anodic dissolution of 100Cr6 steel in NaNO₃ electrolytes of various concentrations and at different temperatures was investigated. Galvanostatic flow channel experiments were used to examine the current efficiency of the steel substrate. Below 6 A cm^–2(zone A), oxygen evolution dominates, while at higher current densities iron dissolution prevails (zone C). Potentiodynamic polarization studies indicated a complete substrate surface passivation up to +1.8V (vs NHE), and periodic fluctuations of the current density at higher anode potentials (> +1.8 V) due to severe oxygen evolution. Rotating cylinder measurements served for polarization studies at lower current densities in the region of dominating oxygen evolution. Scanning electron micrographs revealed a correlation between the current efficiency and the coverage of the substrate surface with an electronically conductive film at current densities of 2, 9 and 20 A cm^–2. The microstructure of the black, solid surface film developing during the high rate anodic dissolution of the steel was found to be heterogeneous and very porous. The main film components, as determined by X-ray diffraction and Auger electron spectroscopical measurements, were amorphous iron oxides, Fe _x O _y , and inert carbides, M₃C, originating from the steel matrix. An activation–repassivation process is proposed, which is responsible for the development of the complex multilayer (multiphase) structure observed at the steel substrate surface.     

Effectiveness of a conductive cementitious mortar anode for cathodic protection of steel in concrete

The paper reports a study on the behaviour of a cementitious conductive overlay anode used for cathodic protection (CP) of steel in concrete. The anode is made of nickel-coated carbon fibres in a cementitious mortar. Tests were carried out on concrete specimens with two layers of rebars that simulated reinforced concrete slabs. Anodic current densities in the range 10-100 mA/m² with respect to the anode surface were imposed. Steel and anode potentials, as well as feeding voltage, were monitored. Four-hour decay and the distribution of current and potential were regularly measured. Galvanostatic polarisation tests were also carried out on the anode material immersed in saturated calcium hydroxide solutions. The maximum anode current output was evaluated. The effectiveness of patch repair of the anode, on areas damaged by excessive current output, is also discussed.     

Transpassive dissolution of mild steel in NaNO3 electrolytes

A study has been made of the transpassive dissolution of mild steel in sodium nitrate solution over a range of current densities from 2 to 100 A cm^–2. The dissolution current efficiency and the anode potential free from the electrolyte IR component were measured in a flow cell; optical and scanning electron microscopy were then used to examine the sample surfaces after the dissolution tests. The results show that during the early stage of transpassive dissolution, the mild steel is covered with a compact, electronically conductive Fe₃O₄ film, and the current is consumed mainly in oxygen generation on the film/electrolyte interface. With increasing anode potential and current density, this film is gradually broken and the underlying metal surface becomes exposed to the electrolyte. At this stage, iron dissolution begins at a high rate. The film rupturing process is strongly dependent on nitrate concentration; the higher this is, the lower is the current density required to rupture the film.     

Dynamic interaction of refractory and molten steel: Effect of alumina-magnesia castables on alloy steel cleanness

High quality alloy steel is an important material needed for social and economic development. It is of great significance to major national projects and defence security. Refractories are used in the smelting process of steel; they are some of the main sources of impurities which have an important effect on the quality of steel. As alumina-magnesia refractories are the main lining materials used for steel refining, the influence of these refractories on the cleanliness of molten steel under dynamic smelting conditions has been studied. The size, quantity, composition, and structure evolution of inclusions in steel are analysed. The results show that after smelting, the content of alloy elements in the steel is stable, and that the total oxygen content and inclusions in the steel are increased by the corrosion of the alumina-magnesia castables. However, the maximum average particle size of the inclusions in the steel was limited to 20?µm, which did not cause large inclusions in the steel or seriously affect the quality of steel. During the dynamic melting process, because of the presence of Si and Mn in the alloy steel, the inclusions changed from homogeneous CaS wrapped Al₂O₃-MgO composite sphere to MnS wrapped egg-shaped structure. The alloy elements in steel were found to be beneficial, as they reduced the effect of alumina and magnesia inclusions on the quality of steel. The results indicate that it is feasible to smelt high quality alloy steel using alumina-magnesia carbon-free castable, and that it would be better to limit the refining time to 45?min during smelting.     

不锈钢管内表面镀铜

介绍了一种开采石油用不锈钢管内表面镀铜的工艺。给出了调整后的工艺流程。重点对不锈钢镀铜的内阳极及其选择作了介绍。内阳极有两种材质,分别为不溶性碳精棒和含磷铜棒。试验中用无磷纯铜代替了含磷铜棒作为酸性镀铜内阳极,并给出了阳极反应的特点与控制方法。批量生产实践证明,单个电流为20A左右,电镀时间20min时,产品质量满足要求。通过高压水冲刷检验,镀层与基体结合良好。     

电化学法对印染废水CODCr的处理效果研究

印染废水成分复杂,可生化降解性差。采用Fe-PbO2/不锈钢为阳极,不锈钢为阴极,活性炭为颗粒电极,电催化氧化处理上海某印染厂废水。当pH为3,电流密度为0.028 A/cm2,硫酸铝浓度为0.16 mol/L,极板距离为6 cm,电解时间为10 min时CODCr去除率达到71.1%,BOD5/CODCr由处理前的0.126上升为0.34,可生化降解性明显提高。Fe-PbO2/不锈钢阳极和不锈钢阳极在印染废水中的循环伏安曲线表明镀PbO2层的不锈钢电极具有较好的催化活性。     

The tribocorrosion behaviour of YSZ coating deposited on stainless steel substrate in 3.5 wt% NaCl solution

The YSZ coating was applied to 304 stainless steel substrate by atmospheric plasma spraying technology, and its electrochemical and tribological properties in 3.5 wt% NaCl solution were studied. In electrochemistry, under the action of cathode and anode potential, observe the changes of corrosion current density and EIS before and after wear. The results show that the YSZ coating has a very low corrosion current density during wear and corrosion compared to 304 stainless steel, and after the condition of the anode potential is applied, the effect of friction on the electrochemical impedance of the YSZ coating is very low, while the 304 stainless steel Impedance performance decreases; In terms of tribology, the friction coefficient of 304 stainless steel in 3.5 wt% NaCl solution is easily affected by potential, and the friction coefficient of YSZ coating relative to 304 stainless steel only changes under high potential. As the potential increases, the material volume loss of 304 stainless steel and YSZ coating increases linearly. From the data, the volume loss caused by the corrosion and wear of 304 stainless steel is much higher than that of YSZ coating.     

Evaluation of electro-coagulation method for decolorization and degradation of organic dyes in aqueous solutions

This research has two parts: at first part electro coagulation (EC) method was used to remove the dye Direct Black 22 (DB22 (in aqueous media. All experiments were done in a 2 liter reactor with two electrodes made of steel (SS-304) as cathodes and one aluminum electrode as anode. Parameters affecting the process, such as anode material, electrolyte concentration, current density, initial pH of solution and the initial dye concentration, were investigated. Total amount of consumed energy was used for determination of optimal conditions. According to the results obtained for DB22 at optimized conditions, color and COD removal percentage were 92% and 85%, respectively. In addition, the current efficiency for aluminum anode in removal of DB22 was 90%. At the second part of the research work, color removal by EC for six different dyes was evaluated. The results showed that dye structure and anode type are very important factors on performance of the process.     

Electrolytic preparation of magnesium perchlorate

The electrochemical preparation of magnesium perchlorate from magnesium chlorate employing a platinum anode and a rotating stainless steel cathode is described. The effect of electrolyte concentration, cathode and anode current densities, pH and temperature of the electrolyte and cathode rotation on current efficiency for the preparation of magnesium perchlorate was studied. A maximum current efficiency of 65–72% was achieved. Based on the results obtained on the laboratory scale, a 100 A cell was designed, fabricated and operated.     

Measurement of anode potentials at high current densities in NaNO3 and NaClO3 media by the current interruption method for metals used in aviation technology

TheIR-free anode potential of mild steel, nickel and four Ni-Cr-Fe alloys were studied at high current densities (1–100 A cm^–2) in NaNO₃ and NaClO₃ solutions. A constant current interruption technique was employed and the flow rate of the electrolytes was 14 ms^–1 (Re = 7370). A plot of the anode potential against logarithm of current density yielded a Tafel line over a broad range of current densities. The plateau visible on the anode potential against current density curve was attributed to salt film formation. This explanation was confirmed by visual observation of the anode surface.     

多维度结合XRF对塑钢窗的快速检验

为建立一种检验塑钢窗物证的方法，利用X射线荧光光谱仪对收集到的40个不同品牌、同一品牌不同系列、同一品牌同一系列不同批次塑钢窗进行检验。采用Niton XL3t GOLDD+手持式荧光光谱仪，通过预实验确定了检测条件：Ag作阳极靶；检测电压为50kV；检测电流为200μA；采集时间为70s，在此条件下对样品进行检测，根据不同塑钢窗样本所测出的特征元素种类及质量分数可对样本进行区分。为了使分类结果科学准确，首先利用主成分分析法对实验结果进行降维处理，指定提取了4个因子，再利用系统聚类和K?Means快速聚类方法对样品数据进行聚类处理，将40个样本分为28类，并利用Fisher判别分析法验证了分类结果的科学合理性。该方法结合谱图分析和化学计量学，能快速、准确、无损地对样品做出分类，为公安基层实际办案提供帮助。     

钛-二氧化铅阳极电解次磷酸钠制备高纯次磷酸

以六室电解槽为反应槽,分别以石墨电极、钛-二氧化铅电极和钛涂钌电极为阳极,不锈钢为阴极电极,研究了电解法制备成本低、纯度高且环境友好的次磷酸新工艺。结果表明：六室电解槽制得的次磷酸杂质少;与国内外常用石墨和钛涂钌阳极材料相比,钛-二氧化铅电极作为阳极材料在阳极电位、产品浓度及产品室电流效率方面性能优良。钛-二氧化铅电极没有固体沉淀,无其他杂质离子产生,阳极液不必更换,只需定期补充电解消耗的水,属于清洁生产。在最佳电解电流、电解温度、原料浓度和电解时间条件下制得次磷酸产品,经减压富集后其杂质含量能够满足电容器生产的要求。     

Zn／A3钢在海水中电偶腐蚀的研究

研究了金属Zn与A3钢在海水中偶接时的电偶腐蚀行为。考察了偶接时间、溶液中Cr浓度、电偶对中阴阳极面积比、实验温度等因素对阳极腐蚀速度的影响。结果表明：偶接时间为24h时,腐蚀速度趋于稳定。腐蚀速度随温度升高,溶液中Cr浓度的增大;阴阳面积比的增大,A3钢的腐蚀速度会相应减慢。     

Material problems in electrowinning of aluminium by the Hall-Heroult process

An overview is given for the process and constructional materials used in the molten salt electrolysis of aluminium by the Hall-Héroult process. Carbon materials, which constitute the anode, the cathode and the side lining, have been and are still the universal front or hot face materials in the electrolytic cell. A comment is made on the various types of anode and on the attempts to substitute the anode carbon by non-consumable ceramic oxide artefacts. The metallic electrical conductors and their joints play an important role in the design and operation of the cells. In this context particular attention is paid to the properties and behaviour of steel as a material for passing the electrolytic current into the anode and cathode up to temperatures of about 950°C.Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht, The Netherlands, September 17th and 18th 1987.     

Corrosion resistance of phosphate coatings obtained by cathodic electrochemical treatment: Role of anode–graphite versus steel

The formation of phosphate coatings by cathodic electrochemical treatment using graphite and steel anodes and evaluation of their corrosion resistance is addressed in this paper. The type of anode used, graphite/steel, has an obvious influence on the composition of the coating, resulting in zinc–zinc phosphate composite coating with graphite anode and zinc–iron alloy–zinc phosphate–zinc–iron phosphate composite coating with steel anode. The corrosion resistance of the coating is found to be a function of the composition of the coating. The deposition of zinc/zinc–iron alloy along with the zinc phosphate/zinc and zinc–iron phosphate using graphite/steel anodes has caused a cathodic shift in the E_corr compared to uncoated mild steel substrates. The i_corr values of these coatings is very high. EIS studies reveal that zinc/zinc–iron alloy dissolution is the predominant reaction during the initial stages of immersion. Subsequently, the formation of zinc and iron corrosion products imparts resistance to the charge transfer process and increases the corrosion resistance with increase in immersion time. The corrosion products formed might consist of oxides and hydroxychlorides of zinc and iron. The study suggests that cathodic electrochemical treatment could be effectively utilized to impart the desirable characteristics of the coating by choosing appropriate anode materials, bath composition and operating conditions.     

Electrochemical oxidation of phenol at boron-doped diamond electrode in pulse current mode

In this study, a pulse current supply was initially used in a BDD anode system (pulse-BDD anode system) for electrochemical oxidation of phenol. The influences of operative parameters (current density, retention time, pulse duty cycle, power frequency) on the system performances were exmamined by response surface methodology (RSM). As for COD degradation efficiency (D_COD) and specific energy consumption (E_s), the influence of retention time was more important than current density and pulse duty cycle, while power frequency hardly presented significant influence. By the comparison with constant current mode, an obvious specific energy consumption reduction was achieved in the pulse-BDD anode system, though the D_COD was slightly lower. The significant E_s decrease might be attributed to the reduction of side reactions and concentration polarization in pulse current mode. The pulse-BDD anode system demonstrated an efficient technology to simultaneously obtain high pollutant degradation efficiency and low energy consumption.