不锈钢在衣康酸介质中的腐蚀行为

利用浸泡腐蚀试验和电化学测试方法研究了３种不锈钢在衣康酸水溶液介质中的腐蚀行为，考察了介质浓度和温度对材料腐蚀的影响。结果表明，在一定范围内，随衣康酸浓度提高或温度升高，不锈钢腐蚀速率也相应增大。在相同条件下，材料的耐蚀性依钢种不同而稍有差别。在衣康酸介质中，不锈钢的阳极极化曲线表现出活化—钝化—过钝化—二次纯化—二次过钝化特征，介质浓度、温度以及材料类型等因素均对其有一定影响。     

Decomposition of 2-chlorophenol by supercritical water oxidation with zirconium corrosion

The 2-chlorophenol (2-CP) was oxidized in a continuous anti-corrosive supercritical water system. The variation of decomposition efficiency by the corrosion of zirconium 702 was also studied at the variation of feed concentration and reaction time. According to AES depth profile, the oxygen penetration depth to zirconium was not proportional to the exposure time. It might stem from the formation of zirconium oxide layer on the surface delaying the corrosion. However, the increase in feed concentration accelerated the corrosion of zirconium. The corrosion of zirconium at low feed concentration led to the improvement of decomposition efficiency due to the catalytic effect of formed zirconium oxides, while that at high feed concentration deteriorated the decomposition efficiency owing to large consumption of oxidant in corrosion.     

Effect of NaOH on the decomposition of halogenated hydrocarbon by supercritical water oxidation

To protect alloys from corrosion phenomena in the supercritical water oxidation (SCWO) process, the effects of neutralizer on the conversion and corrosion were investigated. The surface morphologies of all the alloy coupons exposed to 2,4-Dichlorophenol (2,4-DCP) in the SCWO were significantly changed in microscopic images. The theoretical amount of NaOH as a neutralizer was calculated under the assumption of complete oxidation of 2,4-DCP. The pre-dosed NaOH in the range of 100% to 300% stoichiometric amount could not affect significantly the pH value in the SCWO. Moreover, the pH = 7 was not achieved until 700% stoichiometric amount of NaOH was pre-dosed to the reactor. It is noted that the conversion rate recorded over 99% without oxidant when 800% of NaOH was pre-dosed into the reactor. In addition, under the addition of H₂O₂ as an oxidant, the increased amount of NaOH led to the improvement of conversion rate. The pre-dosed NaOH may contribute to the conversion rate of 2,4-DCP in the SCWO. However, due to low solubility of salt in the SCWO, the fouling problem should be solved in the SCWO process.     

耐海水泵用新型双相不锈钢的研究

研究了耐海水泵用新型双相不锈钢的组织及其耐蚀性能。通过金相显微镜和Ｘ射线衍射进行了金相组织观察与分析，由多种腐蚀试验结果表明，该钢在海水介质中具有优良的耐均匀腐蚀、晶间腐蚀性能，并具有比Ｃ１５钢更高的抗点蚀性能。     

奥氏体不锈钢在Cl~-介质中应力腐蚀研究

评述了奥氏体不锈钢在氯化物介质中应力腐蚀开裂。从环境、冶金和力学等方面论述了ＳＣＣ的主要因素,综合论述了控制奥氏体不锈钢ＳＣＣ的工程参量和安全评定的方法。提出了预防奥氏体不锈钢应力腐蚀的一些措施。     

Corrosion of 2205 duplex stainless steel in chloride medium containing sulfate-reducing bacteria

Sulfate-reducing bacteria (SRB) play significant role in the corrosion of stainless steels exposed to marine and soil environment. Sulfate reduction by bacterial species results in the production of H₂S, which can significantly influence the anodic and cathodic processes and ultimately enhances the corrosion of materials. In the present study, 2205 type duplex stainless steel (DSS) coupons in solution-annealed condition were exposed to chloride medium containing SRB species, Desulfovibrio desulfuricans, for 40 days and examined by microscopy. Etching of the duplex structure, pitting as well as crevice attack were noticed. Similar results were obtained by microscopic studies with coupons exposed for 14 days in medium containing SRB followed by anodic polarization. SEM studies, of crevices observed after anodic polarization, indicated that the attack was initiated at the grain boundaries and slowly encroached into austenite grains. The initiation of attack was also evident from AFM studies of coupon exposed under freely corroding conditions for 7 days. ESCA studies reveal that under anaerobic conditions of SRB growth sulfidation of passive film occurs. The modified passive film found to depolarize the cathodic reactions. The nature and mechanism of SRB attack on DSS and possibility of detection at early stages were discussed.     

Corrosion control methods in supercritical water oxidation and gasification processes

Use of supercritical water (SCW) as a medium for oxidation reactions, conversion of organic materials to gaseous or liquid products, and for organic and inorganic synthesis processes, has been the subject of extensive research, development, and some commercial activity for over 25 years. A key aspect of the technology concerns the identification of materials, component designs, and operating techniques suitable for handling the moderately high temperatures and pressures and aggressive environments present in many SCW processes. Depending upon the particular application, or upon the particular location within a single process, the SCW process environment may be oxidizing, reducing, acidic, basic, nonionic, or highly ionic. Thus, it is difficult to find any one material or design that can withstand the effects of all feed types under all conditions. Nevertheless, several approaches have been developed to allow successful continuous processing with sufficient corrosion resistance for an acceptable period of time. The present paper reviews the experience to date for methods of corrosion control in the two most prevalent SCW processing applications: supercritical water oxidation (SCWO) and supercritical water gasification (SCWG).     

Sulfur transformations during supercritical water oxidation of a Chinese coal

The oxidation of coal in supercritical water was explored by using H₂O₂ as the oxidant. The sulfur-containing components in the effluents were identified. The experiments, which were conducted in a bench scale semi-continuous Supercritical Water Oxidation (SCWO) installation, indicated that the sulfur contained in coal could be gradually oxidized to sulfate in supercritical water medium. The main species containing sulfur in the effluents of coal SCWO were determined as sulfide, thiosulfate, sulfite and sulfate, in which thiosulfate and sulfate were predominant. The effects of the reaction temperature and time on the sulfur transformations during SCWO of coal were also investigated.     

CD-4MCu双相不锈钢在稀硫酸介质中的腐蚀磨损行为

用失重法测定了固溶处理态和固溶+时效处理态CD-4MCu双相不锈钢在稀硫酸介质中的腐蚀磨损速率。结果表明,CD-4MCu在固溶态时硬度低,耐腐蚀磨损性能差;在固溶+时效处理态时硬度高,耐腐蚀磨损性能好。介质温度和浓度升高,CD-4MCu双相不锈钢腐蚀及磨蚀增加,腐蚀磨损交互作用增大。     

Comparative investigation of stainless steels used in drinking water distribution systems

Five stainless steel alloys were tested and compared to find a test method for the qualification of stainless steel used in drinking water systems. Determination of the pitting/critical potentials from the conventional cyclic polarization results was shown to be difficult when stainless steels have high Mo and Cr content. The electrochemical impedance data indicated that results received with the conventional methods do not necessarily reflect the steady state. The low frequency time constant determined from the impedance measurements showed that the anodic polarization should be conducted with very slow scan rate to get information about the mechanism. The steady state investigations were compared with the conventional electrochemical results to propose an electrochemical-based route as a standard qualification method. The qualification method was tested to be valid by a European round-robin-test.     

Classical simulation of acid and base dissociation constants in supercritical water at constant density

Molecular dynamics simulations were performed to investigate the dissociations of water, NaOH and HCl in water at constant density of 0.9 g cm⁻³ at near-critical and supercritical temperatures. Results were in good qualitative agreement with available data, showing increased temperature favouring all dissociations. The dissociation of water was favoured by more negative values of U/T and an increasing entropy tem, whereas the dissociation of HCl showed both decreasing U/T and entropy. NaOH showed an increasing value of U/T which was dominated by an increasing entropy term. Differences in the energy contributions were attributed to the change in solute charges upon dissociation.     

不锈钢在湿法磷酸中腐蚀行为研究

本文采用腐蚀实验和电化学测试方法对不锈钢在湿法磷酸中的腐蚀行为进行了研究，并进行钝化膜的组成与结构分析。研究表明，磷酸中加入ＳＯ４＾２＾－，ｃＬ＾－，Ｆ＾－均提高合金的维钝电流密度和致纯电流浓度，加速材料的腐蚀，这些杂质共存时腐蚀性更大。湿法磷酸中存在的Ｓｉ＾４＾＋，Ａｌ＾３＾＋，Ｍｇ＾２＾＋和Ｆｅ＾３＾＋起缓蚀作用。不锈钢纯化膜主要由Ｃｒ和Ｆｅ的氧化物组成，表面形成致密稳定的Ｃｒ２Ｏ３保护膜是提     

Electrochemical behaviour of passive films on molybdenum-containing austenitic stainless steels in aqueous solutions

Passivation and its breakdown reactions have been studied on Mo-containing stainless steel specimens using different electrochemical techniques. Mo-containing stainless steel specimens were polarized in both naturally aerated NaCl and Na₂SO₄ solutions of different concentrations at 25 ± 0.2 °C between −1000 and 1500 mV versus saturated calomel electrode (SCE). The results of potentiodynamic polarization showed that i_corr and i_c increases with increasing either Cl⁻ or SO₄²⁻ concentration indicating the decrease in passivity of the formed film. EIS measurements under open circuit conditions confirmed that the passivity of the film decrease with increase in either Cl⁻ or SO₄²⁻ concentration.     

Corrosion and passivation behaviors of some stainless steel alloys in molten alkali carbonates

The corrosion and passivation behaviors of two types of stainless steel alloys (ferritic and austenitic steels) in ternary molten Li₂CO₃-Na₂CO₃-K₂CO₃ mixture at different temperatures (475-550 °C) were studied using galvanostatic polarization and cyclic voltammetry. The galvanostatic polarization curves of the investigated alloys illustrate the passivation and passivity breakdown of the alloys. The passivation potential range for the three investigated steel alloys is about 1.15-1.3 V. During this potential range different oxide and spinels are formed, the nature of which depends on the type of alloy and the anodization potential. At high anodic potentials the decomposition of carbonate takes place, leading to passivity breakdown and oxygen evolution. The values of corrosion parameters (R_p, i_o and i_corr) were calculated. The calculated values indicate that the corrosion resistance of the austenitic stainless steel is higher than that of the ferritic steel. The activation energy of the corrosion process was found to be equal to about 70 kJ mol⁻¹. The results of the cyclic voltammetric investigations indicate that the behavior of the austenitic steels is about the same and differs from that of ferritic steel. The corrosion tests in 0.2 M HCl solutions have shown that the oxide scales formed on the surface of the austenitic stainless steels are multilayered, whereas those formed on the ferritic alloy are uniform.     

热浸渗铝硅合金Q235钢的抗高温腐蚀性能研究

研究了Q2 35钢经热浸渗纯铝和不同硅含量的铝合金后的抗高温氧化和抗热腐蚀性能 ,比较了纯铝渗层和铝硅合金渗层的抗高温腐蚀性能 ,并分析了硅元素的作用。结果表明 ,Q2 35钢经热浸渗纯铝和铝硅合金后的抗氧化性能基本接近不锈钢 ,而抗热腐蚀性能则明显优于不锈钢     

Corrosion behaviour of new stainless steels reinforcing bars embedded in concrete

The activities concerned with the evaluation, repair and restoration of structures are estimated to amount to 35% of the total volume of the work in the building sector and this continues to increase. The corrosion of rebars in the reinforced concrete structures (RCS) is the main reason for their degradation, so the use of reinforcing stainless steels seems to be one of the possible solutions with most probabilities of solving this problem. In this work, in order to demonstrate the advantages of using reinforcing stainless steels, the corrosion behaviour of AISI 304 and 316 reinforcements embedded in concrete slabs (C35/45 and C60/70 concrete) with two chloride contents are compared with three low-cost and low-Ni austenoferritic stainless steels and with the conventional carbon steel. The lower chloride contamination selected in this research, was enough to cause the corrosion in the active state of the carbon steel reinforcements, whereas the highest one exceeded the expected contamination in the natural environments, including sea media. The metallic materials remaining in the passive state can be considered, from the point of view of corrosion resistance, adequate as reinforcements in the RCS.     

Corrosion behaviour of low-nickel austenitic stainless steels reinforcements: A comparative study in simulated pore solutions

The use of austenitic stainless steel reinforcements is one of the most reliable methods to assure the durability of reinforced concrete structures exposed to aggressive environments, but the initial cost of the material often limits its use in practice. Nickel is one of the alloying elements that raise most the cost of the stainless steels reinforcements. In this work the corrosion resistance of low-Ni 204Cu reinforcements is compared with that of more traditional austenitic stainless steels such as 304, 304L, 316, 316L and 316Ti. Polarization tests were carried out in simulated carbonated and non-carbonated pore solutions with different chloride concentrations. Results prove the very good corrosion behaviour of 204Cu stainless steel in carbonated media and in non-carbonated, chloride contaminated media. The corrosion resistance of low-Ni type 204Cu is only meaningfully lower than that of more traditional austenitic stainless steels in very highly aggressive solutions.     

铬钼钢的高温环烷酸腐蚀行为研究

在模拟炼厂环境的环烷酸腐蚀(NAC)动态试验中,应用失重法研究了温度、酸值和介质流速对铬钼钢环烷酸腐蚀速率的影响;采用扫描电子显微镜和光学显微镜观察的方法,从微观上分析了铬钼钢的环烷酸腐蚀行为。     

Corrosion behavior of ferritic/martensitic steel P92 in supercritical water

The corrosion behavior of a ferritic/martensitic steel P92 exposed to supercritical water (SCW) at 500–600 °C and 25 MPa was investigated by means of gravimetry, scanning electron microscope/energy dispersive X-ray spectroscopy and X-ray diffraction. A dual-layered oxide scale, which was mainly composed of an outer magnetite layer and an inner magnetite/spinel-mixed layer, formed on P92. The initial oxide scale was rather porous, while the porosity decreased with an increase of exposure time. Oxidation rates at three different temperatures followed the parabolic law. The oxidation at 600 °C was so severe that cracks occurred along grain boundaries in the oxide scale. A probable corrosion mechanism for P92 exposed in SCW was proposed based on the above observations, focusing on oxide formation by oxygen absorption without any metallic dissolution.