循环水中304不锈钢发生点蚀的Cl~-浓度阈值研究

采用电化学法研究了循环水中304不锈钢点蚀电位(Eb)、蚀孔深度、蚀孔数量与氯离子浓度的关系。结果表明,常温下304不锈钢的Eb总是随着氯离子浓度的增大而减小,当氯离子质量浓度小于800 mg/L时,增大氯离子浓度易导致点蚀敏感,而大于该值时增大氯离子浓度不会明显增大点蚀倾向;从蚀孔深度和表面蚀孔数量得出的304不锈钢点蚀倾向由大变小的氯离子质量浓度阈值为770 mg/L。     

再生水用于循环冷却系统时不锈钢腐蚀的研究

采用电化学测试方法研究了再生水用于循环冷却水时对不锈钢腐蚀特性的影响,通过测定弱极化区极化曲线、交流阻抗谱(EIS)和点蚀电位对比分析了TJH-3型缓蚀阻垢剂的缓蚀效果并阐述了其缓蚀原理。研究表明,不加缓蚀阻垢剂不锈钢腐蚀初期钝化膜逐渐发展并于约12 h达到稳定,稳定后平均腐蚀速率极低(约为0.000 15mm/a),但具有较大点蚀倾向。加入TJH-3型缓蚀阻垢剂后钝化膜增长明显增快,膜电阻增大,点蚀倾向显著降低。同时,点蚀电位测试结果表明此复配药剂中各组分对于不锈钢点蚀抑制具有协同作用。     

4-甲基咪唑在不锈钢腐蚀液中缓蚀作用的研究

本文介绍了奥氏不锈钢在Cl-浓度为1.5mol.L-1的缓蚀液中的电化学行为,分析不锈钢在不同温度和不同浓度中缓蚀液的腐蚀电位、腐蚀电流的变化规律,探索缓蚀液对不锈钢腐蚀速率的影响。结果表明:4-甲基咪唑缓蚀液对不锈钢的缓蚀效率在研究范围内随着温度和缓蚀液浓度的增加而增大,4-甲基咪唑是一种较好的高温吸附型缓蚀剂。     

304不锈钢上纳米TiO2涂层的制备与防腐蚀性能研究

采用溶胶–凝胶法和浸渍提拉法在304不锈钢上制备出均匀致密、彩色透明的纳米TiO2防腐蚀涂层。制备的最佳工艺条件是提拉4次,400°C热处理1h。在w(NaCl)=3%的NaCl溶液中的电化学测试表明,纳米TiO2/304不锈钢在有紫外光照射下其腐蚀电位低于304不锈钢基体。纳米TiO2涂层作为非牺牲性阳极对304不锈钢基体具有阴极保护作用和优异的防腐蚀性能。     

基于碳酸氢钠溶液的304与316L不锈钢电化学试验研究

采用电化学噪声、动电位极化和电容测量方法研究了304、316L不锈钢在不同NaHCO3溶液中的电化学行为及生成钝化膜的半导体性质。在NaHCO3溶液中,304、316L不锈钢存在明显相近的钝化区间;点蚀电位、零电流电位随着NaHCO3浓度的增大而减小。在0.5V电位形成钝化膜的Mott-Schottky曲线表明,304、316L不锈钢在NaHCO3溶液中生成的钝化膜为双层结构,具有相近的成膜特性。但随着NaHCO3溶液浓度变化所生成钝化膜的性质也不同,304不锈钢形成的表面膜稳定性稍好于316L。     

不锈钢在循环冷却水中点蚀倾向及点蚀生长动力学研究

本文主要采用恒电位步进法,测定两种不锈钢(18-8、304L)在循环冷却水中的击破电位和保护电位,用动电位扫描法和恒电位法校核。讨论击破电位的随机变化规律、氯离子浓度与温度对两种不锈钢在循环冷却水中击破电位和保护电位的影响。评定了两种不锈钢发生点蚀倾向。并采用作者设计的电解池,进行单蚀孔的测定,并讨论点蚀单孔生长动力学规律。     

塑性变形对AISI304不锈钢组织及耐蚀性的影响

AISI304不锈钢分别在加热180 ℃和低温-70 ℃条件下进行拉伸变形。采用透射电镜观测位错分布,利用铁素体测量仪测定马氏体相(铁磁相)含量,并通过电化学滞后技术分别研究它们在50 ℃条件下0.5 mol·L^-1 MgCl₂水溶液中的腐蚀行为.结果表明：加热180 ℃和低温-70 ℃条件下塑性变形均使AISI304不锈钢中位错密度随变形量增大而增加,AISI304不锈钢在-70 ℃条件下塑性变形时部分奥氏体相转变为马氏体相,而在180 ℃条件下塑性变形时不发生马氏体相变;位错密度的增加使AISI304不锈钢钝化膜的击穿电位略微正移,而马氏体相的增加使击穿电位呈负移趋势,材料耐孔蚀性能降低.     

阻垢缓蚀剂对不锈钢管缓蚀效果的评定方法

用点蚀电位法和失重法评价了七种阻垢缓蚀剂在不同冷却水样中对不锈钢的缓蚀效果。用腐蚀失重法评价阻垢缓蚀剂对不锈钢的缓蚀效果，既不合理也很难测准。点蚀电位法是评价阻垢缓蚀剂对不锈钢缓蚀效果的有效方法，但要选择合适的空白水样。     

孔蚀诱发临界电位的定量关系

引言孔蚀诱发临界电位E_(cp),又称为击破电位或孔蚀电位,是描述小孔腐蚀的一个极为重要的实验物理量.E_(cp)是标志孔蚀是否发生的一个临界值。若电位高出临界电位值时,将会发生小孔腐蚀。孔蚀诱发临界电位反映了不锈钢发生孔蚀的难易程度,故E_(cp)被用来评定不锈钢孔蚀诱发的倾向和其耐孔蚀性能的优劣。奥氏体不锈钢广泛应用于化工、石油、轻工和日常生活中,常常碰到孔蚀问题,故对奥氏体不锈钢的孔蚀诱发临界值的研究具有重要的意义。     

一种复合缓蚀剂对铸铁材料带锈缓蚀保护作用研究

通过浸泡实验检验了单宁酸、环己胺和钼酸钠复合缓蚀剂对带锈铁币的缓蚀效果,采用动电位极化曲线、交流阻抗法研究了铸铁电极在缓蚀剂作用下的电化学行为,并用X射线衍射技术分析了缓蚀作用对试样表面锈层的组成的影响。结果表明,由单宁酸、环己胺和钼酸钠组成的三元复合缓蚀剂对带锈铸铁具有良好的协同缓蚀效果,铸铁电极腐蚀电位正移,且出现了有明显的钝化现象。带锈铁币经缓蚀处理后,表面锈层生成含有Fe_2O_3、α-FeOOH的稳定沉积膜,提高了锈层的耐蚀性能,且锈层颜色变化小,能满足铁质文物保护要求。     

Pitting of AISI 304 stainless steel in bicarbonate and chloride solutions

Metastable and stable pitting on 304 stainless steel (SS304) in 0.1–0.5 m NaCl aqueous solution (pH ~8) has been investigated using a potentiodynamic, a potentiostatic and a weak anodic current galvanostatic techniques. The addition of bicarbonate (0.025–0.5 m) to the solution had an inhibiting effect, manifested by a shift of the pitting potentials to more positive values, a longer induction time for pitting and reduced pit nucleation. The pit nucleation frequency and growth, in the metastable and stable states, decrease as the NaHCO3/NaCl molar concentration increases and pitting is no longer observed for NaHCO3/NaCl molar ratios higher than 3 (four times larger % wt of NaHCO3). Pitting events never occurred at a potential below –0.1 V, fewer metastable events were observed at higher temperature (50°C) and none were observed in chloride free bicarbonate solutions. The inhibiting behaviour of oxyanions is discussed.     

The electrochemical behaviour of stainless steel AISI 304 in alkaline solutions with different pH in the presence of chlorides

Nowadays, stainless steel reinforcements appear as an effective solution to increase the durability of reinforced concrete structures exposed to very aggressive environments. AISI 304 is widely used for this purpose. Although the improved durability of reinforcing AISI 304, when compared to carbon steel, there is a high probability of pitting susceptibility in the presence of chlorides. Thus, the present work aims at studying the passivation and passivation breakdown of AISI 304 in alkaline solutions of different pH (pH from 13 to 9), simulating the interstitial concrete electrolyte. These solutions were contaminated with different concentrations of chloride ions (3% and 10%, as NaCl). The electrochemical behaviour was evaluated by d.c. potentiodynamic polarization and by electrochemical impedance spectroscopy (EIS).The morphological features and the changes observed in the surface composition were evaluated by Scanning Electron Microscopy (SEM) together with EDS chemical analysis.The results evidence that pH plays an important role in the evolution of the film resistance and charge transfer processes. Moreover, the effect is highly dependent upon the chloride content and immersion time.     

A characterization of the inhibiting effect of Cu on metastable pitting in dilute Al-Cu solid solution alloys

Copper additions to aluminum decrease susceptibility to pit initiation provided that Cu is retained in solid solution. This can be observed as an increase in pitting potential with increasing Cu content in an alloy. To further understand this effect, metastable pitting of high purity Al, Al-0.2Cu and Al-2.0Cu exposed to 0.1 M NaCl solutions has been examined in detail. Results show that 0.2 wt.% Cu additions decrease the metastable pit initiation rate by more than an order of magnitude and slow the pit growth rate mainly by decreasing the peak pit current attained. In an Al-2.0 wt.% alloy, metastable pitting events were too rare for rigorous study. Repassivation of metastable pits occurs by a two-stage process in Al-0.2 wt.% Cu alloy. The repassivation rate during the first stage is identical to that of high purity Al and appears to be completely unaffected by Cu in the alloy or in the pit solution. In the second stage, repassivation is slow, but is not believed to affect ultimate pit stability. Overall, Cu additions decrease the probability of stable pit formation by decreasing metastable pit initiation and growth rates.     

Features of electrochemical noise generated during pitting of inhibited A516-70 carbon steel in chloride solutions

The features of electrochemical noise generated during pitting of A516-70 carbon steel in chloride solutions containing Na2CrO4 were investigated. Polarization curves showed that the threshold Cl– concentration in 0.01m Na2CrO4 solution to initiate pitting and the threshold CrO42– concentration in 0.1m NaCl solution to maintain passivation for A516-70 carbon steel were approximately 0.1m and 0.01m, respectively. Noise measurements indicated that above the critical Cl– concentration, the stochastic current fluctuations appeared after 5h of immersion, which was an indication of pit initiation. Increasing CrO42– concentration to 0.05m led to the production of symmetrical current spikes at the start of immersion. The noise pattern changed to frequent fluctuations with small amplitude during immersion. Noise analysis in the frequency domain showed that pitting initiation was characterized by the slope of the PSD plot approaching -2. Extending the immersion time decreased the pitting initiation rate, as indicated by the decreased PSD slope and increased PSD frequency.     

Effects of nitrate ions on the electrochemical synthesis and behavior of polypyrrole films

Effects of nitrate ions on the properties of polypyrrole films electrodeposited in phosphoric acid medium on 304 stainless steel were studied. The presence of nitrate ions enhances the process of oxidation by moving the oxidation potential of monomers toward more cathodic values and increases the current density of oxidation and reduction peaks while it has no effect on the morphology of the films. It is worth mentioning that nitrate ions have doped the formed films as proven by Infrared spectroscopy. Polarization curves and electrochemical impedance spectra performed in 3% NaCl solutions have shown that the doping of polymer films with nitrate ions improves the pitting corrosion resistance of the stainless steel and also increases the ageing time of polypyrrole coating.     

Influence of nanocrystallization on pitting corrosion behavior of an austenitic stainless steel by stochastic approach and in situ AFM analysis

The pitting corrosion behavior of an austenitic stainless steel nanocrystalline (NC) coating, fabricated by magnetron sputtering as well as that of the conventional polycrystalline (PC) alloy have been investigated in 3.5% NaCl solution by stochastic approach and in situ atomic force microscopy (AFM). The results indicate that the pitting corrosion resistance of the NC coating was much higher than that of the PC alloy with higher prevalence of metastable pits and lower rates of stable pit nucleation and growth. The influence of nanocrystallization on the pit initiation and pit growth processes has been discussed according to the in situ AFM observations.     

304L不锈钢在溴离子作用下的点蚀行为

通有含溴离子氮气的３０４ Ｌ不锈钢管,经一段时期的使用后产生了严重点蚀。通过解剖被蚀钢管,采用金相分析,ＳＥＭ 形貌分析及ＥＤＳ成分分析的方法,对本案例点蚀特征进行研究, 发现：蚀孔形核于晶界,并以蚀孔自身扩张和孔内形成次生蚀孔两种方式生长,且蚀孔内壁产生富Ｃｒ 层。最后,就相关的电化学理论进行了探讨,并推测活化态蚀孔内壁的溶解导致了富Ｃｒ 层的产生,而富Ｃｒ 层的存在则是孔内建立局部活化态,次生蚀孔形核的物质基础。     

电解清除氧化皮的304不锈钢盘条耐蚀性的电化学评价

研究了电解清洗黑色和蓝黑色氧化皮304不锈钢盘条在盐酸和氯化钠介质中的耐蚀性能。动电位极化曲线方法测试了清洗后盘条的耐点蚀性能;恒电位充电曲线研究了不锈钢盘条的时间有效性。结果表明,电解清洗后不锈钢具有良好的耐蚀性。表面电子能谱测试表明清洗后不锈钢表面有显著的Mn元素富集,并探讨了Mn元素富集对耐蚀性的影响。