XPS and AES studies of the high temperature corrosion mechanism of Fe-30Cr alloy

Fe-30Cr alloy specimens were pre-oxidized at two different oxygen partial pressures (10^?16 and 10^?19 atm) at 900°C and subsequently exposed to environments containing both oxygen and sulfur. The sulfur and oxygen partial pressures were maintained such that Cr₂O₃ was the stable phase. The Cr₂O₃ scales formed during pre-oxidation became rapidly unstable when exposed to an environment whose composition approached the chromium sulfide-chromium oxide phase boundary; but when exposed to a higher oxygen partial pressure with the same sulfur partial pressure, the preformed scales remained intact. For elucidating the sulfidation mechanisms, the reaction products on the surface were analyzed at different stages of sulfidation by X-ray photo-electron spectroscopy and Auger electron spectroscopy. Correlation of the reaction mechanisms with thermodynamic and transport parameters are discussed.     

用XPS和AES研究锌表面彩色防腐蚀膜

用阴极极化法从钼酸盐和磷酸盐的混合溶液中获得了锌表面彩色转化膜。此膜具有良好的防腐蚀和装饰效果。盐雾试验结果表明,金黄色膜耐蚀性最佳。XPS和AES分析结果表明,该膜层厚度约为75nm;膜表面钼以Mo(VI)状态存在,而在膜内则以Mo(VI)和Mo(IV)共存。从AES深度分布曲线的组成恒定区求得各组成元素的相对原子百分浓度(A.C.%)为:O 56.9%;Mo 26.8％;P 11.0％;Zn 5.3％。     

The stability of localized corrosion

Chloride pitting of iron group metals at noble potentials proceeds in the polishing state dissolution, provided that metal chloride in the pit solution is maintained above a critical concentration. It ceases to progress by pit repassivation if the pit is smaller than a critical size, or transforms into the active state pitting if the pit size is greater. The boundary potential between the polishing state and the active state pitting may be represented by the passivation-depassivation potential in the pit solution of the critical chloride concentration. Crevice corrosion is characterized by the crevice protection potential, at which the hydrogen ion concentration in the crevice solution is equivalent to pH_pd—the passivation-depassivation pH of the crevice metal. It continues to corrode at more noble potentials than the protection potential, where the crevice solution is more acidic than pH_pd, but is inhibited in the less acidic crevice solution at less noble potentials.     

XPS和AES研究镍表面有机防变色膜

月桂酸钝化处理镀镍层的最佳条件为:月桂酸2g/L,pH8,70℃,1min.XPS和AES分析结果表明,月桂酸防变色膜的元素组成(A.C.%)为:C74.0,O17.3,Ni8.7.     

Special aspects of localized High-temperature corrosion

As in aqueous corrosion a localized corrosive attack can be important in high-temperature corrosion of metallic materials and become, unvoluntarily, a lifetime determining factor for combustion systems. Deposit-induced corrosion is the most important form of localized corrosion on alloy 800 and other materials in advanced coal combustion systems. Coal-ash deposits may cause a sulfidation/oxidation reaction which propagates preferentially along grain boundaries into the underlying metallic material. Preferred grain boundary corrosion may also occur in the walls of the fuel nozzle tubes of gas combustion systems. In this case, an oxidation reaction takes place. The lifetime of the tubes can be increased by use of a special alloy 601 H grade. Pitting may be observed in coal combustion systems. It has also been observed on alloy 601 after service in ceramic firing kilns where it is promoted by the presence of chlorine. Additionally, pitting occurs under carburizing conditions (metal dusting) as does cracking being similar in appearance to stress corrosion cracking in aqueous corrosion. Compared to deposit-induced and grain boundary corrosion, crevice corrosion is of minor importance in high-temperature corrosion. Only one example has been identified so far on alloy 600 but which may also be interpreted as a kind of deposit-induced corrosion.     

Indoor atmospheric corrosion in Cuba. A report about indoor localized corrosion

Indoor weight loss of steel, chloride, sulphur compounds and dust deposition rate were determined in six storehouses having different characteristics. Relative humidity and temperature were determined in three storehouses. A model for indoor corrosion of steel depending on time of exposure and deposition of dust, sulphur compounds and chlorides is proposed. Dust deposition plays an important role indoors. The position of the sample has also a significant influence on corrosion. Indoor corrosion aggressivity in Cuban storehouses ranges in classification IC3 and IC4 according to the new ISO proposal of indoor aggressivity.A report about the presence of localized corrosion indoors (filiform like) using a special designed sample is made.     

Protection of metals against corrosion

Metal Science and Heat Treatment -     

Bacterial corrosion of metals. II. Gravimetric investigations of the corrosion of nonferrous metals

The specific kinetic features of the bacterial corrosion of AK-4, AK-6, Д-16л, Д-16п, AMц-8 aluminum alloys; MA-8 magnesium alloy; and БpAЩMц 10-3-1.5 bronze were investigated with the use of tropical strains of bacteria. The protective effectiveness of anodic-oxide coatings applied to aluminum alloys, and that of TsIATIM-221 and AMG-10 compositions were also tested under these conditions.     

An ellipsometric approach to localized corrosion processes

Qualitative uses of ellipsometry, that can provide valuable insights into localized corrosion processes are reviewed. Without attempting to determine optical constants or film thickness with any accuracy, interesting data can be obtained, particularly correlations of passive film growth rates, as a function of localized corrosion factors, with the velocity of stress corrosion cracking or the rates of pit nucleation. Several applications of qualitative ellipsometry are described, relating to pitting and crevice corrosion, and stress corrosion cracking of carbon steels, stainless steels and titanium alloys.     

The localized corrosion of Cr-Ni stainless steel

The kinetics of localized corrosion of Cr-Ni stainless steel is characterized by the quadratic time dependence of the total current density, by the linear increase in the number of pits and by the decrease of the current density in the pits. The pits have a shape of a rotary ellipsoid. The Tafel slope of the metal dissolution in the pits is 0.50 V. The dissolution rate is the highest on the pit bottom and the lowest at the mouth of the pit. The different rate of metal dissolution is caused by the different concentration of chloride ions over the pit surface.     

XPS和AES研究铜表面PMTA防变色膜

本工作对比了各种防铜变色剂的防变色效果,结果表明,1-苯基-5-巯基四氮唑(PMTA)的防变色效果优于化学钝化、电解钝化、苯骈三氮唑(BTA)、羟基苯骈三氮唑(HBT)、2-巯基苯骈噻唑(MBT)。用PMTA处理铜的最佳条件为:PMTA1～1.2g/L,pH=5,20～40℃,4min。XPS和AES分析表明,PMTA在Cu_2O上形成配合物膜,膜中铜为+1价。PMTA分子中的N、S均参与配位。从膜的AES元素深度分布曲线的恒组成区求得的配合物膜组成(A.C.％)为:Cu 40.9,C 32.3,N 16.2,O 7.9,S 2.9。     

The localized corrosion of resistant alloys in chloride solutions

A potentiostatic scratching technique has been used to study the breakdown potentials of stainless steel 304, Incoloy, Inconel 600, Monel 400 and Hastelloy C in chloride solution at pH 8 as a function of chloride activity, temperature and metal cold work. For the first four alloys breakdown occurs through pitting. For Hastelloy C there is no pitting process, and breakdown occurs by a transpassive reaction, probably involving oxidation of Mo and Cr in the film to soluble anions.     

The localized corrosion of resistant alloys in chloride solutions

A potentiostatic scratching technique has been used to study the breakdown potentials of stainless steel 304, Incoloy, Inconel 600, Monel 400 and Hastelloy C in chloride solution at pH 8 as a function of chloride activity, temperature and metal cold work. For the first four alloys break-down occurs through pitting. For Hastelloy C there is no pitting process, and breakdown occurs by a transpassive reaction, probably involving oxidation of Mo and Cr in the film to soluble anions.     

Outdoor-indoor corrosion of metals in tropical coastal atmospheres

Results of indoor and outdoor atmospheric corrosion tests conducted during a long period of time at Cuba and Campeche (Mexico) indicated very high corrosion rates at both sites which have humid-tropical marine climate. We found that the outdoor corrosivity ranges from C3 to >C5 according to ISO 9223 nevertheless metals exposed to sheltered conditions presented higher corrosion rates compared to outdoors, whereas in closed (indoor) environments the corrosion rate significantly decreased. It is recommended to define an additional level of corrosivity for tropical coastal atmospheres in outdoor and sheltered conditions as corrosion depends on the geographical position and exposure conditions.     

Galvanic reactions during localized corrosion on stainless steel

During localized (crevice and pitting) corrosion, a local cell is established between an anode within a crevice or pit and a cathode on the surrounding passive surface. Data are presented to show that concentrated acidic chloride solutions, simulating corrosion product hydrolysis within a crevice or pit, produce potentials which are active (negative) to the normal surface passive potential. This behaviour explains the previously observed active drift of corrosion potential after initiation of crevice or pitting attack in dilute chloride solutions. The active state in concentrated chloride solutions was quite noble (positive) compared to the active state in more dilute solutions. Thus, there is no need to invoke ohmic resistance effects to account for the active state within a crevice or pit.Experiments were devised in which the local anode within a crevice was physically separated from the nearby passive-surface cathode. When the two were coupled together electrically, the cathode surfaces were polarized nearly to the unpolarized local anode potential, with only a few millivolts anodic polarization at the anode within the crevice. The rate of localized corrosion appears from the data to be limited by the rate of dissolved-oxygen reduction on the cathode surfaces. Thus, localized corrosion in dilute chloride solutions will be increased by (a) raising the temperature, (b) adding an oxidizer such as Fe³⁺ ions, or (c) substituting external anodic polarization for dissolved oxidizers.The overall potential, E_corr acquired by a specimen undergoing pitting or crevice corrosion is demonstrated to be near the protection potential, E_p below which pitting corrosion cannot propagate. Any potential active to E_corr and E_p results in cathodic polarization and suppression of the anode reaction in a crevice or pit. Since both E_corr and E_p vary with the extent of previous localized attack, E_p is not a unique property of the alloy as has been sometimes suggested and is of limited value in classifying alloy resistance to localized corrosion.     

The measurement of localized corrosion using electrochemical noise

Measurements of self-generated electrochemical potential fluctuations on electrodes undergoing either pitting or crevice corrosion show that these forms of localized attack have quite distinct noise “signatures” and that these two types of attack can be detected within seconds of their initiation.     

不同电位-pH条件下钼的表面膜的XPS和AES研究

采用 X 射线光电子能谱(XPS)和俄歇电子能谱(AES)方法分析了钼在不同溶液及不同电位-pH 条件下所生成的表面膜。结果表明:(1)在低电位区生成的钝化膜是一种低价(很可能是4价)的氧化物或水合氧化物,在无氧溶液中稳定,膜极薄但保护性很好;(2)在较高电位的过钝化区所生成的表面膜的最终稳态物质是无水 MoO_3;(3)在 FeCl_2溶液中较高电位的第二钝化区中所生成的表面膜,其外层为 Fe_2O_3,内层则可能是由 FeMoO_4组成。AES 和XPS 分析结果证实了本文作者之一(杨武,与 A.Pourbaix 先生合作)早先绘制的 Mo-H_2O系电位-pH 平衡图以及所提出的在钢的局部腐蚀发展过程中钼的阻蚀作用机理的有效性。     

The corrosion behavior of Fe-Mn-Al weld metals

The corrosion resistance of a newly developed iron-base, Fe-Mn-Al austenitic, and duplex weld metal has been examined in the NACE solution consisting of 5 wt.% NaCl, 0.5 wt.% acetic acid, and the balance distilled water. The electrochemical techniques such as potentiodynamic polarization, Tafel plots, linear polarization, cyclic polarization, and open-circuit potential versus time were employed. The Fe-Mn-Al weld metals did not passivate and exhibited high corrosion rates. Fe-Cr-Ni (310 and 316) weld and base metals were also examined in the NACE solution at room temperature. The 310 and 316 base metals were more resistant to corrosion than the as-welded 310 and 316 weld metals. Postweld heat treatment (PWHT) improved the corrosion performance of the Fe-Mn-Al weld metals. The corrosion resistance of Fe-Mn-Al weld metals after PWHT was still inferior to that of the 310 and 316 weld and base metals.     

Lab and field investigations on localized corrosion of casing

The corrosion of casing was investigated in the laboratory and oilfield by series methods of EIS, SEM, EDS, well logging, and field coupon test. Data reveal the middle vertical profile along the casing is greatly threatened by localized form rather than generalized corrosion. The pit initiates in the micro‐pore of the corrosion scale on the surface of the steel. The development of pitting depends on the water type classified by geochemist. The calcium chloride water shows highest acceleration to pitting due to the two orders of magnitude higher concentration of chloride ion by comparing sodium sulfate and sodium bicarbonate water types. The element analysis and microstructure observation were used to further describe the pit propagation. It is proposed to get a better understanding of the corrosion damage of casing in the petroleum industry.