Untersuchungen der Korrosion von Aluminium in Wasser bei hohen Temperaturen und Drucken

Research on the corrosion of aluminium in water at high temperatures and pressures The stationary corrosion rate i_corr of aluminium is measured electrochemically in a 10^?3 m sodium bicarbonate solution at temperatures between 100°C and 200°C using a V4A high pressure loop, the result being Thus, the effective activation energy is 15 kcal/mole. The stationary thicknesses of the oxide layer on aluminium are calculated as a function of the temperature from the corrosion rates and the weight changes of the specimen. The results are compared to the thicknesses measured microscopically.     

Exfoliation corrosion mechanisms in the 7020 aluminium alloy

The first necessary condition for the occurrence of exfoliation corrosion is the existence of a fibrous texture. Transgranular exfoliation corrosion, which can be observed in some instances, develops through grains in which recrystallization is incomplete and which exhibit a substructure with remnants of a fibrous structure. As with intergranular corrosion, the controlling parameter is the formation of continuous anodic zones. In the case of exfoliation corrosion, these anodic zones are localized in planes parallel to the ?fabrication orientation”?. In the case of the welded 7020-T 6 alloy, two types of exfoliation corrosion have been observed, depending upon the nature of the anodic zones:

• The first type is related to the main elements, magnesium and zinc, which precipitate in the grain boundaries as large anodic MgZn₂ particles during a short reheat (welding) at 200° – 250°C.
• The second type is related to the secondary elements, chromium and/or manganese.

It is hypothesized that the precipitation of particle layers, reported by ADENIS, depletes the neighbouring solid solution, thus making it anodic with respect to the rest of the metal. The exfoliation corrosion develops by anodic attack of the following alloys in the T4 condition: For the phenomenon to occur without galvanic current, in addition to chromium or manganese, it is necessary to have iron which depassivates the cathodic reaction and zinc in solid solution (T 4) which lowers, by about 100 m V, the anodic zones potential. The influence of zinc becomes nul when it is precipitated (T 6).     

Der Einfluß von Kriechverformung auf die Ausbildung der Oxidschicht auf der Hochtemperaturlegierung Ni20Cr

Influence of creep deformation on the formation of the oxide layer on the high temperature alloy Ni20Cr The formation of the Cr₂O₃-layer on Ni20Cr has been investigated at 850°C in H₂/H₂O (p(O₂) = 10^?19 bar) under simultaneous creep deformation with flat samples. The damage of the protecting oxide layer by cracks has been observed in dependence on deformation rate and strain. For additional information about the influence of the plastic deformation of the oxide layer and the healing of the cracks, preoxidized samples have been deformed in pure Ar-atmosphere. At strain rates below 10^?9s^?1 cracks cannot be observed. When strain rates < about 3 × 10^?8s^?1 are applied, cracks occur only above grain boundaries of the alloy, at higher strain rates they also lie in regions above the grains of the alloy. For > about 3 × 10^?8s^?1 the crack density depends no more on but only on strain . The different damages of the oxide layers in the two atmospheres allow the conclusion, that at from 10^?9s^?1 to 10^?7s^?1 beside the plasticity of the oxide layer in particular the crack healing influences the sum of the crack openings measurably. With increasing strain rates the contribution of plasticity can be neglected.     

SCC of X‐52 and X‐60 weldements in diluted NaHCO3 solutions with chloride and sulfate ions

Stress corrosion cracking tests were performed in both X‐52 and X‐60 weldments in sodium bicarbonate (NaHCO₃) solutions at 50°C using the Slow Strain Rate Testing (SSRT) technique. Solution concentrations varied between 0.1 to 0.0001 M, and to simulate the NS‐4 solution, chloride (Cl^?) and/or sulfate ( ) ions were added to the 0.01 M solution. Tests were complemented with hydrogen permeation measurements and polarization curves. It was found that the corrosion rate, taken as the corrosion current, I_corr, was maximum in 0.01 M NaHCO₃ and with additions of ions. Higher or lower solution concentrations or additions of Cl^? alone decreased the corrosion rate of the weldment. The SSC susceptibility, measured as the percentage reduction in area, was maximum in 0.01M NaHCO₃. Higher or lower solution concentrations of additions of Cl^? or decreased the SCC susceptibility of the weldment. The amount of hydrogen uptake for the weldment was also highest in 0.01 M NaHCO₃ solution, but it was minimum with the addition of Cl^? or ions. Thus, the most likely mechanism for the cracking susceptibility of X‐52 and X‐60 weldments in diluted NaHCO₃ solutions seems to be hydrogen‐assisted anodic dissolution.     

MB8镁合金植酸转化膜的制备及性能

通过单因素实验优化镁合金植酸转化工艺,发现在植酸体积浓度为10 mL/L,pH=2.5,温度50℃,成膜时间20 min条件下,可在MB8镁合金表面制备出均匀一致的植酸转化膜.该膜层微观形貌与铬酸盐转化膜类似,表面呈现出均匀分布的网状微裂纹,类似于"龟裂的土地",膜层主要成分为Mg,O,P,Mn和C;动电位极化曲线测试...     

Wirkung von schwefelhaltigen Inhibitoren auf die Korrosion von Messing 63/37 in Trichloressigsäure

Action of sulphur containing inhibitors on the corrosion of 63/37 brass in trichloroacetic acid Trichloroacetic acid is highly corrosive to brass. Sodium thioglycolate, sodium diethyl dithio carbamate and carbon disulphide have been studied as corrosion inhibitors for brass (63/37) in trichloroacetic acid. The inhibitive power of sulphur-containing organic compounds is due to chelate formation, the chelate adhering strongly to the metal surface. The efficiencies of above stated inhibitors were found in the following order: .     

Bestimmung der Abtragungsraten von Zirconium,Tantal und der Legierung Tantal-40Niob in fluoridhaltiger azeotroper Salpetersäure mit Hilfe der Radiotracer-Methode

The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acid Zirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10^?6 to 5 · 10^?4 mm/y, for tantalum: 10^?8 to 4 · 10^?6 mm/y, and for the Ta-40Nb alloy: 2 · 10^?7 to 8 · 10^?6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities. The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F^? and at a temperature of 108°C, corrosion rates between 5.3 · 10^?3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced. The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10^?3 mm/y at 50°C/280 ppm F^? and 1.4 · 10^?2 mm/y at 110°C/320 ppm F^?. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude. The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing.     

Ca、Mn元素对Mg-Zn系合金在磷酸盐缓冲液中腐蚀行为的影响

采用XRD、SEM、EDS、三维轮廓仪和失重法等手段研究了Mg-6Zn、Mg-6Zn-1Ca和Mg-6Zn-1Mn合金在磷酸盐缓冲盐溶液(PBS)中的腐蚀行为,并探讨了3种合金的腐蚀机理。结果表明,添加相同含量的Ca和Mn均能使合金的失重率(W_r)降低,但添加Mn元素后(浸泡10d时W_r=3.91%)比添加Ca元素后(W_r=6.78%)合金的失重率更低,说明Mn元素更有抗PBS腐蚀能力,这与Mn的加入在合金表面形成致密的氧化膜有关;同时,Mg-6Zn-1Mn合金在浸泡过程中表面存在点蚀现象,经分析是由第二相与基体构成原电池导致。在420℃不同保温时间(2～20 h)固溶处理后,合金表面的点腐蚀现象随着保温时间的增加而减弱,表明长时间的固溶处理可以减少第二相与镁基体之间的微电偶腐蚀,增加了合金均匀腐蚀的倾向。     

Investigation of the effect of CrO and MoO on carbon steel corrosion using AFM and electrochemical techniques

The effect of chromate ( ) and molybdate ( ) ions on the corrosion of carbon steel in 0.5 M NaCl solution has been studied using electrochemical measurements and atomic force microscopy (AFM) technique. Potentiodynamic polarization data suggest that both and have inhibition effect on carbon steel corrosion, and the inhibition efficiency increases with increase in concentrations of and ; at the same concentration, the inhibition efficiency of is higher than that of . The increase in concentrations of and anions causes a shift of the breakdown potential (E_b) in the positive direction, indicating the inhibitive effect of the added anions on the pitting attack. At the same concentrations, the breakdown potential of is higher than that of . Electrochemical impedance spectroscopy (EIS) tests reveal that the charge transfer resistance and passive film resistance increase with increase in concentrations of or ; at the same concentrations, as for the charge transfer resistance and passive film resistance were bigger than those of . AFM imaging technique shows that local corrosion was inhibited obviously after the addtion of or , and passive film of was much more compact than that of . AFM force–distance curves indicate that the passive film of is much stiffer than that of .     

Electroplated super-hydrophobic Zn-Fe coating for corrosion protection on magnesium alloy

A superhydrophobic Zn-Fe alloy coating was prepared on the surface of a reactive magnesium alloy using a simple, low-cost, eco-friendly method. Firstly, the Zn-Fe coating was obtained in a neutral glycerol Zn-Fe plating solution, which is green, compositionally stable, and non-corrosive to the equipment. And then the superhydrophobic surface with a flower-like microstructure was obtained by grafting myristic acid onto the Zn-Fe coating via a chelation reaction. The water contact angle was >150° and the rolling angle was 3°-4°. The corrosion rate of the two groups of superhydrophobic magnesium alloy samples with electrodeposition time of 30 and 50 min, respectively, was reduced by about 87% compared to that of the bare magnesium alloy. The prepared superhydrophobic coatings exhibit high performance in self-cleaning, abrasion resistance, and corrosion resistance.     

4‐Chloro‐benzoic acid [1,2,4]triazol‐1‐ylmethyl ester as an effective inhibitor of mild steel corrosion in HCl solution

4‐Chloro‐benzoic acid [1,2,4]triazol‐1‐ylmethyl ester (CBT) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M hydrochloric acid solutions was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscope (SEM). The results showed that CBT is an excellent inhibitor for mild steel in acid medium and its inhibition efficiency (IE%) is up to 90.2% at a concentration of 10^?3 M at 298 K. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions. Potentiodynamic polarization studies clearly reveal that CBT acts essentially as mixed‐type inhibitor. Thermodynamic parameters such as adsorption heat ( ), adsorption entropy ( ), and adsorption free energy ( ) were obtained and discussed from experimental data of the temperature studies of the inhibition process at four temperatures ranging from 298 to 333 K. Kinetic parameters activation such as , , , and pre‐exponential factor have been calculated and discussed. Adsorption of the inhibitor on the mild steel surface followed Langmuir adsorption isotherm. The values of the free energy of adsorption indicated that the adsorption of CBT molecule was a spontaneous process, and was typical of chemisorption.     

Spannungskorrosion an Stahl St 37 und an der Aluminium-Legierung AlMg 3 durch staubhaltige Abgase von Zement-Drehöfen

Stress corrosion cracking of steel St 37 and the aluminium alloy AlMg 3 by dust-bearing flue-gases from rotary cement kilns Internals of electrofilters for dedusting flue-gases from rotary cement kilns were destroyed in several cases by stress corrosion cracking. Collector plates of steel St 37 exhibited serious corrosion damages after only two years' operation at temperatures between 60 and 120° C; in these cases an approximately uniform intercrystalline attack had been superimposed by local trough-like to pit-like corrosion. A frame of AlMg 3 for spray-electrodes fails by intercrystalline grain segregation after ribbon-like precipitates had formed on the grain-boundaries during 6 years' operation at 100° C. The characteristic types of destruction could be demonstrated on the surfaces of open cracks and artificially prepared ruptures and with the aid of metallographic specimens. Potential methods for increasing corrosion resistance are indicated.     

High-speed wire electrical discharge machining to create superhydrophobic surfaces for magnesium alloys with high corrosion and wear resistance

Herein, a superhydrophobic surface of AZ31B magnesium alloy prepared by high-speed wire electrical discharge machining and modification with stearic acid is reported. The surface morphology and wettability of the superhydrophobic surface were investigated by scanning electron microscopy and optical contact angle measurement, respectively. A uniform micro-/nanopetal-like structure was shown within the superhydrophobic surface, resulting in a contact angle of 151 ± 0.5° and a sliding angle of 4 ± 0.5°. Notably, the superhydrophobic surface had better corrosion resistance than the bare magnesium alloy, and its corrosion current density was reduced by nearly one order of magnitude. Under both dry and wet friction conditions, the friction coefficient of the superhydrophobic surface was lower than that of the bare magnesium alloy surface, with a much lower wear loss. In addition, the friction coefficient of the superhydrophobic sample was lower than that of the bare magnesium alloy sample under both the dry and wet friction conditions. Thus, the superhydrophobic sample experienced reduced wear and had a low wear rate.     

Susceptibility of highly alloyed austenitic stainless steels to caustic stress corrosion cracking

Slow Strain Rate tests (5 × 10⁻⁶ to 4 × 10⁻⁸ s⁻¹) in 300 g/L sodium hydroxide at 200°C were conducted on highly alloyed austenitic stainless steels with various nickel and chromium concentrations: N08904 (20Cr‐25Ni‐4Mo), N8825 (22.5Cr‐40Ni‐3Mo), N08028 (27Cr‐30Ni‐3.5Mo), R20033 (32.5Cr‐31Ni‐1.5Mo). Stress Corrosion Cracking (SCC) resistance of studied alloys increases in the following order: N08904 → N8825 → N08028 → R20033 in accordance with increasing chromium content. The SCC susceptibility indexes decrease gradually with decreasing of strain rate. In materials exhibiting higher SCC resistance, tests should be conducted at very low strain rates ( < 2 × 10⁻⁷ s⁻¹) to observe indications of SCC. When sulphide ions are added the R20033 steel exhibiting an excellent corrosion behaviour in pure caustic solution, becomes highly susceptible to SCC, even at = 5 × 10⁻⁶ s⁻¹.     

Application limits of Ta and Ta-2.5% W for sulfur acid handling

Long term corrosion test with welded coupons were carried out to determine the application limits of Ta and Ta-2.5% W in sulfuric acid (H₂SO₄). The program included the following two fields of investigation:

• • Determination of corrosion behavior in 90 through 100% H₂SO₄ at temperatures up to 200°C.
• •Determination of corrosion behavior in 96 wt % H₂SO₄ comparing recovered nitration-spent acid and technical grade between 150 and 230°C.

Mainly immersion tests were performed. A comparison of Ta and Ta-2.5 % W showed that in technical H₂SO₄ the alloy performed better than the metal. Regardless of which material was considered, the higher the H₂SO₄ concentration, the lower the temperature necessary to achieve acceptable corrosion behavior. In technical H₂SO₄, the following application limits were revealed: Ta: 96 wt %/200°C – 97 wt %/150°C Ta-2.5% W: 96 wt %/210°C – 97.5 wt %/175°C. Above 97.5 wt % the corrosion resistance decreased rapidly. The recovered nitration-spent acid led to remarkably lower corrosion rates due to small amounts of nitric acid. In these types of acidcontaining oxidizing compounds. 230°C seemed to be satisfactory, provided the wall of the heat exchanger was sufficiently thick.     

Die aktive und passive Molybdän-Elektrode in sauren Lösungen

The active and passive molybdenum electrode in acid solution It follows from the anodic and cathodic thermodynamic polarization curves in the system molybdenum/aqueous solution (p_H 0 to 10) that the favourable behaviour of molybdenum in acid solutions is determined by the extension of the immunity region becomes smaller, but without simultaneous passivation of molybdenum; this fact explains the active behaviour of molybdenum in alcaline solution. The passivation of molybdenum starts as soon as the half cell reaction sets in, where The p_H-dependence of the cathodic passivation potential in acid solutions follows the equation      

Study of the Rate of Corrosion and Its Mechanisms in Aluminum Alloy after the Intense Torsional Plastic Deformation

The research results concerning the rate and mechanism of corrosion in aluminum alloy 6201 of the Al–Mg–Si system in a NACE solution are presented. The alloy was studied in three states: after standard treatment T6 (quenching + aging) and after the intense torsional plastic deformation (ITPD) at the temperatures of 130°C (d_av = 280 nm) and 180°C (d_av = 440 nm). It was shown that the corrosion resistance of alloy after ITPD is lower than in the case of state T6. The corrosion rate of alloy after ITPD at 130°C is higher than that at 180°C. The change in the surface roughness was analyzed.     

Galvanic Corrosion of Al Alloys

In a systematic study of galvanic corrosion of Al alloys the effects of the dissimilar metal, the solution composition and area ratio have been studied using galvanic current and weight loss measurements, In 3.5% NaCl, galvanic corrosion rates of the Al alloys 1100, 20324,2219, 6061 and 7075 decrease with the nature of the dissimilar metal in the order AG>Cu> 4130 steel ?stainless steel ≈Ni>>Inconel 718?Ti-6A1-4V≈?Haynes 188>Sn>Cd. Coupling to zinc did not lead to cathodic protection of all A1 alloys. The potential difference of uncoupled dissimilar metals have been found to be a poor indication of galvanic corrosion rates. Dissolution rates of A1 alloys coupled to a given dissimilar material are higher in 3.5% NaCl than in tapwater and distilled water where they are found to be comparable. In assessing the galvanic corrosion behavior of a given A1 alloy as a function of environment, one has to consider the effect of the dissimilar metal. The dissolution rate of Al 6061 is, for example, higher in tapwater with Cu as cathode than in 3.5% NaCl with SS304L or Ti-6AI-4V as cathode. The effect of area ratio \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document} has been studied in 3.5% NaCl for area ratios of 0.1, 1.0 or 10. The galvanic current was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density \documentclass{article}\pagestyle{empty}\begin{document}$ i_{^g }^A $\end{document} with respect to the anode has been found to be directly proportional to the area ratio (\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document}), while the dissolution rate r_A of the anode was related to area ratio by \documentclass{article}\pagestyle{empty}\begin{document}$ r_A = k_{_2 } (1 + \frac{{A^C }}{{A^A }}) $\end{document}. The results obtained have been explained in terms of mixed potential theory.     

激光表面强化对镁合金在模拟体液中腐蚀行为的影响

目的通过对镁合金表面进行激光强化处理,改善医用AZ91D镁合金在模拟体液中的耐腐蚀性能。方法采用不同脉宽的Nd:YAG脉冲激光对医用AZ91D镁合金表面进行处理,激光能量密度分别为28、23、18 J/mm~2,对激光处理后镁合金强化层的组成、显微结构、厚度、元素分布以及耐腐蚀性能等进行测试和分析。结果 AZ91D经过激光强化处理后形成致密的强化层,强化层中相的组成与基材相的组成相同,均由α-Mg和β-Mg_(17)Al_(12)组成,强化层的厚度达到300μm。Mg和Mg_(17)Al_(12)的X射线衍射峰均向低角度偏移(约0.2°),且镁合金表面晶粒均得到细化,β相的大小从平均55.705μm减小到平均6.447μm。EDS分析表明,经过激光处理后,Mg的质量分数由82.88%减少为70.13%,Al的质量分数由16.28%增加为28.08%,且Al的分布更均匀。激光处理后,镁合金在模拟体液中的电化学测试结果表明,镁合金的腐蚀电位从原来的-1274mV增加到-1215 mV,腐蚀电流密度从8.920×10~(-5) A/cm~2减小为8.826×10~(-6) A/cm~2,同时,阻抗也从原来的1000Ω增加到60 000Ω,可知激光强化镁合金的耐腐蚀性能较原始镁合金的耐腐蚀性能均有一定程度的改善。结论医用AZ91D镁合金在不同脉宽的Nd:YAG脉冲激光处理后,表面晶粒得到了细化,强化层中富集Al,在模拟体液中的耐腐蚀性能得到改善。     

镁合金表面防腐蚀超疏水涂层制备研究进展

镁合金是一种有发展前途的绿色工程金属材料，但其较差的抗腐蚀性能限制了它的大规模应用。对镁合金表面进行超疏水处理，能够极大地提高镁合金的耐腐蚀性能。当超疏水试样浸泡在腐蚀溶液中时，该结构将在腐蚀介质中形成固-气-液界面层，减少镁合金表面与腐蚀介质之间的接触面积，从而降低腐蚀速度。超疏水表面需要满足微纳米结构和低表面能2个必要条件。可以采用二步法或一步法在镁合金表面制备超疏水表面，详细介绍了在镁合金表面构造微纳米结构的方法，包括激光处理、机加工、化学刻蚀、化学镀、电化学沉积、阳极氧化、微弧氧化、水热合成和喷涂等方法。超疏水表面一旦受到机械损伤，微纳米结构无法满足条件，超疏水表面的“气垫效应”消失，腐蚀介质就会直接与微纳米结构接触，因此需要保证构建的微纳米粗糙结构对镁基体具有良好的保护作用并具有自愈功能。通过制备复合涂层，提高下层微纳米结构的自愈合性能，上层涂层的超疏水性与下层涂层的良好物理屏障能力的协同效应可以改善涂层的长久耐腐蚀性能。综述了在镁合金上制备具有良好耐腐蚀性能的复合超疏水表面的方法，并对镁合金超疏水表面防护技术的研究方向进行了展望。