Über die Korrosionsbeständigkeit von Nickel-Tantal-Legierungen

On the corrosion-resistance of nickel-tantalum-alloys The corrosion-resistance of different nickel-tantalum-alloys in concentrated phosphoric acid for use as current-collectors in hydrocarbon fuel-cells was measured potentiostatically in the anodic range at temperatures between 100 and 140°C. An alloy with a tantalum contents of 1 wt% showed active dissolution and high corrosion rates at all potentials, an alloy with 10 wt% tantalum showed a passive range at about 0,7 V and alloys with more than 30 wt% tantalum and tantalum itself showed very low corrosion-rates and self-passivation in phosphoric acid. A temptative explanation of the results by considering electronic properties of the alloys was given.     

Corrosion resistance of electrodeposited RE-Ni-W-P-SiC-PTFE composite coating in phosphoric and ferric chloride

1 Introduction During process, store and use in various kinds of environment, corrosion, wear, fatigue and rupture may happen in all materials and products. These kinds of failure and damages widely occur in industries, causing enormous losses to nationa…     

Corrosion Behavior of Surface-Treated Implant Ti-6Al-4V by Electrochemical Polarization and Impedance Studies

Implant materials for orthopedic and heart surgical services demand a better corrosion resistance material than the presently used titanium alloys, where protective oxide layer breaks down on a prolonged stay in aqueous physiological human body, giving rise to localized corrosion of pitting, crevice, and fretting corrosion. A few surface treatments on Ti alloy, in the form of anodization, passivation, and thermal oxidation, followed by soaking in Hank solution have been found to be very effective in bringing down the corrosion rate as well as producing high corrosion resistance surface film as reflected from electrochemical polarization, cyclic polarization, and Electrochemical Impedance Spectroscopy (EIS) studies. The XRD study revealed the presence of various types of oxides along with anatase and rutile on the surface, giving rise to high corrosion resistance film. While surface treatment of passivation and thermal oxidation could reduce the corrosion rate by 1/5th, anodization in 0.3 M phosphoric acid at 16 V versus stainless steel cathode drastically brought down the corrosion rate by less than ten times. The mechanism of corrosion behavior and formation of different surface films is better understood from the determination of EIS parameters derived from the best-fit equivalent circuit.     

温度对S32304双相不锈钢在工业磷酸中腐蚀的影响

采用实验室模拟浸泡试验,通过失重法、扫描电镜(SEM)和能谱(EDS)等分析手段,对S32304双相不锈钢在不同温度85%工业磷酸溶液中的腐蚀行为进行了研究,确定了其电化学特性、腐蚀速率、腐蚀形貌和腐蚀产物。结果表明,S32304在温度低于85℃的85%工业磷酸中具有较好的抗腐蚀性能,虽然随温度的升高,腐蚀有所加重;当温度高于55℃时,其抗腐蚀性能降低尤为明显。     

Electrochemical characteristics of titanium based biomaterials in artificial saliva

In the last decade, new titanium alloys have been developed in different areas of dentistry, such as Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, and Ti5Al2.5Fe. The aim of this study was to compare the Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, Ti5Al2.5Fe, and Ti6Al4V alloys with the commercial titanium, regarding the corrosion resistance in artificial saliva. In the electrochemical estimations the polarization data are converted into instantaneous corrosion rate values (I_corr). The passivation properties were comparable for the four alloys. The EIS spectra are best fitted using an equivalent circuit (EC), which corresponds to the model of a two‐layer structure for the passive film. High impedance values (in the order of 10⁶ Ω cm²) were obtained from medium to low frequencies for all materials suggesting high corrosion resistance in artificial saliva. The electrochemical and corrosion behavior of Ti6Al4V is not affected on substituting vanadium with niobium, iron, molybdenum, and tantalum.     

Electrochemical behavior of titanium‐tantalum alloys in sulfuric acid solutions

Titanium exhibits a good corrosion resistance in oxidizing acids and neutral media but it is severely attacked in reducing acids. On the contrary, tantalum presents an excellent resistance in both oxidizing and reducing acids, but its high cost limits its use to very aggressive conditions. The titanium‐tantalum alloys are promising materials for use in reducing acids, due to their lower cost and density when compared to tantalum, and their higher corrosion resistance when compared to titanium. Titanium‐20, 40, 60 and 80 wt% tantalum alloys were prepared by arc‐melting and their microstructures were characterized by scanning electron microscopy and X‐ray diffractometry. Their electrochemical behaviors were studied in 20 to 80 wt% sulfuric acid solutions at room temperature, using open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Different behaviors were observed depending on the tantalum content and acid concentration. A clear tendency of increase in corrosion resistance with the increase of tantalum content is observed, especially in 80 wt% sulfuric acid solutions.     

聚苯胺/聚吡咯复合薄膜的制备及其抗腐蚀性能研究

采用循环伏安法在不锈钢表面电聚合聚苯胺/聚吡咯复合薄膜.利用动电位极化曲线法和电化学阻抗法研究了聚苯胺/聚吡咯复合薄膜的耐蚀性及其影响因素.结果表明:在3.5%NaCl溶液中,不锈钢表面覆盖复合膜以后,其自腐蚀电位比无膜和纯聚苯胺膜时提高,耐蚀性能增强,且复合膜的耐蚀性受电解液浓度、扫描次数、扫描速率及扫描上限等因素的影响.电解液中苯胺和吡咯的浓度比及硫酸浓度的高低,都会影响膜的致密度,从而影响膜的耐腐蚀性.电化学参数的改变会影响复合膜的聚合速率,使得复合膜的抗腐蚀能力不同.当苯胺和吡咯浓度比为7:3时,硫酸浓度为1.1 mol/L,扫描次数为25次,扫描速率为60 mV/s,扫描上限为1.2 V时,采用循环伏安法共聚合苯胺和吡咯,可形成沉积致密度高、耐蚀性好的复合膜.     

Protection of low carbon steel in phosphoric acid by potassium iodide

The corrosion of low carbon steel in 2.5 M phosphoric acid at temperature range of 30–60°C in presence and absence of potassium iodide as an inorganic inhibitor in the range of 0.02–0.05 M at static condition has been investigated. Weight loss and polarization techniques were employed in this investigation. The maximum value of inhibitor efficiency obtained was 99.95% at 50°C in presence of 0.05 M inhibitor concentration. The fraction of surface covered calculated from corrosion rates followed the Langmuir adsorption isotherm. Polarization experiments showed that for a given temperature, the curves were shifted towards the potential axis leading to lower the corrosion rates as the inhibitor concentration increased. Potassium iodide inhibits carbon steel corrosion in H₃PO₄ acid by affecting both anodic and cathodic partial reactions with the anodic reaction being more prevailing.     

The effects of temperature and hydrodynamics on the CO2 corrosion of 13Cr and 13Cr5Ni2Mo stainless steels in the presence of free acetic acid

This paper describes the effects of temperature and hydrodynamics on the CO₂ corrosion of two stainless steels in the presence of free acetic acid. The experimental set-up developed in this work was able to evaluate the corrosion behavior of 13Cr and 13Cr5Ni2Mo stainless steels in static conditions with a flow velocity of 1 m s⁻¹ at temperatures of 125, 150 and 175 °C. Electrochemical tests of impedance and linear polarization resistance have been carried out, as well as mass loss tests and surface analysis.     

Corrosion of titanium in phosphoric acid at 250 °C

Corrosion studies of a commercially pure titanium in phosphoric acid solutions at 250 °C were carried out by immersion test in an autoclave. At lower phosphoric acid concentration (0.1 mol/L), the corrosion was mild. At higher phosphoric concentration (1.0 mol/L) corrosion, a 25 μm-thick white corrosion products layer was formed on the samples after 24 h immersion. XRD analysis shows that the white layer consists mainly of titanium oxide phosphate hydrate (π-Ti₂O(PO₄)₂·2H₂O). The corrosion product shows the morphology of fiber bundles. A thermodynamic analysis of the formation of the corrosion product is presented.     

Untersuchungen zum Korrosionsverhalten nichtrostender Stähle in Phosphorsäure in Abhängigkeit von dem Chlorid- und Fluoridgehalt und einer Wärmebehandlung beim Schweißen

Investigations into the corrosion behaviour of stainless steels in phosphoric acid in dependence on the chloride and fluoride contents and a heat-treatment during welding In the present investigation the corrosion behaviour of recently developed high-alloyed austenitic (X 2 NiCrMoCU 25 20) and austenitic-ferritic (X 2 CrNiMoCuN 25 5) steel has been tested towards phosphoric acid, the composition and concentration of which was adjusted to correspond to crude phosphoric acid with varying contents of Cl^?, F^?, Fe³⁺, and SO₃. Current density-voltage curves were recorded on steel test-specimens at room temperature, 45°C, and 80°C. In addition, test-pieces of both steels, after annealing treatment between 800°C and 500°C, as well as welded specimens of similar type were examined for the effect of heat input and consequent structural alterations on the corrosion behaviour. Both steels exhibit good corrosion resistance towards pure phosphoric acid. Cl^? and F^? ion impurities render the acid more aggressive. Austenitie-ferritic steel reacts more sensitively than austenitic steel towards heat input, resulting in deterioration in corrosion resistance. This may be attributed to the precipitation of inter-metallic phases in the ferritic structure.     

Corrosion protection of stainless steel by separate polypyrrole electrode in acid solutions

Galvanic anodic protection (GAP) of stainless steels by doped polypyrrole (PPy) was investigated using chemically synthesized PPy. Separate PPy powder‐pressed electrodes with different surface areas were prepared. Electrochemical properties of PPy electrodes were studied by open circuit potentials (OCPs) and potentiostatic polarization. PPy powder‐pressed electrodes were coupled with 410‐stainless steel electrodes in different concentrations of sulfuric acid solutions, 5 M phosphoric acid solution, and industrial phosphoric acid solution (5 M phosphoric acid + 0.05% chloride ion). Remarkable shift of OCP to the positive direction and sharp decrease of corrosion rate were observed during the coupling experiments, which implies that 410‐stainless steel was transferred to passive state. Results also showed that PPy electrode with sufficient surface area can provide corrosion protection to 410‐stainless steel electrode in highly corrosive acid solution. Based on the experiment results, GAP provided by PPy and PANi (synthesized under similar conditions) was compared.     

Zum Korrosionsverhalten nichtrostender austenitischer Chrom-Nickel-(Molybdän,Kupfer)-Stähle in nahezu wasserfreier Essigsäure

Corrosion of stainless austenitic steels in almost anhydrous acetic acid As-welded samples and looped specimens from 5 differently alloyed stainless steels were tested for up to 246 days in 99,5% to 99,95% acetic acid at 118°C (boiling temperature/normal pressure) and at 150°C; the chloride content was varied between < 1 and 100 ppm. Pitting corrosion – of shallow depth, however (approx. 0,1 mm) – was already observed at surprisingly low chloride concentrations. Only the following were found to be resistant to pitting corrosion:

• – stainless steels 1.4439 and 1.4539, containing approx. 4,5% molybdenum, in 99,5% acetic with < 1 ppm chloride at 118 and 150°C,
• – stainless steels 1.4439 and 1.4539 in 99,9% acetic acid with < 1 ppm chloride at 118°C, and
• – special stainless steel X 2 CrNiMoCuN 20 18 6, containing approx. 6% molybdenum, in 99,5% acetic acid with > 3, < 10 ppm chloride at 118 and 150°C.

Looped specimens and ground as-welded samples showed no sensitivity to transcrystalline, chloride-induced stress corrosion cracking at any of the concentration ranges. High surface-removal rates can be expected if air has access to the specimens; under this condition pitting corrosion and general corrosion may overlap. Contamination of acetic acid with chlorides must be prevented under all circumstances.     

Effect of temperature on anodic behavior of 13Cr martensitic steel in CO2 environment

The corrosion behavior of 13Cr martensitic stainless steel in a CO₂ environment in a stimulated oilfield was studied with potentiodynamic polarization and the impedance spectra technique. The results showed that the microstructure of the surface scale clearly changed with temperature. This decreased the sensitivity of pitting corrosion and increased the tendency toward general (or uniform) corrosion. The capacitance, the charge transfer resistance, and the polarization resistance of the corrosion product scale decrease with increasing temperature from 90 to 120 °C, and thus the corrosion is a thermal activation controlled process. Charge transfer through the scale is difficult and the corrosion is controlled by a diffusion process at a temperature of 150 °C. Resistance charge transfer through the corrosion product layer is higher than that in the passive film.     

The wet corrosion of molybdenum thin film – Part II: Behavior at 85°C

In the past few years there has been increased interest in molybdenum thin films, which are commonly prepared by magnetron sputtering. There is a variety of novel applications of molybdenum such as, for example, components for soft X‐ray optics based on Mo/Si multi‐layers, the back contact in thin film solar cells, NO gas detection, and microelectronics. Molybdenum is, also, widely used as an alloying addition in stainless steels to facilitate the formation of the passive film and to improve resistance to pitting attack. Its corrosion behaviour is complex and many aspects still need to be clarified. During this study, the corrosion behaviour of the PVD‐Mo thin film immersed in aerated sulfate and chloride solutions at 85°C was investigated with both polarization and electrochemical impedance spectroscopy (EIS) measurements. It is apparent that the Mo thin film exhibits increased susceptibility to corrosion in more alkaline environments.     

Interpretation of electrochemically and chemically investigated corrosion behaviors of 316L SS in acid chloride environments

The electrochemical behavior of 316L stainless steel was investigated in acid chloride environments, and pitting potentials were determined electrochemically and chemically. An increase in the anodic maximum current density was observed upon decreasing the cathodic potential from which the scan was initiated to determine the polarization curve. To determine the critical pitting potential through the chemical method, the potential was increased by increasing the concentration of ferric ions in ferric chloride while holding the chloride ion concentration constant with sodium chloride. When 316L stainless steel was immersed in 15 g/1 of FeCl₃6H₂O containing the same chloride ion concentration as 5% NaCl with pH=2 at 57°C, the corrosion potential increased to 0.47 V (SHE) within two minutes due to initial passivation. Immediately after reaching 0.47 V (SHE), which was just above the pitting potential of 0.45 V (SHE) determined electrochemically in 5% NaCl (pH=2, 57°C), the corrosion potential continuously decreased, indicating the onset and propagation of pitting corrosion. A correlation between the electrochemical and chemical methods can be verified if the proper measurements are made and the observations are properly interpreted.     

Untersuchungen über den Einfluß des Gefügezustandes auf das Korrosionsverhalten hochlegierter,rost- und säurebeständiger Stähle in reiner sowie in chloridhaltiger Schwefelsäure

Corrosion Properties of High Alloyed Stainless Steels in Pure as well as in Chloride Containing Sulfuric Acid The corrosion behaviour of the high alloyed stainless steels material no. 1.4439 (X3CrNiMoN17135), 1.4539 (X2NiCrMoCu25205), 1.4503(X3NiCrMoCuTi2723) as well as the reference materials AlSI 316 L and alloy 825 was tested in diluted sulfuric acid (5, 10, 20 and 50%) at 50, 100 and 150°C. The test solutions additionally contained impurities as chlorides and cupric ions. On the material side the effect of various microstructures was checked as well: material as received (commercial production), solution annealed under laboratory conditions, cold deformed and for two selected steels electroslag remelted. Corrosion testing methods are: the immersion test will sheet coupons and the measurement of the weightloss; electrochemical testing, i.e. Current potential-and free corrosion potential-time-curves. No pitting corrosion is observed in the presence of chloride ions. In some cases the general corrosion rate is lowered if chloride ions are present. This beneficial effect of chloride ions, however, is observed only at low chloride concentrations (500 ppm). Annealing under laboratory conditions as well as electroslag remelting does not generally improve the corrosion resistance. A negative effect by cold deformation is only observed for standard stainless steel AlSI 316. Cupric ions added to the 20% sulfuric acid solution improve the corrosion resistance of all steels investigated to that extent, that they can be used in practice up to 100°C provided that the concentration of cupric ions in the solution is sufficiently high (2000 ppm). Electrochemical test results indicate that the positive effect of cupric ions is due to the shift of the free corrosion potential into the potential range of stable passivity. Copper alloyed stainless steels show the highest corrosion resistance.     

Effect of the Heat Treatment on the Corrosion Resistance of Duplex Stainless Steels

Duplex stainless steels (DSS) are biphasic austenitic-ferritic steels in which the best combination of mechanical and corrosion resistance properties is achieved for an almost equal volume fraction of the phases. In this work, the effect of secondary phases precipitation on the corrosion resistance of four DSS grades (2101, 2304, 2205 and 2507), after isothermal aging in the critical temperature range 750-900 °C, was studied. The corrosion resistance was investigated by potentiodynamic polarization tests in both 0.6 M NaCl solution (pH 7) and in an acid chlorinated solution (pH 3) at room temperature. Moreover, the critical pitting temperature was determined according to ASTM G150. The results showed that secondary phases precipitation mainly influenced the resistance to corrosion of the lean duplex grades.     

Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures

This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25–60 °C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest i_G values at 60 °C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H₃PO₄ media from a corrosion point of view for all the temperatures analysed.     

Corrosion Resistance and Color Properties of Anodized Ti-6Al-4V

In this research, color anodizing of Ti-6Al-4V alloy was performed in phosphoric acid solution of 0.4 M concentration and within 30 s in different voltages (10-120 V) of a DC power supply. The effect of anodizing voltages on the color and thickness of anodized layers on Ti-6Al-4V alloy surface was surveyed. Thickness and refractive index of layers were measured by spectrophotometery and reflectance curves. According to the results, thickness of layers increased with increasing anodizing voltage and was in the range of 38-167 nm. Also the refractive index of anodic film was approximately constant at about 2 and increased inconsiderably with increasing anodizing voltage. Corrosion resistance of the anodized samples in 20 and 50 V was surveyed in physiological solutions of Ringer’s solution, Artificial Saliva solution, and Ringer’s + 150 mM H₂O₂ solution at the temperature of 37 °C by potentiodynamic polarization method. The anodized sample in 50 V indicated lower corrosion rate than the non-anodized sample as well as the sample which was anodized in 20 V in all solutions. The non-anodized sample indicated the highest corrosion rate of about 0.25 μA cm⁻².