Kontinuierliche Verfolgung der Korrosion des Stahls X 2 CrNiSi 18 15 in 98%iger Salpetersäure

Continuous Measurement of Corrosion on Steel X 2 CrNiSi 18 15 in 98% Nitric Acid The corrosion rates of iron, chromium and nickel have been measured by means of a radionuclide method for the silicium containing steel X2 CrNiSi 18 15 in 98% nitric acid in the temperature range 30 to 50°C. The corrosion is determined by the interfacial reaction. The growth of the oxide layer depends on the progress of the corrosion attack. The chromium exceed in the oxidic layer can be estimated from the Cr/Fe ratios in the corrosion medium.     

Corrosion of armco iron and model Fe−Cr-Al alloys in oxygen-containing lead melts

We studied the influence of oxygen-containing (6·10⁻³ wt.% O) lead on the corrosion of Armco iron and Fe−16Cr, Fe−16Cr−1Al alloys at a temperature of 650°C under stationary conditions. The front of corrosion propagates according to a linear law and this process is periodically repeated. In each period, an oxide film based on Fe₃O₄ magnetite is formed on the surface of the metal and lead penetrates into the suboxide zone. This leads to the exfoliation the external oxide film and then the process is repeated. Under the indicated testing conditions, alloying with chromium and aluminum intensifies the process of corrosion in iron. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 2, pp. 84–88, March–April, 1997.     

Entwicklung,Eigenschaften, Verarbeitung und Einsatz des hochsiliciumhaltigen austenitischen Stahls X2CrNiSi1815

Development, Properties, Processing and Applications of High-Silicon Steel Grade X2CrNiSi1815 Production, storage and transportation of highly concentrated nitric acid (approximately 98%) frequently occur in containers and vessels made of pure aluminium. In many cases, however, their service life is restricted by the insufficient corrosion resistance of the welds. Though tantalum exhibits a superior resistance to corrosion, it is only used in very specific occasions for cost considerations. Commercial grade austenitic chromium-nickel steels as well as ferritic chromium steels assume a transpassive state under such service conditions, and suffer from intergranular attack even if the structure is free of precipitates. A significant corrosion resistance to highly concentrated nitric acid in combination with good workability and weldability can be achieved by an austenitic chromium-nickel steel alloyed with silicon. For corrosion considerations a silicon contents of at least 3,7 wt. % has to be aimed at. Since the silicon is held in solid solution in the austenitic matrix, the mechanical properties of the special grade X2CrNiSi 18 15 are not very different from those of commercial chromium-nickel steel grades. Welding materials of the same kind are available for manual arc welding as well as for TIG welding. The corrosion resultance of the weld deposit is similar to that of the base metal. However, the tendency of this steel to precipitate intermetallic phases is increased by the silicon addition. There, a proper heat control during welding is a necessary prerequisite in order to avoid intercrystalline attack in the heat-affected zones on both sides of the weld. A silicon contents of approximately 4 wt. % not only improves the corrosion resistance against highly concentrated nitric acid but also results in a considerable improvement when this special steel is used in chromic acid solutions and hot concentrated sulfuric acid. Also the high temperature corrosion resistance of this material is remarkable. Several piping systems, chemical equipment, pumps, and fittings have been in successfull service for several years and proved the excellent properties of the X 2CrNiSi 18 15 specially steel.     

Specific features of the selective dissolution of 12Kh18N10T steel in ozonized sulfuric acid

We study the laws of corrosion-electrochemical behavior and selective dissolution of 12Kh18N10T steel in ozonized aqueous 20, 30, 40, and 70% sulfuric acid solutions. Ozone retards the corrosion rate of the steel only for acid concentrations lower than 40%. In ozonized 30 and 40% H₂SO₄ solutions, the dissolution of nickel and chromium in the course of corrosion of 12Kh18N10T steel becomes slower, but the amount of dissolved chromium is twice as great as that of nickel. We propose a hypothesis on the influence of ozone on the dissolution of components of the steel through the formation of OH⁻ ions, favoring the oxidation of iron and chromium to higher valences, which limits the anodic process. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 5, pp. 69–73, September–October, 2005.     

Entwicklung,Eigenschaften, Verarbeitung und Einsatz des hochsiliciumhaltigen austenitischen Stahls X2 CrNiSi 18 15

Development, Properties, Processing and Applications of High-Silicon Steel Grade X2 CrNiSi 18 15 Production, storage and transportation of highly concentrated nitric acid (approximately 98%) frequently occur in containers and vessels made of pure aluminium. In many cases, however, their service life is restricted by the insufficient corrosion resistance of the welds. Though tantalum exhibits a superior resistance to corrosion, it is only used in very specific occasions for cost considerations. Commercial grade austenitic chromium-nickel steels as well as ferritic chromium steels assume a transpassive state under such service conditions, and suffer from intergranular attack even if the structure is free of precipitates. A significant corrosion resistance to highly concentrated nitric acid in combination with good workability and weldability can be achieved by an austenitic chromium-nickel steel alloyed with silicon. For corrosion considerations a silicon contents of at least 3,7 wt. % has to be aimed at. Since the silicon is held in solid solution in the austenitic matrix, the mechanical properties of the special grade X 2 CrNiSi 18 15 are not very different from those of commercial chromium-nickel steel grades. Welding materials of the same kind are available for manual are welding as well as for TIG welding. The corrosion resultance of the weld deposit is similar to that of the base metal. However, the tendency of this steel to precipitate intermetallic phases is increased by the silicon addition. There, a proper heat control during welding is a necessary prerequisite in order to avoid intercrystalline attack in the heat-affected zones on both sides of the weld. A silicon contents of approximately 4 wt. % not only improves the corrosion resistance against highly concentrated nitric acid but also results in a considerable improvement when this special steel is used in chromic acid solutions and hot concentrated sulfuric acid. Also the high temperature corrosion, resistance of this material is remarkable. Several piping systems, chemical equipment, pumps, and fittings have been in successfull service for several years and proved the excellent properties of the X 2 CrNiSi 18 15 specially steel.     

Monodisperse nickel nanoparticles supported on SiO<Subscript>2</Subscript> as an effective catalyst for the hydrolysis of ammonia-borane

Monodisperse Ni nanoparticles (NPs) have been synthesized by the reduction of nickel(II) acetylacetonate with the borane-tributylamine complex in a mixture of oleylamine and oleic acid. These Ni NPs are an active catalyst for the hydrolysis of the ammonia-borane (AB, H₃N·BH₃) complex under ambient conditions and their activities are dependent on the chemical nature of the oxide support that they were deposited on. Among various oxides (SiO₂, Al₂O₃, and CeO₂) tested, SiO₂ was found to enhance Ni NP catalytic activity due to the etching of the 3.2 nm Ni NPs giving Ni(II) ions and the subsequent reduction of Ni(II) that led to the formation of 1.6 nm Ni NPs on the SiO₂ surface. The kinetics of the hydrolysis of AB catalyzed by Ni/SiO₂ was shown to be dependent on catalyst and substrate concentration as well as temperature. The Ni/SiO₂ catalyst has a turnover frequency (TOF) of 13.2 mol H₂·(mol Ni)⁻¹ · min⁻¹—the best ever reported for the hydrolysis of AB using a nickel catalyst, an activation energy of 34 kJ/mol ± 2 kJ/mol and a total turnover number of 15,400 in the hydrolysis of AB. It is a promising candidate to replace noble metals for catalyzing AB hydrolysis and for hydrogen generation under ambient conditions.     

Corrosion behavior of Cu–SiO<Subscript>2</Subscript> nanocomposite coatings obtained by electrodeposition in the presence of cetyl trimethyl ammonium bromide

Copper silica composite coatings are an attractive alternative to chromium and nickel coatings in order to avoid environmental problems and for application in electrical devices. However, co-deposition of SiO₂ particles with metals occurs to a rather limited extent, generally under 1%, due to the hydrophilicity of SiO₂, which makes the incorporation of particles in a metallic matrix difficult. To overcome this drawback, the influence of cetyl trimethyl ammonium bromide (CTAB) on the deposition and corrosion behavior of Cu–SiO₂ coatings on steel has been studied. It was established that CTAB plays a beneficial role in SiO₂ suspension stabilization, promotes the co-deposition of nanoparticles in the copper matrix and improves the deposit morphology and structure. Consequently, a higher corrosion resistance of Cu–SiO₂ deposits obtained in the presence of CTAB was noticed. The most important effect was observed in the case when CTAB was used in concentration of 10⁻³ M in the electroplating bath.     

Pitting corrosion of 12Kh18AG18Sh steel in chloride solutions

We experimentally established that the corrosion rate of 12Kh18AG18Sh steel in a 22% NaCl solution in the temperature range 20–100°C does not exceed 0.22 g/(m²·h) (or 0.277 mm/year). The material undergoes self-passivation with the formation of a protective passive film of Fe₃O₄+(Fe, Cr)₂O₃+(Mn, Fe)₂O₃. Pitting resistance of steel decreases in solutions with a concentration of chloride ions of above 0.2 mole/liter and temperatures of at least 40°C. We studied selective dissolution of certain components of steel and found that manganese is most soluble. Ionization of chromium occurs more slowly than that of the iron matrix. As a result of selective dissolution of steel, the passive film is depleted of manganese and nitrogen. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 3, pp. 81–85, May–June, 1999.     

Passivity,pitting and corrosion of anodically polarized Fe-Ni alloys in 0.5 M H2SO4 containing Cl−

Iron-nickel alloys containing 0, 20, 40, 60, 80 and 100% Ni (wt%) have been anodically polarized in 0.5 M H₂SO₄ containing Cl^?, and the conditions for passivity, pitting and corrosion with respect to alloy composition and Cl^? concentration broadly defined. Breaks occur in the values of the corrosion properties at about 30% and 70% Ni. It is considered that the corrosion properties of alloys containing up to 30% Ni are determined by the ferrite in the alloy and the low corrosion resistance of its surface film, that alloys containing 30 to 70% Ni have a corrosion resistant film probably similar to a nickel ferrite spinel, and that alloys containing over 70% Ni have properties similar to nickel and probably have a surface film based on a solid solution of iron in NiO.     

Oxidation and corrosion behaviour of mild steel laser alloyed with nickel and chromium

Surface alloys were made on mild steel, coated with nickel and chromium using laser surface alloying. Mild steel was coated with a composite layer of nickel and chromium using the plasma technique. This was followed by laser irradiation using a continuous carbon dioxide laser. Oxidation and corrosion behaviour of these alloys was then determined by carrying out oxidation in air at 800 °C and corrosion tests at room temperatures in 1 n H₂SO₄. With a 75 m layer of nickel and chromium each, it was possible to make surface alloys on mild steel, which had a chromium concentration of 6–7 wt%, but the nickel concentration varied from 10–20 wt%. Oxidation behaviour improved significantly over the as-coated specimen and aqueous corrosion improved considerably.     

Studies on the structure and behaviour of reactively sputtered iron oxide layers on steel surfaces

In a simple diode system for asymmetric radio frequency sputtering, steel specimens were covered with iron oxide and the corrosion behaviour was studied by electrochemical methods. The specimens, which were covered with a compact layer of Fe₂O₃, had film resistances of 10⁸–10¹⁵ Ω cm, due to the conditions of production and the purity of the target material. Potentiometric measurements on steel electrodes covered with quasi-crystalline α-Fe₂O₃ showed a distinct passivation of the basic material in neutral and slightly acid media. An outlook is given concerning future fundamental studies on this problem.     

Electrochemical and surface analytical study of the anodic oxidation of Fe–18% Cr steel in molten NaOH–Li2CO3 mixtures

The anodic oxidation behaviour of a Fe–18%Cr steel in molten NaOH–Li₂CO₃ (50:50 mol%) at 470 °C was characterised by in-situ and ex-situ methods. In-situ electrochemical impedance spectroscopic (EIS) measurements showed that the steady state ionic conductivity of the oxide decreased with potential in the passive range. This indicates an increasing layer thickness or a decrease in the amount of mobile current carriers in the oxide with increasing potential. The two high-frequency time constants in the impedance spectra are most probably related to the semiconductor properties of the corrosion film and interfacial charge transfer, whereas the low-frequency time constant corresponds to the ionic defect transport through the oxide. The surface composition of the corrosion layers was estimated by X-ray Photoelectron Spectroscopy (XPS). The results show that the films can be regarded as mixed iron oxides containing a certain amount of chromium, sodium and lithium.     

Corrosion-mechanical characteristics of the materials of nonmagnetic retaining rings of turbogenerators. III. Crack formation in the course of service

We analyze reasons for failures of rotors and retaining rings of powerful turbogenerators made of traditional materials and establish that corrosion cracking in working media and alternating stresses are the main reasons for failures. Holding specimens made of new 18Mn−18Cr steel under stress in hightemperature water and a 22% NaCl solution leads to transcrystalline corrosion cracking at a rate of 0.5–40·10⁻¹¹ m/sec. In the course of dissolution of high-nitrogen chromium-manganese steels in the electrochemically active state, their corrosion ratei _cor is 0.1–4 mA/cm². Alternating stresses in chloride-containing acidic media most strongly intensify selective dissolution of manganese and then iron and chromium, which is in agreement with results of an analysis of products of corrosion on actual retaining rings. We established that a saturated solution of copper dichloride is the most aggressive medium for high-nitrogen chromium-manganese steels. Even short-term contact of the steel with this solution at room temperature leads to intense pitting, while long-term contact results in catastrophic intercrystalline cracking at a rate of 1.56·10⁻⁹ m/sec. In subsequent stages, this contact causes selective dissolution of the steel and pitting corrosion. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 2, pp. 115–122, March–April, 1998     

Improved wear and corrosion resistance of chromium(III) plating by oxynitrocarburising and steam oxidation

Postsurface treatments, such as oxynitrocarburising and steam oxidation, were applied to amorphous Cr plating on SM45C mild carbon steel obtained from a trivalent (III) chromium bath to improve wear and corrosion properties. Higher wear properties of hardness (HV 1450), wear rate (1.9×10⁻⁶ mm³/rev) and friction coefficient (0.4) were found for both the oxynitrocarburised and the steam-oxidized Cr platings due to the formation of chromium carbide, Cr₇C₃, during the treatments. Excellent corrosion resistance was also observed for the posttreated Cr platings due to the crack healing effect as a result of the formation of iron oxides (Fe₃O₄, Fe₂O₃) and/or nitride (Fe₄N), suggesting that these treatments are highly effective in enhancing wear and corrosion resistance of the chromium platings.     

Corrosion resistance studies on grain-boundary etched drug-eluting stents

In this paper we compare the influence of different microstructures on the corrosion resistance of new drug-eluting stainless steel stents, which have been produced by grain-boundary-selective electrochemical etching processes. The morphology of the stent surfaces was analysed by scanning electron microscopy (SEM), and the surface composition was investigated with Auger electron spectroscopy (AES) as well as with energy dispersive X-ray analysis (EDX). The passivity of the different microstructured stents was studied by cyclovoltammetry in Ringer solution. Release of nickel and chromium was assessed after potentiostatic experiments in Ringer solution by analysing the collected electrolyte with AAS. For stents produced by different two-step etching procedures bringing about ideal morphologies regarding the mechanical and biological properties of the surface, no significant differences in the passivation behaviour could be observed. A two-step process using first nitric acid and oxalic acid in a second step produces stent surfaces with very good corrosion properties: electrochemical analysis shows that the range of stable passivity is the same as for conventional stent surfaces, and low rates of nickel and chromium release are observed. The etching procedures do not seem to change the surface oxide layer composition.     

Oxidation kinetics of silicon carbide whiskers studied by X-ray photoelectron spectroscopy

Silicon carbide whisker surfaces were characterized by X-ray photoelectron spectroscopy (XPS) to determine changes in the surface oxide film which occurred as a result of heating in air at temperatures from 600 to 800 °C. Equations were derived for the calculation of surface oxide film thickness from the SiC to SiO₂ 2p intensity ratios. Oxidation was found to follow a linear rate law in this temperature range for the first 10 nm of oxide growth. An activation energy of 17.2 ± 2.8 kcal mol^–1 (72 ± 12 kJ mol^–1) was measured.     

Thermal Conductivity and Interfacial Thermal Resistance: Measurements of Thermally Oxidized SiO2 Films on a Silicon Wafer Using a Thermo-Reflectance Technique

This article describes the development of a method to measure the normal-to-plane thermal conductivity of a very thin electrically insulating film on a substrate. In this method, a metal film, which is deposited on the thin insulating films, is Joule heated periodically, and the ac-temperature response at the center of the metal film surface is measured by a thermo-reflectance technique. The one-dimensional thermal conduction equation of the metal/film/substrate system was solved analytically, and a simple approximate equation was derived. The thermal conductivities of the thermally oxidized SiO₂ films obtained in this study agreed with those of VAMAS TWA23 within ± 4%. In this study, an attempt was made to estimate the interfacial thermal resistance between the thermally oxidized SiO₂ film and the silicon wafer. The difference between the apparent thermal resistances of the thermally oxidized SiO₂ film with the gold film deposited by two different methods was examined. It was concluded that rf-sputtering produces a significant thermal resistance ((20 ± 4.5) × 10⁻⁹ m²·K·W⁻¹) between the gold film and the thermally oxidized SiO₂ film, but evaporation provides no significant interfacial thermal resistance (less than ± 4.5 × 10⁻⁹ m²·K·W⁻¹). The apparent interfacial thermal resistances between the thermally oxidized SiO₂ film and the silicon wafer were found to scatter significantly (± 9 × 10⁻⁹ m²·K·W⁻¹) around a very small thermal resistance (less than ± 4.5 × 10⁻⁹ m²·K·W⁻¹).     

Electrochemistry of AISI 316L stainless steel in calcium phosphate and protein solutions

The influence of calcium phosphate and serum on the corrosion resistance of AISI 316L stainless steel in 0.9% NaCl solution was investigated. Both substances are responsible for an increase in the pitting corrosion resistance. Calcium phosphate accelerates the rate of film formation, enhances the release of iron and nickel, and retards that of chromium from a corroding surface. Proteins induce the incorporation of phosphorus and calcium in corrosion products. These effects appear to replicate the accumulation of the same elements observed on stainless steels corrodedin vivo.     

Corrosion behaviour of some stainless steel alloys in molten alkali carbonates (I)

In the present work it is aimed to study the corrosion behaviour of two types of stainless steel alloys (one ferritic and two austenitic) in molten Li₂CO₃- Na₂CO₃- K₂CO₃ mixture. This mixture is of interest in corrosion studies because of its low melting point (397°C) and good electrical properties. In this investigation the following techniques of measurements are used: (i) open circuit-potential, (ii) galvanic current, (iii) impedance, (iv) atomic absorption spectroscopy for the determination of the amount of metals dissolved in the melt (v) corrosion tests, carried out on the oxide scales formed during the oxidation of stainless steel alloys in carbonate melt. In this melt the electrode Ag/AgCl was used as a reference electrode. In molten carbonates, the oxide ions originate by self-dissociation according to the equilibrium CO₃ ^2– CO₂ + O^2–. The oxide ions, O^2–, and carbonate ions, CO₃ ^2–, play an important role in the oxidation process of these alloys and their passivation in the carbonate melt. As previously mentioned in references it can be assumed that the oxide scales formed on the alloy surface consist mainly of LiCrO₂ and LiFeO₂. The cathodic path of the corrosion process may be the reduction of CO₂ and/or CO₃ ^2–. The resistance of alloys against corrosion in melt increases with the increase of temperature. This may be due to the increase of concentration of O^2– and CO₂, enhancing both the anodic and cathodic reactions. The activation energy was calculated and found to be 91.496, 23.412 and 37.956 kJ/mol for the alloys 1, 2 and 3 respectively. The above mentioned techniques of measurements showed that the oxide scales of the austenitic stainless steel alloys (2, 3) are more passive and protective than of ferritic stainless steel alloy (1). This means that the resistance against corrosion, in the carbonate melts, of austenitic stainless steel alloys is higher than that of ferritic one.     

Oxidation of electrodeposited black chrome selective solar absorber films

X-ray photoelectron spectroscopy and Auger electron spectroscopy were used to study the composition and oxidation of electrodeposited black chrome films. The outer layer of the film is Cr₂O₃ and the inner layer is a continuously changing mixture of chromium and Cr₂O₃. Initially, approximately 40 vol.% of the chromium was combined as Cr₂O₃ and the percentage of Cr₂O₃ increased to greater than 60 vol.% after heat treatment for only 136 h at 250°C. After 3600 h at 400°C the percentage of Cr₂O₃ increased to as high as 80 vol.%. The thermal emittance decreased approximately linearly with increasing oxide content whereas the solar absorptance remained constant until the percentage of Cr₂O₃ exceeded approximately 70%. Oxidation was slower when the Cr³⁺ concentration in the plating bath was reduced from 16 to 8 g 1^?1 and when black chrome was deposited on stainless steel rather than on sulfamate nickel.