Corrosion at nanoscale; interface barriers and phase competition
The problem of simultaneous growth and competition of intermediate phases during reactive diffusion was analyzed by Gösele and Tu in 1982. In this work we reformulate old problem and propose method based on volume fixed frame of reference. It allows computing the material velocity in the reacting system in which reactions at several moving interfaces occur. All reactions lead to the lattice shift due to the difference of intrinsic diffusivities and different molar volumes. The following peculiarities are taken into account: (1) the deviation from local equilibrium at both interfaces of each moving inter-phase zone (i.e., at each side of the moving phase-boundary); (2) different mobility of the components in the interphase zone; (3) nonzero steps of molar volumes for each component from phase to phase and (5) different physicochemical properties of the interphase zones. We show the scale effect on the kinetic of the corrosion, the non-parabolic reactions, the multiphase scale growth and present the potential applications of the method.
Słowa kluczowe: multiphase system, Kirkendall shift, volume continuity equation, chemical kinetics, interdiffusion
Electrochemical composite coatings: preparation, properties, application
Reinforcement of various inert particles from an electrolytic bath into metallic deposit is law cost and simple technique. Electrochemical codeposition enables the production of a large range of composite materials with unique properties. Such coatings can be used as advanced engineering materials in various application where improved corrosion resistance, high wear resistance, high temperature oxidation resistance, increased hardness or catalytic activity of material is needed,
Słowa kluczowe: composite coating, electroplating, corrosion resistance
Effect of laser shock processing (LSP) on the corrosion resistance of aluminum alloy 2050-T8
Aluminium alloys are very important category of materials due to their high mechanical properties and wide range of industrial applications. It is well known that aluminum alloys are prone to microstructural corrosion (pitting corrosion, intergranular corrosion, etc.). Laser shock processing (LSP) is a serious candidate versus conventional surface treatments to preserve their integrity and to protect them from pitting corrosion damages. In the present paper, the infl uence of LSP on the resistance to localized corrosion of AA2050-T8 is investigated in chloride media. After polishing, sites containing precipitates show lower pitting potentials (around 0 mV vs Ag/AgCl) than the pure matrix (of about 300 mV). Surface observations indicate that pits initiated at Al-Cu-Fe-Mn precipitates. Oxides were not dissolved and no pits were found around them. After LSP, AFM and FE-SEM/EDS observations revealed that some precipitates were debonded from the matrix, resulting in the formation of cavities at the specimen surface. The anodic current measured in sites containing the matrix or cavities was lower than after polishing (0.01 mA/ cm2 instead of 0.1 mA/cm2). A passive domain was found and the current increases from 0 mV. However, no pitting potential could be determined. This indicates that LSP increases the corrosion resistance of such sites. Pitting was detected in a few sites at potential values close to the pitting potentials found on the polished specimens (of about -250 mV).
Słowa kluczowe: aluminium alloy, laser, microstructure, corrosion, capillary techniques
Local study of the effects of mechanical stresses on the growth of ultra-thin oxide films on duplex stainless steels
The aim of this work is to determine if there is a correlation between local strain gradients and the chemical composition of ultra-thin oxide films (thickness of about 20 nm) using micro-strain gauge methods and local Auger spectroscopy. A model system consisting of duplex stainless steels oxidized at 490°C for 2 minutes under secondary vacuum was considered. The obtained results showed that there is no influence of strains on the oxide film thickness. Main differences were observed in the chemical composition of the oxide film. The chromium content in the oxide film increases in the presence of compressive strains. This may explain the beneficial effects of compressive strain on the corrosion resistance of stainless steels. However, it was found that crystallographic orientation has stronger influence than thermal strains.
Słowa kluczowe: duplex stainless steel, passive film, microstructure, corrosion, plastic strain
Microstructure and corrosion behaviour of magnesium alloy AZ91: Influence of rare earths as alloying elements
Magnesium alloys have low densities and potentially high strength/weight ratio, therefore have a great interest for application in automotive, aerospace and bioengineering. However, corrosion resistance is a factor limiting their more wide application. Addition of alloying elements like aluminum and zinc may improve the mechanical and the corrosion behaviour. The purpose of this paper is to study microstructure and corrosion behaviour of magnesium AZ91 and the influence of rare earth elements (mesh metal up to a certain weight) addition. The influence of the main constituent phases on the corrosion behaviour was studied by scanning electron microscopy and energy dispersive X-ray. ? (Matrix) and ß (grain boundary) phases as well as dendrite precipitate of rare earth elements RE (cerium, neodymium, lanthanide) was found. Electrochemical (open circuit potential and potential cyclic polarization) and gravimetric (humidity and marine) methods were used to evaluated the corrosion behaviour. The addition of RE (0.5–4%) has an impact on the corrosion resistance. A significant decrease of the corrosion resistance was obtained with addition of 4%. However the corrosion resistance was improved for addition of certain limit of rare earth elements.
Słowa kluczowe: Mg alloy AZ91, corrosion, microstructure, alloying, rare earth elements
The use of micro-capillary techniques to study the corrosion resistance of AZ91 magnesium alloy at the micro-scale
In the present paper, the corrosion behavior of as-cast AZ91 magnesium alloy is investigated in 0.1 M NaClO4 at 25°C. The specimen microstructure was first investigated using FE-SEM/EDS and AFM. It is composed of Mg17Al12 precipitates, eutectic around precipitates and a-Mg matrix. Electrochemical measurements were then carried out after mechanical polishing, on individual phases using the electrochemical microcell technique and extremely small capillaries (diameters between 5 and 10 nm). A large passive domain was observed in the anodic region in sites containing precipitates. Stable pits were detected between -700 and -200 mV vs. Ag/AgCl. By contrast, the passive domain obtained in the matrix was narrow and stable pitting was observed at -1200!200 mV vs. Ag/AgCl. Eutectic was revealed by etching samples in solution (10 cm3 HF + 90 cm3 H2O) for 12 seconds. Local electrochemical investigations were then performed on the etched surface. Eutectic exhibits an active behavior, without current plateau in the anodic domain. By contrast, a-Mg matrix reveals a passive behavior between -1500 and -800 mV vs. Ag/ AgCl.
Słowa kluczowe: magnesium alloy, microstructure, capillary techniques, corrosion
Influence of the passive film chemical composition and residual stresses on the microelectrochemical behaviour of duplex stainless steels in sodium chloride media
Duplex stainless steels are highly important engineering materials, due to their generally high corrosion resistance combined with high strength and moderate alloy cost (lower nickel and molybdenum content). They have a complex microstructure with comparable volume of austenite and ferrite. Both phases have different chemical composition and mechanical properties. In the present paper, the chemical composition of the passive film formed on both phases of two types of duplex stainless steels (UNS S31803 and UNS S32304) is determined at the microscale using Auger electron spectroscopy (AES). Samples were either mechanically polished (down to diamond pastes) or electrochemically etched in nitric acid. The micro-electrochemical behaviour of the two sets of samples was then determined in sodium chloride media by means of the electrochemical microcell technique (microcapillary diameters in the range of 15-50 µm). The results obtained were analysed considering the chemical composition of passive films. Quantitative relationships between electrochemical parameters and the distribution of chromium and iron species in the oxide layer were found. Due to differences in mechanical properties between ferrite and austenite, a heterogeneous stress distribution is generated in both phases. A method based on thermal-mechanical simulation was used to quantify surface stress gradients at the surface of duplex stainless steels and evaluate its infl uence on the micro-electrochemical behaviour. This was done for the different surface preparations (polishing and electrochemical etching).The role of elastic stresses and the cold-worked layer on the values of corrosion potential was discussed.
Słowa kluczowe: duplex stainless steel, stress, passivity, corrosion, capillary techniques
Application of composite films containing 4-aminobenzoic acid (4-ABA) and poly(3,4-ethylenodioxythiophene) for protection of X20Cr13 steel against corrosion
This work summarizes the results of corrosion studies describing protective properties of films prepared on stainless steel based on a composite coating. The coatings consisted of 4-aminobenzoic acid (4-ABA) and poly(3,4-ethylenodioxythiophene) (PEDOT). The respective films on stainless steel were electrodeposited using cyclic voltammetry. Protective properties of the composite films were evaluated in the acidified sulphate solutions without and with addition of chloride ions.
Słowa kluczowe: 4-aminobenzoic acid, poly(3,4-ethylenodioxythiophene), anticorrosion coating, corrosion protection, stainless steel
Immersion tin coatings - investigation of corrosion properties
Immersion tin coatings of different thickness were deposited on copper foil from methanolulfonic bath. Their corrosion behavior in 0.5 M NaCl solution was determined using potentiodynamic polarization method. The Sn coatings were investigated as received and after ageing. It was observed, that corrosion resistance of 0.3 µm thick Sn layers increased after ageing, whereas the corrosion resistance of thicker layers was changed slightly. These results were compared with those for Sn layers obtained from hydrochloric bath. It was found, that immersion tin coating with various morphology showed different corrosion characteristic after ageing.
Słowa kluczowe: tin, electroless deposition, corrosion properties, ageing
The influence of the exploitation conditions on corrosion of the steam boiler furnace
The research presents the reasons for high-temperature degradation of steel and ceramic elements of the coal fired steam boiler furnace. Corrosive damage of the steel cover of the grate and damages of ceramic elements such as the sealing of grate and ceramic screen were stated in the research. Analysis of scale and slag indicated the presence of fluorine, chlorine, sodium and potassium elements characteristic of biomass burning. Slag contained also above normal quantity of aluminum and iron oxides which leads into the conclusion that the reason for the damages was the use of wrong fuel.
Słowa kluczowe: high temperature corrosion, slag, scale
Corrosion mechanism of gray cast iron in tap and modified water of circulation system of oil processing
The aim of the work was to explain the reason of non-uniform corrosion of gray cast iron in circulation water of oil processing. It was demonstrated that the microstructure inhomogeneity, especially the dispersion of cathodic phase (carbides and graphite), is an important factor determining the formation of micro-galvanic elements and corrosion morphology. Regular and dense distribution of carbides in ferrite matrix (high surface carbide/ferrite ratio in perlite eutectic) leads to uniform electrical field and leads to formation of fine-crystalline anodic product on the metal surface. The presence of large ferrite grains in thin-walled parts of cast is a reason on non-uniform distribution of microgalvanic elements. Non-protective thick corrosion deposit is formed and intercrystalline corrosion of thin-walled parts of cast appears.
Słowa kluczowe: corrosion of cast iron, pumps corrosion, corrosion in circulating water
Electroless nickel plating on carbon fibers – bath stabilizers
Electroless metallization of carbon fibers was investigated with use of Ni-P deposition. Tenax roving of carbon fibers was metallized after preliminary heat treatment on air. The surface of fibers was then catalytically activated in Sn(II) and Pd(II) baths. The Ni-P coating (2–5% mas.P; thickness 0,3–2 µm) was deposited in bath contained nickel(II) sulfate(VI), hypophosphite and glycine (pH = 8,5; 70oC; 5–30 min). In aim to prevent the bath self-decomposition, the stabilizers and wetting agents were added, e.g. thiourea, nitrate(III), arsenate(III), molybdate(VI) and alkylammonium salts. In stabilized baths the time of Ni-P deposition on carbon fiber was considerably prolonged.
Słowa kluczowe: electroless nickel, bath stabilizers, carbon fibers, Ni-P coatings
Influence of ion etching on the properties of duplex layers obtain by gas nitriding and PVD-arc technologies
The aim of this work was the optimalization of technological parameters of duplex processes with the ion etching process and it influence on the duplex layers properties (nitrided layer and TiN coat). The works content technological experiments which was connected with nitriding and PVD-Arc processes and investigations obtained layers. Microstructure and corrosion resistance was investigated, too.
Słowa kluczowe: gas nitriding, nitrided layers, corrosion resistance, duplex layer, PVD-Arc
Hydrogen evolution in concrete modified by silica fume
It has been known that the industrial silica fume containing less than 0.4% Si, used for the modification of concrete reacts with the concrete pore liquid with the evolution of hydrogen. The emission of hydrogen has been also stated in the case of the solid concrete. After the termination of the hydrogen emission at room temperature, the heating of the concrete causes the followed emission. The time of hydrogen emission and the amount of hydrogen increased with the increase of the Si content, temperature and the grain size. Ingress of the evolved hydrogen to the metal may deteriorate the mechanical properties of the reinforced concrete.
Słowa kluczowe: concrete, silica fume, silicon, hydrogen emission, hydrogen effects in metal
Hydrogen entry into iron in sodium hydroxide after imposing anodic polarisation
Hydrogen can enter into iron or steel at anodic potentials when bare metal is exposed, e.g. by film rupture during stress corrosion cracking. Hydrogen permeation rate (HPR) through a 35 nm thick iron membrane was studied with the electrochemical technique in 0.1 M NaOH during cathodic and anodic polarisations at 25oC. Fast anodic polarisation resulted in transients of enhanced HPR which continued to rise despite of decaying anodic current. The enhanced HPR can be ascribed to acidification due to anodic oxidation of iron. It is proposed that the continued rise of HPR during anodic current decay can be explained by the formation of low-protective layers which hinder diffusion of protons out of the metal surface.
Słowa kluczowe: hydrogen entry, iron, NaOH solution, anodic polarization
Corrosion resistance of austenitic steel 316l after unconventional glow discharge nitriding
The nitrided layers produced on 316L austenitic stainless steel by glow discharge plasma nitriding at 490°C in the processing time of 14 h were studied. The location of the samples in the working chamber was as follows: on the cathode of ion furnance, on the ceramic insulator (in the plasma potential mode), on the cathode with assisting shield and on the ceramic insulator with assisting shield. It was stated that use of assisting shields increased both the depth of nitrogen diffusion into nitriding steel and the thickness of surface layers as well.
Słowa kluczowe: glow discharge nitriding, corrosion, stainless steel
The historical copper in the light of corrosion research
Corrosion behavior of historical copper has been investigated in 3% NaCl solution at temperature 8oC (conditions similar to these occuring in the sea water). Research using SEM and fluorescent X-ray analysis in microscale techniques has been indicated the presence of oxygen and chlorine. Occurrence of these compounds has been linked with formation of oxides and complexing Cu+ ions with Cl– ions. Comparison of the electrochemical research for contemporary copper and historical copper has been demonstrated lower corrosion resistance of the historical copper.
Słowa kluczowe: copper, electrochemical research, corrosion, archeology
Comparison of electrochemical characteristics of LaNi4,8Bi0,2 and LaCo4,8Bi0,2 alloys with respect to their hydrogen absorption
The hydrogen absorption ability at LaNi4,8Bi0,2 and LaCo4,8Bi0,2 alloys during their cathodic exposure in 6M KOH solution has been evaluated using three complementary electrochemical methods. The presence of Co in alloy causes increase of anodic current density of as received sample and, thus worsens the passivating properties of the alloy. The LaCo4,8Bi0,2 alloy is capable to absorb greater amounts of hydrogen and it also exhibits higher exchange current for H2O/H2 system in comparison to LaNi4,8Bi0,2 alloy.
Słowa kluczowe: hydrogen storage alloys, anodic polarization, galvanostatic charge/discharge curves, exchange current density
An application of inhibitors for copper corrosion for the protection of 2xxx aluminium alloys
A high strength of 2xxx series aluminium alloys is achieved due to the presence of copper as the alloying element but at the same time corrosion resistance is signifi cantly decreased. In order to increase a corrosion resistance of Al 2017 alloy selected corrosion inhibitors for copper were tested that by the action on copper deposits can delay an onset of Al corrosion. The results of electrochemical measurements shown that in neutral environment of 0.6 M NaCl a benzotriazole was the most effective, while in acidic phosphate solution imitating baths for conversion coatings, the best results for 2-mercaptobenzoxazole (MBX) were obtained.
Słowa kluczowe: aluminium alloys, corrosion, corrosion inhibitors, electrochemical methods
The high temperature corrosion of valve steels in water vapor and acetic acid containing atmosphere
The oxidation kinetics of X33CrNiMn23-8 and X50CrMnNiNbN21-9 valve steel have been studied in oxidizing atmosphere, containing 49.5% of water vapor and 0.5% of acetic acid at temperature equal 1173 K. It has been found that the mechanism of corrosion under these conditions is rather complex. After early stages of the reaction, lasting between 20 and 40 hours, the process follows approximately parabolic kinetics. It has been found that the presence of acetic acid highly increases corrosion rate of X33CrNiMn23-8 steel but has no influence on the corrosion rate of X50CrMnNiNbN21-9 steel with lower chromium concentration.
Słowa kluczowe: high-alloy steel, biofuels, high temperature corrosion, kinetics
Corrosion of dental alloys in the human body
One of the functions having the effect on biocompatibility of material is time of staying in aggressive environment of body fluids. The authors undertook an attempt to determine the nature of changes in the metallic materials after long-term implantation in the oral cavity. The aim of this work was to determine the effect of time of using the material in dental alloys. In this field there are metallographic microscopic examinations and X-ray microanalysis. Preliminary analysis of the results confirms such a wide spread of implantation austenitic steel.
Słowa kluczowe: dental alloys, biocompatibility, corrosion resistance, material examinations
Structure and corrosion properties of glow-discharge nitrided layer produced on AISI 4140 steel
Investigation results under structure and physicochemical properties of the as received and high-temperature glow-gischarge nitrided AISI 4140 steel (1:1 vol. N2/H2 atmosphere, 520oC) are presented in the paper. The structure of the nitrided layer has been evaluated on the basis of microhardness and chemical X-ray analysis on the cross section of the surface layer. The potentiokinetic polarisation curves of the tested steel have been measured in sulphate solutions ([SO2-4] = 0,5M) at three different pH values: 1, 2 or 4. The performed nitriding treatment is prone to clear improvement of corrosion characteristics of the outer layers of the tested steel within the passive range. Nitriding neither affects the corrosion behaviour of the tested steel in active range nor kinetics of cathodic process.
Słowa kluczowe: glow-discharge nitriding, corrosion, low-alloy steel
Oxidation and reduction of Mn-Ni alloy powder
The subject of the presented investigation concern on the very essential industrial problem of the production of porous metallic sinters on the bases of metals of the iron-group. Investigations were carried out on powder of manganese – nickel alloy (Mn70/ Ni30). Metallic sinters were produced according to the proposed method. The alloy powder were placed in the holder shape of flat boat. Such prepared samples were oxidized and reduced respectively. Processes of oxidations and reductions were carried out in relatively low temperature 400-800oC in the atmosphere of air and hydrogen. Obtained metallic sinters were porous with well developed surface.
Słowa kluczowe: Mn-Ni alloy, oxidation, reduction, porous sinter
Organic coating influence on stress corrosion cracking resistance of AlZn5Mg2CrZr welded joints
The article presents results of investigation on stress corrosion cracking (SCC) resistance of new type AlZn5Mg2CrZr welded joints designated for high-load shipbuilding structures, the surface of which were covered by protective coating systems. The research allowed identification, which of the two coating systems applied provides better protection of the welded joints against water and tensile stress impact. The effectiveness of protection against SCC was evaluated by determination of mechanical properties decrease coefficient (KRm and KA5) and by finding durability SCC (t). The investigations were carried out on AlZn5Mg2CrZr welded joints prepared by TIG method using various filler metals. Epoxy coating system (E) provides the best protection of AlZn5Mg2CrZr welded joints against SCC in sea water.
Słowa kluczowe: welded joints, aluminum alloy, coating systems, stress corrosion
The role of paricle surface of MQP-B powder preliminary etching in shaping corrosion resistance of bonded magnets
Investigations under preliminary etching of surface of nanocrystalline MQP-B powder particles on corrosion characteristics of the final magnetic material have been carried out. To evaluate corrosion resistance of non-treated and initially etched powder in vinegar acid and EDTA solutions corresponding potentiokinetic polarization curves have been compared. The potentiokinetic tests have been performed in sulphate (pH = 3 and 4) solutions. The accelerated gravimetric tests were carried out in artificial industrial atmosphere. It is shown that the preliminary chemical etching of the powder surface clearly improves corrosion characteristics of the final magnet, especially in the passive range. Preliminary etching also significantly limits rate of atmospheric corrosion.
Słowa kluczowe: dielectromagnets, nanocrystalline powder, chemical modification, magnets corrosion
Pitfalls in corrosion education
Some dilemmas in corrosion education were indicated. Interpretation problems concerning the high temperature corrosion (metal oxidation laws) and the electrochemical corrosion (passivity and pitting of iron) were outlined.
Słowa kluczowe: corrosion education, metal oxidation, passivity, pitting
Corrosion of nitrided stainless steels with molybdenum
Steels 304L (0.13 wt% Mo) , 316L (2.1 Mo) and 254 SMO (6.1 Mo) were nitrided at 425oC for 30 h and then their corrosion was examined in acidified sodium sulphate solution at various depths of surface layer corresponding to nitrogen concentrations in the range up to 14 wt%. The corrosion resistance of 304L steel decreased with the increasing nitrogen concentration, whereas the resistance of 316L steel was at nitrogen concentrations up to about 6% N higher than that for unnitrided steel. On the surface of the steels with Mo, increased amounts of corrosion products of Mo, Fe and Cr were found. It is suggested that the synergism of N and Mo at the concentrations to about 6% N results from the acceleration of initial dissolution and the following faster formation of a protective layer, with a possible enrichment of the surface in chromium nitrides.
Słowa kluczowe: stainless steels, corrosion, nitrogen, molybdenum
Electrochemical characterization of SmNi5 alloy in sulphate solutions at pH = 2÷13
A preliminary electrochemical corrosion characterization of SmNi5 alloy in sulphate solutions with pH = 2÷13 has been carried out. Potentiokinetic polarization curves of the tested alloy have been measured in potential range –1.7 to +2.0 V vs SCE. Polarisation resistance of the SmNi5 material has been determined for the tested solutions in the vicinity of open-circuit potentials. It is shown that in acidified solutions the SmNi5 alloy undergo active dissolution whereas it passivates effectively only in alkaline environment.
Słowa kluczowe: SmNi5 alloy, sulphate solution, potentiokinetic polarization curves corrosion resistance, polarisation resistance
Electrochemical studies on steel corrosion in solutions simulating carbonated and chloride contaminated concrete
The corrosion of steel in solutions simulating carbonated (pH: 8–12) and chloride contaminated (1% NaCl) concrete was investigated by measuring anodic polarization curves. Inhibition effi ciency of Ca(NO2)2 under such conditions was estimated.
Słowa kluczowe: steel, concrete simulating solution, carbonation, chlorides, corrosion inhibitor
An application of microstructural and microanalytical investigations for evaluation of corrosion degradation
This paper presents the results of investigations carried out to elucidate the cause of corrosion in the heat affected zone of a weld of dissimilar materials on a pipeline of industrial installation. To this end detailed microstructural and microanalytical studies were performed using such techniques as light (LM) and scanning electron microscopy (SEM), energy dispersive (EDS) and fluorescent X-ray spectrometry. Susceptibility to intercrystalline corrosion was also tested. It was shown that corrosion of the pipeline was caused by sensitization of the grain boundaries in the heat-affected zone on the side of the pipe segment made of 321stainless steel leading to the inter-crystalline corrosion. The microanalysis results indicated that susceptibility to inter-crystalline corrosion was caused not by carbon and/or stabilising additions (Ti, Nb) but by the reduction of the chromium content at grains boundaries due to formation of Cr rich oxides during the process of welding.
Słowa kluczowe: inter-crystalline corrosion, austenitic stainless steel, microstructure, X-ray analysis
Defect structure model of CuO oxide
Basing on experimental results reported previously and obtained using marker and two-stage oxidation methods as well as oxidation kinetic rates measurements, the defect structure model of CuO has been presented. It has been demonstrated that the predominant point defects in the discussed oxide, being an intrinsic electronic semiconductor are doubly ionized cation vacancies, the concentration of which increases with oxygen activity with power 1/2.
Słowa kluczowe: CuO, defect structure, mechanism of oxidation
Studies of Crofer 22APU steel behaviors in different oxidizing atmospheres
In the present studies interconnect material Crofer 22APU was investigated with respect to his oxidation behavior in the temperature range required for SOFC application (700-900oC) and different atmospheres containing different oxygen partial pressure. Kinetics and morphology formed scale were studied by XDR, EDX and SEM. Analysis point out that main product of the formed scale was Cr2O3. Spinal (MnCr2O4) was detected too, at all studied atmospheres only at 900oC formed continues layer.
Słowa kluczowe: Crofer 22APU, oxidation, air, water vapour
Corrosion properties of electroless Ni-P layers produced in modified bath by additions of imidazolium ionic liquids
The aim of our study focuses on presentation of the influence of imidazolium ionic liquid (1-buthyl-3-methylimidazolium octylsulfate) on the microstructure and corrosion properties of prepared Ni-P layers by the electroless method in bath with different ionic liquid additions. Surfaces of Ni-P layers were characterized using scanning (SEM) and X-ray diffraction techniques. The polarization and EIS studies of produced layers were realized in 0.5M NaCl solution. The polarization curves j = f(E) and corrosion parameters were determined. The impedance measurements were represented in the form of phases and amplitudes frequencies characteristic and resulting models of equivalent electrical circuits were established. The performed investigations showed insignifi cant influences of ionic liquid additions into basic bath on corrosion properties of electroless Ni-P layers.
Słowa kluczowe: Ni-P layers, ionic liquids, EIS, polarization
Corrosion of inert anodes in cryolite melts. Part I: The bath contamination study
The behaviour of two different compositions based on Cr2O3-NiO-CuO and NiO-Fe2O3-SnO2 was investigated as anode materials in laboratory electrolysis tests for 10 h in a conventional cryolite-based electrolyte. The corrosion of the anodes was assumed to be mass transfer controlled and the transfer of impurities into the electrolyte and subsequently into the cathodically deposited metal was studied. The results indicate that the components of anodes corroded in a controlled manner (for expect of chromium which is probably by chemical reaction controlled). Mass transfer coefficients of species from the anode to the electrolyte were of the order of 10-5 m/s while the mass transfer coefficients for transfer of the species from the electrolyte into the deposited metal were of the order of 10-7 m/s. The contamination of the deposited aluminium with respect to the species from anodes was sufficient, to current specifications for primary grade metal. The extrapolated corrosion rates of the anodes ranged 1.1–1.4/ cm/year, which is acceptable from an industrial perspective.
Słowa kluczowe: aluminium, electrolysis, cryolite, inert anode
Corrosion of inert anodes in cryolite melts. Part II: The metal contamination study
The behaviour of two different compositions based on Cr2O3-NiO-CuO and NiO-Fe2O3-SnO2 was investigated as anode materials in laboratory electrolysis tests for 10 h in a conventional cryolite-based electrolyte. The corrosion of the anodes was assumed to be mass transfer controlled and the transfer of impurities into the electrolyte and subsequently into the cathodically deposited metal was studied. The results indicate that the components of anodes corroded in a controlled manner (for expect of chromium which is probably by chemical reaction controlled). Mass transfer coefficients of species from the anode to the electrolyte were of the order of 10-5 m/s while the mass transfer coefficients for transfer of the species from the electrolyte into the deposited metal were of the order of 10-7 m/s. The contamination of the deposited aluminium with respect to the species from anodes was sufficient, to current specifications for primary grade metal. The extrapolated corrosion rates of the anodes ranged 1,1–1,4/ cm/year, which is acceptable from an industrial perspective.
Słowa kluczowe: aluminium, electrolysis, cryolite, inert anode
Anodic behavior of iron in methanol solutions of electrolytes
The paper presents the study of electrochemical properties of iron in anhydrous methanol, ethanol and n-propanol solutions of lithium perchlorate and lithium chloride. Investigations were performed by means of linear sweep voltammetry. In alcohol – lithium perchlorate solutions iron undergoes passivation. An addition of lithium chloride limits passive range to the potential range of stability of Fe2+ compounds (< -0.2V). The mechanism of iron oxidation in alcohol –LiClO4 – LiCl system has been proposed.
Słowa kluczowe: iron, alcohols, anodic dissolution
High temperature behavior of γ -TiAl alloys coated by nickel aluminide
A nickel aluminide coating was developed on pack cemented Ti48Al and Ti48Al2Cr2Nb alloys by electroplating a Ni film followed by a high Al activity pack cementation. Process was carried out in vacuum with a mixture of fine Al, NH4Cl and Al2O3 powders at 893 K for 2 h. The coated Ti48Al and Ti48Al2Cr2Nb alloys were oxidized in air for up to 200 h. A protective Al2O3 scale formed with oxidation amount 0,001 g/cm2 on coated samples, whereas uncoated alloys oxidation amount were about 0,008-0,010 g/cm2. During oxidation at 1073 K as-coated layer changed and formed different intermetallic phases as NiAl, TiNiAl2, TiAl2, Ti(Al,Ni)3.
Słowa kluczowe: TiAl alloys, oxidation, aluminization, metallic coating
The structure and corrosion resistance of the surface modified Ti6Al4V alloy
This work contains results concerning surface modification of titanium alloy Ti6Al4V with a-C:N:H and a-SiCxNy(H) layers. The layers were produced using the plasma assisted chemical vapour deposition techniques: RFCVD (13,56 MHz, 60 W) and MWCVD (2,45 GHz, 800 W). A gaseous mixture, containing CH4, N2, SiH4 and H2 at various proportions, was introduced into the reactor. The chemical composition and morphology of the layers were investigated using EDS, SEM, XPS methods. The corrosion resistance of the samples was assessed on the basis of voltamperometric curves in a Ringer’s solution and of the analysis of this solution by AAS technique.
Słowa kluczowe: Ti6Al4V alloy, surface modification, corrosion resistance
Anodic dissolution of zinc in alcoholic solutions of electrolytes
Studies of the effect of the kind of alcohol, electrolyte concentration and water (5%) on the anodic dissolution of zinc and the nature of dissolution products were performed. The dissolution products were analyzed by spectroscopic methods (SEM, TEM/EDS, XPS).
Słowa kluczowe: zinc, anodic dissolution, organic solvents, nanoparticles
Influence of mechanical deformation on local electrochemical behaviour of AlMg2 alloy
The electrochemical behaviour of AlMg2 (5052) before and after plastic deformation is presented in this paper. In order to investigate the corrosion resistance of AlMg2 alloy in micro-regions the electrochemical microcell technique was used. The places containing precipitates exhibit higher cathodic current compared to matrix. After plastic deformation the electrochemical activity of matrix and sites containing precipitates increases. However the corrosion behavior of the samples after plastic deformation depends on types of deformations and defects. Lower corrosion resistance in 0.1M NaCl solution of the sample of AlMg2 after plastic deformation is related with the presence of micro-cracks visible on the alloy’s surface.
Słowa kluczowe: microstructural corrosion, aluminium alloys, mechanical stress
Anodic behavior of zinc in ethanol solutions of electrolytes
Anodic behavior of zinc mono-crystal electrode with crystallographic orientation (0001) has been investigated in C2H5OH-LiClO4-LiCl. Similar to methanol solutions the stable anodic product is formed on the metal surface and inhibits anodic dissolution of zinc electrode in the low overpotential range. The surface product, probably Zn(OC2H5) is more stable and more resistant to chloride ions than analog methoxide-compound in methanol solutions of electrolytes. In the presence of low concentration of Cl- the barrier anodic film shows adsorption properties. In the presence of high chloride contents the layer is more conductive and anodic current is determined by diffusion in the film.
Słowa kluczowe: electrochemistry of zinc, corrosion in ethanol
Corrosion properties of the Ni-P/Si3N4 composite layers produced by electroless plating on the aluminum
The present paper is aimed on studies of corrosion properties of nickel Ni-P and composite Ni-P/Si3N4 layers deposited on an aluminum substrate by the chemical reduction method. The corrosion studies have been realized by the electrochemical method: potentiodynamic and impedance spectroscopy in the 0.5M solution of NaCl. The corrosion current, corrosion potential and corrosion rate are determined by the potentiodynamic method. Nyquist and Bode diagrams obtained by the impedance spectroscopy method are established. The equivalent electric circuit and its parameters were determined to interpret impedance spectra. Investigations of the morphology and topography of the produced surface layers and estimation of they corrosion damages are performed by electron scanning microscope techniques.
Słowa kluczowe: composite coatings, corrosion resistance, polarization, impedance spectroscopy
Anticorrosion nitriding – industrial application
Application of anticorrosion gas nitriding for gas springs rods is presented. Properly selected nitriding process parameters allow to form nitrided layer characterized by high corrosion resistance. The corrosion resistance of nitrided layer depends on surface iron nitride layer, which should have correct phase composition (60-70% ? (Fe2-3N) and 40-30% ?’(Fe4N)) and proper of compact (min. 70% thickness of nitride layer) and porous (max. 30% thickness of nitride layer) zones. The paper presents metallographic and corrosion (salt spray test) investigations of nitrided spring rods.
Słowa kluczowe:anticorrosion gas nitriding, nitrided layers, corrosion resistance, gas spring rods
Effect of nitrided layer on ferritic-austenitic steel on hydrogen absorption and desorption
Hydrogen permeation rate through one-side nitrided ferritic-austenitic stainless steel membranes was studied using the electrochemical detection of hydrogen. The membranes were charged with hydrogen electrolitycally generated from an aqueous NaOH solution. After termination of charging, the desorption rate of hydrogen was measured at both sides of the membrane. In this way, the amount of absorbed hydrogen and the role of the nitrided layer in hydrogen absorption and hydrogen desorption were determined. It was found that the nitrided layer impeded both the entry of hydrogen into and the desorption of hydrogen from the membrane. Thus, from the prevention of hydrogen damage, the applied nitriding can exert both the advantageous and disadvantageous effect.
Słowa kluczowe: erritic-austenitic steel, surface nitriding, hydrogen, hydrogen permeation, hydrogen desorption
The influence of oxyanions on the protective properties of amorphous phosphate coating on Al 2024-T3 aluminium alloy
The aim of the work was to determine the influence of permanganate and, molybdate anions on the protective properties of amorphous phosphate coating on AA2024-T3 alloy surface. An independent recipe was a solution with citric acid. Corrosion resistance of the coatings was assessed by means of voltametric and impedance measurements carried out in the sodium sulphate and sodium chloride solution with and without water extract from typical phosphate pigment (PZ-20). The best protection against general corrosion for the treatment in solution containing citric acid was obtained, while the best protection against pitting corrosion for the treatment in MnO4-containing solution. An increase of inhibiting effect was observed in the presence of pigment extract.
Słowa kluczowe: amorphous coating, aluminium alloys, corrosion resistance