Migrating corrosion inhibitors for steel in concrete – truths and mirages
Problems related with the application of penetrating corrosion inhibitors for steel in concrete are outlined. Presented data are taken from published reports and authors’ own studies. Records on the penetration rate of these inhibitors in concrete and time from the inhibitor application on the surface of reinforced concrete till the achievement of its concentration at the steel surface, which is necessary for the inhibition of steel corrosion are reviewed. The efficiency of these inhibitors in chloride contaminated and carbonated concrete are compared. Possible reasons of the observed big discrepancy in published data on the performance of penetrating corrosion inhibitors are indicated.
Słowa kluczowe: corrosion, steel, concrete, corrosion inhibitors, efficiency
Solar-induced heat build-up is undesirable, and even dangerous, in case of coatings for roofs, facades and other building structures, as well as for fuel tanks, shields of cold stores and storehouses. One of the methods to reduce this heat is the application of suitable coatings with high reflectivity. Such coatings, varying in colours, were developed based on spectral characteristic of selected coloured pigments. It has been found that the coatings are very resistant to weathering and their optical properties don’t change upon exposure to UV radiation.
Słowa kluczowe: pigment compositions, absorptive-reflective properties, solar-reflective organic coatings
Influence of anodic passivation of Ti6Al7Nb alloy on its corrosion resistance in Ringer’s physiological solution
Investigations of the corrosion resistance of the Ti6Al7Nb alloy in Ringer’s simulated physiological solution have been presented. On the grounds of electrochemical investigations the influence of the anodic passivation on corrosion potential, polarization resistance and corrosion current density have been determined.
Słowa kluczowe: corrosion resistance, Ti6Al7Nb alloy, anodic passivation
Corrosion and passivation of nitride layers on iron
Corrosion behaviour of iron nitrides E, Y’ and E, Y’ (formed by gas nitriding at 570oC) was examined in neutral and acidifi ed sulphate solutions and in borate buffer of pH 8.4, without and with chlorides or ammonia. In chloride-free solutions, nitride layers showed in comparison with unnitrided iron higher corrosion resistance in neutral and acidifi ed solutions, but lower resistance in the borate buffer. Despite of increased general corrosion, in borate solution with an addition of chloride anions nitride layers exhibited a very high resistance to pitting corrosion. XPS analysis showed that anodic films on nitrided iron contained much larger amounts of iron oxides, in particular of magnetite, than those on untreated iron. It was suggested that the anodic behaviour of nitrided iron in slightly alkaline solution was determined mainly by the effect of evolving ammonia. Increased anodic dissolution can be explained by the formation of soluble complexes with ammonia, whereas increased amounts of magnetite can be due to the ammonia-promoted conversion of FeOOH + Fe(II) to Fe3O4. It was proposed that the enhanced pitting resistance of nitrided iron resulted mainly from the formation of large amounts of iron oxides and from binding of chloride anions into a Fe-NH3-Cl complex.
Słowa kluczowe: iron nitrides, general corrosion, pitting corrosion, passivation, surface films
New environmentally friendly corrosion and scale inhibitors for industrial cooling waters
The results of the electrochemical and potentiokinetic tests concerning the efficiency of anticorrosion protection of mild steel, with selected compounds such as the alkyl-, aryl– and amine–phosphonic acids derivatives or their mixtures with Zn2+ ions and phthalic anhydride, in model water are presented. For the best inhibitive mixtures, corrosion and scale inhibition effectiveness were determined by gravimetric method after various exposure times (24 to 240 hours). Of selected inhibitor mixtures, compositions No. IV containing 50 mg/dm3 butylenodiamino – N,N` – bis [3,4(dihydroxyphenylo)- methylophosphonic acid with 4 mg/dm3 Zn2+ and 2 mg/dm3 phtalic anhydride and composition No VII, containing 50 mg/dm3 1,4-phenylobis-(amino,ethylbisphosphonic) acid, fulfilled international standards for inhibitor protection of industrial cooling water systems within 240 hours exposure time. Those inhibitor mixtures decrease corrosion rate of St3 steel in model water up to 0,03 mm/year and 0,01 mm/year while the deposition rate reaches the level of 0,79 g/(m2·day) and 1,43 g/(m2·day).
Słowa kluczowe: cooling water, inhibitor, carbon steel, phosphonic compounds
Electrochemical investigations of pitting corrosion resistance of glow-discharge nitrided austenitic stainless steel
Electrochemical polarization characteristics of glow-discharge, high-temperature (520oC) nitrided AISI 321 type stainless steel are presented in the paper. The potentiokinetic tests were carried out in acidifi ed, 0.5 M sulphate (pH = 4) solution containing 0.5M of chloride ions. A method of consecutive thinning of surfacial layers of the treated steel has been applied to determine the depth profi les of its pitting- and repasivation potentials.
Słowa kluczowe: glow-discharge nitriding, austenitic steel, pitting corrosion, depth profile
An old method uncovered again – application of corrosimetry in cathodic protection technology
The European normalisation process started after the year 2000 in the scope of cathodic protection technology has led to introduction into standards of not only a conglomeration of requirements contained in former national standards of members, but also of new concepts. The most important include indication of the corrosion rate as the principal cathodic protection criterion. In spite of an established tradition of potential criteria application, corrosion rate measurement in real conditions may become a useful tool for assessment of the effectiveness of anticorrosion protection. In the paper practical application has been presented of a well known measurement method – resistance corrosimetry for assessment of cathodic protection systems of large metal structures.
Słowa kluczowe: cathodic protection, protection criteria, resistance corrosimetry
The ceramic coatings SiO2-Al2O3 prepared by sol-gel method on titanium surface exposited in simulated body fluid
Tri-layer SiO2-Al2O3 protective coatings were prepared with sol-gel method, sintering at the temperature 200oC on titanium. The ceramic coatings were deposited from sol with the dip-coating method. Tetraethoxysilan (TEOS) and aluminium tri-secbutoxide ware used as a precursor. On the basis of potentiodynamic measurements: corrosion potential (E’) at various time exposition samples in Simulated Body Fluid (SBF); current density at potential -750 mVNEK (iE=-750mV, cathodic area); cathodic to anodic transition potential (EK–A); polarization resistance (Rp); current corrosion density (io) and through-coatings (P) have been determined. The ceramic coatings type SiO2-Al2O3 performs a double function: protective properties in the Simulated Body Fluid and bioactive ceramic, on which the surface deposited hydroxyapatite (acknowledgement o SEM).
Słowa kluczowe: sol-gel, SiO2-Al2O3, simulated body fluid, titanium, hydroxyapatite, biomaterial
Corrosion resistance of nitrided layers produced on AISI 316L steel by glow-discharge low-temperature nitriding
Samples made of 316L steel were subjected to low-temperature glow discharge nitriding. The treatment produced diffusion-type surface layers composed of nitrogenexpanded austenite (known as the phase S, i.e. supersaturated solution of nitrogen in austenite). It has been shown that the structure, chemical and phase composition and thickness of the surface layer depended on the treatment pressure. The layers obtained at a higher pressure are thinner, their surface is more developed and the content of nitrogen is lower. They provide higher hardness and high pitting corrosion resistance in 0.5 M NaCl water solution. Decreasing the glow discharge nitriding pressure improves hardness as well as corrosion resistance in the solution with chlorine ions.
Słowa kluczowe: 316L steel, glow-discharge nitriding, S phase, corrosion resistance
Corrosion resistance of vinyl-triethoxy silane films on iron in air and in phosphate solution
Organosilane compounds are used for the improvement of adhesion of organic coatings on metals. In the present work, fi lms of vinyl-triethoxy silane (CH2=CH) Si(OC2H5)3 (WTES) on iron (Fe/WTES system) were examined to determine their ability to protect against corrosion and to evaluate chemical transformations occurring in air and in phosphate solution. After exposure to air for up to 12 days, impedance was measured in 0.01 M Na2HPO4, and surface analysis was carried out with XPS and FTIR. Exposure to air resulted in an increase of charge transfer resistance, indicating an improvement of protective properties of the system. On the basis of the surface analysis it can be proposed that the improvement was caused by the growth of iron oxides at the Fe/VTES interface, by the formation of SiO2 and related species and of polysiloxanes, and by polymerisation of vinyl groups. Immersion in the solution accelerated oxidation of the silane. It has been suggested that apart from improving adhesion, silanes play an important role in the corrosion protection also by their barrier and inhibiting properties.
Słowa kluczowe: silane fi lms, iron, air, phosphate solution, impedance, surface analysis, chemical transformations
Investigations of active pigment anticorrosive efficiency in paint coatings
The investigations of active pigment efficiency in primers for steel substrate have been carried out. Anticorrosive pigments have been received by high temperature synthesis of properly selected mixtures of chemical reagents. The optimum composition of the pigment and its proper concentration in the paint coating were established by accelerated corrosion investigations methods. Anticorrosive efficiency of the pigment was confirmed by potentiodynamic and impedance spectroscopy investigations.
Słowa kluczowe: active pigments, primer coatings, accelerated corrosion investigations, potentiodynamic investigations, impedance spectroscopy
The effect of the nitrided layers on iron on the absorption of hydrogen
Hydrogen permeation through and hydrogen desorption from iron membranes with nitrides Y’, (E+Y’) and E layers, formed by controlled gas nitriding, was studied using the electrochemical detection of hydrogen. Membranes were charged at their nitrided side with hydrogen cathodically generated from 0.1 M NaOH under constant current, at temperature 30oC. After cessation of hydrogen charging, desorption rate of hydrogen was measured at both sides of the membrane. An analysis of the desorption rates enabled to distinguish the diffusible (mobile) hydrogen from the reversibly trapped hydrogen and to determine their amounts and distribution in the membrane. The trapped hydrogen accounted for the majority of the total absorbed hydrogen. Hydrogen trapping was enhanced by the Y’ precipitates and especially by the nitrided compound layers. In spite of high capability to hydrogen trapping, the nitrided layers, owing to low mobility and solubility of the diffusible hydrogen in these layers, impeded the absorption of hydrogen by the metal substrate.
Słowa kluczowe: iron, nitrided layers, hydrogen permeation, hydrogen absorption, hydrogen desorption
Efficiency of penetrating corrosion inhibitor for steel in concrete at various [Cl-]/ [inhibitor] molar ratios
Performance of two penetrating corrosion inhibitors, namely calcium nitrite (CA) and ethanolammonium benzoate (BEA) was studied. Tests were conducted in the solution simulating chloride contaminated concrete (RS = saturated solution of Ca(OH)2 + 1% NaCl). After the initiation of steel corrosion, inhibitor concentration was gradually increased and its efficiency was monitored by impedance and corrosion potential measurements. Tests revealed the high inhibition efficiency for CA and slight effect of BEA. The inhibition efficiency of CA is higher at lower [Cl-]/[inhibitor] molar ratios and at lower degree of corrosion development in the time of inhibitor application.
Słowa kluczowe: concrete, steel, corrosion, inhibitor, nitrite
Improvement of Nd-Fe-B type dielektromagnets resistance against local corrosion by chemical treatment of magnetic powder
Investigations of the chemical treatment of nanocrystalline magnetic powder of Nd-Fe-B type on corrosion characteristics of dielectromagnets have been carried out. To evaluate corrosion resistance of composites made of non-treated and initially etched powder the potentiokinetic polarization curves of the final material have been compared. The potentiokinetic tests in phosphate (pH = 3) solutions have shown that the preliminary chemical treatment of the powder surface clearly improves corrosion behaviour of the final magnets in passive range. At the same time, the powder treatment confines magnets susceptibility to pitting corrosion in presence of 0.03–0.05 M chloride ions.
Słowa kluczowe: neodymium magnets, nanocrystalline powders, powder surface modification, local corrosion
Corrosion resistance of dental metallic material after long-term implantation in the human body
From 3000 years the majority of materials made for implantation in the human body are metals and alloys. During the last century the implantation austenitic steel was the most commonly used. In the past 30 years, it was partly replaced by nickel alloys, cobalt alloys and titanium, but even nowadays it is still widely used as a metallic biomaterial. Apart from the advantages of which a very good mechanical properties are the main ones, implantation steel may act as generator of free atoms and ions, which are risk factors for the organism. One of the functions that influences biocompatibility of the material is the time during which the construction remains in the aggressive environment of body fluids. The authors made an attempt to determine the extent of changes in the metallic materials after long-term implantation in the oral cavity. The aim of this work is to determine the correlation between lifetime and changes of properties of the material used in dental alloys. Metallographic microscopic examinations, X-ray microanalysis and micro hardness fall within the scope of this work. Preliminary analysis of the results confirms such a wide spread of an austenitic implantation steel.
Słowa kluczowe: long-term implantation, X-ray microanalysis, metallographic microscopic examination, micro hardness
Hydrogen transport through nitride layers on iron
Hydrogen permeation through iron membranes with nitrides Y’, (E + Y’) and E layers, formed by controlled gas nitriding, was studied using the electrochemical detection of hydrogen. The nitrided membrane side was charged with hydrogen cathodically generated from 0.1 M NaOH under constant current, at temperature 30oC. Hydrogen permeation through nitrided membranes was 2-3 orders of magnitude lower than that through an unnitrided membrane. On the basis of the nonstationary permeation, the effective diffusion coeffi cients of hydrogen for the nitrided membranes, and than the diffusion coeffi cients characterizing the transport of hydrogen in the nitrided Y’, (E + Y’) and E layers were evaluated. Hydrogen transport was mostly hindered in the outer nitride E layer – the diffusion coeffi cient of hydrogen in this layer was over 4 orders of magnitude lower than that in the unnitrided iron.
Słowa kluczowe: iron, nitride layers, hydrogen permeation, hydrogen diffusion
Chrome-free conversion layers on zinc alloy coatings – preliminary tests
Molybdate conversion layers have been obtained on the Zn–Ni alloy electrogalvanised steel from a solution containing sodium molybdate(VI) and sodium citrate, acidifi ed with phosphoric acid. The layers were deposited at different bath temperatures and different pH values. Chromated samples were used as the reference in order to compare the corrosion resistance properties. The increasing bath’s temperature causes decreasing corrosion resistance (bigger corrosion curents, smaller polarization resistance) in 0,5 M NaCl environment. The best molybdate layers were obtained in temperature 25–40°C. These layers are homogeneous and free of cracks.
Słowa kluczowe: chromating, conversion coating, corrosion resistance, molybdate, citrate
Corrosion resistance of the nitrided layers produced on the AISI 316L sintered steel in the glow-discharge low-temperature processes
The paper presents results of a research of the nitrided layers on the AISI 316L sintered steel, produced in the glow-discharge assisted low-temperature (450şC) nitriding processes. Three different process atmospheres was examined. The paper describes the effect of different nitriding atmospheres on the layers’ thickness, surfaces’ morphology, chemical and phase composition. Corrosion resistance was examined using the electrochemical impedance spectroscopy (EIS) and potentiodynamic methods. The active area factor (AAF), deduced from EIS measurements, has been used to quantify the relationship between the apparent surface of the sinters, and the real surface exposed to corrosion. The EIS results have shown that the corrosion resistance increases (compared to the sinter in the initial state) only for the nitrided layer produced in the process’ atmosphere containing nitrogen and hydrogen in the ratio of 1N2 to 1H2. This result was not however confirmed by the potentiodynamic method.
Słowa kluczowe: 316L sintered steel, glow-discharge nitriding, electrochemical impedance spectroscopy (EIS)
High-temperature corrosion resistance of P91 steel in complex atmospheres with steam
The initial oxidation stages of P91 steel have been investigated in various atmospheres: air/H2O, N2/O2/H2O, He/H2O. The steam concentration in the gas was 1 or 5%. The kinetics of the oxidation process was measured by means of gravimetric method, using a thermobalance. The oxidation temperature was 700oC. The morphology, chemical and phase content of the scales was analysed by means of SEM, EDS and XRD. It has been found that the oxidation process may either be cubic or linear, depending on the type of gas and the steam concentration. The scale formed in the dry gas is very thin. An addition of steam results in a significant increase in the oxidation rate. The scale loses its protective properties. When the partial pressure H2O O2 p = p , the mass gain is approximately twice as high as in dry gas.
Słowa kluczowe: bP91 Steel oxidation, steam, coal power plants
Application of 4-aminobenzoic acid (4-ABA) for manufacturing of protective coatings on stainless steel
Protective properties of films of the 4-aminobenzoic acid doped with K2SO4 in the acidifi ed sulphate solutions without and with addition of 0,5 moldm-3 Cl- ions are compared in present paper. The coatings have been obtained by the cyclic woltamperometry and as the electrode substrate 2H13 stainless steel has been used. It is shown that the tested coatings efficiently protect stainless steel surface in both environments.
Słowa kluczowe: 4-aminobenzoic acid, anticorrosion coating, corrosion protection, stainless steel
Effect of the athermal and deformation transformations of the austenite and glow-discharge nitriding on the corrosion resistance of Ni27Ti2AlMoNb steel
The high-alloy Ni27Ti2AlMoNb steel with a structure of mechanically instable austenite of the TRIP type was subjected to sliding burnishing, which resulted in the formation of deformation martensite, and to an athermal transformation in liquid nitrogen which gave a martensitic-austenitic structure with the features of a duplex structure. The untreated sample, the sample composed of austenite with a martensite zone, and the duplex martensite-austenite sample were subjected to glow discharge assisted nitriding at a temperature of 450oC. The nitriding yielded layers of various thicknesses and various corrosion resistances depending on the kind of the sample. The structure of the steel samples was examined in a scanning electron microscope equipped with a back-scattered electron detector (BSE). The corrosion resistance was determined using the potentiodynamic and impedance methods. The examinations have shown that all the treatments affect signifi cantly the corrosion resistance of the steel.
Słowa kluczowe: glow discharge nitriding, high-nickel chromium-free steel, TRIP effect, deformation martensite, athermal martensite, nitrogen austenite, corrosion resistance
Impedance measurements of a few selected organic compounds in water pore solution modeling carbonated concrete reinforcement with Cl- ions
In the paper, the possibility of using a few selected organic compounds as a new non-toxic inhibitors of the corrosion of steel for carbonated concrete reinforcement with Cl- ions was investigated by impedance method.
Słowa kluczowe: steel, concrete reinforcement, corrosion inhibitors, EIS measurements
Electrochemical characterization of eutectic La3Ni alloy in 0.1M KOH environment
Electrochemical characterization of eutectic La3Ni alloy in deaerated, strong alkaline (pH = 13) aqueous solution has been made. Potentiokinetic polarization curves in wide potential range (–2.0 to +2.0 V vs SCE) have been measured. Electrode potential has been scanned both in anodic- and in cathodic direction. The polarization curves have been interpreted on the basis of thermodynamic data in order to determine the feasible products of partial electrode processes. Attention has been paid to the formation of superfi cial hydride- and oxide layers in the process of alloy polarization. Phase transformations within the superfi cial layers dependent on the potential have been proposed.
Słowa kluczowe: eutectic La3Ni alloy, alkaline solution, passivation, potential – pH diagram
Anticorrosive protection of reinforcement with concrete containing ash from fluidized bed combustion
Results of a research concerning the protection efficiency of reinforcement from corrosion, with concrete enriched with ash from brown coal combustion in fluidized bed in power plant Turów are reported. Polarization technique was used to perform tests in concentrated water extracts from disintegrated concrete. Results were compared with those obtained in a similar way for extracts from concrete without additives and with criteria framing limit values of the parameters of an electrochemical process. The results have shown that the concrete with 15% and 30% ash as cement replacement properly protects reinforcement from corrosion.
Słowa kluczowe: additive to concrete, ash from fluidized bed combustion, protection against reinforcement corrosion, polarization research
Anticorrosive coatings alternate to cadmium coatings
W pracy przedstawiono wyniki badań dotyczących elektrochemicznego otrzymywania cynkowych powłok stopowych (Zn–Ni, Zn–Co, Zn–Sn), które mogłyby zastąpić antykorozyjne powłoki kadmowe. Morfologię i skład chemiczny powłok zbadano za pomocą mikroskopu skaningowego wyposażonego w system mikroanalizy rentgenowskiej EDX. Przeprowadzono także badania odporności korozyjnej w 5% roztworze NaCl metodą woltamperometrii liniowej. Stwierdzono, że najlepszym zamiennikiem powłok Cd mogą być powłoki Zn–Ni, które charakteryzują się podobną odpornością korozyjną. Powłoki Zn–Sn charakteryzują się bardzo porowatą strukturą, co wyklucza możliwość ich zastosowania jako powłok ochronnych dla stali.
Słowa kluczowe: powłoka stopowa, powłoki stopowe zawierające cynk, powłoki alternatywne dla kadmowych, kąpiel pirofosforanowa,
The effect of cooling rate on corrosion resistance of Zn5Al3Cu zinc coatings
The effect of a cooling method of the Zn-Al-Cu type coatings, obtained by the high temperature zinc plating, on their electrochemical corrosion resistance is discussed in the paper. The microstructure of the coatings was heterogeneous and more or less fine-grained depending on the cooling method. Electrochemical potentiodynamic and potentiostatic tests were performed. The obtained results show than thinner coatings are more resistant. Corrosion resistance of all coatings is similar for high value of a potential.
Słowa kluczowe: electrochemical corrosion, Zn-Al-Cu coatings