Sulphide-induced stress corrosion cracking and hydrogen absorption of copper in deoxygenated water at 90°C

Stress corrosion cracking (SCC) of oxygen-free phosphorous-alloyed copper was investigated in sulphide- and chloride-containing deoxygenated water at 90°C with sulphide concentrations of 0.001 and 0.00001 M. Several intergranular defects were found in the specimen exposed to the high sulphide environment. Similar defects were not found in the low sulphide environment, where only slight corrosion on grain boundaries and slip lines occurred. Hydrogen content measurements show an increase in hydrogen uptake of the plastically deformed specimens, which is dependent on the sulphide concentration and on plastic deformation of copper. However, the highest hydrogen content was measured in friction stir welds, welded in air without shielding gas, and tested in the high sulphide environment. The embedded oxide particles in the weld metal act as local hydrogen trapping sites and selectively react with the sulphide solution. A relatively thick air-formed oxide film covers the copper canisters when deposited, which transforms into a sulphide film in the repository conditions. Thus, some of the coupon specimens were pre-oxidised. The conversion of the pre-existing Cu₂O film into Cu₂S film occurs quickly and the transformation is almost 100% efficient. The structure and properties of the Cu₂S films, susceptibility of copper to sulphide-induced SCC and hydrogen uptake of copper in reducing, anoxic repository conditions are discussed.     

Corrosion of copper and silver plates by volcanic gases

Corrosion products that had been formed on copper and silver plates exposed in Miyake Island, where suffered a volcanic eruption in 2000, were analyzed by X-ray techniques to get better understanding of copper and silver corrosion in harsh environment. The exposure experiment was carried out from September 2004 to April 2005. Many kinds of patina were found on copper such as cuprite (Cu₂O), posnjakite (Cu₄SO₄(OH)₆ · H₂O), brochantite (Cu₄SO₄(OH)₆), antlerite (Cu₃SO₄(OH)₄), and geerite (Cu₈S₅). For silver, silver chloride (AgCl) and silver sulfide (Ag₂S) were formed. Although the volcanic activity had greatly subsided, the atmospheric corrosion of copper and silver plates exposed on Miyake Island was mainly affected by volcanic gases, wet-dry cycles in the environment, and sea-salt aerosols.     

Characterisation of corrosion products formed on copper exposed at indoor and outdoor sites with high H2S concentrations

Abstract

Corrosion products formed on copper exposed indoors and outdoors at sites with high hydrogen sulphide (H₂S) concentrations were characterised using several analytical techniques. The crystalline corrosion products that formed on the copper exposed indoors were chalcocite (Cu₂S) and cuprite (Cu₂O), while those that formed on the copper exposed outdoors were chalcocite, cuprite and basic copper sulphates. Surface analysis by X-ray photoelectron spectroscopy revealed differences between the copper exposed indoors and outdoors that are explained by the composition, localisation and oxidation of the corrosion products. The surface morphologies of the corrosion products also differed. Elemental depth profiling by glow discharge optical emission spectroscopy revealed that the corrosion products that formed indoors were mainly chalcocite with cuprite only at and near the surface. In contrast, the corrosion products that formed outdoors were a mixture of chalcocite and cuprite. These differences in corrosion products are attributed to the differences in relative humidity during exposure.     

Hydrogen gas production during corrosion of copper by water

This paper considers the corrosion of copper in water by: (1) short term, open system weight measurements and (2) long term, closed system immersion in distilled water (13,800 h) without O₂ at 21–55 °C. In the latter experiments, the hydrogen gas pressure is measured above the immersed copper and approaches ∼10⁻³ bar at equilibrium. This pressure is mostly due to copper corrosion and greatly exceeds that in ambient air. Accordingly, this measured hydrogen pressure from copper corrosion increases with temperature and has the same dependency as the concentration of OH⁻ in the ion product [OH⁻] [H⁺].     

On the sulphidation mechanism of niobium and some of Nb-alloys at high temperatures

The kinetics and mechanism of niobium sulphidation have been studied as a function of temperature (700-1000 °C) and sulphur pressure (10⁻⁴-10⁴ Pa) in pure sulphur vapour and H₂-H₂S gas mixtures, using microthermogravimetric technique. It has been found that in both different sulphidizing atmospheres the sulphidation process follows parabolic kinetics, being thus diffusion controlled. Marker experiments have shown that the slowest step of the overall reaction rate is the outward diffusion of cations. No influence of small amounts of impurities on the sulphidation rate has been observed in this study. Excellent agreement between calculated and experimentally determined parabolic rate constants has been obtained under the assumption, that the correct formula of the sulphide scale on niobium is Nb_2±yS₃ and not Nb_1+xS₂, as suggested by Gesmundo.It has been found that the rate of niobium sulphidation in H₂-H₂S gas mixtures is much higher than in pure sulphur vapour, strongly suggesting that the dissolution of hydrogen in the growing scale influences the defect structure in this sulphide.     

Effects of blending on surface characteristics of copper corrosion products in drinking water distribution systems

Copper scales formed over 6-months during exposure to ground, surface and saline waters were characterized by EDS, XRD and XPS. Scale color and hardness were light red-brown-black/hard for high alkalinity and blue-green/soft for high SO₄ or Cl waters. Cl was present in surface or saline copper scales. The Cu/Cu₂O ratio decreased with time indicating an e transfer copper corrosion mechanism. Cu₂O, CuO, and Cu(OH)₂ dominated the top 0.5-1 A° scale indicating continuous corrosion. Cu₂O oxidation to CuO increased with alkalinity, and depended on time and pH. Total copper release was predicted using a Cu(OH)₂ model.     

Corrosion behaviour of carbon steel in different concentrations of HCl solutions containing H2S at 90 °C

The corrosion behavior of SAE-1020 carbon steel in H₂S-containing solutions with different concentration of HCl at 90 °C was investigated by weight loss, electrochemical measurements, SEM and XRD analysis. The results showed that the corrosion rate of carbon steel increased with increasing HCl concentration. Uniform corrosion was found on the carbon steel surface in H₂S + HCl solutions, while corrosion cavities were observed in the solution only containing H₂S. The ratio of Faradaic process of total corrosion process increased with the increase of HCl concentration. The corrosion products were solely composed of mackinawite in the H₂S-containing solutions with or without HCl.     

Rate control for copper tarnishing

The reduction of copper sulphide and copper oxides originated during artificial tarnishing of copper is studied using potentiodynamic potential/current density experiments. Six copper surface treatments are considered: mechanical polishing; indoor exposure for 7 days; chemical etching in 1.6 M nitric acid; chemical etching and heating at 160 °C; and chemical etching and dipping in a 9 × 10⁻⁴ M or 0.9 M potassium sulphide (K₂S) solution at 70 °C. Cuprite (Cu₂O) and chalcocite (Cu₂S) are the main compounds formed. A linear relationship with the square root of the scan rate (ν) is obtained by plotting the potentiodynamic potential/current density for the tarnish dissolution processes. A relationship between potential and current density cathodic peaks is not obtained, according to Müller’s model, showing a proportionality factor with the dimensions of a resistance.     

Corrosion behavior of three iron-based model alloys in reducing atmospheres containing HCl and H2S at 600 °C

The corrosion of three Fe-xCr alloys (x = 8, 12, 18 wt.%) was examined at 600 °C in reducing atmospheres containing HCl and H₂S with two different H₂S contents and compared with the behavior of the same materials in H₂S-free H₂-CO₂ and H₂-HCl-CO₂ mixtures producing similar oxygen and chlorine pressures. Exposure to the low-H₂S gas mixture had only a reduced effect on the behavior of Fe-8Cr and Fe-18Cr, but increased significantly the corrosion rate of Fe-12Cr. Increasing the H₂S level accelerated the corrosion of all the alloys, but particularly that of Fe-18Cr. In both cases only minor amounts of sulfur and chlorine were present close to the alloy/scale interface. An increase of the Cr content reduced the corrosion rate in both H₂S gas mixtures, especially in the range 8-12 wt.% Cr, due to a larger volume fraction of Cr₂O₃ in the scale. The results have been discussed on the basis of the thermodynamic stability diagrams of the Fe-O-Cl-S and Cr-O-Cl-S systems.     

Mixed oxidant corrosion in nonequilibrium gasifier environments

The major use of high-temperature steel alloys in gasifiers is in heat exchangers for cooling hot syngas, consisting mainly of CO and H₂ with lesser amounts of H₂O and CO₂ and minor quantities of H₂S and HCl. Metal temperatures range from 250 to 600°C, gas temperatures from 250 to 1200°C. Because of rapid cooling the composition of the gas does not change with temperature. Therefore the gas is not in equilibrium at the metal surface. Calculations show that such gases have lower oxygen and sulfur pressures than equilibrated gases at the same temperature. This makes the results of previous laboratory studies less appropriate for predicting mixed oxidant corrosion in gasifiers. For this reason the present study was carried out using nonequilibrium gas mixtures, similar to gases, produced in entrained-slagging gasifiers. Most corrosion experiments were carried out at 540°C, as this is a common temperature for superheaters and hot-gas cleanup systems. Iron-base model alloys containing 35% Ni, 20% Cr, and various minor alloying additions were studied. Three corrosion regimes were identified over the range of conditions studied, depending on the sulfur-to-oxygen pressure ratio of the gas and the alloy composition. At high P_{S 2}/P_{O 2} ratios a somewhat protective FeCr₂S₄ scale formed on all alloys. Below this layer internal oxidation and sulfidation occurred at a slow rate. At lower P_{S 2}/P_{O 2} ratios nonprotective Fe(Ni, Cr)S external scales formed. These allow rapid internal oxidation of the chromium in the alloy, resulting in high corrosion rates. Under the same conditions very low corrosion rates are obtained when silicon is added to the alloy, because the presence of SiO₂ precipitates makes the internal-oxidation layer protective. Thus, the same corrosion model is operative in all three corrosion regimes: external sulfidation of iron and nickel, together with internal oxidation of chromium and other strong-oxide formers.     

The effect of H2S concentration on the corrosion behavior of carbon steel at 90 °C

The electrochemical behavior of SAE-1020 carbon steel in 0.25 M Na₂SO₄ solution containing different concentrations of H₂S at 90 °C was investigated using the methods of weight loss, electrochemical measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the corrosion rate of carbon steel increased significantly with the increase of H₂S concentration. H₂S accelerated the corrosion rate of SAE-1020 carbon steel by a promoted hydrogen evolution reaction. Severe corrosion cavities were observed on the carbon steel surface in the solutions containing H₂S due to cementites stripped off from the grain boundary. The loose corrosion products formed on the steel surfaces were composed of mackinawite.     

Studies on copper-semiconducting layer-electrolyte systems—II. Galvanostatic anodic polarization of Cu/Cu2S/S2− applying stationary and rectangular pulse techniques

Copper sulphide layers formed by anodically polarizing copper in a Na₂S bath were investigated electrochemically using galvanostatic techniques. The variation in potential of unpolarized copper/copper sulphide electrodes with pS suggested a film of cuprous sulphide containing some cupric sulphide. The overpotential measurements indicated sulphide films of low porosity, deficient in Cu⁺ ions. The transfer coefficients and exchange currents computed from the results were interpreted as a system involving an impervious layer of cuprous sulphide overlayered with a film of cupric sulphide. The influence of Cu²⁺, S^2? and OH^? on the anodic processes are also discussed.     

H2S and O2 influence on the corrosion of carbon steel immersed in a solution containing 3 M diethanolamine

Aqueous solutions with 3 mol L⁻¹ (M) diethanolamine (DEA) concentration are extensively used in the gas processing industry to remove acid gases. However, the degradation of the DEA and the formation of heat-stable salts (HSS) lead to severe corrosion problems. Even worse, equipment corrosion can be magnified by the unavoidable presence of sulphide acid and dissolved oxygen as a result of hydrocarbon (natural gases and crude oil) processing. The aim of this work is to study the combined corrosion effects of DEA, sulphide acid and oxygen on carbon steel. Electrochemical methods revealed that in the 3 M DEA medium without oxygen, corrosion processes are modulated by adsorbed DEA film formation. Furthermore, it was shown that the addition of oxygen and 15 × 10⁻³ mol L⁻¹ (15 mM) H₂S produced the formation of an adherent film on the carbon steel surface. Chemical analyses by EDAX revealed a homogeneous film of corrosion products composed of iron oxide and sulphide formed in DEA solution containing O₂ and H₂S, respectively. Equivalent circuits were used to estimate the parameters associated with ion diffusion through the formed corrosion films. The results showed that the presence of H₂S induced the formation of thin iron sulphide films that provide protective properties to the metal. It is concluded that the presence of oxygen in a sweetening plant should be avoided as DEA degradation can be produced with the subsequent decrease in chelating process efficiency and the increase in corrosion problems.     

Unusual oxidation behaviour of Zr50Cu50 alloy at high temperatures

The oxidation of Zr₅₀Cu₅₀ alloy at 500-700 °C is characterized by preferential oxidation of zirconium, while the excess of copper is accumulated at the alloy-oxide interface forming the Zr₁₄Cu₅₁ phase. The strong reaction at 800 and 850 °C resulted in the total corrosion of the specimens in 21 and 15 h, respectively. The oxidation at elevated temperatures showed an anomalous decrease of the oxygen consumption rate in the temperature range 930-1000 °C, corresponding to the preferentially oriented crystallites of ZrO₂ in the oxide scale at 900 and 1000 °C. The oxide layer consists of ZrO₂ and CuO in the whole temperature interval of the oxidation. The reaction kinetics obeys a parabolic rate law. An activation energy of 92.0 ± 0.3 kJ/mol has been estimated.     

Corrosion characteristics of copper microparticles and copper nanoparticles in distilled water

The corrosion characteristics of copper microparticles and copper nanoparticles in distilled water were investigated in this paper. The Cu²⁺ transformations of copper microparticles and copper nanoparticles in distilled water were tested by using absorbance measurement, the structures of their corrosion products were determined by using XRD and TEM techniques. The results of absorbance measurement show that the corrosion characteristics of copper nanoparticles in distilled water are quite different from that of copper microparticles. The Cu²⁺ transformations ratio of copper microparticles increases slowly with the increasing of immersion time and levels off eventually, but the Cu²⁺ transformations ratio of copper nanoparticles increases sharply with the increasing of immersion time and gets to peak rapidly, and then decreases as the immersion time increases and levels off finally. The results of XRD present that they have different corrosion products, the corrosion products of copper microparticles in distilled water are Cu and CuO, but the nanoparticles are Cu, CuO, Cu(OH,Cl)₂ · 2H₂O and Cu₂(CO₃)(OH)₂. All these differences owe to the size effect of copper particles.     

High temperature corrosion properties of ionic liquids

The corrosion behaviour of several metals and metal alloys (copper, nickel, AISI 1018 steel, brass, Inconel 600) exposed to a typical ionic liquid, the 1-butyl-3-methyl-imidazolium bis-(trifluoromethanesulfonyl) imide, ([C₄mim][Tf₂N]), has been investigated by electrochemical and weight-loss methods. Corrosion current densities have been determined by extrapolation from Tafel plots and by polarization resistance measurements and 48 h immersion tests were performed at 150, 250, 275 and 325 °C. Room temperature results show low corrosion current densities (0.1-1.2 μA/cm²) for all the metals and alloys investigated. At 70 °C, the corrosion current for copper dramatically increases showing a strongly dependence on temperature. At 150 °C copper shows significant weight-loss while nickel, AISI 1018, brass and Inconel do not. At higher temperatures (?275 °C), the copper sample crumbles and localized corrosion occurs for the other metals and alloys.     

Copper corrosion inhibition in O2-saturated H2SO4 solutions

Corrosion inhibition of copper in O₂-saturated 0.50 M H₂SO₄ solutions by four selected amino acids, namely glycine (Gly), alanine (Ala), valine (Val), or tyrosine (Tyr), was studied using Tafel polarization, linear polarization, impedance, and electrochemical frequency modulation (EFM) at 30 °C. Protection efficiencies of almost 98% and 91% were obtained with 50 mM Tyr and Gly, respectively. On the other hand, Ala and Val reached only about 75%. Corrosion rates determined by the Tafel extrapolation method were in good agreement with those obtained by EFM and an independent chemical (i.e., non-electrochemical) method. The chemical method of confirmation of the corrosion rates involved determination of the dissolved Cu²⁺, using ICP-AES (inductively coupled plasma atomic emission spectrometry) method of chemical analysis. Nyquist plots exhibited a high frequency depressed semicircle followed by a straight line portion (Warburg diffusion tail) in the low-frequency region. The impedance data were interpreted according to two suitable equivalent circuits. The kinetics of dissolved O₂ reduction and hydrogen evolution reactions on copper surface were also studied in O₂-saturated 0.50 M H₂SO₄ solutions using polarization measurements combined with the rotating disc electrode (RDE). The Koutecky-Levich plot indicated that the dissolved O₂ reduction at the copper electrode was an apparent 4-electron process.     

High temperature naphthenic acid corrosion and sulphidic corrosion of Q235 and 5Cr1/2Mo steels in synthetic refining media

The corrosion of Q235 and 5Cr1/2Mo steels in synthetic refining media containing naphthenic acid and/or sulphur compounds was studied to evaluate naphthenic acid corrosion (NAC), sulphidic corrosion (SC), and their interaction. Corrosion dependencies on the test duration, temperature, total acid number (TAN) and content of sulphur compound were assessed. Specimens after NAC and SC tests were characterized by SEM/EDX, and XRD. It is found that in liquid phase of media containing only naphthenic acid and at temperature about 230 °C, 5Cr1/2Mo and Q235 steels have almost the same NAC rate, and above 230 °C, 5Cr1/2Mo has a higher NAC rate than Q235 has due to the higher NAC activation energy (63.2 kJ mol⁻¹) of 5Cr1/2Mo than that of Q235 (54.0 kJ mol⁻¹), indicating that increasing temperature accelerates NAC rate of 5Cr1/2Mo more than that of Q235. In oil containing only dimethyl disulphide, the growth of SC film follows parabolic kinetics, and the film of Q235 grows faster than that of 5Cr1/2Mo while SC rate of Q235 is higher than that of 5Cr1/2Mo. In oil containing both naphthenic acid and dimethyl disulphide, 5Cr1/2Mo has a lower corrosion rate than Q235 has. On the basis of “naphthenic acid corrosion index” (NACI), the benefits of 5Cr1/2Mo over Q235 should ascribe to that the pseudo-passive film for 5Cr1/2Mo has better NAC resistance than that for Q235. This is close related to the existing of additional chromium sulphide (Cr₅S₈) on the pseudo-passive film of 5Cr1/2Mo, in contrast with the pyrrhotite (Fe₇S₈) and troilite (FeS) on the film of Q235.     

Chemistry and melting characteristics of fireside deposits taken from boiler tubes in waste incinerators

Twenty-three tube deposits taken from seven heat-recovery boilers of municipal solid waste incinerators were examined by chemical analyses and X-ray diffraction. These deposits were measured by Differential Scanning Calorimeter (DSC) in N₂ to investigate their melting characteristics. Sixteen deposits were used to evaluate their corrosiveness to carbon steel by high-temperature corrosion test conducted at 400 °C for 20 h in 1500 ppm HCl – 300 ppm SO₂ – 7.5%O₂ – 7.5%CO₂ – 20%H₂O – N₂. Total heat of endothermic reactions of the deposits taking place between 200 and 400 °C can be related to the corrosion rate of carbon steel at 400 °C. Corrosion initiated at temperatures when the deposits started to melt, became severe when fused salt constituents increased, and alleviated when the majority of the deposits became fused. The corrosion can be interpreted as fused salt corrosion caused by chloride and sulfate salts.     

High temperature corrosion of pure Fe, Cr and Fe-Cr binary alloys in O2 containing trace KCl vapour at 750 °C

Pure Fe, Cr and Fe-Cr binary alloys were corroded in O₂ containing 298 ppm KCl vapour at 750 °C. The corrosion kinetics were determined, and the microstructure and the composition of oxide scales were examined. During corrosion process, KCl vapour reacted with the formed oxide scales and generated Cl₂ gas. As Cl₂ gas introduced the active oxidation, a multilayer oxide scales consisted of an outmost Fe₂O₃ layer and an inner Cr₂O₃ layer formed on the Fe-Cr alloys with lower Cr concentration. In the case of Fe-60Cr or Fe-80Cr alloys, monolayer Cr₂O₃ formed as the healing oxidation process. However, multilayer Cr₂O₃ formed on pure Cr.