Über den Einfluß der Strömungsgeschwindigkeit und der NaCl-Konzentration auf die Sauerstoffkorrosion unlegierten Stahls in Wässern

Influence of flow velocity and sodium chloride concentration on the oxygen corrosion of unalloyed steels in water Corrosion of mild steel in aerated water normally leads to pitting, and to an enrichment of anions within the pits. Even HCO₃^? ions can support localized corrosion. The intensity of this is remarkably increased by chloride ions. In equilibrium water with Ca²⁺ and HCO₃^? ions and about 40 ppm free CO₂ protective rust layers are formed after about 500 hs exposure not depending on flow rate and salt concentration. These layers decrease the mean corrosion rate to about 0.1 mm/a, but do not prevent localized corrosion. Protective passive layers with extremely low corrosion rates are formed in flowing water with Ca²⁺ and HCO₃^? ions and about 40 ppm free CO₂. The minimum flow rate can be estimated for a 3/4 inch pipe to lie between 0.35 and 1.5 m/s. Investigations with water containing 40 ppm free CO₂ without Ca²⁺ at pH 4.7 and with NaHCO₃ (pH 7.2) show at low pH high corrosion rates – as expected –, and at pH 7.2 formation of protective layers with poor reproducibility in comparison with the situation in equilibrium water. Thus, Ca²⁺ ions support the protective properties of rust layers. HCO₃^? ions are necessary for the formation of protective layers because these are not formed in pure NaCl solutions.     

Role of complexes in inhibition of mild steel by zinc–1-hydroxyethylidene-1, 1-diphosphonic acid mixtures

Abstract

The action of 1-hydrox yethylidene-1, 1-diphosphonic acid (HEDP) in combination with zinc ions as a corrosion inhibitor for mild steel in oxygen containing aqueous solutions has been investigated in relation to the presence of different zinc levels, the presence of aggressive anions, and different pH values. The highest inhibition effect was obtained at a 2·7:1 zinc/HEDP molar ratio, corresponding to 60 ppm zinc, and was associated with a significant anodic effect. In the absence of chloride and with no free forms of the inhibitor components, the zinc-HEDP mixture exhibited good protection over a wide range of pH (6·5-9·5). However, in a weakly acidic medium, protection could not be achieved. Calculations based on the dissociation constants of the HEDP and the stability constants of the possible zinc-HEDP complexes showed that this inhibition can be attributed to the presence of the 2:1 zinc-HEDP complex (Zn₂H_-1L^-) at a sufficient level. It is found that this anionic complex can behave as an anodic, passivating, inhibitor at a concentration as low as 0·00015M (20 ppm zinc-32 ppm HEDP mix ture). This passivity is prevented by the presence of sufficient chloride. The critical chloride concentration in these studies is approximately ten times higher than the complex concentration, in molar terms. It is also found that free phosphonate is aggressive and can prevent passivity due to the preferential formation of soluble iron-HEDP complex. The tolerance of the 2:1 complex to free phosphonate is substantially less than to chloride, approx imately equimolar.     

Electrochemical studies on the corrosion inhibition of AA2024 aluminium alloy by rare earth ammonium nitrates in 3.5% NaCl solutions

The inhibitive effect of Ce(III) and Ce(IV) ammonium nitrate inhibitors on the corrosion behavior of aluminium alloy AA2024 in 3.5% NaCl solution has been investigated. Four different concentrations (10^?2, 10^?3, 10^?4, and 10^?5 M) of the inhibitors were studied. Ce³⁺ and Ce⁴⁺ ions are introduced into the corrosive medium with similar anionic compositions – (NH₄)₂Ce(NO₃)₅ and (NH₄)₂Ce(NO₃)₆. The inhibition efficiency (IE%) of the ions has been evaluated by using electrochemical methods – linear voltammetry (LVA) and electrochemical impedance spectroscopy (EIS). Moreover, the inhibitive ability has been investigated at different duration after addition of these salts into the corrosive media. It is established that the pH of the solutions plays an important role on the inhibition process for both cations. The results revealed that at relatively similar conditions, the cerium (III) ions showed higher inhibition efficiency than cerium (IV) ions, when they were compared to the case without inhibitor.     

Effects of coolant chemistry on corrosion of 3003 aluminum alloy in automotive cooling system

In this work, effects of coolant chemistry, including concentrations of chloride ions and ethylene glycol and addition of various ions, on corrosion of 3003 Al alloy were investigated by electrochemical impedance spectroscopy measurements and scanning electron microscopy characterization. In chloride‐free, ethylene glycol–water solution, a layer of Al‐alcohol film is proposed to form on the electrode surface. With the increase of ethylene glycol concentration, more Al‐alcohol film is formed, resulting in the increase in film resistance and charge‐transfer resistance. In the presence of Cl^? ions, they would be involved in the film formation, decreasing the stability of the film. In 50% ethylene glycol–water solution, the threshold value of Cl^? concentration for pitting initiation is within the range of 100 ppm to 0.01 M. When the ethylene glycol concentration increases to 70%, the threshold Cl^? concentration for pitting is from 0.01 to 0.1 M. In 100% ethylene glycol, there is no pitting of 3003 Al alloy even at 0.1 M of Cl^?. Even a trace amount of impurity cation could affect significantly the corrosion behavior of 3003 Al alloy in ethylene glycol–water solution. Addition of Zn²⁺ is capable of increasing the corrosion resistance of Al alloy electrode, while Cu²⁺ ions containing in the solution would enhance corrosion, especially pitting corrosion, of Al alloy. The effect of Mg²⁺ on Al alloy corrosion is only slight.     

Effect of molybdate ions as corrosion inhibitors of iron in neutral aqueous solutions

Abstract

The effect of molybdate ions on the corrosion of Fe in neutral solutions was investigated by electrochemical measurements (dc polarisation and impedance spectroscopy) together with gravimetric determinations. Studies were conducted in solutions containing sodium hydrogen/sodium sulphate salts with molybdate concentrations ranging between 10^?4 and 10^?2M at pH 8 and 9. Mass loss measurements indicated that about 10^?3M of molybdate was necessary in order to inhibit completely the corrosion of Fe at room temperature. The potentiodynamic polarisation and electrochemical impedance studies gave indications about the mechanism of action of the MoO^2?₄ ion. They also showed that the inhibiting effect of the oxyanion is increased in the presence of dissolved oxygen. Spontaneous passivation of the corroding Fe electrode could happen only in the presence of dissolved oxygen at concentrations greater than 10^?4M. However, passivity was also obtained under potentiodynamic polarisation conditions in deaerated solutions. The effect of the oxygen was attributed to displacement of the corrosion potential into the region of selfpassivation of the steel. Finally, the results indicated that the corrosion inhibition of Fe in neutral solutions by molybdate ions was largely insensitive to pH over the range from 8 to 9.     

The use of cement kiln dust for the removal of heavy metal ions from aqueous solutions

Abstract

The possibility of removal and utilisation of heavy metal (HM) ions from aqueous solutions by cement kiln dust (CKD) has been studied. The experiments have shown that CKD may be used for industrial wastewater decontamination. They revealed that CKD may be used for neutralisation of acidic wastewaters (alkalinity 12–16 meq g^?1) and for removal of HM ions such as Cu(II), Ni(II), Pb(II), Cd(II) and Co(II). CKD acts as an alkaline agent and sorbent. The main crystalline components of CKD are: calcite, CaCO₃ (80% by mass), 10–15% SiO₂ and the remainder is basic calcium silicate, Ca₅(SiO₄)₂(OH)₂. The maximal capacity of CKD to remove Cu(II) is 0·29 g g^?1 CKD (9·1 meq g?1); Ni(II), 0·14 g g^?1 CKD (4·7 meq g^?1); Pb(II), 2·0 g g^?1 CKD (19 meq g^?1); Cd(II), 0·42 g g^?1 CKD (7·4 meq g^?1); and Co(II), 0·20 g g^?1 CKD (6·8 meq g^?1). Interaction of CKD with Cu(II) ions produces devillite Cu₄(CaSO₄)₂(OH)₆·3H₂O, with Pb(II) – basic carbonate Pb₃(CO₃)₂(OH)₂ and with Cd(II) ions – Cd(OH)Cl. The products of interaction of CKD with Ni(II) and Co(II) ions are amorphous: apparently hydrated Ni(OH)₂ and Co(OH)₂.     

Uniform corrosion of titanium in alkaline hydrogen peroxide conditions: influence of transition metals and inhibitors calcium and silicate

Uniform corrosion of titanium was studied in alkaline hydrogen peroxide environments simulating pulp bleaching conditions. Corrosion rates of unalloyed Grade 2 and alloyed Grade 5 were determined as a function of hydrogen peroxide anion (HOO^?) concentration. Influences of calcium and silicate inhibitors and iron and manganese were investigated. Without inhibition titanium corroded at HOO^? content of 200 mg/l: Grade 2 0.4 mm/y and Grade 5 1.4 mm/y. Addition of calcium (Ca²⁺) and silicate (SiO₃^2?) diminished the corrosion of Grade 2 to critical anion level 400 mg/l, but could not protect Grade 5 even at the HOO^? concentration of 300 mg/l. Presence of iron and manganese raised the critical levels of the both grades. High HOO^? anion level was observed as a notable potential difference between titanium and platinum.     

Inhibiting Effect of some Monosaccharides on the Corrosion of Copper in Nitric Acid

Abstract

A study has been made of the inhibitive efficiency of some monosaccharides (glucose, fructose, mannose, galactose, in the concentration range 10^?3M–1·0M) on copper corrosion in HNO₃ (0·01, 0·1 and 1·0 M) at temperatures of 15°, 25° and 35°c. It was found that the structures of the various saccharides (pyranosic or furanosic) affected neither the efficiency nor the mechanism of inhibition. Inhibition was practically zero at concentrations of the monosaccharides between 10^?3 and 10^?1 M, whereas, at 1·0 M, 65–70% inhibition was reached in 0·01 and 0·1 M HNO₃, and 50–60% in 1·0 M HNO₃.

In 1·0 M HNO₃ the saccharides act as cathodic inhibitors (reducing HNO₂ present in the HNO₃ solutions), whereas in 0·1 and 0·01 M HNO₃ they also acted as anodic inhibitors through theformation of an organometallic compound with Cu²⁺, which gave slight protection to the metal surface.     

Synergistic inhibition effect of rare earth cerium(IV) ion and sodium oleate on the corrosion of cold rolled steel in phosphoric acid solution

The synergistic inhibition effect of rare earth cerium(IV) ion (Ce⁴⁺) and sodium oleate (SO) on the corrosion of cold rolled steel (CRS) in 3.0 M phosphoric acid (H₃PO₄) has been investigated by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) methods. The results reveal that SO has a moderate inhibitive effect and its adsorption obeys Temkin adsorption isotherm. Ce⁴⁺ has a poor effect. However, incorporation of Ce⁴⁺ with SO improves the inhibition performance significantly, and exhibits synergistic inhibition effect. SO acts as a cathodic inhibitor, while SO/Ce⁴⁺ mixture acts as a mixed-type inhibitor.     

Influence of hydrostatic pressure on pitting of aluminium in sea water

Abstract

The effect of hydrostatic pressure on the corrosion of aluminium in sea water oj pH 8·2 containing 7ppm dissolved oxygen has been investigated at 20°C. On increasing the pressure from 1 to 300 atm, the corrosion rate increased, an effect attributable to an increase in the rate of the anodic reaction while the cathodic rate remained unchanged. The observed increased susceptibility to pitting corrosion with increasing pressure was found to correlate with the presence of increasing quantities of SO^2?₄ and Cl^? ions in the oxidation layer. The introduction of electron acceptors such as SO^2?₄ and Cl^? into n type compounds such as aluminium oxides increases the density of lattice dejects and promotes breakdown oj the barrier provided by the oxidation layer.     

Effect of phosphine on acid corrosion of iron

The effect of the phosphine-concentration (10^?8–10^?3 M) in strong acid solutions (pH = 0) on the corrosion rate of pure iron and Fe- 0.12% P alloy has been investigated. It was shown that at low concentrations (10^?7–10^?6M), phosphine accelerates the corrosion of iron, whereas at adequately high concentrations (10^?5–10^?3 M) it has inhibitory properties. In the presence of PH₃ the cathodic reduction of hydrogen ions is strongly accelerated. At the same time, the increase in PH₃ concentration causes an increase of surface coverage by PH₃ molecules, which results in the inhibition of both partial electrode processes.     

Annual Contents

Abstract

The electrochemical reduction of Bi₂S₃ films deposited using the successive ionic layer adsorption and reaction method in a Bi(III) solution with a sulphidation agent Na₂S was investigated in Ni²⁺ free background and Ni²⁺ containing electrolytes at different pH. This investigation was carried out by means of cyclic voltammetry, electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy. It has been established that during the reduction of a bismuth sulphide film in the Ni²⁺ free background solution the electrode mass decreases due to Bi₂S₃ film reduction to metallic Bi and the transfer of sulphide ions into the bulk of the solution. At pH=3, the Bi₂S₃ film reduces under the potential region from –0·2 to –0·4 V, while at pH=4 and 5 from –0·4 to –0·6 V. The processes occurring during the reduction of Bi₂S₃ film in the Ni²⁺ containing electrolyte depend on the electroreduction medium. At pH=3, the reduction of Bi₂S₃ film to metallic Bi and Ni²⁺ ions occurs simultaneously under the potential region of the cathodic current peak (–0·2 to –0·4 V). When pH is 4 or 5, the increase in electrode mass is caused by the incorporation of Ni²⁺ ions into the bismuth sulphide film with their partial reduction to the metallic or close to metallic state with the occurrence of structural changes in the film.     

Influence of bath concentration and pH on electrodeposition process of ternary Zn-Ni-Mo alloy coatings

The influence of bath pH and also citrate and molybdate concentration, on the electrodeposition process of ternary Zn-Ni-Mo alloy coatings has been examined. The occurrence of the particular forms of the metal-citrate complexes in the electrolytes was analysed using UV-VIS spectroscopy and on the basis of the stability constants of the complexes. In the solutions with lower pH (4·5 and 5·7), in which free metal ions and ZnHCit^? and NiHCit^? complexes predominate, anomalous codeposition of nickel with zinc took place. In electrolytes with higher pH, containing excess of citrate, in which all the metal ions occur in the form of citrate complexes, and about 20% of the Zn²⁺ and Ni²⁺ ions form a ZnNiCit₂^4? mixed complex, the codeposition changes from anomalous to normal. The percentage of Mo in the alloy increases with the increase in concentration of uncomplexed MoO₄^2? ions in the solution. Alloys with much higher Mo content may be obtained from the bath in which preferential deposition of nickel (normal codeposition) takes place.     

Effects of Halides on the Corrosion of Mild Steel in Molten NaNO3-KNO3 Eutectic

Abstract

The effect of alkali halides on the corrosion behaviour of mild steel in, (Na,K)NO₃ eutectic has been studied at temperatures ranging from 300°–450°c. Steady-state potentials of the steel electrode vary with the concentration of Cl^?, Br^?, and I^? ions according to: E = a + b log C. Gravimetric; measurements show that the corrosion process of steel in the melt without and with halide ions, at concentrations ≤0·l M, is essentially the same, the weight gain being parabolic with time. At higher halide concentrations the corrosion rate is linear with time. The corrosion rate also increases with increase in temperature. Both potential and weight gain measurements show that aggressiveness increases in the order: Cl^?<Br^?<I^?. It is suggested that in this system two opposing forces compete on the steel surface. The oxide ions help in building or repairing a passivating film of Fe₃O₄, whilst the aggressive halide ions attack weak areas in the film and assist the corrosion process. The process which prevails depends on the relative concentrations of the two species.

In the case of fluoride, both the potential and weight gain of steel vary with time in an irregular manner, and no definite relation could be obtained. This has been attributed to the low solubility of fluoride in the melt and to the properties of the corrosion products, in that the film formed does not adhere to the metal surface.     

SCC of X‐52 and X‐60 weldements in diluted NaHCO3 solutions with chloride and sulfate ions

Stress corrosion cracking tests were performed in both X‐52 and X‐60 weldments in sodium bicarbonate (NaHCO₃) solutions at 50°C using the Slow Strain Rate Testing (SSRT) technique. Solution concentrations varied between 0.1 to 0.0001 M, and to simulate the NS‐4 solution, chloride (Cl^?) and/or sulfate ( ) ions were added to the 0.01 M solution. Tests were complemented with hydrogen permeation measurements and polarization curves. It was found that the corrosion rate, taken as the corrosion current, I_corr, was maximum in 0.01 M NaHCO₃ and with additions of ions. Higher or lower solution concentrations or additions of Cl^? alone decreased the corrosion rate of the weldment. The SSC susceptibility, measured as the percentage reduction in area, was maximum in 0.01M NaHCO₃. Higher or lower solution concentrations of additions of Cl^? or decreased the SCC susceptibility of the weldment. The amount of hydrogen uptake for the weldment was also highest in 0.01 M NaHCO₃ solution, but it was minimum with the addition of Cl^? or ions. Thus, the most likely mechanism for the cracking susceptibility of X‐52 and X‐60 weldments in diluted NaHCO₃ solutions seems to be hydrogen‐assisted anodic dissolution.     

Synergistic inhibition of zinc corrosion in 0.5 M NaCl by combination of cerium(III) chloride and sodium silicate

The synergistic inhibition effects of cerium(III) chloride, CeCl₃ and sodium silicate, Na₂Si₂O₅ (water glass) on corrosion of zinc in an aerated 0.5 M NaCl solution at 30°C were examined by polarization measurements. Equimolar mixtures of these inhibitors were markedly effective, indicating that the inhibition efficiencies of the mixture at 1×10⁻⁴ of each inhibitor were 95.9 and 93.6 after immersion of a zinc electrode in the solution for 3 and 120 h, respectively. X-ray photoelectron spectra revealed that a protective layer composed of hydroxylated or hydrated cerium-rich oxide and small amounts of zinc hydroxide and silicate formed on the zinc surface. A high inhibition efficiency of 1×10⁻³ M Na₂Si₂O₅, 97.7% was obtained for corrosion of a zinc electrode which was previously treated in the NaCl solution of 1×10⁻³ M CeCl₃ at 30°C for 30 min.     

Cerium(III) chloride and sodium octylthiopropionate as an effective inhibitor mixture for zinc corrosion in 0.5 M NaCl

It has been reported that cerium(III) chloride CeCl₃ and sodium octylthiopropionate C₈H₁₇S(CH₂)₂COONa (NaOTP) are effective inhibitors for zinc corrosion in 0.5 M NaCl. In this study, synergistic inhibition of zinc corrosion in an aerated 0.5 M NaCl solution by a mixture of these inhibitors was investigated by polarization measurements after immersion of a zinc electrode in the solution for many hours. The inhibition efficiency of 1×10⁻⁴ M CeCl₃ plus 1×10⁻⁵ M NaOTP mixture was high, 95.1% after both 3 and 120 h. X-ray photoelectron spectroscopy and electron-probe microanalysis for the inhibited electrode revealed that the zinc surface was covered with a protective film composed of an hydrated or hydroxylated Ce-rich oxide, a small amount of Zn(OH)₂ and a trace of Zn(OTP)₂ chelate. The inhibition effect of 1×10⁻⁵ M NaOTP in the NaCl solution for the zinc electrode previously treated in 1×10⁻³ M CeCl₃ for 30 min was also examined, indicating a higher inhibition efficiency, 96.3% after immersion of the electrode in the solution for 120 h.     

Synergistic action of vinyl triphenyl phosphonium bromide with various anions on corrosion of steel

Abstract

The effect of mixtures of vinyl triphenyl phosphonium bromide containing various anions on the corrosion rate of steel in 0·5M H₂ SO₄ has been investigated. The inhibition mechanism has been studied by conducting electrochemical polarisation measurements. The inhibitor acts by covering the cathodic area of the metal surface through adsorption of the phosphorus atom. A synergistic effect has been observed for KBr, KI, and KSCN with vinyl triphenyl phosphonium bromide. Thus, an improvement in inhibition was obtained by using mixtures compared with that given by individual components. A probable mechanism for this process is suggested. The degree of surface coverage of iron in acid solution containing 10^-5 M inhibitor was determined for various concentrations of Br^-, I^-, and SCN^-. The inhibiting effectiveness was in the order KI > KSCN > KBr. Protection of 93·8% was given by a mixture of 10^-5 M inhibitor + 10^-2 M KI. It was observed that the protection efficiency was sharply enhanced in the presence of 10^-3 M KI with very low concentrations (10^-5 M–10^-4 M) of the inhibitor.     

Stress—corrosion cracking of austenitic stainless steel in hydrochloric acid media at room temperature

Stress—corrosion cracking of solution quenched, type 304, stainless steel can occur at room temperature in HCl solutions ranging between 5·10^?1M and 1M HCl. The cracking observed in HCl solutions is similar to that previously observed in H₂SO₄ + NaCl and HClO₄ + NaCl solutions. Cracking occurs at ? 0·200 V (NHE), in the active potential region, it is under cathodic control, and it develops in conditions under which the corrosion rate of the external surface area is more or less constant and independent of the HCl concentration, in the range 10^?1 M?1 M HCl. At higher HCl concentrations, corrosion rates increase and uneven, general corrosion occurs instead of cracking. The development of pitting and stress—corrosion cracking under active conditions precludes the conclusion that active—passive cells always play a role in localized corrosion and, in particular, in stress—corrosion cracking. Under these conditions, it has been shown that sensitized and non-sensitized specimens behave similarly (giving rise in both cases to transgranular cracking); active—passive cells, due to chromium depletion at the grain boundaries, are not involved. Active—passive corrosion mechanisms can however arise at more noble potentials (0·100?0·200 V NHE), as in the case of HClH₂O₂ solutions of specific concentration, producing intergranular corrosion of the stainless steel in the sensitized condition.     

Influence of pH on corrosion behavior of carbon steel in simulated cooling water containing scale and corrosion inhibitors

In this paper, the influence of pH on the corrosion behavior of AISI 1020 carbon steel in simulated cooling water was investigated by using electrochemical and surface analysis methods. The results of polarization showed that the corrosion resistance of carbon steel increased with an increase in pH of the simulated water, and the corrosion control process changed from cathodic polarization to anode polarization control. The scale and corrosion inhibitor 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) had a certain anodic corrosion inhibition effect on carbon steel, whereas Zn²⁺ acted as a cathodic inhibitor for carbon steel in simulated water with pH 7–9. In simulated water containing both PBTCA and Zn²⁺, a good synergistic corrosion inhibition was found between PBTCA and Zn²⁺, and their corrosion inhibition effect on carbon steel was the best at pH 8. This was attributed to the formation of Zn(OH)₂ precipitate film in the cathode region and the formation of Zn–PBTCA complex film in the anode region at this pH.