Showing papers in "British Corrosion Journal in 1994"
TL;DR: In this article, a surface modification process has been developed to improve the pitting resistance of high copper aluminium alloys such as 2024 and 7075 without the use of chromates.
Abstract: In a project devoted to the elimination of toxic materials in methods of corrosion protection, a surface modification process has been developed to improve the pitting resistance of high copper aluminium alloys such as 2024 and 7075 without the use of chromates. This process involves immersion in boiling Ce(NO3)3, anodic polarisation in Na2MoO4, and immersion in boiling CeCl3. Very corrosion resistant surfaces were produced on 7075–T6 after applying a pretreatment step which removes copper from the outer surface layers. A chemical and an electrochemical copper removal process have been developed with the actual procedure depending on alloy composition. During exposure in 0·5M NaCl for 30 days no measurable corrosion was indicated by continuous monitoring with electrochemical impedance spectroscopy or by visual observation. For 2024, significant improvement in the resistance to localised corrosion was also obtained. Surface analysis showed increased levels of cerium and molybdenum at locations whic...
50 citations
TL;DR: In this article, the galvanic corrosion data for couples between high alloy stainless steels and other metals in both natural and chlorinated sea water are reviewed, and recommendations for preventive measures are made for the major items used in sea water systems, i.e. valves, heat exchangers, and piping.
Abstract: The galvanic corrosion datafor couples between high alloy stainless steels and other metals in both natural and chlorinated sea water are reviewed. Recommendations for preventive measures are made for the major items used in sea water systems, i.e. valves, heat exchangers, and piping. Some service experiences are presented to show the kind of galvanic problems which can arise and the solutions adopted.
39 citations
TL;DR: In this article, the effect of an increase in hydrostatic pressure (from 1 to 300 atm) on the composition of the corrosion layer formed on 6061 T6 aluminium alloy in sea water was studied using electrochemical and surface analysis techniques.
Abstract: The effect of an increase in hydrostatic pressure (from 1 to 300 atm) on the composition of the corrosion layer formed on 6061 T6 aluminium alloy in sea water was studied using electrochemical (polarisation potentiodynamic curves and impedance measurements) and surface analysis (X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy) techniques. Increasing the hydrostatic pressure caused an increase in the Mg/Al ratio and in the ratio of non-hydrated to hydrated aluminium oxides, so that a more compact film with lower selfrepairing power was formed. Thus, the corrosion current density decreased while the pit nucleation probability increased.
36 citations
TL;DR: In this article, a programmable linear polarisation meter was developed for on-site measurement of the corrosion of steel reinforcement in concrete. But it is not suitable for the measurement of concrete structures.
Abstract: A programmable linear polarisation meter has been developed principally for on site measurement of the corrosion of steel reinforcement in concrete. The special features of this instrument are its programmable potentiostatic mode of operation. a simultaneous 300 Hz ac measurement facility to evaluate the resistance due to the concrete, and an instrument earth connection to maintain a monitoring bar at the same potential as the main reinforcement when they are uncoupled to perform linear polarisation. The features of the instrument are experimentally investigated and assessed.
35 citations
TL;DR: In this article, the presence of the oxide layer on copper surfaces was useful in improving its corrosion resistance in a Sydney tap water, based on simple immersion in acetate buffer or sodium hydroxide solution.
Abstract: Improvement of the corrosion resistance of copper has been accomplished by the deliberate formation of cuprous and cupric oxides on the metal surface, based on simple immersion in acetate buffer or sodium hydroxide solution. Weight loss, potentiodynamic, and potentiostatic polarisation measurements in sodium chloride, ammonia, and sodium bicarbonate solutions demonstrated that the presence of these oxides improved the corrosion resistance of copper considerably. The bicarbonate solution was also found to be a suitable medium for testing the stability of the oxide layers by the electrochemical methods. The presence of the oxide layer on copper surfaces was useful in improving its corrosion resistance in a Sydney tap water.
29 citations
TL;DR: In this article, reinforced mortar specimens were placed in aggressive aqueous solutions and the electrochemical impedance of the reinforcing steel was measured after immersion for 73 weeks at the end of the test, after removal of the mortar cover, the final condition of the reinforced steel was examined visually.
Abstract: Reinforced mortar specimens were placed in aggressive aqueous solutions and the electrochemical impedance of the reinforcing steel was measured after immersion for 73 weeks At the end of the test, after removal of the mortar cover, the final condition of the reinforcing steel was examined visually An equivalent electrical circuit of the interface impedance has been proposed: it includes dispersion terms for taking into account the inhomogeneity of the steel/concrete interface The validity of the model has been assessed by comparing the results of visual examinations with data obtained by electrochemical impedance measurements which were processed according to the model
28 citations
TL;DR: In this article, the effect of some phosphonic acid derivatives on the corrosion behaviour of carbon steel has been investigated in hydrochloric acid solutions by gravimetric and electrochemical methods, and it has been shown that the inhibitive action of diethylenetriaminepentamethylenephosphonic acid depends mainly on the protective inhibitor film formed on the surface of the steel and is independent of changes in solution composition with time.
Abstract: The effect of some phosphonic acid derivatives on the corrosion behaviour of carbon steel has been investigated in hydrochloric acid solutions by gravimetric and electrochemical methods. Some phosphonic acids were found to have inhibitive effects. These effects depend on the molecular structure: on the number of nitrogen atoms and of phosphono groups, but mainly on their position in the molecules, as shown by the differences in corrosion rate in the presence of various phosphonic acids. The variation of polarisation resistance with time suggests that the inhibitive action of diethylenetriaminepentamethylenephosphonic acid depends mainly on the protective inhibitor film formed on the surface of the steel and is independent of changes in solution composition with time.
20 citations
TL;DR: The influence of bicarbonate ions on the stability of copper oxides and pitting corrosion has been studied by the combined use of long term exposure, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and atomic absorption spectroscopy (AAS) as mentioned in this paper.
Abstract: The influence of bicarbonate ions on the stability of copper oxides and pitting corrosion has been studied by the combined use of long term exposure, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and atomic absorption spectroscopy (AAS). Contrary to earlier suggestions that the increasing concentration of bicarbonate ions inhibits copper pitting corrosion owing to the formation of a protective basic copper carbonate film, this study reveals that the lessening of this form of corrosion is a result of bicarbonate stabilisation of the copper oxide films formed before the carbonate salt. Analysis by SEM and XRD showed that the swfaces of specimens coated with copper oxides remained in their original conditions when bicarbonate ion concentration ≥61 mg L−1 or a high ratio of bicarbonate to chloride ions was present. In contrast, pitting corrosion occurred when bicarbonate ion concentration ≤31 mg L−1 was present. The dissolved copper concentrations obtained by AAS decreased with incr...
18 citations
TL;DR: In this article, the behavior of sintered and reaction bonded silicon carbide has been investigated in aqueous HCl, HF, HNO3, and H2SO4, using standard immersion and new electrochemical methods.
Abstract: Silicon carbide ceramics are candidate materials for use in aggressive environments, including those where aqueous acids are present. Standard corrosion testing methods such as immersion testing are not always sufficiently sensitive for these ceramics owing to the very low, almost unobservable, corrosion rates encountered. Using electrochemical methods the corrosion processes can be assisted, leading to higher rates and thus the elucidation of reaction mechanisms. The behaviour of a sintered and a reaction bonded silicon carbide has been investigated in aqueous HCl, HF, HNO3, and H2SO4, using standard immersion and new electrochemical methods. Both materials were passive in HCl, HNO3, and H2SO4 because of the formation of a surface silica film, and were active in HF. In HF, corrosion of sintered silicon carbide was slight and the residual silicon was removed from reaction bonded specimens.
17 citations
TL;DR: Fortynine products, based on cyclohexylamine and morpholine, were evaluated as volatile corrosion inhibitors for mild steel and fifteen showed an effectiveness in excess of 900% and may qualify for commercial application as mentioned in this paper.
Abstract: Forty-nine products, based on cyclohexylamine and morpholine, were evaluated as volatile corrosion inhibitorsfor mild steel. Fifteen showed an effectiveness in excess of 900% and may qualify for commercial application.
15 citations
TL;DR: In this paper, it has been shown that calcium acid phosphate is better than zinc phosphate and is comparable to zinc tetroxychromate as an anticorrosive pigment in a phenolic chlorinated rubber binder.
Abstract: Chromate based anticorrosive pigments are gradually being replaced because of their toxicity and carcinogenic properties. Zinc phosphate has been used to replace chromates but has led to contradictory results, its main difficulty being low solubility. Calcium acid phosphate, which has a higher solubility, could replace zinc phosphate. Evaluations of the degree of rusting on painted panels, corrosion rate measurements, and electrochemical studies (corrosion potential measurements and polarisation curves) have shown that calcium acid phosphate is better than zinc phosphate and is comparable to zinc tetroxychromate as an anticorrosive pigment in a phenolic chlorinated rubber binder. An advantage from an ecological point of view is that calcium ions provide less contamination than zinc ions.
TL;DR: In this article, the pitting susceptibility of 304 stainless steel was evaluated in ferrie chloride solution and it was attributed to the change of chemical composition of the oxide film on the surface.
Abstract: Type 304 stainless steel was oxidised at various temperatures in air. The pitting susceptibility of the oxidised and unoxidised specimens was evaluated in ferrie chloride solution. The increased pitting susceptibility of the oxidised specimens at about 500°C is attributed to the change of chemical composition of the oxide film on the surface.
TL;DR: In this paper, the most appropriate conditions were established by carrying out simulation studies and simplified, cost effective instrumentation using appropriate software was suggested, and its reliability has been checked by studying the case of iron corrosion inhibited by a new class of conducting polymers.
Abstract: Analysis of ac harmonic currents has led to a new technique for measuring corrosion rates. This involves perturbing the system with a non–distorted sinusoidal ac potential and measuring the harmonic currents. However, misleading results can be obta ned if proper experimental conditions are not maintained. The most appropriate conditions were established by carrying out simulation studies and simplified, cost effective instrumentation using appropriate software was suggested. Its reliability has beenchecked by studying the case of iron corrosion inhibited by a new class of conductingpolymers.
TL;DR: The galvanic corrosion behavior of detached electrodeposited Zn-Ni alloy coatings has been investigated during coupling with bare steel under two experimental conditions: total immersion in 600mM NaCl solution and exposure to neutral saltfog.
Abstract: The galvanic corrosion behaviour of detached electrodeposited Zn–Ni alloy coatings has been investigated during coupling with bare steel under two experimental conditions: total immersion in 600mM NaCl solution and exposure to neutral saltfog. Open circuit potential measurements made in NaCl solutions indicated that zinc alloys containing less tha approximately 14 wt-% nickel have potentials which remain negative with respect to steel over long immersion periods, suggesting that the coatings would behave sacrificially. This was confirmed by the galvanic current measurements which showed thatfor extended periods of time, zinc alloy coatings containing less than 14 wt-% nickel were sacrificial towards steel under both total immersion and salt fog conditions. Howeve,~ when the nickel level was increased above 14 wt-%, predominantly non-sacrificial corrosion behaviour was exhibited and steel corrosion was accelerated.
TL;DR: In this paper, the corrosion behavior of C71640 commercial alloy in quiescent, hermetically closed sulphide polluted and unpolluted natural sea water at 25°C was investigated.
Abstract: The corrosion behaviour of Cu–30Ni–2Fe–2Mn commercial alloy (similar to C71640) in quiescent, hermetically closed sulphide polluted and unpolluted natural sea water at 25°C was investigated. The corrosion resistance was examined using free corrosion and electrochemical tests and the surface film was characterised by chemical analysis and X-ray photoelectron spectroscopy. The different susceptibilities to corrosion were closely linked to the initial sulphide concentration; the accelerated attack occurring with an initial sulphide concentration of 4 ppm correlated with the amount of dissolved oxygen in solution and with the chemical composition of the corrosion layer.
TL;DR: In this article, the effects of carbon content, surface condition, temperature, and agitation on the corrosion of steel in sea water were studied under laboratory conditions and field tests were carried out at 2 and 12 m depths.
Abstract: The corrosion of steel in sea water was studied in laboratory as well as field experiments. The effects of carbon content, surface condition, temperature, and agitation on the corrosion of steel in sea water were studied under laboratory conditions. Each of the four factors was studied at two levels: carbon content (0·06/0·43 wt-%), surface preparation method (dry blasted/wet blasted), temperature (20/32° C), and agitation (with/without). The rate of corrosion of steel in sea water was found to increase significantly with increase in temperature and with aeration; the rate was found to decrease with increase in carbon content and with change from dry blasting to wet blasting. Field tests in tropical sea water were carried out at 2 and 12 m depths. No significant difference in corrosion rate was found at these two depths. Average corrosion rates of 0·53 and 0·35 mm/year were measured for exposure periods of 2 and 12 months respectively.
TL;DR: In this article, the corrosion of a mild steel and a medium carbon steel was studied at two sites in Singapore (inland and on a raft in the sea) for three periods.
Abstract: The corrosion of a mild steel and a medium carbon steel has been studied at two sites in Singapore (inland and on a raft in the sea) for three periods, with two surface conditions for each steel. Corrosion of the mild steel is significantly faster on the raft than inland. The steel with the higher carbon content corroded more slowly. An attempt to relate temperature, relative humidity, time of wetness, rainfall, and solar radiation to the corrosion rate of the dry blasted mild steel at the inland site suggests that the penetration depth obtained from weight loss data for samples exposed in the winter months can be expressed as 0·1078+0·00596x μm, where x is the number of hours of wetness, with a correlation coefficient of 0·99. Examination by scanning electron microscopy showed that specimens exposed inland were covered with patches of rust, compared with continuous rust films with continuous cracks on the raft specimens. Energy dispersive spectroscopy showed the rust on the raft specimens to have...
TL;DR: The galvanic corrosion characteristics of detached electrodeposited pure zinc and Zn-Ni alloy coatings have been investigated on coupling with two aerospace aluminium alloys in this article.
Abstract: The galvanic corrosion characteristics of detached electrodeposited pure zinc and Zn–Ni alloy coatings have been investigated on coupling with two aerospace aluminium alloys. Zinc alloys containing up to 24 wt-% nickel were coupled with an Al–Cu alloy, 2014–T6, and an Al–Zn–Mg alloy, 7075–T6, under total immersion conditions in quiescent 600mM NaCl solution. It was found that zinc alloys containing 5–14 wt-% nickel corroded preferentially on coupling with the aluminium alloys and reduced the corrosion rates of the aluminium alloys below those found in the uncoupled state. While pure zinc and Zn–Ni alloys containing <5 wt-% nickel also corroded preferentially on coupling with the aluminium alloys, in such cases the aluminium alloys suffered an accelerated rate of corrosion over that found in the uncoupled state as a result of, it is suggested, the formation of strongly alkaline conditions at the aluminium alloy surface. For zinc alloys containing over 14 wt-% nickel, aluminium alloy corrosion was ...
TL;DR: In this paper, the open circuit potentials of six molybdenum containing stainless steels were measured in Arabian Gulf water under conditions simulating operation in multistage flash evaporation distillers.
Abstract: The variation with time of the open circuit potentials of six molybdenum containing stainless steels was measured in Arabian Gulf water under conditions simulating operation in multistage flash evaporation distillers. The effects of temperature in the range 22–70°C and of sea water concentrated by cold evaporation to between 100 and 150% were examined in detail. With all steels, plots of potential as a function of logarithm of immersion time consisted of two straight line segments: the first, characterised by a lower slope, was attributed to the formation of a very thin, barrier type oxide layer, whereas the second related to longer times of immersion, indicating the formation of a thicker film. The mean rates of thickening of both forms of oxide (δ¯1 and δ¯2) were computed according to open circuit transient theory. Depending on the type of steel, δ¯2/δ¯1 varied between 4·6 and 11·0 below 40°0C and 1·1 and 1·6 at 70°C. Curves representing the variation of δ¯1 and δ¯2 with temperature exhibited ma...
TL;DR: In this article, the mechanism of copper-nickel electrodeposition from citrate solutions on steel substrates has been investigated by cyclic voltammetry and potentiostatic polarisation to determine the influence of the Cu/Ni ratio.
Abstract: The mechanism of copper–nickel electrodeposition from citrate solutions on steel substrates has been investigated by cyclic voltammetry and potentiostatic polarisation to determine the influence of the Cu/Ni ratio. The presence of nickel cations makes copper deposition easier by decreasing the nucleation potential of both copper and nickel. Coatings obtained from three solutions with different Cu/Ni ratios were analysed by scanning electron microscopy and energy dispersive X-ray spectrometry to observe the morphology and the copper and nickel contents in the deposit. The structure was analysed by grazing angle X-ray diffraction and the corrosion resistance was studied by impedance measurements.
Abstract: An effective method of minimising the selfcorrosion of commercial grades of aluminium (about 99% purity) in alkaline media typical of those found in batteries, without sacrificing other electrochemical properties, for example high anode efficiency and low anodic polarisation, is discussed. A stable zincate coating has been found to be very useful in reducing selfcorrosion of 26S and 57S grades of aluminium to a negligible level of 0·04–0·08 mg cm−2 min−1, while yielding high anode efficiency in alkaline media.
TL;DR: In this article, the authors show that at a pressure of 2 bar, or in air after thermal charging in high pressure hydrogen, produces only minimal loss in ductility at particular strain rates for as received or solution treated samples of a stable austenitic stainless steel.
Abstract: Straining in hydrogen at a pressure of2 bar, or in air after thermal charging in high pressure hydrogen, produces only minimal loss in ductility at particular strain rates for as received or solution treated samples of a stable austenitic stainless steel. However, cathodically charging at 80°C introduces a significant embrittlement that is associated with theformation during straining of brittle surface cracks whose depth increases with charging time. The latter effect is related to the depth of penetration of hydrogen and the transformation to martensite that is induced by the combined effect of hydrogen and stress. Removal of the hydrogen and the associated α martensite by subsequent vacuum annealing produces recovery of ductility. The application of a sensitising treatment before charging or testing in hydrogen gives results that are not significantly different.
TL;DR: In this paper, the fatigue crack initiation behavior of a 12%Cr turbine blade alloy (403 stainless steel) was studied at a single alternating stress level of 448 MN m−2 in deaerated solutions of NaOH at pH 10,12, and 14 and in 1M Na4SiO4 solution (pH 10) at 100°C.
Abstract: The fatigue crack initiation behaviour of a 12%Cr turbine blade alloy (403 stainless steel) was studied at a single alternating stress level of 448 MN m−2 in deaerated solutions of NaOH at pH 10,12, and 14 and in 1M Na4SiO4 solution (pH 10) at 100°C. Fatigue life in the hydroxide solution increased with increasing pH and was also good in the silicate solution. Long cracks of similar appearance were found to be initiated on the surface of the steel in all the solutions except NaO H at pH 14, in which short incipient microcracks of a transgranular nature initiated on the specimen surface, regardless of the selective attack that occurred at grain and phase boundaries. It was found that increasing the pH of the hydroxide solution and the presence of the silicate anion both cause the initiated cracks to propagate into the bulk of the material in a transgranular mode, thereby resulting in a longer fatigue life.
TL;DR: In this article, the use of the Bio-Rad MRC-600 laser scanning confocal microscope to image aluminium surfaces in various surface conditions, including as rolled and corroded, was described.
Abstract: Scanning confocal light microscopy offers an alternative three-dimensional imaging technique that can allow a fresh view of surfaces. It can image samples that are wet, coated, or porous and cope with highly irregular surfaces for which the desired depth of field is difficult to study by other methods. Its principal attraction is the quantification of surface topography. At Alcan International, confocal microscopy has been examined as an alternative to scanning electron microscopy parallax techniques in the quantitative understanding of surface critical samples. This paper describes the use of the Bio-Rad MRC-600 laser scanning confocal microscope to image aluminium surfaces in various surface conditions, including as rolled and corroded. Two- and three-dimensional images were produced using the control software supplied with the confocal microscope. However, it was easier to process these images to form quantitative projections that were transferred to a Kontron Ibas image analysis system. On the...
TL;DR: In this article, the ultrahigh strength cupronickel alloy Marinel and the nickel alloy Monel K-500 were saturated with gaseous hydrogen at 450°C and their fatigue behaviour was measured and compared with that of hydrogen free material.
Abstract: The ultrahigh strength cupronickel alloy Marinel and the nickel alloy Monel K-500 were saturated with gaseous hydrogen at 450°C and their fatigue behaviour was measured and compared with that of hydrogen free material. The presence of hydrogen was found to reduce thefatigue properties of Monel K-500, but did not affect the performance of Marinel alloy. No evidence of obvious microstructural change induced by hydrogen was apparent, but use of hydrogen diffusivity data was made in calculations relating to the diffusivity and trapping of hydrogen in the two materials. It was demonstrated that the solubility of hydrogen, the degree of dislocation-hydrogen interaction, and the ease of hydrogen trap formation (as a precursor to crack initiation) were lower in Marinel alloy than in Monel K-500, thus contributing to an explanation of the resistance of Marinel alloy to the debilitating effects of hydrogen.
TL;DR: In this paper, atmospheric exposure tests were conducted on copper in the humid, marine environment of the Arabian Gulf, and the results revealed the oxide scale composition to be CU2O and CU4O3.
Abstract: Atmospheric exposure tests were conducted on copper in the humid, marine environment of the Arabian Gulf. The tests included weight loss monitoring, oxide scale analysis by X-ray diffraction, surface morphology examination by SEM, and the detection of possible surface contaminants by energy dispersive X-ray analysis. Results revealed the oxide scale composition to be CU2O and CU4O3. The green patina mainly consisted of CU4SO4(OH)6 CU4SO4(OH)6.H2O, CuSO4.5H2O, and CuCl2.2H2O. Pitting intensity was not severe; the few isolated pits that appeared seem to have been initiated at CU2O film discontinuities and were probably assisted by crevice creating artefacts. The corrosion rate of copper was estimated at 3·4 μm/year.
TL;DR: The effect of a maraging heat treatment on the mechanical properties and corrosion behaviour of a special grade of heat treatable stainless steel has been studied in this paper, where the authors found that the corrosion properties such as strength and hardness of this steel are enhanced after the maraging heating treatment, but its corrosion resistance is reduced as a result of the formation of intermetallic precipitates at the grain boundaries.
Abstract: The effect of a maraging heat treatment on the mechanical properties and corrosion behaviour of a special grade of heat treatable stainless steel has been studied Although the mechanical properties such as strength and hardness of this steel are enhanced after the maraging heat treatment, its corrosion resistance is reduced as a result of the formation of intermetallic precipitates at the grain boundaries In addition, oxide scales are formed on the surface of the specimens after the heat treatment owing to high temperature oxidation and these scales play an important role in the corrosion behaviour of the aged specimens Corrosion studies have been conducted on underaged, peak aged, and overaged specimens with and without oxide scales and on specimens in the solution annealed condition Impedance and potentiostatic anodic polarisation techniques in 3·5%NaCl of pH 1, 4, 7, and 10 at room temperature have been used The corrosion performance order of this maraging steel with oxide scales in acidic
TL;DR: In this article, the reduction of wear loss of steel balls during the wet grinding of hematite ore was achieved by using corrosion inhibitors, the optimum combination of which produced the highest reduction rate.
Abstract: The reduction of wear loss of steel balls during the wet grinding of hematite ore wasachieved by using corrosion inhibitors, the optimum combination of which produced thehighest reduction rate. A binary component system consisting of Na2SiO3.9H2O and NaNO2 was developed and was found to perform well with an average wear reduction of 39% in 30 min grinding. Moreover, its use in the mill produced no adverse effect on grinding rate and pelletising.
TL;DR: In this paper, hot dip galvanized steel, either on its own or used in conjunction with a paint system, has been found to be successful, although many practical difficulties had to be overcome before its success could be firmly established.
Abstract: Deep level gold mining, with its conditions of high humidity, the presence of large quantities of corrosive, chloride containing underground waters and high levels of abrasives, and the need to accommodate men, machinery, and ore handling systems safely and efficiently, presents great challenges to the practising corrosion engineer. In the present harsh economic climate, it is essential that these corrosion problems are effectively solved. One of the most critical areas in a gold mine is the shaft, steelwork in which is exposed to all the corrosive conditions. Any corrosion protection method must satisfy the requirements of long term durability and minimum maintenance. Hot dip galvanised steel, either on its own or used in conjunction with a paint system, has been found to be successful, although many practical difficulties had to be overcome before its success could be firmly established. This method has also been applied to other steel applications, such as materials handling equipment and pipin...