compounds were tested on carbon steel SAE1018 immersed in a solution like. NACE TM 0177 without and with H2S. Evaluation of the compounds was carried.
Jul 26, 2014 - Structure Under Simulated Field Service Environment. L. Shi, J. Ye ... To guide the scientific applications of organic corrosion inhibitors, China is carrying .... carbon steel were used in this study. ..... reinforcement rust efficien
Passivating inhibitors cause a large anodic shift of the corrosion poten- tial, forcing the metallic surface into the ... such as phosphate, tungstate, and molybdate, that require the presence of oxygen to passivate steel. .... in metal-cleaning proc
Corrosion is controlled by anodic (passivating) inhibitors including nitrate and chromate as well as by cathodic (e.g., zinc salt) inhibitors. Organic inhibitors (e.g., benzotriazole) are sometimes used as secondary inhibitors, especially when excess
Natalya V. Likhanova. Additional information is available at the end of the chapter http://dx.doi.org/10.5772/57252. 1. Introduction. In most industries whose facilities are constituted by metallic structures, the phenomenon of corrosion is invariabl
ability to form a thin, passivating film directly on the anodic portion of metal. Besides chromates and phosphates (or their combina- tions) silicates, nitrites and .... diethylamine, acridine, acriflavin, etc. These materials are used for combating
Dec 8, 2017 - School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, UK. Received: 20 November ... discovery of new, benign organic compounds to fill that role. ..... QSAR/QSPR as an application of artificial neural networks.
Jan 25, 2012 - and corrosion inhibitors (organic and inorganic additives). ... Pitting is a highly localized type of corrosion in the presence of aggressive chloride ...
Oil well stimulation, usually done with hot solutions of hydrochloric acid, may induce ... The total annual cost of corrosion in the oil and gas production industry is ...
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facility can be catastrophic if proper methods of prevention are not utilized. ..... High-temperature corrosion on carburized steels that forms a porous scale of.
the performance of carbon dioxide corrosion inhibitors for oilfield pipelines in the West .... corrosion. The corrosion rate increased nearly 7-fold for both types of ...
Nov 20, 2007 - dependent on the structure and chemical properties of the species formed under the specific ... The synthesized triazo phosphonates are used as inhibitors ..... serves as the basis for all modern corrosion inhibitor formulations.
... 4% of the GDP. Corrosion not only has economic implications, but also social and these engage the safety and ...... synthesized under microwave irradiation and evaluated as CIs for acid environment. Weight loss and .... alcohols isolated from sug
Introduction. Acid treatments have been applied to wells in oil and gas bearing rock formations for many years. Acidizing is probably the most widely used work-over and stimulation practice in the oil industry. By dissolving acid soluble components w
organic and inorganic corrosion inhibitors to the environment has provoked the search .... Polarization studies indicated that inhibitors are acted as mixed type.
and 85% corrosion inhibition efficiency (CIE) respectively while the other salts gave less than 40% ..... 93-97, 2005.  V. P. Persiantsava, (1987) âChemistry ...
Apr 21, 1982 - 'A multifunctional corrosion inhibitor consisting essen-. 18, 19; 106/14.12, ..... concentration upon the breakdown of passivity of type face active ...
Dec 1, 2017 - Figure 3a,b show much less corrosion product, but still show some local attack on the sample in the inhibitor .... Schematic summary of synthesis of thermosensitive ionic microgels via quaternized. Figure 6. ..... are those which are fr
Feb 25, 2013 - Most well-known acid inhibitors for steel corrosion are ... where, Icorr.add and Icorr.free are the corrosion rates in free and inhibited acid, ...
Aug 11, 2018 - Three organic environmentally friendly corrosion inhibitors were ..... metal, acting as a mixed type inhibitor by absorbing onto the metal surface ...
Jun 15, 1988 - phthalocyanines as corrosion inhibiting coatings - poyeriz by .... inhibitors of the phthalocyanine type show promise in a number of forms.
ORGANIC CORROSION INHIBITORS; HOW DO THEY INHIBIT AND CAN THEY REALLY MIGRATE THROUGH CONCRETE? A. Phanasgaonkar,* B. Cherry and M. Forsyth,* Department of Materials Engineering and Australian Maritime Engineering Cooperative Research Centre, Monash University SUMMARY: This work discusses the electrochemical and diffusion properties of several organic amine based inhibitors, with potential remedial applications for concrete in marine environments, in an attempt to develop an understanding of the nature of the inhibition, the level of the inhibition in contrast to typical inorganic inhibitors and the ability of these chemicals to migrate through concrete. The electrochemical measurements, performed in simulated concrete pore water solution, indicate that dicyclohexylamine nitrite and commercially available MCI inhibitor give excellent inhibition for extended periods, whereas dimethylethanolamine gives only moderate and apparently short term protection for steel. In contrast to the organic inhibitors, sodium nitrite behaves as a typical anodic inhibitor, with the corrosion rate being accelerated at lower concentrations. Dicyclohexylamine nitrite also shows evidence of anodic behavior, however the organic component of dicyclohexylamine nitrite provides some corrosion protection even at lower concentrations. If these organic inhibitors are to be used in remedial applications, their significant diffusion through concrete is necessary. It appears that dimethylethanolamine migrates rapidly through concrete, whereas the other species are significantly slower. This will be discussed in greater detail. Keywords: organic inhibitors, inorganic inhibitor, simulated concrete, polarization resistance, corrosion inhibition, organic amines, marine environment, diffusion, migration 1. INTRODUCTION Corrosion inhibitor admixtures have been in use for some time to extend the life of concrete infrastructures. The most common amongst these are the inhibitors based on inorganic nitrites (1-4). These inhibitors generally provide protection by an interfacial process, that is they reinforce the protective film of ferric oxide around the steel by oxidizing ferrous ions (4). In recent years inhibitors based on organic amines have become available with the claimed advantage that, as well as being capable of application as admixtures, they may be applied as remedial agents to the surface of the concrete. It is proposed that these inhibitors, when applied to the surface of an already corroding structure, can diffuse through concrete (5) and once they reach the steel, they form a protective barrier over the metal surface inhibiting further corrosion (6). They can also be used in admixture applications and the amounts required to achieve the desired ctp52.doc
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inhibition are claimed to be lower than inorganic inhibitors (6). There is however, little published work on the mechanisms of the inhibition, the long-term performance of the inhibitors or the effect of their concentration on the level of inhibition.
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The present paper compares the inhibitive action of four systems, an inorganic oxidizing inhibitor, sodium nitrite having nitrite as the main corrosion inhibiting component; a simple organic amine, dimethylethanolamine; a quaternary amine nitrite, dicyclohexylamine nitrite, which may combine the effects of both organic amines and an inorganic oxidizing anion; and an aromatic amine based commercial migratory inhibitor labeled MCI. In particular, the influence of these inhibitors on a prepassivated steel surface, representing the state of the steel in a newly built structure (admixture situation), and a corroding steel surface as would be found in the case of an existing corroding structure (remedial situation), is investigated. The possibility of a synergistic effect of the mechanism of barrier film formation by organic amines and interfacial chemical reactions by inorganic inhibitors will be investigated. Attempts are made to correlate inhibition capacity to the ratio of chloride: nitrite in the case of the nitrite based inhibitors. Since (in the remedial situation at least) the capacity of the inhibitors to perform their function depends upon their rate of migration through concrete, this aspect of their performance will also be examined. In this case the physico-chemical properties of the inhibitors and the permeability of concrete play an important role. These inhibitors may also be called upon to act in concert with cathodic protection. Since, in water, some of these inhibitors are ionic in character, the possibility of a conjoint action of cathodic protection with inhibitors, will be examined. Indeed, in the remedial situation, where an inhibitor is required to reach the steel - concrete interface by migrating through concrete to control further corrosion driven deterioration, this may be the only way in which an appropriate quantity of the inhibitor can be applied at the steel surface in a short time frame. 2. EXPERIMENTAL METHODS 2.1 Linear Polarization Resistance (LPR) Measurements Experiments were carried out in a simulated concrete pore water solution of saturated calcium hydroxide. Fixed concentrations of inhibitors and of corroding chloride ion (chosen to mimic a marine contaminated environment) were used. The chloride concentration of the simulated pore water solution was 1.2% wt. and the concentration of the inhibitors was 0.05 M in the case of both organic and inorganic inhibitors and 1% wt. in the case of the commercial inhibitor MCI. Corrosion rates were estimated using the linear polarization resistance technique, assuming a linear relationship between the corrosion rate and the reciprocal of the polarization resistance icorr = B/Rp, where B is a constant. The inhibitive capacity of each inhibitor is reported as the “% inhibition.” This is the difference in corrosion rates between specimens immersed in inhibited and non inhibited solutions expressed as a percentage of the corrosion rate in the uninhibited solution (or a control solution). Details of the experimental procedure have already been reported (7).
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2.2 Diffusion measurements
Organic amine inhibitors can diffuse through concrete in a gaseous phase besides diffusing as dissolved species in a carrier solvent or water. Laboratory diffusion cells have been developed to measure the diffusion/migration of these inhibitors (Figure I). The diffusion cells have two compartments separated by a concrete membrane. This design allows variability in the type of concrete membrane, i.e., water/cement ratio, aggregate type, membrane thickness etc. Two different water/cement ratios, 0.45 and 0.6, and membrane thickness, 30 mm were used. Compartment A contains an aqueous inhibitor solution and compartment B contains water. The amount of inhibitor diffusing from compartment A to B through the concrete membrane is monitored using an amine sensitive ORION 95-12 electrode(8). The specific amine sensitive electrode uses a hydrophobic gas permeable membrane to separate the sample solution from the electrode internal solution (0.1 M NH4Cl). Dissolved amine in the sample diffuses through the membrane until the partial pressure of the amine is the same on both sides of the membrane. In any given sample the partial pressure of amine is proportional to its concentration and this is related to potential, E via the Nernst equation. The potentials are measured for various known concentrations of a given inhibitor solution and a calibration curve is thus obtained. This curve is used to measure inhibitor concentrations in compartment B of the above cell. 2.3 Electromigration The main consideration in this case is that the organic inhibitor molecule should have a charged component such as a quaternary ammonium ion (R2NH2) in aqueous solution. Such positively charged amine species can be driven to the negatively charged cathode by the application of an electric field, thus enhancing their rate of diffusion. The objective of these studies is to optimize electrical conditions required for successful inhibitor injection. The effect of electric field strength and application time is being investigated and preliminary results will be discussed in the presentation.
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3. RESULTS AND DISCUSSION 3.1 Inhibition Mechanism and Capacity Figures IIA and IIB present the % inhibition as a function of time under “admixture” and “remedial” situations respectively. Under admixture conditions, dicyclohexylamine nitrite and the commercial inhibitor MCI maintained a high level of inhibition up to the end of the test period, whereas the dimethylethanolamine although demonstrating a high initial level of inhibition, exhibited a steady decrease throughout the exposure time; sodium nitrite showed a sudden fall off from its initially high value after about 70 hours exposure. Under remedial conditions, where the steel coupons were initially exposed to the unhindered attack of chloride ions for a certain time, on addition of the inhibitor to the corroding system, a dramatic reversal of the corrosion trend was observed in all the cases. With the exception of the commercial MCI all the inhibitors showed a declining capacity with time. Of the others only the dicyclohexylamine nitrite showed appreciable inhibition capacity after 100 hours. The steady loss in the corrosion mitigation capacity of the inhibitors, observed at longer times in these experiments, is thought to be a crucial factor in determining the long term suitability of a particular inhibitor system. It is postulated that inhibition stems from the active competition between aggressive Clion attack on the protective film and the restoration of this film by fresh inhibitor molecules from the surrounding environment. Anodic inhibitors are assumed to repair the oxide film or adsorb on the bare metal surface exposed by defects in the passive film whilst cathodic inhibitors adsorb on to the passive film thus hindering the cathodic reaction. On this basis the long term trend observed for the different inhibition systems, including the steadily decreasing inhibition in most cases, can be rationalized as follows: like all adsorbed species, the chemisorbed amine molecules have a characteristic residence time at the metal surface. This residence time depends on the balance between the strength of the bond between the nitrogen and the iron ions at the steel surface and the solvating effect of the surrounding electrolyte. In a non aggressive situation, these effects balance and a high level of inhibition is observed. However, in the presence of chloride ions, the site vacated by the inhibitor molecule is equally open for the adsorption of a fresh inhibitor molecule or a chloride ion. The heat of adsorption of the chloride ions on iron has been calculated to be 45 kcal/mole, which is close to the energy of the metalamine bond (9). Hence, it is possible that chloride adsorption at vacated sites occurs in competition with inhibitor adsorption and leads to a depolarization of the anodic reaction and an increase in the rate of corrosion. The exact role played by the inhibitor barrier film formed by the secondary adsorption of the inhibitor molecules over primarily chemisorbed inhibitor molecules needs to be precisely defined in this delicately balanced situation. A comparison of the time dependence of Ecorr (Figure III) in the remedial situation may help in understanding the mode of action of the inhibitors. The initial slow fall in the corrosion potential in all the cases corresponds to the breaking of the passive oxide film in the absence of an added inhibitor. Sodium nitrite is an anodic inhibitor. The marked rise in the corrosion potential and the corresponding increase in inhibitor action may represent ctp52.doc
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the building up of the passive film followed by its subsequent rupture as the available nitrite is used up. In the case of dimethylethanolamine there is a continuous fall in the corrosion potential as the inhibitor efficiency increases, in this is consistent with a predominantly cathodic inhibition process. A possible explanation of the decrease with time of inhibition by the dimethylethanolamine is that the inhibitor is absorbed at bare metal sites, produced by the action of chloride ions on the passive film and the decrease in the inhibitor efficiency corresponds to the complete use of the available inhibitor leading to insufficient inhibitor molecules to “block” new bare metal sites. It should be noted that this mechanism is in some conflict with the trend in the Ecorr values. This is yet to be resolved. Figure IIA- % Inhibition (Admixture) Dicyclohexylamine Nitrite, Dimethylethanolamine, MCI and Sodium Nitrite
Figure III Ecorr vs. SCE (Remedial) Dicyclohexylamine Nitrite, Dimethylethanolamine, MCI and Sodium Nitrite
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Evidence that the chloride attack is responsible for the steady decline of the inhibition with time was obtained by removing coupons that had reached maximum protection during a “remedial” experiment, and placing them into a chloride free environment with and without added inhibitor. In these cases the % inhibition was maintained for at least 700 hours. The behavior of dicyclohexylamine nitrite under “remedial” conditions is complex. Ionization and subsequent hydrolysis (10) will yield NO2 - anions and (R2NH2) + cations and R2NH2OH where R = C6H11. The inhibitor is thus assumed to be both anodic and cathodic. The nitrite anion itself is an anodic inhibitor and hence reacts chemically to assist in repairing the oxide film at bare anodic sites. This can be evidenced by the increase in the Ecorr values on addition of the inhibitor to the corroding steel. Adsorption of the amine component of the inhibitor molecule over the bare metal or oxyhydroxy sites may result in the formation of barrier film. This adsorption of the inhibitor appears fairly rapid as seen from the rise in the % inhibition upon addition of inhibitor. In addition, the cooperative adsorption (7,9,11) of the protonated (R 2NH2)+ groups over the chloride covered sites on the steel surface may result in the stabilization of the inhibitor barrier film and hence a many fold increase in the inhibition level, compared with the other inhibitors. The corrosion potential of coupons exposed to the commercial MCI inhibitor showed a more or less continuous decrease, suggesting that it is acting primarily as a cathodic inhibitor. It differs from the other cathodic inhibitors in that the level of inhibition, once attained is maintained for the duration of the experiment. In the absence of the full knowledge of components of MCI a rationalization of this behavior may be proposed on the basis of the better adsorptive capacity of this inhibitor resulting in a barrier film difficult to break or penetrate by the corrosive chloride ions. Figure IV is concerned with the admixture situation and compares plots of inhibition levels with time for varying concentrations of sodium nitrite and dicyclohexylamine nitrite. The negative inhibition observed in the case of low concentration (0.01M) of sodium nitrite is characteristic of an anodic inhibitor. It appears, for both of the inhibitors, that an increase in the concentration results in a corresponding increase in the inhibition. Sodium nitrite, although showing negative inhibition values at 0.01 M concentration (chloride: nitrite ratio 26.4), improved to the inhibition levels exhibited by dicyclohexylamine nitrite, as the inhibitor concentration level increased to 0.1 M (chloride: nitrite ratio of 2.6). This is in accordance with Berke and Rosenberg (12), who ctp52.doc
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recommend a ratio of chloride to nitrite to be less than 2 in the case of calcium nitrite, for any meaningful inhibition to be obtained. 3.2 Inhibitor Migration In the simulated concrete solution, the concentration of the organic inhibitor at the steelsolution interface is the same as that in the test cell, whereas in reinforced concrete, in the remedial situation, inhibitor concentration at the metal surface is lower than that at the point of inhibitor application. The build up of inhibitor at the rebar will depend on the diffusion rate of the inhibitor from the surrounding areas. Hence a further aim of this work is the determination of the rate of diffusion of the organic amine inhibitors through concrete. This has been achieved by designing a series of “two compartment cells” (5,13) as shown in Figure 1. Diffusion of dicyclohexylamine nitrite, dimethylethanolamine and commercial inhibitor MCI (based on an aromatic amine compound) through 30 mm thick concrete membranes having 0.45 and 0.60 water/cement ratio, is being monitored. Figure V shows the inhibitor, which has migrated through the concrete membrane with water/cement ratio of 0.6, as a percentage of the original concentration in compartment A. In this case, the high permeability of the concrete clearly allows the slow but steady diffusion of the commercial inhibitor MCI; dicyclohexylamine nitrite, however diffuses only to a limited extent. In the case of dimethylethanolamine, though there is an increase in the diffusion up to 1% initially, at longer times, there is a decrease in the concentration. This is unexpected and may be due to either volatilization of the inhibitor from compartment B or physical absorption onto surfaces, which would decrease the “free” amine content. Preliminary experiments using concrete with water/cement ration of 0.45 suggest neither MCI nor dicyclohexylamine nitrite diffuses significantly through this less permeable concrete. On the other hand, dimethylethanolamine shows better diffusion after only 10 days. The insignificant diffusion in the case of dicyclohexylamine nitrite could be attributed to its low solubility in water and comparatively low vapor pressure (14). Figure IV - Comparison of Different Concentrations of Dicyclohexylamine Nitrite and Sodium Nitrite
Figure V - Diffusion through 30 mm Concrete Membrane with Water/Cement Ratio = 0.6
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These early results suggest that the inhibitor diffusion through concrete depend both on the concrete composition/permeability and the physical and chemical properties of the inhibitors. The degree of permeability of concrete is dependent on water/cement ratio, degree of microcracking and thickness of the cover (15). Higher water/cement ratio apparently leads to either a greater number of pores or to larger pores, both of which can lead to increased permeability. High water/cement ratio results in a more rapid migration of inhibitor. The vapor pressure and the solubility of the inhibitor in water are the other two factors determining the transport of these surface applied migratory inhibitors through concrete. A high vapor pressure may, however, result in both faster migration of the inhibitor through concrete towards steel reinforcement and also heavy losses to the atmosphere. Similarly, high solubility of the inhibitor in water might lead to leaching out of the inhibitor. Further, the higher the vapor pressure or solubility is likely to reduce the residence time of the inhibitor molecules in the barrier film formed over the steel surface, thereby adversely affecting the long term inhibition properties. A detailed investigation of all these factors is necessary in order to predict the success rate of migratory inhibitors. Given that most of the amine inhibitors under investigation will be protonated, and therefore positively charged, in aqueous solution, one method to enhance migration of the inhibitors towards steel may be to use electromigration (16). This technique has certainly been used successfully in dechlorination of concrete (17). Work in our laboratories is underway to investigate the synergy between cathodic protection and chemical inhibition. Preliminary experiments have begun based on the diffusion cell described above (Figure I). The effect of electric field strength and application time is being investigated. 4. CONCLUSIONS The results indicate that organic aromatic amine based inhibitors, dicyclohexylamine nitrite and commercial MCI, offer excellent inhibition for longer times in contrast to the inorganic anodic inhibitor sodium nitrite. It is also shown that the effectiveness of these inhibitors is dependent on the relative concentrations of chloride and inhibitor species and the corrosion state of the steel at the time of the treatment. In the case of a quaternary amine inhibitor dicyclohexylamine nitrite, a very high efficiency is observed for extended periods due to the synergistic effect of the mechanism of barrier film formation by organic amines and interfacial chemical reactions by inorganic inhibitors. Preliminary results of the diffusion measurements in the case of concrete with high water/cement ratio indicate that there is a rapid initial diffusion of dimethylethanolamine, and a slow but ctp52.doc
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steady diffusion of commercial MCI. Dicyclohexylamine nitrite diffusion, however, is limited. 5. ACKNOWLEDGMENTS The authors wish to acknowledge Australian Maritime Engineering Cooperative Research Centre for their financial support and Remedial Engineering for their professional support. 6. REFERENCES 1.
M. Rosenberg, J. M. Gaidis, T.G. Kossivas and R. W. Previte, Chloride Corrosion of Steel in Concrete, ASTM Special Technical Publication No 629, pp. 89-99 (1977).
S. Berke, D. W. Pfeifer and T. G. Weil, Concrete International, 10, No 12, pp. 45-55, December (1998).
S. Berke, Concrete International, 13, No 7, pp. 24-27, July (1991).
M. Rosenberg and J. M. Gaidis, Materials Performance, 18, No 11, pp. 45-48, November (1979)
Bjegovic, L. Sipos, V. Ukrainczyk and B. Miksic, Corrosion and Corrosion Protection of Steel in Concrete, vol. 2, ed. Narayan Swamy, pp. 865-877, September 1993).
K. Nmai, S. A. Farrington, and G. S. Bobrowski, Concrete International, 14, No 4, pp. 45-51, April (1992).
Phanasgaonkar, M. Forsyth and B. Cherry, Proceedings of the 13th International Corrosion Conference, paper 178, Melbourne, pp. 963-970, November (1996).
Manual Instruction for Orion Ammonium Electrode Model 95-12.
McCafferty, Corrosion Control by Coatings, Ed. H. Leidheiser, Pennsylvania, pp. 279-317, November (1978).
10. B. A. Miksic, Corrosion 83, California, pp. 308/1-308/14, April (1983). 11. Hackerman, E. S. Snavely Jr., and J. S. Payne Jr., Journal of Electrochemical Society, 113, No. 7, pp. 677-681, July (1966). 12. S. Berke and A. Rosenberg, “Technical Review of Calcium Nitrite Corrosion Inhibitors in Concrete,” Transportation Research Record No. 1211, pp. 18-27 (1991). 13. L. Page, N. R. Short and A. El Tarras, Cem. Conc. Res., 11, p. 396 (1981). 14. United States Patent, No. 4275, 835, Inventor - B. A. Miksic, USA, Issued on June 30 (1981). 15. K. Mehta, Elsevier Science Publisher Limited, pp. 29-58 (1991). ctp52.doc
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16. Hettiarachchi and A. T. Gaynor, Materials Performance, 31, No 3, pp. 62-66, March (1992).