Copper Corrosion Behavior in Simulated Concrete-Pore Solutions
Round 1
Reviewer 1 Report
Thanks to the authors for writing this interesting research paper. Please find below some comment to improve the paper.
Line 18: “EIS impedance values” Please specify which values.
Line 36: “metal in the presence of oxygen diffused at the metal surface.” Please be specific as the presence of oxygen may not be necessary for the corrosion of different metals in the concrete.
Lines 36 to 38: please provide relevant references for these sentences.
Line 39: “According to Halstead’s report [1] copper pipes are used in concrete when there is no contamination with ammonia.” Please more explain the situations/examples where copper has been used in concrete.
Line 43: “copper may have good corrosion resistance in neutral aqueous salt solutions in a wide pH range” please give the values for the pH range
Line 48: “According to Freedman, copper surface should be protected when it comes into contact with concrete mixtures containing high sulphur components, such as ash and fly ash, because they may lower the pH, and promote a relatively acidic environment that is highly corrosive to most metals, including copper [6].” I strongly suggest the authors discuss the influence of Sulphur composition by introducing redox potential rather than pH alteration.
Line 49: “concrete mixtures containing high sulphur components, such as ash and fly ash,” slag as pozzolanic materials is very much famous for high sulphur content, not fly ash.
Line 62: “Difficulties in experimental measurements include the electrode and cell design, the potential drop (IR) in the concrete and its compensation, the development of macro-corrosion cells and the restriction of oxygen diffusion, to mention but a few.” I do not what the authors mean by “to mention but a few.” Please rephrase it.
Line 75: “Despite the use of copper in the construction industry, very little systematic work has been carried out on the behaviour of copper and its alloys in contact with concrete, and their corrosion mechanism in concrete-pore solutions has not yet been clarified.” please give some examples for the wide application of copper in concrete structures.
Line 81: “In structural engineering, the contact of metal and mineral materials (produced with cement) plays an important role from a corrosion-technical point of view.” If you mean interfacial zone, this term is not restricted to structural engineering. Please rectify the sentence.
Line 82: “There are few studies on the corrosion susceptibility of copper exposed to concrete environments, and most of these do not employ electrochemical techniques even though they have the advantage of being practical and fast [33].” Please give more references to match the term “few studies” used in the text.
Lines 104 and 113 :“Table 1 gives the chemical composition of the cement used and that of solution II.” Please give the elemental composition of the extracted solution after filtration in Table 1.
Line 119: “the corrosion products formed were removed from the surface through the cleaning procedure recommended by ASTM G1 standard” please explain the procedure for removal of the corroded layer in the manuscript.
Line 136: “Cyclic Voltammetry was carried with scan rate of 136 25 mV s-1.” Two scan rates were presented in the result section. The scan range of potential in cathodic and anodic directions should also be reported.
Line 173: “Overview XPS spectra acquired from copper surface: (a) full spectrum; (b) and (c) spectrum for Cu2p3 and O1s, respectively.” Please clearly state in the figure title that the measurement is for control sample because the figure title should be independent of the text.
Line 226:” In the case of samples immersed in cement extract (Figure 6b) CuO and CaCO3 were detected, as well as in in solution I.” Please rephrase the sentence.
Line 227;” However, Cu(OH)2 was also detected for both periods of immersion” please rephrase the sentence (what do you mean by both periods of immersion?)
Line 244: “Open circuit potential (o.c.p)” please keep the format of the abbreviation the same as other sections.
Line 314: There is no discussion on the alteration in the CPE values presented in Table 5. Please discuss the CPE values.
Line 315: please provide the chi-squared values for the fitting curves in Table 5. Moreover, please follow the same numbering format for Rcp, Rct, Rp.
Line 391: the authors should explain point 1 of the figure in the text.
Line 394: “It could be noted that with the exception of peak D (reduction of Cu2O to metallic Cu), no other peaks (A, B, C) changed their position. This behaviour indicates that the processes, which correspond to peaks A,B and C, are not completely controlled by diffusion, except for that at peak D [63].”Please explain the criteria that peak D is controlled by diffusion (in addition to the given reference [63]).
Line 410: “The electrochemical tests revealed that the cement extract (solution II) is more aggressive to copper than the sat. Ca(OH)2 (solution I). This difference contibutes to the presence of a variety of ions, as part of the cement, in addition to Ca2+ ions.” I suggest the authors discuss the significance of alkalinity of the solutions to the corrosion behavior of the Cu in calcium hydroxide and cement extract solution. The test results show the pH is the main factor controlling the corrosion behavior of the Cu in the solutions I and II. As mentioned in Line 110 of the manuscript, the pH of calcium hydroxide solution was 12, while the pH of the cement extracted solution was 13. The difference in pH of the solutions is more than one order of magnitude which significantly affects the electrochemical corrosion behavior of Cu in these solutions. Please discuss the influence of different alkalinity of the soliton on the observed electrochemical responses. Please correct the typo “contibutes".
Line 423: “This is another facts, as as consequence of the different aggressivity of both model solution to copper surface.” Similar to the above comment, the test results mostly show the influence of different pH of the solution rather than the effect of different ions.
Author Response
Comments and Suggestions for Authors
Thanks to the authors for writing this interesting research paper. Please find below some comment to improve the paper.
Line 18: “EIS impedance values” Please specify which values.
Res: It was a specified.
Lines 34-35: “metal in the presence of oxygen diffused at the metal surface.” Please be specific as the presence of oxygen may not be necessary for the corrosion of different metals in the concrete.
Res: However, the corrosion could proceed later in the hardened concrete when its pores, capillaries and cavities contain humidity, and dissolved ionic ingredients extracted from the cement are aggressive against metal in the presence of oxygen diffused at the metal surface (except of Aluminum, for example)[1].
Line 37: please provide relevant references for these sentences.
Res: reference [2] was included.
Line 39: “According to Halstead’s report [1] copper pipes are used in concrete when there is no contamination with ammonia.” Please more explain the situations/examples where copper has been used in concrete.
Res: The use of copper in the construction field is fully spread in residential electrical wiring and transport of water, heating, natural gas and refrigeration [4]. On the other hand, it is also used in gutters and downspouts, suspended gutters, vertical walls, crowning of walls, expansion joints for buildings and wall covering [5].
Line 44: “copper may have good corrosion resistance in neutral aqueous salt solutions in a wide pH range” please give the values for the pH range
Res: According to Pourbaix diagrams [6], copper may have good corrosion resistance in aqueous salt solutions in a wide pH range (5 – 12)…
Line 50: “According to Freedman, copper surface should be protected when it comes into contact with concrete mixtures containing high sulphur components, such as ash and fly ash, because they may lower the pH, and promote a relatively acidic environment that is highly corrosive to most metals, including copper [6].” I strongly suggest the authors discuss the influence of Sulphur composition by introducing redox potential rather than pH alteration.
Res: According to Freedman, copper surface should be protected when it comes into contact with concrete mixtures containing high sulphur components, such as slag cement, ash and fly ash, because they may lower the pH, and promote a relatively acidic environment that is highly corrosive to most metals, including copper [9]. Xu, H.C. et al. consider that the copper oxide growth is significantly retarded by the presence of sulfur [10], because the corrosion redox potential in sulphide environments is several hundred millivolts more negative than that required for copper oxide formation [11]. Therefore, this fact suggests that the formation of Cu2S and CuS could occur at values close to the redox potential (corrosion potential, OCP) in cement extract solution.
Line 51: “concrete mixtures containing high sulphur components, such as ash and fly ash, slag as pozzolanic materials is very much famous for high sulphur content, not fly ash.
Res: the word “slag cement” was included.
Line 67: “Difficulties in experimental measurements include the electrode and cell design, the potential drop (IR) in the concrete and its compensation, the development of macro-corrosion cells and the restriction of oxygen diffusion, to mention but a few.” I do not what the authors mean by “to mention but a few.” Please rephrase it.
Res: Reported difficulties in experimental measurements include the electrode and cell design, the potential drop (IR) in the concrete and its compensation, the development of macro-corrosion cells and the restriction of oxygen diffusion [16].
Line 81: “Despite the use of copper in the construction industry, very little systematic work has been carried out on the behaviour of copper and its alloys in contact with concrete, and their corrosion mechanism in concrete-pore solutions has not yet been clarified.” please give some examples for the wide application of copper in concrete structures.
Response is given un line 39: The use of copper in the construction field is fully spread in residential electrical wiring and transport of water, heating, natural gas and refrigeration [4]. On the other hand, it is also used in gutters and downspouts, suspended gutters, vertical walls, crowning of walls, expansion joints for buildings and wall covering [5].
Line 86: “In structural engineering, the contact of metal and mineral materials (produced with cement) plays an important role from a corrosion-technical point of view.” If you mean interfacial zone, this term is not restricted to structural engineering. Please rectify the sentence.
Res: The contact of metal and mineral materials (produced with cement) plays an important role from a corrosion-technical point of view.
Line 87: “There are few studies on the corrosion susceptibility of copper exposed to concrete environments, and most of these do not employ electrochemical techniques even though they have the advantage of being practical and fast [33].” Please give more references to match the term “few studies” used in the text.
Res: There are few studies on the corrosion susceptibility of copper exposed to concrete environments, and most of these do not employ electrochemical techniques even though they have the advantage of being practical and fast [2, 4, 7, 8, 11].
Line 109 :“Table 1 gives the chemical composition of the cement used and that of solution II.” Please give the elemental composition of the extracted solution after filtration in Table 1.
Res: Table 1 gives the chemical composition of the cement used and that of extracted solution II after filtration.
Line 123: “the corrosion products formed were removed from the surface through the cleaning procedure recommended by ASTM G1 standard” please explain the procedure for removal of the corroded layer in the manuscript.
Res: In order to evaluate the damage on the copper surface, the corrosion products formed were removed from the surface of the samples exposed for 720 h, submerged them in a sulfuric acid solution during 2 minutes at 21°C according to the cleaning procedure recommended by ASTM G1 standard [41].
Line 142: “Cyclic Voltammetry was carried with scan rate of 25 mV s-1.” Two scan rates were presented in the result section. The scan range of potential in cathodic and anodic directions should also be reported.
Res: Cyclic Voltammetry was carried with scan range of -1.2 V in cathodic direction and 0.5 V in anodic direction from OCP and with scan rate of 25 mV s-1 and 100 mV s-1.
Line 170: “Overview XPS spectra acquired from copper surface: (a) full spectrum; (b) and (c) spectrum for Cu2p3 and O1s, respectively.” Please clearly state in the figure title that the measurement is for control sample because the figure title should be independent of the text.
Res: Figure 2. Overview XPS spectra acquired from copper control sample surface: (a) full spectrum; (b) and (c) spectrum for Cu2p3 and O1s, respectively.
Line 233:” In the case of samples immersed in cement extract (Figure 6b) CuO and CaCO3 were detected, as well as in in solution I.” Please rephrase the sentence.
Res: In the case of samples immersed in cement extract (Figure 6b), CuO and CaCO3 were also detected.
Line 234;” However, Cu(OH)2 was also detected for both periods of immersion” please rephrase the sentence (what do you mean by both periods of immersion?)
Res: However, Cu(OH)2 was also detected after 720 h of inmersion, and this fact suggests that in solution II (cement extract) the corrosion layer is a mix of two compounds: CuO and Cu(OH)2.
Line 250: “Open circuit potential (o.c.p)” please keep the format of the abbreviation the same as other sections.
Res: 3.2.1. Open circuit potential (OCP).
Line 312: There is no discussion on the alteration in the CPE values presented in Table 5. Please discuss the CPE values.
Res: Magnitude of the exponent n indicates the degree of homogeneity of the surface. The poor homogeneity of the surface is related to some type of pore structure permeating electrolyte, ions and neutral molecules through it [56]. The low Ccp values ( 10-5-10-7 F cm-2 Hz1-ncp) of the copper in both solutions suggest an insignificant contribution of the charge current. At the end of experiment (720 h), the values of ndl (6.3x10-1 - 8.9x10-1, Table 5), for example, indicate that the impedance is not dependent on the presence or absence of redox reactions [56].
Line 328: please provide the chi-squared values for the fitting curves in Table 5. Moreover, please follow the same numbering format for Rcp, Rct, Rp.
Res: In Table 5 chi-squared values for the fitting curves was provided. It was used the same numbering format for Rcp, Rct, Rp.
Line 404 and 415: the authors should explain point 1 of the figure in the text.
Res: In the text of the figures 13 and 14 was added “1 marks the start of scans from open circuit potential”.
Line 407: “It could be noted that with the exception of peak D (reduction of Cu2O to metallic Cu), no other peaks (A, B, C) changed their position. This behaviour indicates that the processes, which correspond to peaks A,B and C, are not completely controlled by diffusion, except for that at peak D [63].”Please explain the criteria that peak D is controlled by diffusion (in addition to the given reference [63]).
Res: It could be noted that with the exception of peak D (reduction of Cu2O to metallic Cu), no other peaks (A, B, C) have a linear dependence between the peak current (ip) and the square root of the scanning speed (v1/2) [68]. This behaviour indicates that the processes, which correspond to peaks A, B and C, are not completely controlled by diffusion because there is a small dependence of the position on scan rate [69]. The peak D is also limited by kinetics, because the peak position is very sensitive to the scan rate, consistent with a process where kinetics is the limiting step.
Line 429: “The electrochemical tests revealed that the cement extract (solution II) is more aggressive to copper than the sat. Ca(OH)2 (solution I). This difference contibutes to the presence of a variety of ions, as part of the cement, in addition to Ca2+ ions.” I suggest the authors discuss the significance of alkalinity of the solutions to the corrosion behavior of the Cu in calcium hydroxide and cement extract solution. The test results show the pH is the main factor controlling the corrosion behavior of the Cu in the solutions I and II. As mentioned in Line 110 of the manuscript, the pH of calcium hydroxide solution was 12, while the pH of the cement extracted solution was 13. The difference in pH of the solutions is more than one order of magnitude which significantly affects the electrochemical corrosion behavior of Cu in these solutions. Please discuss the influence of different alkalinity of the soliton on the observed electrochemical responses. Please correct the typo “contibutes".
Responses:
Line 260: We considerer that the pH difference between the two model solutions is the determing factor in the corrosion potential value and corrosion rate.
Line 417: The results presented in this study indicate that the cement extract solution (pH 13) is more aggressive than that of sat. Ca (OH)2 (pH 12).This difference could be contributed mainly to the lower in one order pH of sat. Ca(OH)2 model solution, as well as to the variety of ions in the cement extract solution.
Line 430: This difference contributes mainly to the lower in one order pH of sat. Ca(OH)2 model solution, than that of cement extract, as well as to the presence of a variety of ions, as part of the cement, in addition to Ca2+ ions.
Line 443: “This is another facts, as as consequence of the different aggressivity of both model solution to copper surface.” Similar to the above comment, the test results mostly show the influence of different pH of the solution rather than the effect of different ions.
Res: This is another facts, as as consequence of the different pH of both model solution to copper surface.
Reviewer 2 Report
The reviewed manuscript addresses the significant problem of interaction of copper elements embedded in concrete. The authors analysed electrochemical reactions occurring on the surface of the copper plate in contact with the solution of synthetic pore liquid and the pore liquid being an extract from cement mortar. In order to assess the problem they used many advanced electrochemical methods and microscopic examinations.
Substantive comments:
1) The scale of the problem was very poorly discussed in the introduction to the article, i.e. in how many cases and in which cases it is necessary to introduce copper elements into concrete.
2) The conclusions only summarize the results of individual studies, while there are no generalisations. Recommendations concerning the necessity or lack of necessity of additional protective coatings, e.g. of plastics on copper tubes introduced into concrete, would be interesting. This would be an analogy to the application of coating protection of steel rebar in concrete by means of epoxy coatings.
Author Response
Comments and Suggestions for Authors
The reviewed manuscript addresses the significant problem of interaction of copper elements embedded in concrete. The authors analysed electrochemical reactions occurring on the surface of the copper plate in contact with the solution of synthetic pore liquid and the pore liquid being an extract from cement mortar. In order to assess the problem they used many advanced electrochemical methods and microscopic examinations.
Substantive comments:
1) The scale of the problem was very poorly discussed in the introduction to the article, i.e. in how many cases and in which cases it is necessary to introduce copper elements into concrete.
Res:
Line 40: The use of copper in the construction field is fully spread in residential electrical wiring and transport of water, heating, natural gas and refrigeration [4]. On the other hand, it is also used in gutters and downspouts, suspended gutters, vertical walls, crowning of walls, expansion joints for buildings and wall covering [5].
2) The conclusions only summarize the results of individual studies, while there are no generalisations. Recommendations concerning the necessity or lack of necessity of additional protective coatings, e.g. of plastics on copper tubes introduced into concrete, would be interesting. This would be an analogy to the application of coating protection of steel rebar in concrete by means of epoxy coatings.
Res: The application of coating protection of steel rebar in concrete was not a subject of this study. For this reason, it was not included.
Reviewer 3 Report
Reviewers' comments:
Manuscript ID: materials-755148
Title: Copper corrosion behaviour in simulated concrete-pore solutions
Manuscript Type: Article
Reviewers' comments:
The manuscript describes the Copper corrosion behaviour in simulated concrete-pore solutions. The manuscript needs a detailed editing. Some markings are made to just illustrate the extent of editing needed. A thorough revision addressing all the concerns is needed and if the authors are prepared to do that it can be considered for a review of the revised manuscript.
The authors need to consider the following comments
- In the Abstract, the authors need to improve.
- The experimental section should be detailed especially for the “Immersion tests and surface characterization”.
- Give the EDS spectrum.
- Give the phase angle.
- In the conclusions, the authors need to improve with more specific short results and conclusions.
- References: there are recent references in 2018, 2019 and 2020 treating the same subject, you can use. And make all references in same format for volume number, page number and journal name, because it is difficult to searching and reading.
- Furthermore, they should add the graphical abstract, it is use full to readers.
So that I recommended this manuscript to major revision and for future process.
Author Response
Reviewers' comments:
The manuscript describes the Copper corrosion behaviour in simulated concrete-pore solutions. The manuscript needs a detailed editing. Some markings are made to just illustrate the extent of editing needed. A thorough revision addressing all the concerns is needed and if the authors are prepared to do that it can be considered for a review of the revised manuscript.
The authors need to consider the following comments
- In the Abstract, the authors need to improve.
Res: The abstract was improved.
- The experimental section should be detailed especially for the “Immersion tests and surface characterization”.
Res: The details of the immersion tests and surface characterization were included.
- Give the EDS spectrum.
Res: The EDS spectrum were added. However, the Editor of this manuscript will have the final decision (to be included or not).
- Give the phase angle.
Res: The phase angle plots were added in the Figure 9.
- In the conclusions, the authors need to improve with more specific short results and conclusions.
Res: we considerer that the conclusions presented in revision are more specific.
- References: there are recent references in 2018, 2019 and 2020 treating the same subject, you can use. And make all references in same format for volume number, page number and journal name, because it is difficult to searching and reading.
Res: several new references were included:
[1] Emregül, K.C.; Aksüt, A.A. The behavior of aluminum in alkaline media. Corros. Sci. 2000, 42, 2051-2067. https://doi.org/10.1016/S0010-938X(00)00055-X
[5] Freire, F. Edificio automatizado de oficinas: uso del cobre en la Arquitectura. Universidad Peruana de Ciencias Aplicadas: Lima, Perú, 2001.
[10] Xu, H.C., Seshadri, G. Kelber, J.A. Effect of Sulfur on the Oxidation of Copper in Aqueous Solution. J. Electrochem. Soc. 2000, 147, 558-561. http://doi.org/10.1149/1.1393232
[52] Nishikata, A.; Ichihara, Y.; Tsuru, T. An application of electrochemical impedance spectroscopy to atmospheric corrosion study. Corros. Sci. 1995, 37, 897-911.
[56] Naseer, A.; Khan, A.Y. (2009). A study of growth and breakdown of passive film on copper surface by electrochemical impedance spectroscopy. Turk. J. Chem. 2009, 33, 739-750. http://doi.org/10.3906/kim-0708-23
[68] Thomas, D.; Rasheed, Z.; Jagan, J.S.; Kumar, K.G. Study of kinetic parameters and development of a voltammetric sensor for the determination of butylated hydroxyanisole (BHA) in oil samples. J. Food Sci. Technol. 2015, 52, 6719-6726. https://dx.doi.org/10.1007%2Fs13197-015-1796-1
- Furthermore, they should add the graphical abstract, it is use full to readers.
Res: previously the graphical abstract was submitted.
So that I recommended this manuscript to major revision and for future process.
Round 2
Reviewer 1 Report
Thanks to the authors for improving the paper.
There is still one main concern in Line 117 of the paper that should be corrected before acceptance, as below:
Line 117: “Composition of cement according to the producer and chemical analysis of the cement extract solution.”
As commented before, the composition of the cement extract solution was not given in Table 1. The table just presents the composition of Portland cement, not cement extract solution. There is no value for the concentration of ions in the cement extract solution.
Note: As can be found in the textbooks/handbooks, the composition of cement extract solution is significantly different from the composition of Portland cement (e.g. Type I). The ions in the cement extract solution are OH, K, Na, S, Si, Al, Ca, etc. with the concentration significantly different from those in the Portland cement.
The Authors must give the concentration of main ions in cement extract solution (at least potassium and sodium in addition to hydroxide ions) or remove the cement extract composition from Table 1.
Line 108: please specify the producer of Portland cement type I used in this study.
Author Response
Response:
We propose to include in Table 1 the composition of the cement reported by the autors in reference [40] and the filtered cement extract ion composition, because they are very similar to the cement used in our study. They have had the possibility to measure ions more precisely using ion chromatography (IC).
[40] Wang, L.; Zhan, S.; Tang, X.; Xiu, Q.; Qian, K. Pore Solution Chemistry of Calcium Sulfoaluminate Cement and Its Effects on Steel Passivation Appl. Sci. 2019, 9, 1092.
In the line 108 was introduced the producer of used cement in our study: CEMEX (CEMEX, S.A.B. de C.V. San Pedro Garza García, N.L., México).
Reviewer 3 Report
The authors revised the manuscript according to the reviewers' comments.
Author Response
Thank you very much for the acceptation of our comments.
Round 3
Reviewer 1 Report
The paper is accepted in the present format.
