Effect of the Atmosphere on the Properties of Aluminum Anodizing

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Unfortunately, the work entitled "Effect of the Atmosphere on the Properties of Aluminum Anodizing” cannot be suitable not only for consideration in Coatings, but also is not ready for review. Two main points can be made:

1. Firstly, methodically and intellectually, the purpose of the work is not clear. Namely, the authors should consider for themselves the essence of the anodizing process itself and understand how the formation and growth of an oxide film occurs on an aluminum sample under the electrochemical effect. And this is not due to the equation on Line 34! Then, perhaps, an answer will be given about the suitability of "injection" (bubbling?) oxygen or air (?). What was meant by the term "air", atmospheric composition (21% oxygen), N₂, or possibly completely indifferent gas, argon (which is usually used in a wide range of the electrochemical researches). And what was this done for, to increase the growth of the film (?) or for corrosion?
2. Secondly, now the manuscript has not been read, spelling by the authors and is not ready for submission. Untranslated words, undisclosed abbreviations, non-subscript characters, different fonts, not specified SI units of measurement, and generally not specified, not according to MDPI standards, given figures, duplication of data in tables and figures, etc., etc. Although we must pay tribute to the manuscript is written in an easy language.

Thus, a lot of work and time may be required for the authors, although in my humble opinion, the first obstacle is unlikely to be overcome.

Author Response

For research article

 

Response to Reviewer X Comments

Point-by-point response to Comments and Suggestions for Authors 1

Comments 1:

 

Unfortunately, the work entitled "Effect of the Atmosphere on the Properties of Aluminum Anodizing” cannot be suitable not only for consideration in Coatings, but also is not ready for review. Two main points can be made:

 

Firstly, methodically and intellectually, the purpose of the work is not clear. Namely, the authors should consider for themselves the essence of the anodizing process itself and understand how the formation and growth of an oxide film occurs on an aluminum sample under the electrochemical effect. And this is not due to the equation on Line 34! Then, perhaps, an answer will be given about the suitability of "injection" (bubbling?) oxygen or air (?). What was meant by the term "air", atmospheric composition (21% oxygen), N₂, or possibly completely indifferent gas, argon (which is usually used in a wide range of the electrochemical researches). And what was this done for, to increase the growth of the film (?) or for corrosion?

Response 1:

Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

The oxidation of aluminum at the aluminum/oxide interface generates the Al³⁺ cations, while O²⁻ or OH⁻ anions form at the oxide/solution interface by the stripping of H⁺ from H₂O molecules. O²⁻ and OH⁻ anions migrate through the film towards the oxide/metal interface. Once there, they react with Al³⁺ cations resulting in oxide formation. Some of the available Al³⁺ cations are not consumed at the oxide/metal interface and they migrate towards the electrolyte. At the oxide/electrolyte interface, additional alumina can be formed by the reaction of the Al³⁺ cations that have migrated from the oxide/metal interface with available O²⁻ anions. Under certain conditions (that will be discussed later on) the Al³⁺ cations are ejected into the electrolyte.[1]

 Equation (1a)

 Equation (1b)

 Equation (1c)

 Equation (1d)

Line 34, page 1, paragraph 2.

 

[The composition of the air (21.79%) was maintained using a filter train that allowed for humidity-free air. Air bubbling was done through a compressor, and the air was drawn from the ambient compressor; This is being used to evaluate the corrosion behavior of the anodized material in different atmosphere] Line 34, page 1, paragraph 2.

 

 

Comments 2: Secondly, now the manuscript has not been read, spelling by the authors and is not ready for submission. Untranslated words, undisclosed abbreviations, non-subscript characters, different fonts, not specified SI units of measurement, and generally not specified, not according to MDPI standards, given figures, duplication of data in tables and figures, etc., etc. Although we must pay tribute to the manuscript is written in an easy language.

Response 2:

Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[These data need to be reused as part of the experimental design; Review of the format throughout the text, compliant with MDPI standards.] All text.

 

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors study a variety of factors that affect oxide formation on aluminum to determine optimum conditions for corrosion resistant anodized aluminum. They present a logical experimental design and provide sufficient experimental detail. 

1.       The authors mention the use of Tescan mira LMU for compositional analysis, but not the technique. Please include the analytical technique (EDS?) used.

2.       On page 2, the authors refer to figure 1a, but there is no “a” in figure 1. Please include units in Figure 1 as well.

3.       How was the composition given in Table 1 determined?

4.       In table 5, the composition is presumably determined by EDX? If this is the case, EDX is not sufficiently quantitative to give composition to two decimal places. I recommend using a secondary quantification technique to confirm the composition with more precision. However, EDX is good for mapping element location. Was this done for the cross sections? EDX mapping of the oxide vs the bulk Al in each cross section would strengthen the assignment of the oxidized layer.

5.       The graphs in figure 5 are very small and hard to read.

6.       Please define MPY in table 6.

Author Response

Point-by-point response to Comments and Suggestions for Authors 2

Comments 1: The authors mention the use of Tescan mira LMU for compositional analysis, but not the technique. Please include the analytical technique (EDS?) used.

Response 1: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

 It was performed by Energy Dispersive Spectroscopy (EDS). Line 144, page 4, paragraph 10.

 

Comments 2: On page 2, the authors refer to figure 1a, but there is no “a” in figure 1. Please include units in Figure 1 as well.

Response 2: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[The 'a' was removed from Figure 1 and the units 'cm' were added in the footer] Line 79 y 81, page 2, paragraph 6.

 

Comments 3: How was the composition given in Table 1 determined?

Response 3: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[Chemical analysis was performed by optical emission spectroscopy]. Line 79 , page 2, paragraph 6.

 

 

Comments 4: In table 5, the composition is presumably determined by EDX? If this is the case, EDX is not sufficiently quantitative to give composition to two decimal places. I recommend using a secondary quantification technique to confirm the composition with more precision. However, EDX is good for mapping element location. Was this done for the cross sections? EDX mapping of the oxide vs the bulk Al in each cross section would strengthen the assignment of the oxidized layer.

Response 4: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[EDS is a semiquantitative analysis, showing an approach of chemical composition of the alumina films. But due to the sensitive of the data and its uses in a parallel study that is conducted in terms of structure and composition of these thin films we can not provide full information that indicates variations in composition, Line 208, page 8, paragraph 17.

 

Comments 5: The graphs in figure 5 are very small and hard to read.

Response 5: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[Yes, cross-sectional analysis was performed using EDX]. Line 256, page 8, paragraph 19

 

 

Comments 6: Please define MPY in table 6.

Response 6: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[Corrosion rate is normally designated as millimeters per inch per year (MPY). The table has been updated to include the term corrosion rate and units]. Line 350, page 14, paragraph 27.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript titled "Effect of the Atmosphere on the Properties of Aluminum Anodizing" by

 Adrián Moises García-Lara et al. studies the influence of different atmospheric conditions on the anodizing process of Al6061 aluminum alloy. The authors systematically examine the effects of temperature, time, and atmospheric conditions (without air, with air, and with oxygen) on the thickness, porosity, electrochemical behavior, and purity of the anodized layers. They have used a 3^3 experimental design, and analyzed the results using SEM, XRD, and electrochemical techniques. Overall, the manuscript presents significant findings in the field of aluminum anodizing. With the suggested major revision, it will be a valuable contribution to the journal.

 

1.     The study employs a 3^3 factorial design. Can you provide a detailed justification for this choice, and discuss how the sample size and number of replicates were determined to ensure statistical power and robustness?

2.     Given that the study investigates the effects of different atmospheric conditions (without air, air, and oxygen), can you elaborate on the specific mechanisms by which these conditions influence the anodizing process at a molecular level? How do these mechanisms correlate with the observed changes in thickness, porosity, and electrochemical behavior?

3.     The potentiodynamic polarization curves indicate changes in electrochemical behavior under different anodizing conditions. Can you provide a detailed analysis of the corrosion mechanisms involved and explain how the different atmospheric conditions might alter the passivation behavior of the anodized layers?

4.     The SEM images and XRD patterns provide insights into the microstructure and phase composition of the anodized layers. Can you discuss any potential limitations of these techniques in accurately characterizing the thickness and purity of the anodized layers? How do you account for these limitations in your interpretations?

5.     The study mentions the influence of atmospheric conditions on the purity of the anodized layers. Can you discuss the types and sources of impurities that might be introduced during the anodizing process, and how they affect the overall properties of the anodized layers? How do you ensure that the observed effects are due to atmospheric conditions and not other extraneous variables?

6.     Figure 5: XRD peaks are penetrating other overlapped spectra and will make it difficult for readers to read the data. A better way should be approached to make this figure acceptable.

7.     Figures 6a, 6b, 6c: The values on x-axis are misleading. The authors have used Log (current density) but forgot to take the logarithm of current density. The reviewer suggests to double check it.

8.     In the reference section, the authors should be consistent with formatting. The entire section needs to be reformatted using the journal’s standard format.

Author Response

Point-by-point response to Comments and Suggestions for Authors 3

Comments 1: The study employs a 3^3 factorial design. Can you provide a detailed justification for this choice, and discuss how the sample size and number of replicates were determined to ensure statistical power and robustness?

Response 1: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[The experimental design was used to determine the 3 most important variables in the optimal condition]. Line 19, page 1, paragraph 1.

 

 

Comments 2: Given that the study investigates the effects of different atmospheric conditions (without air, air, and oxygen), can you elaborate on the specific mechanisms by which these conditions influence the anodizing process at a molecular level? How do these mechanisms correlate with the observed changes in thickness, porosity, and electrochemical behavior?

Response 2: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

From a molecular perspective, there may be a better arrangement; the one with better electrochemical behavior might be more compact. When it is observed that the film is neither compact nor porous, it is assumed that surface defects in the growth of the oxide film may be generated due to the presence of nitrogen from the air, which can be absorbed on the surface of the aluminum or trapped during the film's growth. Sulfur ions might also be absorbed on the aluminum surface. If air is present and the temperature is increased, the growth is limited, and over time the layer may dissolve. With air, increasing the temperature favors growth, but over time it becomes more compact. With oxygen at lower temperatures, the film becomes more uniform. Line 212 , page 8, paragraph

 

 

Comments 3: The potentiodynamic polarization curves indicate changes in electrochemical behavior under different anodizing conditions. Can you provide a detailed analysis of the corrosion mechanisms involved and explain how the different atmospheric conditions might alter the passivation behavior of the anodized layers?

Response 3: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

There are no changes in the mechanisms, but there is a variation in the activation energy. By concentration, it happens when the temperature increases and the time decreases without air. There is a part of the curves that shows mixed polarization in the cathodic part, and the curves indicate control in relation to the slope of the inclines. The controls are the same in all the curves under different atmospheres. In the cathodic part, concentration occurs first, and then very close to the corrosion potential, we have mixed polarization. After this, the entire part is anodic with a stable corrosion rate, which is very rapid. At 30°C-60 min, the corrosion potential (Ecorr) changed to a more noble value because the layer is more compact. Concentration polarization is due to the evaluation of hydrogen. Line  355, page 15, paragraph 23.

 

 

Comments 4: The SEM images and XRD patterns provide insights into the microstructure and phase composition of the anodized layers. Can you discuss any potential limitations of these techniques in accurately characterizing the thickness and purity of the anodized layers? How do you account for these limitations in your interpretations?

Response 4: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[It was used to ensure there was no formation of sulfides and other agents that react with oxygen. It is not for quantifying the film thickness, but to identify that there is not a significant amount of  on the surface, contaminant phases in the aluminum oxide film, and to search for phases that may be on the surface of the material, because the formation is thin but impurities may be present.] Line 169 , page 5 , paragraph 16.

 

 

Comments 5: The study mentions the influence of atmospheric conditions on the purity of the anodized layers. Can you discuss the types and sources of impurities that might be introduced during the anodizing process, and how they affect the overall properties of the anodized layers? How do you ensure that the observed effects are due to atmospheric conditions and not other extraneous variables?

Response 5: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[A filter train was used to prevent humidity and dust.]

 

Comments 6: Figure 5: XRD peaks are penetrating other overlapped spectra and will make it difficult for readers to read the data. A better way should be approached to make this figure acceptable.

Response 6: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

A graph is added showing the increase in the peak that is considered significant.

Line 245, page 10, paragraph 21.

 

Comments 7: Figures 6a, 6b, 6c: The values on x-axis are misleading. The authors have used Log (current density) but forgot to take the logarithm of current density. The reviewer suggests to double check it.

Response 7: Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

[In the figure text, 'potential vs current density (logarithmic density)' was added to the x-axis scale] Line 281, page 11, paragraph 24, 25, 26.

 

Comments 8: In the reference section, the authors should be consistent with formatting. The entire section needs to be reformatted using the journal’s standard format.

Response 8:  Thank you for the review and your timely comments, which will benefit the scientific enhancement of the final document. Accordingly, they have been addressed promptly as mentioned below.

Application of the mdpi format.

 

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

There is essentially no response to Comment 1. In an attempt to respond to Comment 1, the authors provided four equations, which contain three errors. And also ”... The composition of the air (21.79%) was ...” – what is it?

The response to Comment 2 contains “...[These data need to be reused as part of the experimental design; Review of the format throughout the text, compliant with MDPI standards.] All text...” – what is it? There are no highlighted edits in the text, according to Comment 2, so nothing has been corrected.

I would like and expected to change the status now at least to “Reconsider after major revisions” (and in addition to provide the new comments), but unfortunately, now all the previous comments remain valid. Therefore, I ask you to understand me correctly and I have to put ”Reject” again.

Author Response

Respuesta punto por punto a los comentarios y sugerencias para los autores 1

Comentarios 1:

Básicamente, no hay respuesta al Comentario 1. En un intento por responder al Comentario 1, los autores proporcionaron cuatro ecuaciones, que contienen tres errores. Y también "... La composición del aire (21,79%) fue..." – ¿qué es?

 

Respuesta 1:

Gracias por la revisión y sus oportunos comentarios, que beneficiarán el perfeccionamiento científico del documento final. En consecuencia, se han abordado con prontitud, como se menciona a continuación.

Desde una perspectiva fisicoquímica, el proceso de anodizado explica que cuando la corriente pasa a través del electrolito que contiene una solución acuosa de ácido sulfúrico, se libera oxígeno en la superficie del aluminio conectado al ánodo. Este oxígeno permite la oxidación acelerada del aluminio. En el cátodo (acero AISI 304) se libera hidrógeno. En otras palabras, es un proceso de descomposición del agua que genera gases en ambos electrodos. [1]

La primera etapa del proceso de electrólisis tiene lugar en el cátodo, donde se reduce el agua y se forman iones de hidróxido. Estos iones de hidróxido reaccionan con el ácido sulfúrico disociado.

Ecuación (1): Reacción en el cátodo

O₂+2H₂O+4E^-=4OH^- Ecuación (1)

Por otro lado, en la descomposición de H₂SO₄, al entrar en contacto con el agua, se disocia, sufriendo una primera reducción para formar HSO₄^-. A esto le sigue una reducción secundaria hasta que los iones se forman por completo.

Ecuación (2): Un ion de hidrógeno se divide:

H₂SO₄=H⁺_(aq)+HSO₄^-_(aq) Ecuación (2)

Ecuación (3): El último ion de hidrógeno se divide, dejando un átomo de hidrógeno en HSO₄^-.

HSO₄^-=H⁺_(aq)+SO₄^2-_(aq) Ecuación (3)

Finalmente, la reacción ocurre en el ánodo de acuerdo con la Ecuación 4, donde el H₂O se oxida y se genera oxígeno, formando Al₂O₃. En la reacción general, los tres componentes del sistema están presentes, siendo los iones de hidrógeno un producto de la descomposición del agua.

4Al+3H₂SO₄+3H₂O=Al₂O₃+Al₂(SO₄)₃ Ecuación 4

[1] MSc. Ramón Lagos y Dr. Juan Camus, "Artículo anodizado baterías", Revista Cubana de Química, vol. 29, 2017.

Línea 34, página 1, párrafo 2.

 

Con respecto al comentario sobre la composición del aire, 21,79%, queremos aclarar que fue nuestro error no incluir la relación elemental completa \u2012 21O₂/79N₂. Gracias por la observación. Nos gustaría aprovechar esta oportunidad para proporcionar la descripción completa de la composición de acuerdo con el análisis químico proporcionado por el equipo de Thermo Fisher Scientific. El párrafo dice ahora lo siguiente:

[Se utilizó un tren de filtros para obtener aire libre de humedad. El burbujeo del aire se realizaba a través de un compresor que absorbía el aire del ambiente. Los contaminantes quedaron atrapados en el tren de filtros debido a la incrustación manejada por la salida de aire. La composición del aire es de aproximadamente 20,94% de oxígeno (O₂), 78,1% de nitrógeno (N₂), y el resto consiste en gases traza como Ar, CO₂, Ne, CH₄, etcétera.

 

En cuanto al comentario sobre el objetivo de la investigación, este es observar el modo de crecimiento de la película de alúmina sobre el sustrato en función de la atmósfera y evaluar su resistencia a la corrosión. Esto se ilustra en la sección que explica el proceso de anodizado desde una perspectiva fisicoquímica. Cuando la corriente pasa a través del electrolito que contiene una solución acuosa de ácido sulfúrico, se libera oxígeno en la superficie del aluminio conectado al ánodo, lo que permite la oxidación acelerada del aluminio. En el cátodo (acero AISI 304) se libera hidrógeno, lo que indica que se trata de un proceso de descomposición del agua que genera gases en ambos electrodos.

 

Con respecto a los Comentarios 2 anteriores en la versión R1 su pregunta fue la siguiente: En segundo lugar, ahora el manuscrito no ha sido leído, deletreado por los autores y no está listo para su presentación. Palabras no traducidas, abreviaturas no reveladas, caracteres sin subíndices, diferentes fuentes, unidades de medida SI no especificadas y, en general, no especificadas, no de acuerdo con los estándares MDPI, figuras dadas, duplicación de datos en tablas y figuras, etcétera, etcétera. Aunque hay que rendirle homenaje, el manuscrito está escrito en un lenguaje sencillo.

Respuesta 2:

Una vez más, gracias por la revisión y sus oportunos comentarios, que beneficiarán la mejora científica del documento final. En consecuencia, se han abordado con prontitud, como se menciona a continuación.

 

The entire document was reviewed for its writing by a professional. Unspecified abbreviations, characters, and specific fonts were corrected, and it is understood that the system used for the results is the International System of Units (SI) in full.

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have thoroughly addressed all of my concerns and I believe the paper is acceptable for publication.

Author Response

"Thank you for the feedback and for accepting the document in its current form."

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed reviewer's every comment thoroughly and carefully. The reviewer is happy to recommend this article for publication.

Author Response

"Thank you for the feedback and for accepting the document in its current form."