Study of the Microstructure, Corrosion and Optical Properties of Anodized Aluminum for Solar Heating Applications
, Abdelmnim M. Altwaiq 2, Muayad Esaifan 2, Heba Al-Fayyad 1, Ziad Shraideh 3, Iessa Sabbe Moosa 1 and Imad Hamadneh 1Round 1
Reviewer 1 Report
The manuscript entitled "Study of the microstructure, corrosion and optical properties of anodized aluminum for solar heating applications” deals with analysis of the influence of three types of aluminium samples for their use in solar water heating system.
The results given in the manuscript are partially in the scope of the Metals journal. This manuscript is interesting and can find application in the industrial section; however, after reading the manuscript, I found some points that require some revision.
GENERAL COMMENTS
- In this work, rather than characterizing the material and the influence of the surface condition, more emphasis is put on the characterization of the influence of the performance of the heating system. Which is the influence of the surface? Why in some cases; Which surface is better (painted or anodized)? Why?
- Conclusions section should be rewritten. This section cannot be only a list of conclusions; a more elaborated section is needed. Authors should provide a general conclusion/s that answer the big question stated in the introduction.
- English should be revised along the whole manuscript. The required revision is minor, but some revision is required.
- Please, add error bars to data in Figs. 6 to 11.
PARTICULAR COMMENTS
(Page 2) Please, replace “regarding the using anodized commercial” with “regarding the utilization of anodized commercial”
(Page 2) Please, replace “Microstructure study of the used Al” with “Microstructural study as a function of the Al surface”
(Page 2) Please, indicate the supplier (and country) for the Al water containers. I understand that the containers were self-made (from a typical Al profile used in construction). If this is the case, please, clarify it better in the main text.
(Page 6) Please, clarify the composition of the inclusions. These type of secondary particles are commonly seen in Al alloys, but which secondary particles are found in this alloy?
(Page 7) Please, replace “watts” with “Watts”
(Page 7) The right hand side of eq (1) “···W” it is not clear. Please, clarify the meaning: is this referring to the units, the absorbed energy power,…?
(Page 8) Which is the meaning of “Scheme 26.” in the caption of Fig. 6?
Author Response
Reply to Reviewers of
Manuscript ID: metals-1906014
Type of manuscript: Article
Title: Study of the microstructure, corrosion and optical properties of
anodized aluminum for solar heating applications
We thank the referee for his/her comments and invaluable suggestions. Regarding the comments, we would like to state that we appreciate the suggested changes and remarks and that we have followed their instructions and made the necessary changes as explained below.
GENERAL COMMENTS
- In this work, rather than characterizing the material and the influence of the surface condition, more emphasis is put on the characterization of the influence of the performance of the heating system. Which is the influence of the surface? Why in some cases; Which surface is better (painted or anodized)? Why?
Our materials are well characterized since they are commercially available and the scope of our research is to see the influence of the performance of the surface as a direct application in solar heating systems.
Regarding the question: which is a better surface? we have addressed this point several times in the manuscript. For example in the “Abstract” we wrote: “we highly recommend using the commercial blackened anodized Al surface to manufacture solar absorbing heaters. Owing to its similarity of solar radiation absorptivity with the commercial matt black painted Al, excellent corrosion resistance, superior endurance upon long-term exposure to solar radiation, lightweight, low price, and availability. Additionally, the light reflectance% test showed the characteristics of the used solar selective surfaces.”
- Conclusions section should be rewritten. This section cannot be only a list of conclusions; a more elaborated section is needed. Authors should provide a general conclusion/s that answer the big question stated in the introduction.
We agree. The Conclusions section has been rewritten, and even better, combined with the general remarks to strengthen the conclusions.
- English should be revised along the whole manuscript. The required revision is minor, but some revision is required.
We agree. Done.
- Please, add error bars to data in Figs. 6 to 11.
We thank the referee for this important note. From our understanding, adding error bars to the mentioned figures will make the lines/ curves overlap and reduce the clarity of the curves and the whole figure. However, in the “experimental apparatus and equipment” section, we have already mentioned the accuracy of the used devices and measurements. The thermometer accuracy is ± 0.1 0C and the solar intensity meter accuracy is ± 3%. This information will cover this issue for the reader.
PARTICULAR COMMENTS
(Page 2) Please, replace “regarding the using anodized commercial” with “regarding the utilization of anodized commercial”
- Done
(Page 2) Please, replace “Microstructure study of the used Al” with “Microstructural study as a function of the Al surface”
- “Microstructural” is corrected. However it is not “as a function of the Al surface”.
(Page 2) Please, indicate the supplier (and country) for the Al water containers. I understand that the containers were self-made (from a typical Al profile used in construction). If this is the case, please, clarify it better in the main text.
- Section 2. Experimental apparatus and equipment
(Page 6) Please, clarify the composition of the inclusions. These type of secondary particles are commonly seen in Al alloys, but which secondary particles are found in this alloy?
- We used commercially available materials. They are not considered as alloys but high Al percentage material. We agree with the referee that the types on inclusions are good to know if the interest of the study was the composition of the surface and bulk in detail. However, our aim was to study the heat absorbing bevaiour of the surface and such inclusions will have little (if any) effect on the results. In an anodized surface, there are no inclusions since it is well converted into the Al oxide layer.
(Page 7) Please, replace “watts” with “Watts”
(Page 7) The right hand side of eq (1) “···W” it is not clear. Please, clarify the meaning: is this referring to the units, the absorbed energy power,…?
- Corrected
(Page 8) Which is the meaning of “Scheme 26.” in the caption of Fig. 6?
- It means nothing. The “Scheme 26.” appeared after converting the text into the journal’s template. It has been corrected.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
1. This paper has a certain innovation in improving solar thermal efficiency. However, the evaluation of the coating corrosion resistance is oversimplified. The coating material is prone to failure under sun exposure for a long time. This related content was missing, please supplement relevant weather resistance tests, such as UV resistance, salt spray test, and alternate immersion test.
2. The more solar energy is absorbed, the higher the internal temperature of the coating. If the coating is exposed to the outside for a long time, the stability of the coating should be considered. The author should describe if the variation in temperature difference affects the stability and performance.
3. The adhesion of the coating on the aluminum surface is not observed by scanning electron microscopy. In other words, the adhesion evaluation cannot be explained by SEM results. Please select the generally accepted tests to reduce the error during the sample preparation, and provide more reliable evidence about the quality of adhesion.
Therefore, I suggested resubmitting the manuscript after major revisions.
Author Response
Reply to Reviewers of
Manuscript ID: metals-1906014
Type of manuscript: Article
Title: Study of the microstructure, corrosion and optical properties of
anodized aluminum for solar heating applications
We thank the referee for his/her comments and invaluable suggestions. Regarding the comments, we would like to state that we appreciate the suggested changes and remarks and that we have followed their instructions and made the necessary changes as explained below.
Comments and Suggestions for Authors
- This paper has a certain innovation in improving solar thermal efficiency. However, the evaluation of the coating corrosion resistance is oversimplified. The coating material is prone to failure under sun exposure for a long time. This related content was missing, please supplement relevant weather resistance tests, such as UV resistance, salt spray test, and alternate immersion test.
We thank the referee for the important comment. The study of the corrosion resistance was done in an extremely corrosive medium (3.5% NaCl) which is similar to sea water. The corrosion study is not the main scope of this research and is merely done to support the idea of the excellent surface durability of the anodized Al surfaces. On the other hand, our experiments span a few months of the year and we noticed no surface failure or degradation of the anodized layers, as expected. The suggested tests are in our future research plans.
- The more solar energy is absorbed, the higher the internal temperature of the coating. If the coating is exposed to the outside for a long time, the stability of the coating should be considered. The author should describe if the variation in temperature difference affects the stability and performance.
The research was conducted over two seasons (autumn and winter). We have not noticed any performance change or material stability effects due to the variation in temperatures as seen in the results. We also notice that solar absorptivity did not change with time over many experiments. A statement has been added to the manuscript (page 10 - results and discussion section) to clarify this point.
- The adhesion of the coating on the aluminum surface is not observed by scanning electron microscopy. In other words, the adhesion evaluation cannot be explained by SEM results. Please select the generally accepted tests to reduce the error during the sample preparation, and provide more reliable evidence about the quality of adhesion.
We agree with the referee that SEM cannot quantify adhesion on surfaces. We have followed all accepted sample preparation protocols including grinding, polishing and etching stages. Anodization is an electrochemical route that develops an Al203 layer on the surface of the treated Al sheet for different scientific and industrial goals. Such as corrosion resistant, insulation, decoration and wear resistance, and thermal properties. The converted oxide layer of Al203 is in excellent adhesion with mother Al sheet as it is now chemically and physically an intrinsic part of it. Full information about anodization of Al was mentioned with some related references in the manuscript in the results and discussion part (4. 2 Solar water heating).
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Therefore, I suggested resubmitting the manuscript after major revisions.
We hope that we have answered all of your invaluable comments and queries.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
In the current state, the manuscript entitled "Study of the microstructure, corrosion and optical properties of anodized aluminum for solar heating applications" by AlShamailehr et al can be accepted for publication. Authors have addressed all the comments made by the reviewer.
