Advances in Thermochemical Synthesis and Characterization of the Prepared Copper/Alumina Nanocomposites

Round 1

Reviewer 1 Report

In this work, thermochemical synthesis of nanostructured composite powders in Cu-Al2O3 system with 5 wt.% of alumina and their characterization have been studied. The design of experiment and data analysis have been carried out carefully. However, before further consideration m the following issues should be considered and addressed:

1. The novelty aspect is missing; thus this aspect should be highlighted.
2. The sample preparation procedure for the TEM analysis should be included.
3. Do the results of this work comparable with the literature data?
4. The majority of the references are very old, and it is recommended to replace them with the latest works.

Author Response

In this work, thermochemical synthesis of nanostructured composite powders in Cu-Al2O3 system with 5 wt.% of alumina and their characterization have been studied. The design of experiment and data analysis have been carried out carefully. However, before further consideration m the following issues should be considered and addressed:

1. The novelty aspect is missing; thus this aspect should be highlighted.

A novelty of this synthesis is a decreased reduction temperature for chemical reaction of the powder in hydrogen atmosphere at 350 °C, what is an advantage in contrast to 820 °C for 1 h to produce the final Cu–Al₂O₃ nanocomposite powder, as described by Seyedraoufi et al., [23]. It can be very important point for a decrease of production costs. A thermodynamic analysis of the reduction, spray drying and synthesis reactions was performed in order to predict a chemical behavior of the compounds. Amirjan et al. [24] have used artificial neural network to prediction of Cu-Al₂O₃ properties and compare it with measurable values. In order to prepare copper based composites, copper powder with four different amounts of Al₂O₃ reinforcement (1, 1.5, 2, 2.5 wt%) were mechanically alloyed and the consolidated compacts of prepared powders were sintered in five different temperatures of 725–925 ◦C at seven several sintering times of 15–180 min. Guevara et al [25] have studied Synthesis of copper-alumina composites by mechanical milling via an analysis of materials and manufacturing processes. Ha. et al. [26] studied fabrication of Al₂O₃ dispersion strengthened copper alloy by spray in-situ synthesis casting process above 1250°C, as new method. Mohammadi, E. et al. [27] used combustion method for the synthesis of Cu-Al₂O₃, which take place in short time at temperatures higher than 1000°C. Generally, our synthesis method offer costly friendly process for the synthesis of Cu-Al₂O₃ in comparison to other processes [27].

2. The sample preparation procedure for the TEM analysis should be included.

The powder to be tested is suspended in a liquid (water, ethanol or buthanol) with the aid of an ultrasonic device. Depending on particle size, requirements and type of examination, the powder is first ground. By means of a pipette a drop of suspension is taken up and placed on a carbon carrier net. The liquid is then allowed to evaporate (dry) under a lamp, resulting in a C-carrier net with the powder on top. After this powder preparation our sample was studied by TEM Analysis. HRTEM analysis was performed using Philips CM200/FEG.

3. Do the results of this work comparable with the literature data?

Comparative analysis of mechanical properties of produced composites with literature values is presented in Table 1, that is included in this work.

Regarding to the same chemical composition of copper/alumina nanocomposite in comparison to Amirjan [24], the values of electrical conductivity have higher values in all cases, what confirms an advantage for our studied combined strategy.

Table 1:Comparison of the Electrical conductivity and Rockvell Hardness Values (HRF) after sintering at 875 °C and 60 min in our work with values of Amirjan [24]

*IACS (International Annealed Copper Standard)

4. The majority of the references are very old, and it is recommended to replace them with the latest works.

We agree with you to insert new publications. I have injected new 5 publications in our References:

1. Seyedraoufi , Z.A, Saghafian, H., Shabestari, S.G, Thermochemical synthesis of nanostructured Cu-Al₂O₃ composite powder, Ind. Chem. Eng. Q. 2014, 20 (3) 339−344
2. Amirjan, M, Khorsand, H, Siadati, M.H, Farsani, R. E, Artificial Neural Network prediction of Cu–Al2O3 composite properties prepared by powder metallurgy method, Journal Materials Research Technology 2013, 2 (4), 351–355
3. Guevara, A.L, Rodriguez, I.R. , Hernandez, R.V,   Bernal-Correa , R.A, Gutierrez , A.S, -Ramos; A.H & , Synthesis of Copper-Alumina Composites by Mechanical Milling: An Analysis Materials and Manufacturing Processes, 2013, 28, 157-162.
4. Han, S.J, Seo, J., Kyeong-Hwan Choe, K. H,, and Myung-Ho Kim, M.H, Fabrication of Al2O3 Dispersion Strengthened Copper Alloy by Spray, In-Situ Synthesis Casting Process, Mater. Int., 2015, 21, 2, 270-275.
5. Mohammadi, E., Nasiri,, , Khaki, V.J, Zebarjad, S.M.^, Copper-alumina nanocomposite coating on copper substrate through solution combustion, Ceramic International 2018, 44, 3, 15, 3226-3230

Now the number of references amounts 40.

Author Response File: Author Response.pdf

Reviewer 2 Report

Research presented in the manuscript are interesting, TEM examination particularly, but some corrections are needed.

1. Compare please title “Advances in Thermochemical Synthesis and Characterization of the Prepared Copper/Alumina Nanocomposites” with Abstract: This paper presents thermochemical synthesis of nanostructured composite powders in  Cu-Al2O3 system with 5 wt.% of alumina and their characterization, which included:

Composite powder and composite material are not the synonyms.

2. Sentence in Abstract

“Additional research was carried out in order to analyze the  application of the obtained nanocomposite powders for the synthesis of nanostructured composite materials based on copper and alumina by a new method, which is a combination of a  thermochemical procedure and mechanical alloying.” What the Authors would like to express, please indicate proper phrases in the manuscript

3. If in conducted experiments the morphology of composite powder was examined, please show SEM or LM (cross-section) images of the obtained by proposed new technology semi-product in this article.
4. 173 “Figure 3. FIB image of compacted Cu-5wt.% Al2O3.” Add composite sinter (?)
5. 184-185 “Figure 4. TEM analysis of sample after sintering: BF and DF images showing nano-twinning on Cu crystal.” In Fig. 4c there is no twin visible.
6. Figure 6c – nothing visible, please enlarge.
7. Figure 7. The abbreviations HRF and %IACS are not explained in  text, as well as the red line at the level of 50%.
8. The data presented in Figure 7 are imprecise and that figure cannot not be published in this form. The technological procedure applied for each material characterized in this figure is not clear, for example (only?) heat treated, plastic deformation  (plastically deformed?), sintered; Cu-10Ag-4,5Al2O3 no technology of that composite; two points for sintered 875C/1h . The readers have no time and desire for questing in hard to reach references and therefore conditions of composite processing must be characterized.

9. Results of hardness and  electrical conductivity measurements obtained and presented as a new in this article,  should be presented in separate table with full technological history of examined sample and then they can be shown in comparative figure.

10.259-261 sentence “Due to the plastic deformation occurs the deformation strengthening, and after heat treatment occurs the strengthening by annealing. “ Please explain the mechanism of metal strengthening “by annealing”.

11.Fig 8. “Figure 8. Proposed strengthening mechanism.” Caption of this figure is not correct, because it shows microstructure transformation induced by following technological steps only.

Author Response

1. Compare please title “Advances in Thermochemical Synthesis and Characterization of the Prepared Copper/Alumina Nanocomposites” with Abstract: This paper presents thermochemical synthesis of nanostructured composite powders in  Cu-Al2O3 system with 5 wt.% of alumina and their characterization, which included:

Composite powder and composite material are not the synonyms.

According to the newest publication: L. N. Rajeshkumar, Dr.Amirthagadeswaran K S, Variations in the properties of copper-alumina nanocomposites synthesized by mechanical alloying, February 2019, we used Copper/Alumina Nanocomposites. We changed it in Abstract!

This paper presents thermochemical synthesis of copper/alumina nanocomposites in Cu-Al₂O₃ system with 5 wt.% of alumina and their characterization

2. Sentence in Abstract

“Additional research was carried out in order to analyze the application of the obtained nanocomposite powders for the synthesis of nanostructured composite materials based on copper and alumina by a new method, which is a combination of a thermochemical procedure and mechanical alloying.” What the Authors would like to express, please indicate proper phrases in the manuscript

Additional research was carried out in order to analyze the application of the obtained nanocomposite powders for the synthesis of copper/alumina nanocomposites by a new method, which is a combination of a thermochemical procedure and mechanical alloying.

3. If in conducted experiments the morphology of composite powder was examined, please show SEM or LM (cross-section) images of the obtained by proposed new technology semi-product in this article.

SEM Analysis of Cu/Al2O3 powder is presented in my letter with answers for all 4 reviewers

4. 173 “Figure 3. FIB image of compacted Cu-5wt.% Al2O3.” Add composite sinter (?)

Figure 3. FIB image of compacted Cu-5wt.% Al₂O₃ composite sinter

5. 184-185 “Figure 4. TEM analysis of sample after sintering: BF and DF images showing nano-twinning on Cu crystal.” In Fig. 4c there is no twin visible.

We changed it:

Figure 4. TEM analysis of sample after sintering: BF and DF images showing nano-twinning on Cu crystal (4a. and 4b), homogenous distribution of Al₂O₃ particles (4.c)

6. Figure 6c – nothing visible, please enlarge.

You have right-nothing visible. We put new image.

7. Figure 7. The abbreviations HRF and %IACS are not explained in text, as well as the red line at the level of 50%.

HRF -Rockwell Hardness Values

IACS- International Annealed Copper Standard

100% IACS is equivalent to a conductivity of 58.108 megasiemens per meter (MS/m) at 20°C or a resistivity of 1/58.108 ohm per meter for a wire one square millimeter in cross section.

8. The data presented in Figure 7 are imprecise and that figure cannot not be published in this form. The technological procedure applied for each material characterized in this figure is not clear, for example (only?) heat treated, plastic deformation  (plastically deformed?), sintered; Cu-10Ag-4,5Al2O3 no technology of that composite; two points for sintered 875C/1h . The readers have no time and desire for questing in hard to reach references and therefore conditions of composite processing must be characterized.

You have right. We removed this Figure 7 and information about ; Cu-10Ag-4,5Al2O3. We presented our results in Table 1.

9. Results of hardness and electrical conductivity measurements obtained and presented as a new in this article, should be presented in separate table with full technological history of examined sample and then they can be shown in comparative figure.

Sintering of Copper/alumina nanocomposite powders was performed at 875 °C in 60 min in laboratory electro resistant furnace in hydrogen atmosphere in order to avoid oxidation of samples. From the presented results in Table 1 it could be concluded that use of obtained powders for mechanical alloying followed by plastic deformation has a same level of hardness for much lower amount of Al₂O₃, which has a direct consequence in higher values of electrical conductivity. The maximal value of electrical conductivity and Hardness were obtained for the sample with one 1 wt.% percent of Al₂O₃.

Table 1:Electrical conductivity and Rockvell Hardness Values (HRF) after sintering at 875 °C and 60 min

*IACS (International Annealed Copper Standard)

After annealing at 800°C, Rockvell Hardness and electrical conductivity amounted 58 HRF and 61.78 % IACS, respectively.

10.259-261 sentence “Due to the plastic deformation occurs the deformation strengthening, and after heat treatment occurs the strengthening by annealing. “ Please explain the mechanism of metal strengthening “by annealing”.

The annealing treatment increases the system's strength by reducing dislocation emission sources and improves material ductility through strengthening grain boundaries' resistance to intergranular cracks

11. “Figure 8. Proposed strengthening mechanism.” Caption of this figure is not correct, because it shows microstructure transformation induced by following technological steps only.

We changed title of Figure 8.

Figure 8. Microstructure transformation induced by following technological steps: mechanical alloying, heat treatment, plastic deformation and sintering

Author Response File: Author Response.pdf

Reviewer 3 Report

This experimental research was conducted essentially with possibility of their synthesis via thermochemical route. The development of copper-alumina nano composite was studied using thermodynamic analysis of drying and finally thermal decomposition followed by final reduction step. The authors have used different exp. Methods to confirm their results.

Firstly, what is the economic size (cost effect?) of this method and is it a practical way for manufacturing engineering of these composites by this way? Which application for industrial target of this composite?

In your manuscript, please try to improve the following points;

Improve your research design? It is not really suitable very difficult to follow your text.

Your methods that you have described are difficult to follow please in the section of experimental conditions, try to explain very clearly.

Your results and also your discussion should be interpreted well, many paragraphs contain the results of your experiments, you need more interpretations and you can support your conclusions with your results. In the literature, a lot of similar research on these composites mainly production and manufacturing methods and practical industrial applications very economic – cost effect and also soundness methods. Can you make some comparisons of your methods regarding to others already published in the literature.

Author Response

This experimental research was conducted essentially with possibility of their synthesis via thermochemical route. The development of copper-alumina nanocomposite was studied using thermodynamic analysis of drying and finally thermal decomposition followed by final reduction step. The authors have used different exp. Methods to confirm their results.

1. Firstly, what is the economic size (cost effect?) of this method and is it a practical way for manufacturing engineering of these composites by this way?

The economic size (cost effect) of this method shall be calculated via partial operations. This is a practical way for manufacturing engineering of these composites by this way in powder metallurgy based on different applications.

2. Which application for industrial target of this composite?

Because of high strength and electrical properties, this material can be used such as electrode materials for lead wires, relay blades, different contact materials, various switches and specially for electrode materials for spot welding due to high conductivity of copper and high hardness and excellent thermal stability of aluminum.

3. In your manuscript, please try to improve the following points: Improve your research design? It is not really suitable very difficult to follow your text.

At Figure 1 we have presented research design via Flowsheet of the synthesis of Cu-Al₂O₃ nanocomposite powder by the thermochemical procedure. Also we put many new information in order to explain our results and research strategy.

4. Your methods that you have described are difficult to follow please in the section of experimental conditions, try to explain very clearly.

We put new explanations based on literature values and results. We included new table with experimental values and comparison with literature values regarding to an electrical conductivity and hardness the sintering.. We removed the Figure 7.

5. Your results and also your discussion should be interpreted well, many paragraphs contain the results of your experiments, you need more interpretations and you can support your conclusions with your results.

We improved conclusion:

Characterization of produced nanostructured composites in system Cu-Al₂O₃ showed possibility of their synthesis via thermochemical route. The mechanism of formation of copper-alumina nanocomposite was studied using thermodynamic analysis of drying, thermal decomposition, reduction step and homogenization. The reduction of thermally treated powders was performed in hydrogen with flow rate 20 L/h at 350 °C for one hour, where copper oxide was transformed into elementary copper, while Al₂O₃ remained unchanged.

By AEM analysis it was confirmed that homogenous distribution of Al₂O₃ particles was achieved by thermochemical route followed by cold pressing and sintering, a necessary requirement for retaining electrical conductivity of the base metal.

Increasing of the strength of the material was achieved by presence of dislocation density in a copper matrix surrounding the alumina particles, confirmed by TEM analysis.

Additionally selected area diffraction pattern showed possible presence of the third phase formed during sintering stage at interphase containing all three elements in a very narrow region, which additionally reinforces the copper matrix by blocking the grain and sub-grain boundaries. Existence of the third phase in the structure remains to be proven by further indexing and calculations. Proposed strengthening mechanism combines the strengthening in thermo-chemically synthesized composites and strengthening during mechanical alloying. The maximal values of electrical conductivity and hardness were obtained for the sample based on 1.0 wt. % percent of Al₂O₃ in structure. Regarding to the same chemical composition of copper/alumina nanocomposite in comparison to literature values by Amirjan [24], the values of electrical conductivity and hardness are higher in all cases, what confirms an advantage for our studied combined strategy.

The future study can be focused on the kinetics of the thermochemical synthesis of the studied nanocomposites. The economic size (cost effect) of this method shall be calculated via partial operations. This is a practical way for manufacturing engineering of these composites by this way in powder metallurgy based on different applications.

6. In the literature, a lot of similar research on these composites mainly production and manufacturing methods and practical industrial applications very economic – cost effect and also soundness methods. Can you make some comparisons of your methods regarding to others already published in the literature.

We included 5 new publications in order to compare out methods with other methods.

A novelty of this synthesis is a decreased reduction temperature for chemical reaction of the powder in hydrogen atmosphere at 350 °C, what is an advantage in contrast to 820 °C for 1 h to produce the final Cu–Al2O3 nanocomposite powder, as described by Seyedraoufi et al., [23]. It can be very important point for a decrease of production costs. A thermodynamic analysis of the reduction, spray drying and synthesis reactions was performed in order to predict a chemical behavior of the compounds. Amirjan et al. [24] have used artificial neural network to prediction of Cu-Al2O3 properties. In order to prepare copper based composites, copper powder with four different amounts of Al2O3 reinforcement (1, 1.5, 2, 2.5 wt%) were mechanically alloyed and the consolidated compacts of prepared powders were sintered in five different temperatures of 725–925 ◦C at seven several sintering times of 15–180 min. Guevara et al [25] have studied Synthesis of copper-alumina composites by mechanical milling via an analysis of materials and manufacturing processes. Ha, et al. [26] studied fabrication of Al2O3 dispersion strengthened copper alloy by spray in-situ synthesis casting process above 1250°C, as new method. Mohammadi, E. et al. [27] used combustion method for the synthesis of Cu-Al2O3, which rake place in short time at temperatures higher than 1000°C. Generally, our synthesis method offers costly friendly process for the synthesis of Cu-Al2O3 in comparison to other processes [27].

Finally, we put new Table 1 for comparison of our results for electric conductivity and hardness with ones by Amirjan.

Amirjan, M, Khorsand, H, Siadati, M.H, Farsani, R. E, Artificial Neural Network prediction of Cu–Al2O3 composite properties prepared by powder metallurgy method, Journal Materials Research Technology 2013, 2 (4), 351–355

Author Response File: Author Response.pdf

Reviewer 4 Report

In the current study, thermochemical synthesis of nanostructured composite powders in Cu-Al2O3 system with 5 wt.% of alumina and their characterization have been investigated. The work seems to be an interesting study and in spite of  a proper data collection and data analysis, the following issues should be taken into account and addressed:

1. What could be the real application for this composite?
2. In Figure 3, please show the alumina particles by some arrows.
3. Why has the other strengthening mechanisms such as Hall-Petch or Load transfer not been considered as the strengthening mechanism?
4. Which type of interfacial bonding is present between the Cu and alumina?

Author Response

In the current study, thermochemical synthesis of nanostructured composite powders in Cu-Al2O3 system with 5 wt.% of alumina and their characterization have been investigated. The work seems to be an interesting study and in spite of a proper data collection and data analysis, the following issues should be taken into account and addressed:

1. What could be the real application for this composite?

Because of high strength and electrical properties, this material can be used such as electrode materials for lead wires, relay blades, different contact materials, various switches and specially for electrode materials for spot welding due to high conductivity of copper and high hardness and excellent thermal stability of aluminum

2. In Figure 3, please show the alumina particles by some arrows.

We made it as proposed from your side.

3. Why has the other strengthening mechanisms such as Hall-Petch or Load transfer not been considered as the strengthening mechanism?

I added two sentences “As reported by Amirjan [24] with respect to strengthening mechanism of Orawan, with increasing reinforcement amount, the distances between particles in the microstructure will decrease. Therefore, the dislocations can encompass the particles easily and lead to lower values of hardness. We assume the grain size of the composite matrixes microstructure increases with increasing sintering time. According to Hall–Petch effect, larger grain size in microstructure leads to a decrease in hardness values.”

4. Which type of interfacial bonding is present between the Cu and alumina?

Interfacial bonding between the Cu and alumina is eutectic Cu-O bonding, what is according to paper by Beraud et al..

JOURNAL OF MATERIALS SCIENCE 24 (1989) 4545-4554

Journal of Material Science, 1989, 24,

Study of copper-alumina bonding

1. BERAUD* M. COURBIERE*, C. ESNOUF* D. JUVE*, D. TREHEUX* t *

_9ln stitut National des Sciences AppliquOes, GEMPPM, BM. 502,

20 A venue Albert Einstein, 69621 Villeurbanne codex, France

_9E cole Centrale de Lyon, Laboratoire de Metallurgie,

36 Avenue Guy de Collongues, 69131 Ecully codex, France

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Please check:

l.284 "Electrical" - "electrical" and  "Hardness Values" - "hardness values"

l.287 "Hardness" - "hardness"

Author Response

Dear Reviewer,

thank you for your invested time, high support and very valuable comments.

According to your comments, we made corrections in our new version:

I.284 "Electrical"- in "electrical" and "Hardness Values" in "hardness values"

II 287 "Hardness"- in "hardness"

Best regards

Srecko

Reviewer 4 Report

Almost all the issues are considered and addressed and so the manuscript can be accepted in the current form.

Author Response

Dear Reviewer,

thank you very much for your invested time, high support and your valuable comments.

Best regards

Srecko Stopic