Oxidation Behavior, Insulation Resistance, and Permeability of FeSiCr Alloys for Multilayer Inductors
Round 1
Reviewer 1 Report
The manuscript investigated the oxidation behavior, insulation resistance and permeability of FeSiCr alloys. There are many interesting observations. It is well written. It is helpful for the preparation of multilayer inductors with enhanced performance including high insulation resistance and permeability, or inductance. I suggest it can be accepted.
Author Response
Thank you.
Reviewer 2 Report
In this manuscript, authors have systematically investigated the effect of oxygen partial pressure during annealing on the phase formation, insulating oxide layer formation, and electromagnetic properties of FeSiCr alloy. The authors also contrast the effect of annealing temperature in the air with results of the variation of the oxygen partial pressure in the range from 0.21 atm down to 10-5 atm during annealing of FeSiCr compacts at 900°C.
After a careful peer-reviewing process, I must inform you that, the subject of this paper is interesting and can be considered for publication in the journal after a MAJOR REVISION. I believe that the paper contains relevant information for the scientific community focused on the oxidation behavior of Fe-Cr-based alloys. I believe that the results are informative but must be well organized and improved in the next revision(s). Therefore, there are some questions about this submission and some revisions are necessary for this work. The major/minor issues are indicated as follows:
1. Typos and minor grammar errors are common in the manuscript. A considerable number of sentences are not comprehensible, some of which can be due to typos or grammar errors. Also, it is more beneficial to avoid using the “first person” in a scientific manuscript. For example: “we have systematically investigated” or “We contrast the effect of”. Careful proofreading is mandatory for this case.
2. The abstract is not well written. Some details of the experimental processes especially in the oxidation process were missed in the abstract. Please revise this section.
3. The new findings related to this work focused on oxidation properties of FeCr-base alloys and coatings should be stated in the introduction clearly.
4. Please provide the manufacturer/model/code and also the manufacturer country of the raw materials as well as all testing equipment used for all evaluations.
5. Authors must show which questions/problems have been answered in this work. In this case, the correct and detailed information about this study must be provided in this manuscript.
6. In this manuscript, results are well presented, but discussion on the obtained results must be completely provided in this manuscript. As can be seen, a “comprehensive” and “comparative” discussion is missed in this work. This should be provided as well.
7. It is also recommended to provide a step-by-step flowchart for a better description of the preparation process and related tests in section 2.
8. Oxidation behavior based on parabolic or non-parabolic behavior must be completely described in this study.
9. Structural/morphological characteristics must be indicated in figure 1 b and also figure 4 and 5 using textboxes and arrows/indexes.
10. Please provide major findings in the “Conclusions” section with a bullet-point style.
11. There is no description of the future plans for research in the first part of the “Conclusions” section. This should be completed in this section.
12. Recently published references are beneficial for this work. Please check and use new references focused on your work.
13. Also, please double-check and revise the reference list according to the MDPI / Alloys journal requirements.
Author Response
Reviewer 2:
In this manuscript, authors have systematically investigated the effect of oxygen partial pressure during annealing on the phase formation, insulating oxide layer formation, and electromagnetic properties of FeSiCr alloy. The authors also contrast the effect of annealing temperature in the air with results of the variation of the oxygen partial pressure in the range from 0.21 atm down to 10-5 atm during annealing of FeSiCr compacts at 900°C.
After a careful peer-reviewing process, I must inform you that, the subject of this paper is interesting and can be considered for publication in the journal after a MAJOR REVISION. I believe that the paper contains relevant information for the scientific community focused on the oxidation behavior of Fe-Cr-based alloys. I believe that the results are informative but must be well organized and improved in the next revision(s). Therefore, there are some questions about this submission and some revisions are necessary for this work. The major/minor issues are indicated as follows:
- Typos and minor grammar errors are common in the manuscript. A considerable number of sentences are not comprehensible, some of which can be due to typos or grammar errors. Also, it is more beneficial to avoid using the “first person” in a scientific manuscript. For example: “we have systematically investigated” or “We contrast the effect of”. Careful proofreading is mandatory for this case.
Answer: OK. We have checked the whole manuscript for typos and awkward formulations. Moreover, we have rewritten the abstract and have avoided using first person language.
- The abstract is not well written. Some details of the experimental processes especially in the oxidation process were missed in the abstract. Please revise this section.
Answer: OK. We have revised the abstract.
- The new findings related to this work focused on oxidation properties of FeCr-base alloys and coatings should be stated in the introduction clearly.
Answer: We have revised the Introduction. We have included more recent references and reported about the actual status of coatings.
Many other studies have focused on the increasing the resistivity by coating the alloy particles. Insulating coatings are typically classified as organic, inorganic, and composite coatings. Organic coatings are primarily
thermosetting materials, such as epoxy resins, phenolic resins or polyimides. Examples of inorganic coatings include phosphates [5], silica [6], MgO [7], alumina [8], or ferrites [9].
We have pointed out more pronounced the novelty of our results and their meaning in the context of multilayer inductor fabrication.
However, the effect of oxygen partial pressure upon annealing on the oxidation layer formation and electromagnetic properties has not been systematically studied yet. Hence, it is desirable to study the role of oxygen partial pressure for the optimization of FeSiCr-based power multilayer inductors. In addition, a new concept of combining FeSiCr and Ni-Cu-Zn ferrites with Ag metallization to give a composite multilayer inductor was proposed [12], and annealing protocols include T and pO2 as variables as well.
- Please provide the manufacturer/model/code and also the manufacturer country of the raw materials as well as all testing equipment used for all evaluations.
Answer: We have added some missing information, for example:
of sintered toroids was measured using an Agilent E4991A impedance/materials analyzer (Keysight Techn., Santa Rosa, CA, USA) in the frequency range from 1 MHz to 1 GHz.
- Authors must show which questions/problems have been answered in this work. In this case, the correct and detailed information about this study must be provided in this manuscript.
Answer: The manuscript deals with the behavior of the used alloy upon annealing in different T and pO2. The results are clearly communicated with all details.
- In this manuscript, results are well presented, but discussion on the obtained results must be completely provided in this manuscript. As can be seen, a “comprehensive” and “comparative” discussion is missed in this work. This should be provided as well.
Answer: It is difficult or impossible to compare our results with those of other studies, because:
- the effect of T and pO2 on the physical properties was not studied yet
- the effect of other types of coatings or composites is evaluated with respect to power losses. We did not measure losses of our annealed materials.
- It is also recommended to provide a step-by-step flowchart for a better description of the preparation process and related tests in section 2.
Answer: The authors think that a flowchart is not required. The preparation process of the samples is trivial. Measurements and test procedures are standard.
- Oxidation behavior based on parabolic or non-parabolic behavior must be completely described in this study.
Answer: We did not study any time-dependent kinetics of the oxidation process. Therefore, we cannot give any information on the type of kinetics.
- Structural/morphological characteristics must be indicated in figure 1 b and also figure 4 and 5 using textboxes and arrows/indexes.
Answer: The authors do not agree with the reviewer. Fig. 1a clearly shows the particle size distribution measured with laser diffraction, a d50 of 10.3 µm (as reported in the text) is clearly visible.
The particle size of dBET=2.6µm (as derived from BET gas adsorption) agrees well with the primary particle size from the SEM image in Fig. 1b, which shows particle aggregates consisting of smaller primary particles). We have changed the last sentence.
SEM micrographs confirm that the powder consists of agglomerates of size between 5 to 30 µm, built from smaller particles of around 1-3 µm in size
- Please provide major findings in the “Conclusions” section with a bullet-point style.
Answer: We have modified the conclusions:
We have studied the effect of annealing temperature in air and, alternatively, the effect of oxygen partial pressure during annealing at 900°C on the formation of the surface oxide layer and the performance.
With increasing annealing temperature in air:
- the alloy oxidation and chromia layer formation is enhanced
- the alloy composition becomes more Fe-rich
- the insulation resistance increases and the permeability decreases.
With decreasing oxygen partial pressure in the gas atmosphere during annealing at 900°C:
- the formation of an insulating Cr2O3 surface layer is slowed down
- the resistivity decreases somewhat and the permeability increases
This implies, that the pO2 of the gas atmosphere is another important parameter that allows for tailoring the insulating layer thickness, hence the insulating resistance, and the electromagnetic performance of FeSiCr-based inductors
- There is no description of the future plans for research in the first part of the “Conclusions” section. This should be completed in this section.
Answer: We have included future work plans.
These finding will be used to derive optimum annealing regimes of FeSiCr/ferrite composite multilayer inductors with sufficient insulation resistance of the FeSiCr, and negligible Ag migration in the magnetic layers and/or less reaction between Ag and magnetic materials.
- Recently published references are beneficial for this work. Please check and use new references focused on your work.
Answer: We have added new references.
- Also, please double-check and revise the reference list according to the MDPI / Alloys journal requirements.
Answer: OK. Has been done.
Reviewer 3 Report
Dear authors,
You did an interesting work but the presentation of it does not satisfy. My remarks are as follows:
Please improve Abstract by adding the one or two sentences about the motivation for this work. Also, emphasize the importance of the studied problem as well as novelty.
Introduction section does not provide sufficient background analysis and relevant references are missing. Namely, there should be more critical analysis of articles dealing with topic investigated in this manuscript. Only 4 out of 12 references are recent (in the last 5 years).
Please explain/emphasize a value of this research and its importance.
Please decide what to use: K or °C.
Please specify for each method, how many samples were analysed?
You should confront obtained results with results from other researchers dealing with similar issue.
In Conclusion, you should consider using bullet points (1-2 bullet points) from each of the subsections.
Best regards
Author Response
Reviewer 3:
Dear authors,
You did an interesting work but the presentation of it does not satisfy. My remarks are as follows:
Please improve Abstract by adding the one or two sentences about the motivation for this work. Also, emphasize the importance of the studied problem as well as novelty.
Answer: OK. We have modified the abstract. We have tried to put more emphasis on the novelty of the results:
The variation of annealing temperature between 700°C and 900°C in air, and, for the first time, the variation of the oxygen partial pressure during annealing at 900°C, and their effects on the alloy’s oxidation behavior, phase formation, insulation resistance and permeability are demonstrated
Moreover, we have modified the end of the abstract in order to pay attention to the importance of the results
for the development of further generations of multilayer inductors.
The results can be used to design cofiring strategies using reduced oxygen partial pressure for new multilayer inductive components consisting of FeSiCr- and ferrite layers in combination with silver metallization.
Introduction section does not provide sufficient background analysis and relevant references are missing. Namely, there should be more critical analysis of articles dealing with topic investigated in this manuscript. Only 4 out of 12 references are recent (in the last 5 years).
Please explain/emphasize a value of this research and its importance.
Answer: We have revised the Introduction. We have included more recent references and described the s]. Many other studies have focused on the increasing the resistivity by coating the alloy particles. Insulating coatings are typically classified as organic, inorganic, and composite coatings. Organic coatings are primarily
thermosetting materials, such as epoxy resins, phenolic resins or polyimides. Examples of inorganic coatings include phosphates [5], silica [6], MgO [7], alumina [8], or ferrites [9].tate of the art with respect to particle coating and multilayer fabrication problems.
We have pointed out more pronounced the novelty of our results and their meaning in the context of multilayer inductor fabrication.
However, the effect of oxygen partial pressure upon annealing on the oxidation layer formation and electromagnetic properties has not been systematically studied yet. Hence, it is desirable to study the role of oxygen partial pressure for the optimization of FeSiCr-based power multilayer inductors. In addition, a new concept of combining FeSiCr and Ni-Cu-Zn ferrites with Ag metallization to give a composite multilayer inductor was proposed [12], and annealing protocols include T and pO2 as variables as well.
Please decide what to use: K or °C.
Answer: ?? All temperatures are given in °C.
Please specify for each method, how many samples were analysed?
Answer: OK. In general, three pellets and three toroid samples were used for each anneal. These samples were then used for measuring the mass change, resistance and permeability. Finally, one of the samples was used for XRD and SEM/EDX, respectively.
You should confront obtained results with results from other researchers dealing with similar issue.
In Conclusion, you should consider using bullet points (1-2 bullet points) from each of the subsections.
Answer: We have modified the conclusions:
We have studied the effect of annealing temperature in air and, alternatively, the effect of oxygen partial pressure during annealing at 900°C on the formation of the surface oxide layer and the performance.
With increasing annealing temperature in air:
- the alloy oxidation and chromia layer formation is enhanced
- the alloy composition becomes more Fe-rich
- the insulation resistance increases and the permeability decreases.
With decreasing oxygen partial pressure in the gas atmosphere during annealing at 900°C:
- the formation of an insulating Cr2O3 surface layer is slowed down
- the resistivity decreases somewhat and the permeability increases
This implies, that the pO2 of the gas atmosphere is another important parameter that allows for tailoring the insulating layer thickness, hence the insulating resistance, and the electromagnetic performance of FeSiCr-based inductors
- There is no description of the future plans for research in the first part of the “Conclusions” section. This should be completed in this section.
Answer: We have included future work plans.
These finding will be used to derive optimum annealing regimes of FeSiCr/ferrite composite multilayer inductors with sufficient insulation resistance of the FeSiCr, and negligible Ag migration in the magnetic layers and/or less reaction between Ag and magnetic materials.
Sincerely Yours
Round 2
Reviewer 2 Report
Accept as is.
