Metal Powder Production by Atomization of Free-Falling Melt Streams Using Pulsed Gaseous Shock and Detonation Waves

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have included a review of the article in the attachment.

Comments for author File: Comments.pdf

Author Response

We thank the Reviewer for valuable comments. We have made our best to address all the comments. Our response and the corresponding changes in the original manuscript are marked in yellow.

The article presents a patented method of producing metal powders for additive manufacturing by atomizing free-falling melt streams using pulsed cross-flow gaseous shock or detonation waves. It is in line with the development trends of technologies related to additive manufacturing powder production the need for solutions for obtaining metal powders is becoming more and more noticeable, especially on a laboratory scale. The description of the introduction, the experimental part, and the results are exhaustive. However, some doubts appear in it:

1. There is no information on the method of drying the obtained powders.

To address this comment, we have added the following text to section 2.3:

“After the particles are extracted from the water, excess moisture is removed by drying under natural conditions for 48 hours. After drying, the initial powder samples are dry sieved and the fractional composition of individual portions of the powders is studied by different analytical means.”

 

2. Both in the abstract (lines 34-36) and in the conclusions (581-584) the authors write that “the proposed method for the production of finely dispersed metal powders look promising in terms of powder characteristics and cost”, however, the work does not present a cost calculation for selected materials, both on a laboratory and industrial scale. Similarly, apart from the analysis of the size (size distribution) of particles, I did not find information on the phase composition of the obtained powders. I assume that the authors use the same device for many materials, so it would be worth checking whether there are no contaminations from other processes and whether the fuel used (which the authors write about in lines 97-100) does not affect the final product.

To address this comment, we have made the following changes in the manuscript.

First, we removed the mentioning of the approach “cost” in the abstract and in the conclusions, as we did not evaluate this indicator at this stage of the study.

Second, we have added the following paragraph to section 2.4 to indicate that we did not study the effect of shock/detonation waves on the phase composition of studied materials:

“At this preliminary stage of the study, possible changes in phase and chemical composition of the material after the action of shock/detonation waves and high-speed jets of detonation products are not studied.”

 

Third, we have added the following paragraph to section 2.3 to give more details about equipment cleaning and drying before each experiment:

“The experimental procedure implies special precautions to avoid foreign contaminants in the produced powder. First, all elements of the equipment, both laboratory and industrial, are made of stainless steel. Second, the equipment is thoroughly cleaned, washed with water and dried before each experiment.”

 

3. I did not find any calculations regarding the efficiency of the method for materials on a laboratory and industrial scale, e.g. how much powder useful for the selected AM method (with a specific range of powder grain sizes) is obtained from 250 ml and how much from 4 l of liquid material.

To address this comment, we have added the following paragraph to the text at the end of section 4.1:

“Let us consider now the powder production efficiency of the new technology in terms of two criteria, namely, the yield of powder with particle size less than 150 μm (Criterion 1), and the yield of powder with particle size less than 70 μm (Criterion 2). In our experiments, the Criterion 1 provides the following yields: 13% for zinc, 24% for aluminum and 6% for stainless steel, whereas the yields provided by the Criterion 2 are: 7% for zinc, 18% for aluminum and 2 wt.% for stainless steel. Note that the sample mass of the stainless-steel powder looks not representative (85 g out of more than 30 kg), so there may be a large error in this estimate. If one compares these yields with those provided by other available technologies (10–20% [46]), then looks competitive even in its current form without optimization.”

 

4. There is also no information about which AM method, or possibly which methods, the powders would be most suitable for. I assume that, according to the introduction, the authors are aiming at PBF, so it would be worth knowing what percentage of the total powders obtained are actually suitable for it due to the grain size and shape at the current stage.

To address this comment, we have added the following paragraph at the end of section 4.1:

“Such AM technologies as PBF are known to require powders with spherical particles in a size range of 15–45 µm (for LBM/PBF methods), and 45–106 µm (for EBM/PBF methods) [46]. Similar to other available powder production technologies, the proposed technology provides a polydisperse powder, which must be sorted to obtain a powder suitable for use. If one takes the powder fraction of 30–70 μm for this purpose, then the corresponding yields of such powders in our experiments are: 3% for zinc, 9% for aluminum and 2% for stainless steel.”

 

5. I also have some comments regarding the quality of the posted drawings presented as screenshots with a blue background, they do not look very good I would remove the background and frames, e.g. fig. 13 - 15, and similarly, e.g. fig. 3-5c.

All these figures are generated by the software of the FRITSCH ANALYSETTE 22 device and the software does not produce results in any other representation. Nevertheless, in accordance with the reviewer's suggestion, the original figures were digitized and redrawn.

It is very good that the authors write about continuing research at different levels of the operation frequency of the pulsed detonation gun. I think this is a good direction towards obtaining more spherical grains and a dominant amount of the desired size phase.

The work contains 49 literature items (years 1968-2024), 15 of which are publications from the last 5 years.

To sum up, the work is an interesting concept of obtaining metal powders, which, after refinement, may allow obtaining the desired results.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1）Page 2, Lines 40-54: Although the introduction provides an overview of the background of metal powder production, the analysis of the limitations of existing technologies is not in-depth, and the novelty of the proposed method is not highlighted. It is recommended that a discussion of the drawbacks of traditional gas atomization techniques (such as high cost, unsatisfactory particle size distribution, etc.) be added, and the unique advantages of the method presented in this paper be further emphasized.

2）Page 4, Lines 120-125: Tables 1 and 2 list the compositions and properties of the metals used in the experiments, but there is no explanation of why these materials were chosen. It is recommended to provide reasoning for selecting zinc, aluminum alloys, and stainless steel as experimental materials, such as their application scenarios in additive manufacturing or how their physical properties affect the experiment.

3）Pages 5-6, Figure 1 and related description: The description of the experimental setup is quite detailed, but it lacks a discussion on the relationship between key parameters of the setup (such as the operating frequency of the pulse gun, fuel consumption, etc.) and the experimental results.

4）Page 8, Figure 4 and related description: Issue: The particle size distribution of zinc powder shows a wide range, but the specific reasons behind this phenomenon are not explained. It is recommended to add an analysis of the experimental conditions (such as airflow intensity, melt flow rate) to explain why larger particles and agglomeration phenomena occurred.

5）Page 10, Figure 7 and related description: Issue: The particle size distribution of aluminum powder is relatively regular, but no discussion is provided on the differences compared to the zinc powder experiment results. It is recommended to perform a comparative analysis of the experimental results for zinc and aluminum powders, and discuss how the physical properties of the materials, such as density and surface tension, affect the particle size distribution.

6）Page 12, Figure 11 and related description: The particle size distribution of stainless steel powder is relatively large, and there are incomplete atomized particles, but the reasons for this are not thoroughly analyzed.

7）Pages 14-17: The comparative analysis of the particle size distributions of different materials is insufficient and does not fully explain the phenomena observed in the experiments. The theoretical analysis of the multi-stage atomization process lacks support from experimental data. It is recommended to add a discussion on the differences in particle size distribution for zinc, aluminum, and stainless steel powders, and explain them in terms of material properties (such as density, surface tension, and viscosity). In the discussion of the multi-stage atomization process, more experimental data (such as droplet size changes) should be cited to validate the theoretical analysis.

Comments on the Quality of English Language

The quality of the English language in the manuscript is generally acceptable but requires improvement in several areas to enhance clarity, conciseness, and readability. Below are specific comments:

1）Grammar and Sentence Structure: Some sentences are overly long and complex, making them difficult to follow. For example, in the abstract and introduction, sentences contain multiple clauses that could be simplified or broken into shorter sentences.Articles ("a," "an," "the") are sometimes missing or incorrectly used, which affects the precision of the text.

Word Choice:

2）Certain technical terms are repeated excessively (e.g., "pulsed detonation gun"), which could be replaced with appropriate synonyms or abbreviations after the first mention. Phrases like "looks promising" in the abstract and conclusion appear informal for a scientific paper. Consider using more formal expressions such as "demonstrates potential."

3）Ensure consistent use of terminology (e.g., "PDG" vs. "pulsed detonation gun"). Once an abbreviation is introduced, it should be used consistently throughout the text.

Units of measurement and formatting (e.g., "μm," "m/s") should follow a consistent style.

4）Some sections, particularly the discussion and methodology, use technical jargon without sufficient explanation for readers who may not be specialists in the field. Providing brief definitions or context would improve accessibility. Ambiguous phrases such as "by other words" (likely intended as "in other words") should be corrected.

5）Certain points are repeated unnecessarily in different sections (e.g., the description of the PDG operation). Streamlining the content would improve readability.

6）Ensure proper formatting of references and tables, as some entries appear inconsistent or incomplete. Figures and captions should be reviewed for grammatical accuracy and alignment with the main text.

Author Response

We thank the Reviewer for valuable comments. We have made our best to address all the comments. Our response and the corresponding changes in the original manuscript are marked in green.

1）Page 2, Lines 40-54: Although the introduction provides an overview of the background of metal powder production, the analysis of the limitations of existing technologies is not in-depth, and the novelty of the proposed method is not highlighted. It is recommended that a discussion of the drawbacks of traditional gas atomization techniques (such as high cost, unsatisfactory particle size distribution, etc.) be added, and the unique advantages of the method presented in this paper be further emphasized.

To address this comment, we have added the following paragraph to the Introduction section with the new reference ([26]):

“Each of these technologies exhibits its pros and cons [26]. Thus, mechanical grinding is the cheapest powder production method but it commonly provides flattened particles with changed morphologies. Centrifugal atomization provides a wide range of particle sizes with very narrow particle size distribution (PSD) but requires very high rotation speeds for producing fine powders. Gas atomization is suitable for a wide range of metals and alloys and produces spherical particles but requires high gas pressures and provides powders with fine satellites, wide PSDs, and low yields of particles 20–150 µm in size. Liquid (water-assisted) atomization exhibits very high throughputs and wide ranges of particle sizes but requires high liquid pressures and post-process liquid removal and provides powders with small satellites, wide PSDs, low yields of particles 20–150 µm in size, and particles of irregular morphology. Plasma atomization is commonly used for producing Ti powders of highly spherical shape but requires feedstock to either be in wire or powder form and exhibits low productivity and high cost.”

In view of the new reference, all succeeding references are renumbered.

As for the unique advantages of the method presented in this paper, Lines 106 to 125 in the manuscript provide a detailed description of the method novelty. Nevertheless, to emphasize the specific features, we have added the following paragraph:

“Thus, the new gas atomization method used in this paper has several advantages against the conventional gas atomization methods. First, it replaces the high-pressure atomizing gas with the normal-pressure reactive mixture filling the gas generator. Second, the energy required for melt stream atomization is the chemical energy of the reactive mixture in the gas generator rather than the energy of the compressed gas. Third, the gas generator operates in a pulse mode rather than continuously and produces strong shock/detonation waves finely atomizing the melt stream in a catastrophic breakup mode. Fourth, the intensity of shock/detonation waves and the temperature of the detonation products emanating from the gas generator can be easily controlled by changing the composition of the reactive mixture and by the fill of the gas generator. Fifth, the particle size distribution in the atomized melt can be controlled by pulse frequency and the number of gas generators.”

2）Page 4, Lines 120-125: Tables 1 and 2 list the compositions and properties of the metals used in the experiments, but there is no explanation of why these materials were chosen. It is recommended to provide reasoning for selecting zinc, aluminum alloys, and stainless steel as experimental materials, such as their application scenarios in additive manufacturing or how their physical properties affect the experiment.

To address this comment, we have moved the available paragraph from section 2.3 to the beginning of section 2.1:

“The preliminary experiments reported herein are first conducted with metals possessing a relatively low melting point, namely, zinc and aluminum alloy, using the laboratory setup. Thereafter, some experiments are conducted with a melt of stainless steel with a considerably higher melting point. These experiments are performed on the modified industrial setup.”

3）Pages 5-6, Figure 1 and related description: The description of the experimental setup is quite detailed, but it lacks a discussion on the relationship between key parameters of the setup (such as the operating frequency of the pulse gun, fuel consumption, etc.) and the experimental results.

To address this comment, we have added the following statement at the end of section 2.4:

“Also, the scaling criteria for the design of industrial setup are beyond the scope of the current study.”

4）Page 8, Figure 4 and related description: Issue: The particle size distribution of zinc powder shows a wide range, but the specific reasons behind this phenomenon are not explained. It is recommended to add an analysis of the experimental conditions (such as airflow intensity, melt flow rate) to explain why larger particles and agglomeration phenomena occurred.

To address this comment, we have added the following paragraph when discussing Figure 4:

“It is also worth reminding here that the PSD of Fig. 4 is obtained by zinc stream atomization in periodic detonation waves. Accordingly, the completeness of the melt stream processing is determined by the PDG operation frequency. The largest fragments of the melt are simply a part of the free-falling stream that was not exposed to the shock/detonation wave and high-speed flow emanating from the PDG. In this work, the PDG operation parameters are not varied – there is no such a goal (this is part of future research). At this preliminary stage, there is a simple statement of the fact that a certain portion of the metal remains unprocessed. Therefore, Fig. 4 shows the PSD only for particles smaller than a given threshold (250 μm). The factors accompanying the atomization process are analyzed in detail in Section 4.”

5）Page 10, Figure 7 and related description: Issue: The particle size distribution of aluminum powder is relatively regular, but no discussion is provided on the differences compared to the zinc powder experiment results. It is recommended to perform a comparative analysis of the experimental results for zinc and aluminum powders, and discuss how the physical properties of the materials, such as density and surface tension, affect the particle size distribution.

Such a discussion is available in Section 4, thank you. Nevertheless, to be more specific, we have added the following sentence to section 4.1 with the reference [47]:

“Nevertheless, the PSD for aluminum is noticeably shifted towards finer particles and shows the second mode in the submicron range of particle sizes, which is most probably caused by the higher gas-to-melt momentum ratio [47].”

In view of the new reference, all succeeding references are renumbered.

6）Page 12, Figure 11 and related description: The particle size distribution of stainless steel powder is relatively large, and there are incomplete atomized particles, but the reasons for this are not thoroughly analyzed.

To address this comment, we have extended Figure 11 by introducing Figure 11a and Figure 11 b and included additional text:

“Unlike Figure 4 and Figure 7, Figure 11a shows the PMSD of particles over a wider spectrum: up to sizes exceeding 1000 μm. If one follows the general logic adopted herein and analyze the percentage of different particle fractions by the target group, i.e., for particles smaller than 250 µm, one obtains the distribution shown in Figure 11b.” Thereafter we explain the availability of extremely large particles by the considerably lower gas-to-melt momentum ratio.

7）Pages 14-17: The comparative analysis of the particle size distributions of different materials is insufficient and does not fully explain the phenomena observed in the experiments. The theoretical analysis of the multi-stage atomization process lacks support from experimental data. It is recommended to add a discussion on the differences in particle size distribution for zinc, aluminum, and stainless steel powders, and explain them in terms of material properties (such as density, surface tension, and viscosity). In the discussion of the multi-stage atomization process, more experimental data (such as droplet size changes) should be cited to validate the theoretical analysis.

Despite our analysis in section 4.2 is based on the dimensionless criterion like Weber number and characteristic dimensionless breakup time, we also deal with the dimensional times and distances, which indicate that all three metals undergo at least a three-stage atomization. To emphasize this result, we have extended the following sentence in section 4.2:

Thus, the atomization process of the melt stream in the conditions of present experiments is multistage with three and even four stages for all studied metals.

As for the explanation of the obtained particle size distributions, it is hardly possible at this preliminary stage of the study. We believe, such an explanation will be possible when we conduct planned experiments with the fixed gas-to-melt momentum ratio for the different metals.

 

Comments on the Quality of English Language

The quality of the English language in the manuscript is generally acceptable but requires improvement in several areas to enhance clarity, conciseness, and readability. Below are specific comments:

1）Grammar and Sentence Structure: Some sentences are overly long and complex, making them difficult to follow. For example, in the abstract and introduction, sentences contain multiple clauses that could be simplified or broken into shorter sentences. Articles ("a," "an," "the") are sometimes missing or incorrectly used, which affects the precision of the text.

We have asked our English speaking colleague to check the text, thank you.

Word Choice:

2）Certain technical terms are repeated excessively (e.g., "pulsed detonation gun"), which could be replaced with appropriate synonyms or abbreviations after the first mention. Phrases like "looks promising" in the abstract and conclusion appear informal for a scientific paper. Consider using more formal expressions such as "demonstrates potential."

We have made the corresponding changes in the text, thank you.

3）Ensure consistent use of terminology (e.g., "PDG" vs. "pulsed detonation gun"). Once an abbreviation is introduced, it should be used consistently throughout the text.

Units of measurement and formatting (e.g., "μm," "m/s") should follow a consistent style.

We have checked the text and made the corresponding changes, thank you.

4）Some sections, particularly the discussion and methodology, use technical jargon without sufficient explanation for readers who may not be specialists in the field. Providing brief definitions or context would improve accessibility. Ambiguous phrases such as "by other words" (likely intended as "in other words") should be corrected.

We have checked the text and made the corresponding changes, thank you.

5）Certain points are repeated unnecessarily in different sections (e.g., the description of the PDG operation). Streamlining the content would improve readability.

We have checked the text and made the corresponding changes, thank you.

6）Ensure proper formatting of references and tables, as some entries appear inconsistent or incomplete. Figures and captions should be reviewed for grammatical accuracy and alignment with the main text.

We have checked the text and made the corresponding changes, thank you.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

I would like to thank you for the opportunity to review the revised version of your manuscript titled "Metal powder production by atomization of free-falling melt streams using pulsed gaseous shock and detonation waves." After carefully reviewing the manuscript and considering the revisions you have made, I am pleased to inform you that the paper now meets the requirements for publication in the journal.

Your revision addresses the major concerns raised in my initial review, particularly the improvements made in the discussion of the limitations of existing technologies and the novelty of the method you propose. The additional explanations regarding the material selection, the relationship between key experimental parameters and results, and the analyses of particle size distributions for different materials have significantly enhanced the clarity and depth of the manuscript.

I am particularly impressed by the more detailed explanation of the experimental conditions, the comparative analysis of the particle size distributions, and the more robust theoretical analysis supported by experimental data. The manuscript is now much stronger in terms of both scientific rigor and clarity, and I believe it will be a valuable contribution to the field of metal powder production and additive manufacturing.

Therefore, I am happy to recommend the acceptance of the revised manuscript for publication. Congratulations on your work, and I look forward to seeing your paper published in the journal.

Best regards,