Microfabrication of High-Aspect Ratio KNN Lead-Free Piezoceramic Pillar Arrays by Aqueous Gelcasting

Round 1

Reviewer 1 Report

1) please supply the properties of the KNN powder, such as particle size, size distribution , SEM photograph

2) In fig8 , why  the strength of the 42vol% sample got the highest data , and the strength of the sample is decrease with the soild loading increase.

3) Did you measure the piezoelectric propertie of the samples , is there any change with the solid variation.

Author Response

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Reviewer 2 Report

In this manuscript the authors report preparation of KNN- hydantoin epoxy resin suspensions of high solids loadings (up to 48 vol.%) for gelcasting fabrication of micro-pillar arrays with a high aspect ratio. The manuscript is interesting and fits the scope of the Journal. The authors in general provide reasonable explanations to their experimental findings, despite details about dispersion and gelation mechanisms are lacking.

Some suggestions and questions are listed as follows for the authors’ information.

Suggestions

1. The authors are advised to define their symbols in their first use. For example, the use of gamma for the shar rate should be addressed.
2. The experiment of suspension viscosity versus gelation time in Fig. 5 was carried out at a temperature range from 50 to 65 C by (supposedly) rheometry. The testing condition is yet not properly addressed in the experimental section.

 

Questions

1. The title mentions about an aqueous gelcasting process; nonetheless, the authors did not address the amount of water used specifically in their formulation.
2. In the experimental section, 15 wt.% hydantoin epoxy resin was used in their formulation. This weight percent is relative to all the ingredients (including KNN, water, and resin) in the formulation? Please specify.
3. The immediate addition of gelation initiator DPTA to the KNN suspension presents a potential change of suspension viscosity even before the gelation actually occurs. But this has never being mentioned in the manuscript.
4. The authors are advised to add photos of the debound and sintered pillar arrays in their manuscript so that the paper is more complete.

 

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Well written manuscript focusing on essential and not often published topic - the rheology of suspensions, which are intended for aqueous gel casting to obtain piezo-active micro pillar arrays from KNN ceramic powder.

But some information about calcination or sintering are missing and if the sintering will not be defect-free in structure and geometry of pillars then would be results of this paper meaningless.

So, sintering or calcination is neccesary to finish all experiments. Some easy analyses such as TGA and grain size after sintering could be beneficial to support the results.

1) Authors, please read your manuscript carefully and check all typos and the text formatting (dimensions formatting, spacing between value and dimension, ...). For example shear rate ... once as 1000 s-1 and further as 0.1 s^-1 and third option you used is ..activation energy 90.5 kJ/mol. Be consistent through whole text please.

2) Please fix dimension for load rate (mechanical testing), probably 0.5 mm/min and put the number of tested specimens and the confidence interval or standard deviation.

3) Please put the power law function into Figure 4 accompanied with correlation coefficient.

4) I would use smaller magnification of micro pillar array overview in Figure 10. Let’s say, it would be visible more than 5 pillars in each direction.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

Although the novelty of this study was to use (K_0.5Na_0.5)NbO₃ (KNN) ceramic, the characteristics of KNN are not involved in the discussion. The relationship of suspension viscosity with increasing shear rate and dispersant concentration is well discussed. However, these relationships seem to apply to any substance. The results should be compared with other substance such as Pb(Zr, Ti)O₃.

 

The properties of suspension should be influenced by particle size of ceramics. Please add the morphologic information for KNN such as particle size and shape.

 

In lines 18, 56, 60, 142, 145, 169 and 193, the “hydantoin” spelling is mistaken for “hydantion”.

 

In the Results and Discussion section, Figure 1(a) was never mentioned. Please delete Figure 1(a) or mention it in the main text and caption.

 

In line 80, 89 and 107, please do superscript of s-1.

 

In line 89 and 111, please use the same unit in main text(mPa·s) and figure caption(Pa·s).

 

In line 130, please make sure that the formula for yield stress is correct.

 

In Figure 6, please correct the caption on the vertical axis to “Idle time(s)”

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper can be accepted as it  is

Reviewer 2 Report

The authors have addressed my suggestions/comments appropriately in the revised manuscript.  The manuscript should be accepted for publication.

Reviewer 3 Report

The authors met the requirements for the correction of the manuscript, answered my questions sufficiently and justified some steps that were not yet clear to me.
They did a good job during the revision of the manuscript and therefore I have no more questions and I can recommend this manuscript for publication in Ceramics.