The Solid Solution between NaClO₃ and NaBrO₃ Revisited

Round 1

Reviewer 1 Report

Good work and good presentation. As a reader, it was not obvious, why NaBrO₃ and NaClO₃ needed a revisit, what is special about these materials. How these compounds relate to the broad range of readers of this journal. Brief statement on this would increase the value of the article.

Author Response

Authors Answers to Reviewer 1:

Dear Reviewer,

Thank you for your pertinent remarks and comments. We have reconsidered all the analyses of solids that we performed so far. It appears that: (i) the accuracy that we have with our XRPD is one limiting factor for being conclusive with - certainty – on the deviation to Vegard’s law. This is why we wrote in the revised version: a non-Vegard trend is observed which necessitate confirmation with more precise measurements typically using synchrotron radiations. (ii) Our internal review of the data shows fluctuations in the limiting composition of the partial solid solutions. These fluctuations are beyond the uncertainty of our measurements (XRPD and EDX) and are likely to stem from robust metastable equilibria.

Figure 10 and its caption has been modified accordingly.

We hope our answers will be satisfactory,

Sincerely yours,

The authors.

Reviewer 2 Report

The MS minerals-2489148 is dedicated to a system which clearly and comprehensively illustrates complex behavior of systems wherein formation of complete solid solutions can be expected but in fact these are thermodynamically unstable. The authors have developed an approach to the metastable SS and demonstrated its decomposition. The experimental part of the MS is clear and needs little further revision. Overall, the results are relevant, convincing and of evident interest to the potential readers. Therefore, after some, yet essential, corrections I would recommend the MS for publishing in the Journal.

On the contrary, the introductory part is large, and its structure needs essential revision. The authors seem to re-tell all whatever has been reported on the chlorate-bromate system. A large part, in my opinion, can be transferred to the Discussion, and introduction be essentially shortened and re-organized by illustrating all contradictions between the earlier experimental results and their intrerpretations. That the aim of this work was to re-investigate the system I could only deduce from the organization of the experimental part. Some rearrangements and shortening would essentially improve the MS and ensure clearer understanding the problem, aims, and scope. I would also recommend to compare behavior of the investigated system to some others which demonstrate similar features.

Several awrkard sentences throughout the text hinder the understanding their meaning. Just some examples:

Ln 39: "NaClO3 and NaBrO3" belong to achiral molecules" How can salts be molecules?

Ln 57: "In 2005, Viedma reported later..." Was that in 2005 or later?

Ln 98: "ionic structure of S2O62-" all bonds therein are strongly covalent

Ln 123. Reflections forbidden for P2(1)3 may be allowed e.g. for P23, this does not necsssarily imply deviation from cubic symmetry

Ln 238: "stagnant conditions" misleading, maybe "static conditions"?

Ln 240-241: "despite the isomorphous character of NaClO3 and NaBrO3 single phases" does it actially mean "though pure NaClO3 and NaBrO3 are isomorphous"?

Ln 314: "collapse" perhaps "coalesce"?

Ln 322: "putative" perhaps "tentative"?

Ln 339: "details the link between size and homogeneity" perhaps "discusses the relationship"?

Ln 340: "morphologies that are more isomorphous" what does this mean?

Ln 347: "are displayed on Figure 9" awkward, maybe "shown"?

Ln 350: "Furthermore, ..." Some following text is evidently lost!

Ln 364: "A discontinuity of the Vegard's law" should probably be "A deviation from..." There can not be a discontinuity in the law, but in a graphical representation.

Ln 422" Not "big" but "large" or "larger" particles.

Misprints are also present:

Ln 20 "crystalline structure" vs. "crystal structure"; ln 34 "crystalligraphic".

Ln 46: the same reference given in two styles.

Ln 59: "lefthanded and right-handed" please unify spelling

Ln 288: no need to capitalize bromate, it is not a proper name

Ln 294, 425, 468, 521: subscript indices

Ln 319: "shown Figure 7" insert "in"

Author Response

Answers to Reviewer 2:

Dear Reviewer,

Thank you for your pertinent remarks and comments. We have followed your recommendations, and we propose a revised manuscript accordingly.

The Introduction part has been shortened, especially by removing former part 1.3 “Chirality and Deracemization” and part 1.4 “Crystal growth of NaClO₃ and NaBrO₃ crystals in the presence of impurities”. Hence, Introduction part is now mainly focusing on the matter of the subject: (i) the crystal phase relationship between NaClO₃ and NaBrO₃ (section 1.2), chirality, (ii) mixed crystal and existence of solid solution (section 1.3), and (iii) the determination of phase equilibria of the two salts in solution.

Corrections of English:

We hope our answers will be satisfactory,

Sincerely yours,

The authors.

Reviewer 3 Report

The manuscript on solid solutions between NaClO3 and NaBrO3 is overall sound, well structured and with adequate figures and a table. The results are carefully developed from the experimental findings and predominantly sound.

Basically, I have only one remark. The authors show the lattice parameters as a function of composition for the spray-dried samples. This is OK, but the data show results for a meta-stable situation, which can point at deviations, but are not unambiguous.

In this context it would clearly substantiate their conclusion to show the same development of lattice parameters for the particles grown from solution. Especially in the region of demixion, there should be clear plateaus starting from the NaCLO3-rich and a second one originating in the NaBrO3-rich side. The plot of the absolute values can also help in determining the boundary composition and give some hints for the interpretation of the findings for the spray-dried samples. 

Author Response

Answers to Reviewer 3:

Dear Reviewer,

Thank you for your remarks. Below a brief statement on the pertinence of this article in the journal.

This article is submitted in the special issue “Isomorphism and Solid Solutions of Minerals and Related Compounds” of Minerals. Many of the matters discussed in this article are in-line with the special issue key words (see on Minerals | Special Issue : Isomorphism and Solid Solutions of Minerals and Related Compounds (mdpi.com)), and a brief highlight on the interests of this particular system is given below:

The NaClO₃ NaBrO₃ water system has attracted many interests in the scientific communities, for which some examples are cited in the introduction part of this manuscript. First study on phase equilibria of this system is attributed to Swenson and Ricci (see section 1.4), and current manuscript aims at resolving conflicting data about this system: (i) evidence of a miscibility gap (in the solid state) for the NaClO₃-NaBrO₃ mixed crystals, (ii) identification that a complete metastable solid solution that could be obtained by spray-drying under certain conditions, and (iii) proposal to explore further the NaClO₃ NaBrO₃ water system in taking into account chirality.

We hope our answers will be satisfactory,

The authors

Round 2

Reviewer 3 Report

The revised version of the manuscript is complemented by the requested analysis of lattice parameters, which has been my major issue. Many minor revisions and additions help to improve the soundness and precisoon of the study. 

Thus, I can recommend the contribution in its present form for publication.