X-ray and Neutron Study on the Structure of Hydrous SiO2 Glass up to 10 GPa
, Toru Inoue 2,3, Takanori Hattori 4, Asami Sano-Furukawa 4, Shinji Kohara 5,6, Daisuke Wakabayashi 7, Tomoko Sato 2, Nobumasa Funamori 7 and Ken-ichi Funakoshi 8
Sylvain Petitgirard
Round 1
Reviewer 1 Report
This manuscript deals with a very interesting structural study of hydrous silica glass synthesized under high pressure (10GPa). Small angle x-ray scattering (SAXS), x-ray diffraction (XRD) and neutron diffraction (ND) are well adapted techniques for this purpose. Moreover, the authors carried out in situ structural experiments under high pressure.
I have comments and questions:
i) Why to choose an amount of 13% D2O in silica?
ii) Paragraph 4. 1. it is not evident that one observes a phase separation in hydrous silica glass from SAXS experiments (figure 2). Have the curves of the figure 2 been analysed and interpreted? Comments are needed.
iii) Paragraph 4. 2.The comparison between dry and hydrous glass from XRD and ND is not clear; in particular the comments about the respective contribution from H and D for hydrous glass from XRD and ND.
iv) The agreement between the SX(Q) or (SN(Q)) of the hydrous SiO2 with the synthesized SX(Q) or (SN(Q)) of the mixture of SiO2 and the liquid D2O is not so good, as claimed by the authors, not only at the level of the FSDP but also at the level of the other peaks. Does it mean that the assumption of a two-phase mixture is not valid? The authors have to be more convincing about this assumption.
v) A conclusion is missing and must be added. In particular, one asks the following question: where is the molecular water incorporated in the SiO2 glasses? This is not clear to the reader.
The English must be improved.
Some examples of corrections: principal instead of principle, short range order instead of short range structure, medium range order instead of medium range structure, etc
Author Response
We revisited the manuscript according to the reviewers’ comments. The responses (in blue) to the reviewers’ specific comments (in italic) are in a separate attachment. Our manuscript has been brushed up by native proofreading.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review of manuscript 682220
X-ray and Neutron Study on the Structure of Hydrous SiO2 Glass up to 10 GPa
Satoru Urakawa et al
The manuscript details the synthesis of a hydrous (D2O) SiO2 glass and its characterisation using a variety of techniques (optical Raman, SAXS, XRD, ND).
The main conclusions are that not all the D2O is incorporated in the SiO2 structure as hydroxyl groups, but rather form domains of enriched molecular D2O and other domains with Si-OD of less the 100 Å. The physical properties are thus affected compared to anhydrous SiO2, with a higher density at room condition due to the smaller ring size in the glass, the medium range structure is more shrinkable than the anhydrous glass.
Overall the manuscript is well done and concise and data are quite well convened also of very high quality regarding the XRD and ND. However, they should check the use of tenses in their sentences as sometimes it goes form past to present to past again, it needs a bit more consistency (ex: line 111-113). The conclusions bring even more questions about the properties of such material and the authors start to discuss such issues (with He and Ne penetrating the structure of SiO2) at the end of the manuscript and it would have been very nice to have supporting data for that. Also the decompression data would have been quite an addition to the already presented data, or at least extra data on the recovered sample after compression could have helped to understand the amount of permanent densification a little better and to compare it with anhydrous SiO2.
I have a few comments that would need to be addressed before the manuscript can be accepted for publication:
Line 22-23 I would also insist on the properties of glasses in general as a technological material, not only for earth science.
Line 69-72. I appreciate the fact that the authors measured the density of their material. They discuss its higher density mostly because it was synthesized at high pressure. Could it be that the addition of water disrupts the ring size, making them smaller, and thus increasing the compaction of the glass?
Line 75-78. The use of optical Raman is also of great help and the material has been thoroughly investigated prior to X-ray analysis. Later the authors use SAXS with a 35 micrometre beam and see changes in the SAXS pattern in the range 0.05-0.1 Å and conclude that domains of 100 Å are at the origin of such changes. Can the authors elaborate more on this part? And second do they see such differences in intensity with the Raman as well?
line 111: “clumps of” rather than clumpsy
line 131-132: how does the author convert the 0.05-0.1 Å to 110 Å domains? A little explanation here would be helpful for the reader. Is it FFT?
Line 149: missing word at the end of sentence.
Lines 160: only in the neutron data…. reflects the packing fraction.
Section 4.2 is well done and demonstrate the expertise of the authors in the domain. I feel this is somehow missing in total X-ray scattering measurement under pressure in recent years and it is nicely described here.
Figure 4 A and B it is a bit difficult to see the different patterns in these two figures. Can the authors either change their colours or shift them apart?
It is a nice exercise to show that the SiO2 13wt%D2O can be also reproduced by a liner combination of SiO2 + liq. D2O.
Section 4.3 the data shown in this section are of rare quality.
Line 216 remove “much” or rephrase…
Line 218- 220 This is consistent with the structure deduced from SAXS showing that the hydrous SiO2 glass is mainly composed of relatively dry parts rich in SiO2.
Figure 5 C-D, would it be possible to add on top of the peaks the correspondence to Si-O bond distance, Si-Si … to help visualize where the peaks can be found.?
Section 4.4 there is a discussion about the amount of free D2O in the structure. Does the estimate fit the linear combination used earlier between anhydrous SiO2 and lig. D2O to reproduce the XRD pattern at ambient (Fig.4)
The final discussion raised even more question and possible experiments looking at how He and Ne can penetrate or not such material.
I hope these comments will help the authors to polish their manuscript.
Author Response
We revisited the manuscript according to the reviewers’ comments. The responses (in blue) to the reviewers’ specific comments (in italic) are in a separate attachment.
Author Response File: Author Response.pdf
