Comment on “Spectroscopic studies of oxygen speciation in potassium silicate glasses and melts”

Malfait, Wim J.

doi:10.1139/cjc-2014-0587

Cited by 7 publications

(6 citation statements)

References 20 publications

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“…Efforts at re-analyzing these results with different peak assignments have yielded estimates of much higher FO contents that are more consistent with O 1s XPS data (Sawyer et al, 2015), but this interpretation has also been controversial (Malfait, 2015;Nesbitt et al, 2015b). They do serve as reminders that all such fitting exercises are to some extent model-dependent.…”

Section: Accepted Manuscriptmentioning

confidence: 98%

“…This lead to the conclusion that substantial fractions of FO were present that were well above those expected in conventional models of glass structure, with reported K ox values as low as 2 for K 2 O-SiO 2 (Sawyer et al, 2012), increasing to 8 in a more recent report with revised glass compositions (Sawyer et al, 2015), and 14 for Na 2 O-SiO 2 (Nesbitt et al, 2011). For thermodynamic reasons discussed below, these values are surprisingly low, and have been subject to considerable controversy, with discussions of issues of glass composition, spectral fitting methods, and the intriguing possibility that the near-surface regions (a few nm deep) sampled by XPS might be different from the bulk glass (Malfait, 2015;Nesbitt et al, 2015b). In contrast, for Pb silicate glasses near to and even below the critical orthosilicate composition, a BO shoulder in O 1s XPS spectra has long provided evidence for the necessity of significant FO concentrations (Smets and Lommen, 1982); recent fits of higher resolution spectra have yielded K ox values of about 12 (Nesbitt et al, 2015a;Nesbitt and Dalby, 2007), somewhat lower than the result of direct integration of resolved 17 O MAS NMR spectra noted above (Lee and Kim, 2014).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…There has been significant controversy over the XPS findings and accompanying re-analyses of previously published NMR spectra (Malfait, 2015;Nesbitt et al, 2015a;Nesbitt et al, 2015b), including concerns about accuracy of alkali silicate glass compositions and the vagaries of fitting of highly overlapped Gaussian components of both XPS and NMR spectra. In any case there has been a strong, renewed interest in examining the accuracy of the "reaction to completion" approximation.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

See 2 more Smart Citations

“Free” oxide ions in silicate melts: Thermodynamic considerations and probable effects of temperature

Stebbins

2017

Chemical Geology

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Section: Accepted Manuscriptmentioning

confidence: 98%

Section: Accepted Manuscriptmentioning

confidence: 99%

Section: Accepted Manuscriptmentioning

confidence: 99%

See 1 more Smart Citation

“Free” oxide ions in silicate melts: Thermodynamic considerations and probable effects of temperature

Stebbins

2017

Chemical Geology

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“…To address Malfait's analytical concerns, 7 we performed additional microprobe analyses to emphasize precision and accuracy. Our first concern 1 was the homogeneity of the 30 and the two 32 mol% K 2 O glasses (see Sawyer et al, 1 their fig.…”

Section: Homogeneity and Composition Of Glassesmentioning

confidence: 99%

“…Specifically, a recent 2D 29 Si MAF NMR study 6 revealed that potassium disilicate glass is more polymerized than sodium disilicate glass and that there is an unresolved Q 4 peak underneath the Q 3 signal of 29 Si MAS NMR spectra of the potassic glasses. 2,3 Our recent paper 1 avoided a detailed analysis of the 29 Si MAS NMR spectral results of Malfait et al, 2 but in light of this challenge, 7 we are forced to examine their spectral resolution and fitting procedures in the first section of this rebuttal. Specific concerns raised by Malfait 7 are addressed in Appendix A.…”

Section: Introductionmentioning

confidence: 99%

Reply to the comment by Malfait on “Spectroscopic studies of oxygen speciation in potassium silicate glasses and melts”

et al. 2015

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Malfait challenges our XPS results by arguing that the XPS spectroscopic technique cannot be used to determine small amounts of O 2-in potassium silicate glasses. Instead, he claims that there is no free oxide (O 2-) in potassium silicate glasses based primarily on his 29 Si MAS NMR spectroscopic results. In this rebuttal, we demonstrate that O1s XPS and well-resolved 2D 29 Si MAF NMR spectral results of potassium disilicate (K 2 Si 2 O 5 ) glass are consistent with each other and that both techniques indicate the presence of a few mol% of O 2-in the glass. Neither of these techniques, however, supports the interpretation of the 29 Si MAS NMR results presented in the comments of Malfait. The major difficulty relates to the low resolution of the 29 Si MAS NMR spectra, which does not reveal the Q 4 signal beneath a strong Q 3 peak in these spectra. The proof is provided by the 2D 29 Si MAF NMR spectrum of potassium disilicate glass in which both Q 3 and Q 4 peaks are revealed; the 2D 29 Si MAF NMR results for potassium disilicate glass are far more informative than 29 Si MAS NMR spectra. It demonstrates that the potassium disilicate glass (K 2 Si 2 O 5 ) contains greater Q 4 intensity, is more polymerized than previously considered, and that O 2-is present at ϳ2 (±1) mol% in the potassic glass. This O 2-value confirms our O1s XPS results. Specific points raised by Malfait are rebutted in Appendix A.Key words: potassium silicate glasses, free oxide, O1s XPS, 29 Si and 17 O NMR.Résumé : Malfait remet en question nos résultats de XPS selon l'argument que la technique XPS ne peut être utilisée pour doser de faibles quantités d'espèces O 2-dans des verres de silicate de potassium. En contrepartie, il prétend qu'il n'y a pas d'oxyde libre (O 2-) dans les verres de silicate de potassium, en s'appuyant principalement sur ses résultats spectroscopiques de RMN 29 Si en MAS. Dans la présente réplique, nous démontrons que les résultats des spectres XPS O1s et ceux des spectres RMN 29 Si 2D MAF, obtenus en bonne résolution, d'un verre de disilicate de potassium (K 2 Si 2 O 5 ) sont cohérents entre eux et que les deux techniques indiquent la présence dans le verre de quelques mol% d'O 2-. Toutefois, ni l'une ni l'autre de ces techniques ne permet d'appuyer l'interprétation des données RMN 29 Si MAS présentée par Malfait. La principale difficulté provient de la faible résolution des spectres RMN 29 Si MAS qui, dans ceux-ci, ne permet pas de révéler le signal Q 4 sous un pic Q 3 d'envergure. La preuve réside dans le spectre RMN 29 Si 2D MAS du verre de disilicate de potassium, dans lequel les deux pics, Q 3 et Q 4 , sont révélés; les résultats de RMN 29 Si 2D MAS des spectres du verre de disilicate de potassium sont beaucoup plus instructifs que ceux des spectres RMN 29 Si MAS. Ils permettent de démontrer que le verre de disilicate de potassium (K 2 Si 2 O 5 ) contient l'espèce Q 4 en plus grande proportion et qu'il est plus polymérisé qu'on l'avait cru précédemment, et que l'oxygène O 2-y est présent à ϳ2 (±1) mol%. Cette valeur ...

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Spectral Resolution and Raman Q3 and Q2 cross sections in ~40 mol% Na2O glasses

2021

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A comparative study of Raman and 29 Si MAS NMR spectral intensities indicates that Raman Q 2 and Q 3 species cross sections are respectively, 1.07 and 0.97, based on the assumption that they are 1.0 in 29 Si MAS NMR spectra. The Q 2 band of the Raman spectrum is dominantly Lorentzian in shape whereas the Q 3 band is asymmetric. There are two explanations for the asymmetry, one related to alkali-tetrahedral oxygen interactions and the other related to Q n,ijkl clustering. The explanations are not mutually exclusive and both may contribute to production of asymmetric Q 3 bands in Raman and 29 Si MAS NMR spectra. The combination of 29 Si static NMR and high resolution Raman spectroscopy now can provide highly accurate estimates of Q 2 , Q 3 and Q 4 species abundances in glasses containing 35-41 mole % Na2O. It remains to be determined if similar quantification can be achieved over a wider compositional range.The Q species abundances derived from 29 Si MAS and static NMR have been used to evaluate equilibrium constants for the speciation reactions Q 3  Q 4 , Q 2  Q 3 and Q 1  Q 2 . Mass action and mass balance equations then were solved to obtain concentrations of Q 1 , Q 2 , Q 3 , Q 4 and free oxygen (oxygen not bonded to Si) in glasses ranging from 0 to 45 mol% Na2O. The calculated values are consistent with 29 Si NMR, Raman, and O 1s X-ray Photoelectron spectroscopic (XPS) experimental results. Thermodynamic constraints (mass action equations) are more reliable than traditional stoichiometric constraints in extracting Q and O species abundances from spectroscopic data and in testing the accuracy of the results. IntroductionInsights into the short-range structure and chemical speciation of silicate glasses and melts have been obtained mainly by four spectroscopies,

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Comment on “Spectroscopic studies of oxygen speciation in potassium silicate glasses and melts”

Cited by 7 publications

References 20 publications

“Free” oxide ions in silicate melts: Thermodynamic considerations and probable effects of temperature

“Free” oxide ions in silicate melts: Thermodynamic considerations and probable effects of temperature

Reply to the comment by Malfait on “Spectroscopic studies of oxygen speciation in potassium silicate glasses and melts”

Spectral Resolution and Raman Q3 and Q2 cross sections in ~40 mol% Na2O glasses

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