Influence of F content on the composition of Al-rich synthetic phlogopite: Part I. New information on structure and phase-formation from <sup>29</sup> Si, <sup>1</sup> H, and <sup>19</sup> F MAS NMR spectroscopies
Bibliographic record
Abstract
The influence of F content on the formation and stability of Al-rich phlogopite has been investigated. Samples with varying OH/F-ratios and nominal gel compositions of K(Mg 3-x Al x )(Al 1+x Si 3-x O 10 )(OH) y (F) 2-y (0.0 < x < 0.8 and 0.5 < y < 1.8) were studied using 29 Si, 1 H, and 19 F MAS NMR spectroscopies, powder X-ray diffraction, electron-probe microanalysis, and scanning electron microscopy. The synthetic phlogopites were synthesized from sol-gels in cold-seal pressure vessels at 1073 K, 2 kbar. The main phase (phlogopite) and three other impurity phases [corundum (α-Al 2 O 3 ), kalsilite (KAlSiO 4 ), and potassium aluminum hexafluoride (K 3 AlF 6 -0.5H 2 0)] were clearly identified by powder X-ray diffraction and electron-probe microanalysis. For phlogopite, the unit-cell parameters a 0 and b 0 decrease whereas C 0 increases with increasing Al-content (x). The average crystal size of phlogopite is about 1-2 pm. The 29 Si MAS NMR spectra show up to four resonances at approximately -91, -87, -83, and -80 ppm, which can be assigned as Q 3 (n Al) signals with n = 0 - 3. The ideal Si/ iv Al ratio calculated from the initial composition is always lower than that derived experimentally. Hydroxyl-rich compositions indicate an increased Al-content in the tetrahedral sheets, suggesting a stabilizing effect on the formation of Al-rich phlogopite. These conclusions are supported by 1 H and 19 F MAS NMR spectra. The 1 H MAS NMR spectra show a water signal at 4.7 ppm, a signal due to Mg 2 AlOH at 1.8 ppm, and a signal due to Mg 3 OH at 0.7 ppm. The 19 F MAS NMR spectra exhibit a signal for Mg 2 AlF at -150 ppm, one due to AlF 6 (K 3 AlF 6 -0.5H 2 0) at -157 ppm, and one for Mg 3 F at -174 ppm. Comparison of the 1 H and 19 F MAS NMR spectra for different Al- and F- contents reveals a non-statistical distribution of F- and OH-groups at the crystallographic sites in the octahedral sheets where F prefers sites coordinated by three Mg, and OH sites with Al in the next- nearest coordination sphere.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".