Tin and Niobium in Dry and FluidRich H2O, F Silicate Glasses
Bibliographic record
Abstract
The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the Nb and Sn K-edges using beamline 4-3 and 11-2 at SSRL (Stanford, USA). The metal content in the glasses varies between 100 ppm and 5 wt.% (to examine the effects of Nb 2 O 5 and SnO 2 saturation in the melt composition prior quenching). The glasses show variation in composition from peralkaline to peraluminous, with either zero or ∼2 wt.% fluorine. In addition, hydrous glasses were quenched from water-saturated melts at 850 °C and 2 kbar under relatively reducing conditions. Three "haplogranitic" compositions (a model granite in the system Na 2 O-K 2 O-AlO 3 -SiO 2 ) were investigated: peralkaline (labeled "ASI 0.6"), metaluminous ("ASI 1.0") and peraluminous ("ASI 1.2"). One series of haplogranitic glasses ("SQ") were synthesized at intermediate oxygen fugacity conditions (∼10 −9 atm.). In addition, 15 model oxide and silicate compounds of tin and niobium were investigated. The tin-bearing glasses show Sn K-edge XAFS spectra that resemble that displayed by eakerite, a Ca-Sn silicate in which Sn(IV)O 6 octahedra share corners with SiO 4 tetrahedra (⟨Sn-O-Si⟩: 150°). However, the most reduced glasses show significant contributions arising from weakly bound Sn(II)O n complexes. The niobium-bearing glasses show Nb K-edge XAFS spectra that most closely resemble that displayed by vuonnemite, a Na-Ti-Nb silicophosphate. Niobium forms NbO 6 clusters, also bonded to Si/Al second neighbors. The coordination geometry of niobium in the glasses is strongly influenced by both Nb content and alkalinity; H 2 O content does not strongly influence the speciation of niobium. Fluorine-bearing Nb-glasses show unusual XANES spectra, which might be related to a decrease in the coordination number of niobium from 6 to 4 (or 5). However, based on Nb K-edge XANES calculations (FEFF 8), fluorine does not appear to complex niobium.
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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) | 0.002 | 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".