Hydrogen Motion in Magnesium Hydride by NMR
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Bibliographic record
Abstract
In coarse-grained MgH 2, the diffusive motion of hydrogen remains too slow (<10 5 hops s −1 ) to narrow the H NMR line up to 400 °C. Slow-motion dipolar relaxation time T 1D measurements reveal the motion, with hopping rate ω H from 0.1 to 430 s −1 over the range of 260 to 400 °C, the first direct measurement of H hopping in MgH 2 . The ω H data are described by an activation energy of 1.72 eV (166 kJ/mol) and attempt frequency of 2.5 × 10 15 s −1 . In ball-milled MgH 2 with 0.5 mol % added Nb 2 O 5 catalyst, line-narrowing is evident already at 50 °C. The line shape shows distinct broad and narrow components corresponding to immobile and mobile H, respectively. The fraction of mobile H grows continuously with temperature, reaching ∼30% at 400 °C. This demonstrates that this material’s superior reaction kinetics are due to an increased rate of H motion, in addition to the shorter diffusion paths from ball-milling. In ball-milled MgH 2 without additives, the line-narrowed component is weaker and is due, at least in part, to trapped H 2 gas. The spin−lattice relaxation rates T 1 −1 of all materials are compared, with ball-milling markedly increasing T 1 −1 . The weak temperature dependence of T 1 −1 suggests a mechanism with paramagnetic relaxation centers arising from the mechanical milling.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 it