Effect of Doping with Carbon and Boron Nitride on the Hydrogen Absorption in Titanium
Bibliographic record
Abstract
Pure metallic titanium is a fairly good hydrogen-absorbing material, which permits to accommodate up to ∼3.3×10 -3 mol/g Ti, or H/Ti=0.32.The reaction goes fast during reactive milling of Ti in the H 2 atmosphere.The "theoretical limit" of the hydrogen sorption, with all octahedral interstitials occupied by hydrogen atoms, corresponds to the (cubic) titanium hydride TiH 2 .It is known 1,2 that an addition of graphite considerably accelerates the hydrogen uptake in the process of milling.However, the carbonization of the surface ultimately blocks the H 2 absorption.In the search for other additives which could boost the hydrogen uptake in a similar manner, the boron nitride, another layered material, turned out quite ef cient. 2 Even if the maximal sorption rate is inferior to that with the carbon additive, the sorption process is more stable and, in total, accommodates by far more hydrogen, notably in a post-milling absorption, 2 shifting the total hydrogen sorption towards H/Ti=0.2(after 30 min. of milling), 0.88 (66 min.)and 1.95 (205 min.), the last number being close to the theoretical absorption limit.The details of the microscopics of the hydrogen absorption are, however, not obvious.A combined study by X-ray diffraction, electron microscopy and X-ray emission spectroscopy (see details in Ref. 2) revealed the following, in part contradictory, ndings: 1.The phase analysis by the X-ray diffraction shows that the amount of α-Ti and hexagonal BN gradually decreases in the process of milling H 2 absorption, leaving nally (after 206-min.milling) exclusively δ-TiH 1.95 .No traces of TiN or TiB phases have been detected at any stage of the process.2. According the X-ray emission spectroscopy, which probes the local electronic structure in an element-sensitive way, the L 2,3 spectrum of titanium in the milled hydrogen-saturated sample resembles a superposition 40%Ti + 40%TiH 2 + 20%TiN.The K α spectrum of nitrogen in the same sample can be rouphly decomposed as 89.7%BN + 10.3%TiN.An apparent controversy (a noticeable amount of TiN according to XES, but no traces of the nitride phase in the diffraction study) re ects the fact that the X-ray spectroscopy is sensitive to the nearest chemical neighbourhood.A contribution of TiN-like spectrum reveals merely that nitrogen atoms exist either in the boron nitride layers (on the surface of titanium particles), or in the TiN-like neighbourhood, that is, octahedrally coordinated by titanium atoms.The latter situation corresponds to a nitrogen atom in an octahedral interstitial within hexagonal (α) or cubic (TiH 2 -like) titanium lattice.Such a conclusion offers a foundation for a microscopic ab initio study of the electronic structure and chemical bonding.Namely, we adopt a structural model which does not contain BN (in crystalline or molecular form inside the titanium bulk) but allows single nitrogen (and, for the sake of comparison, also boron and carbon) atoms in
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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".