sI and sII Clathrate Hydrate Formation and Amorphization in Aqueous Solutions of NH4F
Bibliographic record
Abstract
In recent years the research on clathrate hydrates has gained more and more attraction, both from fundamental research and applications in gas storage and energy conversion. Especially the field of clathrate hydrates featuring a H2O/NH4F-framework shows promise through the discovery of new crystal clathrate hydrates by the Canadian research group led by John A. Ripmeester. Recently, Fidler et al. were able to show pressure-induced amorphization (PIA) of type sI mixed alcohol clathrate hydrates starting at surprisingly low pressures of 0.72 GPa, much lower than pure H2O clathrates. This thesis expands the understanding of alcohol clathrates and their pressure-stability by synthesizing and analysing a type sII mixed alcohol clathrate hydrate crystallized from a quaternary solution. The solution consists of an aqueous solution of 27 mol % NH4F acting as the host framework for the clathrate cages, as well as MeOH and THF as guest molecules to fill those cages. The ratio of THF, methanol, and host molecules/ions (sum of H2O, NH4+, and F–) of the combined quaternary solution is 1:2:16.76. Well established methods like in-situ high-pressure dilatometry and ex-situ X-Ray Powder Diffraction (XRPD) are used to determine the quality and characteristics of the frozen product. As a key finding, this work demonstrates that the cooling rate has a significant impact on the type of the clathrate hydrate that crystallizes from solution. For higher cooling rates (240±20 K∙min−1) type sI clathrate hydrates and hexagonal ice are obtained, whereas lower cooling rates (6 K∙h−1) predominantly produce type sII clathrate hydrates. Therefore, a type sI clathrate hydrate was synthesized, despite using the ideal stochiometric composition for the type sII clathrate hydrate. The second key finding is that the quaternary type sII clathrate hydrate does not show pressure-induced amorphization (PIA) up to 1.6 GPa. This is surprising considering recent findings that show that the additions of NH4F and alcohol lower the onset pressure for PIA of a sI mixed alcohol clathrate hydrate to 0.72 GPa. To better understand what promotes the stability of this mixed alcohol clathrate hydrate against PIA additional clathrate hydrates were produced by omitting one of the four components (MeOH, THF, NH4F, H2O) during synthesis. All of these ternary clathrate hydrates display lower freezing points. For the ternary MeOH-THF-H2O clathrate hydrate it is evident that pressure-induced amorphization (PIA) is occurring throughout all dilatometry plots.
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How this classification was reachedexpand
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 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.002 |
| Open science | 0.000 | 0.001 |
| 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".