Water Activity Controls the Stability of Amorphous Ca–Mg- and Mg-Carbonates
Bibliographic record
Abstract
Amorphous carbonates are increasingly recognized as important precursors in biomineralization and abiotic carbonate precipitation at ambient temperatures. Understanding the conditions and factors that influence the stability of amorphous Ca-, Ca–Mg-, and Mg-carbonates (ACC, ACMC, and AMC) is essential for understanding how organisms control biomineralization, the creation of functional carbonate nanomaterials, and enhancing engineered and natural CO 2 storage processes. Here, we constrain the intersecting effects of precursor compositions (Mg content) and the action of physisorbed water on the reaction rates and crystallization pathways of ACMC by reacting amorphous carbonates, Ca 1– x Mg x CO 3 · n H 2 O, with compositions of 0.16 ≤ x ≤ 1 under relative humidities (RHs) of 5 to 98 ± 2%. We report the persistence of synthetic amorphous carbonate phases at ≤53% RH on similar time scales to biogenic ACC and ACMC (≥7 months). By contrast, transformation to crystalline phases occurs before 30 days for all compositions of ACMC at 98% RH ( a w ∼ 1) and by 210 days for high and low Mg precursors at 75% RH. These results suggest that a threshold amount of physisorbed H 2 O generated between 75 and 98% RH facilitates crystallization, indicating that structural H 2 O in the amorphous material is not the primary agent of recrystallization in the absence of bulk water.
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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 | 0.001 | 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 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".