Supersaturation-Controlled Synthesis of Dicalcium Phosphate Dihydrate and Nanocrystalline Calcium-Deficient Hydroxyapatite
Bibliographic record
Abstract
The homogeneous and seed-assisted precipitation of dicalcium phosphate dihydrate (DCPD or brushite) and hydroxyapatite (HAP) under controlled supersaturation regimes in chloride media at room temperature (22 °C) is investigated. Prior to their reactive crystallization the metastable zones of precipitation for the two calcium orthophosphates were determined. The effects of supersaturation, reaction time, and seeding on the stoichiometry and crystallinity of these compounds were studied. Acidified solutions (pH ≈ 2.0) of NaH 2 PO 4 (2–90 mmol/L) and CaCl 2 (2–150 mmol/L) were mixed in order to get Ca to P molar ratios in initial solution of 1.0 or 1.67 (the stoichiometric ratios for dicalcium phosphate dihydrate and hydroxyapatite).The supersaturation in solution was built up by the slow addition of 100 mmol/L NaOH solution. In seed-assisted precipitation tests (Ca/P = 1) the metastable calcium phosphate solution (37.5 mmol/L) was neutralized until the precipitation pH of 5 was reached and 10 g/L of seed was added. The homogeneous precipitation of DCPD at pH 5.4 was fast and equilibrium was reached in 30 min. In the presence of seed, the precipitation rate was slower due to reduced supersaturation. Even so, in both cases well crystalline plate-like crystals matching the stoichiometry of brushite were produced. Calcium-deficient hydroxyapatite with nanocrystalline structure (nanocrystallite size ∼20 nm) was produced at pH 7.6 under controlled supersaturation. The homogeneously produced material consisted of irregularly shaped agglomerates of the order of 5–15 μm while the product obtained by seed-assisted precipitation was in the form of rather coarse ( ca . 20–30 μm) and dense spheroids. The highest Ca:P ratio material (Ca:P = 1.58) was obtained with seed-assisted precipitation at a slow addition rate.
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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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".