Pyrolysis of Polycarbosilanes with Pendant Nickel Clusters: Synthesis and Characterization of Magnetic Ceramics Containing Nickel and Nickel Silicide Nanoparticles
Bibliographic record
Abstract
The synthesis and pyrolysis of a series of soluble, air- and moisture-stable nickel-containing polycarbosilanes (Ni-PCS) is described. The reaction of 1-chloro-1-methyl-silacyclobutane with two different acetylides LiC≡CR (R = phenyl or tert -butyl) yielded the silacyclobutane monomers (CH 2 ) 3 SiMe(C≡CR) 2a (R = Ph) and 2b (R = t -Bu). Pt(0)-catalyzed ring opening polymerization of 2a and 2b in the presence of Et 3 SiH gave the alkyne-functionalized polycarbosilanes (PCS) [CH 2 −CH 2 −CH 2 −(Me)Si(C≡CR)] n 3a (R = Ph) and 3b (R = t -Bu) with molecular-weight control. The alkyne groups of the PCS polymers were clusterized with cyclopentadienyl nickel groups to yield samples of Ni-PCSs [CH 2 −CH 2 −CH 2 −(Me)Si(C(NiCp)C(NiCp)R)] n 4a (R = Ph) and 4b (R = tert -Bu) with molecular weights in the range of M n ≈ 8000−36 000. Pyrolysis of these Ni-PCSs yielded ceramics with embedded Ni or Ni silicide nanoparticles. By adjusting the pyrolysis temperature, it was possible to control the formation of either nickel (400 and 600 °C) or nickel silicide (Ni 3 Si and Ni 31 Si 12 ) nanoparticles (900 °C). The substituent group (phenyl or t -butyl), the clusterization percentage, and the pyrolysis time all influenced the yield and properties of ceramic materials. The nickel and nickel silicide nanoparticle-containing ceramics were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), powder X-ray diffraction (PXRD), and superconducting quantum interference device (SQUID) magnetometry. The blocking temperature ( T B ) of the materials was found to strongly depend on the pyrolysis conditions: in the case of the ceramics derived from 4b, T B ≈ 10 K (pyrolysis 600 °C for 1 h), T B ≥ 325 K (600 °C, 12 h) and T B ≈ 135 K (900 °C, 1 h). Depending on the applied temperature (below or above T B ) the ceramics exhibited either ferromagnetic or superparamagnetic behavior.
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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) | 0.001 | 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 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".