Thermal stability and electrical conductivity of carbon-enriched silicon oxycarbide

The effect of microwave treatment on the electric conductivity and structure of a polymer‐derived SiCN ceramic is studied. It is found that the conductivity of the microwave‐treated sample is about 40 times higher than that of the conventional heat‐treated one at the same temperature and dwell time conventionally. The X‐ray diffraction patterns show that both samples are amorphous without obvious crystallization. Raman analysis reveals that the microwave‐treated sample exhibited a narrower full width at half maximum and upper‐shift of G peak. X‐ray photoelectron spectroscopy spectra show that there is a significant sp3‐to‐sp2 transition of free carbon in the microwave‐treated sample. These results suggest that the microwave‐treatment can induce a distinct structure evolution of the free carbon, which contributes to the remarkable enhancement of the conductivity of the sample.

Section: Introductionmentioning

confidence: 99%

Enhanced electric conductivity of polymer‐derived SiCN ceramics by microwave post‐treatment

Shao

et al. 2016

“…As shown in Figure , the activation energies are fairly low; they also decrease with increasing Ni content, which proves that Ni‐activated graphitization results in the percolating conductive network to enable the electrical conductivity for the SiOC–Ni systems. In our previous study, the highest electrical conductivity values always occur at ~400°C due to the SiOC surface oxidation to SiO 2 before the sudden drop, as well as the break down of the conductive turbostratic carbon network under the electrical field. In this study, with the Ar atmosphere, the oxidation problem is not applicable and the electrical conductivity drops after 800‐900°C.…”

Section: Resultsmentioning

confidence: 79%

“…Our previous studies about pure SiOCs report that the SiOC matrix is composed of a homogeneous network of Si–O–C structures and free carbon at 800°C‐1100°C pyrolysis temperatures. The SiC x O y matrix is featureless in which the free carbon is dispersed.…”

Section: Resultsmentioning

confidence: 99%

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Nickel‐containing magnetoceramics from water vapor‐assisted pyrolysis of polysiloxane and nickel 2,4‐pentanedionate

Yang

Gao

et al. 2019

Self Cite

In this study, novel ferromagnetic Ni‐containing silicon oxycarbide (SiOC–Ni) was successfully fabricated from a base polysiloxane (PSO) with the addition of nickel 2,4‐pentanedionate. The resultant SiOC–Ni nanocomposite consists of in situ formed Ni nanocrystallites with a small amount of NiO uniformly dispersed in the amorphous SiOC matrix, and the corresponding nanocrystallite size increases with the increase of the pyrolysis temperature. The formation of nickel silicides (NixSiy) is completely suppressed by the effect of water vapor during the pyrolysis. The fundamental phase evolution process and mechanisms are explained. In an argon atmosphere, the SiOC–Ni materials pyrolyzed at 900°C are stable up to 1000°C with less than 6 wt% weight loss; they exhibit desirable electrical conductivity up to ~900°C with the highest electrical conductivity at ~247 S/m. This series of SiOC–Ni materials also demonstrates exciting ferromagnetic behaviors. Their new semiconducting behavior with soft ferromagnetism presents promising application potentials for magnetic sensors, transformers, actuators, etc.

“…Upon further heating to temperatures above 1000°C, SiO 2 and free carbon phases form in the SiOC matrix; at temperatures above approximately 1300°C, the SiOC matrix further phase separates into additional SiO 2 and carbon, as well as SiC nanocrystals . The formation temperature and content of each of the phases can be controlled by tailoring the polymer precursors and pyrolysis conditions . However, the ceramic yield is generally ≤70% and severely limits the practical uses.…”

Section: Introductionmentioning

confidence: 99%

Effect of additive structure and size on SiO₂ formation in polymer‐derived SiOC ceramics

Erb

2018

Self Cite

Silicon oxycarbide (SiOC) ceramics with highly adjustable properties and microstructures have many promising applications in batteries, catalysis, gas separation, and supercapacitors. In this study, additive structures on the nucleation and growth of SiO2 within SiOC ceramics are investigated by adding cyclic tetramethyl‐tetravinylcyclotetrasiloxane (TMTVS) or caged octavinyl‐polyhedral oligomeric silsesquioxane (POSS) to a base polysiloxane (PSO) precursor. The effects of the 2 additives on the polymer‐to‐ceramic transformation and the phase formation within the SiOC are discussed. POSS encourages SiO2 nucleation and leads to more SiO2 formation with significantly increased ceramic yield, which subsequently leads to higher specific surface of 1557 m2/g with a larger pore size of ∼1.8 nm for the porous SiOC. High TMTVS content decreases both the specific surface area and pore volume of the resulting porous SiOCs. This study demonstrates a new approach of using Si‐rich additive POSS to increase the SiOC yield while maintaining or even increasing the specific surface area.