Electrical properties of biomorphic SiC ceramics and SiC/Si composites fabricated from medium density fiberboard

Abstract

A study has been made of the dependences of the electrical resistivity and the Hall coefficient on the temperature in the range 1.8-1300 K and on magnetic fields of up to 28 kOe for the biomorphic SiC/Si (MDF-SiC/Si) composite and biomorphic porous SiC (MDF-SiC) based upon artificial cellulosic precursor (MDF -medium density fiberboards). It has been shown that electric transport in MDF-SiC is effected by carriers of n-type with a high concentration of ∼1020 cm−3 and a low mobility of ∼0.4 cm2 V−1 s−1. The specific features in the conductivity of MDF-SiC are explained by quantum effects arising in disordered systems and requiring quantum corrections to conductivity. The TEM studies confirmed the presence of disordering structural features (nanocrystalline regions) in MDF-SiC. The conductivity of MDF-SiC/Si composite originates primarily from Si component in the temperature range 1.8-500 K and since ∼500 to 600 K the contribution of MDF-SiC matrix becomes dominant.

Determination of silicon carbide fiber electrical resistivity at elevated temperature

“…At temperatures above 800°C, the sintered SiC resistivity became comparable with the CMC data. The resistivity of biomorphic SiC closely matched the Sylramic‐iBN fibers up to approximately 600°C . Beyond that temperature, the biomorphic SiC did not decrease in resistivity as much as the model estimated for the fibers.…”

“…The ratio of ρ/ρ o (fiber resistivity relative to the initial resistivity at 25°C) was assumed to be exponential based on literature data for chemical vapor infiltrated (CVI) SiC composites with Sylramic‐iBN fibers, sintered SiC, biomorphic SiC, and Hi‐Nicalon fibers (all of which are shown in Figure ). Note that the experimental data from CVI SiC/SiC and this study were both obtained under non‐isothermal conditions.…”

High-temperature dielectric and electromagnetic interference shielding properties of SiCf/SiC composites using Ti3SiC2 as inert filler

“…It can be observed that the increment of complex permittivity with the increasing temperatures is mainly caused by the relaxation loss and conductance loss. For the SiC materials, electron relaxation polarization would be the dominant polarization mechanism and response to the electromagnetic field at high temperatures due to the thermal excitation of SiC materials [37,38]. Arrhenius formula could be used to describe the relationship between relaxation time and temperature under this condition [39]:…”

Temperature-dependent dielectric and microwave absorption properties of SiC /SiC–Al2O3 composites modified by thermal cross-linking procedure

“…It can be observed that the increase of complex permittivity is mainly induced by the relaxation polarization and conductance loss at high temperatures [38]. In the SiC materials, electron relaxation polarization would be the dominant polarization mechanism and response to the electromagnetic field at high temperatures due to the thermal excitation of SiC materials [39,40]. We can use Arrhenius formula to describe the relationship between relaxation time and temperature under this condition [41]:…”