Formation of nanocrystalline graphite in polymer-derived SiCN by polymer infiltration and pyrolysis at a low temperature

Mingxing Li,Laifei Cheng,Fang Ye,Jie Zhou,Conglin Zhang

doi:10.1007/s40145-021-0501-2

Abstract

The microstructure of polymer-derived ceramics (PDCs) was closely related to processing. This study demonstrated that SiCN matrix prepared by polymer infiltration and pyrolysis (PIP) at 900 °C inside a Si3N4 whisker (Si3N4w) preform with submicro-sized pores differed from its powder-consolidated analogue in both the content and structure of free carbon. Chemical analysis showed that PIP process had a higher free carbon yield. Raman spectroscopy and transmission electron microscopy (TEM) observation discovered a higher graphitization degree of free carbon and the existence of nanocrystalline graphite in SiCN matrix. Dielectric properties of Si3N4w/SiCN composites were greatly enhanced when volume fraction of SiCN matrix reached 24.5% due to dielectric percolation caused by highly-lossy free carbon. Reconsolidation of hydrocarbon released during pyrolysis by gas-state carbonization in Si3N4 whisker preform was supposed to account for the high yield and graphitization degree of free carbon in PIP process.

Highlights

Silicon-based polymer-derived ceramics (PDCs) stand out among a large group of advanced ceramic materials owing to their following attractive properties
Researches based on a variety of spectroscopy methods confirmed that free carbon in silicon carbonitrides (SiCNs) is generated from the hydrocarbon side groups that attached to the backbone of the precursor molecules [15,16,17]
In order to study the pyrolysis behaviors of crosslinked PSZ powder as well as that of PSZ inside the porous Si3N4 whisker (Si3N4w)/SiCN composites, thermal gravimetric (TG) analysis coupled with mass spectroscopy (MS) characterizations of these two samples was conducted

Summary

Introduction

Silicon-based polymer-derived ceramics (PDCs) stand out among a large group of advanced ceramic materials owing to their following attractive properties. Researches based on a variety of spectroscopy methods confirmed that free carbon in SiCNs is generated from the hydrocarbon side groups that attached to the backbone of the precursor molecules [15,16,17]. During pyrolysis, these hydrocarbon groups undergo a decomposition process which involves the cleavage of C–H bonds and the formation of sp bonds between carbon atoms. These hydrocarbon groups undergo a decomposition process which involves the cleavage of C–H bonds and the formation of sp bonds between carbon atoms This process can be essentially regarded as a case of the well-known solid-state carbonization of thermosetting polymers, and the resulting carbon is called resin carbon. After graphitization at 2800 °C, the electrical conductivity of carbon fiber increased to 2.0 × 104 S/m [18]

Objectives

Results

Conclusion