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

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.

SiCN Ceramics as Electrode Materials for Sodium/Sodium Ion Cells – Insights from 23Na In‐Situ Solid‐State NMR

“…Defects in the structure, edges in the graphene layers as well as the porous structure provide hostsites for ion adsorption and metal intercalation. [48][49][50][51] Although, such silicon based PDCs have been studied as alternative anode suitable for lithium storage insertion and a corresponding mechanism has been proposed, [52] there are only few works addressing the sodium storage. [53][54][55] In this paper, we briefly investigate the fundamental sodium storage properties of a silicon-based polymer-derived SiCN ceramic (PDCs) as an anode material in a Swagwelok-type ex-situ cell setup, before moving to our main target, the 23 Na in-situ solid-state NMR spectroscopy (ssNMR) of the system in cylindrical sodium/sodium ion cells [56][57][58] which enables us to monitor structural changes of the sodium/sodium ion environments and their reversibility during the cycling process in an active cell.…”

“…Hereby, the silicon atoms are tetrahedral surrounded by carbon and oxygen or nitrogen, whereas carbon in segregated phase exhibits sp 2 hybridized bonds. Defects in the structure, edges in the graphene layers as well as the porous structure provide host‐sites for ion adsorption and metal intercalation [48–51] . Although, such silicon based PDCs have been studied as alternative anode suitable for lithium storage insertion and a corresponding mechanism has been proposed, [52] there are only few works addressing the sodium storage [53–55] …”

High temperature structure evolution of SiBZrOC quinary polymer derived ceramics

“…The intensity ratio of D and G bands, I (D)/ I (G), reflects the graphitization of carbon materials, and it decreased with increasing graphitization. The diameter of free carbon cluster can be calculated using eqn (6), 36,37 shown in Table 2. The intensity of G band increases dramatically at above 1600 °C, and accordingly the I (D)/ I (G) rapidly decreases to 0.13 at 1600 °C, which leads to a large L a of 38.1 nm.…”

“…This is probably owing to the partial substitution of C with B atoms, which could increase the crystallinity of carbon. 37,38 The D′ bands at 1608 cm −1 is considered to be the fingerprint of BC 3 site formed by the substitution of B for C atom. 9 This substitution of C by B atom introduces a local distortion within the graphite layer planes, and thus formed crystalline defects.…”

“…The electron deficiency of boron with respect to carbon causes a decrease in the repulsive interaction between the π-electron clouds of adjacent graphene layers, allowing these layers to come closer together, and thus lead to the increased graphitization degree of free carbon. 37,38…”