Effect of the pyrolysis atmosphere on the mechanical properties of polymer‐derived SiOC and SiCN

Abstract

Mechanical properties of polymer‐derived ceramics are usually measured on samples pyrolyzed in inert atmosphere. Here, we report the hardness and elastic modulus of SiOC and SiCN pyrolyzed in both inert (Ar) and reactive (CO2) atmosphere. The external surface of the specimens exposed to the pyrolysis gas was characterized by Vickers microhardness measurements and infrared spectroscopy. The elastic modulus was evaluated by three‐point bending tests on thin (150‐200 µm) and dense specimens. Polished sections of the SiOC samples were prepared to study, by energy‐dispersive X‐ray spectroscopy (EDXS) and nanoindentation, how the elemental composition, hardness, and elastic modulus vary from the surface toward the bulk. For both compositions, pyrolysis in CO2 leads to a strong decrease in the hardness and elastic modulus. The hardness of both the samples pyrolyzed in CO2 approaches the typical value for fused silica, suggesting that CO2 selectively breaks the Si–C and Si–N bonds and leads to the formation of a silica‐like network. EDXS and nanoindentation reveal that the modification induced by the CO2 flow extends below the surface at least for a thickness of about 30 µm.

On the pyrolysis of a methyl‐silsesquioxane in reactive CO2 atmosphere: A TG/MS and FT‐IR study

“…On the other hand, when CO 2 is used as pyrolysis atmosphere, the resulting silicon oxycarbide does not contain any more Si─C bonds and turns into an SiO 2 /C free nanocomposite 22 . Following these findings, we were able to process, from the same siloxane precursor, SiOC/C free and SiO 2 /C free materials and compare their properties, namely electrochemical, 26 mechanical, 27 and their high‐temperature stability 28 to get insights into the role played by the presence of Si─C bonds in the silica‐based network.…”

UV‐curable inorganic precursors enable direct 3D printing of SiOC ceramics

“…They consist in two major phases where Si-C/Si-O bonds coexist together with an amorphous carbon phase. 9 The Int J Appl Ceram Technol. 2023;20:141-152.…”

“…SiOC ceramics have generally high density, hardness, and temperature resistance. They consist in two major phases where Si‐C/Si‐O bonds coexist together with an amorphous carbon phase 9 . The presence of an excess of free carbon will inhibit the formation of crystalline SiC until 1500°C, stabilizing thus the amorphous structure of SiOC.…”

Processing and 3D printing of SiCN polymer‐derived ceramics

“…In particular, for polysilazanes preceramic polymers, thermal crosslinking or crosslinking using a chemical reagent (such as catalyst or peroxide) in various concentrations is used. 21,[33][34][35][36] Comparatively, less attention has been paid to the effects of the catalyst concentration and crosslinking duration on the ceramic yield, crosslinking temperature, and ceramic density. These factors become increasingly important in particular for the case of AM of PDCs.…”