Abstract
Ceramic matrix composite (CMC) materials have been considered a desired solution for lightweight and high-temperature applications. Simultaneously, among all different CMC reinforcements, polymer-derived ceramic (PDC) fibres have gained attention for the intrinsic thermal stability and mechanical strength with simple and cost-effective synthesis techniques. Here, carbon-rich SiOCN fibres were synthesized via hand-drawing and polymer pyrolysis of a hybrid precursor of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasilazane (TTCSZ) and poly-acrylic acid (PAA). The type of silazane reported in this work is considered as a major precursor for SiCN; however, it is unspinnable, due to its unfavourable physical properties (low viscosity) and chemical structure (cyclic rather than linear structure). The introduction of PAA to TTCSZ to create a hybrid precursor remarkably improved the spinnability of the silazane and should be widely applicable to other unspinnable PDC pre-ceramic polymers. Investigations on the structural and compositional development of the fibres were mainly conducted via Raman spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance and thermo-gravimetric analysis to determine spinnability, free carbon content, cross-linking and pyrolysis behaviour of the fibres, respectively.
Highlights
Over the past few decades, there has been a rising desire for new structural aerospace materials with lightweight, high modulus and high thermal stability that has motivated the advance of royalsocietypublishing.org/journal/rsos R
The chemical compositions of polymer-derived ceramic (PDC) hybrid fibres are determined by X-ray photoelectron spectroscopy (XPS) depth-profiling survey scans and the results are listed in table 1
The hybrid fibres pyrolysed at 800°C showed a good thermal stability up to 1000°C with the weight loss of 4.5 wt%, while the thermal gravimetric analysis (TGA) curve of cross-linked hybrid samples gives an estimation of ceramic yield of this TTCSZ/poly-acrylic acid (PAA) combination
Summary
Over the past few decades, there has been a rising desire for new structural aerospace materials with lightweight, high modulus and high thermal stability that has motivated the advance of royalsocietypublishing.org/journal/rsos R. Over the last three decades, silicon-based advanced ceramics with a variety of desirable properties, such as remarkable chemical resistance, thermal stability and mechanical strength, have been designed with the help of straightforward polymer-to-ceramic conversion [3,4]. There are many types of PDCFs developed over 20 years ago and still commercially available from various manufacturers, such as Hi-Nicalon (from COI), Sylramic (from UBE), etc Both oxide and non-oxide (from polymer pyrolysis route) ceramic fibres are widely applied for high-temperature applications. 1,3,5,7-tetramethyl1,3,5,7-tetravinyl-cyclotetrasilazane (referred as TTCSZ hereafter) is an organosilazane, whose properties have not been reported its siloxane analogue, 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane is a common precursor for SiOC ceramic This type of silazane is crosslinkable at elevated temperature, but it is not known to form fibres in its neat form. Characterization, pyrolysis and phase formation are discussed in detail for TTCSZ/PAA hybrid fibres
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