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Surfaces, Interfaces, and Applications
Nanochannel-diffusion controlled nitridation of polycarbosilane for diversified SiCN fibers with interfacial gradientSiCxNy phase and enhanced high-temperature stability Xin Long, Changwei Shao, Shanshan Wang, and Jun Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b00828 • Publication Date (Web): 14 Mar 2019 Downloaded from http://pubs.acs.org on March 14, 2019
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ACS Applied Materials & Interfaces
Nanochannel-Diffusion Controlled Nitridation of Polycarbosilane for Diversified SiCN Fibers with Interfacial Gradient-SiCxNy Phase and Enhanced High-Temperature Stability Xin Long, Changwei Shao*, ShanShan Wang, Jun Wang* College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, PR China
ABSTRACT Diversified SiCN fibers with gradient-SiCxNy phase in the interfacial regions between the major phase of carbon-rich SiC phase and Si3N4 phase were prepared via nanochannel-diffusion controlled nitridation of polycarbosilane fibers under different NH3 flow rate. The obtained fibers with excellent mechanical properties showed a different nanostructure and improved high-temperature behavior comparing with polysilazanes- and polysilylcarbodiimides-derived SiCN ceramics. The enhanced high-temperature properties could be contributed to the inhibition of carbothermal reduction of Si3N4 phase by the gradient-SiCxNy phase in the interfacial region between Si3N4 phase and carbon-rich SiC phase. Meanwhile, the suitable amount of interfacial SiCxNy phase as well as the fine distributed microstructure can be helpful to inhibit the high-temperature crystallization of both SiC phase and Si3N4 phase. Additionally, a nanostructural model has been proposed to understand the effect of interfacial gradient-SiCxNy phase and compositional dependent high-temperature behavior of obtained SiCN fibers. Our findings provide a novel strategy to prepare SiCN-based ceramic materials with excellent high-temperature stabilities, which we expect to possess great potential in structural and (multi)functional applications at high-temperatures and under harsh environments. KEYWORDS: polycarbosilane fibers; SiCN fibers; interfacial region; high-temperature
INTRODUCTION Si-based advanced ceramics, including SiC, SiCN, SiCO and SiBCN et al., have recently attracted extensive attention due to their great potential for high-temperature structural and functional applications [1~3]. They adopt remarkable thermal stability, excellent resistance to 1
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creep, oxidation and corrosion, as well as adjustable semiconducting properties [4~5]. Polymer-derived method is one of the most important approaches for preparing these kinds of materials, especially for fibers. These polymer-derived ceramic fibers are widely applied as reinforced material in advanced ceramic matrix composite (CMCs) in the field of aerospace [6~8]. The high-temperature behavior of these fibers can be drastically altered by compositional and microstructural modification. Much efforts have been devoted to polymer-derived SiC fibers for the improvement of their high-temperature performance [9~12]. However, research on the multinary systems, such as SiCN fibers, is still lacking. Polymer-derived SiCN fibers usually contains amorphous Si-C-N networks composed of tetrahedral mixed units of SiCxN4-x (0
