Effect of Hydrogen Atmosphere on Pyrolysis of Cured Polycarbosilane Fibers

Abstract

SiC-based fibers with various chemical compositions were synthesized using an irradiation-curing process. Polycarbosilane (PCS) fibers were cured by irradiation with an electron beam in a helium atmosphere. The cured PCS fibers were pyrolyzed at 1300°C under controlled hydrogen or argon atmospheres, and SiC fibers with C/Si of 0.84 to 1.56 were obtained. The fibers consisted of <1.0 wt% O, <0.2 wt% N, <0.1 wt% H, with the balance being Si and C. The mechanism of pyrolytic transformation of cured PCS to SiC-based ceramics was investigated using TG/DTA analysis. Greater mass losses were observed during pyrolysis in a hydrogen atmosphere than in argon. This result suggests that the hydrogen atmosphere suppresses H 2 evolution and helps to remove excess carbon as CH 4 during pyrolysis. The microstructure and mechanical properties of the resulting SiC-based fibers were found to be very dependent on their C/Si chemical compositions.

Mechanical Properties of Chemically Vapor-Infiltrated Silicon Carbide Structural Composites with Thin Carbon Interphases for Fusion and Advanced Fission Applications

“…[3][4][5] However, as improved SiC fibers became available, experiments started to demonstrate good tolerance of SiC/ SiC composites to neutron irradiation. [5][6][7] Those SiC fibers, which consist primarily of a polycrystalline form of cubic SiC and are termed Generation-III SiC fibers, 8) are now commercially available as Hi-NicalonÔ Type-S (Nippon Carbon Co., Tokyo, Japan) 9) and TyrannoÔ-SA (Ube Industries, Ltd., Ube, Japan).…”

Assessment of Silicon Carbide Composites for Advanced Salt-Cooled Reactors

“…The Hi-Nicalon™ process has been taken a step further, by incorporating decarburization process in an hydrogen environment, with the introduction of Hi-Nicalon™ Type-S SiC fiber with a near theoretical density fiber and very low excess carbon and oxygen [37]. At the same time, the Tyranno™ SA3 fiber was developed through a very different route of sintering with aluminum addition to the original polymer precursor, which resulted in similarly very low contents of excess carbon and oxygen [38].…”

Hot Corrosion, Oxidation and Their Effects on the Tensile Strength of SiC Fiber in Alkaline Melts

“…7) The reaction layer blanketed the fiber yarn and contained many trapped bubbles which were formed during the release of CO, CO 2 and SO 2 (Fig. 5).…”

“…In present study, in order to investigate the hot corrosion and oxidation and their effects on tensile properties of HiNicalonÔ fiber which contains excess carbon (C/Si ¼ 1:39 atomic), 7) the Hi-NicalonÔ fiber coated with a film of varied alkaline melts was oxidized and corroded in air. HiNicalonÔ fiber is a continuous, multi-filament fiber bundle with 500 filaments of $14 mm diameter, and density of 2.74 Mg/m 3 .…”