Kinetics of Passive Oxidation of Hi-Nicalon-S SiC Fibers in Wet Air: Relationships between SiO2Scale Thickness, Crystallization, and Fiber Strength

Understanding the strength degradation of glass and carbon fibers due to exposure to liquids over time is important for structural applications. A model has been developed for glass fibers that links the strength reduction in water to the increase of the Griffith flaw size of the fibers. The speed of the increase is determined by regular chemical dissolution kinetics of glass in water. Crack growth and strength reduction can be predicted for several water temperatures and pH, based on the corresponding dissolution constants. Agreement with experimental results for the case of water at 60 °C with a pH of 5.8 is reasonably good. Carbon fibers in water and toluene and glass fibers in toluene do not chemically react with the liquid. Subsequently no strength degradation is expected and will be confirmed experimentally. All fiber strength measurements are carried out on bundles. The glass fibers are R-glass.

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Passive-Oxidation Kinetics of High-Purity Silicon Carbide from 800o to 1100oC

Journal of the American Ceramic Society ◽

10.1111/j.1151-2916.1996.tb08724.x ◽

1996 ◽

Vol 79 (11) ◽

pp. 2897-2911 ◽

Cited By ~ 94

Author(s):

C. Eric Ramberg ◽

Gary Cruciani ◽

Karl E. Spear ◽

Richard E. Tressler ◽

Charles F. Ramberg

Keyword(s):

Silicon Carbide ◽

High Purity ◽

Oxidation Kinetics ◽

Passive Oxidation ◽

High Purity Silicon ◽

Kinetics Of

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Microstructural Investigation of Strength Degradation in A Developmental Cvd Sic Fiber At 2000° C

Microscopy and Microanalysis ◽

10.1017/s1431927600010606 ◽

1997 ◽

Vol 3 (S2) ◽

pp. 743-744

Author(s):

A. Garg ◽

D. R. Hull ◽

R. T. Bhatt

Keyword(s):

Fiber Strength ◽

Chemical Vapor ◽

High Strength ◽

Pyrolytic Carbon ◽

Microstructural Investigation ◽

Sic Fibers ◽

Sic Fiber ◽

Heat Treated ◽

Carbon Coated ◽

Increasing Demand

SiC fibers fabricated by chemical vapor deposition (CVD) methods are being used as reinforcement for metal and ceramic matrix materials because of their high modulus, high strength and good corrosion resistance. These fibers have a complex composite microstructure consisting of a pyrolytic-carbon coated graphite core and a SiC sheath which is often protected by a single or a double layer of carbon-rich coating. Commercially available SCS-6 SiC fibers with a diameter of ˜ 140 μm have been most widely in use for composite fabrication. However, with an ever increasing demand for thinner and stronger fibers, an experimental SiC fiber with a diameter of ˜ 50 μm and having a C-rich SiC sheath was developed by Textron Specialty Materials. The as-fabricated tensile strength of this fiber was found to be ˜ 6 GPa, which is ˜ 50 % higher than that of the SCS-6 fiber.While the room temperature tensile strengths of these fibers heat treated for 1 h in Ar to temperatures ≤ 1600° C were better than those of the SCS-6 fiber, strength of the 2000° C heated fibers decreased to < 1 GPa.

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