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Silicon Carbide Oxidation in High‐Pressure Steam
Author(s) -
Cheng Ting,
Tortorelli Peter F.
Publication year - 2013
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12328
Subject(s) - materials science , cristobalite , silicon carbide , amorphous solid , steam explosion , carbide , metallurgy , composite material , chemical engineering , chemistry , crystallography , quartz , pulp and paper industry , engineering
Silicon carbide is a candidate cladding for fission power reactors that can potentially provide better accident tolerance than zirconium alloys. SiC has also been discussed as a host matrix for nuclear fuel. Chemical vapor–deposited silicon carbide specimens were exposed in 0.34–2.07 MPa steam at low gas velocity (~50 cm/min) and temperatures from 1000°C to 1300°C for 2–48 h. As previously observed at lower steam pressure of 0.15 MPa, a two‐layer SiO 2 scale was formed during exposure to these conditions, composed of a porous cristobalite layer above a thin, dense amorphous SiO 2 surface layer. Growth of both layers depends on temperature, time, and steam pressure. A quantitative kinetics model is presented to describe the SiO 2 scale growth, whereby the amorphous layer is formed through a diffusion process and linearly consumed by an amorphous to crystalline phase transition process. Paralinear kinetics of SiC recession were observed after exposure in 0.34 MPa steam at 1200°C within 48 h. High‐pressure steam environments are seen to form very thick (10–100 μm) cristobalite SiO 2 layers on CVD SiC even after relatively short‐term exposures (several hours). The crystalline SiO 2 layer and SiC recession rate significantly depend on steam pressure. Another model is presented to describe the SiC recession rate in terms of steam pressure when a linear phase transition k l governing the recession kinetics, whereby the reciprocal of recession rate is found to follow a negative unity steam pressure power law.