Monazite Coatings on SiC Fibers II: Oxidation Protection

Abstract

The effect of monazite on the oxidation of SiC was studied in laboratory and dry air. Monazite inhibited the oxidation of Tyranno‐SA™, Tyranno‐ZX™, Sylramic, and Hi‐Nicalon SiC fibers. Oxidation of pure chemical vapor deposition SiC and undoped SiC single crystals was not inhibited by monazite. Dry oxidation of both uncoated and monazite‐coated Tyranno‐SA™ fibers initially displayed parabolic kinetics with an activation energy of 180–190 kJ/mol. Subsequently, the oxidation rate of monazite‐coated fibers increased and the oxide‐scale growth rate approached that of the uncoated fibers. No differences in the composition or structure of the silica oxidation product could be detected between uncoated and coated fibers using transmission electron microscopy and energy‐dispersive spectroscopy. Possible mechanisms of the inhibition of SiC oxidation by monazite are discussed.

Mechanical and microstructural characterisation of SiC- and SiBNC-fibre reinforced CMCs manufactured via PIP method before and after exposure to air

“…Mogilevski et al reported parabolic rate constants (K p ) of 30 nm 2 /min for oxidation of Tyranno SA3 TM fibres at a temperature of 1100 • C (exposure time: ≤ 20 h, dry air: ≤5 ppm H 2 O). 49 Taken this into account, silica with a thickness of ∼190 nm formed after 20 h at 1100 • C in dry air which is slightly lower than silica thickness measured in this study for an atmosphere with ∼2.7% water vapour content. Hence, in spite of full active oxidation of pyc-fibre coating, SiC-fibres being embedded in a relatively dense SiCN-matrix exhibit a significantly lower silica formation (at least 1/3) compared to single fibres without matrix.…”

“…silica formation on Tyranno SA3 TM fibres after exposure (T = 1200 • C, t = 10 h) to laboratory air with a water vapour content of ∼1-1.6% (silica thickness ∼700 nm) is approximately 2.75 times higher compared to that in dry air (silica thickness ∼250 nm). 49 Considering water vapour content in the laboratory air of ∼2.7% in this study, a measured silica thickness of ∼215 nm on Tyranno SA3 TM fibres in SiC pyc /SiCN after exposure to air (T = 1100 • C, t = 20 h) is in the same range as silica thicknesses reported for single fibres in dry air. Mogilevski et al reported parabolic rate constants (K p ) of 30 nm 2 /min for oxidation of Tyranno SA3 TM fibres at a temperature of 1100 • C (exposure time: ≤ 20 h, dry air: ≤5 ppm H 2 O).…”

“…Silica formation on SiC-fibres is associated with fibre strength degradation. [49][50][51][52][53][54] Thus, the decrease of bending and tensile strength of SiC pyc /SiCN after exposure to air is mainly caused by fibre strength degradation as well as increase of fibre/matrix bonding due to silica formation.…”

Microstructural features of the ZrO2 interfacial coatings on SiC fibers before and after exposition to air at high temperatures

“…Several oxidation resistant and crack-deflecting materials including monazite, alumina/silica, stabilized zirconia, and others were proposed as appropriate candidates for interphase zone in CMC's. [2][3][4][5][6][7][8] Some information is available in publications, describing the behavior of the stabilized ZrO 2 -coated SiC fibers exposed to air at high temperatures. 9,10 Preliminary studying of the peculiarities of morphology and nanorelief of two zirconia-coated fibers, namely, Hi-Nicalon TM and Tyranno-SA TM before and after exposition to air at 1000 • C using atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that these features are greatly dependent on the type of SiC fibers.…”

Oxidation behavior and kinetics of ZrB2 containing SiC chopped fibers

“…Therefore the oxidation of these secondary species has to be considered as well. The oxidation of sintered SiC fibers belonging to the 3rd generation, like Hi-Nicalon S and Tyranno SA3 [22,23], has been extensively studied in Wright Patterson labs in dry and wet air [24][25][26][27]. They reported parabolic kinetics in both dry air and laboratory air during the initial oxidation stage at 1000-1200 • C, with an activation energy on the order of 180-190 kJ/mol, which is close to the value reported for the oxidation of single crystal 6H-SiC [25].…”