Borosilicate Glass‐Induced Fiber Degradation of SiC/BN/SiC Composites Exposed in Combustion Environments

Opila, Elizabeth J.; Robinson, R. Craig; Verrilli, Michael J.

doi:10.1111/ijac.12499

Cited by 46 publications

(42 citation statements)

References 30 publications

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“…Finally, although BN crystallites are clearly present in the residual fiber coating, the experimental measurements are insufficient to rule out the possibility that some oxidation of BN has occurred. Similar oxidation sequences have been observed in the vicinity of deep matrix cracks in CMCs with initially hermetic MI matrices, suggesting that these processes are not unique to PIP‐processed CMCs …”

Section: Discussionsupporting

confidence: 59%

“…Longer cracks and additional tortuosity in full‐scale composites could sufficiently reduce the gaseous fluxes to alter the reaction kinetics and change the dominant reaction mechanisms. The latter view is supported by experiments showing that, under constrained oxidant supply, SiC fibers may oxidize preferentially to the BN fiber coatings …”

Section: Introductionmentioning

confidence: 88%

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Intermediate Temperature Internal Oxidation of a SiC/SiCN Composite with a Polymer‐Derived Matrix

2016

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SiC-based composites exhibit oxidative embrittlement at intermediate temperatures. Although the mechanisms of internal oxidation in composites with initially hermetic matrices have been studied extensively, comparable studies on composites with semipermeable matrices, such as those produced by polymer infiltration and pyrolysis, have not been reported. The present article focuses on the latter class of composites, specifically a SiC f /SiCN m with a dual BN/Si 3 N 4 fiber coating. It describes detailed SEM and TEM analyses of the microstructure before and after oxidation in dry air or water vapor at 800°C. The results show that internal oxidation is more aggressive in water vapor and occurs appreciably even in the absence of an applied stress. The sequence of oxidation of the constituent phases appears to be consistent with the underlying thermodynamic hierarchy for the respective oxidation reactions. Notably, contrary to existing models based on preferential oxidation of BN coatings, oxidation occurs first on the SiC fiber surfaces and the Si 3 N 4 overcoat; crystalline BN remains even after significant fiber and matrix oxidation has occurred. The results are discussed in terms of rate-controlling kinetic processes, the effect of oxidant type, and applied stress.

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Section: Discussionsupporting

confidence: 59%

Section: Introductionmentioning

confidence: 88%

Intermediate Temperature Internal Oxidation of a SiC/SiCN Composite with a Polymer‐Derived Matrix

2016

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“…The calculated B 2 O 3 : SiO 2 mole ratio in Sylramic iBN oxides ranged from 0.03:1 to 0.2:1, which is multiple times lower than the ~ 1.3:1‐4.8:1 molar ratios of B 2 O 3 : SiO 2 from XPS measurements of oxides reported by Quemard et al that formed from the oxidation of a seal coat layer comprised of SiC nanocrystals in a B 4 C matrix. Significant oxidation of SiC fiber and matrix components was observed by others where the boria free surface in CMC composites was limited to open channels or adjacent microcracks . These findings indicate that excessive SiC oxidation can occur in conditions where the free surface for B 2 O 3 volatilization is restricted.…”

Section: Discussionmentioning

confidence: 64%

“…Although formation of the low viscosity glass sealed the matrix cracks, considerable SiC fiber recession adjacent to regions of a thick borosilicate glass was also observed . Other studies found the oxidation rates of Si‐based materials to accelerate in the presence of boron (B) . Parabolic rate constants (k p ) from a few of these studies conducted at 800°C are extrapolated here to 1 atm of dry oxygen (O 2 ) using derived SI units.…”

Section: Introductionmentioning

confidence: 99%

“…16,17 Other studies found the oxidation rates of Si-based materials to accelerate in the presence of boron (B). [19][20][21][22][23] Parabolic rate constants (k p ) from a few of these studies conducted at 800°C are extrapolated here to 1 atm of dry oxygen (O 2 ) 19,22,23 using derived SI units. The k p values were~0.3 mg 2 cm À4 h À1 for B 4 C-50 mol% SiC composites, 19 2 9 10 À3 mg 2 cm À4 h À1 for Hi-Nicalon TM fibers embedded in B 2 O 3 powder, 22 and up to 60 mg 2 cm À4 h À1 for Si coupons coated with sol-gel-derived borosilicate glass layers having nominal B 2 O 3 concentrations ranging from 1 to 30 mol%.…”

Section: Introductionmentioning

confidence: 99%

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Silicon carbide fiber oxidation behavior in the presence of boron nitride

McFarland

Opila

2018

J Am Ceram Soc

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The oxidation behavior of Sylramic SiC fibers without a boron nitride surface layer was compared to Sylramic iBN SiC fibers with a boron nitride surface layer by conducting thermogravimetric analysis in dry O2 at temperatures ranging from 800 to 1300°C for times up to 100 hours. Sylramic fibers followed the Deal and Grove oxidation kinetic model. A transient period of accelerated oxidation kinetics was observed with Sylramic iBN fibers. Raman spectroscopic analysis of oxidized fibers provided evidence for a borosilicate glass structure. The boron concentrations in the oxides, quantified by inductively coupled plasma‐optical emission spectrometry, were correlated with the weight change behavior, oxide thickness, and fiber recession of the oxidized fibers. Oxides formed from Sylramic iBN fibers were typically higher in boron concentration, which led to initial rapid oxidation rates that were 3‐10 times faster than observed for pure SiC. Slower oxidation rates followed as the oxide surface became increasingly enriched with SiO2 due to boria volatilization, thus limiting boria effects on SiC fiber oxidation kinetics. The accelerated high‐temperature oxidation of SiC fibers due to the presence of BN are discussed in terms of the borosilicate glass structure and composition.

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A Review of SiC Fiber Oxidation with a New Study of Hi‐Nicalon SiC Fiber Oxidation

Wilson

Opila

2016

Adv Eng Mater

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The linear and parabolic oxidation rate constants and activation energies for SiC fibers available in the literature are reviewed for the first time. Oxidation experiments are also conducted with Hi-Nicalon SiC fibers over 700-1 300 C in dry O 2 with thermogravimetric analysis. Linear oxidation kinetics are observed from 700 to 800 C and parabolic kinetics are observed from 900 to 1 300 C. The linear and parabolic oxidation rate constant activation energies are determined to be 83 and 108 kJ mol À1 , respectively. These kinetic results are compared with the literature values. Differences in oxidation behavior are assessed as a function of fiber composition.

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Borosilicate Glass‐Induced Fiber Degradation of SiC/BN/SiC Composites Exposed in Combustion Environments

Cited by 46 publications

References 30 publications

Intermediate Temperature Internal Oxidation of a SiC/SiCN Composite with a Polymer‐Derived Matrix

Intermediate Temperature Internal Oxidation of a SiC/SiCN Composite with a Polymer‐Derived Matrix

Silicon carbide fiber oxidation behavior in the presence of boron nitride

A Review of SiC Fiber Oxidation with a New Study of Hi‐Nicalon SiC Fiber Oxidation

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