Thermodynamic Calculations and Phase Stabilities in the Y-Si-C-O System

Cupid, Damian M.; Seifert, Hans Jürgen

doi:10.1007/s11669-006-9014-5

Cited by 38 publications

(15 citation statements)

References 22 publications

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“…10,16 It is soft (Vickers hardness B6 GPa) and machinable, and has a low shear modulus, which originates from bond strength differences between strong Si-O bonds and weak Y-O chemical bonds. 10,16 g-Y 2 Si 2 O 7 is thermochemically compatible with SiC and SiO 2 , 21 and it has a thermal expansion coefficient (B4 Â 10 À6 1C À1 ) similar to SiC. 22 This combination of properties is intriguing and suggests that g-Y 2 Si 2 O 7 may possibly be a fiber-matrix interphase for SiC-SiC CMCs.…”

Section: Introductionmentioning

confidence: 99%

Rare-Earth Disilicates As Oxidation-Resistant Fiber Coatings for Silicon Carbide Ceramic-Matrix Composites

Boakye

Mogilevsky

Hay

et al. 2011

Journal of the American Ceramic Society

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Current SiC‐based ceramic–matrix composites (SiC–SiC CMCs) rely on carbon or boron nitride fiber–matrix interphases for toughness and flaw tolerance. However, oxidation of these interphases can be performance limiting in many CMC applications. The γ‐polymorph of the rare‐earth disilicates (RE2Si2O7) is a potential oxidation‐resistant alternative to carbon or BN. The formation of γ‐Y2Si2O7 and γ‐Ho2Si2O7 at different temperatures and processing environments was investigated. Silica–yttrium hydroxide and silica–holmium hydroxide dispersions were made and heat treated at 1200°–1400°C for 8 h in air and argon. LiNO3 was added to the dispersions to enhance the formation of γ‐Y2Si2O7 and γ‐Ho2Si2O7. The effects of excess silica and LiNO3 dopant on the formation of γ‐Y2Si2O7 were investigated. Coatings of Y2Si2O7 and Ho2Si2O7 were made on α‐SiC plate and SCS–0 SiC fiber using these dispersions. These were heat treated in argon and argon—500 ppm oxygen mixtures at 1400°C/8 h. For coatings heat treated in argon—500 ppm oxygen mixtures, X‐ray diffraction showed the formation of single phase γ‐Ho2Si2O7 and a mixture of γ and β‐Y2Si2O7 at 1400°C. Scanning electron microscopic image analysis gave an estimate of 18 vol% of excess silica for γ‐Y2Si2O7 formed with high Si:Y ratio and ∼5 vol% excess silica for material formed with lower Si:Y ratio. Transmission electron microscopy of samples directly beneath indentations showed both extensive dislocation slip and fracture.

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Section: Introductionmentioning

confidence: 99%

Rare-Earth Disilicates As Oxidation-Resistant Fiber Coatings for Silicon Carbide Ceramic-Matrix Composites

Boakye

Mogilevsky

Hay

et al. 2011

Journal of the American Ceramic Society

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“…A similar phenomenon was studied in the context of interface reactions in YMS coatings applied to C/C–SiC composites. Modeling and experimental evidence indicate that YMS reacts with SiO 2 formed as the SiC oxidizes ultimately yielding a mixture of YDS and excess SiO 2 once the YMS has been consumed . The materials described in this study are expected to exhibit analogous behavior at longer oxidation times in air with the fraction of SiO 2 ‐rich phases increasing with respect to the crystalline silicates.…”

Section: Discussionmentioning

confidence: 85%

“…Modeling and experimental evidence indicate that YMS reacts with SiO 2 formed as the SiC oxidizes ultimately yielding a mixture of YDS and excess SiO 2 once the YMS has been consumed. 28,43 The materials described in this study are expected to exhibit analogous behavior at longer oxidation times in air with the fraction of SiO 2 -rich phases increasing with respect to the crystalline silicates. In a volatilizing environment, however, the loss of SiO 2 will counteract the tendency toward SiO 2 accumulation in the scale.…”

Section: Discussionmentioning

confidence: 93%

Yttrium Bearing Silicon Carbide Matrices for Robust Ceramic Composites

Poerschke

Levi

2012

J. Am. Ceram. Soc.

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Application of SiC‐based ceramic matrix composites (CMCs) in combustion environments demands the use of an environmental barrier coating (EBC) to prevent volatilization of the protective SiO2 scale in flowing water vapor. The EBC only provides protection while present on the surface; cracking and spallation of the coating leaves the underlying SiC vulnerable to the oxidation–volatilization processes. A robust matrix material chemically tailored to regrow a yttrium silicate scale in the event of EBC loss has been developed by incorporating yttrium bearing species including YB2, Y2O3, and Y5Si3 into the SiC. During oxidation a borosilicate glass helps seal cracks while Y2O3 and SiO2 react to form Y2Si2O7 for environmental protection. Candidate compositions were oxidized for 10 min to 100 h at 1400°C and for 24 h at 1500°C to understand the scale growth. The prospects for effectively applying this approach in CMCs are discussed.

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“…Amorphous silica, which forms during MoSi 2 oxidation, tends to transform into cristobalite prior or during reaction with ZrO 2 [3,46,49]. Also, some Y 2 Si 2 O 7 is observed, which suggests a reaction between the remaining amorphous SiO 2 and Y 2 O 3 [57].…”

Section: Oxidation Phenomenamentioning

confidence: 99%

Kinetics of zircon formation in yttria partially stabilized zirconia as a result of oxidation of embedded molybdenum disilicide

et al. 2019

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This is an author's version published in: http://oatao.univ-toulouse.fr/24028 a b s t r a c t Recently MoSi 2 sacrificial particles embedded in yttria partially stabilized zirconia (YPSZ) have been proposed as attractive healing agents to realize significant extension of the lifetime of the thermally loaded structures. Upon local fracture of the YPSZ, the embedded healing particles in the path and in the vicinity of the crack react with the oxygen atoms transported via the crack and first fill the crack with a viscous glassy silica phase (SiO 2 ). The subsequent reaction between this freshly formed SiO 2 and the existing tetragonal ZrO 2 of the YPSZ leads to the formation of rigid crystalline zircon (ZrSiO 4 ), which is key in the crack-healing mechanism of YPSZ based materials. The isothermal kinetics of the self-healing reaction and the mechanism of zircon formation from the decomposing MoSi 2 and the surrounding YPSZ were assessed via X-ray diffraction (XRD). The obtained results revealed that at 1100 C the reaction between amorphous SiO 2 and YPSZ is completed after about 10 h. For a more accurate determination of the kinetics of the self-healing reaction, bilayer samples of YPSZ e MoSi 2 (with and without boron addition) were annealed in air over a temperature range of 1100e1300 C. This led to the formation of a MoSi 2 /amorphous (boro)silica/zircon/YPSZ multi-layer, which was investigated with scanning electron microscopy (SEM) and electron probe X-ray microanalysis (EPMA). Kinetic modeling of the growth of zircon and silica or borosilicate layers showed that zircon growth was dominated by the diffusion of Si 4þ in zircon whereas the growth of the silica or borosilicate layer was controlled by oxygen diffusion. Moreover, a significant increase in the rate of ZrSiO 4 formation was observed due to the presence of B in the MoSi 2 particles.

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Thermodynamic Calculations and Phase Stabilities in the Y-Si-C-O System

Cited by 38 publications

References 22 publications

Rare-Earth Disilicates As Oxidation-Resistant Fiber Coatings for Silicon Carbide Ceramic-Matrix Composites

Rare-Earth Disilicates As Oxidation-Resistant Fiber Coatings for Silicon Carbide Ceramic-Matrix Composites

Yttrium Bearing Silicon Carbide Matrices for Robust Ceramic Composites

Kinetics of zircon formation in yttria partially stabilized zirconia as a result of oxidation of embedded molybdenum disilicide

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