Polymorphism in the Lu2−xYxSi2O7 system at high temperatures

Becerro, Ana Isabel; Escudero, Alberto

doi:10.1016/j.jeurceramsoc.2005.04.029

Cited by 16 publications

(8 citation statements)

References 25 publications

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“…2), and is refractory, melting at 17751C. [7][8][9][10][11][12][13][14][15] The mechanical properties of g-Y 2 Si 2 O 7 are comparable with LaPO 4 (monazite), 10,16 which has been demonstrated to function as a weak fiber-matrix interphase in oxide-oxide CMCs. 17 However, LaPO 4 monazite decomposes in the reducing atmospheres typical for processing SiC-SiC CMCs, and the rare-earth disilicate La 2 Si 2 O 7 forms by reaction between SiO 2 and LaPO 4 under reducing atmosphere.…”

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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“…Based on XRD peak broadening, the powder had crystallite sizes of 360 nm. 49 The luminescence of all nanoparticles was checked by irradiating them with 365 nm UV light. Samples that displayed luminescence were checked for scintillation using the Cu Xrays of the powder diffractometer.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…For the sample prepared by solid state method at 1400 °C, the particles consisted of two phases: Lu 2 Si 2 O 7 and Lu 2 SiO 5 . Based on XRD peak broadening, the powder had crystallite sizes of 360 nm …”

Section: Resultsmentioning

confidence: 99%

Synthesis of Scintillating Ce³⁺-Doped Lu₂Si₂O₇ Nanoparticles Using the Salt-Supported High Temperature (SSHT) Method: Solid State Chemistry at the Nanoscale

Egodawatte

Zhang

Posey

et al. 2019

ACS Appl. Nano Mater.

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The synthesis of lutetium silicate nanoparticles doped with Ce 3+ using the new salt-supported high temperature (SSHT) method is reported. This mechanochemical−thermal method enables the synthesis of nanoparticles without aggregation even after long calcination times of 48 h at high temperatures. These nanoparticles are characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR). Their optical properties, including UV luminescence and X-ray scintillation, are reported. These nanoparticles show strong luminescent and scintillation behavior. This SSHT method is general and can be used for the synthesis of other ternary and quaternary nanoparticle systems.

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“…The designed EBC includes a Y 2 Si 2 O 7 bond coat, mullite intermediate layer, and Yb 2 Si 2 O 7 top layer. The Y 2 Si 2 O 7 bond coat material is selected based on the following factors: (1) CTE of Y 2 Si 2 O 7 (∼ 3.9 ×10 −6 /°C) 99 close to that of SiC (∼ 4.5 ×10 −6 /°C) 100 ; (2) Y 2 Si 2 O 7 can provide excellent adherence on the surface of the SiC/SiC substrate and coexists stably with SiO 2 , which is the oxidation product of the SiC/SiC substrate; (3) the melting point of Y 2 Si 2 O 7 is about 1775°C, 99,101 which is greater than the melting point of Si; and (4) the thermal conductivity is 3.0 W/m·K above 300°C, which is lower than that of most other di‐silicates 102 . In their study, finite element models are utilized to simulate residual thermal stress at 1500°C.…”

Section: Bond Coatmentioning

confidence: 99%

Research status of bond coats in environmental barrier coatings

Zhang

Park

Zhang

et al. 2022

Int J Applied Ceramic Tech

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Bond coats in environmental barrier coatings (EBCs) prevent oxidants from penetrating the substrate, mediate the mismatch of the coefficient of thermal expansion (CTE), and improve the adhesion strength between adjacent layers. However, the development of bond coats is rarely studied systematically. In this paper, the research status of the bond coats in EBCs is introduced in detail, including the materials and deposition methods. Thus far, Si, modified‐Si, mullite, etc., have been employed as bond coats. Nevertheless, visible drawbacks of each bond coat limit their application at high‐temperatures in extreme environments. Si bond coat is easily oxidized and forms thermally grown oxides that form cracks, resulting in delamination, spallation, and failure of EBCs. In the Si–HfO2 bond coat, the optimal ratios of Si/HfO2, deposition methods, distribution of Si and HfO2, and oxidation of Si remain completely unsolved. For mullite bond coat, SiO2 suffers selective evaporation in the water vapor environment, and the ratios of the Al2O3 and SiO2 in mullite coatings restrict its service lifetime. HfSiO4 is a potential candidate acting as a next‐generation bond coat in EBCs is proposed. Furthermore, choosing reasonable deposition methods is beneficial to improve the performances of the bond coats in EBCs.

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Polymorphism in the Lu2−xYxSi2O7 system at high temperatures

Cited by 16 publications

References 25 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

Synthesis of Scintillating Ce³⁺-Doped Lu₂Si₂O₇ Nanoparticles Using the Salt-Supported High Temperature (SSHT) Method: Solid State Chemistry at the Nanoscale

Research status of bond coats in environmental barrier coatings

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Polymorphism in the Lu2−xYxSi2O7 system at high temperatures

Cited by 16 publications

References 25 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

Synthesis of Scintillating Ce3+-Doped Lu2Si2O7 Nanoparticles Using the Salt-Supported High Temperature (SSHT) Method: Solid State Chemistry at the Nanoscale

Research status of bond coats in environmental barrier coatings

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Synthesis of Scintillating Ce³⁺-Doped Lu₂Si₂O₇ Nanoparticles Using the Salt-Supported High Temperature (SSHT) Method: Solid State Chemistry at the Nanoscale