Polymorphism under pressure of the disilicates of the heavier lanthanoids Ln2Si2O7 (Ln = Tm, Yb, Lu)

Bocquillon, G.; Chateau, C.; Loriers, C.; Loriers, J.

doi:10.1016/0022-4596(77)90060-3

Cited by 47 publications

(26 citation statements)

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“…We may assume, therefore that crystal structure of the new phase is probably B-type Lu 2 Si 2 O 7 , the disilicate polymorph that has not been observed till now. Bocquillon et al [9] observed similar Lu silicate but only at high pressure (above 80 kbar). Upon further heating to 1200 • C (trace E) well known C-Lu 2 Si 2 O 7 with thortveitite structure is formed (trace H -PDF 35-0326).…”

Section: Xrdmentioning

confidence: 67%

“…However, structural data presented in this work clearly show that at temperature of 1000 • C B-type disilicate with Lu 4 [Si 3 O 10 ][SiO 4 ] formula exists as at least metastable phase at normal pressure. Cell parameters of the high pressure B-Lu 2 Si 2 O 7 phase [9] differ from those determined in this work, so that the cell volume is 1.4% smaller (cf. Table 2).…”

Section: Discussionmentioning

confidence: 86%

“…According to Bocquillon et al [9] the only disilicate phase stable at normal pressure is C-type Lu 2 Si 2 O 7 with thortweitite structure. Pressure in excess of 80 kbar was necessary to obtain B-type polymorph.…”

Section: Discussionmentioning

confidence: 99%

“…For 1:1 composition (orthosilicate-Lu 2 O[SiO 4 ]) A-and B-types were observed [4][5][6]. Very rich crystallochemistry occurs for 1:2 composition (disilicate-Lu 2 Si 2 O 7 ), where five different structures: B [7], C [4,8], D [9], L [10] and X [9,11] were discovered. Among those only C, D and X are "true" disilicates and contain [Si 2 O 7 ] groups, while B and L forms contain both [Si 3 O 10 ] and [SiO 4 ] units.…”

Section: Introductionmentioning

confidence: 98%

“…Among those only C, D and X are "true" disilicates and contain [Si 2 O 7 ] groups, while B and L forms contain both [Si 3 O 10 ] and [SiO 4 ] units. Bocquillon et al [9] studied P-T (pressure-temperature) diagram of the phase stability of Lu 1:2 silicates and concluded that at normal pressure C-type phase is thermodynamically stable over entire temperature range. At pressure above 20 kbar …”

Section: Introductionmentioning

confidence: 98%

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Section: Xrdmentioning

confidence: 67%

Section: Discussionmentioning

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Section: Discussionmentioning

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Section: Introductionmentioning

confidence: 98%

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Formation and characterization of Lu silicate nanoparticles in amorphous SiO2

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In Situ Generated β‐Yb₂Si₂O₇ Containing Coatings for Steel Protection in Extreme Combustion Environments

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et al. 2021

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The rapid permeation and degradation of silazane‐based coatings by water vapor limit their application in combustion environments. Hence, this work reports on the reaction of the oligosilazane Durazane 1800 with an appropriate Yb‐complex by a molecular approach and its application as protective thin coatings (1.2 µm) for AISI 304 in comparison with the benchmark Durazane 2250 in combustion‐like environments. Fourier transform infrared‐ and nuclear magnetic resonance‐spectroscopy elucidate the reaction mechanism and the chemical structure of the resulting Yb‐modified silazanes, whereas elemental and X‐ray diffractometry analyses confirm the formation of crystalline β‐Yb2Si2O7 and SiO2 after pyrolysis at 1000 °C in air. Energy dispersive spectroscopy and X‐ray photoelectron spectroscopy profile analyses show the enhanced diffusion of Fe, Cr, and Mn from the substrate into the Yb50 coating, which is responsible for a better adhesion (23.7 MPa), scratch tolerance (38 N), and a decreased coefficient of thermal expansion‐mismatch to the substrate, resisting 9 thermal cycles between 1000 and 20 °C. Despite the low Yb‐silicate content (6.8 wt%), only minor damage is caused to the Yb50 coating after wet oxidation in moist flowing air (1000 °C for 15 h), whereas the Durazane 2250 coating spalled‐off. This is a clear indication of the potential of the Yb2Si2O7‐containing coatings to protect metals and ceramics in extreme combustion environments.

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In Situ Generated Yb₂Si₂O₇ Environmental Barrier Coatings for Protection of Ceramic Components in the Next Generation of Gas Turbines

Leite

Degenhardt²,

Krenkel

et al. 2022

Adv Materials Inter

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CO 2 emissions should be cut in half by 2050 compared to 2009 in order to limit the increase in the world average temperature to 2 °C. Despite the advances in renewable energy alternatives, their supply strongly depends on favorable weather conditions and their efficient storage is still difficult. Thus, the key factor for the transition towards a more sustainable future relies on decarbonizing power generation. Alone the substitution of heavy fossil fuels by natural gas can decrease the related emissions in ≈50%. [1][2][3][4] Nevertheless, a developing interest has been shown for carbon-free sources as ammonia and liquid hydrogen, which are potential fuel alternatives to produce energy with a cleaner emission profile. [5] Besides the compactness and low maintenance costs, gas turbines can operate with versatile fuel sources, which make them a natural choice for the efficient production of energy. For this reason, they have found increasing service in the past 40 years in the power industry both among utilities and industrial plants as well as for aviation. [6] In combined cycle operation and with inlet temperatures exceeding 1400 °C, efficiencies as high as 63% can be achieved. [2] Therefore, different strategies are adopted to protect the currently used Nibased superalloys such as the deposition of yttria-stabilized-zirconia thermal barrier coatings (TBC) and intensive film cooling. This standard is, however, not realistic when considering service for considerable amount of times (t > 10 000 h), since the rapid creep of the TBC at above 900 °C, associated with the great mismatch between its coefficient of thermal expansion (CTE) with the alloy, increase the risk of spallation and limit the use of metal-based components in turbine engines. [7][8][9][10] Especially envisioning the use of carbon-free fuel sources in future gas turbines like hydrogen or ammonia, water vapor is one of the main products of combustion, which intensifies the degradation of these alloys. [5,[11][12][13] Hence, advances towards reduced greenhouse gas emissions and more efficient gas turbines require their substitution by more robust materials resistant to oxidation and corrosion, which can endure service at higher temperatures.Due to their reduced density, lower CTE (3-5.5 × 10 −6 K −1 ), high temperature creep resistance and melting points, nonoxide silicon based ceramics as Si 3 N 4 , SiC, and SiC/SiC composites stand out for application in combustion environments. [14][15][16][17][18][19][20][21] In face of an accelerating climate change, the reduction and substitution of fossil fuels is crucial to decarbonize energy production. Gas turbines can operate with versatile fuel sources like natural gas and future fuels such as hydrogen and ammonia. Furthermore, thermal efficiencies above 60% can be achieved using non-oxide silicon-based ceramic components. However, water vapor is one of the main combustion products leading to rapid corrosion because of volatilization of the protective SiO 2 layer at 1200 °C. An in situ generated Yb 2 Si 2 ...

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Polymorphism under pressure of the disilicates of the heavier lanthanoids Ln2Si2O7 (Ln = Tm, Yb, Lu)

Cited by 47 publications

References 3 publications

Formation and characterization of Lu silicate nanoparticles in amorphous SiO2

Formation and characterization of Lu silicate nanoparticles in amorphous SiO2

In Situ Generated β‐Yb₂Si₂O₇ Containing Coatings for Steel Protection in Extreme Combustion Environments

In Situ Generated Yb₂Si₂O₇ Environmental Barrier Coatings for Protection of Ceramic Components in the Next Generation of Gas Turbines

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Polymorphism under pressure of the disilicates of the heavier lanthanoids Ln2Si2O7 (Ln = Tm, Yb, Lu)

Cited by 47 publications

References 3 publications

Formation and characterization of Lu silicate nanoparticles in amorphous SiO2

Formation and characterization of Lu silicate nanoparticles in amorphous SiO2

In Situ Generated β‐Yb2Si2O7 Containing Coatings for Steel Protection in Extreme Combustion Environments

In Situ Generated Yb2Si2O7 Environmental Barrier Coatings for Protection of Ceramic Components in the Next Generation of Gas Turbines

Contact Info

Product

Resources

About

In Situ Generated β‐Yb₂Si₂O₇ Containing Coatings for Steel Protection in Extreme Combustion Environments

In Situ Generated Yb₂Si₂O₇ Environmental Barrier Coatings for Protection of Ceramic Components in the Next Generation of Gas Turbines