Stability of the Y₂O₃–SiO₂ system in high‐temperature, high‐velocity water vapor

Abstract

High‐temperature, high‐velocity water vapor (steam‐jet) exposures were conducted on Y2O3, Y2SiO5, Y2Si2O7, and SiO2 for 60 hours at 1400°C. Volatility of Y2O3 was not observed. Phase‐pure Y2SiO5 exhibited SiO2 loss forming Y2O3 and porosity. A mixed porous and dense Y2SiO5 layer formed on the surface of Y2Si2O7 due to SiO2 depletion. The mechanisms and kinetics of the reaction between SiO2 and H2O(g) to form Si(OH)4(g) from Y2SiO5, Y2Si2O7, and SiO2 are discussed.

Materials challenges in hydrogen-fuelled gas turbines

“…However, the poor chemical compatibility between pyrochlores and the alumina TGO layer requires the use of YSZ as an intermediate diffusion-barrier layer [28], as illustrated in Figure 5. Alternative bond coats under consideration are Al 2 O 3 forming MAX phases such as Cr 2 AlC [65] and Ti 2 AlC [66]. The MAX phases are polycrystalline nanolaminates of ternary carbides and nitrides, named from their general formula of M n + 1 AX n (where M is a transition metal, A is an A group (mostly IIIA and IVA) element, X is C and/or N, and n = 1-3).…”

“…Volatilisation is not completely avoided as these coating materials also comprise Si, but it is greatly reduced compared to a non-coated SiC/SiO 2 surface. The evaporation rate from the coated material is proportional to the surface activity of Si, and for this reason RE 2 SiO 4 is preferred over RE 2 Si 2 O 4 , despite the latter having a better TEC match with the substrate [66,72].…”

Interactions of Na2SO4 and yttrium‐silicate environmental barrier coatings at 825°C

“…Reaction mechanisms of high‐velocity steam and siliceous debris with EBC materials are well‐studied 8,11–15 …”

“…[7][8][9][10] Reaction mechanisms of high-velocity steam and siliceous debris with EBC materials are wellstudied. 8,[11][12][13][14][15] However, another damage mechanism that limits the lifespan of turbine engine coatings is Na 2 SO 4 -induced hot corrosion. Hot corrosion occurs when salt from marine environments and sulfur from high-temperature processing (e.g., coal gasification, oil refining) 16,17 are ingested into a gas turbine engine during service.…”

Experimental Determination of Phase Equilibria in the REM2O3-SiO2 (REM = Y/Yb/La) Systems at Elevated Temperature

“…But REM containing materials have crucial applications in many important industries due to their unique properties [4,5]. For example, compounds of the REM2O3-SiO2 systems, in particular, yttrium, ytterbium and lanthanum silicates, have proved to be promising materials for high temperature structural applications and rare earth (RE) silicates have been recognized as the third generation of EBC materials for silicon-based ceramics [6][7][8][9]. A remarkable progress has been achieved in the bonding, thermal treatment and doping of rare-earth silicates in order to improve their performance [5][6][7][8][9].…”