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All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Crystallization and characterization of Y2O3-SiO2 glasses

Glasses in the yttria-silica system with 20-40 mol pct Y2O3 have been subjected to recrystallization studies after melting at 1900-2100 C in W crucibles in 1 and 50 atm N2. The TEM and XRD results obtained indicate the presence of the delta, gamma, gamma-prime, and beta-Y2Si2O7 crystalline phases, depending on melting and quenching conditions. Heat-treatment in air at 1100-1600 C increased the amount of crystallization, and led to the formation of Y2SiO5, cristobalite, and polymorphs of Y2Si2O7. Also investigated were the effects of 5 and 10 wt pct zirconia additions.

Drummond, C. H., III↗
NASA NTRS1991

Crystallization and characterization of Y2O3-SiO2 glasses

Glasses in the yttria-silica system with 20 to 40 mol pct Y2O3 were subjected to recrystallization studies after melting at 1900 to 2100 C in W crucibles in 1 and 50 atm N2. The TEM and XRD results obtained indicate the presence of the delta, gamma, gamma prime, and beta-Y2Si2O7 crystalline phases, depending on melting and quenching conditions. Heat treatment in air at 1100 to 1600 C increased the amount of crystallization, and led to the formation of Y2SiO5, cristabalite, and polymorphs of Y2Si2O7. Also investigated were the effects of 5 and 10 wt pct zirconia additions.

Drummond, Charles H., III↗
NASA NTRS1998

Anisotropic Optical-Response of Eu-doped Yttrium Orthosilicate

Eu-doped yttrium orthosilicate (Eu(3+) : Y2SiO5) had been a subject being investigated for coherent time-domain optical memory and information processing applications since its ultraslow optical dephasing was discovered several years ago. In this crystal the weakly allowed (7)F0 - (5)D0 transition of europium ions exhibits a sufficient long dephasing time and no spectral difli.usion on a time scale of several hours at low temperature, thus an information pattern or data can be stored as a population grating in the ground state hyperfine levels. On the other hand, the study on photon-echo relaxation shows that the dephasing time T2 of Eu (3+) and other rare-earth ions doped YAG, YAlO3 strongly depends on the intensity of the excitation pulses. In Eu (3+) :YAlO3, an exponential decay of photon-echo with T2 = 53 microseconds if the excitation pulses are weak (5 vJ/pulse) was observed. However, when the excitation pulses are strong (80 pJ/pulse) they observed a much shortened T2 with a highly nonexponential decay pattern. The conclusion they derived is that the intensity-dependent dephasing rate effects are quite general, and it depends on how much the excitation intensity varies. In this paper we use transient grating formation technique showing that a temporal lattice distortion may only occur along crystal c axis, caused by EU (3+) excitation. At high excitation level the produced exciton in conduction band may also couple to the dynamical lattice relaxation process, giving rise to an apparently much shortened dephasing time.

Liu, Huimin↗
NASA NTRS2018

Corrigendum to "Mass Spectrometric Measurements of the Silica Activity in the Yb2O3-SiO2 System and Implications to Assess the Degradation of Silicate-Based Coatings in Combustion Environments"

The authors regret that errors appeared in the above manuscript.The corrections that need to be made are highlighted in yellow in the thermodynamic cycle of Table 2. The enthalpies in reactions 2, 5 and 6 are negative. Now that the enthalpies in reactions 2, 5 and 6 are negative, the correct enthalpy of formation of Yb2SiO5 is 2774 11 kJ mol-1. Also, the correct element in the formula Y2SiO5 on the right side of equation 2 is Yb instead Y.

Costa, Gustavo↗
NASA NTRSDate not supplied

Environmental Barrier Coating Surface Temperature Mapping Using a Compatible Er-Doped Sc 2 SiO 5 Temperature-Sensing Layer

Accurate surface temperature-mapping capabilities in the 1300 to 1500 °C range are needed for SiC/SiC ceramic matrix composites protected by environmental barrier coatings (EBCs) under testing in turbine engine environment facilities. The strong background thermal radiation at these higher temperatures is a challenging issue. Er-doped Y 2 SiO 5 was previously shown to be capable of achieving luminescence lifetime-based temperature mapping up to 1560 °C as a standalone material. However, compatibility issues between an Er-doped Y 2 SiO 5 surface temperature sensing layer and an underlying Sc 2 Si 2 O 7 -based EBC topcoat limited temperature mapping of the EBC surface to a maximum of 1380 °C. Therefore, an Er-doped Sc 2 SiO 5 temperature sensing layer has been subsequently developed with better compatibility with the Sc2Si2O7-based EBC topcoat. Localized spot temperature measurements as well as luminescence lifetime imaging-based temperature mapping were demonstrated up to 1535 °C from a 15 µm thick Er-doped Sc 2 SiO 5 layer at the surface of a Sc2Si2O7-based EBC topcoat, a significant improvement over the Er-doped Y2SiO5 layer 1380 °C temperature sensing limit. No degradation of the Er-doped Sc 2 SiO 5 temperature sensing surface layer was observed.

temperature measurement↗