A solution of the diffusion equation for double oxidation in dry oxygen including lazy exchange between network and interstitial oxygen

Oxidation of an Fe-Cr-Al-Y-Zr alloy forming an alumina scale in a Ga2O atmosphere at 1473 K

“…A mullite/quartz reaction tube described in Section II was implemented after calculating the permeability of oxygen through quartz by the procedure described by Norton and Seybolt. [23] The oxygen diffusion coefficient of 2.04 ϫ 10 Ϫ8 cm 2 /s, extrapolated from the data provided by Norton and Seybolt, was determined for a temperature of 1473 K. The time needed to achieve steady-state flow or the lag time was determined with the wall thickness (d wall ) and the oxygen diffusion coefficient as follows: [3] The oxygen partial pressure within the ampoule becomes 2.7 ϫ 10 Ϫ4 kPa after achieving steady state at 93 hours at 1473 K. [30] The foregoing calculations are based on the diffusion coefficient acquired from permeability experiments, which best simulates the present study compared to other studies on the mechanisms of oxygen diffusion in quartz [31][32][33][34][35] and critically reviewed by Lamkin et al [36] The foregoing calculations assumed that the initial oxygen potential was constant and obviously changes within the ampoule until steady state is reached, but clearly the oxygen potential shifts during long-term exposure when air surrounds the capsule. Thus, an argon atmosphere was used to surround the ampoule and to minimize the effects of inward diffusion of oxygen during the transition period, as well as at steady state.…”

Oxygen-excess amorphous SiO2 with 18O-labeled interstitial oxygen molecules

“…The diffusion of interstitial O 2 in a-SiO 2 can be regarded basically as permeation [3][4][5][6][7][8][9][10], however, exchange between interstitial O 2 and oxygen atoms in the a-SiO 2 network also takes place, particularly at high temperatures [11][12][13][14][15]. The activation energy for the oxygen exchange is~2 eV [13][14][15] and is much larger than that of the permeation (diffusion) of interstitial O 2 (~0.8-1.2 eV [3,8,9,[16][17][18]).…”

“…The activation energy for the oxygen exchange is~2 eV [13][14][15] and is much larger than that of the permeation (diffusion) of interstitial O 2 (~0.8-1.2 eV [3,8,9,[16][17][18]). Thus, the contribution of the oxygen exchange increases with an increase in temperature.…”

Matrix Development for Water Vapor Resistant SiC-Based Ceramic Matrix Composites

“…Similar differences between the oxygen diffusivity in single crystal and polycrystalline Al2O3 have been observed 145 . Y2Si2O7 and Y2SiO5 have a lower oxygen diffusivity than SiO2 (permeation) 143 and single crystal Y2O3 105 , constituents of Y2Si2O7 and Y2SiO5, and a greater oxygen diffusivity than SiO2 (network) 141 150,151 diffusion rates through yttrium silicate EBCs and ceramic composite matrices, critical for life prediction of engine components that require service lives > 10,000 hours.…”

“…It is important to note that the oxygen diffusivity in Y2O3 105 is 7 -8 orders of magnitude greater than SiO2 (network exchange) 141 and similar to that for SiO2 (permeation) 143 The formation of Y2O3 from yttrium silicides requires the selective oxidation of yttrium from the alloy and thus the growth rate of Y2O3 may be controlled by diffusion in the scale or in the alloy 162 . If the growth rate of Y2O3 were controlled by diffusion in the scale then Y2O3…”