J. Kimmel et al. /Journal of the European Ceramic Society 22(2002)2769-2775 2773 Middle Fig. 9. Recession of BSAS top layer EBC on the inner liner after 13, 937-h field test. engine test are presented in Figs. 7 and 8, respectively. A three-layer EBC that was applied to both liners con sisted of a BSAs top layer, a mullite or mulli te +BSAs intermediate layer, and a silicon bottom layer. A layer of silica was formed during the engi test due to oxidation of the silicon layer. The EBC on 妈点 he inner liner consisted of silicon (90-125 um), silica (60-100um), mullite(75-100um), and bsas(150-200 Hm). On the outer liner, the EBC consisted of silicon (75-140 um), silica(25-60 Hm), mullite+ BSAS (175- 225m), and bsas(175-200um). The three-layer EBC system used on the outer liner performed better than on the inner liner. The addition Fig 10. EBC after recession of BSAS top layer on the outer liner after 13.937-h field test. The EBC is still protective even after some recession of BSAS to mullite in the intermediate layer minimized/ of the BSAS top layer reduced cracks and porosity in that layer, resulting in reduced oxidation of the silicon layer, and thus better protection of the liner. In addition, separation at the interface of the mullite intermediate layer and the silica layer was greatly reduced with the addition of bSAs lumina These results are consistent with Keiser rig testing results A mullite BSAs intermediate layer was used to ,alumina coat the SiC/Sic liners used in first two Malden Mills and the sixth Texaco engine tests. Recession of the Bsas top layer, which was not observed in over 5000-h Keiser rig tests at ORNL was observed on both liners exposed to engine environ- ment(Fig. 9). The main difference between the Keiser rig and combustion environment is the gas velocity Velocity plays an important role in the volatilization of silica. 2 The Keiser rig operates at low velocities, less Fig. Il. Mullite phase separation of the intermediate layer into silica and alumina phases. Silica volatilization within the mullite layer leads than 1 cm/s, versus gas velocities on the order of 85 m/s to porosity in the engine. The low velocity in the Keiser rig does not allow for complete volatilization, and recession results was consistent with 6500 h of Keiser Rig testing at are reported based upon oxidation depth. Fortunately, 1200oC. In order to reduce the bsas recession in future even after partial BSAS recession, the EBC was still engine tests, either its thickness can be increased or the protective(Fig. 10). A uniform layer of approximately composition modified to achieve a more resistant top 30 um of silica has formed after engine testing, which layerengine test are presented in Figs. 7 and 8, respectively. A three-layer EBC that was applied to both liners con￾sisted of a BSAS top layer, a mullite or mulli￾te+BSAS intermediate layer, and a silicon bottom layer. A layer of silica was formed during the engine test due to oxidation of the silicon layer. The EBC on the inner liner consisted of silicon (90–125 mm), silica (60–100 mm), mullite (75–100 mm), and BSAS (150–200 mm). On the outer liner, the EBC consisted of silicon (75–140 mm), silica (25–60 mm), mullite+BSAS (175– 225 mm), and BSAS (175–200 mm). The three-layer EBC system used on the outer liner performed better than on the inner liner. The addition of BSAS to mullite in the intermediate layer minimized/ reduced cracks and porosity in that layer, resulting in reduced oxidation of the silicon layer, and thus better protection of the liner. In addition, separation at the interface of the mullite intermediate layer and the silica layer was greatly reduced with the addition of BSAS. These results are consistent with Keiser rig testing results. A mullite+BSAS intermediate layer was used to coat the SiC/SiC liners used in first two Malden Mills and the sixth Texaco engine tests. Recession of the BSAS top layer, which was not observed in over 5000-h Keiser rig tests at ORNL, was observed on both liners exposed to engine environ￾ment (Fig. 9). The main difference between the Keiser rig and combustion environment is the gas velocity. Velocity plays an important role in the volatilization of silica.1,2 The Keiser rig operates at low velocities, less than 1 cm/s, versus gas velocities on the order of 85 m/s in the engine. The low velocity in the Keiser rig does not allow for complete volatilization, and recession results are reported based upon oxidation depth. Fortunately, even after partial BSAS recession, the EBC was still protective (Fig. 10). A uniform layer of approximately 30 mm of silica has formed after engine testing, which was consistent with 6500 h of Keiser Rig testing at 1200 C. In order to reduce the BSAS recession in future engine tests, either its thickness can be increased or the composition modified to achieve a more resistant top layer. Fig. 9. Recession of BSAS top layer EBC on the inner liner after 13,937-h field test. Fig. 10. EBC after recession of BSAS top layer on the outer liner after 13,937-h field test. The EBC is still protective even after some recession of the BSAS top layer. Fig. 11. Mullite phase separation of the intermediate layer into silica and alumina phases. Silica volatilization within the mullite layer leads to porosity. J. Kimmel et al. / Journal of the European Ceramic Society 22 (2002) 2769–2775 2773