2770 J. Kimmel et al. /Journal of the European Ceramic Society 22(2002)2769-2775 The rate of SiC recession is, thus, controlled by the volatility rate of silica rather than the oxidation rate of Hole The recession of SiC in high pressure, water vapor environments was quantified at Oak Ridge National Laboratory (ORNL). SiC material was tested in the ORNL high temperature, high steam rig(Keiser rig) at 1200C, 10 atm total and 1. 5 atm water vapor pressures for periods of 500 h at a time. Long term testing has shown that the recession rate is approximately 90 um in 1000 h.6 The SiC recession rates seen in the Keiser rig is onsistent with the engine tests. The need for an ebC to achieve the goal of 30.000-h life The fifth Csgt field test of cfcc liners at Texaco Fig. 1. A hole in the EBC spalled area of the inner liner after the was the first test of EBC protected liners in a gas tur 13.937-h field test. bine. The test was stopped in November 2000 after 13, 937-h of engine operation with 59 starts/stops when lense, adherent silica layer that constitutes a barrier to a small hole was observed in the inner liner during further oxidation. However, combustion environments routine borescope inspection. The maximum CFCC consist of approximately 10% water vapor, as well as liner hot wall temperatures were estimated to be oxygen, carbon dioxide, nitrogen, and hydrogen. Water 1200C. Honeywell Advanced Composites Incorp vapor raises the oxidation rate of Sic by more than an rated(HACD) fabricated the inner and outer liners used order of magnitude. In addition. the silica scale formed in the test. The inner liner was made of a Hi-Nicalon volatilizes in a water vapor environment, leading to SiC-Si composite made by the melt infiltration (MI higher rates of degradation. process. The outer liner was made of an Enhanced Hi Water vapor volatilizes the silica scale primarily by Nicalon/Sic composite made by the che emica vapor the following reaction: infiltration(CVI) process. Boron nitride was used as the fiber/matrix interfacial coating for the inner liner and Sio2(s)+2H20(g)->Si(oh)(g) pyrolitic carbon for the outer liner. Prior to EBC appli cation, a seal coat of Sic was applied on both liners The silica volatilization occurs very quickly and using a chemical vapor deposition process. The seal coat bits a linear rate constant. In conditions such as com- was applied in two steps. An initial seal coat was bustion environments where both SiC oxidation and applied immediately after the fabrication of the two SiO2 volatilization occurs, paralinear kinetics are liners. An additional seal coat was given prior to EBC observed. The overall sample weight change is the sum application, which occurred several months after first of the weight gain due to the growth of the scale and the seal coat application. The EBCs were applied to the gas- weight loss due to volatilization of silica. Over long path surfaces of the two liners by UTRC using a ther periods of time, oxide growth occurs at the same rate as mal spray process. The eBC system consisted of three oxide volatilization so that a constant oxide thickness is layers, each layer approximately 125 um in thickness formed. After a constant oxide thickness is established. silicon mullite and barium strontium aluminum near weight loss and Sic recession rates are observed.(BSaS)was used for the inner liner, and silicon Forward Cold side Forward Hot Side 8 20.3cm 1016cm Fig. 2. Environmental barrier coated Hi-Nicalon/SiC-Si MI inner liner after the 13,937-h field test.dense, adherent silica layer that constitutes a barrier to further oxidation. However, combustion environments consist of approximately 10% water vapor, as well as oxygen, carbon dioxide, nitrogen, and hydrogen. Water vapor raises the oxidation rate of SiC by more than an order of magnitude. In addition, the silica scale formed volatilizes in a water vapor environment, leading to higher rates of degradation. Water vapor volatilizes the silica scale primarily by the following reaction: SiO2(s)+2H2O(g)!Si(OH)4(g) The silica volatilization occurs very quickly and exhi￾bits a linear rate constant. In conditions such as com￾bustion environments where both SiC oxidation and SiO2 volatilization occurs, paralinear kinetics are observed. The overall sample weight change is the sum of the weight gain due to the growth of the scale and the weight loss due to volatilization of silica. Over long periods of time, oxide growth occurs at the same rate as oxide volatilization so that a constant oxide thickness is formed. After a constant oxide thickness is established, linear weight loss and SiC recession rates are observed. The rate of SiC recession is, thus, controlled by the volatility rate of silica rather than the oxidation rate of SiC.35 The recession of SiC in high pressure, water vapor environments was quantified at Oak Ridge National Laboratory (ORNL). SiC material was tested in the ORNL high temperature, high steam rig (Keiser rig) at 1200 C, 10 atm total and 1.5 atm water vapor pressures for periods of 500 h at a time. Long term testing has shown that the recession rate is approximately 90 mm in 1000 h.6 The SiC recession rates seen in the Keiser rig is consistent with the recession rates seen in the first four engine tests. The need for an EBC to achieve the goal of 30,000-h life was apparent. The fifth CSGT field test of CFCC liners at Texaco was the first test of EBC protected liners in a gas tur￾bine. The test was stopped in November 2000 after 13,937-h of engine operation with 59 starts/stops when a small hole was observed in the inner liner during routine borescope inspection. The maximum CFCC liner hot wall temperatures were estimated to be 1200 C. Honeywell Advanced Composites Incorpo￾rated (HACI) fabricated the inner and outer liners used in the test. The inner liner was made of a Hi-Nicalon/ SiC-Si composite made by the melt infiltration (MI) process. The outer liner was made of an Enhanced Hi￾Nicalon/SiC composite made by the chemical vapor infiltration (CVI) process. Boron nitride was used as the fiber/matrix interfacial coating for the inner liner and pyrolitic carbon for the outer liner. Prior to EBC appli￾cation, a seal coat of SiC was applied on both liners using a chemical vapor deposition process. The seal coat was applied in two steps. An initial seal coat was applied immediately after the fabrication of the two liners. An additional seal coat was given prior to EBC application, which occurred several months after first seal coat application. The EBCs were applied to the gas￾path surfaces of the two liners by UTRC using a ther￾mal spray process. The EBC system consisted of three layers, each layer approximately 125 mm in thickness; silicon, mullite and barium strontium aluminum silicate (BSAS) was used for the inner liner, and silicon, mullite Fig. 1. A hole in the EBC spalled area of the inner liner after the 13,937-h field test. Fig. 2. Environmental barrier coated Hi-Nicalon/SiC-Si MI inner liner after the 13,937-h field test. 2770 J. Kimmel et al. / Journal of the European Ceramic Society 22 (2002) 2769–2775