Fusion Engineering and Design 83(2008)1490-1494 Contents lists available at Science Direct Fusion engineering and design ELSEVIER journalhomepagewww.elsevier.com/locate/fusengdes Oxidation behavior of SiC/Sic composites for helium cooled solid breeder blanket S Nogami,, N Otake A Hasegawa,Y Katoh, A Yoshikawa, M. Satou Y Oya, K Okino Mepterime sc e and mech ence and Energy Tohoku University, 6-6-01, Aramaki-oza-Aoba, Aoba-ku, Sendai 980-8579, Japan nology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6138 USA Radiochemistry Research Laboratory, Faculty of Science, Shizuoka University, 836, Ohya, Suruga-ku, Shizuoka 422-8529, Japan ARTICLE INFO A BSTRACT In order to evaluate the oxidation behavior and mechanism of Sic/Sic com with conventional Available online 25 July 2008 pyroliticgraphite interface(Pyc-SiC/SiC)and advanced multilayer interface( ML-Sic/SiC)in a HCSB blanket environment, a thermal gravimetric analysis(tga)in He O2 environment at 1000C and 1200. was erformed. The Pyc-SiC/ SiC at 1200 Cand the MI at1000°Cand1200° showed relatively smaller eight change during oxidation because Sio2 formed on the Sic-matrix and Sic-fiber sealed the specime surface before the Pyc interface recession by gasification of graphite due to relatively high Sioz formation hermal gravimetric analysis rate. While the Pyc-SiC/Sic at 1000C showed significant weight loss because the specimen surface was Helium cooled solid breeder blanket not sealed by Sio2 and significant Pyc interface recession occurred due to relatively slow Sioz formation. O 2008 Elsevier B V. All rights reserved. 1. Introduction The purpose of this study is to evaluate the oxidation behavior nd mechanism of SiC/Sic composites with conventional pyrolite Silicon carbide(Sic) fiber reinforced Sic matrix composite graphite interface(PyC-SiC/SiC) and advanced multilayer inter- (SiC/SiC composite)is one of the candidate structural materials for face(ML-Sic/Sic)in He+O2 environment. A thermal gravimetric fusion reactor blanket because of its low induced radioactivity, analysis(TGa)was performed as an experimental approach for excellent high temperature mechanical properties and excellent evaluation. diation resistance [1]. Helium(He)gas cooled solid breeder blan ket(HCSB)has been considered as one of the blanket desig concepts using the sic/Sic composite for relatively high tempera- 2. Experimental ure plant operation[2. Chemical stability, especially an oxidation resistance, might be a key issue to be solved for the HCSB struc- Sic/SiC composites used in this work were fabricated by Hy therm. Reinforced Sic fiber was 1D Hi-Nicalon Type-S fiber. tural material because He gas in the HCSB might include partial sic matrix was p-SiC fabricated using an isothermal chemi oxygen. cal vapor infiltration (Cvi) process. The average thickness of The desired strength of SiC/Sic composite can be given by an optimised interface layer between the fiber and matrix In order to interface layers(pyrolitic graphite and Sic/c multilayer) 1000nm. mprove its mechanical properties, advanced interfaces such as a Monolithic B-SiC and monolithic pyrolitic graphite were also Sic/C multilayer and a porous SiC have been developed [3]. How- examined for comparison with the composite. They were fabricated oy oxidation under fusionreactor operating condition, for example, neering and Shipbuilding Company, Ltd. and by TOYO TANSO, Ltd C(s)+O2(g)=CO2(g) ith shape shown Table 1. The"ax b surface"in Table 1 of the block specimens 2C(s)+O2(g)=2c(g) was mechanically polished using 0.5 um diamond slurry. The axis"direction in the left figure of Table 1 corresponds to the fiber axis direction of the composite, crystalline growth direction of the orresponding author. Tel: +81 22 795 7924: fax: +81 22 7957924 monolithic B-SiC and a-axis of graphite structure of the monolithic pyrolitic grap 'S-see front matter 2008 Elsevier B.v. All rights reserved. 0.1016 fusengdes.2008.06004
Fusion Engineering and Design 83 (2008) 1490–1494 Contents lists available at ScienceDirect Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes Oxidation behavior of SiC/SiC composites for helium cooled solid breeder blanket S. Nogami a,∗, N. Otakea, A. Hasegawaa, Y. Katohb, A. Yoshikawac, M. Satoua, Y. Oyac, K. Okunoc a Department of Quantum Science and Energy Engineering, Tohoku University,6-6-01, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579, Japan b Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6138, USA c Radiochemistry Research Laboratory, Faculty of Science, Shizuoka University, 836, Ohya, Suruga-ku, Shizuoka 422-8529, Japan article info Article history: Available online 25 July 2008 Keywords: SiC/SiC composite Oxidation Interface Thermal gravimetric analysis Helium cooled solid breeder blanket abstract In order to evaluate the oxidation behavior and mechanism of SiC/SiC composites with conventional pyrolitic graphite interface (PyC-SiC/SiC) and advancedmultilayer interface (ML-SiC/SiC) in a HCSB blanket environment, a thermal gravimetric analysis (TGA) in He + O2 environment at 1000 ◦C and 1200 ◦C was performed. The PyC-SiC/SiC at 1200 ◦C and theML-SiC/SiC at 1000 ◦C and 1200 ◦C showed relatively smaller weight change during oxidation because SiO2 formed on the SiC-matrix and SiC-fiber sealed the specimen surface before the PyC interface recession by gasification of graphite due to relatively high SiO2 formation rate. While the PyC-SiC/SiC at 1000 ◦C showed significant weight loss because the specimen surface was not sealed by SiO2 and significant PyC interface recession occurred due to relatively slow SiO2 formation. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Silicon carbide (SiC) fiber reinforced SiC matrix composite (SiC/SiC composite) is one of the candidate structural materials for a fusion reactor blanket because of its low induced radioactivity, excellent high temperature mechanical properties and excellent radiation resistance [1]. Helium (He) gas cooled solid breeder blanket (HCSB) has been considered as one of the blanket design concepts using the SiC/SiC composite for relatively high temperature plant operation [2]. Chemical stability, especially an oxidation resistance, might be a key issue to be solved for the HCSB structural material because He gas in the HCSB might include partial oxygen. The desired strength of SiC/SiC composite can be given by an optimised interface layer between the fiber and matrix. In order to improve its mechanical properties, advanced interfaces such as a SiC/C multilayer and a porous SiC have been developed [3]. However, SiC/SiC composites have a possibility of interface degradation by oxidation under fusion reactor operating condition, for example, by the following reactions [4]: C(s) + O2(g) = CO2(g) (1) 2C(s) + O2(g) = 2CO(g) (2) ∗ Corresponding author. Tel.: +81 22 795 7924; fax: +81 22 795 7924. E-mail address: shuhei.nogami@qse.tohoku.ac.jp (S. Nogami). The purpose of this study is to evaluate the oxidation behavior and mechanism of SiC/SiC composites with conventional pyrolitic graphite interface (PyC-SiC/SiC) and advanced multilayer interface (ML-SiC/SiC) in He + O2 environment. A thermal gravimetric analysis (TGA) was performed as an experimental approach for evaluation. 2. Experimental SiC/SiC composites used in this work were fabricated by Hypertherm. Reinforced SiC fiber was 1D Hi-Nicalon Type-S fiber. SiC matrix was -SiC fabricated using an isothermal chemical vapor infiltration (ICVI) process. The average thickness of the interface layers (pyrolitic graphite and SiC/C multilayer) was 1000 nm. Monolithic -SiC and monolithic pyrolitic graphite were also examined for comparison with the composite. They were fabricated using a chemical vapor deposition (CVD) process by Mitsui Engineering and Shipbuilding Company, Ltd. and by TOYO TANSO, Ltd., respectively. Samples were machined into blocks with shape shown in Table 1. The “a × b surface” in Table 1 of the block specimens was mechanically polished using 0.5 m diamond slurry. The “Zaxis” direction in the left figure of Table 1 corresponds to the fiber axis direction of the composite, crystalline growth direction of the monolithic -SiC and a-axis of graphite structure of the monolithic pyrolitic graphite. 0920-3796/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2008.06.004
S Nogami et aL Fusion Engineering and Design 83(2008)1490-1494 Po2=1500ppm,1000C Po2=150p0m,1200C E品EU5 ML-SiC/SiC B-SiC EEE PyC-SiC/SiC ML-SIC/SIC Py C-SiC/SiC Graphite Graphite Fig. 1. The weight change behavior of the two types of Sic/SiC composites(Pyc-SiC/SiC and ML-SiCSiC) monolithic B-SiC and monolithic pyrolitic graphite at 1000.C and 1200°cfor100h. Oxidation tests were carried out using a TGA system(TGA51-H, PyC-SIC/SIC ML-SIC/SIC SHIMADZU Corp ) Mixtures of He with 1500 ppm O, were used Samples were heated from room temperature to the test tempera- ture(1000°and1200°at40° min, and then held at the test temperature for 100 h Experimental conditions included 100 sccm flow rate and system pressure of 1 atm. The oxidation behavior of Sic in the conditions of this work was known as a passive oxidation. by the following re. Sic(s)+ 202(g)= SiO2(s)+CO2(g SiC(s)+3/202(g)= SiO2(s)+ CO(g) Morphology observation of the oxidised specimen was pe ormed using a field emission scanning electron microscope (FE-SEM, S-2250N, Hitachi Ltd ) Microstructure and composition of the oxide layer were examined using a secondary ion mass spectroscopy(SIMS, Model 6600, ULVAC-PHI Inc )and X-ray photo electron spectroscopy(XPS, ESCA 1600, ULVAC-PHI Inc ) 3. Results and discussion Fig. 2. Morphology observation of the two types of SiC/SiC composites(Pyc-SiCSiC and ML-SiCsic)after oxidation at 1000C and 1200.C. 3. 1. Weight and morphology chang Typical morphology observation by FE-SEM of the two types of Fig. 1 shows the weight change behavior of the two types of SiC/Sic composites(Pyc-Sic/ SiC and ML-SiC/Sic)after oxidation at Sic/Sic composites(Pyc-SiC/SiC and ML-Sic/SiC), monolithic B-Sic 1000C and 1200"C was shown in Fig..Fig 3 shows the fractured and monolithic pyrolitic graphite during oxidation at 1000C and surface of the Pvc-siCSic composite before and after oxidation 1200C for 100h. The Pyc-SiC/SiC showed significant weight loss at 1000.C. The recession of the Pyc interface layer of the Pyc Sic/Sic after oxidation at 1000C was clearly observed If assum up to 20 h and almost no change after 20 h at 1000 C The mono- that the weight loss of Pyc-Sic/Sic at 1000 C up to 20h was only lithic pyrolitic graphite also showed disappeared before 100 h On the other hand, very small weight due to the recession of Pyc interface, the linear reaction rate con- hange of the PyC-Sic/SiC at 1200oC. the ML-Sic/SiC at 1000 C and stant (k1)of Pyc interface was calculated to 7.12 x 10-5kg/m2/s 1200°Candβ- Sic at1000°cand1200° C was observed, which was smaller than the resolution of the TGa system. Before Oxidation After Oxidation Table 1 pe and geometry PyC interface layer Recession of PyC SiC fiber a(mm) b(mm) t(mm) C fiber Fiber axis direction Monolithic B3-SiC 2 Crystalline growth direction Monolithic Pyc 2 0.5-1.5 a-axis of graphite Fig 3. Fractured surface of the Pyc-SiC/SiC composite before and after oxidation at
S. Nogami et al. / Fusion Engineering and Design 83 (2008) 1490–1494 1491 Fig. 1. The weight change behavior of the two types of SiC/SiC composites (PyC-SiC/SiC and ML-SiC/SiC), monolithic -SiC and monolithic pyrolitic graphite at 1000 ◦C and 1200 ◦C for 100 h. Oxidation tests were carried out using a TGA system (TGA51-H, SHIMADZU Corp.). Mixtures of He with 1500 ppm O2 were used. Samples were heated from room temperature to the test temperature (1000 ◦C and 1200 ◦C) at 40 ◦C/min. and then held at the test temperature for 100 h. Experimental conditions included 100 sccm flow rate and system pressure of 1 atm. The oxidation behavior of SiC in the conditions of this work was known as a passive oxidation. SiC changes into SiO2 by the following reaction equations [4]: SiC(s) + 2O2(g) = SiO2(s) + CO2(g) (3) SiC(s) + 3/2O2(g) = SiO2(s) + CO(g) (4) Morphology observation of the oxidised specimen was performed using a field emission scanning electron microscope (FE-SEM, S-2250N, Hitachi Ltd.). Microstructure and composition of the oxide layer were examined using a secondary ion mass spectroscopy (SIMS, Model 6600, ULVAC-PHI Inc.) and X-ray photoelectron spectroscopy (XPS, ESCA 1600, ULVAC-PHI Inc.). 3. Results and discussion 3.1. Weight and morphology change Fig. 1 shows the weight change behavior of the two types of SiC/SiC composites (PyC-SiC/SiC and ML-SiC/SiC), monolithic -SiC and monolithic pyrolitic graphite during oxidation at 1000 ◦C and 1200 ◦C for 100 h. The PyC-SiC/SiC showed significant weight loss up to 20 h and almost no change after 20 h at 1000 ◦C. The monolithic pyrolitic graphite also showed significant weight loss and disappeared before 100 h. On the other hand, very small weight change of the PyC-SiC/SiC at 1200 ◦C, the ML-SiC/SiC at 1000 ◦C and 1200 ◦C and -SiC at 1000 ◦C and 1200 ◦C was observed, which was smaller than the resolution of the TGA system. Table 1 Specimen shape and geometry Material a (mm) b (mm) t (mm) Z-axis SiC/SiC composite 2 1.5 1–2 Fiber axis direction Monolithic 3-SiC 2 1.5 0.5 Crystalline growth direction Monolithic PyC 2 1.5 0.5–1.5 a-axis of graphite Fig. 2. Morphology observation of the two types of SiC/SiC composites (PyC-SiC/SiC and ML-SiC/SiC) after oxidation at 1000 ◦C and 1200 ◦C. Typical morphology observation by FE-SEM of the two types of SiC/SiC composites (PyC-SiC/SiC and ML-SiC/SiC) after oxidation at 1000 ◦C and 1200 ◦C was shown in Fig. 2. Fig. 3 shows the fractured surface of the PyC-SiC/SiC composite before and after oxidation at 1000 ◦C. The recession of the PyC interface layer of the PyCSiC/SiC after oxidation at 1000 ◦C was clearly observed. If assuming that the weight loss of PyC-SiC/SiC at 1000 ◦C up to 20 h was only due to the recession of PyC interface, the linear reaction rate constant (kl) of PyC interface was calculated to 7.12 × 10−5 kg/m2/s. Fig. 3. Fractured surface of the PyC-SiC/SiC composite before and after oxidation at 1000 ◦C.
S Nogami et aL/ Fusion Engineering and Design 83(2008)1490-1494 107 Matrix. 1000oC Fiber、10009 105 104 103 Depth [nm Depth [nm] 10 28 ≌104 Fig. 4. SIMS spectra as a function of the depth from the oxidized surface for the sic-matrix and Sic-fiber of the Pyc-SiC/SiC composite after oxidation at 1000 C and 1200.C While that of the monolithic pyrolitic graphite was calculated to The parabolic oxidation rate constant(kp) of the monolithic B-Sic 6.04x 10-5kg/m2/s. These values were very similar, therefore, the was 5.20 x 10-8kg/m2/s /2 for 1000C and 2.53 x 10-7kg/m2/s/2 major cause of weight loss in PyC-SiC/SiCat 1000C up to 20 hmight for 1200 C The curves in Fig. 5 are the trend curves calculated using e due to the PyC interface recession by gasification of graphite by those kp value the eqs. (1)and(2). while, the interface region after oxidation at Fig 6 shows the Si-2p XPS spectra for the(a)Sic-matrix and (b) 1200C partly or wholly sealed by reaction phase, which might be SiC-fiber of the Pyc-SiCSic composite after oxidation at 1200.C Sio2 formed on the Sic-matrix and Sic-fiber by the eqs. ( 3)and(4). a function of the depth from the oxidized surface(D). Almost no On the other hand, almost no change was clearly observed for the difference between the Sic-matrix and Sic-fiber was observed. The ML-SiCSiC after oxidation at 1000C and 1200C. 3. 2. Characterization of oxidised layer Fig 4 shows the SIMS spectra as a function of the depth from he oxidized surface for the Sic-matrix and Sic-fiber of the py c SiC/SiC composite after oxidation at 1000Cand 1200 C The depth was measured using a scanning probe microscope(Model P-10, ◇β-siC,1200℃ KLA-Tencor) after sputtering by Cs-ion of the SIMS. Almost no dif- ◆阝-SiC,10o℃ rence between the sic-matrix and sic-fiber was observed. the △Mati100℃ formation of Sio2 layer and reduction and disappearance of Sic ▲Matrⅸx1200℃ vas observed on the surface of the oxidized matrix and fiber of O Fiber,1000℃ he Py C-SiCSiC. Fig. 5 shows the thickness of Sio2 layer evaluated ● Fiber.1200℃C by the SIMS spectra for the monolithic B-SiC and Sic-matrix and Sic-fiber of the Py C-Sic/SiC composite after oxidation at 1000C and 1200C. The Sioz layer thickness was almost the same after 100 h oxidation among the monolithic B-SiC, Sic-matrix and Sic Oxidation Time [h] fiber. The oxidation behavior of the monolithic B-Sic in this work Fig. 5. The thickness of Sioz, layer of monolithic B-Sic and Sic-matrix and Sic-fiber might obey the parabolic rule described in the open literatures [5. of the Pyc-sic Sic after oxidation at 1000.C and 1200
1492 S. Nogami et al. / Fusion Engineering and Design 83 (2008) 1490–1494 Fig. 4. SIMS spectra as a function of the depth from the oxidized surface for the SiC-matrix and SiC-fiber of the PyC-SiC/SiC composite after oxidation at 1000 ◦C and 1200 ◦C. While that of the monolithic pyrolitic graphite was calculated to 6.04 × 10−5 kg/m2/s. These values were very similar, therefore, the major cause of weight loss in PyC-SiC/SiC at 1000 ◦C up to 20 hmight be due to the PyC interface recession by gasification of graphite by the Eqs. (1) and (2). While, the interface region after oxidation at 1200 ◦C partly or wholly sealed by reaction phase, which might be SiO2 formed on the SiC-matrix and SiC-fiber by the Eqs. (3) and (4). On the other hand, almost no change was clearly observed for the ML-SiC/SiC after oxidation at 1000 ◦C and 1200 ◦C. 3.2. Characterization of oxidised layer Fig. 4 shows the SIMS spectra as a function of the depth from the oxidized surface for the SiC-matrix and SiC-fiber of the PyCSiC/SiC composite after oxidation at 1000 ◦C and 1200 ◦C. The depth was measured using a scanning probe microscope (Model P-10, KLA-Tencor) after sputtering by Cs-ion of the SIMS. Almost no difference between the SiC-matrix and SiC-fiber was observed. The formation of SiO2 layer and reduction and disappearance of SiC was observed on the surface of the oxidized matrix and fiber of the PyC-SiC/SiC. Fig. 5 shows the thickness of SiO2 layer evaluated by the SIMS spectra for the monolithic -SiC and SiC-matrix and SiC-fiber of the PyC-SiC/SiC composite after oxidation at 1000 ◦C and 1200 ◦C. The SiO2 layer thickness was almost the same after 100 h oxidation among the monolithic -SiC, SiC-matrix and SiC- fiber. The oxidation behavior of the monolithic -SiC in this work might obey the parabolic rule described in the open literatures [5]. The parabolic oxidation rate constant (kp) of the monolithic -SiC was 5.20 × 10−8 kg/m2/s1/2 for 1000 ◦C and 2.53 × 10−7 kg/m2/s1/2 for 1200 ◦C. The curves in Fig. 5 are the trend curves calculated using those kp value. Fig. 6 shows the Si-2p XPS spectra for the (a) SiC-matrix and (b) SiC-fiber of the PyC-SiC/SiC composite after oxidation at 1200 ◦C as a function of the depth from the oxidized surface (D). Almost no difference between the SiC-matrix and SiC-fiber was observed. The Fig. 5. The thickness of SiO2 layer of monolithic -SiC and SiC-matrix and SiC-fiber of the PyC-SiC/SiC after oxidation at 1000 ◦C and 1200 ◦C.
S Nogami et aL Fusion Engineering and Design 83(2008)1490-1494 93 Si-O Si-C Si-O2 Si-C D=400 D=0 105100 Binding Energy [e\ Fig. 6. The Si-2p XPS spectra for the(a) sic-matrix and (b) sic-fiber of the Pyc-sicsiC composite after oxidation at 1200C as a function of the depth from the oxidized surface(D). peaks with the biding energy of about 107ev for the Sic-matrix 3.3. Oxidation mechanism of Sic/Sic composite and 105 eV for the Sic-fiber were clearly observed near the speci- men surface(D180 nm). Therefore, this region( D=150-180 nm) disappear due to its recession. Therefore, the TGa spectrum was might consist of mixture of Sio and Sic. considered to show very small weigh (a) (b) 02 SiC-matrix SiC-matrix 000°C Py C-interface SiC-matrix SiC-fiber SiC-fiber PyC SiC-fiber SiC-matrix SiC-matrix 1200°C PyC-interface SiC-fiber (c) (d) Fig. 7. Schematic illustration of oxidation behavior of Pyc-SiC/SiC composite at 1000'C and 1200"C
S. Nogami et al. / Fusion Engineering and Design 83 (2008) 1490–1494 1493 Fig. 6. The Si-2p XPS spectra for the (a) SiC-matrix and (b) SiC-fiber of the PyC-SiC/SiC composite after oxidation at 1200 ◦C as a function of the depth from the oxidized surface (D). peaks with the biding energy of about 107 eV for the SiC-matrix and 105 eV for the SiC-fiber were clearly observed near the specimen surface (D 180 nm). Therefore, this region (D = 150–180 nm) might consist of mixture of SiO2 and SiC. 3.3. Oxidation mechanism of SiC/SiC composite Fig. 7 shows the schematic illustration of the oxidation behavior of the PyC-SiC/SiC composite at 1000 ◦C and 1200 ◦C [4,9]. For the oxidation of the PyC-SiC/SiC at 1000 ◦C (see (a) and (b) of Fig. 7), since the formation rate of SiO2 layer on the specimen surface is relatively low, the recession of PyC interface layer might continue and the interface region was not sealed by SiO2. Therefore, the TGA spectrum was considered to show the significant weight loss up to 20 h due to the PyC interface recession and almost no change after 20 h due to the very small SiO2 formation. For the oxidation of the PyC-SiC/SiC at 1200 ◦C (see (c) and (d) of Fig. 7), since the formation rate of SiO2 layer on the specimen surface is relatively high, the interface region might be sealed by SiO2 at the early stage of the oxidation test before the PyC interface disappear due to its recession. Therefore, the TGA spectrum was considered to show very small weight change. Fig. 7. Schematic illustration of oxidation behavior of PyC-SiC/SiC composite at 1000 ◦C and 1200 ◦C
1494 S Nogami et aL/ Fusion Engineering and Design 83(2008)1490-1494 Though the oxidation behavior of the interface region of the ML- 3) Almost no morphology change was clearly observed for the ml SiC/SiC composite was not clearly detected by FE-SEM observation, Sic/ Sic after oxidation at1000°cand1200°C it might be similar to the oxidation behavior of the PyC-SiC/SiC at (4)The similar formation behavior of Sio, layer was observed on 1200 C because of relatively narrow Py c region of the Ml interface. the surface of the oxidized sic-matrix and sic-fber this oxida- The Py c region of the ml interface might be sealed by Sioz formed ion behavior might obey the parabolic rule on the Sic-matrix, Sic-fiber and Sic-layer of the interface at the arly stage of the oxidation test. Acknowledgement 4. Conclusion This work was supposed by the JUPITER-ll (Japan-USA Program of Irradiation Testing for Fusion Research ID) program. Oxidation behavior and mechanism of Sic/SiC composites with conventional pyrolitic graphite interface and advanced multilayer References interface in a HCSb blanket environment was evaluated by tGa in He +Oz environment. The PyC-SiCSiC at 1200oC and the ML- 11 Y Katoh, LL Snead, C.H. Henager Jr, A Hasegawa, A Kohyama, B Riccardi, H Sic/Sic at 1000C and 1200C showed relatively small weigh hange. While the Pyc-SiC/SiCat 1000Cshowed significant weight loss due to the Pyc interface recession. The details of the experi- 3I LL Snead, M.C. Osborne, RA. Lowden, J. Strizak, R_. Shinavski, KL More, W-s mental results of this work are summarised as follow Eatherly, J. Bailey, A.M. 4]L Filipuzzi, R. Naslain, J Am Ceram Soc. 77(2)(1994)467-480. (1)The Py C-SiC/SiC showed significant weight loss up to 20 h and almost no change after 20 h at 1000C. While, very eight [61 JE. Moulder, W.F. Stickle, P.E. SoboL. K.D. Bomben, Handbook of x Ray Photoelec. change of the Pyc-SiC/SiC at 1200 C and the ML-Sic/Sic at terpretation of XPS Data, Physical Electronics, 1995. 1000°and1200° was observed. (2) The recession of the Pyc interface layer of the PyC-Sic/ SiC after g7_engan, RE Stahlbush. NS. Saks, AppL Phys. Lett. xidation at 1000 C was clearly observed. While, the interface [8]Y Hijikata, H Yamaguchi, M. Yoshikawa, S Yoshida, Appl. Surf. Sci. 184(2001) region after oxidation at 1200C partly or wholly sealed by [9] L Filipuzzi, G. Camus, R. Naslain, J.Am. Ceram Soc.77(2)(1994)459-466 action phase of Sio2
1494 S. Nogami et al. / Fusion Engineering and Design 83 (2008) 1490–1494 Though the oxidation behavior of the interface region of the MLSiC/SiC composite was not clearly detected by FE-SEM observation, it might be similar to the oxidation behavior of the PyC-SiC/SiC at 1200 ◦C because of relatively narrow PyC region of the ML interface. The PyC region of the ML interface might be sealed by SiO2 formed on the SiC-matrix, SiC-fiber and SiC-layer of the interface at the early stage of the oxidation test. 4. Conclusion Oxidation behavior and mechanism of SiC/SiC composites with conventional pyrolitic graphite interface and advanced multilayer interface in a HCSB blanket environment was evaluated by TGA in He + O2 environment. The PyC-SiC/SiC at 1200 ◦C and the MLSiC/SiC at 1000 ◦C and 1200 ◦C showed relatively small weight change.While the PyC-SiC/SiC at 1000 ◦C showed significant weight loss due to the PyC interface recession. The details of the experimental results of this work are summarised as follows: (1) The PyC-SiC/SiC showed significant weight loss up to 20 h and almost no change after 20 h at 1000 ◦C.While, very small weight change of the PyC-SiC/SiC at 1200 ◦C and the ML-SiC/SiC at 1000 ◦C and 1200 ◦C was observed. (2) The recession of the PyC interface layer of the PyC-SiC/SiC after oxidation at 1000 ◦C was clearly observed. While, the interface region after oxidation at 1200 ◦C partly or wholly sealed by reaction phase of SiO2. (3) Almost no morphology change was clearly observed for the MLSiC/SiC after oxidation at 1000 ◦C and 1200 ◦C. (4) The similar formation behavior of SiO2 layer was observed on the surface of the oxidized SiC-matrix and SiC-fiber. This oxidation behavior might obey the parabolic rule. Acknowledgement This work was supposed by the JUPITER-II (Japan-USA Program of Irradiation Testing for Fusion Research II) program. References [1] Y. Katoh, L.L. Snead, C.H. Henager Jr., A. Hasegawa, A. Kohyama, B. Riccardi, H. Hegeman, J. Nucl. Mater. 367–370 (2007) 659–671. [2] L. Giancarli, V. Chuyanov, M. Abdou, M. Akiba, B.G. Hong, R. Lasser, C. Pan, Y. ¨ Strebkov, J. Nucl. Mater. 367–370 (2007) 1271–1280. [3] L.L. Snead, M.C. Osborne, R.A. Lowden, J. Strizak, R.J. Shinavski, K.L. More, W.S. Eatherly, J. Bailey, A.M. Williams, J. Nucl. Mater. 253 (1998) 20–30. [4] L. Filipuzzi, R. Naslain, J. Am. Ceram. Soc. 77 (2) (1994) 467–480. [5] T. Goto, H. Homma, T. Hirai, T. Narushima, Y. Iguchi, High Temp. Corros. Mater. Chem. (1998) 395–408. [6] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X Ray Photoelectron Spectroscopy: A Reference Book of Standard Spectra for Identification and Interpretation of XPS Data, Physical Electronics, 1995. [7] G.G. Jernigan, R.E. Stahlbush, N.S. Saks, Appl. Phys. Lett. 77 (2000) 1437–1439. [8] Y. Hijikata, H. Yamaguchi, M. Yoshikawa, S. Yoshida, Appl. Surf. Sci. 184 (2001) 161–166. [9] L. Filipuzzi, G. Camus, R. Naslain, J. Am. Ceram. Soc. 77 (2) (1994) 459–466