Oxidizing environment influence on 2D-SiC/ BN/ Sic composite 719 3.2.2.3 The BN/Sic-matrix interface. Figure 9 the near-edge fine structure of the Si-L2, 3 edge may shows the interface between the SiC matrix and the suggest that Si atoms are involved in both Sic and BN interphase. It is coarse and porous with a SiO2 5(Fig. 12). An additional hrem study could thickness of about 35 nm. Although the feature of ermit to afford more information about the rela this zone appeared similar to the interface observed tive organization of SiC, SiO2 and C. Furthermore on the same composite tested at room temperature, close to this intcrface, inside the boron nitride the composition is significantly modified. EELs some silica has also been detected analyses have revealed high concentration of oxy- 3. 2.2. 4 Analysis of the cracks. Along a decohe gen (50 at%), silicon (34 at%)and carbon(16 sion at the fiber/BN interface, EELS analyses at%), instead of carbon in the original compo revealed the presence of Si, O and B atoms. Car site.5 Additionally, the damped two pre-peaks in bon was also revealed, but it remains under the quantitative limit, while no nitrogen was detected The average atomic ratio O/Si was equal to 1 3 and the boron concentration was below 5 at% On the other hand the chemical characterization of a crack that phase allows to determine an average atomic com position of 34% B, 28%N, 20%O, 10%C and 8% Si, The near edge structure of the Si-L2 3 peak exhibits a double peak on the edge onset. It is similar to the one previously seen at the fiber/BN interface and corresponds to the presence, in this crack, of Si-o bonds in a SiO, structure 50 Although, in both cases, the presence of boron oxide could be considered from the surstoichiometry 2 10 um 1 10 um Fig3.(a) Cross-section of a 2D-SiC/BN/SiC composite,(b) Fig. 4. Interfacial zone showing crystalline or amorphous in the external part and (c)in the middle of a fibers tow.Oxidizing environment influence on 2D-SiC/BN/SiC composites 719 3.2.2.3 The BN/SiC-matrix interface. Figure 9 shows the interface between the SIC matrix and the BN interphase. It is coarse and porous with a thickness of about 35nm. Although the feature of this zone appeared similar to the interface observed on the same composite tested at room temperature, the composition is significantly modified. EELS analyses have revealed high concentration of oxy￾gen (50 at%), silicon (34 at%) and carbon (16 at%), instead of carbon in the original compo￾site.i5 Additionally, the damped two pre-peaks in (b) the near-edge fine structure of the Si-L2,3 edge may suggest that Si atoms are involved in both Sic and Si0215 (Fig. 12). An additional HREM study could permit to afford more information about the rela￾tive organization of Sic, Si02 and C. Furthermore, close to this interface, inside the boron nitride, some silica has also been detected. 3.2.2.4 Analysis of the cracks. Along a decohe￾sion at the fiber/BN interface, EELS analyses revealed the presence of Si, 0 and B atoms. Car￾bon was also revealed, but it remains under the quantitative limit, while no nitrogen was detected. The average atomic ratio O/Si was equal to 1.3 and the boron concentration was below 5 at%. On the other hand, the chemical characterization of a crack that propagates radially into the inter￾phase allows to determine an average atomic com￾position of 34% B, 28% N, 20% 0, 10% C and 8% Si. The near edge structure of the Si-L2,3 peak exhibits a double peak on the edge onset. It is similar to the one previously seen at the fiber/BN interface and corresponds to the presence, in this crack, of Si-0 bonds in a Si02 structure.** Although, in both cases, the presence of boron oxide could be considered from the surstoichiometry (4 (b) Fig. 3. (a) Cross-section of a 2D-SiC/BN/SiC composite, (b) Fig. 4. Interfacial zone showing crystalline or amorphous in the external part and (c) in the middle of a fibers tow. masses after a tensile test of 70 h, at 600°C in air