N. Bunjes et al. Journal of Non-Crystalline Solids 353(2007)1567-1576 b Fig 3.(a) Bright field image and(b) EDP of 3c thermolyzed at 1050C/4 h/Ar. After thermolysis of the polymers at 1400C for 2 h in of the sample, the distribution seems to be almost an argon atmosphere the samples contained Sic crystals homogeneous. and a BNCx phase as was indicated by XRD(Fig. 2(a)) The EDP of 5c/1400( Fig 4(b) confirms this result. The 3. 2. Samples annealed at 1600-1800C observed diffraction rings can be attributed to Sic, while wo diffuse signals corresponding to the (0002) and toTo characterize materials obtained by annealing the(1010) /(1011)reflections of graphite are usually at higher temperatures, 3c and 5c, which had been assigned to the BNCx phase [20]. The TEM bright field thermolyzed at 1400C, were heat treated at different tem- image(Fig. 4(a)) taken from this sample shows homoge- peratures for 5 h in an argon atmosphere. A typical micro- neously distributed grains of nearly uniform size and shape structure obtained by TEM analysis of 5c annealed at with diameters of about 7.5 nm(3c)or 20-30 nm (5c) 1600C is shown in Fig. 5. From the bright field image which are embedded in a matrix phase. Since Sic and (BF) it is obvious that nano-sized grains are embedded in BNCx are the only phases present in significant amounts matrix phase Compared to the as-thermolyzed ceramic in this material and BNCx crystallization is usually hin- 5c/1400( Fig. 4)the grain size distribution is larger with dered, the grains most probably represent Sic crystals. diameters ranging from about 10 to 50 nm and an average Unfortunately, the elemental distribution images obtained grain size of 26 nm. by ESI(not shown here) cannot be interpreted unequivo- The chemical composition was analyzed by electron cally. Because of the small grain size and the thickness spectroscopic imaging(ESI). The results are presented in b CL=580 mn Fig 4.(a)Bright field image and(b)EDP of 5e thermolyzed at 1400C/ h/ArAfter thermolysis of the polymers at 1400 C for 2 h in an argon atmosphere the samples contained SiC crystals and a BNCx phase as was indicated by XRD (Fig. 2(a)). The EDP of 5c/1400 (Fig. 4(b)) confirms this result. The observed diffraction rings can be attributed to SiC, while two diffuse signals corresponding to the (0 0 0 2) and to the (1 0 1 0)/(1 0 1 1) reflections of graphite are usually assigned to the BNCx phase [20]. The TEM bright field image (Fig. 4(a)) taken from this sample shows homoge￾neously distributed grains of nearly uniform size and shape with diameters of about 7.5 nm (3c) or 20–30 nm (5c) which are embedded in a matrix phase. Since SiC and BNCx are the only phases present in significant amounts in this material and BNCx crystallization is usually hin￾dered, the grains most probably represent SiC crystals. Unfortunately, the elemental distribution images obtained by ESI (not shown here) cannot be interpreted unequivo￾cally. Because of the small grain size and the thickness of the sample, the distribution seems to be almost homogeneous. 3.2. Samples annealed at 1600–1800 C To characterize materials obtained by annealing at higher temperatures, 3c and 5c, which had been thermolyzed at 1400 C, were heat treated at different tem￾peratures for 5 h in an argon atmosphere. A typical micro￾structure obtained by TEM analysis of 5c annealed at 1600 C is shown in Fig. 5. From the bright field image (BF) it is obvious that nano-sized grains are embedded in a matrix phase. Compared to the as-thermolyzed ceramic 5c/1400 (Fig. 4) the grain size distribution is larger with diameters ranging from about 10 to 50 nm and an average grain size of 26 nm. The chemical composition was analyzed by electron spectroscopic imaging (ESI). The results are presented in Fig. 3. (a) Bright field image and (b) EDP of 3c thermolyzed at 1050 C/4 h/Ar. Fig. 4. (a) Bright field image and (b) EDP of 5c thermolyzed at 1400 C/2 h/Ar. 1570 N. Bunjes et al. / Journal of Non-Crystalline Solids 353 (2007) 1567–1576