N. Chala et al 175 875nm FIG4. Height mode image of the surface of Nicalon fiber RESULTS AND DISCUSSION from the areas scanned in both images (Ta- ble 2). HI-Nicalon has Figures 4 and 5 show height mode images roughness than Nicalon, but the roughness of Nicalon and HI-Nicalon fibers, respec- amplitude of both fibers is quite low, on the tively. Topographic views of the profiles order of 45nm. Taking into consideration are shown in Figs. 6 and 7. Notice the nod- such factors as the radius of the tip, type of ular surface profile in both fibers. It is spec- scanner, size of features being imaged, and ulated that these nodules form during pro- number of pixels in the image, the uncer cessing Melt-spinning processes are used tainty in the roughness measurements was to manufacturc Nicalon and HI-Nicalon fi- calculated as +0.67nm From Figs 6 and 7 bers(Fig 8). Polycarbosilane is spun and a section analyses were also conducted to green fiber, ready for sintering, is obtained. provide a graphic profile of the roughness The difference in processing between fibers( Fig 9). A line was drawn on the image and lies in the next steps. In Nicalon, the green the corresponding roughness profiles were fiber is cured by oxidation and pyrolyze plotted. Notice that both fibers have similar HI-Nicalon, on the other hand, is cured by profiles. Notice, however, that the rough an electron beam and then pyrolyzed this ness is more uniform in Nicalon than in procedure lowers the oxygen content HI-Nicalon. This may be critical during fi- verged roughness profiles were taken ber sliding, as a large amplitude between a FIG. 5. Height mode image of the surface of HI-Nicalon fiber202 N. Chawla et al. 87.5 nm FIG. 4. Height mode image of the surface of Nicalon fiber. RESULTS AND DISCUSSION Figures 4 and 5 show height mode images of Nicalon and HI-Nicalon fibers, respec￾tively. Topographic views of the profiles are shown in Figs. 6 and 7. Notice the nod￾ular surface profile in both fibers. It is spec￾ulated that these nodules form during pro￾cessing. Melt-spinning processes are used to manufacture Nicalon and HI-Nicalon fi￾bers (Fig. 8). Polycarbosilane is spun and a green fiber, ready for sintering, is obtained. The difference in processing between fibers lies in the next steps. In Nicalon, the green fiber is cured by oxidation and pyrolyzed. HI-Nicalon, on the other hand, is cured by an electron beam and then pyrolyzed; this procedure lowers the oxygen content. Averaged roughness profiles were taken from the areas scanned in both images (Ta￾ble 2). HI-Nicalon has a somewhat higher roughness than Nicalon, but the roughness amplitude of both fibers is quite low, on the order of 4-5nm. Taking into consideration such factors as the radius of the tip, type of scanner, size of features being imaged, and number of pixels in the image, the uncer￾tainty in the roughness measurements was calculated as ?0.67nm. From Figs. 6 and 7, section analyses were also conducted to provide a graphic profile of the roughness (Fig. 9). A line was drawn on the image and the corresponding roughness profiles were plotted. Notice that both fibers have similar profiles. Notice, however, that the rough￾ness is more uniform in Nicalon than in HI-Nicalon. This may be critical during fi￾ber sliding, as a large amplitude between a 100 50 nm 0 FIG. 5. Height mode image of the surface of HI-Nicalon fiber