500um (b) 500um (c) 5nm Figure 8.7 Very high temperature pyrocarbon (processing temperature:2,100C):(a)Cross- polarized light on polished surface(PCH4=0.5 KPa);(b)Same in cross section (after Tombrel and Rappeneau,1965);(c)Same pyrocarbon in high resolution TEM(after Goma and Oberlin,1985). a turbostratic structure and a high degree of preferred orientation(Guenter,1962;Tombrel and Rappeneau,1965).In this case authors speak about direct deposition of carbon with a perfectly oriented turbostratic structure. 2.4 Pyrocarbons issued from new rapid densification processes The new processes as thermal gradient(Golecki et al.,1995)or pressure-pulse-CVI(Dupel et al.,1994)or film boiling (David et al.,1995;Bruneton et al.,1997),all provide classical textures or combinations of classical features known in CVD,except the possible mixed structures in the case of liquid immersion in the rapid densification process:mosaic pitch- based-and pyrolytic-type carbons(Rovilain,1999;Beaugrand,2000)as shown in Fig.8.8c. It is noteworthy that rough laminar is much easily produced by I-CVI than by any other process.In most cases,regenerative laminar(REL)(see Section 3.3)is obtained with the new rapid densification processes. ©2003 Taylor&Francisa turbostratic structure and a high degree of preferred orientation (Guenter, 1962; Tombrel and Rappeneau, 1965). In this case authors speak about direct deposition of carbon with a perfectly oriented turbostratic structure. 2.4 Pyrocarbons issued from new rapid densification processes The new processes as thermal gradient (Golecki et al., 1995) or pressure-pulse-CVI (Dupel et al., 1994) or film boiling (David et al., 1995; Bruneton et al., 1997), all provide classical textures or combinations of classical features known in CVD, except the possible mixed structures in the case of liquid immersion in the rapid densification process: mosaic pitch￾based- and pyrolytic-type carbons (Rovilain, 1999; Beaugrand, 2000) as shown in Fig. 8.8c. It is noteworthy that rough laminar is much easily produced by I-CVI than by any other process. In most cases, regenerative laminar (REL) (see Section 3.3) is obtained with the new rapid densification processes. Figure 8.7 Very high temperature pyrocarbon (processing temperature: 2,100 C): (a) Cross￾polarized light on polished surface (PCH4  0.5 KPa); (b) Same in cross section (after Tombrel and Rappeneau, 1965); (c) Same pyrocarbon in high resolution TEM (after Goma and Oberlin, 1985). 5 nm (a) (c) (b) 500 µm 500 µm © 2003 Taylor & Francis