based on their appearance when observed under polarized light (on polished sections) The main concern was the deposition using the fluidized-bed CVD in a broad range of temperature. Then,Kotlensky et al.(1971),Granoff and Pierson (1973),and principally Lieberman and Pierson(1974,1975)documented the case of carbon composite infiltration at low tem- perature(T<1400C)and low partial pressure of hydrocarbon.They were the first to study the texture in relation with the processing conditions:matrix texture fall into three major types identified as rough laminar(RL),smooth laminar(SL),and isotropic pyrocarbons(D). They were the first to establish the important low temperature transition between rough and smooth laminar for infiltration process. 2.1 The low temperature transition:SL←→RL(8O0-l,400°C Nowadays,the transition between high and low density pyrocarbons is well established.It is under control of the gas phase species,itself controlled by the residence time (Dupel et al., 1995),the temperature or pressure.Transition is due to a change in the heterogeneous growth mechanisms in the range of 800-1,400C(Feron et al.,1999).These transitions could be called the CVI transitions because it is of major concern in 3D preform infiltration(Lavenac et al.,2000).A progressive passage from SL to a low-density I was also clearly established at very short residence time (and/or lower temperature and pressure)(Lavenac et al,2001).This passage occurs through the intermediate of dark laminar(DL)(Doux,1994)by a progressive increase of disclination defects in the hexagonal lattice,the pentagons (Bourrat et al.,2001): SL←→RL 2.1.I Smooth laminar pyrocarbon(SL) When observed by reflected light SL is characterized by a medium reflectance(see Fig.8.1). (Reflectance measures the ratio of light reflected by the polished surface.)Under cross- polars SL exhibits a large and well defined extinction cross known as the "Maltese-cross" (around fiber cross-sections).When rotating the stage,the rolling extinction parallel to the polars is smooth,thus this texture is called "smooth"laminar pyrocarbon.An example of this texture is provided on Fig.8.1a.When measured,the density is found to be intermedi- ate 1.8<d<1.95.The anisotropy is medium too:extinction angle,Ae,measured in cross- polarized light is 12<Ae<18 on a scale which goes up to 22 (see Section 5.3).The orientation angle,OA,measured by electron diffraction is 40<OA<70.OA measures the disorder along the anisotropy plane which decreases down to 15. 2.1.2 Rough laminar pyrocarbon (RL) This texture has a high reflectance.When observed with the polarizer alone and because of carbon dichroism,a gray branch parallel to the polarizer appears around fiber cross- sections:reflectance is higher parallel to the graphene planes.Under crossed polars a highly contrasted Maltese-cross appears around the fiber cross sections(Fig.8.1b).The extinction of the branches is irregular.For that reason it is called"rough"laminar.The roughness is provided by the prismatic texture due to the formation of fine cones generated on fiber ©2003 Taylor&Francisbased on their appearance when observed under polarized light (on polished sections). The main concern was the deposition using the fluidized-bed CVD in a broad range of temperature. Then, Kotlensky et al. (1971), Granoff and Pierson (1973), and principally Lieberman and Pierson (1974, 1975) documented the case of carbon composite infiltration at low tem￾perature (T  1400 C) and low partial pressure of hydrocarbon. They were the first to study the texture in relation with the processing conditions: matrix texture fall into three major types identified as rough laminar (RL), smooth laminar (SL), and isotropic pyrocarbons (I). They were the first to establish the important low temperature transition between rough and smooth laminar for infiltration process. 2.1 The low temperature transition: SL ↔ RL (800–1,400 C) Nowadays, the transition between high and low density pyrocarbons is well established. It is under control of the gas phase species, itself controlled by the residence time (Dupel et al., 1995), the temperature or pressure. Transition is due to a change in the heterogeneous growth mechanisms in the range of 800–1,400 C (Féron et al., 1999). These transitions could be called the CVI transitions because it is of major concern in 3D preform infiltration (Lavenac et al., 2000). A progressive passage from SL to a low-density I was also clearly established at very short residence time (and/or lower temperature and pressure) (Lavenac et al., 2001). This passage occurs through the intermediate of dark laminar (DL) (Doux, 1994) by a progressive increase of disclination defects in the hexagonal lattice, the pentagons (Bourrat et al., 2001): SL ↔ RL 2.1.1 Smooth laminar pyrocarbon (SL) When observed by reflected light SL is characterized by a medium reflectance (see Fig. 8.1). (Reflectance measures the ratio of light reflected by the polished surface.) Under cross￾polars SL exhibits a large and well defined extinction cross known as the “Maltese-cross” (around fiber cross-sections). When rotating the stage, the rolling extinction parallel to the polars is smooth, thus this texture is called “smooth” laminar pyrocarbon. An example of this texture is provided on Fig. 8.1a. When measured, the density is found to be intermedi￾ate 1.8  d  1.95. The anisotropy is medium too: extinction angle, Ae, measured in cross￾polarized light is 12  Ae  18 on a scale which goes up to 22 (see Section 5.3). The orientation angle, OA, measured by electron diffraction is 40  OA  70. OA measures the disorder along the anisotropy plane which decreases down to 15. 2.1.2 Rough laminar pyrocarbon (RL) This texture has a high reflectance. When observed with the polarizer alone and because of carbon dichroism, a gray branch parallel to the polarizer appears around fiber cross￾sections: reflectance is higher parallel to the graphene planes. Under crossed polars a highly contrasted Maltese-cross appears around the fiber cross sections (Fig. 8.1b). The extinction of the branches is irregular. For that reason it is called “rough” laminar. The roughness is provided by the prismatic texture due to the formation of fine cones generated on fiber © 2003 Taylor & Francis