LPCVD and characterization of boron-containing pyrocarbon materials

Abstract

Pyrocarbon materials containing various amounts of boron have been prepared by LPCVD from BCl 3 -C 3 H 8 -H 2 precursor mixtures. The growth rate is increased with respect to pure pyrocarbon deposition. By increasing BCl 3 / (C 3 H 8 + BCl 3 ) ratio up to 85%, the incorporation of boron can reach 33 at.%. A small amount of boron (e.g. 8 at.%) highly enhances the anisotropy of pyrocarbon, as evidenced by optical microscopy, X-ray diffraction and transmission electron microscopy (selected area diffraction and lattice fringes techniques). X-ray photoelectron spectroscopy has shown that a large fraction of the boron atoms are included by substitution in the carbon layers, the remaining boron atoms belongs to a boron-rich amorphous part of the material. As boron content increases beyond 8 at.%, the anisotropy of the boron-rich pyrocarbon decreases, due to the limited growth and stacking of the carbon layers. Also, amorphous boron-rich regions are more and more abundant as the total amount of boron increases. The oxidation resistance of the C(B) materials is better than that of pure pyrocarbon. It is mainly due to the improvement of the structural organization for the low boron content materials and to the coating of the whole material with a stable boron oxide for materials with a higher boron content.

Preparation and Mechanical Properties of Carbon Fiber Reinforced (BC x –SiC) n Multilayered Matrix Composites

“…By fitting the B 1s XPS spectrum, the proportions of B 1s components with different types of chemical states are achieved, as listed in Table 2. The components at 187.8 and 188.9 eV can be associated with a boron carbide such as B 4 C and a boron atom included by substitution in the graphitic structure, as proposed by William et al [12] and Jacques et al [13]. The high energy components at 190.…”

Synthesis and oxidation behavior of boron-substituted carbon powders by hot filament chemical vapor deposition

“…By CVD methods, it has been found that the boron concentrations in the obtained B x C 1−x materials were mainly in the range of 15-19 at% [13][14][15] , which means the existence of one ordered BC 5 compound. As far as we know, the obtained B x C 1−x materials with high boron concentrations are amorphous or turbostratic films [12][13][14][15][16][17][18][19] . These samples with film form are difficult to explore their oxidation behavior.…”

“…Boron-substituted graphite materials, referred to as B x C 1−x (0<x<0.25), have been studied theoretically [5][6][7] and experimentally [8][9][10][11][12][13][14][15][16][17][18][19][20] . Structural and electronic properties of some ordered B x C 1−x compounds have been investigated using different calculational methods [5][6][7] .…”

“…Jones and Thrower [4] have proposed that the inhibiting effect by substitutional boron on carbon oxidation was directly proportional to the boron concentration in the compound. The B x C 1−x materials with high boron concentrations are thermodynamically metastable and can only be obtained by nonequilibrium techniques, like various chemical vapor deposition (CVD) methods [12][13][14][15][16][17][18][19] . By thermal CVD at 800℃ using benzene and boron trichloride as gas sources, Kouvetakis et al [12] obtained one novel compound BC 3 , in which the boron concentration reached 25 at.%.…”

Research on precision‐calibration techniques for selected area electron diffraction patterns of pyrocarbon

“…In research on the microstructures of pyrocarbon, the selected area electron diffraction (SAED) technique is often employed to analyze the misorientation degree and space between (002) planes (d002). The orientation angle (OA) is defined as the opening angle corresponding to the full width at half maximum (FWHM) of the intensity along the (002) ring reflection (Bourrat et al, 2000;Jacques et al, 1996). OA is an important parameter to characterize the texture of pyrocarbon.…”