TEM characterization of some crude or air heat-treated SiC Nicalon fibres

• Published in: Journal of materials science Vol. 24; no. 9; pp. 3361 - 3370
• Main Authors: MANIETTE, Y, OBERLIN, A
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.09.1989
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Exact sciences and technology; Technical ceramics; Heat treatment; Transmission electron microscopy; Silicon Carbides; Microstructure; Ceramic fiber
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/BF01139066

Commercial Nicalon fibres were prepared by thin transverse sectioning and studied by TEM. A progressive tilting of the incident beam enabled exploration of the selected-area diffraction (SAD) pattern along two orthogonal directions, increasing the tilting angle (dark-field (DF) imaging). The lattice fringes technique was also used. The samples were Nicalon 001, 101, and 201 fibres, the latter also being studied after heat treatment in air at 1300 C for 48 h. The SAD pattern of the 001 fibre only shows the SiC111 intense halo whereas the other samples show all the SiC (111, 220 and 311) strongly scattered beams, indicating a microcrystalline state. Correspondingly, DF imaging does not indicate any localised measurable scattering domain for 001. Only bright dots can be seen, less than 1 nm in size. The other fibres show SiC microcrystals respectively 2nm (101), 3 nm (201) and up to 7 nm (heat-treated 201) in extent. Free aromatic carbon, shaped in small units less than 1 nm in size fills up the interstices between SiC. These units tend to lie flat on SiC. In heat-treated fibres, they form incomplete layers around the edges. In addition, the heat-treated 201 fibre show a 1 micron thick layer of cristobalite at the fibre surface. These crystals are poltypes. 18 refs.