Precursor‐derived Covalent Ceramics*

Abstract

The preparation of ceramic materials from preceramic compounds provides a means for the synthesis of new materials which cannot be obtained by conventional methods. An example is shown in the figure, which shows carbon‐fiber‐reinforced silicon carbide coated with silicon carbonitride prepared by dip‐coating the substrate with a slurry made of polyhydridomethylsilazane and silicon powder. Progress and applicational examples are reviewed magnified image.

Atomic Structure and Diffusion in Amorphous Si-B-C-N by Molecular Dynamics Simulation

“…Such a local compositional mixture of atoms is expected to be disadvantageous to transformation of the amorphous state into thermodynamically stable crystalline phases such as Si 3 N 4 , SiC and BN. 17) Phase separation of the amorphous state, which would take place before crystallization, requires rearrangement of the amorphous network and atomic diffusion. In this section, we examine selfdiffusion behavior in amorphous Si-B-C-N.…”

“…17) At high temperatures before crystallization, the amorphous network will undergo rearrangement so as to bring about phase separation into Si 3 N 4 -rich, BN-rich and SiCrich regions. Since constituent atoms are homogeneously distributed in the amorphous state, diffusion processes are necessary for the crystallization behavior.…”

“…Bill et al also suggested that boron has a retarding effect on atomic mobility in amorphous Si-B-C-N, from their experimental observations of the microstructures after crystallization. 17) To clarify the physical origin of the unexpected thermal stability of amorphous Si-B-C-N, however, it is necessary to examine the amorphous network and effects of boron and carbon atoms on diffusion processes when these atoms are homogeneously distributed in the amorphous state.…”

ポリビニルシラザン由来の非晶質 Si-C-N モノリスの作製と圧縮変形

“…3,4 Many kinds of ceramic fibers have been developed using polymer precursor method, since continuous SiC fibers were obtained by this method in the 1970s. [5][6][7] Bulk amorphous ceramics such as Si-C-N and Si-B-C-N have been fabricated by pyrolyzing the isostatically pressed and warm pressed preceramic powders.…”

Compressive Deformation of Partially Crystallized Amorphous Si-B-C-N Ceramics at Elevated Temperatures

“…[4][5][6] Bulk amorphous ceramics such as Si-C-N and Si-B-C-N have been developed by pyrolyzing the isostatically pressed and warm pressed preceramic powders. [7][8][9][10][11] However, it is difficult to fabricate no porosity ceramic monoliths by these processes since porosity is necessary to remove the gas species during pyrolysis.…”