Crystalline silicon carbide (SIC) fiber was produced by a new, simple procedure. Activated carbon fiber (ACF) was reacted with gaseous silicon monoxide and was converted to SIC fiber at elevated temperature and reduced pressure. The reaction was completed at temperatures as low as 1473 K. The reacted fiber consisted of submicrometer particles which were not observed in the original ACF. The S i c crystal size in the reacted fiber was approximately 30 nm. The microstructure of the fiber became dense after it was heat-treated in air at 1573 K or in nitrogen gas at 1873 K.
Absorption spectra of a nematic liquid-crystalline molecule (4-butyl-4′-ethoxyazobenzene) were measured in sandwich-type cells with very thin gaps which ranged from 0.2 to 1.0 μm when the cells were empty. The intensity ratio of the first (354 nm) to second (240 nm) band in the liquid state (86 °C) decreases as the state changes into liquid-crystalline (LC) states (70 and 48 °C). According to results of dichroism analysis and MO calculation, the 354 nm and 240 nm bands are due to π-π* transitions polarized along the molecular long and short axes, respectively (with an angle of about 66°to each other). This finding coupled with an assumption that the molecular orientation of the liquid state is isotropic, allows a qualitative discussion on the orientation of molecule in the LC state, leading to a conclusion that the molecular long axis against the cell surface takes two kinds of orientation with respective tendencies to be parallel in the interface region and perpendicular in the bulk region.
Radical ions of some 9-substituted anthracene derivatives have been prepared in polymer film by γ-irradiation at 77 K. By use of the polarized absorption spectra of these radical ions, the absorption spectra have been resolved into two components (resolved spectra), the transition moments of which are polarized parallel to the molecular long and short axes, respectively. Correlation of the characteristic absorption bands is discussed briefly.
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