Compacts of TiB, with densities approaching 100% are difficult to obtain using pressureless sintering. The addition of S i c was very effective in improving the sinterability of TiB,. The oxygen content of the raw TiB, powder used in this research was 1.5 wt%. X-ray photoelectron spectroscopy showed that the powder surface consisted mainly of TiO, and B,O,. Using vacuum sintering at 1700°C under 13-0.013 Pa, TiB, samples containing 2.5 wt% S i c achieved 96% of their theoretical density, and a density of 99% was achieved by HIPing. TEM observations revealed that S i c reacts to form an amorphous phase. TEM-EELS analysis indicated that the amorphous phase includes Si, 0, and Ti, and X-ray diffraction showed the reaction to be TiO, + S i c + SiO, + TIC. Therefore, the improved sinterability of TiB, resulted from the SiO, liquid phase that was formed during sintering when the raw TiB, powder had 1.5 wt% oxygen.
Maternal sound stress (800 Hz; 77 dB, every other minute for 15 min/day, from day 10 to 18 of gestation), combined with forced swimming stress (15 min/day), was found to cause potentiation of sound-induced loss of locomotor activity, referred to as emotional behavior, of male offspring, but not that of female offspring, at 4 weeks of age. Maternal stress also caused an increase in the total number of errors by male, but not female offspring in the water-maze test at 6 weeks of age. These effects of stress on emotional behavior and learning behavior were abolished when dams were pretreated with buspirone (30 min before the stress, from day 8 to 18 of gestation). Thus, prenatal stress might have sex-dependent effects on emotional behavior and learning ability of neonatal rats.
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